Population regulation of a dominant rain forest tree by a major seed predator
We take advantage of a fortuitous local extinction and recolonization of white-lipped peccaries (WLPs) at the Cocha Cashu Biological Station in southeastern Peru to assess the impact of this high-biomass seed predator on the recruitment of a dominant member of the tree community, the palm Astrocaryum murumuru. WLPs were common at Cocha Cashu in the mid-1970s. In 1978, the species vanished from the entire region and did not reappear until 1990. To assess the impacts of the presence-absence of WLPs on Astrocaryum recruitment, we conducted transect counts of both the number and spatial distribution of palm seedlings in 1978 (when WLPs were present), in 1990 (after a 12-yr absence of WLPs), and in 1999 (after 10 yr of recovery). Other factors affecting recruitment, such as climate variability, differences in tree fecundity, and fluctuations of vertebrate and invertebrate seed predators were also examined as alternative hypotheses for any changes in seedling spatial distribution and abundance. In the absence of WLPs, the density of Astrocaryum seedlings increased 1.7-fold, and the spatial distribution of seedlings with respect to safe sites was significantly altered. After the return of WLPs to the study area, seedling density dropped to its former level, and the spatial distribution of seedlings with respect to safe sites returned to the same pattern found 21 yr earlier in 1978. None of the other factors investigated varied systematically with the census intervals. These results demonstrate that the absence of a single, albeit important, member of a diverse seed predator guild can have a major impact on the demography of a common tree species. We infer that individual seed predators can play central roles in regulating the demography of tropical trees, as envisioned many years ago by Janzen and Connell, and that their extirpation or extinction can have cascading effects in tropical ecosystems.
Silman, MR; Terborgh, JW; Kiltie, RA
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