Temporal niche shifts can shape predator–prey interactions by enabling predator avoidance, enhancing feeding success, and reducing competition among predators. Using a community-based conservation approach, we investigated temporal niche partitioning of mammalian predators and prey across 12 long-term camera trap surveys in the Pacific slope and Talamanca Cordillera of Costa Rica. Temporal overlap and segregation were investigated between predator–prey and predator–predator pairs using overlap analysis, circular statistics, and relative abundance after accounting for differences in habitat, season, and human impact among sites. We made the assumption that predators select abundant prey and adjust their activity to maximize their temporal overlap, thus we predicted that abundant prey with high overlap would be preferred prey species for that predator. We also predicted that similar-sized pairs of predator species with the greatest potential for competitive interactions would have the highest temporal segregation. Our results supported the existence of temporal niche separation among the eight species of predators—the smaller Leopardus felids (ocelot, margay, oncilla) were primarily nocturnal, the largest felids (jaguar and puma) and coyote were cathemeral, and the smaller jaguarundi and tayra were mostly diurnal. Most prey species (67%) were primarily nocturnal versus diurnal or cathemeral (33%). Hierarchical clustering identified relationships among species with the most similar activity patterns. We discuss the primary prey and competitor species predicted for each of the eight predators. Contrary to our prediction, the activity pattern of similar-sized intraguild competitors overlapped more than dissimilar-sized competitors, suggesting that similar-sized predators are hunting the same prey at the same time. From this we conclude that prey availability is more important than competition in determining circadian activity patterns of Neotropical predators. Our results indicate the presence of a delicate balance of tropical food webs that may be disrupted by overhunting, leading to a depauperate community consisting of ubiquitous generalists and endangered specialists. With Central America a hotspot for hunting-induced “empty forests,” community-based conservation approaches may offer the best road to reduce illegal hunting and maintain the biodiversity and community structure of tropical forest systems.

The persistence of coat color polymorphisms-such as the coexistence of melanistic and "wild-type" coat color-is an ongoing evolutionary puzzle. We tested the predictions of Gloger's rule and the Temporal Segregation hypothesis that propose that melanistic individuals will (a) occur more frequently in closed tropical forest versus open habitat due to camouflage and thermoregulation advantages and (b) be more active during brighter times of the circadian and lunar cycle because black pigmentation is cryptic under bright illumination. Based on 10 years of camera trap records of jaguar and oncilla from dense tropical forest in Costa Rica, we compared activity and relative abundance of non-melanistic wild-type morphs (rosetted or spotted) versus melanistic morphs. Twenty-five percent of jaguar records in dense forest were melanistic compared with the global average of 10% in both open and closed habitats; 32% of oncilla records were melanistic compared with 18% overall in Brazil. Overlap analysis indicated that melanistic jaguars were more active during daylight hours compared with non-melanistic jaguars, which were more nocturnal and crepuscular. Likewise, melanistic oncillas were significantly more diurnal than non-melanistic oncillas; melanistic oncillas were also more active during full moon, while nonmelanistic oncillas were less active. These results imply that melanistic jaguar and oncilla enjoy the adaptive benefits of superior camouflage when inhabiting dense forest and accrue a fitness advantage when hunting during conditions of brighter illumination. If true, natural selection would ensure that melanistic individuals persist when dense forest is retained but may be threatened by deforestation and accelerating human presence.

The clumping parameter related to the distribution of schistosome parasites is obtained by fitting a negative binomial distribution to data collected from patients in a village in Brazil; the natural uninfected and parasite-induced snail host mortality rates are obtained from laboratory data. These values are used in a schistosomiasis model proposed earlier by the authors, and a disease transmission parameter from snails to humans is estimated. Finally, the effect of chemotherapy of humans is assessed using prevalence of morbidity as a measure of the level of schistosome infection in a human population. (~)

Biomphalaria glabrata snails infected with Schistosoma mansoni were collected during consecutive seasons from a site in Brazil known to have a very high percentage of infected snails. Schistosoma mansoni cercariae from single snails were used to infect individual mice, and the recovered adult worms were genetically assessed using a mtVNTR marker. The number of unique parasite genotypes found per snail was compared to expected abundance values, based on the infection prevalence at the site, to determine the distribution of S. mansoni infections within the snail population. The observed distributions and those from previous studies were used to examine the relationship between schistosome prevalence and aggregation across a wide range of prevalence values. Our analysis showed that prevalence was inversely related to the degree of parasite overdispersion, and at high prevalence, S. mansoni infections were randomly distributed among snails.

An increasing body of evidence indicates that moonlight influences the nocturnal activity patterns of tropical mammals, both predators and prey. One explanation is that brighter moonlight is associated with increased risk of predation (Predation Risk hypothesis), but it has also been proposed that nocturnal activity may be influenced by the sensory ecology of a species, with species that rely on visual detection of food and danger predicted to increase their activity during bright moonlight, while species relying on non-visual senses should decrease activity (Visual Acuity hypothesis). Lack of an objective measure of “visual acuity” has made this second hypothesis difficult to test, therefore we employed a novel approach to better understand the role of lunar illumination in driving activity patterns by using the tapetum lucidum as a proxy for “night vision” acuity. To test the alternative predictions, we analyzed a large dataset from our long-term camera trap study in Costa Rica using activity overlap, relative abundance, and circular statistical techniques. Mixed models explored the influence of illumination factors (moonrise/set, cloud cover, season) and night vision acuity (tapetum type) on nocturnal and lunar phase-related activity patterns. Our results support the underlying assumptions of the predation risk and visual acuity models, but indicate that neither can fully predict lunar-related activity patterns. With diurnal human “super predators” forcing a global increase in activity during the night by mammals, our findings can contribute to a better understanding of nocturnal activity patterns and the development of conservation approaches to mitigate forced temporal niche shifts.