Strategies of a small nectarivorous marsupial, the western pygmy-possum, in response to seasonal variation in food availability

The influence of weather and moon phase on small mammal activity

Small mammals are commonly surveyed using live trapping but the influence of weather conditions on trap success is largely unknown. This information is required to design and implement more effective field surveys and monitoring. We tested the influence of weather and moon phase on capture rates of small mammals in the Murray Mallee region of semi-arid Australia. We used extensive pitfall trapping data collected at 267 sites, totalling 54492 trap-nights. We built regression models to explore the relationship between the capture rates of five species and daily meteorological conditions, and across families of mammals, including dasyurids, burramyids and rodents. A relationship common to several taxa was the positive influence of high winds (>20km h−1) on capture rates. We also identified differences between taxa, with warmer overnight temperatures increasing capture rates of mallee ningaui but decreasing those of Bolam’s mouse. This makes it difficult to determine a single set of ‘optimal’ meteorological conditions for surveying the entire community but points to conditions favourable to individual species and groups. We recommend that surveys undertaken in warmer months encompass a variety of meteorological conditions to increase capture rates and provide a representative sample of the small mammal community present in a landscape.

The interrelationship between torpor expression and nest site use of western and eastern pygmy-possums (Cercartetus spp.)

Physiology and behaviour are closely linked, making knowledge of the interaction between species’ energetics and activities important when attempting to understand how animals function in the wild. I examined torpor use by western pygmy-possums (Cercartetus concinnus) and eastern pygmy-possums (C. nanus) in relation to nest site characteristics and movement patterns. In coastal mallee heath in winter, C. concinnus nested beneath leaf litter at the base of dead Banksia ornata, where they employed torpor on 69% of observed days. In warm temperate sclerophyll forest, C. nanus nested in tree hollows of Eucalyptus spp. and used torpor on 64% of days in winter and 10% in summer. Torpor was used in nest sites that were buffered from outside temperature extremes. Both species frequently reused nest sites and while C. nanus was more likely to employ torpor in a previously used site, site familiarity did not influence torpor use for C. concinnus. Additionally, C. nanus was more likely to use torpor in hollows with a higher relative thickness in both seasons. No relationship was found between range size and the number of tracking days or capture body mass, though sample sizes were small. I suggest that the thermal attributes of nest sites influence torpor use for both species and this is likely vital for maintaining a positive energy balance, stressing the importance of preserving habitat with ample potential nest sites for conservation management.

Thermoregulatory value of cracking-clay soil shelters for small vertebrates during extreme desert conditions

Deserts exhibit extreme climatic conditions. Small desert-dwelling vertebrates have physiological and behavioral adaptations to cope with these conditions, including the ability to seek shelter. We investigated the temperature (T) and relative humidity (RH) regulating properties of the soil cracks that characterize the extensive cracking-clay landscapes of arid Australia, and the extent of their use by 2 small marsupial species: fat-tailed and stripe-faced dunnarts (Sminthopsis crassicaudata and Sminthopsis macroura). We measured hourly (over 24-h periods) the T and RH of randomly-selected soil cracks compared to outside conditions, during 2 summers and 2 winters. We tracked 17 dunnarts (8 Sminthopsis crassicaudata and 9 Sminthopsis macroura) to quantify their use of cracks. Cracks consistently moderated microclimate, providing more stable conditions than available from non-crack points, which often displayed comparatively dramatic fluctuations in T and RH. Both dunnart species used crack shelters extensively. Cracks constitute important shelter for small animals during extreme conditions by providing a stable microclimate, which is typically cooler than outside conditions in summer and warmer in winter. Cracks likely play a fundamental sheltering role by sustaining the physiological needs of small mammal populations. Globally, cracking-clay areas are dominated by agricultural land uses, including livestock grazing. Management of these systems should focus not only on vegetation condition, but also on soil integrity, to maintain shelter resources for ground-dwelling fauna.

Novel Consequences of Bird Pollination for Plant Mating

Pollinator behaviour has profound effects on plant mating. Pollinators are predicted to minimise energetic costs during foraging bouts by moving between nearby flowers. However, a review of plant mating system studies reveals a mismatch between behavioural predictions and pollen-mediated gene dispersal in bird-pollinated plants. Paternal diversity of these plants is twice that of plants pollinated solely by insects. Comparison with the behaviour of other pollinator groups suggests that birds promote pollen dispersal through a combination of high mobility, limited grooming, and intra- and interspecies aggression. Future opportunities to test these predictions include seed paternity assignment following pollinator exclusion experiments, single pollen grain genotyping, new tracking technologies for small pollinators, and motion-triggered cameras and ethological experimentation for quantifying pollinator behaviour.

Marsupial population dynamics in a tropical rainforest: intraspecific competition and nonlinear effect of rainfall

Population fluctuations are the result of the combined action of endogenous (feedback structure) and exogenous factors (large- and local-scale climate variables). In this paper, we used a 13-year time series to identify the feedback structure in a population of the brown 4-eyed opossum Metachirus nudicaudatus and to test a hypothesis on the effects of El Niño Southern Oscillation and rainfall using Royama’s theoretical framework. Metachirus nudicaudatus was regulated by a strong 1st-order negative feedback, with intraspecific competition for food resources as the probable factor governing the endogenous system. Contrary to our expectations, El Niño did not explain the marsupial dynamics better than 1-year lagged rainfall, that may operate in 2 different manners: as a nonlinear perturbation effect influencing the strength of density dependence (intraspecific competition and intraguild predation) or as a lateral perturbation effect influencing the carrying capacity of the environment.

As flutuações populacionais são resultado da ação conjunta de fatores endógenos (estrutura de retroalimentação) e exógenos (variáveis climáticas locais e de larga escala). A partir de uma série temporal de 13 anos, nós identificamos a estrutura de retroalimentação da população da cuíca marrom de quatro olhos Metachirus nudicaudatus , e testamos hipóteses a respeito dos efeitos do El Niño Oscilação Sul e chuva utilizando a abordagem teórica de Royama. Metachirus nudicaudatus é regulado por uma forte retroalimentação negativa de primeira ordem, com a competição intraespecífica por recursos alimentares como o provável fator que rege o sistema endógeno. Ao contrário do que esperávamos, o El Niño não explicou a dinâmica populacional deste marsupial melhor do que a chuva com a defasagem de 1 ano, que pode atuar em duas formas: como um efeito de perturbação não-linear, influenciando a força da dependência densidade (competição intraespecífica e predação intraguilda), ou como um efeito de perturbação lateral, influenciando a capacidade de suporte do ambiente.

REVIEW: Can habitat selection predict abundance?

Habitats have substantial influence on the distribution and abundance of animals. Animals' selective movement yields their habitat use. Animals generally are more abundant in habitats that are selected most strongly. Models of habitat selection can be used to distribute animals on the landscape or their distribution can be modelled based on data of habitat use, occupancy, intensity of use or counts of animals. When the population is at carrying capacity or in an ideal-free distribution, habitat selection and related metrics of habitat use can be used to estimate abundance. If the population is not at equilibrium, models have the flexibility to incorporate density into models of habitat selection; but abundance might be influenced by factors influencing fitness that are not directly related to habitat thereby compromising the use of habitat-based models for predicting population size. Scale and domain of the sampling frame, both in time and space, are crucial considerations limiting application of these models. Ultimately, identifying reliable models for predicting abundance from habitat data requires an understanding of the mechanisms underlying population regulation and limitation.

Response of eastern pygmy possums, Cercartetus nanus, to selective logging in New South Wales: home range, habitat selection and den use

Context Selective logging of native forests creates a mosaic of disturbance histories; however, little is known about how different taxa respond to such a mosaic. Aims We followed adaptive-management principles to test logging and burning impacts on eastern pygmy possums, Cercartetus nanus (Geoffroy and Desmarest, 1817), by undertaking a large-scale field experiment that coincided with harvesting. We predicted that home range would increase after logging because of a reduction in resources (food and/or dens) and because hollows suitable for denning would decrease, resulting in greater use of unlogged patches and alternate dens. Methods We radio-tracked C. nanus in a before-and-after logging experiment to investigate home range, habitat selection and den use. We tracked 50 possums, some individuals for a maximum of 8 months, within control, recently logged and regrowth (5 years since logging) sites. Key results Home ranges were variable (0.04–19.5 ha), with males having significantly larger home ranges. We were unable to detect a difference in home-range size between controls and the first year after logging and burning, or regrowth 5 years after logging. Home ranges comprised a mosaic of disturbed and undisturbed areas, and possums did not avoid logged habitat in their home ranges, indicating that logging did not significantly influence habitat selection. We suggest that possums were not sensitive to selective logging and burning because nectar-producing plants are adapted to fire disturbance and because a variety of den sites were used, most commonly in tree hollows and fallen logs, which were commonly left as logging residue. Indeed, possums frequently denned in logged patches, both recently after logging (63% of dens) and in regrowth 5 years after logging (76% of dens). Counts of fallen hollow logs at each site indicated that their density was not reduced by logging, with regrowth sites having the greatest abundance of logs (260 ha–1). Conclusions The mosaic of disturbance created by selective logging operations did not negatively affect home range or den selection of C. nanus. Implications Ecologically sustainable logging practices that include a range of mitigation measures to protect biodiversity can be compatible with the management of threatened species. Assessment of the effectiveness of these methods often will rely on scientific research.