Consequences of frugivore-mediated seed dispersal for the spatial and genetic structures of a neotropical palm

Abstract

The idiosyncratic behaviours of seed dispersers are important contributors to plant spatial associations and genetic structures. In this study, we used a combination of field, molecular and spatial studies to examine the connections between seed dispersal and the spatial and genetic structures of a dominant neotropical palm Attalea phalerata. Field observation and genetic parentage analysis both indicated that the majority of A. phalerata seeds were dispersed locally over short distances (<30 m from the maternal tree). Spatial and genetic structures between adults and seedlings were consistent with localized and short-distance seed dispersal. Dispersal contributed to spatial associations among maternal sibling seedlings and strong spatial and genetic structures in both seedlings dispersed near (<10 m) and away (>10 m) from maternal palms. Seedlings were also spatially aggregated with juveniles. These patterns are probably associated with the dispersal of seeds by rodents and the survival of recruits at specific microsites or neighbourhoods over successive fruiting periods. Our cross-cohort analyses found palms in older cohorts and cohort pairs were associated with a lower proportion of offspring and sibling neighbours and exhibited weaker spatial and genetic structures. Such patterns are consistent with increased distance- and density-dependent mortality over time among palms dispersed near maternal palms or siblings. The integrative approaches used for this study allowed us to infer the importance of seed dispersal activities in maintaining the aggregated distribution and significant genetic structures among A. phalerata palms. We further conclude that distance- and density-dependent mortality is a key postdispersal process regulating this palm population.