Frugivore foraging decisions influence seed dispersal patterns

Binod Borah, Biology, Utah State University, Logan, UT and Noelle G. Beckman, Department of Biology and Ecology Center, Utah State University, Logan, UT

Background/Question/Methods
As they navigate their environment, frugivores make foraging decisions that influence seed dispersal processes. Frugivores make decisions that can reduce costs of travel, increase their resource gain, and minimize the number of unprofitable attempts. We hypothesize that decisions based on sensory cues and memory would differ from decisions that are random, with consequences for seed dispersal distances and dispersion patterns of depositions sites. Compared to a random forager, we predict that frugivores select nearby and more productive resource patches and avoid revisiting resource patches. Consequently, they disperse seeds that are nearer to removal locations and more clumped than random dispersion patterns. To test these predictions, we use relocation data of two frugivorous primates: Gray-cheeked Mangabey and White-handed Gibbon. First, we use a multinomial patch movement model to test whether frugivores select nearby or productive resources and avoid previously used resources. Second, we use an integrated step selection function to test if frugivores move towards their resources directedly using sensory cues and memory. Finally, we combine these model outputs to simulate foraging events and compare resulting seed dispersal distances and dispersion patterns of deposition sites to patterns that arise from a random forager.
Results/Conclusions
Our results show that decisions made by frugivores based on sensory cues and memory result in dispersal distances and dispersion of seed deposition sites that differ from those of a random forager. Both primate species selected resource patches that were nearer and more productive than those chosen by a random forager. They also avoided patches that were recently visited and moved directedly towards their resources. These foraging and navigation decisions generated shorter seed dispersal distances and more clumped seed deposition sites compared to patterns generated by a random forager. Because spatial patterns of seeds resulting from seed dispersal processes influence seed survival, germination, and later demographic processes, our results indicate that the decisions frugivores make while foraging and navigating their environment have consequences for plant demography.