Modeling spatial information transfer across trophic levels

Background/Question/Methods

Differences in spatial and temporal scale are intrinsic to many cross-species interactions. While intra-species population processes tend to take place at a single scale, cross-species interactions link each species’ response to the environment, and propagate environmental information across scales. We explore how scale disparities affect the ability of prey and predators to track resource patterns in a spatially heterogeneous environment.

To address this question, we describe a novel variation on the lattice model. Our model consists of two interacting lattices with different grain sizes, and an underlying layer of spatially explicit environmental variation. A prey species inhabits the fine-grained lattice, while a predator species inhabits the coarse-grained lattice. For a given grain disparity, cells of the fine-scale lattice nest exactly into coarse-scale lattice cells.

 

The dynamics of both populations are characterized by stochastic and density-dependent demographic processes. Prey deaths and predator births are linked to the size of each population at the coarse-grained level with a Holling type 1 response, but predators are blind to the fine-grained heterogeneity of prey distributions. Changing the ratio between the two lattices allows us to study scale transition explicitly.

Results/Conclusions

Our results show how scale disparity in a predator-prey interaction affects the distributions of both species. In particular, we demonstrate the effect of scale disparity on the coexistence of both species in a predator-prey system. We also show how increasing the scale disparity influences the ability of predator populations to track the distributions of resources needed by the prey. Our results also reveal the effect of scale disparity on the existence of prey refuges, due to the predators’ insensitivity to fine-scale structure. Taken together, these results have implications for our understanding of how spatial factors and population dynamics differently contribute to the formation of species distribution patterns.