Why is dispersal important?
Seed dispersal is a poorly understood phenomenon of great conservation importance, since it is both affected by global change and affects the ability of plants to respond to global change. Dispersal, along with pollination, is one of the most threatened processes of a plant’s life cycle (Neuschulz et al. 2016). Defaunation, fragmentation, climate change, and invasive species alter dispersal processes (McConkey et al. 2012, Travis et al. 2013). More than one-quarter of vertebrate seed dispersers are threatened with extinction (Aslan et al. 2013). The loss of frugivores due to overhunting, forest fragmentation, and logging has reduced the number of seeds removed and dispersal distances for many plant species (Markl et al. 2012). In addition, climate change is predicted to affect dispersal ability by altering wind dynamics, plant height, phenology, water dynamics, and frugivore populations (Parolin 2006, Travis et al. 2013, Mokany et al. 2014). These changes in dispersal due to global change may affect whether populations can persist or spread to unoccupied areas (Neubert and Caswell 2000). For example, bushmeat poaching in Thailand has reduced densities of mammalian seed dispersers of the canopy tree Choerospondias axillaris, and as a result population demographic modeling predicts long-term population decline for the tree (Brodie et al. 2009). By contrast, dispersal has increased for many other species due to the vast global transportation network, leading to plant invasions (Banks et al. 2015). A plant's ability to shift ranges in response to climate change is dependent in part upon its ability to reach suitable habitats via dispersal (McConkey et al. 2012, Travis et al. 2013). Changes in dispersal can also affect diversity and ecosystem function. For example, loss of large frugivores could reduce carbon sequestration in the Amazon through changes in community composition (Bello et al. 2015). Finally, dispersal influences evolution, since movement of individuals affects genetic diversity and the adaptation capacity of species (Kremer et al. 2012), and dispersal-related traits are subject to selection (Eriksson 2016). For example, Crepis sancta rapidly evolved heavier fruits lacking a pappus, with reduced dispersal ability, in response to fragmentation (Cheptou et al. 2008); and Euterpe edulis evolved smaller seeds in areas lacking large frugivores (Galetti et al 2013).