Male and female western gorilla diet: preferred foods, use of fallback resources, and implications for ape versus old world monkey foraging strategies.

Most of what is currently known about western gorilla (Gorilla gorilla) diet is based on indirect studies using fecal samples and trail signs rather than measures based on direct observations. Here we report results on adult male and female western gorilla foraging behavior, based on systematic focal observations and nutritional analyses of foods. We found that western gorillas, like other apes, are highly selective ripe fruit specialists, seeking fruit high in energy, low in antifeedants, and rare in the environment. During seasonal fruiting peaks, fruit accounted for up to 70% of feeding time. When ripe fruit was scarce, gorillas increased time spent feeding on leaves and nonpreferred fruits and herbs. Leaves were the major fallback food, accounting for up to 70% of feeding time in males and 50% in females during periods of fruit scarcity. In spite of large differences in body size, the sexes were remarkably similar in their overall diet, not differing in time spent feeding on fruit or preferred herbs. However, the male consistently fed more often and on a greater variety of leaves than did females, whereas females fed more often on fallback herbs and termites. Our findings, when considered in light of previous findings on sympatric mangabeys, indicate that the foraging strategy of western gorillas is broadly similar to that of chimpanzees and orangutans, and distinct from that of old world monkeys.

The Raw and the Stolen. Cooking and the Ecology of Human Origins.

Cooking is a human universal that must have had widespread effects on the nutrition, ecology, and social relationships of the species that invented it. The location and timing of its origins are unknown, but it should have left strong signals in the fossil record. We suggest that such signals are detectable at ca. 1.9 million years ago in the reduced digestive effort (e.g., smaller teeth) and increased supply of food energy (e.g., larger female body mass) of early Homo erectus. The adoption of cooking required delay of the consumption of food while it was accumulated and/or brought to a processing area, and accumulations of food were valuable and stealable. Dominant (e.g., larger) individuals (typically male) were therefore able to scrounge from subordinate (e.g., smaller) individuals (typically female) instead of relying on their own foraging efforts. Because female fitness is limited by access to resources (particularly energetic resources), this dynamic would have favored females able to minimize losses to theft. To do so, we suggest, females formed protective relationships with male co-defenders. Males would have varied in their ability or willingness to engage effectively in this relationship, so females would have competed for the best food guards, partly by extending their period of sexual attractiveness. This would have increased the numbers of matings per pregnancy, reducing the intensity of male intrasexual competition. Consequently, there was reduced selection for males to be relatively large. This scenario is supported by the fossil record, which indicates that the relative body size of males fell only once in hominid evolution, around the time when H. erectus evolved. Therefore we suggest that cooking was responsible for the evolution of the unusual human social system in which pair bonds are embedded within multifemale, multimale communities and supported by strong mutual and frequently conflicting sexual interest.

Seed dispersal by neotropical seed predators.

From a plant's perspective, the difference between a seed predator and a seed disperser should be straightforward: attract animals that will disperse seeds and defend seeds from potential predators. Unlike pulp-eating frugivores, seed predators regularly encounter diverse plant protective mechanisms. The purpose of this paper is to examine feeding constraints, morphological adaptations, and the mechanical process of seed predation. While there is evidence that some seed predators cause severe losses to seed crops, there is also evidence that seed predators enhance seed dispersal and germination. We also examine four methods by which neotropical seed predators may contribute to dispersal. 1) Seed predators examined here ingested fruit when seeds were full-sized, but not yet mature (i.e., seeds of mature fruit may be avoided by seed predators and available for dispersal by other frugivores). 2) Sympatric seed predators may ingest seeds from different plants thus reducing overall predator load on any individual plant. 3) Seed predators that manipulate seeds (e.g., remove pericarp and seed coat) may enhance germination if the prepared seeds are dropped, discarded, or buried and not ingested. 4) Small seeds may miss mastication and swallowed intact with a food bolus. The last mechanism is the most likely to contribute to seed dispersal by the widest array of vertebrate seed predators, but primate seed predators may facilitate seed dispersal using all four mechanisms. Therefore, the traditional dichotomy of seed predator vs. seed disperser oversimplifies the interactions between seed predators and plants.