The use of time and space by male and female gerbils exploiting a pulsed resource

Social behaviour and foraging success of little egrets (Egretta garzetta)

Intraspecific interactions among predators can change the game between a predator and its prey. Individuals of different size or sex can differ in their responses to conspecific competitors. We studied intraspecific interactions among pairs of little egrets (Egretta garzetta) while foraging on responsive prey (comet goldfish, Carassius auratus). Testing little egrets in an artificial patchy environment both singly and while engaged in social forging in pairs (male & female) at two prey densities, allowed us to explore individual differences in foraging success. We found sexual dimorphism with males being bigger and more aggressive than females. However, female foraging success was positively affected by the time they spent foraging with a conspecific male, suggesting they might be able to mitigate male aggressiveness with an indirect positive interaction. Despite the presence of direct interactions between individuals in the pair, egret foraging success was not affected by such interactions, nor by prey density. Our results demonstrate the importance of sex and an individual's ability to adjust its social behaviour based on the behaviour of others in this predator-prey foraging game.

Advances in population ecology and species interactions in mammals

The study of mammals has promoted the development and testing of many ideas in contemporary ecology. Here we address recent developments in foraging and habitat selection, source–sink dynamics, competition (both within and between species), population cycles, predation (including apparent competition), mutualism, and biological invasions. Because mammals are appealing to the public, ecological insight gleaned from the study of mammals has disproportionate potential in educating the public about ecological principles and their application to wise management. Mammals have been central to many computational and statistical developments in recent years, including refinements to traditional approaches and metrics (e.g., capture-recapture) as well as advancements of novel and developing fields (e.g., spatial capture-recapture, occupancy modeling, integrated population models). The study of mammals also poses challenges in terms of fully characterizing dynamics in natural conditions. Ongoing climate change threatens to affect global ecosystems, and mammals provide visible and charismatic subjects for research on local and regional effects of such change as well as predictive modeling of the long-term effects on ecosystem function and stability. Although much remains to be done, the population ecology of mammals continues to be a vibrant and rapidly developing field. We anticipate that the next quarter century will prove as exciting and productive for the study of mammals as has the recent one.

Everybody loses: intraspecific competition induces tragedy of the commons in Allenby's gerbils

Interference competition may lead to a tragedy of the commons in which individuals driven by self-interest reduce the fitness of the entire group. We investigated this hypothesis in Allenby's gerbils, Gerbillus andersoni allenbyi, by comparing foraging behaviors of single vs. pairs of gerbils. We recorded strong interference competition within the foraging pairs. Competition reduced the amount of time the gerbils spent foraging, as well as foraging efficiency since part of the foragers' attention was directed toward detecting competitors (apparent predation risk). Single gerbils harvested significantly more food than the combined efforts of two gerbils foraging together. Competition reduced the success of both individuals within a pair by more than 50%, making this a case of the tragedy of the commons where each individual's investment in competition reduces the success of all individuals within the group, including its own. Despite their great costs, competitive behaviors will be selected for as long as one individual achieves higher fitness than the other. In nature, interspecific interactions, such as predation risk, may act to reduce and regulate the deleterious effects of intraspecific competition.

Microhabitat use and foraging behaviour of Sminthopsis youngsoni (Marsupialia:Dasyuridae) in arid central Australia

In this study, fluorescent pigment tracking was used to determine the microhabitat use and foraging behaviour of a small insectivorous marsupial, Sminthopsis youngsoni (the lesser hairy-footed dunnart), in the dunefields of the Simpson Desert, south-western Queensland. In total, 25 successful trails were traced over the duration of this study, between March 1996 and April 1998. Nocturnal foraging trails were identified, then the distance travelled by the dunnart through each microhabitat type (nine in all) was measured and accumulated for each trail and compared with surrounding available microhabitats along control trails. This provided an index of selectivity of microhabitat use. Terrestrial invertebrates were collected from both actual and control trails to measure food availability. Dunnarts strongly selected open microhabitats when foraging, with the periphery of spinifex hummocks (up to 20 cm from the edge of a spinifex hummock) being favoured. Spinifex itself was avoided unless shelter was sought (i.e. immediately after release). Potential invertebrate prey captured along the actual trails travelled by dunnarts tended to occur in greater numbers and were larger than those captured along the control trails, indicating that dunnarts can accurately locate resource-rich areas in which to forage. Clearly, the foraging strategies used by this species enable it to successfully exploit patchy and unpredictable food resources, thereby ensuring its continued persistence and relative abundance in an unstable environment.