The evolutionary effects of spatial structure and its impact on predator-prey persistence

Background/Question/Methods

Spatial structure, or the non-random interaction between individual organisms, can significantly impact population dynamics, even changing the expected persistence of interacting species. Historically, theory addressing the effects of spatial structure on interacting species has excluded evolutionary dynamics. But the evolutionary impact of spatial structure on species persistence has the potential to be important, particularly for species participating in exploitative interactions. Without spatial structure, natural selection can drive the evolution of more voracious exploiters, increasing their risk of extinction through overexploitation of their resource.  A handful of theoretical studies in the literature address the evolutionary effects of spatial structure; however, these studies largely focus on pathogen-host interactions, with few to no studies addressing other important types of exploitative interactions. Here we test whether the evolutionary effects of spatial structure, and the consequences for persistence, generalize from pathogens to true predators when predator movement is taken into account. Building from existing spatial models of host-pathogen interactions, we simulate a simple predator-prey interaction under different assumptions of predator and prey movement, including density-independent movement, density-dependent movement, and different rates of movement. 

Results/Conclusions

We show that the effects of spatial structure can be generalized to true predators—in the presence of spatial structure, the predator evolves a less than maximal attack rate, leading to the coexistence of predator and prey. Not surprisingly, the degree to which spatial structure affects the predator’s evolutionary trajectory depends on the demographic details of the system. As with pathogen-host interactions, the predator attack rate increases with the prey reproduction rate and with the predator death rate. In general, the predator’s attack rate increases with an increasing rate of movement, whether density-dependent or independent, although when the prey reproduction rate is low, the predator evolves a lower attack rate regardless of the rate of movement. The implications of this study are that the evolutionary effects of spatial structure can lead to more stable predator-prey interactions. It is likely that the evolutionary effects of spatial structure can be further extended to plant-herbivore interactions. At a larger scale, these results suggest that spatial structure may enhance community stability.