Predator coexistence through emergent fitness equalization

Abstract

The competitive exclusion principle is one of the oldest ideas in ecology and states that without additional self-limitation two predators cannot coexist on a single prey. The search for mechanisms allowing coexistence despite this has identified niche differentiation between predators as crucial: without this, coexistence requires the predators to have exactly the same R* values, which is considered impossible. However, this reasoning misses a critical point: predators' R* values are not static properties, but affected by defensive traits of their prey, which in turn can adapt in response to changes in predator densities. Here I show that this feedback between defense and predator dynamics enables stable predator coexistence without ecological niche differentiation. Instead, the mechanism driving coexistence is that prey adaptation causes defense to converge to the value where both predators have equal R* values ("fitness equalization"). This result is highly general, independent of specific model details, and applies to both rapid defense evolution and inducible defenses. It demonstrates the importance of considering long-standing ecological questions from an eco-evolutionary viewpoint, and showcases how the effects of adaptation can cascade through communities, driving diversity on higher trophic levels. These insights offer an important new perspective on coexistence theory.

Rapid evolution promotes fluctuation-dependent species coexistence

“…With increasing evidence for rapid contemporary evolution on ecological timescales (Hendry 2016), an interest in developing a broader theory of species coexistence that incorporates rapid evolution and eco-evolutionary feedbacks has grown (Tachikawa 2008; Kremer & Klausmeier 2013; Wittmann & Fukami 2018; Hart et al 2019; van Velzen 2020; Yamamichi et al 2020). By allowing for rapid evolution in mechanistic resource competition models, we have identified a new solution to the paradox of the plankton, deriving from relative nonlinearity of competition.…”

“…A wealth of empirical evidence has accumulated over the last few decades indicating that rapid contemporary evolution on ecological timescales (Hendry 2016) can be essential for understanding population dynamics (Yoshida et al 2003; Bell 2017). More recently, evidence has begun to emerge that rapid evolution can also be a significant driver of community dynamics amongst competing species, and in particular play an important role in regulating species coexistence (Lankau 2011; Vasseur et al 2011; Mougi 2013; Hiltunen et al 2017; Wittmann & Fukami 2018; Hart et al 2019; Germain et al 2020; van Velzen 2020; Yamamichi et al 2020). To date, however, rapid evolution has only been shown to promote species coexistence when there is either a trade-off between traits optimal for intraspecific and interspecific competition (Lankau 2011; Vasseur et al 2011; Mougi 2013; Wittmann & Fukami 2018; Yamamichi et al 2020) or fine-tuning of prey defenses and predator foraging efforts (Kondoh 2003; van Velzen 2020).…”

“…With increasing evidence for rapid contemporary evolution on ecological timescales 1 , there has been an interest in developing a broader theory of species coexistence that incorporates rapid evolution [8][9][10]12 . By allowing for rapid evolution in mechanistic resource competition models, we have identified a new mechanism by which relative nonlinearity of competition promotes coexistence.…”

Rapid evolution promotes fluctuation‐dependent species coexistence

“…2011; Mougi 2013; Wittmann & Fukami 2018; Yamamichi et al . 2020) or fine‐tuning of prey defences and predator foraging efforts (Kondoh 2003; van Velzen 2020). Here we provide a previously unrecognised pathway for rapid evolution to promote coexistence via temporal fluctuations: differences in the rate of adaptation to fluctuating environments.…”

Reproducing the virus‐to‐copepod link in Arctic mesocosms using host fitness optimization

“…Recent theoretical work has demonstrated how coexistence on a single resource is possible, both between viruses and predators (Thingstad and Våge 2019) and between predators in general (van Velzen 2000), in models where host/prey traits are made adaptive. We have here included such a mechanism in an established food‐web model and shown how this can reproduce observed patterns in virus abundance and dynamics in two contrasting mesocosm experiments.…”