Consequences of animal foraging patterns for seed dispersal and tree demography

Background/Question/Methods

Seed dispersal by animals is critical for tree population dynamics, because seed dispersal enables seeds to escape high conspecific density near parent trees and reach favorable locations for establishment. However the consequences of different movement patterns for seed dispersal, and ultimately, tree population dynamics, remain largely unknown. We developed simulation models for animal seed dispersal and tree establishment by quantifying spatial patterns of seed deposition that emerge from mechanistic models of animal movement.  This approach enables us to apply theoretical knowledge on animal movement to ask, how do differences in foraging patterns affect seed dispersal? Because animal seed dispersers are threatened by overhunting in many tropical forests and different species of animal seed dispersers have different movement patterns, answering this question has direct conservation relevance. We contrasted the seed dispersal consequences of three movement models: Brownian motion, modified Levy Flight, and memory-based movement.  Brownian motion represents random movements, independent of fruiting tree location, while the Levy flight represents long-ranging mammals and the memory-based model represents animals that move directly between fruit trees. We simulated animal movement paths, paired movement distances with gut passage times to generate seed dispersal kernels, and explored consequences of movement for tree demography.

Results/Conclusions

Our three models yielded widely different foraging patterns with consequences for seed dispersal and tree demography. In the memory-based movement model animals spend most of their time near fruiting trees, leading to higher seed deposition beneath conspecific fruiting trees. The Levy Flight model resulted in a higher probability of long distance seed dispersal and fewer seeds deposited beneath conspecific trees.  The Brownian motion model resulted in significantly different seed dispersal patterns compared to either of the more mechanistic models.  Due to different patterns of seed deposition in relation to parent trees, animal movement patterns also had important effects on tree demography. Our results provide a framework for linking theories of animal movement to plant demography and suggest that long-ranging, opportunistic frugivores, including bears, small carnivores and elephants, are likely to play a critical role in demography of fruiting trees.