Abrupt community transitions and cyclic evolutionary dynamics in complex food webs

Abstract

Understanding the emergence and maintenance of biodiversity ranks among the most fundamental challenges in evolutionary ecology. While processes of community assembly have frequently been analyzed from an ecological perspective, their evolutionary dimensions have so far received less attention. To elucidate the eco-evolutionary processes underlying the long-term build-up and potential collapse of community diversity, here we develop and examine an individual-based model describing coevolutionary dynamics driven by trophic interactions and interference competition, of a pair of quantitative traits determining predator and prey niches. Our results demonstrate the (1) emergence of communities with multiple trophic levels, shown here for the first time for stochastic models with linear functional responses, and (2) intermittent and cyclic evolutionary transitions between two alternative community states. In particular, our results indicate that the interplay of ecological and evolutionary dynamics often results in extinction cascades that remove the entire trophic level of consumers from a community. Finally, we show the (3) robustness of our results under variations of model assumptions, underscoring that processes of consumer collapse and subsequent rebound could be important elements of understanding biodiversity dynamics in natural communities.

A new dimension: Evolutionary food web dynamics in two dimensional trait space

“…In large communities these patterns combine to produce evolutionary 636 outbursts, that is the recurring emergence of higher trophic levels for a limited 637 25 period. These are similar to the cycling between high and low trophic com-638 munity states, discovered by [65,66]. The build-up of these higher trophic…”

The role of biotic forces in driving macroevolution: beyond the Red Queen

“…For instance, they show that in the absence of extrinsic forcing, biotic interactions can create coevolutionary trait dynamics in which the number of species fluctuates widely in a periodic or chaotic fashion [36]. Biotically driven mass extinctions or extinction cascades are also demonstrated in these models [36,39,43]. Takahashi et al's [39] model features food webs that alternate between two community states: they repeatedly build up and evolve towards a quasi-stable state that is very vulnerable to perturbation, where demographic stochasticity triggers an extinction cascade, starting the cycle again.…”

“…Biotically driven mass extinctions or extinction cascades are also demonstrated in these models [36,39,43]. Takahashi et al's [39] model features food webs that alternate between two community states: they repeatedly build up and evolve towards a quasi-stable state that is very vulnerable to perturbation, where demographic stochasticity triggers an extinction cascade, starting the cycle again. In Allhoff et al's [43] model, periods of increasing specialization in the food web are interrupted by extinction cascades; the trigger for the cascades is the arrival of a new mutant form that escapes specialist predation, and therefore can increase to great numbers and displace other species.…”

“…Other models produce food webs with a very stable structure [44], and there are ongoing efforts to identify the factors (e.g. functional responses and trophic interactions) that stabilize and destabilize evolving food webs (see discussions in [39,43]). …”

“…The 'expansion and crash' hypothesis is loosely based on ideas from ecosystem theory [48] and food-web models (e.g. [39]). …”