Seed Dispersal

Abstract

Dispersal of seeds is one of the most critical aspects of reproductive ecology. In general, a majority of seeds fall below the parent plant. A proportion of them are dispersed away from the parent. Most of the plants depend on external agents for seed dispersal (Corlett 1998; Dennis et al. 2007; Cousens et al. 2008). Seed dispersal provides many advantages to plants: escape from specialist predators and pathogens prevalent under the parent, prevention of intraspecific competition, location of seeds in ecological safe sites where they can successfully germinate and establish seedlings (Janzen 1970; Connell 1971), colonization of new habitats and enhanced seed-mediated gene flow (Howe and Smallwood 1982; Peres et al. 1997; Fenner and Thompson 2005; Pinto et al. 2009). The locations of seed deposition by dispersers are generally random and unpredictable. However, some dispersers may deposit seeds predictably at sites favourable for seedling establishment. This has been referred to as directed dispersal (Wenny and Levey 1998; Wenny 2000). For example, in Ocotea endresiana, a shade-tolerant Neotropical montane tree in Costa Rica, four of the five species of birds involved in seed dispersal disperse seeds randomly, but the fifth species, a bellbird, predictably disperse seeds under song perches located in the canopy gaps (Wenny and Levey 1998). Seedling survival was higher from bellbird dispersed seeds than from those dispersed by the other species. Thus, seed dispersal enables plants to escape from the sources of mortality that are concentrated around the parent and increases the probability of colonizing suitable habitats.