No abstract

Poaching is rapidly extirpating African forest elephants (Loxodonta cyclotis) from most of their historical range, leaving vast areas of elephant-free tropical forest. Elephants are ecological engineers that create and maintain forest habitat; thus, their loss will have large consequences for the composition and structure of Afrotropical forests. Through a comprehensive literature review, we evaluated the roles of forest elephants in seed dispersal, nutrient recycling, and herbivory and physical damage to predict the cascading ecological effects of their population declines. Loss of seed dispersal by elephants will favor tree species dispersed abiotically and by smaller dispersal agents, and tree species composition will depend on the downstream effects of changes in elephant nutrient cycling and browsing. Loss of trampling and herbivory of seedlings and saplings will result in high tree density with release from browsing pressures. Diminished seed dispersal by elephants and high stem density are likely to reduce the recruitment of large trees and thus increase homogeneity of forest structure and decrease carbon stocks. The loss of ecological services by forest elephants likely means Central African forests will be more like Neotropical forests, from which megafauna were extirpated thousands of years ago. Without intervention, as much as 96% of Central African forests will have modified species composition and structure as elephants are compressed into remaining protected areas. Stopping elephant poaching is an urgent first step to mitigating these effects, but long-term conservation will require land-use planning that incorporates elephant habitat into forested landscapes that are being rapidly transformed by industrial agriculture and logging.

a b s t r a c tHuman hunting is widespread in tropical forests and can substantially alter the plant-animal interactions that drive tree recruitment. Seed predation is a strong determinant of plant reproductive success, but it remains unclear how defaunation modifies this process. We examined the effects of hunting-induced defaunation on seed predation and seedling establishment, using replicated exclosure treatments at six sites across a defaunation gradient in northeastern Gabon. We monitored 5580 seeds of eight commercially important tree species that varied in seed traits such as size and dispersal mode. Rodents caused the greatest seed mortality for all species, removing $60% of accessible seeds. In comparison, invertebrates and fungi together caused just 6% of seed mortality. With protection from rodents, more than twice as many seeds established as seedlings, demonstrating that vertebrate seed predation was a strong filter on recruitment. With increasing defaunation, the proportion of seeds removed by rodents increased significantly, and seedling establishment decreased significantly, for most species. In heavily defaunated sites, with the lowest abundances of large mammals, seed removal by rodents increased by 63% and seedling establishment decreased by 42% compared to sites with intact fauna. Diminished seedling establishment is likely to reduce the regeneration of many tree species -including some with commercial importance -in hunted forests, with detrimental economic consequences. In turn, declines in timber regeneration may increase the likelihood that selectively logged forests are converted to nonforest land uses with little conservation value. Appropriate management could preclude these outcomes, to the benefit of both wildlife and natural timber regeneration.

Large-bodied game species are in decline in tropical forests worldwide due to unsustainable extraction levels by hunters, which can result in cascading effects on vertebrate community structure. In this study, we examine the density responses of primate populations to different levels of hunting pressure in the Madre de Dios river basin, Peru. Across three surveyed sites, both small- and mid-sized primates exhibited population-level density compensation in response to the extirpation of sympatric large primates. Small primate density at one heavily hunted site was 5x that of a comparable nonhunted site, while the highest density of mid-sized primates was recorded at mid-level hunting pressure. Primate response to hunting pressure appears to be influenced by reproductive rate, with strong interspecific variability. High reproductive rate, infrequent extraction, and the relaxation of competitive interactions with extirpated large primates appear to facilitate increasing density of the smallest-bodied species. Evidence from elsewhere in the Madre de Dios basin suggests that large primates are particularly slow to recover from past hunting pressure, with continuing recovery even in sites that have not been hunted for several decades. These variable density responses to hunting pressure alter inter-specific and community dynamics, with potentially expansive short- and long-term ecosystem-level effects.

In seed predation studies, removal of a seed is only the first step of a dynamic process that may result in dispersal rather than seed death. This process, termed seed fate, has received little attention in African forests, particularly in Central Africa. We experimentally assessed the initial steps of seed fate for two tree species-the large-seeded Pentaclethra macrophylla and the relatively small-seeded Gambeya lacourtiana-in northeastern Gabon. Specifically, we evaluated whether seed size and seed consumer identity are important determinants of seed fate. We established experimental stations under conspecific fruiting trees, each comprising three seeds fitted with telemetric thread tags to facilitate their recovery, and a motion-sensitive camera to identify visiting mammals. In total, animals removed 76 tagged seeds from experimental stations. Small Murid rats and mice primarily removed small Gambeya seeds, whereas large-bodied rodents and mandrills primarily removed large Pentaclethra seeds. Gambeya seeds were carried shorter distances than Pentaclethra seeds and were less likely to be cached. The two large-bodied rodents handled seeds differently: Cricetomys emini larderhoarded nearly all (N = 15 of 16) encountered Pentaclethra seeds deep in burrows, while Atherurus africanus cached all (N = 5 of 5) encountered Pentaclethra seeds singly under 1-3 cm of leaf litter and soil, at an average distance of 24.2 m and a maximum distance of 46.3 m from experimental stations. This study supports the hypothesis that seed fate varies based on seed size and seed consumer identity, and represents the first telemetric experimental evidence of larderhoarding and scatterhoarding in the region.Abstract in French is available with online material.