21 Post - dispersal seed fate of some cloud forest tree species in Costa Rica

Research on post-dispersal seed fates has expanded rapidly in the past 20 years. The finding that rodents worldwide scatterhoard many types of seeds and that such scatterhoarding is a second stage of dispersal for some plants has led to the realization that one cannot assume that seed removal is equivalent to seed predation (Forget et al., 1998; Jansen, 2003). Several studies indicate that secondary dispersal can be an important phase of plant recruitment (Forget and Milleron, 1991; Vander Wall, 1992; Forget, 1993; Levey and Byrne, 1993; BohningGaese et al., 1999; Brewer and Rejmanek, 1999; Hoshizaki et al., 1999). Therefore, simply observing post-dispersal seed removal is insufficient evidence to assess the importance of primary dispersal patterns unless the fate of removed seeds is also assessed. A variety of organisms, ranging from rodents to beetles to microorganisms, interact with dispersed seeds but the roles they play are poorly known (Steele et al., 1996). Despite several well-documented examples of secondary dispersal (Vander Wall and Longland, 2004), the extent to which most vertebrate-dispersed plant species benefit from secondary dispersal is unknown. In a given habitat with dozens to hundreds of plant species, it is difficult to predict which species might benefit from secondary dispersal because we lack analyses of plant characteristics that may be associated with secondary dispersal syndromes. Perhaps the best example of a secondary dispersal syndrome is the presence of antattracting elaiosomes on seeds with ballistic primary dispersal (Passos and Ferreira, 1996; Gomez and Espadaler, 1998). For trees and other woody species, the occurrence of secondary dispersal syndromes is much less clear. Dung beetles act as secondary dispersers for seeds in mammalian dung but apparently not for seeds regurgitated or defecated by birds (Andresen and Feer, Chapter 20, this volume). As dung beetles are selecting dung rather than seeds, a syndrome for this type of secondary dispersal is unlikely. Rodents are important seed predators and dispersers worldwide, and defining a syndrome for rodent dispersal may be possible (Vander Wall and Longland, Chapter 18, this volume). Caviomorph rodents that act as both primary and secondary dispersers tend to scatterhoard large seeds (> 1 g) that have some physical defence such as a thick or hard seed coat. Smaller rodents eat a wide variety of smaller seeds but the extent of scatterhoarding in these species is poorly known (Price and Jenkins, 1986; Brewer and Rejmanek, 1999;