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Differential effects of mammalian seed predators on the regeneration of five Papua New Guinean tree species and implications for sapling recruitment

Abstract: Although herbivores may account for a significant source of seed and seedling mortality in many tropical tree species, plant species differ in their response to seed damage. Here we investigate the relative effects of seed predation on the regeneration of five tree species in a mid-elevation Papua New Guinean rain forest. Exclosure treatments and shade-house experiments were monitored from November 2004 to March 2006 to assess the differential effects of seed predation on seed viability and seedling growth. Results indicate that although seed predators attack all five focal species, they influence the seedling populations in two, Cerbera floribunda and Microcos grandiflora, and minimally affect the seedling populations of Terminalia impediens, Pandanus penicillus and Endiandra latifolia in the years measured. Predation and germination frequencies were compared to the abundance of focal species at several life stage classes to explore potential correlations between species-specific seed mortality patterns and life stage distributions. We found that the species-specific influence of mammalian seed predators correlated with abundance distributions in three life stages. Species with high survivorship after seed predator attacks displayed a significant decrease in abundance from the seedling-to-sapling transition, while those species with high seed mortality demonstrated relatively even distributions of seedlings, saplings and adults (> 10 cm dbh). These contrasting patterns suggest that differential seed predation effects on regeneration may play a key role in the recruitment of individuals to the sapling stage.