Ecology Letters, (2004) 7: 1058–1067 doi: 10.1111/j.1461-0248.2004.00668.x REPORT Aggregated seed dispersal by spider monkeys limits recruitment to clumped patterns in Virola calophylla
Abstract Sabrina E. Russo1* and The initial spatial pattern of seed deposition influences plant population and community Carol K. Augspurger2 structure, particularly when that pattern persists through recruitment. In a vertebrate- 1Department of Animal Biology, dispersed rain forest tree, Virola calophylla, we found that spatially aggregated seed University of Illinois, 505 S. deposition strongly influenced the spatial structure of later stages. Seed dispersion was Goodwin Ave., Urbana, IL clumped, and seed densities were highest underneath V. calophylla females and the 61801, USA sleeping sites of spider monkeys (Ateles paniscus), the key dispersal agent. Although these 2Department of Plant Biology, site types had the lowest per capita seed-to-seedling survival, they had the highest University of Illinois, 505 S. seedling/sapling densities. Conversely, seed and seedling/sapling densities were lowest, Goodwin Ave., Urbana, IL 61801, USA and seed survival was highest, at sites of diurnal seed dispersal by spider monkeys. *Correspondence and present Negative density-dependent and positive distance-dependent seed survival thinned seed address: Center for Tropical clumps. Nonetheless, the clumped dispersion at sleeping and parental sites persisted to Forest Science – Arnold Arbor- the seedling/sapling stage because differences in seed deposition were large enough to etum Asia Program, Harvard offset differences in seed survival among these site types. University, 22 Divinity Avenue, Cambridge, MA 02138, USA. Keywords E-mail: [email protected] Ateles paniscus, dispersion, Myristicaceae, neotropical forest, Peru, recruitment, seed dispersal, seed survival, seedlings, Virola calophylla.
Ecology Letters (2004) 7: 1058–1067
the variation in seed density generated by dispersal agents, INTRODUCTION particularly in forest communities. An increasing number of Seed dispersal results in colonization of potential recruit- studies has revealed patterns of seed deposition in forests ment sites and establishes the initial template of offspring either by using seed traps and inverse modelling or by dispersion. It therefore can strongly influence the spatial developing mechanistic models of the behaviour of dispersal distribution of adult plants in a landscape (Howe & agents to simulate seed dispersion (Nathan & Muller- Smallwood 1982; Schupp & Fuentes 1995). The spatial Landau 2000). These studies suggest that seed deposition is distribution of individuals, in turn, mediates intra- and often spatially aggregated, particularly for vertebrate- interspecific interactions, such as density-dependent mor- dispersed tree species (Schupp et al. 2002). tality and competition, and the balance of these interactions Second, the spatial pattern of seed deposition and the affects species coexistence (Chesson 2000). Thus, under- recruitment consequences of that pattern affect the density standing the role of seed dispersal in the development of and dispersion of plants in later life stages (Hubbell 1980; spatial pattern in plant populations is critical to explanations McCanny 1985). One mechanism that has figured prom- of plant community structure (Levin 1974; Hurtt & Pacala inently in explaining tree dispersion, particularly in tropical 1995; Chesson 2000). forests (Hubbell 1980; Augspurger 1983a; Clark & Clark The development of spatial pattern in plant populations 1984; Condit et al. 1992), is survival that depends upon results from a set of processes governing the pattern of seed the density of seeds, seedlings, and/or saplings or their deposition and a set of post-dispersal processes that modify distance from a conspecific adult (Janzen 1970; Connell that pattern during recruitment (Schupp & Fuentes 1995; 1971). Such non-random survival resulting from natural Schupp 1995). First, the spatial extent of seed dispersal enemies, such as seed predators and seedling pathogens, restricts the suite of potential sites for recruitment (Howe & can thin clumps of seeds and seedlings and produce Smallwood 1982). However, there are few descriptions of spatial patterns that differ from what would result simply seed dispersion at spatial scales large enough to encompass from random thinning of the initial seed deposition