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A trait-based approach to community assembly: Partitioning of species trait values into within- and among-community components
Abstract
Plant functional traits vary both along environmental gradients and among species occupying similar conditions, creating a challenge for the synthesis of functional and community ecology. We present a trait-based approach that provides an additive decomposition of species' trait values into alpha and beta components: beta values refer to a species' position along a gradient defined by community-level mean trait values; alpha values are the difference between a species' trait values and the mean of co-occurring taxa. In woody plant communities of coastal California, beta trait values for specific leaf area, leaf size, wood density and maximum height all covary strongly, reflecting species distributions across a gradient of soil moisture availability. Alpha values, on the other hand, are generally not significantly correlated, suggesting several independent axes of differentiation within communities. This trait-based framework provides a novel approach to integrate functional ecology and gradient analysis with community ecology and coexistence theory.
... Trait-gradient analysis is a trait-based framework to complete traitscale matches that provides a guideline to select traits (Ackerly et al., 2006;Ackerly & Cornwell, 2007). Using this framework, species trait values can be decomposed into alpha and beta components: trait alpha components refer to the within-community dimension of niche differentiation, while beta trait components refer to the among communities dimension of niche differentiation (Cavender-Bares et al., 2009;Silvertown et al., 2006). ...
... All traits data were transformed to a log scale before analysis. We calculated the community-weighted mean trait (p j ; Equation 1) and species mean trait value (t i ; Equation 2; Ackerly & Cornwell, 2007). ...
... The community weighted mean trait and species mean trait values were further partitioned into beta (β i ; Equation 3) and alpha (α i ; Equation 4) components by using trait-gradient analysis (Ackerly & Cornwell, 2007). Alpha trait components are the difference between a species trait values and the mean of co-occurring species; beta trait components refer to a species position along a gradient defined by community-level mean trait values (Ackerly & Cornwell, 2007). ...
Assessing plant diversity during community succession based on plant trait and phylogenetic features within a community (alpha scale) and among communities (beta scale) could improve our understanding of community succession mechanism. However, whether changes of community functional diversity at alpha and beta scale are structured by different traits and whether integrating plant traits and phylogeny can enhance the ability in detecting diversity pattern have not been studied in detail. Thirty plots representing different successional stages were established on the Loess Plateau of China and 15 functional traits were measured for all coexisting species. We first analyzed the functional alpha and beta diversity along succession by decomposing species trait into alpha and beta components and then integrated key traits with phylogenetic information to explore their roles in shaping species turnover during community succession. We found that functional alpha diversity increased along successional stages and was structured by morphological traits, while beta diversity decreased during succession and was more structured by stoichiometry traits. Phylogenetic alpha diversity showed congruent pattern with functional alpha diversity because of phylogenetic conservation of trait alpha components (variation within community), while beta diversity showed incongruent pattern due to phylogenetic randomness of trait beta components (variation among communities). Furthermore, only integrating relatively conserved traits (plant height and seed mass) and phylogenetic information can raise the detecting ability in assessing diversity change. Overall, our results reveal the increasing niche differentiation within community and functional convergence among communities with succession process, indicating the importance of matching traits with scale in studying community functional diversity and the asymmetry of traits and phylogeny in reflecting species ecological differences under long-term selection pressures.
... However, a community is a mixture of species, and it is the individual species that ultimately experience environmental filtering or competition. So, species' attributes (i.e., trait mean and range) can offer complementary insights into biodiversity maintenance processes [17,26]. One crucial aspect of the species-level analysis is that a species' trait values can be divided into within-and among-community components [17]. ...
... So, species' attributes (i.e., trait mean and range) can offer complementary insights into biodiversity maintenance processes [17,26]. One crucial aspect of the species-level analysis is that a species' trait values can be divided into within-and among-community components [17]. The withincommunity component, commonly denoted as alpha-trait value, describes how the trait value of a focal species relative to coexisting species varies; thus attributed to competitionmediated biotic filtering. ...
... To quantify plot-level community-weighted mean (P j ) and trait range (R j ) values for each trait, we followed Ackerly and Cornwell [17]. Utilizing the same approach, we quantified species-level trait mean (t i ), alpha-trait value (α i ), beta-trait value (β i ) and niche breadth (R i ) for each trait and species. ...
Although ecologists often emphasize the roles of environmental- versus biotic-filtering in structuring forest communities, the relative importance of these processes could vary among undisturbed versus disturbed forests. To test this assumption, we gathered leaf traits and site conditions data from intact mature forests (control), moderately disturbed shrublands, and severely disturbed plantations from subtropical China. We found that plantations had higher leaf area, specific leaf area, leaf nitrogen and phosphorus concentrations but lower leaf thickness, dry matter content, and C:N than the shrubland or mature forest, suggesting the dominance of resource acquisition strategy in plantations versus conservation strategy in the mature forests. Plantations also had significantly lower trait ranges than mature forest or shrubland, suggesting the play of stringent environmental filtering in the plantation. However, intraspecific trait variations in leaf dry matter content and C:N were substantial in plantation, while interspecific variation in leaf thickness was high in mature forests, suggesting the importance of intra- versus inter-specific competition in plantation versus mature forests. Results from our species-level analysis were consistent with the community-level results mentioned above. Overall, our study demonstrates the shifting importance of environmental and biotic filtering from disturbed to undisturbed forests.
... The community weighted mean (CWM) of functional traits at the species level was used to test the phylogenetic signal [38], and the trait data were log10 transformed. The formula for CWM is as follows [39]: ...
... We selected SLA, LDMC, and LTP as leaf economic spectrum (LES) traits [41,42]. The CWM of functional traits at the community level was used for the analysis, and the formula for CWM is as follows [39]: ...
A lakeside is a functional transition zone that connects the lake aquatic ecosystem and the land ecosystem. Understanding the community assembly mechanism is crucial for regional ecological restoration, habitat management, and biodiversity conservation. However, research on the terrestrial plant community assembly in lakesides under anthropogenic disturbance is still lacking. The present study used phylogeny and functional traits to assess the community assembly of three habitat types with different anthropogenic disturbances in Dianchi lakeside. The factors that influenced the community assembly were also explored. Results indicated that the phylogenetic signals of all the examined functional traits of the dominant species were weak, suggesting that the traits were convergent. The community phylogenetic and functional structures of the different habitat types showed random patterns. Thus, the assembly of terrestrial plant communities in the three habitat types was driven by competitive exclusion and neutral processes in Dianchi lakeside. The trait trade-off strategies of species in the different habitats varied with the different habitat types. Anthropogenic disturbance played an important role in the process of community assembly. The present study provides a scientific basis for the assessment and management of ecological restoration in Dianchi lakeside and other plateau lakes and enriches the knowledge on the community assembly mechanism of disturbed plant communities.
... If species' traits change along an environmental gradient in the opposite direction as traits change due to turnover in community composition (i.e. cover of different functional types), trait-environment relationships at the community level can be weak (Ackerly & Cornwell, 2007;Messier et al., 2017). ...
... In our case, environmental conditions may be relatively extreme such that all within-species trait patterns are monotonic with increasing fire frequency but would not be so under less limiting nitrogen conditions. Another hypothesis is that plasticity (contributing to within-species variation) and adaptive evolution (underpinning among-species variation) allow trait-environment and even trait-trait relationships within species to become decoupled from among-species patterns (Ackerly & Cornwell, 2007; F I G U R E 5 Correlations between specific leaf area (SLA, cm 2 /g) and foliar nitrogen by mass (%N) calculated at two categorical scales: (a) by functional group (across fire frequencies) and (b) by fire frequency (across functional groups). The black dashed line is fit to all data within the panel while the coloured lines are fit within the categories in the panel (e.g. ...
The functional response of plant communities to disturbance is hypothesised to be controlled by changes in environmental conditions and evolutionary history of species within the community. However, separating these influences using direct manipulations of repeated disturbances within ecosystems is rare. We evaluated how 41 years of manipulated fire affected plant leaf economics by sampling 89 plant species across a savanna-forest ecotone. Greater fire frequencies created a high-light and low-nitrogen environment, with more diverse communities that contained denser leaves and lower foliar nitrogen content. Strong trait–fire coupling resulted from the combination of significant intraspecific trait–fire correlations being in the same direction as interspecific trait differences arising through the turnover in functional composition along the fire-frequency gradient. Turnover among specific clades helped explain trait–fire trends, but traits were relatively labile. Overall, repeated burning led to reinforcing selective pressures that produced diverse plant communities dominated by conservative resource-use strategies and slow soil nitrogen cycling.
... Here, we classified oribatid mite traits into α-and β-niche dimensions to disentangle the processes contributing to the assembly of communities (Ackerly & Cornwell, 2007). Generally, α-niche traits are related to resource use and β-niche traits to coping with abiotic factors. ...
Forest soils are a critical component of terrestrial ecosystems and host a large number of animal decomposer species. One diverse and abundant decomposer taxon is oribatid mites (Acari: Oribatida), whose species composition varies with forest type and tree species composition. We used functional traits that indicate different niche dimensions, to infer assembly processes of oribatid mite communities in monocultures and mixed forests of native and introduced tree species. We found that coexisting species differed more in the resource‐related niche dimension, i.e., reproductive mode and trophic guild, than in the morphological dimension, e.g., body length and width, sclerotization and concealability. These results suggest that both filtering and partitioning processes structure oribatid mite communities. In native European beech forests, but not in non‐native Douglas fir forests, oribatid mites were mainly structured by filtering processes acting via traits related both to environmental tolerance and to resources. Furthermore, oribatid mite trait diversity, but not phylogenetic diversity, differed significantly between monocultures and mixed forests, demonstrating that multidimensional diversity indices provide additional information on soil biodiversity. Overall, the study provides evidence that traits representing different niche dimensions need to be considered for understanding assembly processes in soil animal communities and thereby soil biodiversity.
... A majority of trait studies, both within invasion ecology as well as other trait subjects, are focused at the across-species level (i.e. interspecific variation); however, there is growing recognition that intra-specific trait variation (ITV) can also be important, and contribute to community or ecosystem level functioning (Ackerly and Cornwell 2007;Fajardo and Piper 2011;Kumordzi et al. 2014;Siefert et al. 2015;Fajardo and Siefert 2018). It has been proposed that high phenotypic trait plasticity is a common characteristic of successful invaders, which may allow rapid adaptation to biotic or abiotic conditions in new environments (Geng et al. 2004;Davidson et al. 2011). ...
It is often speculated that non-native invasive species undergo rapid changes in their phenotypic properties (i.e., traits) that provide adaptive advantage in their new environment. However, few studies have directly compared traits of invasive non-native species with their native counterparts to reveal whether such phenotypic changes occur, and which stages of initial introduction and subsequent invasion contribute to these shifts. We studied trait variation of an invasive tree, Pinus contorta, which is native to northwestern North America and invasive in the Patagonia region of South America (i.e., Argentina and Chile). Commercial plantations of P. contorta were introduced extensively in Patagonia from the 1970s onward, from an unknown seed origin within the Pacific Northwest, USA, where three sub-species are found, including subsp. contorta, latifolia, and murrayana. We employed a home-versus-away study approach, where we compared mean growth, defense, and reproduction trait values, and mean within-stand trait variation (Coefficient of Variation, CV) of Patagonia plantations, with the three native sub-species. We further compared mean traits, and trait CVs between invasive P. contorta and the Patagonia plantations from which they escaped. Patagonia plantations shared the most similar mean trait values with subsp. latifolia and murrayana, suggesting possible source populations. However, both mean trait values and trait CVs of Patagonia plantations differed from all three native sub-species, indicating potential founder effects, population bottlenecks, and/or plastic responses to their new environment that occurred during or after introduction. We also found evidence for selective change during invasion; however, these differences did not suggest growth traits were prioritized over defense traits, which was inconsistent with hypotheses that invaders exhibit an evolutionary trade-off between defense traits and growth traits. Our study highlights that processes occurring both at first introduction and establishment, as well as the subsequent invasion phase can influence the phenotype of successful invaders.
... Functional diversity has been used mainly to understand the mechanisms underpinning the relationship between diversity and ecosystem functions (Gross et al., 2017;Mason et al., 2005), and community assembly and niche partitioning (Cornwell & Ackerly, 2009;Kraft & Ackerly, 2014;Kraft et al., 2008). Approaches assessing functional diversity have been designed similarly to the methods to quantify taxonomic diversity, for instance by estimation of alpha and beta trait diversity (Ackerly & Cornwell, 2007), by assessment of functional groups (Petchey & Gaston, 2006) or by various diversity indexes that summarize the richness, evenness and divergence within a community as a continuous index (Mason et al., 2005). ...
Shade trees in agroforestry systems confer ecosystem services, such as enhanced soil fertility from diverse litter inputs, microclimate regulation via shade, and disease mitigation through trophic and abiotic interactions. With this thriving role of agroforestry in sustainable agriculture, particularly for tree crops, systematic and reliable methods to select shade trees for specific agroecosystem outcomes are crucial.
Plant functional traits offer a framework to describe, select and manage shade trees. Over the last decade, shade tree leaf functional traits and whole plant traits have been assessed in agroforestry systems. Yet, we lack amalgamated information on (i) what we know about shade tree trait relationships with functions to achieve desired agroecosystem outcomes, (ii) how decades of shade tree selection by farmers impacts agroforests inter‐ and intraspecific trait diversity, and (iii) which shade tree traits should be considered for achieving farmer priorities.
We consolidate literature on Coffea arabica (coffee) and Theobroma cacao (cocoa) agroforestry systems to summarize the role of shade tree functional traits in three key ecosystem functions: soil fertility, microclimate modification and crop productivity. We compile global and regional datasets on tree functional trait diversity to show the functional space of agroforestry tree species compared with the overall functional space observed in plants.
Despite, or maybe because of, high shade tree diversity, shade tree trait characterization remains coarse and commonly measured at the community scale in the literature. Based on published trait data, we show that farmers adjust the functional composition of shade trees to increase the recycling of soil nutrients (high leaf nitrogen), the production of wood (skewing towards lower wood densities) and the production of fruits (tendency towards high seed size). Common shade trees in coffee and cocoa systems fall in the mid‐range of leaf acquisitive to conservative strategies, providing evidence that expanding shade tree portfolios can improve, or even accelerate, functions.
Synthesis and applications : Based on the agroforestry literature and on trait‐environment relationships, we propose a matrix of shade tree traits that influence desirable agroecosystem outcomes for farmers, which can guide fine‐scale coordination of trait expression and agroforestry functions.
... Variation in functional traits can contribute to strong complementarity and are usually defined as morphological and physiological traits that affect plant fitness through their effects on plant performance (Violle et al., 2007). Functional traits can be used to assess and predict resource use efficiency and competitive ability for a given resource pool (Lavorel and Garnier, 2002;Ackerly & Cornwell, 2007). Functional traits can be plastic, where different individuals of a given cultivar exhibits different physiological or morphological traits in response to a variable environment (Wainwright et al., 2018) or different neighbors . ...
Despite being visually cryptic, conspecific cultivar mixtures increase diversity and can increase productivity in agricultural systems. However, the mechanisms underlying this increase are unclear. In natural systems, differences in traits among species and among ecotypes correspond with diversity-increased productivity, but whether these attributes are important in cultivar mixtures is still unclear. To explore how cultivar mixtures affect agroecosystem productivity and the roles of trait dissimilarity, we conducted a four-year (2017-2020) field experiment in Northeast China with maize. The experimental treatments included eight single cultivar mono-cultures, four two-cultivar mixtures, one four-cultivar mixture, one six-cultivar mixture and one eight-cultivar mixture. Experiments were arranged in a randomized complete block design with three replications. Across the four years, all cultivar mixture combinations increased aboveground biomass and crude protein in grain by 7.0% and 4.1%, respectively, compared to the average of the eight monocultures. Grain yield, aboveground biomass, and grain crude protein in overyielding cultivar combinations increased by 2.0-9.0%, 13.0-20.0% and 4.8-10.7%, respectively, compared to the average of the component monocultures of each mixture over four years. We calculated positive complementarity effects for grain yield, aboveground biomass and grain crude protein. All selection effects of cultivar mixtures were negative or neutral. There were strong positive correlations between complementarity effect and functional trait dissimilarity in cultivar mixtures, based on grain yields (P< 0.010), aboveground biomass (P< 0.001) and grain crude protein (P< 0.050), whereas there were no such positive relationships between selection effects and functional trait dissimilarity. Moreover, we found higher levels of trait dissimilarity for shoot diameter, leaf area and specific leaf area in cultivar mixtures than in monocultures. Also, the shoot diameter, leaf area and specific leaf area of specific cultivars were higher in mixtures than in monocultures. Our results indicated that niche complementarity derives from functional trait dissimilarity, and strong complementarity effects correlate with greater functional trait dissimilarity in cultivar mixtures. These findings provide evidence that plasticity in traits, rather than only inherent traits, contributed to the diversity effects, and the greater functional trait dissimilarity among cultivars in mixtures can increase crop productivity via increasing cryptic diversity in agroecosystems. Our results link changes to plant aboveground traits in cultivar mixtures, which shed light on yield advantages in diverse agroecosystems.
... Among these factors, functional trait dissimilarity has received increasing attention in recent years as it better reflects niche partitioning among species (Chen et al., 2016;Lasky et al., 2014;Uriarte et al., 2010). In particular, functional traits that reflect species' resource acquisition strategies are considered crucial for empirically assessing and predicting how species allocate and compete for local resource pools (Ackerly & Cornwell, 2007;Lavorel & Garnier, 2002). The complementarity of plant resource use (light and soil nutrients) increases with greater dissimilarity among neighbourhood species (Muledi et al., 2020;Schwilk & Ackerly, 2005;Violle et al., 2012) by using spatiotemporal stratification, different chemical forms of nutrients or improving nutrient availability (Diaz et al., 2004;Pornon et al., 2007). ...
Plant nutrient stoichiometry is of critical importance to productivity and nutrient cycling in terrestrial ecosystems. The impacts of tree species diversity on productivity have been well studied at the stand level. However, it is unclear how neighbourhood interactions impact the foliar nutrient stoichiometry of trees at the neighbourhood scale and how plant mycorrhizal associations can mediate such effects.
We randomly selected eight tree species from a large‐scale biodiversity experiment with mixtures up to 32 tree species in subtropical China to assess the effects of species richness, phylogenetic and trait dissimilarities and competition on the foliar nutrient stoichiometry of focal trees associated with either arbuscular mycorrhizal (AM) or ectomycorrhizal (EM) fungi. We further investigated whether neighbourhood diversity can alter focal tree growth by regulating C:N:P stoichiometry.
Neighbourhood species richness had no significant impact on the foliar C:N, N:P or C:P for both AM and EM trees. Increased neighbourhood phylogenetic dissimilarity significantly decreased the foliar N:P and C:P of AM trees but did not affect those of EM tree species. Foliar C:N, N:P and C:P of AM trees decreased with increasing neighbour trait (specific leaf area, root diameter, wood density dissimilarity, total trait) dissimilarities, while those of EM trees increased or remained unchanged. The increase of the neighbourhood competition index resulted in an increase in the foliar C:N of AM tree species but not EM tree species. The structural equation model analysis revealed that the increase of neighbourhood phylogenetic dissimilarity and functional trait dissimilarity indirectly enhanced tree growth of AM trees by decreasing foliar C:N. Conversely, the increase of neighbourhood‐specific root length and wood density dissimilarity indirectly reduced the growth of EM trees by increasing foliar N:P.
Synthesis . Our results indicate that neighbourhood trait dissimilarity regulated tree foliar stoichiometry and growth performance, but the effects depended on the mycorrhizal type of trees. Our findings highlight the importance of tree mycorrhizal associations for better understanding the relationship between plant diversity and ecosystem functions.
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... In other words, the environment may act as a "filter," allowing a community to contain only species having certain adaptive traits necessary for existing in that environment (e.g. Cavender- Bares et al. 2004;Ackerly & Cornwell 2007). For instance, species communities may respond to modifications of the environment or climate change according to their species traits, ultimately causing a variation in the diversity and composition of these communities at either spatial or temporal scale or both. ...
Biotic and abiotic factors can act as filters for determining the species composition of biological communities. We aimed to identify abiotic factors driving the assembly of bat communities in Eastern Mediterranean pine plantations along a north–south climatic gradient, as they are crucial forest habitats for the assessment and conservation of these communities. We expected that bat communities are predominantly shaped by environmental filtering. We conducted acoustic sampling in 35 pine plantations in Israel and analyzed recordings for species identification. We used the ESLTP analysis, an extension of the three-table ordination (RLQ analysis), to explore relationships between environmental characteristics, species occurrences, and functional traits of species while accounting for phylogenetic relationships between species and spatial distribution of the communities. Communities showed phylogenetic and trait clustering. Climatic conditions and forest vegetation composition shaped communities of bats, affecting the distribution of traits related to foraging behaviors, vegetation clutter, and the ability of bats to maneuver in it. Maneuverable species were associated with the northern Mediterranean climatic zone, with a scarce cover of drought-tolerant small shrubs and grassland. Fast flyers were associated with the center-south semi-arid area, with abundant drought-tolerant small shrubs and grassland. These forces might have a predominant role in the assembly of these communities, presumably due to the stressful climatic conditions of the study area. The ESLTP approach can be extended to other taxa and environments to predict species responses to disturbance and environmental changes and give insights into environmental management.
... In other words, the environment may act as a "filter," allowing a community to contain only species having certain adaptive traits necessary for existing in that environment (e.g. Cavender- Bares et al. 2004;Ackerly & Cornwell 2007). For instance, species communities may respond to modifications of the environment or climate change according to their species traits, ultimately causing a variation in the diversity and composition of these communities at either spatial or temporal scale or both. ...
Biotic and abiotic factors can act as filters for determining the species composition of biological communities. We aimed to identify abiotic factors driving the assembly of bat communities in Eastern Mediterranean pine plantations along a north-south climatic gradient, as they are crucial forest habitats for the assessment and conservation of these communities. We expected that bat communities are predominantly shaped by environmental filtering. We conducted acoustic sampling in 35 pine plantations in Israel and analyzed recordings for species identification. We used the ESLTP analysis, an extension of the three-table ordination (RLQ analysis), to explore relationships between environmental characteristics, species occurrences, and functional traits of species while accounting for phylogenetic relationships between species and spatial distribution of the communities. Communities showed phy-logenetic and trait clustering. Climatic conditions and forest vegetation composition shaped communities of bats, affecting the distribution of traits related to foraging behaviors, vegetation clutter, and the ability of bats to maneuver in it. Maneuverable species were associated with the northern Mediterranean climatic zone, with a scarce cover of drought-tolerant small shrubs and grassland. Fast flyers were associated with the center-south semi-arid area, with abundant drought-tolerant small shrubs and grassland. These forces might have a predominant role in the assembly of these communities, presumably due to the stressful climatic conditions of the study area. The ESLTP approach can be extended to other taxa and environments to predict species responses to disturbance and environmental changes and give insights into environmental management.
... The simple analysis that we conducted here also invites further investigation of trait-environment correlations using this unprecedented dataset for Australian taxa. First, while our treatment of species-by-site combinations as independent data points represents the totality of trait variation across sites emerging from both species turnover and across-site intra-specific variation, it does not partition the relative contribution of these components to the observed patterns (Ackerly & Cornwell, 2007). Identifying the sources of this variation would have important implications for our understanding of how trait-climate patterns have emerged historically, and how resilient communities will be to future change (Dong et al., 2020). ...
... We used trait-gradient analysis to access the intraspecific variation along the environmental gradient (Ackerly and Cornwell, 2007). The individual trait values were plotted against community-mean trait values which were strongly determined by external filters at a large scale, such as abiotic factors. ...
Leaf stoichiometric traits are central to ecosystem function and biogeochemical cycling, yet no accepted theory predicts their variation along environmental gradients. Using data in the China Plant Trait Database version 2, we aimed to characterize variation in leaf carbon and nitrogen per unit mass (Cmass, Nmass) and their ratio and to test an eco-evolutionary optimality model for Nmass. Community-mean trait values were related to climate variables by multiple linear regression. Climatic optima and tolerances of major genera were estimated; Pagel's λ was used to quantify phylogenetic controls, and Bayesian phylogenetic linear mixed models to assess the contributions of climate, species identity, and phylogeny. Optimality-based predictions of community-mean Nmass were compared to observed values. All traits showed strong phylogenetic signals. Climate explained only 18 % of C:N ratio variation among species but 45 % among communities, highlighting the role of taxonomic replacement in mediating community-level responses. Geographic distributions of deciduous taxa were separated primarily by moisture and evergreens by temperature. Cmass increased with irradiance but decreased with moisture and temperature. Nmass declined with all three variables. C:N ratio variations were dominated by Nmass. The coefficients relating Nmass to the ratio of maximum carboxylation capacity at 25 ∘C (Vcmax25) and leaf mass per area (Ma) were influenced by leaf area index. The optimality model captured 68 % and 53 % of variation between communities for Vcmax25 and Ma, respectively, and 21 % for Nmass. We conclude that stoichiometric variations along climate gradients are achieved largely by environmental selection among species and clades with different intraspecific trait values. Variations in leaf C:N ratio are mainly determined by Nmass, and optimality-based modelling shows useful predictive ability for community-mean Nmass. These findings should help to improve the representation of C:N coupling in ecosystem models.
... For example, environmental filtering may contribute to which species potentially co-occur due to common habitat conditions and/or geography [14,15], or the effect of the habitat size on co-occurrence patterns [16,17]. More recently, trait-based analyses have been considered to test whether, and to what extent, communities are structured by environmental filtering and/or biotic interactions [18,19]. However, whether species traits are significant predictors of species co-occurrence patterns remains little explored in communities with multiple trophic levels and biotic interactions, with some studies focused on communities of birds [20], invertebrates [21] and plants [22]. ...
Trait-based analyses have been successful in determining and predicting species association outcomes in diverse communities. Most studies have limited the scope of this approach to the biotic responses of a small number of species or geographical regions. We focused on determining whether three biologically relevant traits (body size, temperature preference and trophic level) influence the patterns of co-occurrence between multiple species. We used fish species presence/absence from 9204 lakes in Ontario, Canada, to obtain effect sizes of 2001 species-pair co-occurrence values, using a null model approach. Euclidean distances between each species-pair were calculated for each of the three traits selected. Multiple regression models and randomization tests were used to determine the direction and significance of the relationship of each trait with the observed co-occurrence values. The results show that species temperature preference was significantly related to co-occurrence patterns, indicating the effect of environmental filtering. Trophic level was significantly related to co-occurrence values for both linear and quadratic terms, suggesting that segregation between species is driven by large differences in this trait (predation effects). Unexpectedly, body size was not significantly related to the observed co-occurrence patterns. We provide a new approach to test relationships between species assemblages and trait conditions.
... Species were sampled considering the mass-ratio hypothesis (Grime 1998), i.e. we measured leaf traits for species that contributed 58-86% (mean ± SD = 76% ± 6.4%) of the total basal area of each plot (5-29 species per plot; S4). Overall, LFTs were determined for 125 tree species and then scaled to community level to generate community scores (Ackerly and Cornwell 2007). ...
... Such complexity must be integrated within a functional approach using appropriate metrics together with other issued considerations (Gallien et al., 2014;Gallien & Carboni, 2017;Thuiller et al., 2010). Functional distinctiveness reflects niche differentiation between a specific NIS and other cooccurring species, known as the alpha niche concept (Ackerly & Cornwell, 2007). Implementation of this concept to biological invasions is strongly recommended to study how the trait expression of a given NIS could influence its establishment, by exploiting unique resources or displaying singular behaviour (Stubbs & Wilson, 2004;Thuiller et al., 2010). ...
Our understanding of the community assembly processes acting on non‐indigenous species (NIS), as well as the relationship with native species is limited, especially in marine ecosystems. To overcome this knowledge gap we here develop a trait‐based approach based on the functional distinctiveness metric to assess niche overlap between NIS and native species, using high‐resolution data on benthic invertebrate communities in the Baltic Sea. Our results show that NIS retain a certain degree of similarity with native species, but display one or a few singular unique traits (e.g., bioturbation ability). Furthermore, we demonstrate that community assembly processes, including both environmental filtering and limiting similarity affect NIS establishment, but that their effects may be highly context dependent, as illustrated by pronounced spatial patterns in distinctiveness. Finally, our trait‐based approach provides a generic framework applicable to other areas and organisms, to better understand and address biological invasions.
... On one hand, asymmetric (hierarchical) competition for a shared limiting resource may select for an optimal suite of traits that maximize a competitor's ability to acquire the resource. This would lead to a negative relationship between competition strength and functional diversity (Ackerly & Cornwell., 2007). On the other hand, the theory of limiting similarity posits that competing species must demonstrate sufficient differences in their niches to persist, which would lead to a positive relationship between competition strength and functional diversity (MacArthur & Levins, 1967;Meszéna et al., 2006). ...
Competition should play a key role in shaping community assembly and thereby local and regional biodiversity patterns. However, identifying its relative importance and effects in natural communities is challenging because theory suggests that competition can lead to different and even opposing patterns depending on the underlying mechanisms. Here, we have taken a different approach: rather than attempting to indirectly infer competition from diversity patterns, we compared trait diversity patterns in odonate (dragonfly and damselfly) communities across different spatial and temporal scales along a natural competition–predation gradient. At the local scale (within a community), we found that trait diversity increased with the size of top predators (from invertebrates to fish). This relationship is consistent with differences in taxonomic diversity, suggesting that competition reduces local trait diversity through competitive exclusion. Spatial (across communities) and temporal (within communities over time) trait variation peaked in communities with intermediate predators indicating that both high levels of competition or predation select for trait convergence of communities. This indicates that competition acts as a deterministic force that reduces trait diversity at the local, regional, and temporal scales, which contrasts with patterns at the taxonomic level. Overall, results from this natural experiment reveal how competition and predation interact to shape biodiversity patterns in natural communities across spatial and temporal scales and provide new insights into the underlying mechanisms.
... community weighted trait means; Grime, 1998), are subject to environmental selection at three levels: (1) species composition due to environmental filtering (Kraft et al., 2015;Duarte et al., 2018), (2) species relative abundance (Martin & Canham, 2020), and (3) intraspecific variation (Gratani, 2014;Henn et al., 2018;Monroe et al., 2020). Where community traits differ systematically over environmental gradients (Ackerly & Cornwell, 2007), the three mechanisms above operate predominately at large, intermediate, and local scales, respectively. This pattern is consistent with spatial gradients of hydraulic traits, where there is a general trend from communities with high P50, small HSMs, and high leaf water potentials in regions of high water availability, to the opposite trait values in drier regions (Anderegg, 2015;Trugman et al., 2020). ...
Atmospheric conditions are expected to become warmer and drier in the future, but little is known about how evaporative demand influences forest structure and function independently from soil moisture availability, and how fast‐response variables (such as canopy water potential and stomatal conductance) may mediate longer‐term changes in forest structure and function in response to climate change.
We used two tropical rainforest sites with different temperatures and vapour pressure deficits (VPD), but nonlimiting soil water supply, to assess the impact of evaporative demand on ecophysiological function and forest structure. Common species between sites allowed us to test the extent to which species composition, relative abundance and intraspecific variability contributed to site‐level differences.
The highest VPD site had lower midday canopy water potentials, canopy conductance ( g c ), annual transpiration, forest stature, and biomass, while the transpiration rate was less sensitive to changes in VPD; it also had different height–diameter allometry (accounting for 51% of the difference in biomass between sites) and higher plot‐level wood density.
Our findings suggest that increases in VPD, even in the absence of soil water limitation, influence fast‐response variables, such as canopy water potentials and g c , potentially leading to longer‐term changes in forest stature resulting in reductions in biomass.
... some limitations, in particular when it comes to understanding positive biodiversity effects: first, traits often co-vary because of evolutionary trade-offs between ecological strategies 32,33 , which makes it difficult to distinguish correlation from causation in trait-based analyses of BEF experiments. Second, while traits often are associated with environmental conditions 19,34 (e.g. correlation between specific leaf area and soil moisture), it remains unclear whether differences in these traits drive the studied diversity effect, or whether other, unknown trait differences that correlate with these underlie the observed effects. ...
In plant communities, diversity often increases productivity and functioning, but the specific underlying drivers are difficult to identify. Most ecological theories attribute positive diversity effects to complementary niches occupied by different species or genotypes. However, the specific nature of niche complementarity often remains unclear, including how it is expressed in terms of trait differences between plants. Here, we use a gene-centred approach to study positive diversity effects in mixtures of natural Arabidopsis thaliana genotypes. Using two orthogonal genetic mapping approaches, we find that between-plant allelic differences at the AtSUC8 locus are strongly associated with mixture overyielding. AtSUC8 encodes a proton-sucrose symporter and is expressed in root tissues. Genetic variation in AtSUC8 affects the biochemical activities of protein variants and natural variation at this locus is associated with different sensitivities of root growth to changes in substrate pH. We thus speculate that - in the particular case studied here - evolutionary divergence along an edaphic gradient resulted in the niche complementarity between genotypes that now drives overyielding in mixtures. Identifying genes important for ecosystem functioning may ultimately allow linking ecological processes to evolutionary drivers, help identify traits underlying positive diversity effects, and facilitate the development of high-performance crop variety mixtures.
... Nevertheless, until recently, the tools for quantifying convergence or divergence, especially in the ecologicalevolutionary context of community assembly, remained poorly developed. The modern approach, focusing on traits or trait syndromes (Ackerly 2004;Ackerly and Cornwell 2007;de Bello et al. 2012;Ottaviani et al. 2018) rather than vegetation textural aspects such as the lifeform composition seems to be promising. ...
Mediterranean-type ecosystems (MTEs) are members of the zonobiome S1 (Ethesial Zone). Five regions support MTEs—two in the Northern Hemisphere and three in the Southern Hemisphere. The latter, including the Chilean, Cape (South Africa), and Australian MTE, are the subject of this chapter. MTEs have attracted much attention from biogeographers mainly because of a disproportionally high species diversity and endemism and ecologists because of remarkable physiognomic similarity, often explained by convergent evolutionary processes. This chapter focuses on four intriguing issues associated with the Southern-Hemisphere MTEs, namely (1) one-clade domination of Australian MTE woodlands by eucalypts, (2) very low tolerance against the fire of the Chilean MTE, (3) lack of flammable woodlands in the Cape region, and (4) low-key presence of annuals in the MTEs of the Cape and Australia.KeywordsAustralian eucalypt woodlandsCaliforniaCape fynbosChilean MatorralEvolutionary biome assemblyMediterranean BasinSouthwest Australian Floristic RegionOld stable landscapes
... However, by modelling single traits independently of each other, univariate approaches ignore the correlations existing between the multiple trait values in communities. This is an important issue since traits are inherently correlated at the community-level to form specific combinations of traits (Ackerly & Cornwell, 2007;Bruelheide et al., 2018;Callis-Duehl et al., 2017;Fajardo & Siefert, 2018;Fonseca et al., 2000;Fornoff et al., 2017;Helsen et al., 2021;Li et al., 2017). These combinations of mean traits are a key concept in functional biogeography since they are markers of assembly processes, environmental filters, ecosystem functioning and services. ...
Aim
Understanding how combinations of ecological traits at the community‐level vary with environmental conditions is crucial to anticipate and respond to the biodiversity crisis. While this topic is popular, most attempts to analyse and predict multiple traits in space and time ignore the inherent correlations between these traits. In doing so, the predicted traits in unobserved environments are likely to be flawed (i.e. unrealistic trait combinations). Here, we propose a framework that addresses this methodological question in functional biogeography.
Innovation
Our framework relies on joint trait distribution models to quantify how combinations of mean trait values at the community level co‐vary as a function of environmental conditions. Making use of joint probabilities and the constraints imposed by trait correlations, our framework not only predicts the most suitable combination of traits in a given environment but also the envelope of possible alternatives. This innovation allows visualizing how the correlation structure between traits imposes a strong constraint (or not) on the expected combination of traits in a given environment. The stronger trait correlations, the smaller the envelope of likely alternative states. We provide an R package implementing our framework.
Main Conclusions
Applied to plant communities in the French Alps, our framework quantifies the variation of trait combinations at the community‐level along environmental gradients that, otherwise, could not be identified. Strong correlations in community mean leaf traits led to a low diversity of alternative combinations of community means, which can only vary along the acquisition‐conservation spectrum. Instead, height varied partly independently of leaf traits, leading to a higher diversity in the combinations of mean community traits. Our framework allows for a more integrated understanding and prediction of the distribution of traits, thus moving a descriptive functional biogeography to a more predictive science.
... Violle et al. (2012) showed the importance of including intraspecific variability to get a better understanding of the environmental filters acting on the vegetated community rather than using mean trait values per species present in the community. This was a revision of the concepts of alpha and beta niches (Pickett and Bazzaz, 1978), which allow understanding the effects of environmental filters on intraspecific and interspecific trait variability (Ackerly and Cornwell, 2007). ...
In the last three decades, quantitative approaches that rely on organism traits instead of taxonomy have advanced different fields of ecological research through establishing the mechanistic links between environmental drivers, functional traits, and ecosystem functions. A research subfield where trait-based approaches have been frequently used but poorly synthesized is the ecology of seagrasses; marine angiosperms that colonized the ocean 100M YA and today make up productive yet threatened coastal ecosystems globally. Here, we compiled a comprehensive trait-based response-effect framework (TBF) which builds on previous concepts and ideas, including the use of traits for the study of community assembly processes, from dispersal and response to abiotic and biotic factors, to ecosystem function and service provision. We then apply this framework to the global seagrass literature, using a systematic review to identify the strengths, gaps, and opportunities of the field. Seagrass trait research has mostly focused on the effect of environmental drivers on traits, i.e., "environmental filtering" (72%), whereas links between traits and functions are less common (26.9%). Despite the richness of trait-based data available, concepts related to TBFs are rare in the seagrass literature (15% of studies), including the relative importance of neutral and Frontiers in Plant Science (2023) A trait-based framework for seagrass ecology: Trends and prospects. niche assembly processes, or the influence of trait dominance or complementarity in ecosystem function provision. These knowledge gaps indicate ample potential for further research, highlighting the need to understand the links between the unique traits of seagrasses and the ecosystem services they provide. KEYWORDS functional ecology, trait-based approach, seagrass traits database, ecosystem service vulnerability, response-effect framework
... For each plot, we computed the community-weighted mean (CWM), that is the mean trait value of all species present weighted by species abundances. CWM is a widely used trait-based statistic which is expected to reflect trait-environment relationships (Ackerly & Cornwell, 2007). ...
Widespread forest loss and fragmentation dramatically increases the proportion of forest areas located close to edges. Although detrimental, the precise extent and mechanisms by which edge proximity impacts remnant forests remain to be ascertained.
By combining unmanned aerial vehicle laser scanning (UAV‐LS) with field data from 46 plots distributed at varying distances from the edge to the forest interior in a fragmented forest of New‐Caledonia, we investigated edge influence on forest structure, composition, function, above‐ground biomass (AGB) and microclimate. Using simple linear regressions, structural equation modelling and variance partitioning, we analysed the direct and indirect relationships between distance to edge, UAV‐LS‐derived canopy structural metrics, understorey microclimate, AGB, taxonomic and functional composition while accounting for the potential influence of fine‐scale variation in topography.
We found that the distance to the closest forest edge was strongly correlated with canopy structure and that canopy structure was better correlated to forest composition, function, biomass and microclimate than distance to the closest forest edge. This suggests that the influence of edge is mediated by changes in canopy structure. Plots located near the edge exhibited a lower canopy with more gaps, higher microclimate extremes, lower biomass, lower taxonomic and functional diversity as well as denser wood and lower specific leaf area. UAV‐LS‐derived canopy structural metrics were relevant predictors of understorey microclimate, biomass and taxonomic and functional composition. Overall, the influence of topography was marginal compared to edge effects.
Synthesis. Accounting for fine‐scale variation in canopy structure captured by UAV‐LS provides insights on the multiple edge impacts on key forest properties related to structure, diversity, function, biomass and microenvironmental conditions. Integrating UAV‐LS‐derived data can foster our understanding of cascading and interacting impacts of anthropogenic influence on tropical forest ecosystems and should help to improve conservation strategies and landscape management policies.
... The ability of species to respond to changes in environmental conditions and resource availability are related to functional traits, which are defined as "measurable morphological, physiological or phenological features of species that impact their fitness via their effects on demographic features" . Functional traits also mediate the responses associated with fundamental processes such as species dispersal, establishment, and persistence (Ackerly and Cornwell, 2007;De Bello et al., 2013;Zambrano et al., 2019). The increase in species abundance with traits facilitating colonization and persistence, especially in isolated and/or smaller fragments, is a response that alters the growth and, eventually, the occurrence of some populations in the long term, changing the species composition and dynamics (Dupré and Ehrlén, 2002;May et al., 2013). ...
With more than 2,600 species and 181 genera, palms (Arecaceae) are one of the
most diverse and widely distributed plant families in tropical environments (Baker and Dransfield, 2016). Although they make up a modest portion of the above-ground biomass in most neotropical forests (DeWalt and Chave, 2004), their contribution increases in places where palms are dominant (Muscarella et al., 2020). In the Amazon forests, palms are hyperdominant elements(ter Steege et al., 2013). Their sheer abundance secures them a key role in forest function and forest structure (Boukili and Chazdon, 2017). Palms provide food for a wide variety of animal species (Onstein et al., 2017), including key resources for frugivores, which in turn disperse canopy trees that store most of the carbon in mature forests (Bello et al., 2015). Many human groups value palms and use them as raw material for building, food, drink, clothing, fuel, and medicine (Sylvester et al., 2012).
Palms tissues stretch the limits of plant cells to reach tree-like heights while
preserving mechanical stability and long-term function using only apical meristems
(Tomlinson, 2006). Little is known about the functional mechanisms governing
palms’ adaptation to environmental gradients, despite their ecological significance
and distinctive morphological and physiological structure. Here, we summarize the
functional role of palms from a variety of perspectives, which concentrate on the
analysis of functional traits and their influence on adaptation to environmental gradients. Contributions are grouped into the analysis of functional traits and conservation issues.
... Functional diversity is more sensitive to disturbance as compared to species diversity (Zhang et al., 2015). Quantitative methods to determine functional diversity indices are developed in many previous investigations (Suding et al., 2008;Ackerly & Cornwell, 2007;Laliberte & Legendre, 2010;. These researchers also depicted the importance of comparison studies of diversity indices to rectify the confusion of researchers to select the best method. ...
... Trait-based approaches have been actively spreading in microbial ecology recently [15,46]. However, a number of problems complicate their use by researchers. ...
We propose the trait-based method for quantifying the activity of functional groups in the human gut microbiome based on metatranscriptomic data. It allows one to assess structural changes in the microbial community comprised of the following functional groups: butyrate-producers, acetogens, sulfate-reducers, and mucin-decomposing bacteria. It is another way to perform a functional analysis of metatranscriptomic data by focusing on the ecological level of the community under study. To develop the method, we used published data obtained in a carefully controlled environment and from a synthetic microbial community, where the problem of ambiguity between functionality and taxonomy is absent. The developed method was validated using RNA-seq data and sequencing data of the 16S rRNA amplicon on a simplified community. Consequently, the successful verification provides prospects for the application of this method for analyzing natural communities of the human intestinal microbiota.
... The interactions between plant traits and their surrounding environment determine the performance of individual species and the composition and structure of their communities [94,95], which can be directly measured through trait-trait and trait-environment relationships [96,97]. From a global perspective, plant functional traits and climate are determinants of major ecosystem functions, including productivity, as well as water-and carbon-use strategies [98,99]. ...
Freshwater ecosystems are of worldwide importance for maintaining biodiversity and sustaining the provision of a myriad of ecosystem services to modern societies. Plants, one of the most important components of these ecosystems, are key to water nutrient removal, carbon storage, and food provision. Understanding how the functional connection between freshwater plants and ecosystems is affected by global change will be key to our ability to predict future changes in freshwater systems. Here, we synthesize global plant responses, adaptations, and feedbacks to present-day and future freshwater environments through trait-based approaches, from single individuals to entire communities. We outline the transdisciplinary knowledge benchmarks needed to further understand freshwater plant biodiversity and the fundamental services they provide.
... Plant functional traits are codetermined by species identity (genetic factors) and environment (Scheiner and Lyman, 1991;Weiher and Keddy, 1995). Environments promote the coexistence of species with similar functional traits in local habitats, but intraspecific trait variations cause differences in the life history strategy of a certain species or different species (Ackerly and Cornwell, 2007;Auger and Shipley, 2013;Siefert et al., 2015;Kumordzi et al., 2019). However, the species composition of a plant community differs with the environment. ...
Plants growing in forests at different succession stages in diverse habitats may adopt various life strategies from the perspective of plant functional traits. However, species composition differs with forest succession, and the effects of forest succession on traits have often been explored without considering the effects of species identity. We comprehensively investigated intraspecific variations in 12 traits of six overlapping species (two tree species and four understory shrub species) in three typical subtropical evergreen broad-leaved forests at different succession stages in eastern China. We found that intraspecific variations differed among traits. Fine root specific length presented large intraspecific variation, leaf area, specific leaf area and fine root tissue density showed medium intraspecific variations, and other traits displayed small intraspecific variations. Trees and understory shrubs in the early-stage forest exhibited higher leaf thickness, dry matter contents and tissue densities of leaves, roots, twigs, and stems and lower leaf area and specific leaf area. Those in the medium- and late-stage forests displayed contrasting trait characteristics. From the perspective of plant functional traits, plants in the early-stage forest formed a series of trait combinations for a resource conservative strategy with a low growth rate to adapt to fragile habitats with poor soil nutrients and changeable soil temperature and humidity, and those in the medium- and late-stage forests (especially the former) formed converse trait combinations for a resource acquisitive strategy with a high growth rate to adapt to low light availability and strongly competitive habitats. Our study reveals that plants in forests at different succession stages adopt various life strategies and provides data to the TRY and China plant trait databases.
... Indeed, the evolution of arboreality is linked with natural history strategies to cope with different environmental conditions and resources, with an evolutionary sequence from strictly ground to strictly arboreal ant groups (Nelsen et al. 2018). Nevertheless, we did not find a strong phylogenetic signal in the morphological traits considered here and opted to conduct all analyses under the habitat filter paradigm (Ackerly and Cornwell 2007). Interestingly, more than half of the genera collected in this study occurred in both strata, and only one subfamily was exclusive of a given stratum (Dorylinae, with only two species). ...
There is often a vertical stratification of the vegetation in tropical forests, where each forest stratum has a unique set of environmental conditions, including marked differences in habitat heterogeneity, physical complexity, and microclimate. Additionally, many tropical forests are highly seasonal, and we need to consider the temporal variation in environmental conditions when assessing the functional aspects of their organisms. Here, we tested the hypothesis that vertical stratification and seasonality shape tropical ants’ functional ecology and that there are differences in the functional trait diversity and composition between arboreal and ground-dwelling ant communities. We collected ants in the arboreal and ground strata in the rainy and dry seasons in six different areas, measuring seven morphological traits to characterize their functional ecology and diversity. Irrespective of the season, we found a distinct functional composition between arboreal and ground-dwelling ants and a higher functional richness on the ground. However, ground ants were more functionally redundant than arboreal ants. The differences in functional richness and redundancy between ant inhabiting strata and season could also be observed in the community-weighted mean traits: arboreal and ground ant traits can be distinguished in Weber’s length, mandible length, eye length, and eye position on the head capsule. The differences in these functional traits are mainly related to the ants’ feeding habits and the complexity of their foraging substrates. Overall, by providing the first systematic comparison of continuous traits between arboreal and ground-dwelling ants, our study opens new investigation paths, indicating important axes of functional diversification of tropical ants.
... It is commonly accepted that biological communities are nonrandomly assembled and represent the combined result of ecological and historical processes (Gravel et al. 2006;Kraft and Ackerly 2014;Pearson et al. 2018). Ecological processes involve the species' environmental requirements and their interspecific relationships (Ackerly and Cornwell 2007). For example, the environment may act as a "filter", allowing a community to consist only of species that can persist under the biotic and abiotic conditions in that environment due to the possession of certain morphological, physiological or ecological traits (Cavender-Bares et al. 2004;Kraft and Ackerly 2014;Blonder et al. 2015). ...
We applied a step-down factor analysis (SDFA) and multi-site generalised dissimilarity modelling (MS-GDM) to local flea communities harboured by small mammals (i.e., collected at small sampling sites over a short time period) in two South American regions (Patagonia and the Northwestern Argentina) with the aim of understanding whether these communities were assembled via niche-based or dispersal-based processes. The SDFA allows us to determine whether clusters of flea assemblages across different types of climates, vegetation and soils can be distinguished (suggesting niche-based assembly). MS-GDM allows us to determine whether a substantial proportion of the variation in flea species turnover is explained by specific climate-associated, vegetation-associated and soil-associated variables (indicating niche-based assembly) or host turnover (indicating dispersal-based assembly). Mapping of assemblages on climate, vegetation and soil maps, according to their loadings on axis 1 or axis 2 of the SDFA, did not provide clear-cut results. Clusters of similar loadings could be recognized within some, but not other, climate, vegetation and soil types. However, MS-GDM demonstrated that the effect of environmental variables (especially air temperature) on flea compositional turnover was much stronger than that of host turnover, indicating the predominance of niche-based processes in local community assembly. A comparison of our results with those on the mechanisms that drive species assembly in regional communities allows us to conclude that local and regional communities result from the joint action of niche-based and dispersal-based processes, with the former more important at a smaller spatial scale and the latter at a larger spatial scale.
Questions
We assessed interactions between climate change, bedrock types and snow cover duration on the trajectories of taxonomic and functional composition of subalpine plant communities. We predict (i) an increase in species richness on siliceous bedrock due to a reduced competition and a decrease in richness on calcareous bedrock due to increasing drought stress; (ii) decreasing snow cover duration should induce a higher shrub encroachment in hollows as compared to ridges; and (iii) increasing growing season temperature should induce taller sizes and more conservative growth traits, in particular in hollows.
Location
Subalpine belt of the Grandes Rousses mountain range, southwestern Alps (France).
Methods
189 vegetation plots were sampled in 1997 and 2017–2018. The duration of snow cover was assessed during two years in 1995–1997 and five functional traits were measured on 108 species in 2021. We performed multivariate analyses, quantified community‐weighted means (CWM) of traits and used ANOVAs to detect responses to local‐scale factors and changes in snow cover, temperature and precipitation since 1997 according to a nearby meteorological station.
Results
Overall, taxonomic composition weakly changed and changes were more dependent on the position of communities along the snow cover duration gradient than on their bedrock type. The abundance of drought‐tolerant species increased at the border of hollows and there was, over all communities, a slight increase in the abundance of dwarf shrubs and tall herbaceous species, a strong decrease in short herbaceous species and, thus, an overall decrease in species richness. There were important overall changes in CWM of size traits, in particular leaf area which increased the most in hollows irrespective of bedrock types.
Conclusion
In this subalpine site the effects of decreasing snow cover duration overwhelmed the effects of bedrocks, which may explain the overall increase in competitive species and decrease in species richness.
Light availability and seed dispersal can play a determinant role for plant growth and survival. The intricate interplay among these factors, coupled with pronounced topographic and elevational variation, may influence forest composition and structure. Despite the structural significance of palms within the Atlantic Forest, they are scarcely represented in both inventories and ecological studies. Additionally, functional trait variation among palm species is barely tested, and species are usually categorized into one or two functional types. We examined a palm community in terms of floristic composition and species replacement along an elevation gradient from 0 to 1400 m. Furthermore, we measured a set of morpho-physiological traits strongly associated with growth and survival strategies, such as photosynthetic capacity through Rapid Light Curves, leaf traits, height and fruit size and number. Our findings reveal highest richness from 300 to 800 m. Otherwise, palm density increased along elevation, peaking after 1200 m, mainly associated with E. edulis increase in density along elevation. Additionally, traits associated with enhanced light capture and dispersal capacity, i.e., higher photosynthetic capacity, height, and fruit number, were common among species widely distributed along the entire elevation gradient, such as Euterpe edulis M. and Geonoma schottiana M. In contrast, species with narrower distributions, exhibit the opposite traits. In conclusion, in our study area there is an integral role of light response and dispersal capacity in shaping the palm community structure in the Atlantic Forest along an elevation gradient from 0 to 1400 m.
Trait diversity, including trait turnover, that differentiates the roles of species and communities according to their functions, is a fundamental component of biodiversity. Accurately capturing trait diversity is crucial to better understand and predict community assembly, as well as the consequences of global change on community resilience. Existing methods to compute trait turnover have limitations. Trait space approaches based on minimum convex polygons only consider species with extreme trait values. Tree‐based approaches using dendrograms consider all species but distort trait distance between species. More recent trait space methods using complex polytopes try to harmonise the advantages of both methods, but their current implementation has mathematical flaws.
We propose a new kernel integral method (KIM) to compute trait turnover, based on the integration of kernel density estimators (KDEs) rather than using polytopes. We explore how this approach and the computational aspects of the KDE computation can influence the estimates of trait turnover. The novel method is compared with existing ones using justified theoretical expectations for a large number of simulations in which the number of species and the distribution of their traits is controlled for. The practical application of KIM is then demonstrated using data on plant species introduced to the Pacific Islands of French Polynesia.
Analyses on simulated data show that KIM generates results better aligned with theoretical expectations than other methods and is less sensitive to the total number of species. Analyses for French Polynesia data also show that different methods can lead to different conclusions about trait turnover and that the choice of method should be carefully considered based on the research question.
The mathematical properties of methods for computing trait turnover are crucial to consider because they can have important effects on the results, and therefore lead to different conclusions. The novel KIM method provided here generates values that better reflect the distribution of species in trait space than other methods. We therefore recommend using KIM in studies on trait turnover. In contrast, tree‐based approaches should be kept for phylogenetic diversity, as phylogenetic trees will then reflect the speciation process.
The variability in traits within species (intraspecific trait variability; ITV) has attracted an increased interest in functional ecology, as it can profoundly influence the detection of functional trait patterns, calculation of functional diversity (FD), and assessments of ecosystem functioning. This renewed focus stems from the recognition that species are not homogeneous entities but rather mosaics of individuals with varying traits. Researchers dealing with FD have increasingly recognized this issue, and consequently, multiple methods have emerged to explicitly incorporate ITV into FD calculations. Some methods treat individuals as the unit of analysis, while others characterize trait distributions around their means. Ecologists navigating this landscape of methods may face challenges in selecting the most appropriate approach to address their research questions. This synthesis provides an overview and guidelines on how and when to use the different methods available to quantify ITV in biological assemblages and integrate it into FD. As a case study, we computed correlations on simulated assemblages with varying degrees of trait variability. Our findings suggest that the choice of FD metric should be guided primarily by the ecological question being addressed and, to a lesser extent, by the number and types of traits. Simulations revealed strong correlations among FD metrics that account for ITV, particularly those indicating the size of the occupied functional trait space. As evidence accumulates and shows how ITV is key to shaping species' fitness and distribution as well as affecting ecosystem functioning, this synthesis will serve as a conceptual and practical tool inspiring and guiding researchers to integrate ITV in functional diversity analyses.
Biotic and abiotic factors can act as filters for determining the species composition of biological communities. We aimed to identify abiotic factors driving the assembly of bat communities in Eastern Mediterranean pine plantations along a north–south climatic gradient, as they are crucial forest habitats for the assessment and conservation of these communities. We expected that bat communities are predominantly shaped by environmental filtering. We conducted acoustic sampling in 35 pine plantations in Israel and analyzed recordings for species identification. We used the ESLTP analysis, an extension of the three‐table ordination (RLQ analysis), to explore relationships between environmental characteristics, species occurrences, and functional traits of species while accounting for phylogenetic relationships between species and spatial distribution of the communities. Communities showed phylogenetic and trait clustering. Climatic conditions and forest vegetation composition shaped communities of bats, affecting the distribution of traits related to foraging behaviors, vegetation clutter, and the ability of bats to maneuver in it. Maneuverable species were associated with the northern Mediterranean climatic zone, with a scarce cover of drought‐tolerant small shrubs and grassland. Fast flyers were associated with the center‐south semi‐arid area, with abundant drought‐tolerant small shrubs and grassland. These forces might have a predominant role in the assembly of these communities, presumably due to the stressful climatic conditions of the study area. The ESLTP approach can be extended to other taxa and environments to predict species responses to disturbance and environmental changes and give insights into environmental management.
Aim
There is widespread support that species richness increases with the available energy of an ecosystem, but the mechanisms underlying this driver of biodiversity patterns remain elusive. We evaluated gradients of functional diversity to test whether the higher species richness of productive, structurally diverse environments is due to a greater range of niches being supported by the abiotic conditions present (environmental filtering), greater availability of biotic resource and habitat niches (more niches) or increasing functional similarity of species (niche packing).
Location
Australia.
Taxon
Birds and mammals.
Methods
We used structural equation modelling to evaluate the relative contributions of climatic harshness (actual evapotranspiration, AET) and the availability of resource (gross primary productivity, GPP) and habitat (tree height) niches on taxonomic richness and functional richness, dispersion and evenness. We performed parallel analyses within 15 bioclimatic zones and continentally to evaluate the scaling of biodiversity gradients and the shifting balance between niche‐based mechanisms along environmental gradients.
Results
All continental diversity gradients were primarily associated with energy variables, but while species richness of both taxa and all functional diversity measures of bird assemblages increased with AET, mammal functional diversity was more strongly associated with GPP gradients. Results were more variable at the regional scale, but species richness gradients along tree height (birds and mammals) and GPP (mammals) within bioclimatic zones tended not to be paralleled by increases in functional richness or dispersion.
Main Conclusions
The niche‐based explanations of biodiversity gradients varied in importance with scale, position on environmental gradients and taxonomic group. At the continental extent, bird biodiversity gradients were structured by environmental filtering by climatic harshness, while mammal biodiversity was related to the increasing availability of resource niches with increasing productivity. Niche packing was more prominent at the regional scale, especially in bioclimatic zones where productivity and vegetation height were less limiting, and in mammal assemblages, suggesting that biodiversity patterns scale differently for birds and mammals.
The United States of America has a diverse collection of freshwater mussels comprising 301 species distributed among 59 genera and two families (Margaritiferidae and Unionidae), each having a unique suite of traits. Mussels are among the most imperilled animals and are critical components of their ecosystems, and successful management, conservation and research requires a cohesive and widely accessible data source. Although trait-based analysis for mussels has increased, only a small proportion of traits reflecting mussel diversity in this region has been collated. Decentralized and non-standardized trait information impedes large-scale analysis. Assembling trait data in a synthetic dataset enables comparison across species and lineages and identification of data gaps. We collated data from the primary literature, books, state and federal reports, theses and dissertations, and museum collections into a centralized dataset covering information on taxonomy, morphology, reproductive ecology and life history, fish hosts, habitats, thermal tolerance, geographic distribution, available genetic information, and conservation status. By collating these traits, we aid researchers in assessing variation in mussel traits and modelling ecosystem change.
The geometric morphometrics methods were used to evalu¬ate differences in the variability of the size and shape of the mandible in experimental groups of descendants of BALB/c, CBA and BC/IPAE linear mice with standard (control) and two disturbed diets of the mother: diet-1 – nutrition with oat grains during pregnancy and feeding of offspring; diet-2 – change of the mother’s diet from oatmeal monodiet to the standard nutrition after the birth of young mice. The most significant contribution to changeability of centroid sizes (CS) was made by the factor “diet” (D), not “line” (L), as well as by the interaction of factors “L x D”. The influence of the factor “sex” (S) did not manifest itself. The variation in the shape of the mandible was caused mainly not by factor D but by factor L. The maternal diet regimes had an ambiguous effect on the growth and development: diet-1 caused growth inhibition and destabilization of mandible morphogenesis, whereas diet-2 made sizes, shape and stability of morpho¬genesis in all lines similar to the control groups. The results can be used to solve a number of problems on population ecology, as well as taken into account in the field of medical perinatal nutritional science.
Improved estimation of climate niches is critical, given climate change. Plant adaptation to climate depends on their physiological traits and their distributions, yet traits are rarely used to inform the estimation of species climate niches, and the power of a trait‐based approach has been controversial, given the many ecological factors and methodological issues that may result in decoupling of species' traits from their native climate.
For 107 species across six ecosystems of California, we tested the hypothesis that mechanistic leaf and wood traits can robustly predict the mean of diverse species' climate distributions, when combining methodological improvements from previous studies, including standard trait measurements and sampling plants growing together at few sites. Further, we introduce an approach to quantify species' trait‐climate mismatch.
We demonstrate a strong power to predict species mean climate from traits. As hypothesized, the prediction of species mean climate is stronger (and mismatch lower) when traits are sampled for individuals closer to species' mean climates.
Improved resolution of species' climate niches based on mechanistic traits can importantly inform conservation of vulnerable species under the threat of climatic shifts in upcoming decades.
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The ongoing global environmental change poses a serious threat to rivers. Comprehensive knowledge of how stressors affect biota is critical for supporting effective management and conservation strategies. We evaluated the major gradients influencing spatial variability of freshwater biodiversity in continental Spain using landscape-scale variables representing climate, land use and land cover (LULC), flow regime, geology, topography, and diatom ( n = 117), macroinvertebrate ( n = 441), and fish ( n = 264) communities surveyed in minimally impacted streams. Redundancy analysis identified the environmental factors significantly contributing to community variability, and specific multivariate analyses (RLQ method) were used to assess trait–environment associations. Environmental variables defined the major community change gradients (e.g., mountain–lowland). Siliceous, steep streams with increased precipitation levels favored stalked diatoms, macroinvertebrates with aquatic passive dissemination, and migrating fish. These traits were replaced by adnate diatoms, small macroinvertebrates, and non-migratory fish in lowland streams with warmer climates, calcareous geology, agriculture, and stable flow regimes. Overall, landscape-scale environmental variables better explained fish than diatom and macroinvertebrate community variability, suggesting that these latter communities might be more related to local-scale characteristics (e.g., microhabitat structure, substrate, and water physicochemistry). The upslope environmental gradient of river networks (e.g., slope, temperature, and LULC changes) was paralleled to the observed taxonomy-based and trait-based spatial variability. This result indicates that global change effects on riverine biodiversity could emerge as longitudinal distribution changes within river networks. Implementing management actions focusing simultaneously on water temperature, hydrological regime conservation (e.g., addressing LULC changes), and river continuity might be the best strategy for mitigating global change effects on river biodiversity.
Documento con 16 tesis desarrolladas durante el periodo de 2018-2023 bajo mi dirección o codirección (7 de doctorado, 4 maestría y 5 de licenciatura) de estudiantes de cuatro instituciones de educación superior que incluyen a la Universidad Juárez del Estado de Durango, a la Universidad Autónoma de Nuevo León, a el Instituto Tecnológico del El Salto y la Universidad de Concepción Chile
Les connaissances sur l’utilisation du substrat par les juvéniles des migrateurs, en particulier celles de lamproies (ammocètes), restent parcellaires. En effet, les dimensions abiotiques (e.g. profondeurs, vitesses, granulométries des substrats, morphologies des chenaux actifs) et biotiques (e.g. interactions biologiques avec les macroinvertébrés) de l’habitat sont souvent étudiées isolément lors de la caractérisation des zones de nourriceries (banquettes à ammocètes). Le projet DUSTT propose de s’appuyer sur les compétences déjà acquises par notre équipe et d’aider au développement d’une méthode de photogrammétrie subaquatique (immergée), en y intégrant une composante biotique à l’étude des habitats propices au développement des stades critiques : les juvéniles de lamproies. Nos résultats montrent que la technique de photogrammétrie a été déployée avec un taux de réussite de 63%. Ce pourcentage de réussite, tout comme les densités des ammocètes au sein des banquettes et la composition des communautés de macroinvertébrés benthiques étaient variables dans l’espace (i.e., différents cours d’eau) et dans le temps (i.e., différentes périodes d’échantillonnage). La photogrammétrie a permis de générer, avec une précision millimétrique, des descripteurs statistiques et empiriques des variations surfaciques des banquettes. Le modèle prédictif final de la colonisation des banquettes par les ammocètes inclut, notamment, des descripteurs photogrammétriques (e.g., épaisseur moyenne du substrat) couplés à des métriques biologiques (e.g., pourcentage d’éphémères dans la communautés). In fine, les connaissances acquises via le projet DUSTT sur les relations entre les espèces et leur environnement (abiotiques comme biotiques) permettent de mettre en évidence un nouvel indicateur d’habitabilité des milieux à l’échelle du microhabitat. Cet indicateur pourrait être ainsi utile à la prise de décisions sur la mise en place d’actions de suivi et de gestion des populations migratrices amphihalines à destination des gestionnaires et des acteurs de l’environnement.
Premise of the study:
Continental-scale leaf trait studies can help explain how plants survive in different environments, but large datasets are costly to assemble at this scale. Automating the measurement of digitized herbarium collections could rapidly expand the data available to such studies. Here machine learning was used to identify and measure leaves from existing, digitised herbarium specimens. The process was developed, validated, and applied to analyses of relationships between leaf size and climate within and among species for two genera: Syzygium (Myrtaceae) and Ficus (Moraceae).
Methods:
Convolutional Neural Network (CNN) models were used to detect and measure complete leaves in images. Predictions of a model trained with a set of 35 randomly selected images and a second model trained with 35 user selected images were compared using a set of 50 labelled validation images. The validated models were then applied to 1227 Syzygium and 2595 Ficus specimens digitised by the National Herbarium of New South Wales, Australia. Leaf area measurements were made for each genus and used to examine links between leaf size and climate.
Key results:
The user selected training method for Syzygium found more leaves (9347 vs 8423) using fewer training masks (218 vs 225), and found leaves with a greater range of sizes than the random image training method. Within each genus, leaf size was positively associated with temperature and rainfall, consistent with previous observations. However, within species, the associations between leaf size and environmental variables were weaker.
Conclusions:
CNNs detected and measured leaves with levels of accuracy useful for trait extraction and analysis and illustrate the potential for machine learning of herbarium specimens to massively increase global leaf trait datasets. Within species relationships were weak, suggesting population history and gene flow have a strong effect at this level. Herbarium specimens and machine learning could expand sampling of trait data within many species, offering new insights into trait evolution. This article is protected by copyright. All rights reserved.
A better understanding on the mechanisms driving plant biomass allocation in different ecosystems is an important theoretical basis for illustrating the adaptive strategies of plants. To date, while the effects of habitat conditions on plant biomass allocation have been widely studied. However, it is less known how plant community traits and functions (PCTF) affect biomass allocation, particularly in alpine grassland ecosystems. In this study, community-weighted means (CWM) were calculated at the community level using five leaf functional traits, and the relationships between PCTF and biomass trade-offs were explored using correlation analysis, variation partitioning analysis, and structural equation modeling. We found that the trade-off values were greater than zero in both alpine meadow (AM) and alpine steppe (AS) across the Tibetan Plateau, but showed different values of 0.203 and 0.088 for AM and AS, respectively. Moreover, the critical factors determining biomass allocation in AS were species richness (scored at 0.69) and leaf dry matter content of CWM (CWMLDMC, scored at 0.42), while in AM, the key factors were leaf dry matter content (CWMLDMC, scored at 0.48) and leaf carbon content of CWM (CWMLC, scored at ﹣0.45). In particular, both CWMLDMC and species richness in AS, as well as CWMLDMC and CWMLC in AM were primarily regulated by precipitation. In summary, precipitation tends to drive biomass allocation in alpine grasslands through its effects on PCTF, hence highlighting the importance of PCTF in regulating plant biomass allocation strategies along precipitation gradients.
Contents
Chapter 1 General Aspects – Current and Further Perspectives 1
Marcelo L. Larramendy and Guillermo Eli Liwszyc
Chapter 2 Development of Aquatic Bird Indicators of Sub-lethal
Mercury Exposure and Risk in Wild Populations of Water
Birds in the Everglades (Florida, United States of America) 6
J. Zabala and P. Frederick
2.1 Background and Study Area Description 6
2.1.1 Mercury: Local Emissions, Worldwide
Contamination 6
2.1.2 The Everglades 7
2.1.3 Mercury Contamination in the Everglades 11
2.1.4 Development of a Field Sampling Protocol 12
2.1.5 Development of Mercury Exposure
Indicators – Tissues 13
2.2 Results 15
2.2.1 Sub-lethal Effects: Results from
Experimental Studies 15
2.2.2 Evidence of Mercury Effects in Field
Conditions 16
2.3 General Discussion, Lessons Learnt and Pros and
Cons of Our and Alternative Approaches 18
2.3.1 Evidence and Estimation of Hg Effects in
Natural Populations 18
2.3.2 Indicator Tissues: Comparative Advantages,
Limitations and Uncertainty 19
Issues in Toxicology No. 45
Bird and Reptile Species in Environmental Risk Assessment Strategies
Edited by Guillermo Eli Liwszyc and Marcelo L. Larramendy
r The Royal Society of Chemistry 2023
Published by the Royal Society of Chemistry, www.rsc.org
ix
2.4 Conclusion and Advice for Similar Cases or Final
Remarks 24
Acknowledgements 24
References 24
Chapter 3 The Importance of Ecological Traits in Assessing
Seabird Vulnerability to Environmental Risks 33
Can Zhou, Joan A. Browder and Yan Jiao
3.1 Introduction 33
3.2 Failings of the Standard Approach 34
3.3 Vulnerability to Anthropogenic and Natural Risks 34
3.4 Challenges for an Observational Study 35
3.5 A Trait-based Approach 37
3.5.1 An Ecological Dimension Reduction
Technique 37
3.5.2 Useful Traits for Ecological Risk Evaluation 39
3.5.3 Trait-based Prediction 41
3.6 Other Challenges 43
3.6.1 Correlation vs. Causation 43
3.6.2 The Default of No Risk 43
3.6.3 Ecological Regulation 44
3.6.4 Climate Change and Variability 44
3.6.5 Other Approaches 47
Disclaimer 47
Acknowledgements 47
References 47
Chapter 4 A Review of the Levels and Distribution Patterns of
Organochlorine Pesticides in the Eggs of Wild Birds
in India 54
Dhananjayan Venugopal, Jayakumar Samidurai,
Jayanthi Palaniyappan, Jayakumar Rajamani and
Muralidharan Subramanian
4.1 Introduction 54
4.1.1 Organochlorine Pesticides 54
4.1.2 Organochlorine Pesticides – Marketing and
Consumption 56
4.2 Pesticides – Indian Scenario 56
4.3 Impact of Pesticides in Eggs of Wild Birds in India 57
4.3.1 OCP Residues in Birds’ Eggs 57
x Contents
4.3.2 Variation in Residue Levels Based on Species
and Food Habits 64
4.3.3 Eggshell Thinning and Reproductive
Impairment 66
4.4 Conclusions and Further Recommendations 66
References 67
Chapter 5 Impacts of Agricultural Intensification on Farmland Birds
and Risk Assessment of Pesticide Seed Treatments 73
Julie Ce´line Brodeur and Maria Bele´n Poliserpi
5.1 The Intensification of Agriculture 73
5.2 Agricultural Intensification and Bird Declines 74
5.3 Impact of Pesticides on Birds: Direct vs. Indirect Effects 77
5.3.1 Direct Effects 77
5.3.2 Indirect Effects 78
5.4 Seed Treatment With Pesticides: Impacts on Birds 79
5.4.1 Agricultural Intensification Through Seed
Treatment 79
5.4.2 Bird Exposure to Pesticide-treated Seeds 80
5.5 Assessment of Risks of Pesticide-treated
Seeds to Birds 81
5.5.1 Regulatory Environmental Toxicity Testing 81
5.5.2 Tier I Risk Assessment 83
5.5.3 Refinements and Weight-of-evidence
Risk Assessment 83
5.5.4 Future Directions 85
References 85
Chapter 6 Teratological Effects of Pesticides in Reptiles – A Review 97
A. Garceˆs and I. Pires
6.1 Introduction 97
6.2 Reptiles as Sentinel Species 99
6.3 Teratological Effects of Pesticides on Reptiles 99
6.3.1 Order Testudinata 99
6.3.2 Order Rhynchocephalia 102
6.3.3 Order Crocodilia 102
6.3.4 Order Squamata 103
6.4 Final Remarks 104
6.5 Conclusion 105
Acknowledgements 105
References 105
Contents xi
Chapter 7 Combined Impact of Pesticides and Other Environmental
Stressors on Reptile Diversity in Irrigation Ponds
Compared to Other Animal Taxa 110
Hiroshi C. Ito and Noriko Takamura
7.1 Introduction 110
7.2 Biological Communities in Irrigation Ponds 112
7.2.1 Biological Communities 112
7.2.2 Reptiles 112
7.3 Combined Impact of Multiple Stressors on Reptile
Diversity Compared to Other Animal Taxa 114
7.4 Impact of Each Stressor on Reptile Diversity
Compared to Other Animal Taxa 116
7.4.1 Concrete Bank Protection, Water Depth
Reduction and Macrophyte Decline 116
7.4.2 Eutrophication and Pesticide Pollution 119
7.4.3 Invasive Alien Species 120
7.5 Perspective: Usefulness of Turtles as Bioindicators 121
7.6 Conclusion 123
Acknowledgements 123
References 123
Chapter 8 Current Progress in Developing Standardized Methods for
Reptilian Toxicity Testing to Inform Ecological Risk
Assessment 130
Scott M. Weir, Monica R. Youssif, Taylor Anderson and
Christopher J. Salice
8.1 Background on Reptile Toxicity Testing 130
8.1.1 Lack of Reptile Toxicity Data in the Literature 130
8.1.2 Lack of Standardized Methods 131
8.2 Progress in Standardized Methods for Reptile
Ecotoxicology/Ecological Risk Assessment 131
8.2.1 Early Efforts in Reptile Toxicology 131
8.2.2 Oral Dosing Methods Using Gelatin Capsules
to Accommodate Small Reptiles 133
8.2.3 Standardization of Methods and Developing
Breeding Assay Using Anolis Species in
Reptile Ecotoxicology 137
8.2.4 Moving Beyond Oral Exposure Dosing: The
Potential Importance of Dermal Exposure
and Toxicity 144
xii Contents
8.3 Conclusions 144
Acknowledgements 145
References 146
Chapter 9 Morphological and Molecular Evidence of Active Principle
Glyphosate Toxicity on the Liver of the Field Lizard
Podarcis siculus 151
Mariailaria Verderame, Teresa Chianese and Rosaria Scudiero
9.1 Introduction 151
9.2 Lizards in Contaminated Environments 152
9.3 Effects of Pure GLY on the Liver of P. siculus
Specimens 154
9.4 GLY-induced Changes in P. siculus Liver Histology 155
9.5 GLY-induced Changes in the Expression and
Synthesis of Proteins in the P. siculus Liver 158
9.6 Conclusion 161
Acknowledgements 162
References 162
Chapter 10 What Is Caiman latirostris Teaching Us About Endocrine
Disruptors? 169
M. Durando, G. H. Galoppo, Y. E. Tavalieri, M. V. Zanardi
and M. Mun˜oz-de-Toro
10.1 Ecophysiological Characteristics of the Broadsnouted
Caiman (Caiman latirostris) 169
10.1.1 Sex Determination 170
10.1.2 Reproduction 170
10.1.3 Hatchling Growth and Development 171
10.1.4 Feeding Habits, Social Behavior and
Longevity 171
10.1.5 Sexual Dimorphism 171
10.2 Endocrine-disrupting Chemicals 172
10.2.1 Mechanism of Action of EDCs 173
10.2.2 Types of EDCs 173
10.3 Caiman latirostris as a Sentinel of Environmental
Pollution 174
10.4 EDCs and Their Effects on Reproductive Features 175
10.4.1 Natural Exposure 175
10.4.2 Experimental Exposure 177
10.5 EDCs and Their Effects on the Thyroid
Histofunctional Characteristics 182
Contents xiii
10.6 Conclusions 183
Acknowledgements 183
References 184
Chapter 11 The Broad-snouted Caiman (Caiman latirostris): A Model
Species for Environmental Pesticide Contamination
Assessment Through Molecular Markers 196
L. M. Odetti, M. F. Simoniello, P. A. Siroski and G. L. Poletta
11.1 Caiman latirostris: Life History Characteristics and
Population Situation in Argentina 197
11.1.1 Geographical Distribution and
Sustainable Use Programs 197
11.1.2 Environmental Problems Associated With
Agricultural Expansion and the Use of
Pesticides 198
11.2 Why Use C. latirostris as a Sentinel of Pesticide
Contamination? 200
11.2.1 Evidence of Pesticide Effects on the
Broad-snouted Caiman 200
11.2.2 Identification and Development of
Gene Expression Markers 202
11.3 Future Perspectives 209
Acknowledgements 209
References 209
Chapter 12 Epilogue and Final Remarks 217
Guillermo Eli Liwszyc and Marcelo L. Larramendy
Reference 226
Subject Index 227
With the expansion of human settlements and the environmental changes brought on by human activity and pollutants, toxicology and risk assessment of bird and reptile species is becoming increasingly of interest to toxicologists involved in environmental research. This book focuses specifically on environmental risk assessment in non-conventional bird and reptile species.
Bird and Reptile Species in Environmental Risk Assessment Strategies will be an ideal companion to toxicologists and ecologists interested in risk assessment in the environments of birds and reptiles, particularly those with an interest in the impact introduced by human activity. The book will also be of interest to those working in conservation biology, biological invasion, biocontrol and habitat management.
An important aim of plant ecology is to identify leading dimensions of ecological variation among species and to understand the basis for them. Dimensions that can readily be measured would be especially useful, because they might offer a path towards improved worldwide synthesis across the thousands of field experiments and ecophysiological studies that use just a few species each. Four dimensions are reviewed here. The leaf mass per area-leaf lifespan (LMA-LL) dimension expresses slow turnover of plant parts (at high LMA and long LL), long nutrient residence times, and slow response to favorable growth conditions. The seed mass-seed output (SM-SO) dimension is an important predictor of dispersal to establishment opportunities (seed output) and of establishment success in the face of hazards (seed mass). The LMA-LL and SM-SO dimensions are each underpinned by a single, comprehensible tradeoff, and their consequences are fairly well understood. The leaf size-twig size (LS-TS) spectrum has obvious consequences for the texture of canopies, but the costs and benefits of large versus small leaf and twig size are poorly understood. The height dimension has universally been seen as ecologically important and included in ecological strategy schemes. Nevertheless, height includes several tradeoffs and adaptive elements, which ideally should be treated separately. Each of these four dimensions varies at the scales of climate zones and of site types within landscapes. This variation can be interpreted as adaptation to the physical environment. Each dimension also varies widely among coexisting species. Most likely this within-site variation arises because the ecological opportunities for each species depend strongly on which other species are present, in other words, because the set of species at a site is a stable mixture of strategies.
Leaf size variation with respect to climate was studied at 35 sample sites reported in the literature from the Western Hemisphere. The variation in leaf size was analyzed by plotting the sample sites on Holdridge's (1967) life zone chart and comparing the percentage of species having large leaves (greater than 20.25 sq cm in area) in the different life zones. Four foliar belts were identified in the tropical basal and altitudinal belts. Three of these foliar belts were identified earlier in a field study carried out in Costa Rica (Dolph and Dilcher in press). The fourth foliar belt is not found in Costa Rica because it is confined to very dry basal belt life zones. It was concluded that leaf size cannot be used to identify specific life zones or climates in either extant or fossil floras.
Multiple studies have shown that biodiversity loss can impair ecosystem processes, providing a sound basis for the general application of a precautionary approach to managing biodiversity. However, mechanistic details of species loss effects and the generality of impacts across ecosystem types are poorly understood. The functional niche is a useful conceptual tool for understanding redundancy, where the functional niche is defined as the area occupied by a species in an n-dimensional functional space. Experiments to assess redundancy based on a single functional attribute are biased towards finding redundancy, because species are more likely to have non-overlapping functional niches in a multi-dimensional functional space. The effect of species loss in any particular ecosystem will depend on i) the range of function and diversity of species within a functional group, ii) the relative partitioning of variance in functional space between and within functional groups, and iii) the potential for functional compensation (degree of functional niche overlap) of the species within a functional group. Future research on functional impairment with species loss should focus on identifying which species, functional groups, and ecosystems are most vulnerable to functional impairment from species loss, so that these can be prioritized for management activities directed at maintaining ecosystem function. This will require a better understanding of how the organization of diversity into discrete functional groups differs between different communities and ecosystems.
Links between plant traits and the environment, i.e. sets of plant attributes consistently associated with certain environmental conditions, are the consequence of the filtering effect of climatic, disturbance and biotic conditions. These filters determine which components of a species pool are assembled into local communities. We aimed at testing for consistent association between plant traits and climatic conditions along a steep regional gradient, divided into 13 climatically homogeneous sectors, in central‐western Argentina. We analyzed 19 vegetative and regeneration traits of the 100 most abundant species along the gradient. For each trait, we tested for homogeneity of frequencies of different categories between sectors and the regional species pool, using the χ ² statistic. We rejected H 0 in 71% of the pair‐wise comparisons, which strongly suggests a ‘filtering effect’ of climatic factors on key plant functions. Vegetative traits were filtered more often than regeneration traits. Specific leaf area, life span, ramification, canopy height, leaf weight ratio, carbon investment into support tissue and pollination mode were the traits showing differences in the largest number of pair‐wise comparisons.
This is probably the first attempt to detect, on a quantitative, statistically conservative basis, consistent linkages between climatic factors and numerous plant traits, over a broad spectrum of environmental conditions and plant growth forms. We discuss the advantages and limitations of this approach in predicting vegetation structure and functioning under present environmental conditions, and those expected for the next century as a consequence of global change.
This is the second edition of a multi-author book first published in 1992. It deals with all aspects of plant regeneration by seeds, including reproductive allocation, seed dispersal and predation, longevity, dormancy and germination. All chapters have been updated, and four new chapters added on seed size, seedling establishment, the role of gaps, and regeneration from seed after fire.
Convergence in interspecific leaf trait relationships across diverse taxonomic groups and biomes would have important evolutionary and ecological implications. Such convergence has been hypothesized to result from trade-offs that limit the combination of plant traits for any species. Here we address this issue by testing for biome differences in the slope and intercept of interspecific relationships among leaf traits: longevity, net photosynthetic capacity (A(max)), leaf diffusive conductance (G(s)), specific leaf area (SLA), and nitrogen (N) status, for more than 100 species in six distinct biomes of the Americas. The six biomes were: alpine tundra-subalpine forest ecotone, cold temperate forest-prairie ecotone, montane cool temperate forest, desert shrubland, subtropical forest, and tropical rain forest. Despite large differences in climate and evolutionary history, in all biomes mass-based leaf N (N-mass), SLA, G(s), and A(max) were positively related to one another and decreased with increasing lea
Bringing together leaf trait data spanning 2,548 species and 175 sites we describe, for the first time at global scale, a universal spectrum of leaf economics consisting of key chemical, structural and physiological properties. The spectrum runs from quick to slow return on investments of nutrients and dry mass in leaves, and operates largely independently of growth form, plant functional type or biome. Categories along the spectrum would, in general, describe leaf economic variation at the global scale better than plant functional types, because functional types overlap substantially in their leaf traits. Overall, modulation of leaf traits and trait relationships by climate is surprisingly modest, although some striking and significant patterns can be seen. Reliable quantification of the leaf economics spectrum and its interaction with climate will prove valuable for modelling nutrient fluxes and vegetation boundaries under changing land-use and climate.
In order to find and define any assembly rules for communities, we must first investigate the patterns among species assemblages. We used a series of null models to test for patterns in wetland plant composition al the level of species, functional guilds, and traits. At the species level, we found significant checkerboard and nestedness patterns. Three functional guilds had some tendency to contribute a constant percentage to species richness, but after Bonferroni correction there was no significant pattern. Coexisting plant species showed no consistent overall pattern of morphological dispersion. However, when we considered each of 11 traits in turn, we found that 4 traits were overdispersed and 3 were underdispersed. Thus there are morphological assembly rules that constrain wetland plant community composition. These results reconcile contrasting views of community assembly. Communities can be simultaneously structured by a tension between two forces: abiotic external forces that constrain certain traits within limits and biotic internal forces that tend to keep coexisting species from being too similar. Because our sites vary along a fertility/disturbance gradient, we also investigated how trait dispersion varies in space. Trait dispersion increases with soil Fertility; soil phosphorus explains about 36% of the variance in mean nearest neighbor distance. Species richness tends to decline with mean nearest neighbor distance, which contrasts with the general pattern for animal assemblages.
As a follow-up to the recent interest in simple additive models for diversity partitioning, we have used the analogy with ANOVA models to propose a consistent framework that allows both (i) apportioning the amount of regional diversity into environmentally and/or geographically-related components (ii) detecting individual species' habitat preferences using permutation tests. We addressed geographical aspects by relating diversity partition to dissimilarity measurements. An illustration based on an inventory of trees in a tropical rain forest of French Guiana is provided.
1. Specific leaf area is a variable implicated in a number of functional aspects of plant ecology, including gas exchange, relative growth rate and palatability. 2. Six leaf attributes (water content, lamina thickness, protruding vein thickness, dry weight, lamina area and specific leaf area) were determined on a collection of 572 leaves. The data set was derived from 194 individual plants, 34 species, 32 genera, 18 families and both classes of angiosperms. All species except one (a shrub) were herbaceous. All species were from sunny habitats. 3. Structured relationships between these six variables were obtained. These relationships consisted of path analyses, multiple regressions and major axis (allometric) regressions. 4. There was an interspecific allometric trend for leaf dry weight to increase more rapidly than leaf surface area, resulting in larger leaves naving a lower specific leaf area. This trend did not exist at an intraspecific level. 5. Path analysis showed that the most important direct effect on specific leaf area was the water content of the leaf. Increasing water content resulted in a larger specific leaf area. The direct effect of lamina thickness was to decrease specific leaf area but lamina thickness itself was affected by leaf water content. 6. These effects on specific leaf area were mediated through variation in leaf dry weight. Leaf surface area appeared to be independent of the other five variables. 7. These results help to explain two unresolved general patterns in plant comparative ecology: (1) why net photosynthetic rate is not positively correlated with maximum relative growth rates and (2) why there is a negative correlation between maximum relative growth rate and seed size.
1Potential height, which spans at least an order of magnitude across species, is considered an important indicator of light capture strategy. Still, it remains unclear how potential height is coordinated with other traits that influence height growth rate, stem persistence and performance in low light. We proposed that contrasting correlations between potential height and other plant attributes would be observed for sets of species selected to span two hypothetical axes of light availability within mature forest and time since disturbance.2We selected 45 perennial rain forest species in Australia's wet tropics to span gradients of light availability and successional status and measured potential height together with traits influencing light capture and regeneration strategy on mature individuals. The traits included leaf mass per area, leaf nitrogen, wood density, stem mass per length, branch mass fraction and seed mass.3Potential height was significantly correlated with numerous traits among species selected to span each of the two gradients. Height was positively correlated with leaf mass area−1, leaf nitrogen and seed mass and negatively correlated with leaf area ratio at the branch tip along both light and successional gradients. Height was positively correlated with wood density along the successional axis, with the opposite relationship along the light gradient.4Trait relationships differed in either slope or intercept between the two gradients, reflecting different strategic trade-offs. At a given height, shorter species in the successional gradient were characterized by lower leaf mass area−1, lighter wood, smaller seeds, lower leaf nitrogen and lower leaf area ratio at the branch tip than similar sized species along the light gradient.5The results of this study support the idea of two distinct, trait-mediated axes of coexistence among short and tall plant species within vegetation. In several cases, trait relationships were weak or non-significant when species groupings were merged, indicating the importance of separating out the two sets for comparative studies.
Multiple studies have shown that biodiversity loss can impair ecosystem processes, providing a sound basis for the general application of a precautionary approach to managing biodiversity. However, mechanistic details of species loss effects and the generality of impacts across ecosystem types are poorly understood. The functional niche is a useful conceptual tool for understanding redundancy, where the functional niche is defined as the area occupied by a species in an n-dimensional functional space. Experiments to assess redundancy based on a single functional attribute are biased towards finding redundancy, because species are more likely to have non-overlapping functional niches in a multi-dimensional functional space. The effect of species loss in any particular ecosystem will depend on i) the range of function and diversity of species within a functional group, ii) the relative partitioning of variance in functional space between and within functional groups, and iii) the potential for functional compensation (degree of functional niche overlap) of the species within a functional group. Future research on functional impairment with species loss should focus on identifying which species, functional groups, and ecosystems are most vulnerable to functional impairment from species loss, so that these can be prioritized for management activities directed at maintaining ecosystem function. This will require a better understanding of how the organization of diversity into discrete functional groups differs between different communities and ecosystems.
Aim To provide the first global quantification of the slope and shape of the latitudinal gradient in seed mass, and to determine whether global patterns in seed mass are best explained by growth form, vegetation type, seed dispersal syndrome, or net primary productivity (NPP).
Location Global.
Methods We collected seed mass data for 11,481 species × site combinations from around the world. We used regression to describe the latitudinal gradient in seed mass, then applied general linear models to quantify the relative explanatory power of each of the variables hypothesized to underlie the latitudinal gradient in seed size.
Results There is a 320-fold decline in geometric mean seed mass between the equator and 60°. This decline is not linear. At the edge of the tropics, there is a sudden 7-fold drop in mean seed mass. The strongest correlates of the latitudinal gradient in seed mass are plant growth form, and vegetation type, followed by dispersal syndrome and NPP. A model including growth form, vegetation type, dispersal syndrome and NPP explains 51% of the variation in seed mass. Latitude explains just 0.2% of the residual variation from this model.
Main conclusions This is the first demonstration of a major decrease in seed size at the edge of the tropics. This drop in seed mass is most closely correlated with changes in plant growth form and vegetation type. This suggests that the drop in seed mass might be part of a sudden change in plant strategy at the edge of the tropics.
Humans are altering the composition of biological communities through a variety of activities that increase rates of species invasions and species extinctions, at all scales, from local to global. These changes in components of the Earth's biodiversity cause concern for ethical and aesthetic reasons, but they also have a strong potential to alter ecosystem properties and the goods and services they provide to humanity. Ecological experiments, observations, and theoretical developments show that ecosystem properties depend greatly on biodiversity in terms of the functional characteristics of organisms present in the ecosystem and the distribution and abundance of those organisms over space and time. Species effects act in concert with the effects of climate, resource availability, and disturbance regimes in influencing ecosystem properties. Human activities can modify all of the above factors; here we focus on modification of these biotic controls. The scientific community has come to a broad consensus on many aspects of the relationship between biodiversity and ecosystem functioning, including many points relevant to management of ecosystems. Further progress will require integration of knowledge about biotic and abiotic controls on ecosystem properties, how ecological communities are structured, and the forces driving species extinctions and invasions. To strengthen links to policy and management, we also need to integrate our ecological knowledge with understanding of the social and economic constraints of potential management practices. Understanding this complexity, while taking strong steps to minimize current losses of species, is necessary for responsible management of Earth's ecosystems and the diverse biota they contain. Based on our review of the scientific literature, we are certain of the following conclusions: 1)Species' functional characteristics strongly influence ecosystem properties. Functional characteristics operate in a variety of contexts, including effects of dominant species, keystone species, ecological engineers, and interactions among species (e.g., competition, facilitation, mutualism, disease, and predation). Relative abundance alone is not always a good predictor of the ecosystem-level importance of a species, as even relatively rare species (e.g., a keystone predator) can strongly influence pathways of energy and material flows. 2)Alteration of biota in ecosystems via species invasions and extinctions caused by human activities has altered ecosystem goods and services in many well-documented cases. Many of these changes are difficult, expensive, or impossible to reverse or fix with technological solutions. 3)The effects of species loss or changes in composition, and the mechanisms by which the effects manifest themselves, can differ among ecosystem properties, ecosystem types, and pathways of potential community change. 4)Some ecosystem properties are initially insensitive to species loss because (a) ecosystems may have multiple species that carry out similar functional roles, (b) some species may contribute relatively little to ecosystem properties, or (c) properties may be primarily controlled by abiotic environmental conditions. 5)More species are needed to insure a stable supply of ecosystem goods and services as spatial and temporal variability increases, which typically occurs as longer time periods and larger areas are considered. We have high confidence in the following conclusions: 1)Certain combinations of species are complementary in their patterns of resource use and can increase average rates of productivity and nutrient retention. At the same time, environmental conditions can influence the importance of complementarity in structuring communities. Identification of which and how many species act in a complementary way in complex communities is just beginning. 2)Susceptibility to invasion by exotic species is strongly influenced by species composition and, under similar environmental conditions, generally decreases with increasing species richness. However, several other factors, such as propagule pressure, disturbance regime, and resource availability also strongly influence invasion success and often override effects of species richness in comparisons across different sites or ecosystems. 3)Having a range of species that respond differently to different environmental perturbations can stabilize ecosystem process rates in response to disturbances and variation in abiotic conditions. Using practices that maintain a diversity of organisms of different functional effect and functional response types will help preserve a range of management options. Uncertainties remain and further research is necessary in the following areas: 1)Further resolution of the relationships among taxonomic diversity, functional diversity, and community structure is important for identifying mechanisms of biodiversity effects. 2)Multiple trophic levels are common to ecosystems but have been understudied in biodiversity/ecosystem functioning research. The response of ecosystem properties to varying composition and diversity of consumer organisms is much more complex than responses seen in experiments that vary only the diversity of primary producers. 3)Theoretical work on stability has outpaced experimental work, especially field research. We need long-term experiments to be able to assess temporal stability, as well as experimental perturbations to assess response to and recovery from a variety of disturbances. Design and analysis of such experiments must account for several factors that covary with species diversity. 4)Because biodiversity both responds to and influences ecosystem properties, understanding the feedbacks involved is necessary to integrate results from experimental communities with patterns seen at broader scales. Likely patterns of extinction and invasion need to be linked to different drivers of global change, the forces that structure communities, and controls on ecosystem properties for the development of effective management and conservation strategies. 5)This paper focuses primarily on terrestrial systems, with some coverage of freshwater systems, because that is where most empirical and theoretical study has focused. While the fundamental principles described here should apply to marine systems, further study of that realm is necessary. Despite some uncertainties about the mechanisms and circumstances under which diversity influences ecosystem properties, incorporating diversity effects into policy and management is essential, especially in making decisions involving large temporal and spatial scales. Sacrificing those aspects of ecosystems that are difficult or impossible to reconstruct, such as diversity, simply because we are not yet certain about the extent and mechanisms by which they affect ecosystem properties, will restrict future management options even further. It is incumbent upon ecologists to communicate this need, and the values that can derive from such a perspective, to those charged with economic and policy decision-making.
We examined variation in leaf size and specific leaf area(SLA) in relation to the distribution of 22 chaparral shrub species on small-scale gradients of aspect and elevation. Potential incident radiation (insolation) was estimated from a geographic information system to quantify microclimate affinities of these species across north- and south-facing slopes. At the community level, leaf size and SLA both declined with increasing insolation, based on average trait values for the species found in plots along the gradient. However, leaf size and SLA were not significantly correlated across species, suggesting that these two traits are decoupled and associated with different aspects of performance along this environmental gradient. For individual species, SLA was negatively correlated with species distributions along the insolation gradient, and was significantly lower in evergreen versus deciduous species. Leaf size exhibited a negative but non-significant trend in relation to insolation distribution of various species. At the community level, variance in leaf size increased with increasing insolation. For individual species, there was a greater range of leaf size on south-facing slopesm while there was an absence of small-leaved species on north-facing slopes. These results demonstrate that analyses of plant functional traits along environmental gradients based on community-level averages may obscure important aspects of traits variation and distribution among constituent species
According to conventional wisdom, functional diversity is exclusively a consequence of species having evolved adaptations to fill different niches within a heterogeneous environment. This view anticipates only one optimal combination of trait values in a given environment, but it is also conceivable that alternative designs of equal fitness in the same environment might evolve. To investigate that possibility, we use a genetic algorithm to search for optimal combinations of 34 functional traits in a realistic model of tree seedling growth and survival. We show that separate lineages of seedlings evolving in identical environments result in many alternative functional designs of approximately equal fitness.
A significant proportion of the global diversity of flowering plants has evolved in recent geological time, probably through adaptive radiation into new niches. However, rapid evolution is at odds with recent research which has suggested that plant ecological traits, including the beta- (or habitat) niche, evolve only slowly. We have quantified traits that determine within-habitat alpha diversity (alpha niches) in two communities in which species segregate on hydrological gradients. Molecular phylogenetic analysis of these data shows practically no evidence of a correlation between the ecological and evolutionary distances separating species, indicating that hydrological alpha niches are evolutionarily labile. We propose that contrasting patterns of evolutionary conservatism for alpha- and beta-niches is a general phenomenon necessitated by the hierarchical filtering of species during community assembly. This determines that species must have similar beta niches in order to occupy the same habitat, but different alpha niches in order to coexist.
There is considerable debate about whether community ecology will ever produce general principles. We suggest here that this can be achieved but that community ecology has lost its way by focusing on pairwise species interactions independent of the environment. We assert that community ecology should return to an emphasis on four themes that are tied together by a two-step process: how the fundamental niche is governed by functional traits within the context of abiotic environmental gradients; and how the interaction between traits and fundamental niches maps onto the realized niche in the context of a biotic interaction milieu. We suggest this approach can create a more quantitative and predictive science that can more readily address issues of global change.
Current methods of calculating niche breadth are often inadequate for plant study. Classical analysis techniques of genotype-environment interaction are offered as a better method of quantifying the niches of organisms, particularly plants. The analysis which is widely used in the fields of genetics and crop and stock breeding can be used to examine ecological relationships between genotypes in a population, populations of a species, or species within a community. The analysis gives measures of the relative niche breadth (equability) and magnitude of response between organims being compared. All that is required for input into the analysis is the performance of each organism (entity) in a number of environments (states). Quantification of the environment is not necessary and different resource gradients can be lumped together in a single analysis. A step-by-step description of the analysis is given. The techniques are demonstrated with two examples, one using a hypothetical data set and the other employing data from the classic experiments of Clausen, Keck, and Hiesey on Potentialla glandulosa. This analysis has advantages over classical niche metrics in that the magnitude or level of response of organisms is measured as well as the breadth of response.
Analyses of the California flora involving nearly 2,500 taxa are presented which show that there are correlations between the weights of individual seeds and environmental conditions in which their producers normally grow. These differences in seed weight appear to be adaptive and result from compromises between increased nutrition of the seedling which would result from larger food reserves in heavier seeds and increased dispersibility and increased reproductive output which are provided when smaller seeds are produced in larger numbers. Literature and experiments show a general positive correlation between seed weights and rates of shoot and root growth, at least within species. Herbs (annual and perennial), shrubs and trees are necessarily treated separately in the calculations in this paper (for seed weights increase progressively in a series from annual herb to tree when to California flora or any particular community type within it are considered). Raw seed weights are reduced to a series of classes (on a logarithmic basis) before means for floras or community types are calculated. Generalizations arrived at from considerations of @'native@' species in @'natural@' plant communities are confirmed by their applicability to @'introduced@' species now forming various kinds of @'weed@' communities in California. Finally, species lists from actual stand analyses, including both @'native@' and @'introduced@' species, are utilized to provide the data for more precise analyses. For herbaceous plants, seed weights are higher, on the average, for taxa whose seedlings are exposed to the risk of drought soon after establishment (giving faster root-development). Such a relationship can be demonstrated for species of a single genus or, on a combination basis, for community types as a whole and can be put on a quantitative basis by subjectively ordinating community types (in relation to the likelihood of drought stress hitting the seedlings) and making rank correlations with mean seed weight for each community type. The relation holds even for desert communities (where large-seeded perennials produce large root-systems but small-seeded ephemerals complete at least their seedling development in temporarily mesic conditions). In coastal communities, the importance of wind-dispersal of the seeds of species whose seedlings become established in rock crevices outweighs any droughtiness of the habitat in favoring smaller seeds than typify the community types generally. Correlations of herb seed-weight with likelihood of seedlings becoming established in shade or in conditions of severe competition are less marked for California than Salisbury found them to be in England. For shrubs, shading and competitive stress appear to be more influential factors in promoting increased mean seed weight but for trees moisture availability again appears to be most important. Another kind of correlation is established; between mean seed weight and altitude at which the plants occur. With decreasing length of the growing season as Californian mountains are ascended the mean seed weight (whether measured on a subspecies, species or community type basis) also decreases. This appears to represent the selection of a strategy in which a reduction in the availability of photosynthate is reflected in smaller seeds rather than in reduced output as found in Ranunculus by Johnson and Cook. Although taxa introduced to California have fitted with the rules holding for native plants, they tend to have slightly heavier seeds than native species growing in climatically similar habitat types. This difference may be particularly related to human influence in making such habitats somewhat more xeric. Improved methods of analysis are suggested and further correlations which might be sought are discussed.
The vegetations found in the mediterranean climate regions of the world are highly convergent in form, although they have had distinct evolutionary histories. There are numerous selective forces in this climatic type, such as fire, drought, high temperatures, rainfall unpredictability, and mineral deficiencies. These multiple selective forces are often interacting and involve the biotic as well as the physical components. A solution to any one of these selective forces in turn creates new adaptive challenges. Thus, the total possible solutions to the various combinations of forces becomes limited, leading to convergence in form and function.
The adaptation of barley varieties was studied by the use of grain yields of a randomly chosen group of 277 varieties from a world collection, grown in replicated trials for several seasons at three sites in South Australia. For each variety a linear regression of yield on the mean yield of all varieties for each site and season was computed to measure variety adaptation. In these calculations the basic yields were measured on a logarithmic scale, as it was found that a high degree of linearity was thereby induced. The mean yield of all varieties for each site and season provided a quantitative grading of the environments; and from the analysis described, varieties specifically adapted to good or poor seasons and those showing general adaptability may be identified. The study of the adaptation of the whole population of varieties was facilitated by the use of a two-dimensional plot (scatter diagram), with mean yield and regression coefficient as coordinates for each variety. Though wide variation was evident in both mean yield and sensitivity to environment as characterized by the regression coefficient, the variation in sensitivity was proportionately less among varieties with higher mean yield, and the varieties with highest mean yield exhibited, within very narrow limits (regression coefficients close to 0.8), a similar degree of adaptation to all environments over the wide range, especially of seasonal conditions, typical of the South Australian cereal belt. Varieties from particular geographic regions of the world showed a similarity in type of adaptation, which provides a useful basis for plant introduction. Phenotypic stability and physiological and morphological characteristics of groups of varieties with specific or general adaptability are discussed in relation to plant introduction and breeding.
Excerpt
This concluding survey1 of the problems considered in the Symposium naturally falls into three sections. In the first brief section certain of the areas in which there is considerable difference in outlook are discussed with a view to ascertaining the nature of the differences in the points of view of workers in different parts of the field; no aspect of the Symposium has been more important than the reduction of areas of dispute. In the second section a rather detailed analysis of one particular problem is given, partly because the question, namely, the nature of the ecological niche and the validity of the principle of niche specificity has raised and continues to raise difficulties, and partly because discussion of this problem gives an opportunity to refer to new work of potential importance not otherwise considered in the Symposium. The third section deals with possible directions for future research.
The Demographic
The study of interspecific variation in plant ecological strategies has revealed suites of traits associated with leaf life span and with maximum levels of water deficit (measured as leaf water potentials). Here, the relationship between these sets of traits was examined in a study of 20 co-occurring chaparral shrubs that vary in leaf habit, rooting depth, and regeneration strategies. Leaf life span (LLS) and minimum seasonal water po-tentials (min) were not significantly correlated, suggesting that they are associated with independent aspects of functional variation. Multiple regression analyses of a large suite of physiological, functional, and phenological attributes in relation to these two ''anchor traits'' supported this view. Short LLS was significantly associated with high specific leaf area, high carbon assimilation and leaf nitrogen (per mass), early onset of growth, and a multistemmed, short stature growth form. This suite of traits was also associated with opportunistic regeneration following physical disturbance. Area-based gas exchange was not tightly linked to LLS. Low min (i.e., greater water deficit) was associated with high wood density, small vessel diameters, thin twigs, low leaf area : sapwood area ratios, and early onset of leaf abscission. Among the evergreen species, this suite of traits was most characteristic of post-fire seeders, which depend on high drought tolerance for post-fire regeneration of seedlings. Plant stature was the only trait associated with both the LLS axis and the min axis of functional variation. A two-dimensional strategy space, approxi-mately defined by LLS and min , can be used to distinguish contrasting strategies of drought tolerance vs. avoidance, and alternative modes of regeneration following fire and other disturbance. This conceptual scheme illustrates the strength of a trait-based approach to defining plant strategies in relation to resource availability and disturbance.
Summary • We sought evidence among the plant species of a New Zealand sand dune community that limiting similarity controls the ability of species to coexist. Sampling was at four spatial scales, from a single point up to a scale of 50 m2. Twenty-three functional characters were measured on each of the species, covering the morphology of the shoot and root systems and nutrient status, and intended to represent modes of resource acquisition. • Patterns of association between plant species at the four scales were examined for any tendency for plants with similar functional characters to coexist less often than expected at random (e.g. if a point has three species, do they have notably different characters?) The observed results were compared with the patterns expected under a null model using a range of test statistics. • A test over all characters found that the mean dissimilarity between nearest-neighbour species in functional space, and the minimum dissimilarity, were greater than expected under the null model at the 0.5 × 0.5 m scale. This supports the MacArthur & Levins model, although the actual community did not show an even spread of species over functional space. • Limiting similarity effects were seen even more consistently in separate characters when within-species variation was taken into account to calculate measures of overlap. The characters involved were mainly those related to rooting patterns and leaf water control, and thus perhaps reflecting the acquisition of nutrients and/or water. • Our results seem to be amongst the most convincing support for the theory of limiting similarity, and the only example involving vegetative processes in plant communities. The characters involved suggest that species can more readily coexist if they differ in their water-use pattern, reducing competition between them. Journal of Ecology (2004) 92, 557–567
Ecologists need to analyze their field data to interpret relationships within plant and animal communities and with their environments. The purpose of this book is to show ecologists and environmental scientists what numerical and statistical methods are most useful, how to use them and interpret the results from them, and what pitfalls to avoid. Subjects treated include data requirements, regression analysis, calibration (or inverse regression), ordination techniques, cluster analysis, and spatial analysis of ecological data. The authors take pains to use only elementary mathematics and explain the ecological models behind the techniques. Exercises and solution are provided for practice. This is the only book written specifically for ecologists that explains such techniques as logistic regression, canonical correspondence analysis, and kriging (statistical manipulation of data). This is a reissue of a book first published in 1987 by Pudoc (The Netherlands). Contents List of contributors; Preface to first edition; Acknowledgement; List of symbols; Dune meadow data; 1. Introduction R. H. G. Jongman; 2. Data collection J. C. Jager and C. W. N. Looman; 3. Regression C. J. F. ter Braak and C. W. N. Looman; 4. Calibration C. J. F. ter Braak; 5. Ordination C. J. F. ter Braak; 6. Cluster analysis O. F. R. van Tongeren; 7. Spatial aspects of ecological data P. A. Burrough; 8. Numerical methods in practice: case-studies P. A. Burrough, J. A. F. Oudhof, A. Barendregt, R. H. G. Jongman and T. J. van de Nes; References; Index.
In landscapes subject to intensive agriculture, both soil fertility and vegetation disturbance are capable of impacting strongly, evenly and simultaneously on the herbaceous plant cover and each tends to impose uniformity on the traits of constituent species. In more natural and ancient grasslands greater spatial and temporal variation in both productivity and disturbance occurs and both factors have been implicated in the maintenance of species‐richness in herbaceous communities. However, empirical data suggest that disturbance is the more potent driver of trait differentiation and species co‐existence at a local scale. This may arise from the great diversity in opportunities for establishment, growth or reproduction that arise when the intensity of competition is reduced by damage to the vegetation.
In contrast to the diversifying effects of local disturbances, productivity‐related plant traits (growth rate, leaf longevity, leaf chemistry, leaf toughness, decomposition rate) appear to be less variable on a local scale. This difference in the effects of the productivity and disturbance filters arises from the relative constancy of productivity within the community and the diversity in agency and in spatial and temporal scales exhibited by disturbance events. Also, evolutionary responses to disturbances involve minor adaptive shifts in phenological and regenerative traits and are more likely to occur as micro‐evolutionary steps than the shifts in linked traits in the core physiology associated with the capacity to exploit productive and unproductive habitats.
During the assembly of a community and over its subsequent lifespan filters with diversifying and convergent effects may operate simultaneously on recruitment from the local species pool and impose contrasted effects on the similarity of the trait values exhibited by co‐existing species. Moreover, as a consequence of the frequent association of productivity with the convergence filter, an additional difference is predicted in terms of the effects of the two filters on ecosystem functioning. Convergence in traits selected by the productivity filter will exert effects on both the plant community and the ecosystem while divergent effects of the disturbance filter will be restricted to the plant community.
1 If different factors inhibiting plant growth, e.g. low rainfall or low soil nutrients, were to select for species that have similar constellations of traits, then the unfavourable factors might usefully be grouped together as ‘stress’.
2 We offer a method for assessing this issue. A species mixture at a site is described by a point on a plane with two traits as axes. Change along an environmental gradient is then represented as a trajectory across the trait-plane. Trajectories along different environmental gradients are compared.
3 We measured leaf width, specific leaf area (SLA) and mature canopy height for the 386 perennial species found at 46 sites spread along rainfall and soil total phosphorus gradients in south-eastern Australia. Each trait was lognormally distributed across species within sites, hence the mean of log10(trait) satisfactorily described the species mixture at each site.
4 Combinations of assemblage-mean leaf width with SLA followed similar trajectories as rainfall and soil total P decreased. For these traits in this setting, the method indicated that low rainfall and low soil P favour similar trait-combinations.
5 Mature plant height also decreased along both rainfall and soil P gradients, and thus was positively correlated with leaf width and SLA at the level of assemblage means. The rainfall trajectories involving height behaved differently from the soil P trajectories, especially at rainfalls below c. 400 mm year−1, where assemblage-mean height declined much further than at low soil P.
6 Across all species, traits were only very loosely correlated (r2 from 0.04 to 0.17). For leaf width and SLA, evolutionary divergences were positively correlated, both before and after cross-correlation with divergence in rainfall and soil P was removed. This latter measures evolutionary divergence correlation within habitat. For height the picture was more complicated. Considering these within-habitat divergence correlations, species that were taller at maturity tended to have lower SLA and leaf width. This pattern is the reverse of the broad geographical correlation of assemblage means, showing that the patterns across assemblages result from species being selectively sifted from the regional flora into sites, not from evolutionary or cross-species correlations.
7 The trait-combination trajectory approach showed some commonalities between low soil nutrient and low rainfall habitats with regard to traits favoured in species occurring there, but also some differences. The approach has potential for clarifying which environmental factors can usefully be grouped together as ‘stress’, and which trait combinations can usefully be regarded as part of a syndrome favoured by stress.
Wood density (D
t), an excellent predictor of mechanical properties, is typically viewed in relation to support against gravity, wind, snow, and other environmental forces. In contrast, we show the surprising extent to which variation in D
t and wood structure is linked to support against implosion by negative pressure in the xylem pipeline. The more drought-tolerant the plant, the more negative the xylem pressure can become without cavitation, and the greater the internal load on the xylem conduit walls. Accordingly, D
t was correlated with cavitation resistance. This trend was consistent with the maintenance of a safety factor from implosion by negative pressure: conduit wall span (b) and thickness (t) scaled so that (t/b)2 was proportional to cavitation resistance as required to avoid wall collapse. Unexpectedly, trends in D
t may be as much or more related to support of the xylem pipeline as to support of the plant.
An attempt is made to review the whole range of plants able to cope with shortages of mineral nutrients, water or light for at least a substantial part of their lives. In the past insufficient attention has been paid to quantitative measurements of the tolerance of various species for lack of resources. Growth rate at a low level of supply and mere survival are the variables to be considered. Problems in defining tolerance arise where a collection of species shows a negative correlation between survival at a low level of supply and growth rate under these conditions; in at least some circumstances a balance between survival and growth rate is important. Plants coping with lack of major resources display one of three strategies: ‘low-flexibility’, ‘switching’ or ‘gearing-down’. The essential features of the low-flexibility strategy are long-lived leaves, low maximum relative growth rates, and inflexibility of form and of gas exchange rates when resource-shortage is relieved, both in seedlings and in adults. Plants which show the switching strategy display the low-flexibility strategy as young seedlings, but are flexibile in form as older plants, and commonly have high relative growth rates then. The gearing-down strategy is based on an ability to reduce strongly the respiration rate when resources are in short supply, both as seedlings and as adult. In some cases this involves shedding of parts which would otherwise consume respiratory substrate. Plants showing this strategy have some characteristics which are the opposite of those shown by plants with the low-flexibility strategy: short-lived leaves, and high flexibility in form and in rates of gas exchange. All three strategies are represented among plants tolerant of the most extreme shortages of nutrients, water and light. It is concluded that while ecologists should attempt to reduce the complexities of nature to an oligo-dimensional framework of generalizing ideas, it is not reasonable to expect that any very simple scheme – such as might be represented by three or four reference points in one plane – will have generality on a world scale.
All organisms, especially terrestrial plants and other sessile species, interact mainly with their neighbors, but neighborhoods can differ in composition because of dispersal and mortality. There is increasingly strong evidence that the spatial structure created by these forces profoundly influences the dynamics, composition, and biodiversity of communities. Nonspatial models predict that no more consumer species can coexist at equilibrium than there are limiting resources. In contrast, a similar model that includes neighborhood competition and random dispersal among sites predicts stable coexistence of a potentially unlimited number of species on a single resource. Coexistence occurs because species with sufficiently high dispersal rates persist in sites not occupied by superior competitors. Coexistence requires limiting similarity and two-way or three-way interspecific trade-offs among competitive ability, colonization ability, and longevity. This spatial competition hypothesis seems to explain the coexistence of the numerous plant species that compete for a single limiting resource in the grasslands of Cedar Creek Natural History Area. It provides a testable, alternative explanation for other high diversity communities, such as tropical forests. The model can be tested (1) by determining if coexisting species have the requisite trade-offs in colonization, competition, and longevity, (2) by addition of propagules to determine if local species abundances are limited by dispersal, and (3) by comparisons of the effects on biodiversity of high rates of propagule addition for species that differ in competitive ability.
1. There is a limit to the similarity (and hence to the number) of competing species which can coexist. The total number of species is proportional to the total range of the environment divided by the niche breadth of the species. The number is reduced by unequal abundance of resources but increased by adding to the dimensionality of the niche. Niche breadth is increased with increased environmental uncertainty and with decreased productivity. 2. There is a different evolutionary limit, L, to the similarity of two coexisting species such that a) If two species are more similar than L, a third intermediate species will converge toward the nearer of the pair. b) If two species are more different than L, a third intermediate species will diverge from either toward a phenotype intermediate between the two.
We study two kinds of mechanistic and spatial models of plant competition in heterogeneous environments. First, we study lottery models in which the outcome of competition among juveniles for vacant space is determined by one of several underlying mechanistic submodels. Environmental heterogeneity that affects the outcome of competition is present in all of these models and may be spatial, temporal, biotic in origin, abiotic in origin, or any mixture of these. The principal result is that the models predict coexistence if the plant species are sufficiently dissimilar-if they sufficiently partition the spatial, temporal, biotic, or abiotic environmental heterogeneity. Second, we study a complex forest-simulation model of competition among individuals for light and a nutrient. Whereas the nonspatial version of this model predicts that a single species will outcompete all others, the spatial version predicts that coexistence is possible. We show that the results for the analytically tractable models appear to explain the cause and pattern of coexistence in the simulation model.
The focus of most ideas on diversity maintenance is species coexistence, which may be stable or unstable. Stable coexistence can be quantified by the long-term rates at which community members recover from low density. Quantification shows that coexistence mechanisms function in two major ways: they may be
a) equalising because they tend to minimise average fitness differences between species
b) stabilising because they tend to increase negative intraspecific interactions relative to negative interspecific interactions
Stabilising mechanisms are essential for species coexistence and include traditional mechanisms such as resource partitioning and frequency-dependent predation, as well as mechanisms that depend on fluctuations of population densities and environemntal factors in space and time. Equalising mechanisms contribute to stable coexistence because they reduce average fitness inequalities which might negate the effects of stabilising mechanisms. Models of unstable coexistence, in which species diversity decays over time, have focused almost exclusively on equalising mechanisms. These models would be more robust if they included stabilising mechanisms, which arise in many and varied ways but need not be adequate for full stability of a system. Models of unstable coexistence invite a briader view of diversity maintenence incorporating species turnover.
Aim Our aim was to quantify climatic influences on key leaf traits and relationships at the global scale. This knowledge provides insight into how plants have adapted to different environmental pressures, and will lead to better calibration of future vegetation–climate models.
Location The data set represents vegetation from 175 sites around the world.
Methods For more than 2500 vascular plant species, we compiled data on leaf mass per area (LMA), leaf life span (LL), nitrogen concentration (N mass ) and photosynthetic capacity (A mass ). Site climate was described with several standard indices. Correlation and regression analyses were used for quantifying relationships between single leaf traits and climate. Standardized major axis (SMA) analyses were used for assessing the effect of climate on bivariate relationships between leaf traits. Principal components analysis (PCA) was used to summarize multidimensional trait variation.
Results At hotter, drier and higher irradiance sites, (1) mean LMA and leaf N per area were higher; (2) average LL was shorter at a given LMA, or the increase in LL was less for a given increase in LMA (LL–LMA relationships became less positive); and (3) A mass was lower at a given N mass , or the increase in A mass was less for a given increase in N mass . Considering all traits simultaneously, 18% of variation along the principal multivariate trait axis was explained by climate.
Main conclusions Trait‐shifts with climate were of sufficient magnitude to have major implications for plant dry mass and nutrient economics, and represent substantial selective pressures associated with adaptation to different climatic regimes.
List of contributors Preface to first edition Acknowledgement List of symbols Dune meadow data 1. Introduction R. H. G. Jongman 2. Data collection J. C. Jager and C. W. N. Looman 3. Regression C. J. F. ter Braak and C. W. N. Looman 4. Calibration C. J. F. ter Braak 5. Ordination C. J. F. ter Braak 6. Cluster analysis O. F. R. van Tongeren 7. Spatial aspects of ecological data P. A. Burrough 8. Numerical methods in practice: case-studies P. A. Burrough, J. A. F. Oudhof, A. Barendregt, R. H. G. Jongman and T. J. van de Nes References Index.
Species diversity may be additively partitioned within and among samples (alpha and beta diversity) from hierarchically scaled studies to assess the proportion of the total diversity (gamma) found in different habitats, landscapes, or regions. We developed a statistical approach for testing null hypotheses that observed partitions of species richness or diversity indices differed from those expected by chance, and we illustrate these tests using data from a hierarchical study of forest-canopy beetles. Two null hypotheses were implemented using individual- and sample-based randomization tests to generate null distributions for alpha and beta components of diversity at multiple sampling scales. The two tests differed in their null distributions and power to detect statistically significant diversity components. Individual-based randomization was more powerful at all hierarchical levels and was sensitive to departures between observed and null partitions due to intraspecific aggregation of individuals. Sample-based randomization had less power but still may be useful for determining whether different habitats show a higher degree of differentiation in species diversity compared with random samples from the landscape. Null hypothesis tests provide a basis for inferences on partitions of species richness or diversity indices at multiple sampling levels, thereby increasing our understanding of how alpha and beta diversity change across spatial scales.
Fitting a line to a bivariate dataset can be a deceptively complex problem, and there has been much debate on this issue in the literature. In this review, we describe for the practitioner the essential features of line‐fitting methods for estimating the relationship between two variables: what methods are commonly used, which method should be used when, and how to make inferences from these lines to answer common research questions.
A particularly important point for line‐fitting in allometry is that usually, two sources of error are present (which we call measurement and equation error), and these have quite different implications for choice of line‐fitting method. As a consequence, the approach in this review and the methods presented have subtle but important differences from previous reviews in the biology literature.
Linear regression, major axis and standardised major axis are alternative methods that can be appropriate when there is no measurement error. When there is measurement error, this often needs to be estimated and used to adjust the variance terms in formulae for line‐fitting. We also review line‐fitting methods for phylogenetic analyses.
Methods of inference are described for the line‐fitting techniques discussed in this paper. The types of inference considered here are testing if the slope or elevation equals a given value, constructing confidence intervals for the slope or elevation, comparing several slopes or elevations, and testing for shift along the axis amongst several groups. In some cases several methods have been proposed in the literature. These are discussed and compared. In other cases there is little or no previous guidance available in the literature.
Simulations were conducted to check whether the methods of inference proposed have the intended coverage probability or Type I error. We identified the methods of inference that perform well and recommend the techniques that should be adopted in future work.
Wood density and vessel characteristics are functionally interrelated, yet they may have distinct ecological associations. In a comparative study of 51 angiosperm species ranging from chaparral shrubs to riparian trees, we examined relationships among wood density and vessel traits and their ecological correlates. Mean vessel lumen area and vessel density (number mm(-2)) varied widely (7- to 10-fold). In multivariate analyses, both vessel traits were negatively correlated with wood density, which varied more narrowly (< 2-fold). Vessel density and lumen area were inversely related across species, allowing a broad range of vessel traits within a narrow range of wood density. Phylogenetic independent contrasts indicated correlated inverse evolutionary change in vessel traits. Each trait had a distinct pattern of ecological correlation -- wood density was most strongly associated with soil water, and vessel traits showed contrasting relationships with plant height. Within a narrow range of wood density, there was significant variation in vessel traits. Given their particular ecological associations, the results suggest that wood density and vessel traits describe two distinct ecological axes.
The tissue traits and architectures of plant species are important for land-plant ecology in two ways. First, they control ecosystem processes and define habitat and resources for other taxa; thus, they are a high priority for understanding the ecosystem at a site. Second, knowledge of trait costs and benefits offers the most promising path to understanding how vegetation properties change along physical geography gradients. There exists an informal shortlist of plant traits that are thought to be most informative. Here, we summarize recent research on correlations and tradeoffs surrounding some traits that are prospects for the shortlist. By extending the list and by developing better models for how traits influence species distributions and interactions, a strong foundation of basic ecology can be established, with many practical applications.