11Seed Dispersal Ch 10

A seed shadow is the spatial distribution of all seeds dispersed from an individual plant (Janzen, 1970; Nathan and Muller-Landau, 2000; Schupp et al., 2002). The sum of seed shadows across all individuals in a population plus those seeds dispersed from other populations makes up seed rain. For vertebrate-dispersed species, seed shadows are the primary outcome of plant–frugivore interactions, yet we know very little about how different frugivore species contribute to them. For instance, a few frugivore species might contribute disproportionately to long-distance dispersal (LDD) events, while another subset of dispersers might contribute to the local, short-distance dispersal (see Dennis and Westcott, Chapter 9, this volume). In addition, seed delivery to specific microhabitats might be provided by only a few species out of the whole frugivore assemblage (Reid, 1989; Wenny and Levey, 1998; Jordano and Schupp, 2000; Jordano et al., 2007). For years, studies of seed dispersal have been severely limited in their potential to characterize seed shadows and to assess the contribution different species of frugivore make to their extent and reach in distance and space (i.e. the dispersal kernels; see Portnoy and Willson, 1993; Clark et al., 1999; Bullock and Clarke, 2000; Nathan, Chapter 11, this volume). The main difficulty has been to succeed in assigning a tree source for a dispersed seed and then link that information with both the species of frugivore that delivered the seed and the subsequent establishment success for the seedling. These are the three basic pieces of information that we need to account for seed shadows: source of seeds, dispersal vector, and establishment outcome. Variations in seed shadow pattern and extent between individual plants in a population can be large, and the summed seed shadows can generate very complex patterns of seed rain. Marked peaks and troughs in 2-D seed