The effect of space in plant-animal mutualistic networks:: insights from a simulation study

The topology of plant-animal mutualistic networks has the potential to determine the ecological and evolutionary dynamics of interacting species. Many mechanisms have been proposed as explanations of observed network patterns; however, the fact that plant-animal interactions are inherently spatial has so far been ignored. Using a simulation model of frugivorous birds foraging in spatially explicit landscapes we evaluated how plant distribution and the scale of bird movement decisions influenced species interaction probabilities and the resulting network properties. Spatial aggregation and limited animal mobility restricted encounter probabilities, so that the distribution of animal visits per plant deviated strongly from the binomial distribution expected for a well-mixed system. Lack of mixing in turn resulted in a strong decrease in network connectance, a weak decrease in nestedness, stronger interactions, greater strength asymmetry and the unexpected presence/absence of some interactions. Our results suggest that spatial processes may contribute substantially to structure plant-animal mutualistic networks.