Publications by authors named "Timothy G O'Brien"

In order to understand how the effects of land-use change vary among taxa and environmental contexts, we investigate how three types of land-use change have influenced phylogenetic diversity (PD) and species composition of three functionally distinct communities: plants, small mammals, and large mammals. We found large mammal communities were by far the most heavily impacted by land-use change, with areas of attempted large wildlife exclusion and intense livestock grazing, respectively, containing 164 and 165 million fewer years of evolutionary history than conserved areas (~40% declines). The effects of land-use change on PD varied substantially across taxa, type of land-use change, and, for most groups, also across abiotic conditions.

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When predators are removed or suppressed for generations, prey populations tend to increase and when predators are re-introduced, prey densities should fall back to pre-control levels. In cases of apparent competition where there are alternate abundant and rare prey species, rare species may decline further than expected or disappear altogether. Recently, concern about the impact of recovering predator populations on wildlife in Laikipia County, Kenya, has led to questions of whether lions (Panthera leo, IUCN Red List Vulnerable) exert top-down pressure on Grevy's zebra (Equus grevyi, IUCN Red List Endangered).

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Article Synopsis
  • Plasmodium knowlesi is transmitted from macaques to humans via anopheline mosquitoes, and understanding the geographical distribution of this malaria is essential for assessing disease risk.
  • Researchers used presence data from macaque and mosquito species, a boosted regression tree model, and environmental data to predict the habitats where these species thrive.
  • The findings indicate that the transmission risk is higher in disturbed forest areas due to the presence of both macaque hosts and mosquito vectors, particularly in regions where human activity has altered the landscape.
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Increasingly, the restoration of large carnivores is proposed as a means through which to restore community structure and ecosystem function via trophic cascades. After a decades-long absence, African wild dogs (Lycaon pictus) recolonized the Laikipia Plateau in central Kenya, which we hypothesized would trigger a trophic cascade via suppression of their primary prey (dik-dik, Madoqua guentheri) and the subsequent relaxation of browsing pressure on trees. We tested the trophic-cascade hypothesis using (1) a 14-year time series of wild dog abundance; (2) surveys of dik-dik population densities conducted before and after wild dog recovery; and (3) two separate, replicated, herbivore-exclusion experiments initiated before and after wild dog recovery.

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Reliable assessments of species' status are prerequisites for monitoring the success of conservation programmes. However, survey conditions such as terrain and inaccessibility, compounded by the low densities of many species across Southeast Asia and other parts of the world are considerable barriers to obtaining robust populations estimates. We used an occupancy-based approach and multi-model inference to generate occupancy and abundance estimates for northern white-cheeked crested gibbons Nomascus leucogenys and southern white-cheeked crested gibbons N.

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Successful conservation of large terrestrial mammals (wildlife) on private lands requires that landowners be empowered to manage wildlife so that benefits outweigh the costs. Laikipia County, Kenya, is predominantly unfenced, and the land uses in the area allow wide-ranging wildlife to move freely between different management systems on private land. We used camera traps to sample large mammals associated with 4 different management systems (rhinoceros sanctuaries, no livestock; conservancies, intermediate stocking level; fenced ranches, high stocking level; and group ranches, high stocking level, no fencing, pastoralist clan ownership) to examine whether management and stocking levels affect wildlife.

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Juvenile and adult females in two wild groups of wedge-capped capuchin monkeys (Cebus olivaceus) were observed nursing from other adult females. The context of the interactions varied with participants but always involved a higher-ranking female nursing from a lower-ranking female. This behavior appears to be an example of an exploitative interaction in which the suckling female benefits at the expense of the nursing female.

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