PhD Thesis
The insectivorous marsupial Family Dasyuridae is endemic to Australia and Papua New Guinea. Dasyurids have a variety of life history strategies and are found in a wide range of habitats, latitudes and elevations. This makes them useful for exploring life history evolution, biogeographical patterns and macroecological theory. The life history and persistence of dasyurids are thought to be tightly linked to the distribution of their arthropod prey in space and time, but we currently have a limited understanding of the mechanisms. Arthropods are declining globally, and evidence suggests that climate change is already linked to changes in arthropod availability in the northern hemisphere. Understanding the relationship between insectivorous marsupials and their arthropod prey has become particularly important, as in 2018 two species from the dasyurid genus Antechinus were federally listed as endangered, and populations of other dasyurids appear to be declining across Australia.
The aim of this thesis was to combine biogeography, macroecology and life history to determine what is influencing the distribution and persistence of Australian insectivorous marsupials from the Family Dasyuridae, with a focus on antechinus species in Queensland. I addressed evolution, rarity patterns and phenological relationships between dasyurid marsupials and their arthropod prey.
Chapter 2 investigated how life history traits co-vary and are related to climatic variables, specifically how the evolution of dasyurid life history is related to productivity and predictability, and how environmental drivers are linked to patterns of life history variability. Based on analysis of data on life history characteristics of female dasyurids throughout Australia, there was evidence of two life history axes. The reproductive output axis including litter size and supernumerary young was related to annual rainfall and productivity, while position on the semelparity – iteroparity axis was associated with predictability of rainfall and arthropod availability. These results suggested how climate change might affect dasyurid marsupials and provide a broader understanding of their life history evolution that can be applied in a global context.
Previous global and Australian studies have found that population density in mammals is lower in the tropics than at temperate latitudes. Chapter 3 tested whether dasyurids show a latitudinal gradient in population density, focusing on antechinus population density across latitudes and elevations in Queensland. Data from the literature, combined with intensive trapping and arthropod sampling showed that dasyurids were rarest in the tropics and that antechinus population density was lowest at low latitudes and elevations. Population density was constrained by winter arthropod availability, which was associated with winter rainfall. High elevation sites maintained high arthropod availability throughout the year because they received orographic rainfall. These results help to explain rarity of antechinus species in the seasonal subtropics and tropics, including the Endangered silver-headed antechinus (A. argentus) in central Queensland, and the restricted Atherton antechinus (A. godmani) and rusty antechinus (A. adustus) in far north Queensland. The results also highlight the importance of Australian mountain-tops as refuge areas for insectivorous marsupials.
Chapter 4 focused on timing of breeding and distribution of antechinus species across mountains in Queensland. I used the same data collection approaches as in chapter 3 to determine timing of breeding, evolutionary age of antechinus and arthropod availability across elevations and latitudes. The results demonstrated that antechinus in Queensland do not rely solely on photoperiodic cues to trigger breeding. They are able to use local environmental conditions to time breeding so that lactation coincides with timing of peak arthropod availability. Timing of antechinus breeding and flushes in arthropod availability occurred progressively later as elevation increased. More ancient Antechinus species had small ranges on mountain-tops and less flexible breeding seasons. Taken together, these results suggest that in Queensland, ancient antechinus species restricted to high elevations are likely to be most at risk from climate change, if the timing of peak arthropod availability changes.
This thesis has contributed to life history, biogeography and macroecology theory at large and small spatial scales. It has enhanced our understanding of the relationship between dasyurid marsupials and their arthropod prey, and provided important information that can help us to deduce why certain dasyurids are rarer than others.