What are the difficulties in studying dispersal?
Although these examples and others demonstrate that seed dispersal can have an impact on biodiversity, our understanding of the role of seed dispersal in plant fitness and community composition remains incomplete. Dispersal processes can operate over local spatial and short temporal scales but establish patterns over regional to landscape scales and play out over a long temporal scale (tens to thousands of years depending on the lifespan of the plant). Plants are difficult to manipulate at the spatial, temporal, or organizational scales needed to assess the full influence of dispersal. Moreover, analysis of spatial models containing realistic assumptions about processes at multiple scales and in heterogeneous environments is a computational and mathematical challenge. Models predicting extinction risk of species are typically based on simplistic assumptions of dispersal, do not consider multiple human impacts that can disrupt dispersal, and are hampered by limited data. Because we do not yet understand the population- and community-level importance of seed dispersal relative to other interspecific interactions (e.g., pollination, herbivory, etc.) or to dynamics at other plant life stages, we are currently unable to predict where and when seed dispersal is likely to impact biodiversity. We need to better understand the fundamental link between seed dispersal and biodiversity in order to generalize among species and systems and make appropriate conservation/management responses related to seed dispersal.