[Show abstract][Hide abstract] ABSTRACT: Fraser et al. (Reports, 17 July 2015, p. 302) report a unimodal relationship between productivity and species richness at regional and global scales, which they contrast with the results of Adler et al. (Reports, 23 September 2011, p. 1750). However, both data sets, when analyzed correctly, show clearly and consistently that productivity is a poor predictor of local species richness.
[Show abstract][Hide abstract] ABSTRACT: How ecosystem productivity and species richness are interrelated is one of the most debated subjects in the history of ecology. Decades of intensive study have yet to discern the actual mechanisms behind observed global patterns. Here, by integrating the predictions from multiple theories into a single model and using data from 1,126 grassland plots spanning five continents, we detect the clear signals of numerous underlying mechanisms linking productivity and richness. We find that an integrative model has substantially higher explanatory power than traditional bivariate analyses. In addition, the specific results unveil several surprising findings that conflict with classical models. These include the isolation of a strong and consistent enhancement of productivity by richness, an effect in striking contrast with superficial data patterns. Also revealed is a consistent importance of competition across the full range of productivity values, in direct conflict with some (but not all) proposed models. The promotion of local richness by macroecological gradients in climatic favourability, generally seen as a competing hypothesis, is also found to be important in our analysis. The results demonstrate that an integrative modelling approach leads to a major advance in our ability to discern the underlying processes operating in ecological systems.
[Show abstract][Hide abstract] ABSTRACT: Despite the progress made in explaining trophic interactions through the stoichiometric interplay between consumers and resources, it remains unclear how the number of species in a trophic group influences the effects of elemental imbalances in food webs. Therefore, we conducted a laboratory experiment to test the hypothesis that multispecies producer assemblages alter the nutrient dynamics in a pelagic community. Four algal species were reared in mono- and polycultures under a 2 × 2 factorial combination of light and nutrient supply, thereby contrasting the stoichiometry of trophic interactions involving single vs. multiple producer species. After 9 d, these cultures were fed to the calanoid copepod Acartia tonsa, and we monitored biomass, resource use, and C:N:P stoichiometry in both phyto- and zooplankton. According to our expectations, light and N supply resulted in gradients of phytoplankton biomass and nutrient composition (C:N:P). Significant net diversity effects for algal biomass and C:N:P ratios reflected the greater responsiveness of the phytoplankton polyculture to altered resource supply compared to monocultures. These alterations of elemental ratios were common, and were partly triggered by changes in species frequency in the mixtures and partly by diversity-related changes in resource use. Copepod individual biomass increased under high light (HL) and N-reduced (-N) conditions, when food was high in C:N but low in C:P and N:P, whereas copepod growth was obviously P limited, and copepod stoichiometry was not affected by phytoplankton elemental composition. Correspondingly, copepod individual biomass reflected significant net diversity effects: compared to expectations derived from monocultures, copepod individuals feeding on algal polycultures remained smaller than predicted under HL and N-sufficient (+N) conditions but grew larger than predicted under HL, -N and low light +N conditions. In conclusion, multiple producer species altered the stoichiometry of trophic interactions between phyto- and zooplankton, with divergent effects under high and low resource supply.
[Show abstract][Hide abstract] ABSTRACT: There is growing interest in the integration of macroecology and palaeoecology towards a better understanding of past, present, and anticipated future biodiversity dynamics. However, the empirical basis for this integration has thus far been limited. Here we review prospects for a macroecology-palaeoecology integration in biodiversity analyses with a focus on marine microfossils [i.e. small (or small parts of) organisms with high fossilization potential, such as foraminifera, ostracodes, diatoms, radiolaria, coccolithophores, dinoflagellates, and ichthyoliths]. Marine microfossils represent a useful model system for such integrative research because of their high abundance, large spatiotemporal coverage, and good taxonomic and temporal resolution. The microfossil record allows for quantitative cross-scale research designs, which help in answering fundamental questions about marine biodiversity, including the causes behind similarities in patterns of latitudinal and longitudinal variation across taxa, the degree of constancy of observed gradients over time, and the relative importance of hypothesized drivers that may explain past or present biodiversity patterns. The inclusion of a deep-time perspective based on high-resolution microfossil records may be an important step for the further maturation of macroecology. An improved integration of macroecology and palaeoecology would aid in our understanding of the balance of ecological and evolutionary mechanisms that have shaped the biosphere we inhabit today and affect how it may change in the future.
[Show abstract][Hide abstract] ABSTRACT: Exotic species dominate many communities; however the functional significance of species’ biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands.
[Show abstract][Hide abstract] ABSTRACT: Predator diversity and abundance are under strong human pressure in all types of ecosystems. Whereas predator potentially control standing biomass and species interactions in food webs, their effects on prey biomass and especially prey biodiversity have not yet been systematically quantified. Here, we test the effects of predation in a cross-system meta-analysis of prey diversity and biomass responses to local manipulation of predator presence. We found 291 predator removal experiments from 87 studies assessing both diversity and biomass responses. Across ecosystem types, predator presence significantly decreased both biomass and diversity of prey across ecosystems. Predation effects were highly similar between ecosystem types, whereas previous studies had shown that herbivory or decomposition effects differed fundamentally between terrestrial and aquatic systems based on different stoichiometry of plant material. Such stoichiometric differences between systems are unlikely for carnivorous predators, where effect sizes on species richness strongly correlated to effect sizes on biomass. However, the negative predation effect on prey biomass was ameliorated significantly with increasing prey richness and increasing species richness of the manipulated predator assemblage. Moreover, with increasing richness of the predator assemblage present, the overall negative effects of predation on prey richness switched to positive effects. Our meta-analysis revealed strong general relationships between predator diversity, prey diversity and the interaction strength between trophic levels in terms of biomass. This study indicates that anthropogenic changes in predator abundance and diversity will potentially have strong effects on trophic interactions across ecosystems.This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Plant elemental composition can indicate resource limitation, and changes in key elemental ratios (e.g. plant C:N ratios) can influence rates including herbivory, nutrient recycling, and pathogen infection. Although plant stoichiometry can influence ecosystem-level processes, very few studies have addressed whether and how plant C:N stoichiometry changes with plant diversity and composition. Here, using two long-term experimental manipulations of plant diversity (Jena and Cedar Creek), we test whether plant richness (species and functional groups) or composition (functional group proportions) affects temporal trends and variability of community-wide C:N stoichiometry.Site fertility determined the initial community-scale C:N ratio. Communities growing on N-poor soil (Cedar Creek) began with higher C:N ratios than communities growing on N-rich soil (Jena). However, site-level plant C:N ratios converged through time, most rapidly in high diversity plots. In Jena, plant community C:N ratios increased. This temporal trend was stronger with increasing richness. However, temporal variability of C:N decreased as plant richness increased. In contrast, C:N decreased over time at Cedar Creek, most strongly at high species and functional richness, whereas the temporal variability of C:N increased with both measures of diversity at this site.Thus, temporal trends in the mean and variability of C:N were underlain by concordant changes among sites in functional group proportions. In particular, the convergence of community-scale C:N over time at these very different sites was mainly due to increasing proportions of forbs at both sites, replacing high mean C:N (C4 grasses, Cedar Creek) or low C:N (legumes, Jena) species. Diversity amplified this convergence; although temporal trends differed in sign between the sites, these trends increased in magnitude with increasing species richness. Our results suggest a predictive mechanistic link between trends in plant diversity and functional group composition and trends in the many ecosystem rates that depend on aboveground community C:N.This article is protected by copyright. All rights reserved.
[Show abstract][Hide abstract] ABSTRACT: Humans dominate many important Earth system processes including the nitrogen (N) cycle. Atmospheric N deposition affects fundamental processes such as carbon cycling, climate regulation, and biodiversity, and could result in changes to fundamental Earth system processes such as primary production. Both modelling and experimentation have suggested a role for anthropogenically altered N deposition in increasing productivity, nevertheless, current understanding of the relative strength of N deposition with respect to other controls on production such as edaphic conditions and climate is limited. Here we use an international multiscale data set to show that atmospheric N deposition is positively correlated to aboveground net primary production (ANPP) observed at the 1-m2 level across a wide range of herbaceous ecosystems. N deposition was a better predictor than climatic drivers and local soil conditions, explaining 16% of observed variation in ANPP globally with an increase of 1 kg N·ha−1·yr−1 increasing ANP...
[Show abstract][Hide abstract] ABSTRACT: About 60 years ago, the critical depth hypothesis was proposed to describe the occurrence of spring phytoplankton blooms and
emphasized the role of stratification for the timing of onset. Since then, several alternative hypotheses appeared focusing
on the role of grazing and mixing processes such as turbulent convection or wind activity. Surprisingly, the role of community
composition—and thus the distribution of phytoplankton traits—for bloom formation has not been addressed. Here, we discuss
how trait variability between competing species might influence phytoplankton growth during the onset of the spring bloom.
We hypothesize that the bloom will only occur if there are species with a combination of traits fitting to the environmental
conditions at the respective location and time. The basic traits for formation of the typical spring bloom are high growth
rates and photoadaptation to low light conditions, but other traits such as nutrient kinetics and grazing resistance might
also be important. We present concise ideas on how to test our theoretical considerations experimentally. Furthermore, we
suggest that future models of phytoplankton blooms should include both water column dynamics and variability of phytoplankton
traits to make realistic projections instead of treating the phytoplankton bloom as an aggregate community phenomenon.
[Show abstract][Hide abstract] ABSTRACT: Biodiversity-ecosystem functioning (BEF) research has been a major topic in ecology for over 2 decades, and recent meta-analyses have confirmed biodiversity to be a driver of ecosystem processes and services. To date, the vast majority of BEF studies have been conducted experimentally, and it is unclear whether their outcomes can be transferred to natural communities and ecosystems. The major challenge faced in the analysis of observational data is to incorporate direct and indirect processes which influence the response variable of interest. Consequently, the statistical methods used to analyze such relationships must accommodate the multivariate nature of these data. One multivariate approach, viz. structural equation modeling, has already been applied to BEF research in terrestrial and freshwater ecosystems. In this study, we applied a structural equation model to monitoring data on marine phytoplankton communities, including data on environmental parameters, community structure, and measures of productivity. Our aim was to ascertain whether similar patterns and processes driving BEF relationships as described for other ecosystem types are evident in marine phytoplankton communities. We found that different aspects of biodiversity (richness, evenness) are significantly linked to ecosystem functions (productivity, resource use efficiency). These relationships are embedded in a multitude of direct and indirect links between environmental factors, community diversity, and productivity. Overall, our analysis confirms patterns observed in terrestrial and freshwater ecosystems and highlights the importance of incorporating multivariate methods for a better understanding of BEF processes in natural ecosystems.
Full-text · Article · Mar 2015 · Marine Ecology Progress Series
[Show abstract][Hide abstract] ABSTRACT: Biodiversity−ecosystem functioning (BEF) research has been a major topic in ecology for over 2 decades, and recent meta-analyses have confirmed biodiversity to be a driver of eco- system processes and services. To date, the vast majority of BEF studies have been conducted experimentally, and it is unclear whether their outcomes can be transferred to natural communi- ties and ecosystems. The major challenge faced in the analysis of observational data is to incorpo- rate direct and indirect processes which influence the response variable of interest. Consequently, the statistical methods used to analyze such relationships must accommodate the multivariate nature of these data. One multivariate approach, viz. structural equation modeling, has already been applied to BEF research in terrestrial and freshwater ecosystems. In this study, we applied a structural equation model to monitoring data on marine phytoplankton communities, including data on environmental parameters, community structure, and measures of productivity. Our aim was to ascertain whether similar patterns and processes driving BEF relationships as described for other ecosystem types are evident in marine phytoplankton communities. We found that differ- ent aspects of biodiversity (richness, evenness) are significantly linked to ecosystem functions (productivity, resource use efficiency). These relationships are embedded in a multitude of direct and indirect links between environmental factors, community diversity, and productivity. Overall, our analysis confirms patterns observed in terrestrial and freshwater ecosystems and highlights the importance of incorporating multivariate methods for a better understanding of BEF processes in natural ecosystems.
Full-text · Article · Mar 2015 · Marine Ecology Progress Series
[Show abstract][Hide abstract] ABSTRACT: Body size is related to an extensive number of species traits and ecological processes and has therefore been suggested as an effective metric to assess community changes and ecosystem’s state. However, the applicability of body size as an ecological indicator in benthic environments has been hindered by the poor knowledge of the factors influencing the size spectra of organisms. By applying biological trait analysis (BTA) and generalized linear models to a species dataset collected in the German Wadden Sea (53°41′14′′ N, 7°14′19′′ E) between 1999 and 2012, we show that the size structure of the macrobenthic community changes predictably along environmental gradients. Specifically, body size increases with increasing current-induced shear stress and sediment organic matter content. In addition, the presence of oyster–mussel reefs in one of the sampling stations enhanced the survival of species belonging to the smallest size categories in habitats with high hydrodynamic energy. This was probably due to the local sheltering effects, which together with biodeposition also increased organic matter in the sediment, likely favoring large deposit feeders as well. Our results suggest that body size can be a useful trait for estimating effects of anthropogenic stressors, such as organic enrichment or alteration of hydrodynamic regime and could therefore be effectively included in current monitoring programs of intertidal macrobenthic communities.
[Show abstract][Hide abstract] ABSTRACT: In time of scarcity of fossil energies, microalgae are attracting interest as a potential source of renewable energy due to their high growth rates and potential high lipid contents. Additionally, cultivation may be an abatement measure to remove surplus nutrients from eutrophicated ecosystems. At present, microalgal cultivations for biomass production are run mainly in monocultures, which are easily contaminated with competing microalgae or grazers. Furthermore, hetero-trophic bacteria are highly abundant and may strongly reduce the yield in the target microalgae through competition for nutrients. In three laboratory experiments, we tested whether heterotrophic flagellates (Oxyrrhis marina and Cafeteria roenbergensis) can make nutrients bound in bacteria available for marine diatoms (Coscinodiscus granii and Odontella sinensis) and can shift the competition for inorganic nutrients towards the microalgae. Cultures were run with and without flagellates, under different conditions: without an external carbon source, in presence of organic matter (barley grains) or biogas wastewater. The presence of flagellates had a posi-tive effect on microalgal growth, but this was context and species specific. The presence of the flagellates affected the maximum algal growth rates (r) especially in Coscinodiscus granii. A maximal biomass increase (29.93±2.98 %) (mean ± standard deviation, n=3) was observed for Coscinodiscus granii in F/2 + Si medium. Furthermore, although the flagellates were attributed to the detrital fraction, their presence resulted in a significant reduc-tion of detritus. In conclusion, heterotrophic flagellates have the potential to increase nutrient use efficiency especially in algae bioreactors with slow-growing large phytoplankton taxa. This effect may be particularly relevant in organic polluted water.
Full-text · Article · Feb 2015 · Journal of Applied Phycology
[Show abstract][Hide abstract] ABSTRACT: Aquatic and terrestrial ecosystems are tightly linked through the fluxes of organisms and matter. However, aquatic and terrestrial
ecologists have mainly studied these ecosystems separately, a “splendid isolation” historically fostered by disciplinary boundaries
between institutes and funding schemes. Here, we synthesize the progress made in joint aquatic and terrestrial research and
suggest new approaches to meeting future research challenges in changing environments. Aquatic and terrestrial organisms use
cross-system subsidies to a comparable extent and addressing reciprocal subsidies is therefore necessary in order to understand
biodiversity and functioning of both aquatic and terrestrial ecosystems. We suggest that the metaecosystem framework could
be expanded to explicitly consider cross-system fluxes of matter differing in magnitude and quality. We further advocate the
inclusion of cross-system analyses at broader spatial extents, for which remote-sensing applications would be a useful tool
in environmental research at the land–water interface. A cross-ecosystem approach would therefore be valuable for a more thorough
understanding of ecosystem responses to various stressors in the face of rapid environmental change.
[Show abstract][Hide abstract] ABSTRACT: Ejectisomes are extrusive organelles found in cryptophytes with a potential role in grazer
avoidance/deterrence. In order to test whether ejectisome concentrations in the cells vary with nutrient
supply, two Cryptomonas and a Chroomonas species were subjected to nutrient starvation (i.e.,
depletion of N, P, or S), and compared to nutrient-replete controls. Since changes in pigmentation
were observed after two weeks, cells were harvested by centrifugation after three weeks, lysed, and
analysed further after adjustment to equal protein concentrations. For all three strains, absorption
spectroscopy revealed significant reductions of proteins functioning in photosynthesis (i.e., biliproteins
and chlorophyll bearing polypeptides) under N-starvation. Depletion of P and S caused significant
losses of these proteins for the strain Cryptomonas S2, too. Sodium dodecyl sulfate polyacrylamide
gel electrophoresis followed by Western immunoblotting using an antiserum directed against
reconstituted, ejectisome-like filaments revealed significant reductions in the amounts of ejectisins
for N-starved cells in all three species and for P- and S-depleted cells of the Chroomonas species.
The reduction in ejectisins was not significant for the two Cryptomonas strains when P- or S-starved.
The maintenance of at least a certain amount of ejectisomes obviously obtains a similar priority as
the maintenance of a minimal photosynthetic apparatus.
[Show abstract][Hide abstract] ABSTRACT: Humans are modifying the availability of nutrients such as nitrogen (N) and phosphorus (P), and it is therefore important to understand how these nutrients, independently or in combination, influence the growth and nutrient content of primary producers. Using meta-analysis of 118 field and laboratory experiments in freshwater, marine and terrestrial ecosystems, we tested hypotheses about co-limitation of N and P by comparing the effects of adding N alone, P alone, and both N and P together on internal N (e.g. %N, C:N) and P (e.g. %P, C:P) concentrations in autotroph communities. In particular, we tested the following predictions. First, if only one nutrient was limiting, addition of that nutrient should decrease the concentration of the other nutrient, but addition of the non-limiting nutrient would have no effect on the internal concentration of the limiting nutrient. If community co-limitation was occurring then addition of either nutrient should result in a decrease in the internal concentration of the other nutrient. Community co-limitation could also result in no change – or even an increase – in N concentrations in response to P addition if P stimulated growth of N fixers. Finally, if biochemically dependent co-limitation was occurring, addition of a limiting nutrient would not decrease, and could even increase, the concentration of the other, co-limited nutrient. We found no general evidence for the decrease in the internal concentration of one nutrient due to addition of another nutrient. The one exception to this overall pattern was marine systems, where N addition decreased internal P concentrations. In contrast, P addition increased internal N concentrations across all experiments, consistent with co-limitation. These results have important implications for understanding the roles that N and P play in controlling producer growth and internal nutrient accumulation as well as for managing the effects of nutrient enrichment in ecosystems.
[Show abstract][Hide abstract] ABSTRACT: Loss of plant diversity influences essential ecosystem processes as aboveground productivity, and can have cascading effects on the arthropod communities in adjacent trophic levels. However, few studies have examined how those changes in arthropod communities can have additional impacts on ecosystem processes caused by them (e.g. pollination, bioturbation, predation, decomposition, herbivory). Therefore, including arthropod effects in predictions of the impact of plant diversity loss on such ecosystem processes is an important but little studied piece of information. In a grassland biodiversity experiment, we addressed this gap by assessing aboveground decomposer and herbivore communities and linking their abundance and diversity to rates of decomposition and herbivory. Path analyses showed that increasing plant diversity led to higher abundance and diversity of decomposing arthropods through higher plant biomass. Higher species richness of decomposers, in turn, enhanced decomposition. Similarly, species-rich plant communities hosted a higher abundance and diversity of herbivores through elevated plant biomass and C:N ratio, leading to higher herbivory rates. Integrating trophic interactions into the study of biodiversity effects is required to understand the multiple pathways by which biodiversity affects ecosystem functioning.
[Show abstract][Hide abstract] ABSTRACT: Background/Question/Methods
Can diversity simultaneously affect a wide variety of different ecosystem functions? Despite first studies analyzing effects of diversity on multiple ecosystem functions having revealed stronger diversity effects than studies looking at single functions this questions remains little studied. As an often used approach, the number of species contributing to functioning has been shown to increases with the number of studies, years, or functions considered. Yet, conclusions based on the number of contributing species have been criticized and recent methodological advances have proposed alternatives.
Here we used multivariate statistics to investigate the relationship between plant diversity and multifunctionality. We based our analysis on more than 100 functions measured along an experimental gradient of grassland plant diversity ranging from 1 to 60 species. The set of ecosystem functions included various above- and below-ground processes, e.g. cover, LAI, plant biomass, soil nutrients, and abundance data of plant-associated invertebrates such as earthworms, pollinators and herbivores. Using principle component analysis based on the value of each function in each plot we investigated (1) correlations and trade-offs between functions, (2) the functional fingerprint and (3) the overall level of expressed functioning of each plot and (4) the relationships of all these parameters to plant species richness.
Relationships between the investigated functions spanned the whole spectrum from strong positive correlation (association) to almost perfect negative correlation (trade-off). Intermediate between these extremes, a large number of functions were independent from each other, thus showed correlations around zero. Consequently, a large number of axes (23) was needed to explain at least 75% of the variation observed in the multifunctional space. Plant diversity correlated strongly with the first principle component axis (r=0.67, p<<0.001) while axes of higher order did not show any relationships with plant diversity. This indicates that especially the functions associated with the first principal component axis change along the plant diversity gradient. To calculate an index of multifunctionality, we extendend the “averaging approach” from single functions to a multivariate measure by summing scores for the first 30 principle component axes. The resulting multifunctionality index increased highly significantly with plant diversity from predominantly negative values at low diversity to positive values at high diversity (F1,76=8.26; p=0.005). Thus, plots of high diversity supported more functions at above average levels than low diversity plots. Results from our multivariate approach are compared to other proposed approaches to measure multifunctionality.