American Society of Naturalists

Matthew A. Barbour (Jan 2021)

Mathematical model shows that ecological character displacement generally destabilizes food webs

Read the Article (Just Accepted)

Evolution makes competitive ecosystems more fragile

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Species evolve and adapt within an ecosystem where they interact with other species. But how does evolution affect this ecosystem of interactions? Does evolution make an ecosystem more or less sensitive to sudden changes in the environment?

A researcher from the University of Zurich sought to answer these questions using a mathematical model. He modeled a particular type of evolution called ecological character displacement. This type of evolution occurs when predators compete for prey and has created much of the biological diversity we see in the natural world.

In one model, he created a scenario where a predator could attack two distinct types of prey without a competitor. In a second model, he pitted two predators against each other in competition. After allowing the predators to evolve, he disturbed each model ecosystem to compare how sensitive they were to a sudden change in the environment, i.e., how long it took for the ecosystem to return to normal after being disturbed.

He found that the ecosystem with competition was more sensitive to a disturbance than the ecosystem without competition. This increased sensitivity was because competing predators evolved to have a bigger impact on their prey. This suggests that species in competitive ecosystems are more vulnerable to extinction if the environment were to change suddenly.

This curious finding suggests that the same evolutionary process that creates biological diversity also makes diversity more vulnerable to extinction. If this is true, many ecosystems may be more fragile than we realize.

Abstract

Ecological character displacement is an adaptive process that generally increases phenotypic diversity. Despite the fact that this diversification is due to an eco-evolutionary feedback between consumers competing for shared resources, its consequences for food-web dynamics have received little attention. Here, I study a model of two consumers competing for two shared resources to examine how character displacement in consumer attack rates affects resource abundances and the resilience of food webs to perturbations. I found that character displacement always strengthened consumer-resource interactions whenever consumers competed for resources that occurred in different habitats. This increase in interaction strength resulted in lower resource abundances and less resilient food webs. This occurred under different evolutionary tradeoffs and in both simple and more realistic foraging scenarios. Taken together, my results show that the adaptive process of character displacement may come with the ecological cost of decreasing food-web resilience.