@article{SoliveresMaestreUlrichetal.2015, author = {Soliveres, Santiago and Maestre, Fernando T. and Ulrich, Werner and Manning, Peter and Boch, Steffen and Bowker, Matthew A. and Prati, Daniel and Delgado-Baquerizo, Manuel and Quero, Jose L. and Sch{\"o}ning, Ingo and Gallardo, Antonio and Weisser, Wolfgang W. and M{\"u}ller, J{\"o}rg and Socher, Stephanie A. and Garcia-Gomez, Miguel and Ochoa, Victoria and Schulze, Ernst-Detlef and Fischer, Markus and Allan, Eric}, title = {Intransitive competition is widespread in plant communities and maintains their species richness}, series = {Ecology letters}, volume = {18}, journal = {Ecology letters}, number = {8}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {1461-023X}, doi = {10.1111/ele.12456}, pages = {790 -- 798}, year = {2015}, abstract = {Intransitive competition networks, those in which there is no single best competitor, may ensure species coexistence. However, their frequency and importance in maintaining diversity in real-world ecosystems remain unclear. We used two large data sets from drylands and agricultural grasslands to assess: (1) the generality of intransitive competition, (2) intransitivity-richness relationships and (3) effects of two major drivers of biodiversity loss (aridity and land-use intensification) on intransitivity and species richness. Intransitive competition occurred in >65\% of sites and was associated with higher species richness. Intransitivity increased with aridity, partly buffering its negative effects on diversity, but was decreased by intensive land use, enhancing its negative effects on diversity. These contrasting responses likely arise because intransitivity is promoted by temporal heterogeneity, which is enhanced by aridity but may decline with land-use intensity. We show that intransitivity is widespread in nature and increases diversity, but it can be lost with environmental homogenisation.}, language = {en} } @article{VenailGrossOakleyetal.2015, author = {Venail, Patrick and Gross, Kevin and Oakley, Todd H. and Narwani, Anita and Allan, Eric and Flombaum, Pedro and Isbell, Forest and Joshi, Jasmin Radha and Reich, Peter B. and Tilman, David and van Ruijven, Jasper and Cardinale, Bradley J.}, title = {Species richness, but not phylogenetic diversity, influences community biomass production and temporal stability in a re-examination of 16 grassland biodiversity studies}, series = {Functional ecology : an official journal of the British Ecological Society}, volume = {29}, journal = {Functional ecology : an official journal of the British Ecological Society}, number = {5}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0269-8463}, doi = {10.1111/1365-2435.12432}, pages = {615 -- 626}, year = {2015}, abstract = {Hundreds of experiments have now manipulated species richness (SR) of various groups of organisms and examined how this aspect of biological diversity influences ecosystem functioning. Ecologists have recently expanded this field to look at whether phylogenetic diversity (PD) among species, often quantified as the sum of branch lengths on a molecular phylogeny leading to all species in a community, also predicts ecological function. Some have hypothesized that phylogenetic divergence should be a superior predictor of ecological function than SR because evolutionary relatedness represents the degree of ecological and functional differentiation among species. But studies to date have provided mixed support for this hypothesis. Here, we reanalyse data from 16 experiments that have manipulated plant SR in grassland ecosystems and examined the impact on above-ground biomass production over multiple time points. Using a new molecular phylogeny of the plant species used in these experiments, we quantified how the PD of plants impacts average community biomass production as well as the stability of community biomass production through time. Using four complementary analyses, we show that, after statistically controlling for variation in SR, PD (the sum of branches in a molecular phylogenetic tree connecting all species in a community) is neither related to mean community biomass nor to the temporal stability of biomass. These results run counter to past claims. However, after controlling for SR, PD was positively related to variation in community biomass over time due to an increase in the variances of individual species, but this relationship was not strong enough to influence community stability. In contrast to the non-significant relationships between PD, biomass and stability, our analyses show that SR per se tends to increase the mean biomass production of plant communities, after controlling for PD. The relationship between SR and temporal variation in community biomass was either positive, non-significant or negative depending on which analysis was used. However, the increases in community biomass with SR, independently of PD, always led to increased stability. These results suggest that PD is no better as a predictor of ecosystem functioning than SR.Synthesis. Our study on grasslands offers a cautionary tale when trying to relate PD to ecosystem functioning suggesting that there may be ecologically important trait and functional variation among species that is not explained by phylogenetic relatedness. Our results fail to support the hypothesis that the conservation of evolutionarily distinct species would be more effective than the conservation of SR as a way to maintain productive and stable communities under changing environmental conditions.}, language = {en} } @article{WackerMarzetzSpijkerman2015, author = {Wacker, Alexander and Marzetz, Vanessa and Spijkerman, Elly}, title = {Interspecific competition in phytoplankton drives the availability of essential mineral and biochemical nutrients}, series = {Ecology : a publication of the Ecological Society of America}, volume = {96}, journal = {Ecology : a publication of the Ecological Society of America}, number = {9}, publisher = {Wiley}, address = {Washington}, issn = {0012-9658}, doi = {10.1890/14-1915.1}, pages = {2467 -- 2477}, year = {2015}, abstract = {The underlying mechanisms and consequences of competition and diversity are central themes in ecology. A higher diversity of primary producers often results in higher resource use efficiency in aquatic and terrestrial ecosystems. This may result in more food for consumers on one hand, while, on the other hand, it can also result in a decreased food quality for consumers; higher biomass combined with the same availability of the limiting compound directly reduces the dietary proportion of the limiting compound. Here we tested whether and how interspecific competition in phytoplankton communities leads to changes in resource use efficiency and cellular concentrations of nutrients and fatty acids. The measured particulate carbon : phosphorus ratios (C:P) and fatty acid concentrations in the communities were compared to the theoretically expected ratios and concentrations of measurements on simultaneously running monocultures. With interspecific competition, phytoplankton communities had higher concentrations of the monounsaturated fatty acid oleic acid and also much higher concentrations of the ecologically and physiologically relevant long-chain polyunsaturated fatty acid eicosapentaenoic acid than expected concentrations based on monocultures. Such higher availability of essential fatty acids may contribute to the positive relationship between phytoplankton diversity and zooplankton growth, and may compensate limitations by mineral nutrients in higher trophic levels.}, language = {en} } @article{WeithoffRochaGaedke2015, author = {Weithoff, Guntram and Rocha, Marcia R. and Gaedke, Ursula}, title = {Comparing seasonal dynamics of functional and taxonomic diversity reveals the driving forces underlying phytoplankton community structure}, series = {Freshwater biology}, volume = {60}, journal = {Freshwater biology}, number = {4}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0046-5070}, doi = {10.1111/fwb.12527}, pages = {758 -- 767}, year = {2015}, abstract = {In most biodiversity studies, taxonomic diversity is the measure for the multiplicity of species and is often considered to represent functional diversity. However, trends in taxonomic diversity and functional diversity may differ, for example, when many functionally similar but taxonomically different species co-occur in a community. The differences between these diversity measures are of particular interest in diversity research for understanding diversity patterns and their underlying mechanisms. We analysed a temporally highly resolved 20-year time series of lake phytoplankton to determine whether taxonomic diversity and functional diversity exhibit similar or contrasting seasonal patterns. We also calculated the functional mean of the community in n-dimensional trait space for each sampling day to gain further insights into the seasonal dynamics of the functional properties of the community. We found an overall weak positive relationship between taxonomic diversity and functional diversity with a distinct seasonal pattern. The two diversity measures showed synchronous behaviour from early spring to mid-summer and a more complex and diverging relationship from autumn to late winter. The functional mean of the community exhibited a recurrent annual pattern with the most prominent changes before and after the clear-water phase. From late autumn to winter, the functional mean of the community and functional diversity were relatively constant while taxonomic diversity declined, suggesting competitive exclusion during this period. A further decline in taxonomic diversity concomitant with increasing functional diversity in late winter to early spring is seen as a result of niche diversification together with competitive exclusion. Under these conditions, several different sets of traits are suitable to thrive, but within one set of functional traits only one, or very few, morphotypes can persist. Taxonomic diversity alone is a weak descriptor of trait diversity in phytoplankton. However, the combined analysis of taxonomic diversity and functional diversity, along with the functional mean of the community, allows for deeper insights into temporal patterns of community assembly and niche diversification.}, language = {en} }