Size‐Related Differential Seed Predation in a Heavily Defaunated Neotropical Rain Forest

Abstract

Hunting and habitat loss represent an increasingly common anthropogenic impact. Available evidence suggests that defaunation is typically differential: medium/large mammals are most affected while small rodents are less affected, or even favored. In heavily impacted areas, such as Los Tuxtlas, the residual mammalian fauna is dominated by small rodents. We tested the expectation that if small rodents will preferentially attack small‐seeded species, large‐seeded species may escape predation in the absence of medium/large seed predators and that this may affect germination and, possibly, recruitment. Experiments with caged rodents (Heteromys desmarestianus) under laboratory conditions showed a preference for smaller seeds. A field experiment involving seeds of contrasting size showed that small, unprotected seeds experienced a predation risk 30‐times larger than protected seeds, while the effect of protection was not significant for large seeds. These patterns of predation led to significant differences in germination: protected small‐seeded species had a fourfold greater germination than unprotected small‐seeded species, while germination was not significantly different between exposed and protected large seeds. The observed contrasts in germination suggest that under heavy defaunation, small‐seeded species are likely to be penalized by the overabundance of small rodents, while large‐seeded species escape predation. Our results are consistent with the observation of dense seedling carpets dominated by large‐seeded species in the understory of Los Tuxtlas. We speculate that the patterns we uncovered may explain, at least partly, the impoverished diversity of the understory vegetation that characterizes heavily defaunated understories and that this has the potential to affect forest regeneration.

Bushmeat hunting changes regeneration of African rainforests

“…Similar to several other studies [5,13,26], we found that the large rodent seed predators were more common in the hunted sites, despite the fact that these are also hunted. We have no data on the smaller, mostly nocturnal, rodents, which might quantitatively be even more important seed predators [29].…”

“…Recent studies from the Neotropics have demonstrated compositional changes in the forest understory associated with the decline in populations of large dispersers [5,13,[28][29][30][31]. At present, such evidence is rare in African forests (but see [20,32,33]).…”

Slow recovery of a secondary tropical forest in Southeast Asia

“…2). Large seeded species without animal dispersal agents necessarily re-colonize slowly (Corlett, 1998;Dirzo et al, 2007;Kitamura et al, 2002;Wunderle, 1997), and smaller seeded species that are dispersed by mammal or birds (e.g., S. elongatus, Calophyllum spp., B. sumatrana) may not establish deep into the secondary forest if their animal dispersers avoid secondary forest (Wunderle, 1997).…”

Experimental defaunation of terrestrial mammalian herbivores alters tropical rainforest understorey diversity

“…For example, it is known that the loss of medium and large body-sized vertebrates reduces seed dispersal distances, especially of large-seeded plants [9,10]. Moreover, extirpation of vertebrate seed predators and herbivores favours escape of large seeds and their seedlings from vertebrate attack [9,[11][12][13]. In addition, defaunation affects the role of animal trampling as a source of seedling damage and mortality [14,15].…”