Feeding in fear? How adult male western chimpanzees (Pan troglodytes verus) adjust to predation and savanna habitat pressures.

OBJECTIVES: We evaluated risk-sensitive foraging in adult male western chimpanzees (Pan troglodytes verus) occupying a savanna environment at Fongoli, Senegal. The aim of this study was to determine how the risks of predation and heat stress influenced their behavior while feeding on a key food, fruit of the baobab tree (Adansonia digitata). MATERIALS AND METHODS: Proximity of fruiting baobab trees to anthropogenic landmarks were compared to food intake, feeding rate, and behavioral indicators of fear in adult males (N = 11) at Fongoli. Additionally, we compared foraging to vegetative habitats, baobab ripe fruit nutritive quality, surface water availability, and foraging party composition. RESULTS: Fruit abundance increased with proximity to anthropogenic landmarks, and chimpanzees exhibited higher frequencies of antipredator behaviors as they approached these risky areas. However, predation risk did not deter adult males from visiting these fruiting trees; instead, risky foraging bouts were associated with higher food intakes and longer feeding times. Additionally, higher feeding rates were observed in open-canopy habitats, and this behavior may have minimized their risk of heat stress. CONCLUSIONS: Adaptations that minimize predation risk are widespread in mammalian prey species, but these traits are poorly understood in chimpanzees. Great apes encounter few nonhuman predators capable of successfully capturing and killing them; thus, such events are rarely observed. Although people rarely hunt chimpanzees in Senegal, we found that adult males perceived humans as predators and adjusted their behavior while foraging in risky habitats. From an applied perspective, risk-taking behavior is important for understanding and mitigating the problem of crop-feeding in locations where chimpanzees and humans live in sympatry.

A complex relationship between moonlight and temperature on the foraging behavior of the Alabama beach mouse.

Most animal species forage with risk from an ensemble of predators, wherein some predators are themselves prey to the others. A forager's behavior should reflect a synthesis of the effect of environmental conditions on both marginal predation risk and rates of energy accumulation. Here, a forager's giving-up density [GUD] is analyzed for signs of these complex signals. Specifically, we hypothesized that temperature can reverse the effect of moonlight intensity on Alabama beach mouse (Peromyscus polionotus ammobates) GUD because changes in temperature change the ensemble of predators from homeothermic taxa with better vision than the mouse to ectothermic taxa with worse vision than the mouse. We fit several models to GUD measurements taken over a broad range of temperatures and nocturnal luminosities. We obtained strong information-theoretic support for a model that is consistent with our hypothesis of temperature-dependent reversal of the effect of nocturnal illumination on mouse GUD. Signals in GUDs can reveal complex effects of optimal foraging at multiple trophic levels, which is especially informative when direct measurement of taxonomic sources of predation is not feasible.

Mammalian Herbivores Alter the Population Growth and Spatial Establishment of an Early-Establishing Grassland Species.

Plant-herbivore interactions influence the establishment context of plant species, as herbivores alter the community context in which individual species establish, and the spatial relationship between individuals and their source population as plants invade. This relationship can be described using an establishment kernel, which takes into account movement through seed dispersal, and subsequent establishment of adults. Mammalian herbivores are hypothesized to influence plant population growth and establishment through a combination of consumption of seeds and seedlings, and movement of seeds. While the movement abilities of plants are well known, we have very few empirical mechanistic tests of how biotic factors like mammalian herbivores influence this spread potential. As herbivores of all sizes are abundant on the landscape, we asked the question, how do mammalian herbivores influence the population growth, spatial establishment, and the community establishment context of an early-recruiting native prairie legume, Chamaecrista fasciculata? We planted C. fasciculata in source populations within a four-acre tallgrass prairie restoration in plots with and without herbivores, and monitored its establishment with respect to distance from the source populations. We found that herbivores decreased population growth, and decreased the mean and range establishment distance. Additionally, C. fasciculata established more often without herbivores, and when surrounded by weedy, annual species. Our results provide insight into how the interactions between plants and herbivores can alter the spatial dynamics of developing plant communities, which is vital for colonization and range spread with fragmentation and climate change. Mammalian herbivores have the potential to both slow rates of establishment, but also determine the types of plant communities that surround invading species. Therefore, it is essential to consider the herbivore community when attempting to restore functioning plant communities.

Rapid Morphological Change in the Masticatory Structures of an Important Ecosystem Service Provider.

Humans have altered the biotic and abiotic environmental conditions of most organisms. In some cases, such as intensive agriculture, an organism's entire ecosystem is converted to novel conditions. Thus, it is striking that some species continue to thrive under such conditions. The prairie deer mouse (Peromyscus maniculatus bairdii) is an example of such an organism, and so we sought to understand what role evolutionary adaptation played in the success of this species, with particular interest in adaptations to novel foods. In order to understand the evolutionary history of this species' masticatory structures, we examined the maxilla, zygomatic plate, and mandible of historic specimens collected prior to 1910 to specimens collected in 2012 and 2013. We found that mandibles, zygomatic plates, and maxilla have all changed significantly since 1910, and that morphological development has shifted significantly. We present compelling evidence that these differences are due to natural selection as a response to a novel and ubiquitous food source, waste grain (corn, Zea mays and soybean, Glycine max).

The Influences of Conspecific and Heterospecific Residents on Colonization.

To determine if dispersing prairie voles, Microtus ochrogaster, are prevented from establishing home ranges in habitat already occupied by conspecifics or potentially competitive species, voles were introduced into enclosed populations of: the same species; southern bog lemmings, Synaptomys cooperi; cotton rats, Sigmodon hispidus; or an empty enclosure. The results indicated that colonization by dispersing voles was negatively affected by resident conspecifics. Introduced females were more strongly affected than males during the vegetative growing season but not during the nongrowing season when reproductive activity is typically low. Resident bog lemmings also negatively affected colonization by dispersing voles. However, both sexes of introduced voles were similarly affected in both seasons. There was no evidence of postcolonization competitive effects, suggesting that interspecific competition does not occur between established resident individuals. Cotton rats, which have only recently become part of the small mammal community in Kansas, did not adversely affect colonization by dispersing voles or have adverse post-colonization effects on their survival and reproduction. The ability of residents to inhibit colonization by another species may facilitate the coexistence of M. ochrogaster and Synaptomys cooperi by retarding the competitive exclusion of either species until annual fluctuations in reproduction and density create an abundance of suitable but unoccupied space. This type of coexistence is similar to the storage effect in lottery models of competitive coexistence.

Threat of hantavirus pulmonary syndrome to field biologists working with small mammals.

Low risk for hantavirus pulmonary syndrome (HPS) has been reported among biologists engaged in fieldwork with rodents. The overall probability of acquiring HPS when working with rodents appears to be 1 in 1,412 (0.00071). Nonetheless, a causal link between HPS and lack of personal protective equipment (PPE) use is suggested by some investigators. However, supporting data are incomplete and consequently misleading. A recent HPS case was assumed to be acquired during rodent-handling activities, although substantial peridomestic exposure was evident. Regulatory groups interpret inadequate data as evidence of the need for excessive and inappropriate PPE, which can hamper field research and instructional efforts. PPE recommendations should be reviewed and revised to match the risk associated with different types of fieldwork with small mammals.

Rodents balancing a variety of risks: invasive fire ants and indirect and direct indicators of predation risk.

We used foraging trays to compare how oldfield mice, Peromyscus polionotus, altered foraging in response to the presence of fire ants, Solenopsis invicta, and in the presence of direct (predator urine) and indirect (sheltered or exposed microhabitat, moonlight, and precipitation) indicators of predation risk. Foraging reductions elicited by S. invicta were greater than reductions in response to well-documented indicators of risk (i.e., moonlit nights) and the presence of predator urine. The presence of S. invicta always led to reduced foraging, but the overall impact of S. invicta was dependent upon microhabitat and precipitation. When S. invicta was not present, foraging was greater in sheltered microhabitats compared to exposed microhabitats. S. invicta made sheltered microhabitats equivalent to more risky exposed microhabitats, and this effect was especially pronounced on nights without precipitation. The effect of S. invicta suggests that interactions with S. invicta may entail a potentially heavy cost or that presence of S. invicta may represent a more reliable indicator of imminent competition or predation compared to indirect cues of risk and predator urine. The presence of S. invicta led to reduced foraging under situations when foraging activity would otherwise be greatest (i.show $132#e., under vegetative cover), potentially reducing habitat quality for P. polionotus and the distribution of seeds consumed by rodents.

Corridors affect plants, animals, and their interactions in fragmented landscapes.

Among the most popular strategies for maintaining populations of both plants and animals in fragmented landscapes is to connect isolated patches with thin strips of habitat, called corridors. Corridors are thought to increase the exchange of individuals between habitat patches, promoting genetic exchange and reducing population fluctuations. Empirical studies addressing the effects of corridors have either been small in scale or have ignored confounding effects of increased habitat area created by the presence of a corridor. These methodological difficulties, coupled with a paucity of studies examining the effects of corridors on plants and plant-animal interactions, have sparked debate over the purported value of corridors in conservation planning. We report results of a large-scale experiment that directly address this debate. In eight large-scale experimental landscapes that control for patch area and test alternative mechanisms of corridor function, we demonstrate that corridors not only increase the exchange of animals between patches, but also facilitate two key plant-animal interactions: pollination and seed dispersal. Our results show that the beneficial effects of corridors extend beyond the area they add, and suggest that increased plant and animal movement through corridors will have positive impacts on plant populations and community interactions in fragmented landscapes.