Movement-based coexistence does not always require a functional trade-off

Abstract

The theory for movement-based coexistence between species largely focuses on metacommunities, and thereby ignores small-scale, station-keeping movements, such as when animals forage inside their home range. At this scale, there are numerous examples of positive correlations across species between traits that the current theory would expect to correlate negatively. The current theory indeed emphasizes functional tradeoffs, such as the colonization-competition or dominance-discovery tradeoff. Using simulations, I generated a counter-example to formally demonstrate that these functional tradeoffs are not a necessary condition for movement-based coexistence. First, I reformulated the tradeoffs in the context of animal movement ecology. In a spatial grid representing the potential home range of the study individuals, I modelled the patch depletion and renewal cycles, and the associated movement decisions, using spatial reaction norms incorporated into a spatially-explicit, two-consumer one-resource Lotka-Volterra model. I made these reaction norms species-specific, so that some species allocated more time to exploring for resource while others allocated more time to exploiting known resource. Under this time allocation tradeoff, I generated the desired example in which coexistence happened irrespective of the direction of the covariation between traits. More generally, under the time allocation tradeoff hypothesis, the species-specific space use patterns constituted true functional traits and captured an otherwise neglected aspect of the ecological niche.