Decomposing dispersal limitation: limits on fecundity or seed distribution?

Abstract

ummary 1. The term 'dispersal limitation' represents two distinct component processes: the number of seeds produced (fecundity) and the spatial pattern of the seed rain (distribution). We present a quantitative evaluation of these component processes of dispersal limitation for a tropical forest tree community. 2. Using a regularly spaced grid of 289 seed traps (0.5 m 2 each), we monitored the seed rain into 1.44 ha of upper Amazonian floodplain forest for 6 years whilst concurrently monitoring sapling recruitment in a 0.81-ha subplot centred within the seed-trapping grid. This arrangement allowed us to compare the spatial pattern of seed rain with that of sapling recruitment. 3. We endeavoured to distinguish between undispersed and dispersed seeds by applying a series of criteria to seeds collected in the traps and by removing from certain analyses all seeds that fell under reproductive conspecifics. Gross fecundity of 30 common species that contribute to the advanced regeneration was uniformly low and the rain of dispersed seeds was lower still, being <1.0 m )2 year )1 in every case. 4.The rain of dispersed seeds with respect to conspecific reproductives closely matched the recruitment of saplings, whereas gross seed rain (all seeds, including undispersed seeds) did not. 5. Synthesis. 'Dispersal limitation' in this faunally intact Amazonian forest is primarily attributable to a scant rain of dispersed seeds, i.e. fecundity limitation, whereas the distribution of dispersed seeds, being random for most species, appears adequate. Evidence from this and earlier research at the same site indicates that the per-capita success of dispersed seeds is many times higher than that of undispersed seeds. Thus, seed dispersal kernels that do not distinguish between dispersed and undispersed seeds are likely to be biologically misleading.

Bushmeat hunting changes regeneration of African rainforests

“…A possibility is that seed predation is different between hunted and protected sites. In the hunted sites, primate-dispersed seeds are likely aggregated below fruiting trees [27], where they can be more profitably exploited by seed predators, than if they were more evenly dispersed on the forest floor [55,56]. This could cause large seed predators to switch towards primate-dispersed seeds away from abiotically dispersed seeds [57,58], which are often smaller [32].…”

“…Quantitatively, restricted seed dispersal occurs when dispersers' activity is insufficient to disperse all seeds away from parents [53,54]. If the species with restricted dispersal are the dominant competitors, less competitive species might win in their absence; a situation described by Hurtt & Pacala [51] as winning by forfeit and recently tested by Terborgh et al [27].…”

“…Even in faunally intact forests, dispersal is often fecundity limited [27], and few seeds reach safe sites where they can germinate. In the hunted sites, this small fraction of seeds is nearly completely lost for primate-dispersed species.…”

Frugivory and Seed Dispersal Patterns of the Red-Ruffed Lemur, <b><i>Varecia rubra,</i></b> at a Forest Restoration Site in Masoala National Park, Madagascar

“…In a recruitment study in a Peruvian rainforest, most recruited saplings arose from dispersed seeds and not from undispersed seeds that fell under the crowns of the parent plants [Terborgh et al, 2011]. In this study, V. rubra deposited a majority of seeds ≥ 10 m from the parent tree and long-distance dispersal was rare.…”

Seedling recruitment factors in low‐diversity Hawaiian wet forest: towards global comparisons among tropical forests

“…Seedling abundance across the landscape (and its opposite, ''seedling limitation'') is determined by seed limitation and establishment limitation; in turn, seed limitation arises from source limitation and is determined by adult seed production and dispersal limitation (quantitative definitions in Fig. 1; Nathan and Muller-Landau 2000, Terborgh et al 2011. The relative importance of seed and establishment limitations highlights the fundamental ecology and the general mechanisms for species coexistence within given ecosystems.…”