No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Relating plant species and functional diversity to community δ13C in NE Spain pastures
Abstract
The relationship of plant species and functional diversities to community-level δ13C, as a proxy for water carbon relations, was assessed in pastures from two climatic regions in NE Spain. Overall, community δ13C was negatively related to species diversity, but positively related to functional diversity. However, pronounced differences between climatic regions were found: smaller variations in δ13C and thus carbon–water relations were observed for communities under humid conditions, which had higher species diversity but were more functionally redundant than communities under arid conditions. Thus, if species and functional diversities affect plant carbon–water relations at the community and hence at the ecosystem level seems to depend strongly on functional redundancy, i.e., the overlap in plant traits among the species present.
... However, evidence about such a relationship is scarce and contradictory [7]. In the last two decades, a growing body of evidence has indicated that species affect ecosystem functions via their traits [8][9][10]; these reports were summarized in review papers e.g., [11,12]. The fact that coexisting species with similar traits are present in a given assemblage indicates that there is not a general relationship between species richness and ecosystem functions, and thus it is impossible to attribute variations in ecosystem function exclusively to taxonomic causes [7,8,13,14]. ...
... In the last two decades, a growing body of evidence has indicated that species affect ecosystem functions via their traits [8][9][10]; these reports were summarized in review papers e.g., [11,12]. The fact that coexisting species with similar traits are present in a given assemblage indicates that there is not a general relationship between species richness and ecosystem functions, and thus it is impossible to attribute variations in ecosystem function exclusively to taxonomic causes [7,8,13,14]. ...
... Indeed, the decreasing number of species will not necessarily affect a given ecosystem function, if the persistence of other species having the same strategies is ensured. On the contrary, the loss of some species bearing unique trait values is expected to alter the ecosystem functions dramatically [7,8,15]. The maintenance of ecosystem functioning under species loss is known as functional redundancy [16]. ...
Predicting how biodiversity affects ecosystem functioning requires a multifaceted approach based on the partitioning of diversity into its taxonomic and functional facets and thus redundancy. Here, we investigated how species richness (S), functional diversity (FD) and functional redundancy (FR) are affected by forest structure. Sixty-eight abandoned coppice-with-standards plots were selected in two mountain areas of the Apennine chain. We performed linear models to quantify the influence of structural parameters on S, FD and FR of clonal traits. Each diversity facet was affected differently by structural parameters, suggesting a complex interweaving of processes that influence the understory layer. Namely, tree layer density influences S, the height of the standards affects the lateral spread and persistence of clonal growth organs, and diameter of standards affects the FD of the number of clonal offspring. Opposite relationships compared to FD was found for the FR, suggesting how clonal traits play a key role in species assemblage. The observation that structural parameters exert opposite impact on FR seems to indicate a counterbalance effect on ecosystem stability. Multifaceted approaches yield a better understanding of relationship between forest structure and understory, and this knowledge can be exploited to formulate indications for more sustainable management practices.
... White, grey and black horizontal bars indicate overwinter, vertical mobility and summer grazing periods, respectively. earlier publication (de Bello et al., 2009). Briefly, d 13 C values for all 134 plant species sampled ranged from À19.4 to À31.9‰. ...
... However, variability in plant sources during the overwinter period may not be understood as evidence of similar plant species diversity in high mountain locations. On the contrary, in our reference subalpine pastures, plant communities showed the highest species diversity (demonstrated by species richness and Simpson's Diversity Index), but a reduced functional diversity, as compared to the Mediterranean communities (de Bello et al., 2005de Bello et al., , 2009). This suggests a lower trait dissimilarity (or 'distance') among species in subalpine pastures than in Mediterranean communities. ...
... more enriched than the d 13 C values in low altitude pastures (Monegros, 256 m; Castelldans, 321 m or Vilamajor, 709 m). The values from these pastures (max: À26‰; min: À28‰) were measured in plants collected at the beginning of May, just after the spring rainfall peak, at the time of maximum vegetation growth (de Bello et al., 2009). In other words, plants were sampled under optimal conditions for the site (wet spring). ...
Although the frequency of pastoral activities involving vertical sheep mobility has decreased over the last century, this is a herding strategy still used in the Ebro basin, where animals move from overwintering valley locations up to the Pyrenees from late spring to early autumn. Such practice allows herders to avoid the worst climatic conditions, seasonally balancing the great contrast between ecological zones in this region, from dry lowland Mediterranean steppe to wet mountain subalpine grasslands. As recent regional archaeological works have suggested, the altitudinal movement of flocks may have begun with the first early Neolithic groups settled in this territory. Here we investigate through stable isotope analyses one of the last flocks that still performs this activity. Sheep specimens were analyzed by sequential analyses (δ¹³C and δ¹⁸O) in bioapatite of tooth enamel, allowing detection of seasonal changes. Tooth series are interpreted according to rainfall distribution, seasonal patterns in δ ¹⁸O of meteoric water, vegetation changes and δ¹³C values in pastures along the altitudinal gradient in the area. Vertical movements in sheep sequential series are recognized by an inverse relationship between δ¹³C and δ¹⁸O values. Monthly δ¹⁸O values in meteoric water obtained in valley and mountain locations describe the same type of seasonal oscillation, with high values during the warm months and low values during the cold months. Pastures analyzed along the altitudinal gradient showed a decrease in δ¹³C values with altitude, linked to the seasonal availability of precipitation and vegetation differences among locations. These results define a new analytical and conceptual framework for the interpretation of archaeological samples in this region.
... Hence, the carbon isotopic signature has been frequently and successfully used as an indicator for water use and drought stress of C3 plants in functional studies (e.g. Adams and Grierson, 2001;de Bello et al., 2009;Mariotte et al., 2013;Wrage et al., 2009). ...
... Biodiversity-ecosystem functioning (BEF) studies found that drought stress might be decreased at higher levels of plant diversity in grasslands (e.g. Caldeira et al., 2001;de Bello et al., 2009;Mariotte et al., 2013), either by facilitative interactions or complementarity in resource use among plant species. However, whether higher plant diversity increases water use efficiency and therefore ecosystem resilience is still controversially debated (e.g. ...
... Higher diversity was clearly associated with more negative δ 13 C values in biomass indicating that plant diversity buffers against drought stress in agriculturally managed grasslands. These results are in accordance to findings from Spanish pastures (de Bello et al., 2009) and small-scale biodiversity experiments with grassland species (Caldeira et al., 2001;Mariotte et al., 2013). Jumpponen et al. (2005) similarly found a diversity effect on the δ 13 C signal of two legume species including T. pratense, but did not find an effect in other species under study such as T. repens and D. glomerata. ...
Land-use change and intensification play a key role in the current biodiversity crisis. The resulting species loss can have severe effects on ecosystem functions and services, thereby increasing ecosystem vulnerability to climate change. We explored whether land-use intensification (i.e. fertilization intensity), plant diversity and other potentially confounding environmental factors may be significantly related to water use (i.e. drought stress) of grassland plants. Drought stress was assessed using δ13C abundances in aboveground plant biomass of 150 grassland plots across a gradient of land-use intensity. Under water shortage, plants are forced to increasingly take up the heavier 13C due to closing stomata leading to an enrichment of 13C in biomass. Plants were sampled at the community level and for single species, which belong to three different functional groups (one grass, one herb, two legumes).
... The carbon isotope composition (d 13 C) of leaf tissues, which measures the ratio of 13 C to 12 C (‰), is an integrated, long-term measure of the ratio between internal and ambient CO 2 concentrations (c i /c a ), which affects discrimination against the carbon isotope 13 C during CO 2 fixation by Rubisco (Farquhar et al. 1989). Although a number of factors might influence the variation of d 13 C, it can be used to provide first insights into water-carbon relations in plants (with less negative d 13 C values largely suggesting higher stomata closure within a species and, across taxa at a given location, species with higher intrinsic water use efficiency; Seibt et al. 2008;de Bello et al. 2009b). ...
... It also leads to a compensatory increase in photosynthetic capacity of the remaining or new leaves. In this sense, the already less negative d 13 C values at the dry site (suggesting stronger water saving strategies; Jumpponen et al. 2005;de Bello et al. 2009b) tended to be further increased by mowing. This suggests that the lower soil water content, accompanied by a less dense canopy with increased light irradiation and higher water vapour deficit, could lead to plants growing with more closer stomata and with increased water saving strategies. ...
QuestionTrait scaling relationships involve multiple trade‐offs and allometric constraints between the traits of co‐existing species. Alternative trait relationships, particularly between plant size and other traits, are expected in response to combinations of different biotic and abiotic filters. To what extent does the expected convergence in plant attributes to water shortage and disturbance produce different trait scaling relationships in dry vs wet meadows under various disturbance regimes? LocationsOne test meadow in South Bohemia and one in South Moravia (i.e. wet vs dry Central Europe meadows), Czech Republic. Methods
Selected species were sampled in mown and abandoned plots within each site. Several plant traits were measured to provide information on plant strategies related to growth, resource acquisition and carbon–water economy. ResultsTrait differentiation among co‐existing species was strong in both meadows, and generally stronger than differentiation caused by mowing and site effects. Different trait scaling relationships with plant height were observed across the meadows, particularly showing a more independent trait differentiation linked to water–carbon economy at the dry site. Mowing tended to reinforce the effect of water limitation on traits and on trait scaling. In contrast, mowing cessation tended to resemble the effect of humid conditions on trait relationships. Conclusions
The results advocate incorporating trait scaling relationships between species into vegetation models and community assembly assessments, therefore accounting for processes of plant co‐existence along combined spectra of light, water and disturbance regimes. These gradients affect alternative life‐history strategies and possibly sustain different species co‐existence patterns based on different trait scaling. The results particularly advocate a convergence in traits and trait scaling relationships in response to the combination of disturbance and water limitation.
... An increasing number of recent studies have examined patterns of variation in functional diversity in the field, including in response to land use (Flynn et al., 2009;Laliberté et al., 2010) and specifically to grazing (Hadar et al., 1999;Walker et al., 1999;de Bello et al., 2006de Bello et al., , 2009Cingolani et al., 2007;Pillar et al., 2009). these studies complement more numerous and advanced analyses of the response of community-level means to changing land use and other environmental conditions (reviewed by Lavorel et al., 2007; see also Pakeman et al., 2008Pakeman et al., , 2009), but still, little is known overall about how functional diversity changes in response to combined environmental gradients such as climate and disturbance , making it difficult to project the future Downloaded by [223.99.253.67] at 03:17 26 March 2014 structure and function of ecosystems. ...
... For single traits, this index has a parallel behavior across land use treatments to Mason's functional divergence (Mason et al., 2005;Grigulis et al., unpubl.). Calculations were performed using an excel macro (de Bello et al., 2009). ...
Only a few studies have examined responses of grassland functional diversity to management and major environmental gradients, in order to address the question of whether grassland use can promote functional divergence. For five grassland sites in Israel, Portugal, the Czech Republic, Mediterranean France, and the French Alps, where traditional grassland management is being abandoned, we quantified community-weighted means (CWM) and functional divergence (FDvg) for the three Leaf-Height-Seed (LHS) traits, individually and in combination. Responses of CWM and FDvg to land use were analyzed by mixed linear models with aridity, phosphorus, fertility, and the fractions of grasses and annuals as covariates.
Responses of community-weighted traits to land use were consistent with current knowledge. More intense management favored plants with more rapid resource acquisition (high Specific Leaf Area, or SLA), whereas abandonment or less intense grassland management increased the dominance by tall plants with more conservative strategies (low SLA). Seed weight did not respond to land use. For the three traits and their combination, functional divergence decreased in response to land use change overall. Detailed responses, however, varied depending on sites and especially their climate. At the two French sites, traditional site management promoted functional divergence within communities by suppressing dominance by large perennial tussocks, whereas at the two Mediterranean sites it is likely that the drier climate promoted a functionally diverse pool of species tolerant to grazing.
This study demonstrates how simultaneous analyses of variations in community-mean traits and functional divergence for a focused set of traits offer promising avenues to understand mechanisms of community response to environmental change.
... Similarly, d 13 C in plant and soil are also of broad ecological interest [18]. In C3 plants, which represent Central European grassland vegetation, d 13 C abundances in biomass are first of all affected by water availability and drought stress, but show also significant interactions with nutrient availability and fertilization [2,19]. ...
... Additionally, d 13 C values are related to a different contribution of CO 2 from soil respiration to plant photosynthesis y [6,20] and thus contain valuable ecological information related to agricultural management. Furthermore, was shown to be related to functional aspects of plant communities [18]. ...
Distinguishing organic and conventional products is a major issue of food security and authenticity. Previous studies successfully used stable isotopes to separate organic and conventional products, but up to now, this approach was not tested for organic grassland hay and soil. Moreover, isotopic abundances could be a powerful tool to elucidate differences in ecosystem functioning and driving mechanisms of element cycling in organic and conventional management systems. Here, we studied the δ15N and δ13C isotopic composition of soil and hay samples of 21 organic and 34 conventional grasslands in two German regions. We also used Δδ15N (δ15N plant - δ15N soil) to characterize nitrogen dynamics. In order to detect temporal trends, isotopic abundances in organic grasslands were related to the time since certification. Furthermore, discriminant analysis was used to test whether the respective management type can be deduced from observed isotopic abundances.
Isotopic analyses revealed no significant differences in δ13C in hay and δ15N in both soil and hay between management types, but showed that δ13C abundances were significantly lower in soil of organic compared to conventional grasslands. Δδ15N values implied that management types did not substantially differ in nitrogen cycling. Only δ13C in soil and hay showed significant negative relationships with the time since certification. Thus, our result suggest that organic grasslands suffered less from drought stress compared to conventional grasslands most likely due to a benefit of higher plant species richness, as previously shown by manipulative biodiversity experiments. Finally, it was possible to correctly classify about two third of the samples according to their management using isotopic abundances in soil and hay. However, as more than half of the organic samples were incorrectly classified, we infer that more research is needed to improve this approach before it can be efficiently used in practice.
... The carbon isotope composition (d 13 C) of leaf tissues, which measures the ratio of 13 C to 12 C (‰), is an integrated, long-term measure of the ratio between internal and ambient CO 2 concentrations (c i /c a ), which affects discrimination against the carbon isotope 13 C during CO 2 fixation by Rubisco (Farquhar et al. 1989). Although a number of factors might influence the variation of d 13 C, it can be used to provide first insights into water-carbon relations in plants (with less negative d 13 C values largely suggesting higher stomata closure within a species and, across taxa at a given location, species with higher intrinsic water use efficiency; Seibt et al. 2008;de Bello et al. 2009b). ...
... It also leads to a compensatory increase in photosynthetic capacity of the remaining or new leaves. In this sense, the already less negative d 13 C values at the dry site (suggesting stronger water saving strategies; Jumpponen et al. 2005;de Bello et al. 2009b) tended to be further increased by mowing. This suggests that the lower soil water content, accompanied by a less dense canopy with increased light irradiation and higher water vapour deficit, could lead to plants growing with more closer stomata and with increased water saving strategies. ...
Question: Trait scaling relationships involve multiple trade-offs and allometric
constraints between the traits of co-existing species. Alternative trait relationships,
particularly between plant size and other traits, are expected in response
to combinations of different biotic and abiotic filters. To what extent does the
expected convergence in plant attributes to water shortage and disturbance produce
different trait scaling relationships in dry vs wet meadows under various
disturbance regimes?
Locations: One test meadow in South Bohemia and one in South Moravia (i.e.
wet vs dry Central Europemeadows), Czech Republic.
Methods: Selected species were sampled in mown and abandoned plots within
each site. Several plant traits were measured to provide information on plant
strategies related to growth, resource acquisition and carbon–water economy.
Results: Trait differentiation among co-existing species was strong in both
meadows, and generally stronger than differentiation caused by mowing and
site effects. Different trait scaling relationships with plant height were observed
across the meadows, particularly showing a more independent trait differentiation
linked to water–carbon economy at the dry site. Mowing tended to reinforce
the effect of water limitation on traits and on trait scaling. In contrast,
mowing cessation tended to resemble the effect of humid conditions on trait
relationships.
Conclusions: The results advocate incorporating trait scaling relationships
between species into vegetation models and community assembly assessments,
therefore accounting for processes of plant co-existence along combined spectra
of light, water and disturbance regimes. These gradients affect alternative lifehistory
strategies and possibly sustain different species co-existence patterns
based on different trait scaling. The results particularly advocate a convergence
in traits and trait scaling relationships in response to the combination of disturbance
and water limitation.
... Among the scales of regional species group and local communities, diversity exhibits patterning that is the focus of a large amount of management activities (Rogers et al., 2001). A large body of studies on rangeland ecosystems, including natural grasslands, suggests that the function of ecosystem is largely dependent on biodiversity ( Balvanera et al., 2006;Diaz et al., 2007;de Bello et al., 2009). Also, it can thus be used to indicate the ecophysiological response of plants and communities to environmental factors, providing more understanding on the functional benefit of biodiversity for ecosystem functioning in diverse ecosystems (de Bello et al., 2009). ...
... A large body of studies on rangeland ecosystems, including natural grasslands, suggests that the function of ecosystem is largely dependent on biodiversity ( Balvanera et al., 2006;Diaz et al., 2007;de Bello et al., 2009). Also, it can thus be used to indicate the ecophysiological response of plants and communities to environmental factors, providing more understanding on the functional benefit of biodiversity for ecosystem functioning in diverse ecosystems (de Bello et al., 2009). In a simple definition, biodiversity is the total sum of all biotic variation from genes to ecosystems (Purvis and Hector, 2000). ...
... Therefore, the worldwide averages in this study should be applicable to most areas including China. In addition, the 13 C signature of biomass can be influenced by geographical differences (essentially climatic difference, including rainfall gradient, light, temperature…) (Farquhar and Richards, 1984;Weiguo et al., 2005;de Bello et al., 2009;Yang et al., 2012) and the regional species (Farquhar et al., 1982;Ren and Yu, 2011), and this may be important for more regionally applicable values. The 13 C signatures of crude oil from all over the world can be found in Table S2. ...
Carbon isotope signatures are used to gain insight into sources and atmospheric processing of carbonaceous aerosols. Since elemental carbon (EC) is chemically stable, it is possible to apportion the main sources of EC (C3/C4 plant burning, coal combustion, and traffic emissions) using a dual ¹⁴C-¹³C isotope approach. The dual-isotope source apportionment crucially relies on accurate knowledge of ¹³C source signatures, which are seldom measured for EC. In this work, we present ¹³C signatures of organic carbon (OC) and EC for relevant sources in China. EC was isolated for ¹³C analysis based on the OC/EC split point of a thermal-optical method (EUSAAR_2 protocol). A series of sensitivity studies were conducted to investigate the EC separation and the relationship of the thermal-optical method to other EC isolation methods. Our results show that, first, the ¹³C signatures of raw materials and EC related to traffic emissions can be separated into three groups according to geographical location. Second, the ¹³C signature of OC emitted by the flaming combustion of C4 plants is strongly depleted in ¹³C compared to the source materials, and therefore EC is a better tracer for this source than total carbon (TC). A comprehensive literature review of ¹³C source signatures (of raw materials, of TC, and of EC isolated using a variety of thermal methods) was conducted. Accordingly, we recommend composite ¹³C source signatures of EC with uncertainties and detailed application conditions. Using these source signatures of EC in an example dual-isotope source apportionment study shows an improvement in precision. In addition, ¹³C signatures of OC were measured at three different desorption temperatures roughly corresponding to semi-volatile, low-volatile, and non-volatile OC fractions. Each source category shows a characteristic trend of ¹³C signatures with desorption temperature, which is likely related to different OC formation processes during combustion.
... As suggested by Cadotte et al. (2011) ecological redundancy may drive the negative relationship between these two diversity facets (Cadotte et al., 2011), which mainly occurs in species rich assemblages (Loreau, 2004;Naeem, 1998). Similar to our results, de Bello et al. (2009) found an increase in functional redundancy associated to an increase in taxonomic diversity in alpine pastures in the Catalonian Pre-Pyrenees. Our results indicate that the volume of trait space was occupied by a few species, and when species richness increased, the new species were not functionally different from those already present (Díaz and Cabido, 2001). ...
... According to the review by Kohn (2010), C 3 plants growing in open environments show a mean δ 13 C value of − 26.5‰ (range − 29‰ to − 25‰) including those that thrive under a wide range of mean annual precipitation, mean annual temperature and altitude. In the northeast of the Iberian Peninsula, pasture plants never reach values higher than~− 26‰, even those located in environments with a lower amount of precipitation as represented by the Monegros area (256 m; < 300 mm/yr) (de Bello et al., 2009;Tornero et al., 2018). Assuming a conservative maximum δ 13 C value of − 26.5‰ for pasture plants growing in open environments of Terrassa (286 m; 678.2 mm/yr; idescat.cat ...
The Late Antiquity to the Early Middle age transition in the North Eastern Iberian Peninsula was a historical period of cultural, social and political changes. Both Germanics and North African peoples settled in this region in successive migratory waves. The impact of these population movements on the cultural habits of the local population has been barely explored. This paper explores the dietary changes of the population who were buried in the necropolis of the Churches of Sant Pere de Terrassa (Barcelona, Spain) during the Visigoth (fifth to eighth centuries ad) and Carolingian periods (ninth to tenth centuries ad). This study investigates the δ¹³C and δ¹⁵N stable isotopic values in bone collagen from 68 human samples and 36 faunal remains in order to improve the understanding of dietary changes that occurred during this transition. The results indicate a human diet based on C3-plants and livestock sources. On average, the Visigoth samples exhibited an enriched isotopic signal compared to that of the Carolingian period, which may be attributed to the consumption of high trophic level of animal protein. Some δ¹³C results of the adult human samples suggest that C4-plants (most probably millet) made proportionately smaller but significant contributions to the diet during the Visigoth period. The paleodietary data obtained here will be important for future further studies focused on the transition from the Late Antiquity to the Early Medieval period in the Iberian Peninsula, and the attending regional scale of changes. This will also give insight about how profound a transformation in policy and economy occurred during that period affected human consumer patterns in the region.
... Increasing and protecting the plant diversity are ecologic management layouts to conduct the terrestrial ecosystems (Fakhimi-Abarghoie et al., 2011). Two aspects of plant diversity involving plant richness (number of species) and evenness (monotonic distribution and abundance of species individuals) are simultaneously evaluated (Bello et al., 2009). ...
Harvester ants are known as one of the most renowned bio-disturbances in the
arid and semi-arid ecosystems that affecte vegetation by collecting seeds and harvesting
plants. It seems that physiognomy of plant association in steppe shrub land of Roodshoor,
Saveh Iran has been highly changed by harvester ants‟ activities that caused to conduct
this research. The study was carried out on active and inactive nests and control site from
June to August 2012. Diversity indices and functional groups such as vegetative form,
longevity, and photosynthesis type were analyzed as compared to criteria in three sites.
Results showed that richness, diversity, and vegetation cover in the ant colonies through
increasing the annual forbs and rare species (Campanula stricta and Lepidium vesicarium)
were more than the control site. For evenness index, however, there was no significant
difference between the control and nest sites. In contrast, the function of plant community
in the active nests due to the decrease of dominant shrub frequency of the area that is
Artimisia siberi by Messor spp. was less than the control site. Low diversity, richness,
plant function, and high vegetation cover in inactive nests were also observed as the results
of the presence and activities of the ants in the active nests. Hence, the ant activities in the
active and inactive nests can bring out micro sites with different plant associations so that
regarding high density and quantity of the ant nests in all the area, it can decrease the key
plants and change their functions. It therefore will debilitate the stability and function of
this rangeland ecosystem.
... These results coincide with those reported about higher temporal stability of above-ground biomass in grasslands than in sown pastures [43,44], and further demonstrate that grasslands stabilize function in time more than sown pastures. The higher stability in grasslands is consistent with the presence of a larger number of species and probably more functional diversity [45]. It could be expected that higher species diversity in grasslands will encompass a wider set of adaptive traits, such as diverse vegetative and reproductive phenologies and root depths, compared with sown pastures. ...
... Trait values of the species present were obtained from two traitbases, i.e. the LEDA traitbase [39], and the CLO-PLA traitbase [40] and complemented by specific standardized measurements for SLA [41] in the field. Only few trait values were acquired from de Bello et al. [42]. One important factor in the response of species to warming could be trait plasticity [43] which is considered one of the major means by which species can cope with new environmental conditions [44]. ...
Plant functional traits underlie vegetation responses to environmental changes such as global warming, and consequently influence ecosystem processes. While most of the existing studies focus on the effect of warming only on species diversity and productivity, we further investigated (i) how the structure of community plant functional traits in temperate grasslands respond to experimental warming, and (ii) whether species and functional diversity contribute to a greater stability of grasslands, in terms of vegetation composition and productivity. Intact vegetation turves were extracted from temperate subalpine grassland (highland) in the Eastern Pyrenees and transplanted into a warm continental, experimental site in Lleida, in Western Catalonia (lowland). The impacts of simulated warming on plant production and diversity, functional trait structure, and vegetation compositional stability were assessed. We observed an increase in biomass and a reduction in species and functional diversity under short-term warming. The functional structure of the grassland communities changed significantly, in terms of functional diversity and community-weighted means (CWM) for several traits. Acquisitive and fast-growing species with higher SLA, early flowering , erect growth habit, and rhizomatous strategy became dominant in the lowland. Productivity was significantly positively related to species, and to a lower extent, functional diversity, but productivity and stability after warming were more dependent on trait composition (CWM) than on diversity. The turves with more acquisitive species before warming changed less in composition after warming. Results suggest that (i) the short-term warming can lead to the dominance of acquisitive fast growing species over conservative species, thus reducing species richness, and (ii) the functional traits structure in grassland communities had a greater influence on the productivity and stability of the community under short-term warming, compared to diversity effects. In summary, short-term climate warming can greatly alter vegetation functional structure and its relation to productivity.
... This pattern might have been enhanced by the coincidence of the most severe excess of the recommended stocking rate and the most arid conditions. However, we suggest that the stronger response at drier conditions is also related to the fact that functional redundancy (i.e., number of species within a functional group sensu Walker 1992) tends to be lower in dry, compared to more humid rangeland systems (de Bello et al. 2009). Likewise in our study, the most arid site (central Nama Karoo) had the lowest number of species per functional type (cf. ...
A general understanding of grazing effects on plant diversity in drylands is still missing, despite an extensive theoretical background. Cross-biome syntheses are hindered by the fact that the outcomes of disturbance studies are strongly affected by the choice of diversity measures and the spatial and temporal scales of measurements. The aim of this study is to overcome these weaknesses by applying a wide range of diversity measures to a data set derived from identical sampling in three distinct ecosystems. We analyzed three fence-line contrasts (heavier vs. lighter grazing intensity) representing different degrees of aridity (from arid to semi-arid) and precipitation regimes (summer rain, winter rain) in southern Africa. We tested the impact of grazing intensity on multiple aspects of plant diversity (species and functional group level, richness and evenness components, alpha and beta diversity, composition) at two spatial scales and both for 5-yr means and inter-annual variability. Heavier grazing reduced total plant cover and substantially altered the species and functional composition in all sites. However, a significant decrease in species alpha diversity was detected only in one of the three sites. By contrast, alpha diversity of plant functional groups responded consistently across ecosystems and scales with a significant decrease at heavier grazing intensity. The cover-based measures of functional group diversity responded more sensitively and more consistently than functional group richness. Beta diversity of species and functional types increased under heavier grazing, showing that at larger scales the heterogeneity of the community composition and the functional structure were increased. Heavier grazing mostly increased interannual variability of alpha diversity, while effects on beta diversity and cover were inconsistent. Our results suggest that species diversity alone may not adequately reflect the shifts in vegetation structure that occur in response to increased grazing intensity in the dryland biomes of southern Africa. Compositional and structural changes of the vegetation are better reflected by trait-based diversity measures. In particular, measures of plant functional diversity that include evenness represent a promising tool to detect and quantify disturbance effects on ecosystems. Finally, studying the combined effects of climate change and land-use intensification on biodiversity stability is important.
... However, we found that the component of species diversity responsible for this insurance is functional redundancy, and not functional diversity. Indeed, notwithstanding the high correlation between species diversity and functional diversity, and between species diversity and functional redundancy, which corroborates de Bello et al. (2009a), functional redundancy and functional diversity were independent. This also explains why the correlation between species diversity and community functional stability was weaker compared to that between functional redundancy and stability; i.e. species diversity contains functional diversity, which in turn did not show a significant link to community functional stability and therefore adds noise to the correlation between species diversity and stability. ...
Questions
Functional redundancy in assemblages may insure ecosystem processes after perturbation potentially causing temporary or permanent local species extinctions. Yet, functional redundancy has only been inferred by indirect evidence or measured by methods that may not be the most appropriate. Here, we apply an existing method to measure functional redundancy, which is the fraction of species diversity not expressed by functional diversity, to assess whether functional redundancy affects community resilience after disturbance.
Location
Subtropical grassland, south B razil (30°05′46″S, 51°40′37″W).
Method
Species traits and community composition were assessed in quadrats before grazing and after community recovery. Grazing intensity ( G ) was measured in each quadrat. We used traits linked to grazing intensity to define functional redundancy ( FR ) as the difference of G ini– S impson index of species diversity ( D ) and R ao's quadratic entropy ( Q ). Also, with the same traits, we defined community functional stability ( S ) as the similarity between trait‐based community composition before grazing and 47 and 180 d after grazing ending. Using path analysis we assessed different postulated causal models linking functional diversity ( Q ), functional redundancy ( FR ), grazing intensity ( G ) and community‐weighted mean traits to community stability ( S ) under grazing.
Results
Path analysis revealed the most valid causal model FR → S ← G , with a significant positive path coefficient for FR → S and a marginally significant negative one for S ← G . Since FR and G were independent in their covariation and in their effects on S , the model discriminated community resistance to grazing (the effect of G on S ) from community resilience after grazing caused by functional redundancy (indicated by the effect of FR on S ).
Conclusion
We show that expressing functional redundancy mathematically is a useful tool for testing causal models linking diversity to community stability. The results support the conclusion that functional redundancy enhanced community resilience, therefore corroborating the insurance hypothesis.
... As expected, drier conditions promoted the predominance of plant communities with low SLA cwm and higher values of d 13 C cwm , indicating a more efficient use of water (Farquhar, O'Leary & Berry 1982), consistent with other previous studies (e.g. Cunningham, Summerhayes & Westoby 1999;De Bello et al. 2009). ...
Plant species composition and community functional structure (i.e. trait composition at the community level) result from a hierarchy of environmental filters that constrain which species and traits tend to be dominant in a given habitat.
We quantified variation in community functional structure along natural gradients of soil resources using several above‐ and below‐ground parameters and explored links among these attributes to determine whether plant resource economics can be applied at the community level in a Mediterranean rangeland of southern France.
Limitation by nitrogen, soil water and soil depth were the main ecological factors driving the functional response at the community level. Most of the community functional parameters considered in this study were more dependent on nitrogen limitation than on the other two factors, mostly related with the acquisition–conservation trade‐off at both the leaf and the root level.
We found a strong coordination between above‐ground and below‐ground components, with a high level of concordance along the resource gradients explored. As an example, tissue dry matter content – both in leaves and roots – was positively related to nitrogen limitation. These findings indicate that the leaf economic spectrum paradigm (resource conservation in resource‐poor habitats versus resource acquisition in resource‐rich habitats) can be extrapolated to the below‐ground component and extends to a plant community spectrum.
Changes in the functional structure of communities were promoted by two complementary components of variation: (i) the replacement of species with highly contrasting resource‐use strategies and, to a lesser extent, (ii) the intraspecific variation in several above‐ground traits.
Synthesis . This study showed that soil water and nutrient limitations are the main drivers controlling functional community structure in the Mediterranean rangelands studied and that shifts in this structure were mainly due to species turnover. In addition, we provided evidence for a plant community economics spectrum , based on a strong coordination between above‐ and below‐ground components in these resource‐limited communities.
... Despite that leaf 15 N discriminated among mycorrhizal groups, the hypothesis that plant species with low LMA (and presumably a resource-acquisition strategy) have a low dependence on mycorrhizal interactions for N-uptake (i.e., higher leaf 15 N values) was not supported by our data. In contrast, the hypothesis expecting a positive relationship between LMA and δ 13 C was supported at both the species and the community level, in accordance with the strong association of LMA with plant water-use efficiency reported in previous studies (Cunningham et al. 1999; de Bello et al. 2009). Are LMA and LDMC relationships consistent at the species and community levels? ...
Background and aims
Soil factors are driving forces that influence spatial distribution and functional traits of plant species. We test whether two anchor morphological traits—leaf mass per area (LMA) and leaf dry matter content (LDMC)—are significantly related to a broad range of leaf nutrient concentrations in Mediterranean woody plant species. We also explore the main environmental filters (light availability, soil moisture and soil nutrients) that determine the patterns of these functional traits in a forest stand.
Methods
Four morphological and 19 chemical leaf traits (macronutrients and trace elements and δ13C and δ15N signatures) were analysed in 17 woody plant species. Community-weighted leaf traits were calculated for 57 plots within the forest. Links between LMA, LDMC and other leaf traits were analysed at the species and the community level using standardised major axis (SMA) regressions
Results
LMA and LDMC were significantly related to many leaf nutrient concentrations, but only when using abundance-weighted values at community level. Among-traits links were much weaker for the cross-species analysis. Nitrogen isotopic signatures were useful to understand different resource-use strategies. Community-weighted LMA and LDMC were negatively related to light availability, contrary to what was expected.
Conclusion
Community leaf traits have parallel shifts along the environmental factors that determine the community assembly, even though they are weakly related across individual taxa. Light availability is the main environmental factor determining this convergence of the community leaf traits.
... is could suggest that once larger-scale filters have imposed constraints on functional trait composition, additional processes could shape the diversity of species coexisting at the local level. e increase in species diversity at sites with higher sand content, followed only by a reduction in FDiv for leaf nitrogen, could for instance suggest an increase in trait redundancy between species, i.e. more species having more similar traits (de Bello et al. 2009). Soils with higher sand content are generally less productive, having lower organic matter and limited ability to retain water (the correlation with sand % was 0.475 and 0.42 respectively). ...
Understanding the influence of the environment on the functional structure of ecological communities is essential to
predict the response of biodiversity to global change drivers. Ecological theory suggests that multiple environmental factors
shape local species assemblages by progressively filtering species from the regional species pool to local communities.
!ese successive filters should influence the various components of community functional structure in different ways.
In this paper, we tested the relative influence of multiple environmental filters on various metrics of plant functional
trait structure (i.e. ‘community weighted mean trait’ and components of functional trait diversity, i.e. functional
richness, evenness and divergence) in 82 vegetation plots in the Guisane Valley, French Alps. For the 211 sampled
species we measured traits known to capture key aspects of ecological strategies amongst vascular plant species, i.e. leaf
traits, plant height and seed mass (LHS). A comprehensive information theory framework, together with null model
based resampling techniques, was used to test the various environmental effects. Particular community components of
functional structure responded differently to various environmental gradients, especially concerning the spatial scale at
which the environmental factors seem to operate. Environmental factors acting at a large spatial scale (e.g. temperature)
were found to predominantly shape community weighted mean trait values, while fine-scale factors (topography and
soil characteristics) mostly influenced functional diversity and the distribution of trait values among the dominant
species. Our results emphasize the hierarchical nature of ecological forces shaping local species assemblage: large-scale
environmental filters having a primary effect, i.e. selecting the pool of species adapted to a site, and then filters at finer
scales determining species abundances and local species coexistence. !is suggests that different components of functional
community structure will respond differently to environmental change, so that predicting plant community responses
will require a hierarchical multi-facet approach.
... In most of the case studies considered, species diversity and FD were correlated significantly (P \ 0.05), even if the covariation was sometimes week (low R). The Rao index of FD is a mathematical generalization of the Simpson index, where the Simpson index is the upper limit for its values (de Bello et al. 2009). Consequently, purely mathematically, we cannot expect that these two values will be completely independent. ...
Rigorous and widely applicable indicators of biodiversity are needed to monitor the responses of ecosystems to global change and design effective conservation schemes. Among the potential indicators of biodiversity, those based on the functional traits of species and communities are interesting because they can be generalized to similar habitats and can be assessed by relatively rapid field assessment across eco-regions. Functional traits, however, have as yet been rarely considered in current common monitoring schemes. Moreover, standardized procedures of trait measurement and analyses have almost exclusively been developed for plants but different approaches have been used for different groups of organisms. Here we review approaches using functional traits as biodiversity indicators focussing not on plants as usual but particularly on animal groups that are commonly considered in different biodiversity monitoring schemes (benthic invertebrates, collembolans, above ground insects and birds). Further, we introduce a new framework based on functional traits indices and illustrate it using case studies where the traits of these organisms can help monitoring the response of biodiversity to different land use change drivers. We propose and test standard procedures to integrate different components of functional traits into biodiversity monitoring schemes across trophic levels and disciplines. We suggest that the development of indicators using functional traits could complement, rather than replace, the existent biodiversity monitoring. In this way, the comparison of the effect of land use changes on biodiversity is facilitated and is expected to positively influence conservation management practices.
KeywordsBioindicators-Birds-Carabids-Collembola-Functional diversity-Macroinvertebrates-Community weighted mean trait-Standardized biodiversity monitoring
... These results coincide with those reported about higher temporal stability of above-ground biomass in grasslands than in sown pastures [43,44], and further demonstrate that grasslands stabilize function in time more than sown pastures. The higher stability in grasslands is consistent with the presence of a larger number of species and probably more functional diversity [45]. It could be expected that higher species diversity in grasslands will encompass a wider set of adaptive traits, such as diverse vegetative and reproductive phenologies and root depths, compared with sown pastures. ...
In the Neotropics the predominant pathway to intensify productivity is generally thought to be to convert grasslands to sown pastures, mostly in monoculture. This article examines how above-ground net primary productivity (ANPP) in semi-natural grasslands and sown pastures in Central America respond to rainfall by: (i) assessing the relationships between ANPP and accumulated rainfall and indices of rainfall distribution, (ii) evaluating the variability of ANPP between and within seasons, and (iii) estimating the temporal stability of ANPP. We conducted sequential biomass harvests during 12 periods of 22 days and related those to rainfall. There were significant relationships between ANPP and cumulative rainfall in 22-day periods for both vegetation types and a model including a linear and quadratic term explained 74% of the variation in the data. There was also a significant correlation between ANPP and the number of rainfall events for both vegetation types. Sown pastures had higher ANPP increments per unit rainfall and higher ANPP at the peak of the rainy season than semi-natural grasslands. In contrast, semi-natural grasslands showed higher ANPP early in the dry season. The temporal stability of ANPP was higher in semi-natural grasslands than in the sown pastures in the dry season and over a whole annual cycle. Our results reveal that, contrary to conventional thinking amongst pasture scientists, there appears to be no increase in ANPP arising from replacing semi-natural grasslands with sown pastures under prevailing pasture management practices in seasonally dry climates, while the temporal distribution of ANPP is more even in semi-natural grasslands. Neither sown pastures nor semi-natural grasslands are productive towards the end of the dry season, indicating the potential importance of the widespread practice of retaining tree cover in pastures.
1. Intraspecific trait variability is a crucial, often neglected, component of functional diversity (FD) in ecological communities. In particular, uncertainty remains as to the importance of intraspecific variability in the quantification of FD.
2. To explore this uncertainty, we propose two methods addressing two critical and complementary, but largely unexplored, questions: (i) what is the extent of within- vs. between-species FD in different communities? and (ii) to what extent is the response of FD to environment because of compositional turnover vs. intraspecific trait variability across habitats? The methods proposed to address these questions are built on a variance partitioning approach and have the advantage of including species relative abundance, therefore taking into account species dominance and rarity. For each of the questions, we illustrate one dedicated case study in semi-natural grasslands with associated sampling strategies.
3. The decomposition of total community variance into within- vs. between-species effects can be implemented in a manner similar to the decomposition of quadratic entropy on pairwise individual dissimilarity. The approach can be applied with single and multiple traits, although it proves more informative for single traits. It can prove particularly useful when assessing the role of different sources of trait variability in the assembly of communities.
4. The assessment of the relative contribution of intraspecific trait variability and species turnover to the response of FD to environment is based on a variance partitioning comparing FD indices computed (i) either using individuals measured in a specific habitat alone (FDhabitat) or (ii) all individuals measured across different habitats (FDfixed). This approach provides a more complete understanding of the response of FD to environment.
5. We further propose a guide to apply these two methods and to choose the most suitable method for intraspecific trait measurements. Assessing the role of intraspecific trait variability should allow a more comprehensive understanding of the processes that link species and ecosystems.
Author Summary
The world is currently experiencing a rapid loss of species, prompting investigation into the role of biodiversity on the functioning of ecosystems. Many recent studies have shown that high diversity of plants, pollinators, and predators is related to high plant growth, pollination, and predation, respectively. Many of these studies involved controlled experiments, yet results were highly variable, indicating that the environment may affect the relationship between species diversity and these ecosystem functions. In a heterogeneous environment, different species can occupy different microhabitats, or use different resources. This reduces competition between species, and can mean that diverse assemblages perform their ecosystem functions at elevated rates. Here we examine rates of three important functions in different natural, nonexperimental ecosystems: plant biomass production in German grasslands, parasitism rates across five habitat types in coastal Ecuador, and coffee pollination in agroforestry systems in Indonesia. We demonstrate that the effect of diversity on these processes increases in environments where limiting resources (soil nutrients, host insects, and coffee flowers, respectively) are spatially heterogeneous. These real world patterns, combined with previous experiments suggest that biodiversity may have its greatest impact on the functioning of diverse, naturally heterogeneous ecosystems.
Functional diversity is a component of biodiversity that generally concerns the range of things that organisms do in communities and ecosystems. Here, we review how functional diversity can explain and predict the impact of organisms on ecosystems and thereby provide a mechanistic link between the two. Critical points in developing predictive measures of functional diversity are the choice of functional traits with which organisms are distinguished, how the diversity of that trait information is summarized into a measure of functional diversity, and that the measures of functional diversity are validated through quantitative analyses and experimental tests. There is a vast amount of trait information available for plant species and a substantial amount for animals. Choosing which traits to include in a particular measure of functional diversity will depend on the specific aims of a particular study. Quantitative methods for choosing traits and for assigning weighting to traits are being developed, but need much more work before we can be confident about trait choice. The number of ways of measuring functional diversity is growing rapidly. We divide them into four main groups. The first, the number of functional groups or types, has significant problems and researchers are more frequently using measures that do not require species to be grouped. Of these, some measure diversity by summarizing distances between species in trait space, some by estimating the size of the dendrogram required to describe the difference, and some include information about species abundances. We show some new and important differences between these, as well as what they indicate about the responses of assemblages to loss of individuals. There is good experimental and analytical evidence that functional diversity can provide a link between organisms and ecosystems but greater validation of measures is required. We suggest that non-significant results have a range of alternate explanations that do not necessarily contradict positive effects of functional diversity. Finally, we suggest areas for development of techniques used to measure functional diversity, highlight some exciting questions that are being addressed using ideas about functional diversity, and suggest some directions for novel research.
Functional diversity is hypothesised as being beneficial for ecosystem functions, such as productivity and resistance to invasion. However, a precise definition of functional diversity, and hence a framework for its quantification, have proved elusive. We present a definition based on the analogy of the components of species diversity – richness, evenness and divergence. These concepts are applied to functional characters to give three components of functional diversity – functional richness, functional evenness and functional divergence. We demonstrate how each of these components may be calculated. It is hoped that our definition of functional diversity and its components will aid in elucidation of the mechanisms behind diversity/ecosystem-function relationships.
Attempts to unveil the relationships between the taxonomic diversity, productivity and stability of ecosystems continue to generate inconclusive, contradictory and controversial conclusions. New insights from recent studies support the hypothesis that species diversity enhances productivity and stability in some ecosystems, but not in others. Appreciation is growing for the ways that particular ecosystem features, such as environmental variability and nutrient stress, can influence biotic interactions. Alternatives to the diversity-stability hypothesis have been proposed, and experimental approaches are starting to evolve to test these hypotheses and to elucidate the mechanisms underlying the functional role of species diversity.
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.
There is growing recognition that classifying terrestrial plant species on the basis of their function ( into 'functional types') rather than their higher taxonomic identity, is a promising way forward for tackling important ecological questions at the scale of ecosystems, landscapes or biomes. These questions include those on vegetation responses to and vegetation effects on, environmental changes ( e. g. changes in climate, atmospheric chemistry, land use or other disturbances). There is also growing consensus about a shortlist of plant traits that should underlie such functional plant classifications, because they have strong predictive power of important ecosystem responses to environmental change and/or they themselves have strong impacts on ecosystem processes. The most favoured traits are those that are also relatively easy and inexpensive to measure for large numbers of plant species. Large international research efforts, promoted by the IGBP-GCTE Programme, are underway to screen predominant plant species in various ecosystems and biomes worldwide for such traits. This paper provides an international methodological protocol aimed at standardising this research effort, based on consensus among a broad group of scientists in this field. It features a practical handbook with step-by-step recipes, with relatively brief information about the ecological context, for 28 functional traits recognised as critical for tackling large-scale ecological questions.
Concern is growing about the consequences of biodiversity loss for ecosystem functioning, for the provision of ecosystem services, and for human well being. Experimental evidence for a relationship between biodiversity and ecosystem process rates is compelling, but the issue remains contentious. Here, we present the first rigorous quantitative assessment of this relationship through meta-analysis of experimental work spanning 50 years to June 2004. We analysed 446 measures of biodiversity effects (252 in grasslands), 319 of which involved primary producer manipulations or measurements. Our analyses show that: biodiversity effects are weaker if biodiversity manipulations are less well controlled; effects of biodiversity change on processes are weaker at the ecosystem compared with the community level and are negative at the population level; productivity-related effects decline with increasing number of trophic links between those elements manipulated and those measured; biodiversity effects on stability measures ('insurance' effects) are not stronger than biodiversity effects on performance measures. For those ecosystem services which could be assessed here, there is clear evidence that biodiversity has positive effects on most. Whilst such patterns should be further confirmed, a precautionary approach to biodiversity management would seem prudent in the meantime.
Global environmental change affects the sustained provision of a wide set of ecosystem services. Although the delivery of ecosystem services is strongly affected by abiotic drivers and direct land use effects, it is also modulated by the functional diversity of biological communities (the value, range, and relative abundance of functional traits in a given ecosystem). The focus of this article is on integrating the different possible mechanisms by which functional diversity affects ecosystem properties that are directly relevant to ecosystem services. We propose a systematic way for progressing in understanding how land cover change affects these ecosystem properties through functional diversity modifications. Models on links between ecosystem properties and the local mean, range, and distribution of plant trait values are numerous, but they have been scattered in the literature, with varying degrees of empirical support and varying functional diversity components analyzed. Here we articulate these different components in a single conceptual and methodological framework that allows testing them in combination. We illustrate our approach with examples from the literature and apply the proposed framework to a grassland system in the central French Alps in which functional diversity, by responding to land use change, alters the provision of ecosystem services important to local stakeholders. We claim that our framework contributes to opening a new area of research at the interface of land change science and fundamental ecology.
We revisit the relationship between plant water use efficiency and carbon isotope signatures (delta(13)C) of plant material. Based on the definitions of intrinsic, instantaneous and integrated water use efficiency, we discuss the implications for interpreting delta(13)C data from leaf to landscape levels, and across diurnal to decadal timescales. Previous studies have often applied a simplified, linear relationship between delta(13)C, ratios of intercellular to ambient CO(2) mole fraction (C (i)/C (a)), and water use efficiency. In contrast, photosynthetic (13)C discrimination (Delta) is sensitive to the ratio of the chloroplast to ambient CO(2) mole fraction, C (c)/C (a) (rather than C (i)/C (a)) and, consequently, to mesophyll conductance. Because mesophyll conductance may differ between species and over time, it is not possible to determine C (c)/C (a) from the same gas exchange measurements as C (i)/C (a). On the other hand, water use efficiency at the leaf level depends on evaporative demand, which does not directly affect Delta. Water use efficiency and Delta can thus vary independently, making it difficult to obtain trends in water use efficiency from delta(13)C data. As an alternative approach, we offer a model available at http://carbonisotopes.googlepages.com to explore how water use efficiency and (13)C discrimination are related across leaf and canopy scales. The model provides a tool to investigate whether trends in Delta indicate changes in leaf functional traits and/or environmental conditions during leaf growth, and how they are associated with trends in plant water use efficiency. The model can be used, for example, to examine whether trends in delta(13)C signatures obtained from tree rings imply changes in tree water use efficiency in response to atmospheric CO(2) increase. This is crucial for predicting how plants may respond to future climate change.
Understanding and forecasting changes in plant communities, ecosystem properties, and their associated services requires a mechanistic link between community shifts and modifications in ecosystem properties. In this study, we test the hypothesis that plant traits can provide such a link. Using subalpine grasslands in the central French Alps as a case study, we investigate the response of plant traits to changes in soil resource availability and disturbance regimes associated with changing grassland management as well as the effects of changes in plant traits on measured ecosystem properties. We found that fertilization leads to greater specific leaf area and leaf nitrogen content which leads to greater productivity and faster litter decomposition, and that grazing leads to higher leaf toughness and leaf dry matter content which leads to lower productivity and slower decomposition compared to mowing. A state and transition model was used as a flexible conceptual tool for integrating data on community composition, plant traits, and ecosystem properties in the context of managementmediated successional dynamics in subalpine grasslands. Focusing on the biology driving the transition between grassland states, we incorporated plant traits into the formulation of a state and transition model and demonstrated how they could be used to provide a mechanistic link between community shifts and ecosystem properties under complex management regimes with strong land-use legacies.
Measurements of trait community composition are known to be sensitive to the way species abundance is assessed, but not to what extent. This was investigated by considering two of the most commonly used indices of community trait composition, trait averages and functional diversity, in bee communities along a post-fire environmental gradient. The indices were computed using three different species abundance measurements (log and unlog number of individuals and species occurrence only) and 5 traits. For certain traits, the responses of the indices to fire varied according to how species abundance was measured. The measurements that took species abundance into account in the most distinct way (e.g., occurrence vs. unlog data) produced the least similar results for all traits. Species were then grouped into different classes on the basis of their relative abundance (i.e., dominants, subdominants, and rare species). As a result, the measure that attaches the highest importance to the abundance of species (unlog data) related mostly to the dominant species traits, while the measure attaching the lowest (i.e., species occurrence) related more to rare species traits. Species diversity was mostly independent of trait averages and functional diversity, regardless of the measure of species abundance used. We also quantified functional redundancy (i.e., the potential minus the observed functional diversity in each community). When more weight was attached to species abundance, redundancy decreased and tended to be less correlated with species diversity. Overall, the way species abundance is taken into consideration in indices of functional composition offers promising insights into the way community assembly mechanisms respond to environmental changes.
Functional redundancy has often been assumed as an intuitive null hypothesis in biodiversity experiments, but theory based on the classical Lotka-Volterra competition model shows that functional redundancy sensu stricto is incompatible with stable coexistence. Stable coexistence requires differences between species which lead to functional complementarity and differences between the yields of mixtures and monocultures. Only a weaker version of functional redundancy, i.e. that mixture yields lie within the range of variation of monoculture yields, is compatible with stable coexistence in Lotka-Volterra systems. Spatial and temporal environmental variability may provide room for functional redundancy at small spatial and temporal scales, but is not expected to do so at the larger scales at which environmental variations help maintain coexistence. Neutral coexistence of equivalent competitors, non-linear per capita growth rates, and lack of correlation between functional impact and biomass may provide the basis for the existence of functional redundancy in natural ecosystems. Overall, there is a striking parallel between the conditions that allow stable coexistence and those that allow overyielding.
The earth's biosphere is altered by human beings at an unprecedented rate. Conversion of natural ecosystems to agricultural land and urban developments has already changed one third to one half of the earth's ice-free terrestrial surface, impacting ecosystem services on a continental scale. Also, the breakdown of biogeographic barriers, by international travel and trade, has caused species to extend their range far beyond their natural range, invading and changing the properties of entire ecosystems. Probably the most dramatic of all man caused direct changes of the biosphere is, however, the rapid decline of biological diversity. In contrast to agricultural land that can be reconverted to forests or invading species that can—with large efforts—be eradicated from an invaded area, the genetic code of extinct species is irreversibly lost. Three functional mechanisms have been proposed here to explain the observed positive effect of bio-diversity on ecosystem functioning—selection effect, resource facilitation, and niche complementarity. Consequently, positive biodiversity effects on ecosystem functioning should largely result of statistical likelihood rather than ‘‘true’’ diversity effects. Despite the growing body of scientific literature addressing the effect of biodiversity on ecosystem functioning, only a few studies have directly tested the functional mechanisms described above. In these studies, the application of stable isotopes as tools—both as tracers and at natural abundance levels—has significantly advanced the understanding of the functional mechanisms underlying the biodiversity and ecosystem functioning relationship. This chapter highlights the studies that have directly addressed the functional mechanisms of biodiversity and ecosystem functioning using stable isotopes. The stable isotopes have been established as a valuable and indispensable tool that allows to link community and ecosystem ecology, but research on biodiversity and ecosystem functioning could benefit much more by combining classical methodology with stable isotope analyses.
Although the structure and composition of plant communities is known to influence the functioning of ecosystems, there is as yet no agreement as to how these should be described from a functional perspective. We tested the biomass ratio hypothesis, which postulates that ecosystem properties should depend on species traits and on species contribution to the total biomass of the community, in a successional sere following vineyard abandonment in the Mediterranean region of France. Ecosystem-specific net primary productivity, litter decomposition rate, and total soil carbon and nitrogen varied significantly with field age, and correlated with community-aggregated (i.e., weighed according to the relative abundance of species) functional leaf traits. The three easily measurable traits tested, specific leaf area, leaf dry matter content, and nitrogen concentration, provide a simple means to scale up from organ to ecosystem functioning in complex plant communities. We propose that they be called ''functional markers,'' and be used to assess the impacts of community changes on ecosystem properties induced, in particular, by global change drivers.
Plant species composition and species response to grazing are fundamental to the management of grazing lands. Reliable prediction of grazing responses from species’ traits would be a major step forward in generalizing knowledge and management beyond the locality. Recently results have been presented showing that plant species’ responses to grazing in subhumid grasslands in Argentina and Israel could be predicted from simple traits: height, leaf size, life history and specific leaf area (SLA). This study assessed whether those relationships between traits and grazing responses hold for Australian semi‐arid and arid shrublands and woodlands.
Eleven lists of grazing responses from five published grazing studies were matched with a plant trait data set. Trait distributions were compared between response groups pooled across studies. Relationships between traits and grazing response were also assessed, both within and across studies, using meta‐analysis.
Overall there was little evidence for predictability of grazing responses with simple traits in the semi‐arid and arid shrublands and woodlands. There were relationships between grazing response and life history and growth form, and some weak evidence for grazing increasers having high SLA.
Synthesis and applications . It was concluded that prediction of grazing responses with simple traits is less clear in semi‐arid and arid rangelands, which are characterized by openness at ground level and high diversity of growth forms, compared with subhumid grasslands that have structurally simple, continuous swards. The finding that species’ traits may have differing predictive capacity for grazing responses in different situations means that we need more empirical studies in different situations. The most important contrasts between situations for investigation are likely to be on axes of rainfall/productivity and evolutionary history of grazing.
In the face of large‐scale environmental changes, predicting the consequences for species composition from species’ traits can be a major step towards generalizing ecological patterns and management. Few studies, however, have explored the applicability of this tool in relation to different climatic conditions. Here, the changes in species composition along a gradient of sheep‐grazing pressure (high, low, abandonment) were used to test whether a common set of plant functional traits (PFT) would provide consistent predictions of species’ responses to grazing in different biogeographical regions.
Data were collected across an altitudinal and climatic gradient from Mediterranean rangelands to subalpine grasslands in north‐eastern Spain. Species’ responses were calculated using partial constrained ordination to account only for the effect of grazing intensity. Regression trees and general linear models were applied to identify traits that could predict species’ responses.
Results were mostly consistent with the ruderal vs. competitive strategy ( sensu Grime ), in terms of life cycle, life form and plant height, and their expected responses to repeated disturbance.
However, the predictive capacity of the investigated traits changed with climatic conditions. Traits generally related to grazing did not show a strong repeatability across the climatic gradient. Convergent selection of climatic conditions and grazing indicated that plant features might reflect an adaptation to multiple selective forces. The climatic conditions acted as filters on the pool of PFT available and shifted the relevance of plant traits as potential predictors. Results were not substantially different after applying phylogenetically independent contrasts (PIC).
Synthesis and applications . At a local scale, plant functional traits are useful tools in predicting species’ responses to grazing and, for conservation purposes, identifying species vulnerable to land‐use changes. However, predictions cannot be extrapolated from one climatic region to another. The methodology proposed in this study to detect predicting traits can be applied more generally. Regression trees, in particular, appear to be a useful tool because they account for non‐additive effects and allow visualizations of trait combinations.
The consequences of globally declining biodiversity and climate change for ecosystem functions are intensively debated topics in ecological research. However, few studies have investigated potential interactions, or the combined effects of both scenarios, for ecosystem functioning. In the work presented here we tested the hypothesis that increasing plant diversity acts as insurance for ecosystem functions during extreme weather events which are predicted by climate change scenarios.
We measured the effect of plant diversity on above‐ and below‐ground productivity in semi‐natural grasslands following experimentally induced early summer drought. To test the insurance hypothesis directly, we determined in each community the range of δ ¹³ C values of individual plant species as drought stress indicators.
Increasing plant diversity significantly enhanced below‐ground productivity as a consequence of simulated drought, while above‐ground productivity was reduced independently of plant diversity.
Plants shifting carbon allocation to below‐ground compartments during drought maintain various aspects of ecosystem services and functions. Although we were not able to detect physiological evidence for the insurance hypothesis, we conclude from our below‐ground results that plant diversity is an essential entity of ecosystems for maintaining ecosystem functions in a changing climate.
Interspecific and temporal variations in presumed water‐use efficiency, as measured by carbon isotope discrimination (Δ), were examined in a Greek semiarid herbaceous grassland, and the hypothesis tested that competition for water is a factor in determining vegetation structure.
Experiments were conducted for 3 years in an upland grassland consisting of exclusively C 3 perennial species. The most abundant species were the grasses Poa pratensis L., Lolium perenne L. and Festuca valida (Uechtr.) Penzes; the forbs Achillea millefolium L., Plantago lanceolata L. and Taraxacum officinale Weber ex Wigg; and the legume Trifolium repens L.
Rooting depth did not explain plant Δ in this shallow‐soil site, where soil moisture was concentrated in the top of the profile.
Although temporal variation for Δ was significant within most species, changes in ranking of species were slight throughout three growing seasons.
Δ Was negatively related to species biomass production, which means that species’ abundances were positively related to species’ water‐use efficiencies. Δ Was positively related to leaf N content, which we interpret as an autocorrelation with water availability.
The results of this study are consistent with the notion that, in an environment where water is scarce, plants may compete effectively by increasing their potential water‐use efficiency as measured by Δ, and that species abundance is regulated by competition‐driven water depletion.
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
We investigated the role of water use in a Mediterranean grassland, in which diversity was experimentally manipulated, and a positive relationship was observed between plant species richness and productivity. Soil moisture patterns and stable carbon isotope ratios (δ13C) in leaves indicated greater water use by plants growing in species-rich mixtures compared to monocultures. These results suggest that complementarity or facilitation may be the mechanism responsible for the positive relationship between plant diversity and ecosystem processes.
Separating the mechanisms that influence ecosystem functioning has been a goal of recent high profile experiments. Integrating the various experimental and analytical methods that attempt this goal across terrestrial and aquatic ecosystems, as well as careful definition of ‘complementarity’, produces novel insights and valuable lessons about new directions for research. (1) Experimental designs differ in temporal scale and whether standing stock or another ecosystem process was the response variable. (2) Mathematically identical variables in different designs have contrasting ecological interpretations. For example, different sets of ecological processes can contribute to different variables in different experimental designs. (3) The frequency of transgressive overyielding of standing stock (e.g. total above ground biomass) in polycultures implies little about the prevalence of transgressive overyielding in other ecosystem processes. (4) Measuring the contribution to ecosystem functioning of individual species, rather than just total ecosystem functioning of a polyculture, is not essential for estimating effects of complementarity. (5) Further research will profit from distinguishing standing stock from all other ecosystem functions. (6) None of the analytic methods can distinguish the effects of individual processes or mechanisms such as resource use differentiation, facilitation, or allelopathy, for which additional experimental treatments are required.
We established monocultures and 16 unique mixed communities of 12 native grasses, legumes and non‐N 2 ‐fixing forbs. We identified species having a greater or lesser yield in the mixed communities than expected from monoculture data as winners and losers, respectively. To test our hypothesis that performance of the subordinate species (losers) is mainly controlled by light availability, whereas the dominant species (winners) are sensitive to the availability of below‐ground resources, we traced the effects of number of species, light transmission in the community and foliar N concentration on plant photosynthesis through leaf C isotope composition (δ ¹³ C).
Phalaris arundinacea and Phleum pratense , the two tallest grass species, yielded more in mixtures than expected, as, initially, did Dactylis glomerata . Festuca ovina , the smallest grass, and Ranunculus acris , a forb, had smaller yield in mixtures than expected. For most species, observed mixture yields did not deviate significantly from those expected.
Decreases in transmitted light decreased δ ¹³ C in D. glomerata , Lotus corniculatus and Rumex acetosa . The δ ¹³ C of Trifolium pratense and L. corniculatus was affected by increasing number of species in the plant community even after accounting for the transmitted light. In P. arundinacea , δ ¹³ C increased with increasing foliar %N, as expected for the tallest, dominant species.
Species showing a positive, significant relationship between δ ¹³ C and transmitted light were relatively low growing and unable to establish dominance in multispecies communities due to shading by larger dominants.
We conclude that above‐ground competition is crucial in determining C isotope composition among the subordinate species, whereas the dominant species are more strongly affected by below‐ground resources. Different factors thus dictate the physiological performance of species according to the size‐distribution hierarchy in the community.
Different components of biodiversity may vary independently of each other along environmental gradients giving insights into the mechanisms that regulate species coexistence. In particular, the functional diversity (FD) or the presence of rare or endemic species in natural assemblages do not necessarily increase with species diversity. We studied if different components of plant species diversity (species richness, Simpson diversity, evenness) varied similarly to FD (measured as a generalization of the Simpson index) and rarity along grazing intensity and climatic gradients. Plots under different sheep grazing regimes (high and low intensity, abandonment) were surveyed in five locations along a climatic gradient in north-eastern Spain, from semi-arid lowland to moist upland locations. Variation in species diversity, functional diversity and rarity followed different patterns. Species diversity was lowest in water-stressed environments (arid locations and southern aspects) and increased with grazing more makedly in humid locations. The FD was comparable between the most species-poor and species-rich locations and decreased with grazing in the moistest location, i.e. where species diversity markedly increased. The FD did not show a strong correlation with species richness nor with the Simpson index and less specious communities could show the highest functional diversity. The rarest species in the region were more frequently found in the abandoned areas, which held the lowest species diversity. Consequently, the mechanisms that enhance the diversity of species do not necessarily support a functional differentiation among those species or the maintenance of rare species in a region. We hypothesize that the degree of dependence of functional diversity on species diversity might be mostly related to the amplitude of the species’ traits pool and on how species partition the niche space available.
The grass flora of Namibia (374 species in 110 genera) shows surprisingly little variation in 13C values along a rainfall gradient (50–600 mm) and in different habitat conditions. However, there are significant differences in the 13C values between the metabolic types of the C4 photosynthetic pathway. NADP-ME-type C4 species exhibit the highest 13C values (–11.7 ) and occur mainly in regions with high rainfall. NAD-ME-type C4 species have significantly lower 13C values (–13.4 ) and dominate in the most arid part of the precipitation regime. PCK-type C4 species play an intermediate role (–12.5 ) and reach a maximum abundance in areas of intermediate precipitation. This pattern is also evident in genera containing species of different metabolic types. Within the same genus NAD species reach more negative 13C values than PCK species and 13C values decreased with rainfall. Also in Aristida, with NADP-ME-type photosynthesis, 13C values decreased from –11 in the inland region (600 mm precipitation) to –15 near the coast (150 mm precipitation), which is a change in discrimination which is otherwise associated by a change in metabolism. The exceptional C3 species Eragrostis walteri and Panicum heterostachyum are coastal species experiencing 50 mm precipitation only. Many of the rare species and monotypic genera grow in moist habitats rather than in the desert, and they are not different in their carbon isotope ratios from the more common flora. The role of species diversity with respect to habitat occupation and carbon metabolism is discussed.
Species and functional group (grasses, legumes, creeping nonlegume forbs, rosette nonlegume forbs) richness of species assemblages composed of 16 species from four functional plant groups were manipulated to evaluate the productivity-diversity relationships in a greenhouse pot experiment. Pots were filled with sand, and supplied at two levels of nutrients. The plants were grown in monocultures, two, four, eight and 16 species mixtures. Individual two, four, and eight species mixtures differed in the richness of functional groups. Although the two characteristics of biodiversity, i.e. species and functional group richness, were necessarily correlated, it was shown that it is possible to separate their effect statistically, and also test for their common effect without pronounced loss of test power. There was a pronounced increase of average aboveground biomass and a mild increase in belowground biomass with biodiversity. The effect of functional group richness was more pronounced than the effect of the number of species. By using the method of Loreau and Hector (Nature 411 (2001) 72), selection and complementarity effects were statistically separated, and the overyielding index was calculated as a ratio of the productivity of a mixture to the productivity of its most productive component (to demonstrate transgressive overyielding). Positive values of complementarity and transgressive overyielding were both found, particularly in some rich communities and under high nutrient levels. Complementarity significantly increased only with functional group richness and mainly under high nutrients in the belowground biomass. Some species, when grown in monocultures, had decreased productivity under higher nutrients, and thus were more productive in mixtures than in monocultures. It seems that those species suffered from too high nutrient levels when grown in monocultures, but not in the presence of other species, which were able to use the nutrients in high concentrations and effectively decrease the nutrient levels. As a consequence, mixtures of high diversity were always more productive under high nutrients. The difference in species proportions between high and low nutrients, characterized by chord distance, increased with species richness. The relative change in productivity decreased with the number of functional groups. This suggests that species richness might lead to stabilization of aggregate characteristics (like total productivity) under changing environmental conditions by changing the proportions of individual species.
The aim of the study was to investigate how plant species’ composition, soil parameters and nutrient concentrations in plant biomass differ between fertilized and control plots 62 years after the last fertilizer application on a sub-alpine grassland.A piece of land called the Grass Garden (GG), fertilized with wood ash and manure for at least 200 years, was rediscovered in the Giant Mts. (Krkonoše, Karkonosze) in 2006. The last fertilization was applied in 1944. The central part of GG (treatment A), the edge of GG (treatment B) and never-fertilized control plots outside of GG (treatment C) were distinguished.Sixty-two years after the last fertilization Nardus stricta was dominant in treatment C and Deschampsia cespitosa and Avenella flexuosa in treatments A and B. The predominance of these grasses was first described in 1786 and repeatedly during the 19th and 20th centuries and indicated the long-term stability of plant species’ composition in the sub-alpine grassland. In the case of GG, long-term fertilization has had a long-term “stable after-effect” upon differences in plant species’ composition.Ca concentration in the soil was more than two times higher in treatments A and B than in the control, indicating that it was very difficult to deplete applied Ca even on extreme podzol soils and under the climatic conditions of the sub-alpine vegetation belt.In above-ground plant biomass, Mg and P concentrations and N:P ratio were still significantly affected by treatment.
Increasingly research suggests that the level of internal regulation of function in agroecosystems is largely dependent on the level of plant and animal biodiversity present. In agroecosystems, biodiversity performs a variety of ecological services beyond the production of food, including recycling of nutrients, regulation of microclimate and local hydrological processes, suppression of undesirable organisms and detoxification of noxious chemicals. In this paper the role of biodiversity in securing crop protection and soil fertility is explored in detail. It is argued that because biodiversity mediated renewal processes and ecological services are largely biological, their persistence depends upon the maintenance of biological integrity and diversity in agroecosystems. Various options of agroecosystem management and design that enhance functional biodiversity in crop fields are described.
The concept of species redundancy in ecosystem processes is troublesome because it appears to contradict the traditional emphasis in ecology on species singularity. When species richness is high, however, ecosystem processes seem clearly insensitive to considerable variation in biodiversity. Some elementary principles from reliability engineering, where engineered redundancy is a valued part of systems design, suggest that we should rethink our stance on species redundancy. For example, a central tenet of reliability engineering is that reliability always increases as redundant components are added to a system, a principle that directly supports redundant species as guarantors of reliable ecosystem functioning. I argue that we should embrace species redundancy and perceive redundancy as a critical feature of ecosystems which must be preserved if ecosystems are to function reliably and provide us with goods and services. My argument is derived from basic principles of reliability engineering which demonstrate that the probability of reliable system performance is closely tied to the level of engineered redundancy in its design. Empirical demonstrations of the value of species redundancy in ecosystem reliability would provide new insights into the ecology of communities and the value of species conservation.
Redundancia de Especies y Confiabilidad del Ecosistema
El concepto de redundancia de especies en procesos ecológicos es problemático puesto que aparentemente contradice el énfasis tradicional en ecologia sobre la singularidad de las especies. Sin embargo, cuando la riqueza de especies es alta, los procesos del ecosistema parecen claramente insensibles a variaciones considerables de la biodiversidad. Principios elementales de confiabilidad en ingenieria, donde la redundancia es evaluada como parte del diseño de sistemas, sugiere que deberíamos repensar nuestra postura sobre la redundancia de especies. Por ejemplo, un principio central de confiabilidad ingenieril es que la confiabilidad siempre incrementa cuando componentes redundantes son agregados al sistema, un sistema que directamente soporta especies redundantes como garante del funcionamiento del ecosistema. Yo argumento que deberíamos abarcar la redundancia de especies y percibir redundancia como una característica crítica del ecosistema que debe ser conservada si los ecosistemas funcionaran confiablemente y nos provean de bienes y servicios. Demostraciones empíricas de el valor de la redundancia de especies en confiabilidad de ecosistemas provee nuevas intuiciones dentro de la ecología de comunidades y el valor de la conservación de las especies.
Functional diversity is a component of biodiversity that generally concerns the range of things that organisms do in communities and ecosystems. Here, we review how functional diversity can explain and predict the impact of organisms on ecosystems and thereby provide a mechanistic link between the two. Critical points in developing predictive measures of functional diversity are the choice of functional traits with which organisms are distinguished, how the diversity of that trait information is summarized into a measure of functional diversity, and that the measures of functional diversity are validated through quantitative analyses and experimental tests. There is a vast amount of trait information available for plant species and a substantial amount for animals. Choosing which traits to include in a particular measure of functional diversity will depend on the specific aims of a particular study. Quantitative methods for choosing traits and for assigning weighting to traits are being developed, but need much more work before we can be confident about trait choice. The number of ways of measuring functional diversity is growing rapidly. We divide them into four main groups. The first, the number of functional groups or types, has significant problems and researchers are more frequently using measures that do not require species to be grouped. Of these, some measure diversity by summarizing distances between species in trait space, some by estimating the size of the dendrogram required to describe the difference, and some include information about species' abundances. We show some new and important differences between these, as well as what they indicate about the responses of assemblages to loss of individuals. There is good experimental and analytical evidence that functional diversity can provide a link between organisms and ecosystems but greater validation of measures is required. We suggest that non-significant results have a range of alternate explanations that do not necessarily contradict positive effects of functional diversity. Finally, we suggest areas for development of techniques used to measure functional diversity, highlight some exciting questions that are being addressed using ideas about functional diversity, and suggest some directions for novel research.
The relationship between plant diversity and productivity has largely been attributed to niche complementarity, assuming that plant species are complementary in their resource use. In this context, we conducted an 15N field study in three different grasslands, testing complementarity nitrogen (N) uptake patterns in terms of space, time, and chemical form as well as N strategies such as soil N use, symbiotic N fixation, or internal N recycling for different plant species. The relative contribution of different spatial, temporal, and chemical soil N pools to total soil N uptake of plants varied significantly among the investigated plant species, within and across functional groups. This suggests that plants occupy distinct niches with respect to their relative N uptake. However, when the absolute N uptake from the different soil N pools was analyzed, no spatial, temporal, or chemical variability was detected, but plants, and in particular functional groups, differed significantly with respect to their total soil N uptake irrespective of treatment. Consequently, our data suggest that absolute N exploitation on the ecosystem level is determined by species or functional group identity and thus by community composition rather than by complementary biodiversity effects. Across functional groups, total N uptake from the soil was negatively correlated with leaf N concentrations, suggesting that these functional groups follow different N use strategies to meet their N demands. While our findings give no evidence for a biodiversity effect on the quantitative exploitation of different soil N pools, there is evidence for different and complementary N strategies and thus a potentially beneficial effect of functional group diversity on ecosystem functioning.
Recent experiments on grassland ecosystems have shown that biodiversity can enhance ecosystem processes such as plant biomass production. Functional complementarity is generally regarded as the main class of mechanisms generating these effects of biodiversity on ecosystem functioning. Although intuitively appealing and supported by some data, the complementarity hypothesis has been little explored theoretically using mechanistic approaches. Here, we present a simple dynamical model for a light-limited terrestrial ecosystem to assess the effects of species diversity on light competition and total biomass in plant communities. Our model shows that competitive relaxation (reduction in average light competition intensity) due to differences in foliar architecture among species enhances total plant biomass in mixtures, but that competitive imbalance (generated by the variance of the average light competition intensity experienced by different species) can either reinforce the effect of competitive relaxation or counteract it and contribute to reducing total plant biomass. Thus, complementary resource use is not enough to increase total plant biomass in species-rich communities; competitive balance among species also plays an important role. We propose an operational measure of light-use complementarity using empirical field data on light absorption to test the presence of complementarity in natural plant communities.
A language and environment for statistical computing ISBN: 3-900051-07-0: URL: http://www.R-project.org Diversity, metabolic types and dC-13 carbon isotope ratios in the grass flora of Namibia in relation to growth form, precipitation and habitat conditions
- R Development
- Team Schulze
- E D Ellis
- R Schulze
- W Trimborn
R Development Core Team, 2007. A language and environment for statistical computing. ISBN: 3-900051-07-0: URL: http://www.R-project.org. Schulze, E.D., Ellis, R., Schulze, W., Trimborn, P., 1996. Diversity, metabolic types and dC-13 carbon isotope ratios in the grass flora of Namibia in relation to growth form, precipitation and habitat conditions. Oecologia 106, 352–369.
A language and environment for statistical computing
- R Development
- Core Team
R Development Core Team, 2007. A language and environment for statistical
computing. ISBN: 3-900051-07-0: URL: http://www.R-project.org.
The ecological role of biodiversity in agroecosystems
- Altieri
Resource heterogeneity moderates the biodiversity–function relationship in real world ecosystems
- Tylianakis