Search

It is well known that ecological and evolutionary processes act in concert while shaping biological communities. Diversification can, for example, arise through ecological opportunity and adaptive radiations and competition play an essential role in such diversification. Eco-evolutionary components of competition are thus important for our understanding of community assembly. Such understanding in turn facilitates interpretation of trait- and phylogenetic community patterns in the light of the processes that shape them. Here, I investigate the link between competition, diversification, and trait- and phylogenetic- community patterns using a trait-based model of adaptive radiations. I evaluate the paradigm that competition is an ecological process that drives large trait- and phylogenetic community distances through limiting similarity. Contrary to the common view, I identify low or in some cases counterintuitive relationships between competition and mean phylogenetic distances due to diversification late in evolutionary time and peripheral parts of niche space when competition is weak. Community patterns as a function of competition also change as diversification progresses as the relationship between competition and trait similarity among species can flip from positive to negative with time. The results thus provide novel perspectives on community assembly and emphasize the importance of acknowledging eco-evolutionary processes when interpreting community data., (© 2021. The Author(s).)

A general goal in community ecology and evolutionary biology is to understand how diversity has arisen. In our attempts to reach such goals we become increasingly aware of interacting ecological and evolutionary processes shaping biodiversity. Ecological opportunity and adaptive radiations can, for example, drive diversification in competitive communities but little is known about how such processes propagate through trophic levels in adaptive radiation cascades. I use an eco-evolutionary model of trait-based ecological interactions and micro-evolutionary processes to investigate the macro-evolutionary aspects of predator diversification in such cascades. Prey diversification facilitates predator radiation through predator feeding opportunity and disruptive selection. Predator radiation, however, often disconnects from the prey radiation as the diversification progresses. Only when predators have an intermediate niche width, high predatory efficiency, and high evolutionary potential can radiation cascades be maintained over macro-evolutionary time scales. These results provide expectations for predator response to prey divergence and insight into eco-evolutionary feedbacks between trophic levels. Such expectations are crucial for future studies that aim for a better understanding of how diversity is generated and maintained in complex communities.

Losses and gains in species diversity affect ecological stability 1-7 and the sustainability of ecosystem functions and services 8-13 . Experiments and models have revealed positive, negative and no effects of diversity on individual components of stability, such as temporal variability, resistance and resilience 2,3,6,11,12,14 . How these stability components covary remains poorly understood 15 . Similarly, the effects of diversity on overall ecosystem stability 16 , which is conceptually akin to ecosystem multifunctionality 17,18 , remain unknown. Here we studied communities of aquatic ciliates to understand how temporal variability, resistance and overall ecosystem stability responded to diversity (that is, species richness) in a large experiment involving 690 micro-ecosystems sampled 19 times over 40 days, resulting in 12,939 samplings. Species richness increased temporal stability but decreased resistance to warming. Thus, two stability components covaried negatively along the diversity gradient. Previous biodiversity manipulation studies rarely reported such negative covariation despite general predictions of the negative effects of diversity on individual stability components 3 . Integrating our findings with the ecosystem multifunctionality concept revealed hump- and U-shaped effects of diversity on overall ecosystem stability. That is, biodiversity can increase overall ecosystem stability when biodiversity is low, and decrease it when biodiversity is high, or the opposite with a U-shaped relationship. The effects of diversity on ecosystem multifunctionality would also be hump- or U-shaped if diversity had positive effects on some functions and negative effects on others. Linking the ecosystem multifunctionality concept and ecosystem stability can transform the perceived effects of diversity on ecological stability and may help to translate this science into policy-relevant information.