Hania Lada

Distinguishing past from present gene flow along and across a river: the case of the carnivorous marsupial (Antechinus flavipes) on southern Australian floodplains

Humans have altered many floodplain ecosystems around the world by clearing vegetation, building towns and regulating river flows. Studies discerning gene flow and population structure of floodplain-dwelling animals are rare yet are necessary for understanding the effects of human actions on native populations. In south-eastern Australia, the yellow-footed antechinus (Antechinus flavipes) is the only carnivorous marsupial on many lowland floodplains, yet our knowledge of impacts of human activities is limited. The control region of mitochondrial DNA and 11 microsatellite DNA markers were used to explore historic and current gene flow in A. flavipes across and along the Murray River. Simulations were carried out to test different migration models. We found evidence for historic gene flow along and across the river but inferred that small towns and farmland or cleared floodplain sections restricted current gene flow along the river. Populations along the river appear to be isolated, and should be maintained at large enough sizes to avoid genetic problems such as inbreeding depression and loss of evolutionary potential. We also investigated whether 50-year-long maintenance of high water levels for irrigation in summer, at the time of juvenile dispersal, has led to restrictions in gene flow across the river. We found no evidence for restrictions to gene flow across the river and suggest that large floods and dropping tree branches may aid dispersal across the river.

Responses of a Carnivorous Marsupial (Antechinus Flavipes) to Local Habitat Factors in Two Forest Types

Abstract Ecosystems around the world have been degraded or destroyed by human activities, including regulation of river flows, clearance of vegetation, and removal of fallen timber. In southeastern Australia much of the original vegetation was converted to farmland. Remaining forests such as hilly box–ironbark and floodplain river red gum (Eucalyptus camaldulensis) are mostly regrowth. The yellow-footed antechinus (Antechinus flavipes) inhabits both types of forests and is the only small, native, carnivorous mammal on most floodplains in southeastern Australia. In this region, frequency of flooding has been reduced by regulation of river flows, which has led to decline in conditions favorable for flood-adapted terrestrial and aquatic organisms. Here, we compared numbers of A. flavipes in box–ironbark forests, and in river red gum forests that were deprived of floods; partially inundated with environmental flows; flooded naturally; and watered in large, artificial floods. We found that abundance of A. flavipes on floodplains and in box–ironbark forests increased with larger volumes of fallen timber and with greater numbers of large, old trees. In river red gum forests, numbers of 2nd-year females increased with proximity to flood locations. For conservation purposes, we recommend preservation of large trees, restoration of fallen timber on forest floors, and spring flooding of floodplains.

Genetic reconstruction of the population dynamics of a carnivorous marsupial (Antechinus flavipes) in response to floods

Human activities such as regulating river flows, logging and removing fallen timber adversely affect floodplain ecosystems around the world. Studies of the dynamics of floodplain‐dwelling populations will help to understand the effects of altered flood regimes and to manage and restore floodplains. The yellow‐footed antechinus (Antechinus flavipes) is the only small, native, carnivorous mammal (Marsupialia) on many degraded floodplains in south‐eastern Australia, where its abundance appears to increase with proximity to floods, which is partly due to enhanced survival (as inferred from increased abundance of second‐year females). We analysed population genetic patterns and maternity among samples collected following the period of postnatal dispersal, in the years preceding and following planned floods, at different distances from flood locations along the Murray River. Our genic and genotypic analyses of mitochondrial DNA (mtDNA) control region haplotypes and 11 microsatellite loci demonstrated high immigration rates into sites in close proximity to floods. All sampled males emigrated from their natal sites to points of capture, while some females were philopatric. There were high rates of dispersal of males among all sites within a partially flooded forest, while females dispersed more to locations closest to inundations rather than to distant places. These results suggest that environmental flows are beneficial to antechinus both by enhancing adult survival and promoting dispersal of females.

Potential future scenarios for Australia's native biodiversity given on-going increases in human population

Most natural assets, including native biodiversity (our focus), are under increasing threat from direct (loss of habitat, hunting) and indirect (climate change) human actions. Most human impacts arise from increasing human populations coupled with rises in per capita resource use. The rates of change of human actions generally outpace those to which the biota can respond or adapt. If we are to maintain native biodiversity, then we must develop ways to envisage how the biota may be affected over the next several decades to guide management and policy responses. We consider the future for Australias native biodiversity in the context of two assumptions. First, the human population in Australia will be 40million by 2050, which has been mooted by federal government agencies. Second, greenhouse gas emissions will track the highest rates considered by the Intergovernmental Panel on Climate Change. The scenarios are based on major drivers of change, which were constructed from seven key drivers of change pertinent to native biodiversity. Five scenarios deal with differing distributions of the human population driven by uncertainties in climate change and in the human responses to climate change. Other scenarios are governed largely by global change and explore different rates of resource use, unprecedented rates of technological change, capabilities and societal values. A narrative for each scenario is provided. The set of scenarios spans a wide range of possible future paths for Australia, with different implications for the future of native biodiversity.

A method to identify drivers of societal change likely to affect natural assets in the future, illustrated with Australia's native biodiversity

Human society has a profound adverse effect on natural assets as human populations increase and as global climate changes. We need to envisage different futures that encompass plausible human responses to threats and change, and become more mindful of their likely impacts on natural assets. We describe a method for developing a set of future scenarios for a natural asset at national scale under ongoing human population growth and climate change. The method involves expansive consideration of potential drivers of societal change, a reduction of these to form a small set of key drivers to which contrasting settings are assigned, which we use to develop a set of different scenarios. We use Australias native biodiversity as the focus to illustrate the method.

Relating demographic characteristics of a small mammal to remotely sensed forest-stand condition.

Many ecological systems around the world are changing rapidly in response to direct (land-use change) and indirect (climate change) human actions. We need tools to assess dynamically, and over appropriate management scales, condition of ecosystems and their responses to potential mitigation of pressures. Using a validated model, we determined whether stand condition of floodplain forests is related to densities of a small mammal (a carnivorous marsupial, Antechinus flavipes) in 60 000 ha of extant river red gum (Eucalyptus camaldulensis) forests in south-eastern Australia in 2004, 2005 and 2011. Stand condition was assessed remotely using models built from ground assessments of stand condition and satellite-derived reflectance. Other covariates, such as volumes of fallen timber, distances to floods, rainfall and life stages were included in the model. Trapping of animals was conducted at 272 plots (0.25 ha) across the region. Densities of second-year females (i.e. females that had survived to a second breeding year) and of second-year females with suckled teats (i.e. inferred to have been successful mothers) were higher in stands with the highest condition. There was no evidence of a relationship with stand condition for males or all females. These outcomes show that remotely-sensed estimates of stand condition (here floodplain forests) are relatable to some demographic characteristics of a small mammal species, and may provide useful information about the capacity of ecosystems to support animal populations. Over-regulation of large, lowland rivers has led to declines in many facets of floodplain function. If management of water resources continues as it has in recent decades, then our results suggest that there will be further deterioration in stand condition and a decreased capacity for female yellow-footed antechinuses to breed multiple times.

Historic and current genetic population structure in two pond-dwelling macroinvertebrates in massively altered Australian woodland landscapes.

Aquatic ecosystems around the world have been massively altered through vegetation clearance and changed flow regimes accompanying agricultural development. Impacts may include disrupted dispersal for aquatic species. We investigated this in lentic (standing) waterbodies in agricultural and predominantly forested landscapes of the box-ironbark region of central Victoria, Australia. We hypothesised that higher representation in forested than agricultural landscapes (i.e. ‘forest-bias’) for a species may reflect an ability to disperse more easily through the former, resulting in lower genetic structure in forested than in agricultural landscapes. Conversely, ‘cosmopolitan’ species would show no difference in genetic structure between landscape types. Molecular genetic analyses of a forest-biased diving beetle, Necterosoma wollastoni, and a cosmopolitan waterboatman, Micronecta gracilis, revealed the following, for both species: (1) no evidence for long-term barriers to gene flow in the region, (2) lack of contemporary genetic differentiation over 30 000 km2 and (3) random distribution of related genotypes in space, implying that neither forest nor farmland inhibits their dispersal in a concerted fashion. Taken together, these results indicate very high gene flow and dispersal in the past and present for both these species. Massive landscape change may have little impact on movement patterns of lentic invertebrates that have evolved high dispersal capabilities.

Polymorphic nuclear markers for aquatic macroinvertebrates Anisops hackeri, Micronecta gracilis and Necterosoma wollastoni

In Australia, aquatic macroinvertebrates have faced massive changes to their habitats because of human actions. Here, we have developed nuclear, polymorphic markers for the waterboatmen Micronecta gracilis (Hemiptera), a backswimmer Anisops hackeri (Hemiptera), and a diving beetle Necterosoma wollastoni (Coleoptera). These markers will allow us to study gene flow and genetic diversity in these species in massively altered forested and agricultural landscapes.