Seed-size variation determines interspecific differential predation by mammals in a neotropical rain forest

Abstract

It has been suggested that the anthropogenically driven loss of herbivorous mammals might lead to changes in the recruitment patterns of tropical rain forest plants, but few studies have examined the explicit mechanisms that might account for this effect. Here we propose a conceptual model linking differential mammalian defaunation and differential plant recruitment. We posit that in the absence of medium/large herbivores but with small rodent granivores still present (i.e. differential defaunation), predation pressure will be greater on small-seeded species than on large-seeded species. We tested such differential predation hypothesis (DPH) by means of a series of experiments directed to assess: 1) seed consumption by small rodents in laboratory cages; 2) seed-removal rates in small rodent enclosures in the field and 3) removal of seeds placed on the forest floor and exposed to either the full complement of mammals or only small rodents. Seeds used in the experiments were arranged in pairs consisting of species from the same taxonomic family but with a contrasting size (large, small). We found: 1) a significantly greater consumption of smaller seeds (a 2.3-to 20.5-fold difference) in cages and 2) a significantly greater removal of small-seeded species (a 3.7-to 65-fold difference) in field enclosures. Results of seed removal experiments in free-access plots and selective exclosures were more complex, with a general absence of significant differences among treatments but we found that predation was in general concentrated on smallseeded species and small rodents were the predominant visitors to the plots. This, together with the overall short distance of dispersal among large seeds suggest that in differentially defaunated forests large-seeded species are more likely to escape predation. We posit that such size related differential predation may lead to the floristic impoverishment observed in some defaunated forests.

The numerical and functional responses of a granivorous rodent and the fate of Neotropical tree seeds

“…Our findings and other studies clearly indicate H. desmarestianus does not consume Attalea cohune nuts (Mendoza and Dirzo 2007), but they do prey regularly on nuts of Astrocaryum mexicanum Martinez-Gallardo 1998, Brewer andRejma´nek 1999). In contrast, they showed a more complex pattern with production of Astrocaryum mexicanum fruits.…”

“…Fruit size has been shown to be a critical factor influencing removal rates of fruits (Forget et al 1998, Mendoza andDirzo 2007), but it may be less important a factor for caching. Removal rates and the total proportion of fruits removed by H. desmarestianus in the BNR were generally proportional to fruit size, but caching rates were not.…”

Seed Predation by Rodents and Implications for Plant Recruitment in Defaunated Atlantic Forests

“…), knowledge of which rodents prey upon seeds and what seed traits are selected is needed. However, most of the studies on seed predation are not able to identify the seed predators (Mendoza & Dirzo , Boissier et al . , Galetti et al .…”

An Experimental Test of Competition among Mice, Chipmunks, and Squirrels in Deciduous Forest Fragments

“…in the American Southwest determines whether plant communities are dominated by grasses or shrubs, with critical consequences for primary production, the water cycle, and animal community dynamics [6]–[8]. Rodents in tropical and temperate forests can control tree recruitment patterns by their actions as seed predators or seed dispersers [9]–[11]. Voles ( Microtus spp.)…”