Peter J. Jarman

MATING SYSTEM AND SEXCUL DIMORPHISM IN LARGE TERRESTRIAL, MAMMALIAN HERBIVORES

Sexual dimorphism in mammals is not entirely satisfactorily explained by the models that are advanced to account for it among birds. This may be because species‐specific styles of being dimorphic, and of attaining mature dimorphic state, are not clearly recognized. Mature dimorphism is a syndrome involving body size, appearance and weaponry; each facet and the whole syndrome may have functions in both fighting and signalling. The mature dimorphic stage has to be reached by growth and change from juvenile and sub‐adult states.

Teaching an endangered mammal to recognise predators

The possibility of conditioning captive-reared animals to fear predators prior to release into the wild is often discussed, but rarely attempted. Here we show that captive-reared rufous hare-wallabies Lagorchestes hirsutus, a species of marsupial that became extinct in the Australian mainland in 1991, become more cautious after conditioning to fear predators that they will encounter after release. The predators, cats and foxes, are not historical enemies of hare-wallabies, but captive-reared predator-naive rufous hare-wallabies reacted cautiously to them in captivity, suggesting either some genetic recognition abilities for a generalised mammalian predator, or perhaps that hare-wallabies are simply generally cautious in the presence of an unknown animal. Rufous hare-wallabies became even more cautious after two conditioning techniques were used to teach them to associate a fright with a fox or cat. We suggest that conditioning about predators may be a valuable adjunct to many management programmes involving release of predator-naive endangered animals.

Group size and activity in eastern grey kangaroos

Abstract Eastern grey kangaroos, Macropus giganteus, graze in open-membership groups and are hunted by dingoes, Canis familiaris dingo. Kangaroos in groups of different sizes were simultaneously observed on a homogeneous pasture and their activities were recorded. All major environmental variables, except group size, were the same for all individuals. There was a strong positive correlation between group size and time spent feeding and a negative one with time spent looking around, the relationship being best described by asymptotic curves. Kangaroos in small groups were significantly more likely than those in large groups to stand upright when looking around, a posture interpreted as indicating more intense altertness.

Drain it, dam it: alteration of water regime in shallow wetlands on the New England Tableland of New South Wales, Australia

Shallow, still-water wetlands on the New England Tablelands, an upland region of eastern Australia, have changed in the past 160 years in their types, abundance and in the diversity of their water regimes. These changes have been natural, intentional or the unintentional consequences of management actions. Changing attitudes and land-use and management practices have led to a large proportion of natural wetlands being drained or dammed, but with a relatively high proportion of those remaining being conserved in some way. The water regimes of those that remain have been greatly altered, usually increasing their stability (more continuously either inundated or dry). Farm dams and domestic water-storage dams are two new and distinct wetland types that are far more numerous than the wetland types in the original landscape. We discuss how changes in water regime have modified wetland attributes. Two case studies: Mother of Ducks Lagoon and the Llangothlin group of lagoons, are used as examples of how attitudes towards wetlands and reasons for water regime alteration have interacted with the tenure and management of wetlands on local, regional, national and international scales.

Monsoonal Australia : landscape, ecology and man in the northern lowlands

This work covers the history of the landscape, the climate, the vegetation, the vertebrate animals, Aboriginal association with the land, and conservation and the future.

Learning for life: Training marsupials to recognise introduced predators

Raising endangered species in captivity for reintroduction necessarily results in animals that lack appropriate skills for coping with problems to be faced in the wild, such as predators. Using classical conditioning techniques involving linking fear of a live dog with the image of a fox, we demonstrate an adjusted fear response for two wallaby species (rufous bettongs Aepyprymnus rufescens, quokkas Setonix brachyurus). No differences in response to the fox were found for wild-caught and captive-born bettongs, even though wild-caught subjects were likely to have encountered canids prior to capture. Attempts to condition a fear response by quokkas to an odour were unsuccessful. An attempt to induce fear of the stuffed fox by linking to fear of humans in quokkas was unsuccessful, but quokkas generalised from fear of the dog to fear of the fox, despite a delay of several weeks. Trained dogs offer a valuable and ethically acceptable mechanism for improving the ability of captive-reared (or sequestered) animals to recognise and cope with predators.

Adjustment of offspring sex ratios in relation to the availability of resources for philopatric offspring in the common brushtail possum

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, previous tests of local resource competition in mammals have used indirect measures of resource availability and have focused on sex–ratio variation between species or individuals rather than between local populations. Here, we show that the availability of den sites predicts the offspring sex ratio in populations of the common brushtail possum. Female possums defend access to dens, and daughters, but not sons, occupy dens within their mothers range. However, the abundances of possums in our study areas were determined principally by food availability. Consequently, in food–rich areas with a high population density, the per–capita availability of dens was low, and the cost of having a daughter should have been high. This cost was positively correlated with male bias in the sex ratio at birth. Low per capita availability of dens was correlated with male bias in the sex ratio at birth.

Body size, age and paternity in common brushtail possums ( Trichosurus vulpecula )

Sexual selection should produce sexual size dimorphism in species where larger members of one sex obtain disproportionately more matings. Recent theory suggests that the degree of sexual size dimorphism depends on physical and temporal constraints involving the operational sex ratio, the potential reproductive rate and the trade‐off between current reproductive effort and residual reproductive value. As part of a large‐scale experiment on dispersal, we investigated the mating system of common brushtail possums inhabiting old‐growth Eucalyptus forest in Australia. Paternity was assigned to 20 of 28 pouch‐young (maternity known) genotyped at six microsatellite loci. Male mating success was strongly related to body size and age; male body weight and age being highly correlated. Despite disproportionate mating success favouring larger males, sexual size dimorphism was only apparent among older animals. Trapping and telemetry indicated that the operational sex ratio was effectively 1 : 1 and the potential reproductive rate of males was at most four times that of females. Being larger appeared to entail significant survival costs because males ‘died‐off’ at the age at which sexual size dimorphism became apparent (8–9 years). Male and female home ranges were the same size and males appeared to be as sedentary as females. Moreover, longevity appears to be only slightly less important to male reproductive success than it is to females. It is suggested that a sedentary lifestyle and longevity are the key elements constraining selection for greater sexual size dimorphism in this ‘model’ medium‐sized Australian marsupial herbivore.

Macropod studies at Wallaby Creek. IX Exposure and responses of eastern grey kangaroos to dingoes

Kangaroos at Wallaby Creek lived with the persistent presence of dingoes in the valley, there being no place, time of year or of day when kangaroos could be free of risk. An adult kangaroo might encounter dingoes a few hundred times in its life. Dingoes appeared not to be selective for the sizes of groups of kangaroos that they contacted. Large adult males and females with medium pouch young were overrepresented in the samples of kangaroos contacted by dingoes. No kangaroos ignored the detected presence of dingoes; all became alert, and most fled. The distances at which they became alert to a dingo group depended upon the kangaroo groups size, larger groups never being surprised by dingoes at short range as were some smaller groups. On average larger groups fled when the dingoes were further away. Among classes of kangaroos, large adult males fled least far, and tended to react to dingoes less strongly (in terms of alertness or flight) than other classes. They also exhibited two forms of defence, taking to water when pursued and warding off attack, that other classes did not show.

Diet and feeding selectivity of common wombats

The seasonal diets and feeding selectivity of common wombats (Vombatus ursinus) in mountainous eucalypt forest, eucalypt woodland and pasture were determined using faecal analysis. Grass species contributed the largest proportion (95%) of epidermal fragment area in faecal pellets, with at least 20 species being eaten. The most abundant grasses in pellets in all seasons were the tough, wiry snow grasses (Poa sieberiana and P. labillardieri), with Microlaena stipoides comprising a substantial proportion of the diet in summer and autumn. Grass leaf was the most abundant plant part in pellets (81%), with grass stem and grass sheath comprising 11%. The seasonal proportion of grass seedhead in pellets varied from just traces during autumn and winter to a substantial component of the diet during summer (21% of epidermal fragments in pellets). Forbs comprised less than 1% of pellet material, and tree or shrub species were not detected in the diet. Feeding selectivity (and hence dietary niche breadth) varied seasonally; wombats become less selective in their feeding as plant diversity and abundance decreased. Positive selection was shown for monocots and negative selection for forbs. Grass species were eaten in broadly similar proportions to their abundances in the field, but with moderate to strong selection or rejection of a few species.