Space: The Final Frontier of Predator Evolution?

Abstract

Interactions between individual organisms are often structured in space. Population spatial structure has important ecological consequences. Theoretical evidence suggests that the evolutionary effects can be equally significant, especially for exploitative species. With only a few exceptions, this theory focuses on pathogens. I review the existing literature to show that evolutionary spatial effects are strongest when host and pathogen dispersal are local and when host reproduction is relatively low. Under these conditions, the pathogen is subject to a competition-persistence tradeoff (increased competitive ability comes at the cost of decreased persistence) that favors the evolution of intermediate pathogen transmission rates.

Although existing literature clearly demonstrates that spatial structure impacts pathogen evolution, lacking is a comprehensive understanding of the role of host and pathogen ecology. Through comprehensive simulations of spatial host-pathogen models I show that the predicted pathogen transmission rate differs from the non-spatial prediction depending on the host reproduction rate, infected host death rate, and the shape or existence of a transmission-virulence tradeoff. In conjunction, I show that the effects of spatial structure cannot be fully understood through a commonly used quantitative method.

The effect of spatial structure on pathogens is postulated to extend to true predators. However, true predators are characterized by ecology that is unique relative to pathogens. Through additional simulations of spatial predator-prey models I show the influence of three unique aspects of ecology on true predator evolution: the prey conversion efficiency (the ratio of predators produced per prey consumed), the magnitude of predator death relative to the prey death rate, and the rate of predator movement. Despite their unique ecology, however, there are consistent trends in the influence of common aspects of ecology.

Based on how spatial structure influences true predator evolution, spatial structure may also influence the evolution of entire food webs. Using simple population dynamic models I show that randomly constructed three and five species food webs are predicted to be evolutionarily unstable in both spatial and non-spatial contexts. However, I suggest spatial structure is still likely to play an important evolutionary role and should be considered more carefully in studies of evolutionary food web assembly.