Top predator restricts the niche breadth of prey: effects of assisted colonization of Tasmanian devils on a widespread omnivorous prey.

Few landscape-scale experiments test the effects of predators on the abundance and distribution of prey across habitat gradients. We use the assisted colonization of a top predator, the Tasmanian devil (Sarcophilus harrisii), to test the impacts of predation on the abundance, habitat use and temporal activity of a widespread prey species, the omnivorous common brushtail possum (Trichosurus vulpecula). Before introduction of devils to Maria Island, Tasmania, Australia, in 2012, possums were abundant in open grasslands as well as forests. Predation by devils caused high mortality of possums in grasslands, but individuals with access to trees had a higher survival probability. Possum abundance declined across the whole island from 2012-2016, as possums disappeared almost completely from grasslands and declined in drier forests with more open understorey. Abundance remained stable in wet forests, which are not preferred habitat for possums but provide better refuge from devils. Abundance and habitat use of possums remained unchanged at a control site on the adjacent Tasmanian mainland, where the devil population was low and stable. This study demonstrates how spatial variation in predator-caused mortality can limit both abundance and habitat breadth in generalist prey species, excluding them entirely from certain habitats.

Contrasting population manipulations reveal resource competition between two large marsupials: bare-nosed wombats and eastern grey kangaroos.

Resource competition is an important interaction that can structure ecological communities, but is difficult to demonstrate in nature, and rarely demonstrated for large mammals including marsupials. We analysed 10 years of population survey data to investigate resource competition between bare-nosed wombats (Vombatus ursinus) and eastern grey kangaroos (Macropus giganteus) at two sites to assess whether resource competition is occurring. At one site, wombat abundance was reduced by increased mortality from mange disease, whereas at the other site, kangaroo abundance was reduced primarily by culling. We used the modified Lotka-Volterra competition (LVC) models to describe the mechanism of resource competition and fitted those models to the empirical data by maximum likelihood estimation. We found strong negative relationships between the abundance of wombats and kangaroos at each site, and resource competition was also mechanistically supported by the modified LVC models. The estimated competition coefficients indicate that bare-nosed wombats are a slightly superior competitor of eastern grey kangaroos than vice versa, and that intraspecific competition is almost twice as strong as interspecific competition. In addition, this study facilitated the calculation of the transmission rate associated with mange disease at one site (0.011), and the removal rate owing to culling, the introduction of a predator species, and drought at the other site (0.0006). Collectively, this research represents a rare empirical demonstration of resource competition between large mammals and contributes new insight into the ecology of two of Australia's largest grazing marsupials.

Lateralization of mother-infant interactions in a diverse range of mammal species.

Left-cradling bias is a distinctive feature of maternal behaviour in humans and great apes, but its evolutionary origin remains unknown. In 11 species of marine and terrestrial mammal, we demonstrate consistent patterns of lateralization in mother-infant interactions, indicating right hemisphere dominance for social processing. In providing clear evidence that lateralized positioning is beneficial in mother-infant interactions, our results illustrate a significant impact of lateralization on individual fitness.

Early expression of manual lateralization in bipedal marsupials.

Robust lateralization in forelimb use has recently been found in bipedal, but not quadrupedal, marsupial mammals. The link between bipedality and handedness, occurring in both marsupials and primates, remains to be investigated. To shed light on the developmental origins of marsupial manual lateralization, infants of macropod marsupials were examined before and shortly after the acquisition of habitual bipedal posture and locomotion. Forelimb preferences were assessed in natural, not artificially evoked, behaviors of infant red-necked wallaby in the wild and infant eastern gray kangaroo in free-ranging captivity. Pouch young of both species showed population-level left-forelimb preference when manipulating food objects, such as leaves and grass blades. This result provides the first report of lateralization in pouch young marsupials and rare evidence of lateralized manual activity in early mammalian ontogenesis. Young-at-foot juveniles of eastern gray kangaroo preferred to use the left forelimb to manipulate the mother's pouch edge as previously shown for red-necked wallaby. In both species, the direction of biases in manipulative behavior for young-at-foot and pouch young was the same as in adults. Forelimb preferences in offspring were positively correlated with the forelimb preferences of their mothers. Our results strongly suggest that the emergence of individual and population-level forelimb preferences in macropod infants precedes the onset of independent standing and locomotion. In all probability, manual lateralization in bipedal marsupials, such as kangaroos and wallabies, is not determined by the acquisition of habitual bipedality in the course of ontogenesis. (PsycINFO Database Record

Parallel Emergence of True Handedness in the Evolution of Marsupials and Placentals.

Recent studies have demonstrated a close resemblance between some handedness patterns in great apes and humans. Despite this, comparative systematic investigations of manual lateralization in non-primate mammals are very limited. Among mammals, robust population-level handedness is still considered to be a distinctive human trait. Nevertheless, the comprehensive understanding of handedness evolution in mammals cannot be achieved without considering the other large mammalian lineage, marsupials. This study was designed to investigate manual lateralization in non-primate mammals using the methodological approach applied in primate studies. Here we show that bipedal macropod marsupials display left-forelimb preference at the population level in a variety of behaviors in the wild. In eastern gray and red kangaroos, we found consistent manual lateralization across multiple behaviors. This result challenges the notion that in mammals the emergence of strong "true" handedness is a unique feature of primate evolution. The robust lateralization in bipedal marsupials stands in contrast to the relatively weak forelimb preferences in marsupial quadrupeds, emphasizing the role of postural characteristics in the evolution of manual lateralization as previously suggested for primates. Comparison of forelimb preferences in seven marsupial species leads to the conclusion that the interspecies differences in manual lateralization cannot be explained by phylogenetic relations, but rather are shaped by ecological adaptations. Species' postural characteristics, especially bipedality, are argued to be instrumental in the origin of handedness in mammals.