Apex Carnivores Research Articles

Journals' impact and pecking order: tyranny and tyrannosaurs

Journals' impact and pecking order: tyranny and tyrannosaurs

From overlooking to concealed: predator avoidance in an apex carnivore

Abstract Many prey species select bed sites that reduce the risk of being caught off guard. We investigated bed sites used by an apex predator (gray wolf, Canis lupus) before and after individuals were approached by humans (N = 48 trials). On 9 out of 10 days, the unprovoked wolves rested at sites high in the terrain with a good overview (overlooking sites). After being approached, they resettled on more concealed sites lower in the terrain. Solitary yearlings used less overlooking sites than adults both before and after disturbance. The study provides experimental evidence that wolves’ behavioural response to approaching humans is analogous to predator avoidance in prey species.

Anatomy and affinities of large archosauromorphs from the lower Fremouw Formation (Early Triassic) of Antarctica

ABSTRACT The vertebrate assemblage of the lower Fremouw Formation has been studied for nearly 50 years, but many components remain poorly known. We describe a partial presacral vertebra and the distal end of a left humerus collected just above the Permian–Triassic boundary in the Shackleton Glacier region of the central Transantarctic Mountains. Our identification of these specimens as archosauromorphs that represent at least one taxon of large-bodied archosauriform increases the known reptile diversity of the Fremouw Formation considerably, and provides the first definitive evidence for the presence of Archosauriformes in the Early Triassic of Antarctica. These records increase faunal similarities between the lower Fremouw Formation and other Early Triassic assemblages. Although the lower Fremouw assemblage is typically considered a subset of the coeval Lystrosaurus Assemblage Zone (LAZ) of South Africa, the discrepancy in inferred body size between the Antarctic specimens and Proterosuchus fergusi, coupled with the fact that the LAZ of the Karoo Basin has been sampled much more thoroughly, suggests a real disparity in the maximum body size of apex carnivores between the lower Fremouw assemblage and the LAZ. The lower Fremouw specimens also demonstrate that one or more lineages of archosauriform had attained the large body size characteristic of later members of the clade very soon after the end-Permian mass extinction. This offers a point of contrast with the global pattern of post-extinction terrestrial communities, which are typified by a marked reduction in body size (the ‘Lilliput effect’).

Beyond demography and delisting: ecological recovery for Yellowstone's grizzly bears and wolves

This paper addresses the question, when are threatened or endangered species really recovered? The US Endangered Species Act enables the de-listing of species once demographic criteria are met. In the Greater Yellowstone ecosystem, two protected apex carnivores, grizzly bears ( Ursus arctos) and wolves ( Canis lupus), face removal from federal government protection due to population increases, a point at which they are expected to be integrated components of this ecosystem. We tested the assumption that these two carnivores are playing normative ecological roles in the Yellowstone ecosystem by comparing the extent to which wolves and bears have re-instilled anti-predator responses in a primary prey species, moose ( Alces alces), within wolf and bear recovery zones. As a type of control, we contrasted female moose from two areas in Alaska with different predator regimes to those in Wyoming. Populations from mainland Alaska, a region with a relatively intact carnivore assemblage, responded significantly more to odors of both carnivores. In contrast, a basic anti-predator reaction was lacking in Wyoming; and responses to grizzly bear odor only nominally increased after dependent young experienced heightened mortality. Additionally, the level of response among Alaskan moose living under virtual predator-free conditions for 25+ years closely resembled that of conspecifics in Wyoming. That such striking variation in prey responses exists re-enforces critical ecological differences between predator-intact and -defunct systems. Thus, although grizzly bears and wolves in the Yellowstone area will most likely be de-listed within the next few years, whether such action would be ecologically defensible is arguable. At this point in the recovery process, these predators may currently have limited ecological impacts in large portions of this region, at least as gauged by one potentially important prey species, moose. Although our data suggest ecologically incomplete conditions, other indices of carnivore recovery that include responses of other important prey species such as elk ( Cervus elaphus), may be more in tune with carnivore activities. We recommend that different types of ecological data available throughout recovery zones be used in consort with demographic criteria to evaluate when endangered carnivores are more fully integrated into their ecosystems. And, in the event of a disparity between these criteria, we also encourage a dialogue focusing on approaches towards bringing ecological conditions in concordance with demographic criteria, irrespective of whether one considers increasing population levels beyond the current target levels required for de-listing,and/or simply, additional time for the recovery process.

Notes on the Rearing of Tiger Cubs

Apex predators are crucial for maintaining ecological patterns and processes, yet humans hinder their ability to fulfil this role by displacing them from the landscape. Many apex predator species such as African lions (Panthera leo) are experiencing catastrophic declines as a result of competition with growing human populations. Increasing our understanding of the competitive interactions between lions and humans, as well as identifying thresholds of lion tolerance to human activities are important both for lion conservation and our understanding of apex predator ecology in the Anthropocene. We investigated the relative and cumulative influences of anthropogenic pressures on lion occurrence across a 73 000 km2 multi-use landscape in southern Africa. We developed occupancy models from replicated detection/non-detection spoor surveys across gradients of anthropogenic and biotic features. We tested the two hypotheses that African lions were most limited by 1) interference competition with humans or 2) exploitative competition with humans and evaluated the relative contribution of individual anthropogenic and biotic variables to lion occurrence. Our models predicted that lions occupied 49% of the landscape. The strongest determinants of lion occupancy were negative associations with pastoralism and bushmeat poaching, and a positive association with preferred prey. Thus, lions in this landscape are limited by a combination of interference and exploitative competition with poachers and pastoralists. However, interference competition with pastoralism was the biggest driver limiting lion occupancy, with a clear disturbance threshold for lions cumulating in a near complete loss of lions from the landscape when cattle surpass 21% occurrence. This study provides a predictive understanding of the top-down impacts of humans on the world's vulnerable apex carnivores.