Can diet niche partitioning enhance sexual dimorphism?

Classic evolutionary theory suggests that sexual dimorphism evolves primarily via sexual and fecundity selection. However, theory and evidence are beginning to accumulate suggesting that resource competition can drive the evolution of sexual dimorphism, via ecological character displacement between sexes. A key prediction of this hypothesis is that the extent of ecological divergence between sexes will be associated with the extent of sexual dimorphism. As the stable isotope ratios of animal tissues provide a quantitative measure of various aspects of ecology, we carried out a meta-analysis examining associations between the extent of isotopic divergence between sexes and the extent of body size dimorphism. Our models demonstrate that large amounts of between-study variation in isotopic (ecological) divergence between sexes is nonrandom and may be associated with the traits of study subjects. We, therefore, completed meta-regressions to examine whether the extent of isotopic divergence between sexes is associated with the extent of sexual size dimorphism. We found modest but significantly positive associations across species between size dimorphism and ecological differences between sexes, that increased in strength when the ecological opportunity for dietary divergence between sexes was greatest. Our results, therefore, provide further evidence that ecologically mediated selection, not directly related to reproduction, can contribute to the evolution of sexual dimorphism.

Multiscale nest-site selection of ducks in the western boreal forest of Alberta

There is limited data regarding the nesting ecology of boreal ducks and their response to industrial development, despite this region being an important North American breeding area. We investigated how landcover and oil and gas development affect third-order nest-site selection of boreal ducks. We located duck nests in Alberta's western boreal forest between 2016 and 2018. We used multiscale analysis to identify how scale affects the selection of a resource using generalized linear mixed-effects models and determined what scale-optimized combination of landscape features were most important in describing where ducks nest. We located 136 nests of six species of upland nesting ducks between 2016 and 2018. The magnitude, direction, and best spatial scale varied by resource. For landcover, ducks selected nest-sites associated with mineral wetlands (300 m) and open water (300 m). Ducks avoided greater densities of seismic lines (300 m) and pipelines (2500 m) but selected nest-sites associated with borrow pits (300 m) and roads (1000 m). We used our models to predict important duck nesting habitat in the boreal forest, which can support conservation and management decisions. We recommend conservation actions target the conservation of mineral wetlands and associated habitats within this working landscape. Further research is necessary to understand the adaptive consequences of nest-site selection and how industrial development influences important nest predators.

Balancing stakeholder interests in kangaroo management – historical perspectives and future prospects

Kangaroos are commercially harvested in five mainland states of Australia, with the harvest regulated by state government wildlife management agencies and overseen by the Commonwealth government. Non-commercial culling is permitted, and although most kangaroos have traditionally been taken by the commercial kangaroo harvesting industry, the proportion taken non-commercially has increased in recent years. Management plans that guide the regulation of the harvest support the management objectives of wildlife management agencies and the kangaroo industry, but the plans do not successfully address the objectives of other stakeholders including pastoralists and animal protection groups, which focus on minimising the grazing impacts of kangaroos and animal welfare issues respectively. We reviewed the objectives outlined in the management plans for kangaroos in the Australian rangelands and examined alternative systems for managing natural resources to identify if improvements to management could be made. Current management plans for kangaroos principally use fixed harvest rates that are responsive only to the state of the kangaroo population and not to changes in the environments in which kangaroos live. This type of management is reactive, and opportunities for improving management of the environment are limited. A viable alternative is active adaptive management which focuses on explicit measurement of the response of the natural system to management actions and use of this information to modify interventions to better meet management objectives. Active adaptive management is appropriate when management actions can strongly influence system state but the impacts of management are uncertain. We argue that the management of kangaroos and the environments in which they live would benefit from the adoption of an active adaptive management approach by wildlife management agencies.

Evaluating wildlife management by using principles of applied ecology: case studies and implications

Context The broad concepts and generalisations that guide conduct of applied ecology, including wildlife management, have been reviewed and synthesised recently into 22 prescriptive and three empirical principles. Aims The aim of this study was to use these principles to evaluate three on-ground wildlife management programs and assess the utility of the principles themselves. Key results Case studies of long-term management of national park biodiversity impacted by feral pigs (Sus scrofa), and of conservation and harvest of red kangaroos (Macropus rufus) and mallards (Anas platyrhnchos), were selected to provide a representative range of management objectives, spatial scales and land tenures, and to include both native and introduced species. Management documents and a considerable scientific literature were available for all three programs. The results highlight similarities and differences among management activities and demonstrate the 25 principles to differing degrees. Most of the prescriptive principles were demonstrated in both the management and the scientific literature in all three programs, but almost no use was made of the three empirical principles. We propose that use of the prescriptive principles constitutes evidence that these programs meet both societal and scientific expectations. However, the limited use of the empirical principles shows gaps in the three programs. Conclusions The results suggest that evaluating other wildlife management programs against the principles of applied ecology is worthwhile and could highlight aspects of those programs that might otherwise be overlooked. Little use was made of the empirical principles, but the the Effort–outcomes principle in particular provides a framework for evaluating management programs. Implications The effort–outcomes relationship should be a focus of future applied research, and both prescriptive and empirical principles should be integrated into wildlife management programs.