%0 Journal Article
%T Predator coexistence through emergent fitness equalization
%A Ellen van Velzen
%J Ecology - Wiley Online Library
%D 2019
%R https://doi.org/10.1002/ecy.2995
%X 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. The competitive exclusion principle is one of the oldest ideas in community ecology and states that two predators cannot coexist on a single prey (Gause 1934, Hardin 1960). Each predator suppresses prey density to the level where it is just barely able to persist (the R* principle, Tilman 1982), which prevents coexistence: whichever predator has the lower value for R* can suppress the prey to a density where its competitor can no longer persist, thereby driving it extinct. As a consequence, coexistence of two predators limited solely by the same prey would require them to have exactly the same R* value, which would require a coincidence of such magnitude that it is generally held to be impossible. This mathematically rock©\solid result stands in stark contrast with the rich diversity of many natural communities, and reconciling this contradiction has inspired a long search for mechanisms that may enable coexistence (Chesson 2000). This has uncovered a wide range of possibilities, falling into several broad categories. First, there are mechanisms directly causing a disadvantage to the more common competitor, such as self©\limitation (Levin 1970) or frequency©\dependent predation by
%U https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecy.2995