Christopher N Johnson

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There is growing recognition of the important roles played by predators in regulating ecosystems and sustaining biodiversity. Much attention has focused on the consequences of predator-regulation of herbivore populations, and associated trophic cascades. However apex predators may also control smaller 'mesopredators' through intraguild interactions. Removal(More)
Ecologists seek to understand patterns of distribution and abundance of species. Studies of distribution often use occurrence data to build models of the environmental niche of a species. Environmental suitability (ES) derived from such models may be used to predict the potential distributions of species. The ability of such models to predict spatial(More)
Plants contain a variety of chemical defenses that strongly affect feeding rates in captive mammals, but their effects on the fitness of wild herbivores are largely unknown. This is because the complexity of defensive compounds, and herbivores' counteradaptations to them, make their effects in the wild difficult to measure. We show how tannins interact with(More)
Extinctions of megafauna species during the Late Quaternary dramatically reduced the global diversity of mammals. There is intense debate over the causes of these extinctions, especially regarding the extent to which humans were involved. Most previous analyses of this question have focused on chronologies of extinction and on the archaeological evidence(More)
The arrival of the dingo in mainland Australia is believed to have caused the extinction of three native vertebrates: the thylacine, the Tasmanian devil and the Tasmanian native hen. The dingo is implicated in these extinctions because, while these three species disappeared during the late Holocene of mainland Australia in the presence of the dingo, they(More)
The local-resource-competition hypothesis predicts that where philopatric offspring compete for resources with their mothers, offspring sex ratios will be biased in favour of the dispersing sex. This should produce variation in sex ratios between populations in relation to differences in the availability of resources for philopatric offspring. However,(More)
BACKGROUND Life-threatening disorders of heart rhythm may arise during infancy and can result in the sudden and tragic death of a child. We performed exome sequencing on 2 unrelated infants presenting with recurrent cardiac arrest to discover a genetic cause. METHODS AND RESULTS We ascertained 2 unrelated infants (probands) with recurrent cardiac arrest(More)
Invasive species are regarded as one of the top five drivers of the global extinction crisis. In response, extreme measures have been applied in an attempt to control or eradicate invasives, with little success overall. We tested the idea that state shifts to invasive dominance are symptomatic of losses in ecosystem resilience, due to the suppression of(More)
Giant vertebrates dominated many Pleistocene ecosystems. Many were herbivores, and their sudden extinction in prehistory could have had large ecological impacts. We used a high-resolution 130,000-year environmental record to help resolve the cause and reconstruct the ecological consequences of extinction of Australia's megafauna. Our results suggest that(More)
The young males of many species of mammals move away from their parents and settle in new home ranges before starting to breed, while females are likely to stay for life near their places of birth (Greenwood 1980; Packer 1979; Dobson 1982; Waser and Jones 1983). The dispersal of some juveniles has often been interpreted as a mechanism for the avoidance of(More)