Abstract: Seed dispersal is a critical step in the life of plants, but plants that rely on animals to disperse their seeds face dire consequences as large-bodied animals decline worldwide. Can we predict which plant species will be hardest hit? One approach is to assess the connections individual plant species have with their seed-dispersing mutualists. A greater number of mutualists is thought to confer resilience to the loss of certain dispersers, whereas species with few mutualists may be more vulnerable to coextinction. Another, more difficult, way to predict the consequences of mutualism loss is to quantify the individual benefits that seed dispersal provides, and use these numbers to estimate the plant’s ability to regenerate with few or no dispersers. The Mariana Islands provide a unique natural experiment to assess how tree species vary in the consequences of seed disperser decline and loss because three islands in the system have an intact, degraded, or extirpated seed disperser assemblage. My ongoing work shows that, as expected, plant species with many seed dispersers in the intact system also maintain high dispersal services in the degraded system. However, preliminary work shows that plants that have many dispersers and frequent dispersal also rely much more heavily on dispersal for survival. Instead of being resilient, these species appear to have the most negative consequences of complete disperser loss. Combining data on the seed dispersal network with data on demographic consequences of the mutualism, this perspective questions the assumed relationship between mutualist number and resilience, and may improve predictions about the impacts of seed disperser loss.
UW Biology Graduate Student Symposium 