Diana Fisher

The speed of animal extinction

A section of this project would be suitable for an honours or conservation masters project.

The three main categories of past extinction causes are invasive species, habitat loss, and over-exploitation. The project would test if mean lag times between invasive predator arrival and extinction is more rapid than mean lag times between habitat loss and extinction, for species with one main identified cause of extinction (an invasive predator vs habitat loss). Adult individuals can sometimes persist for long periods in habitat that is poor for recruitment (a mechanism of 'extinction debt'). Extinctions due to invasive predators can be very rapid. For example, the red fox Vulpes vulpes is likely to have been responsible for many of the >30 mammal species extinctions on mainland Australia between the 1860s and 1950s, and the range decline (population extinction) of about 40% of surviving mammal species. Medium-sized mammals declined the most and are the preferred prey size of foxes. Evidence from museum collectors and expeditioners of European descent, and First Nations accounts suggest rapid decline and local extinction of susceptible native mammal species as the fox encountered them in its spread from its introduction site in Victoria northwards and westwards. For example, in early 20th century administrative districts in New South Wales, a detailed study of bettong and fox records showed that bettongs disappeared within five years of fox arrival in each district (Short 1998). Studies in 2018 and 2025 provide detailed coordinates and dated records of the trajectory of fox invasion. I have a database of coordinates and dated records of mammal decline trajectories. This project would analyse the mean and variability of the lag time between fox arrival and population loss of Australian mainland mammals that have declined, and test correlates of this lag time (body size, climate zone, phylogeny etc). Other data sources for this project include the many worldwide island, lake / spring, and mountain-top species eradicated by habitat loss or invasive species with known dates of threat arrival and extinction.

Another aspect of this project could investigate the speed of decline of non-threatened species.

Species with indicators such as small populations or existing range or population decline are more likely to become extinct, so they are placed in a threatened category by the IUCN Red List and national lists- NT, VU, EN, CR, or EX (rather than the non-threatened category LC). However, there are many examples of common species (LC) suddenly declining to extinction or near-extinction without an intervening period passing through progressively higher categories of risk. This project would test if the incidence of species jumping from least concern to critically endangered or extinct is increasing over time, by analysing past Red List categories and the years when species moved from LC to CR or EX and any intervening categories, to test if there is a bias towards later years in species jumping from non threatened to nearly extinct or extinct. It would also test if rates of common species becoming threatened are similar to rates of species moving between threat categories. These rates can tell us if extinction rates are likely to accelerate, improve accuracy of estimates of extinction rate in different taxa, and how much the cost of addressing the extinction crisis is escalating.

We can also compare the rate of movement between categories for different taxonomic groups and regions, and the frequency of skipping categories, which is an indicator of poor knowledge of the status of these species.

Projects on life history evolution including - sexual selection in animals with male-only semelparity

A section of this project would be suitable for an honours or conservation masters project.

An analysis in this paper https://www.pnas.org/doi/10.1073/pnas.1310691110 tested if semelparous marsupials (that reproduce once in a lifetime) have larger testes and longer mating duration than iteroparous marsupials in the same families (that reproduce repeatedly). They did- this is evidence that intense post-mating male competition is a component of the evolution of life history in these taxa. All other animals with male-only semelparity are arthropods. This project would analyse species in Families of ants, bees, mantids and spiders that contain some species with male-only semelparity, to test if greater semelparity (fewer males surviving after mating) is associated with indices of higher male reproductive investment in sperm volume and mate guarding, that indicate intense sperm competition. This project would involve 1) measuring body parts of museum specimens (pedipalp size and body size) as well as specimens of insects and spiders that you collect in the field (pedipalp size, body size, testes size of mature males / spermatophore volume where available), 2) measuring body parts of digital images of insects and spiders from published sources, 3) using published data on testes size in mature males and the loss of body parts during mating, to calculate male investment in mating (testes size accounting for body size, proportion of body mass lost, time). The main analyses are phylogenetic regressions. This project is part of an ARC grant, there is a PhD student and a postdoc in my group working on other aspects of the evolution and implications of animal semelparity. There would be a co-supervisor who is a specialist in behavioural and evolutionary ecology of spiders and insects.

Identifying causes of initial bias to improve the Threatened Species Index

This project would be suitable for an honours or conservation masters project.

Overall Threatened Species Index (TSX) curves and individual time series and taxa show a glitch in the first two or three years- the curve nearly always drops or rises before it settles into a more consistent trajectory (https://tsx.org.au/). This project would test the potential reasons for this. These glitches might be due to a sampling bias artefact related to the choice of initial sampling site. Many studies have addressed spatial bias, such as surveying mainly near roads. Few studies have addressed bias that comes from sampling at certain times in the trajectory of a fluctuating population. Over-sampling of one phase of a fluctuating population (e.g. at a time and place of maximum abundance) is demographic sampling bias. Demographic sampling bias comes from researchers typically choosing thriving populations to study (so that their projects are feasible, or because these are most likely to be detected). In these cases most short term studies will report declines, because fluctuating populations with stable long-term means tend to decline in the short term following a peak (this is 'regression to the mean'). Overestimated declines are also expected if researchers preferentially monitor populations in steady decline and ignore stable ones- this might also be likely in the TSX time series. However, regression to the mean implies that underestimates of decline will ensue if studies focus on recently-declined populations, as these are likely to be in a short term increase phase. This project can use aggregated data to find which curves have which pattern, and understand why this initial glitch occurs. We have access to metadata for the TSX curves and can see which types of studies increase or decrease initially. We might expect that single-species studies might be more likely to initially decline from a peak, and community studies that have not chosen a site based on single species abundance might not show this pattern, as the site was not chosen based on that species. Some researchers provided data later than the start of a long-term study, and some from the start. Birds and mammals would be good data sets to test this.

30 years of macropod population dynamics at Idalia National Park

This project would be suitable for an honours or conservation masters project.

The former grazing property Idalia National Park (western Queensland) was gazetted in 1992, when cattle were removed. From 1993 to 2019, University of Queensland students helped to conduct standardised annual surveys and pasture assessment during the 3rd year course 'outback ecology'. They used distance sampling to estimate abundance of five kangaroo and wallaby species. This included the threatened bridled nailtail wallaby for most of this period. In 1996 there was a translocation of the bridled nailtail wallaby to this site, which failed in 2015. We also have rainfall and predator baiting records. This project would analyse the relative importance of drivers of population change and time lags in macropods of different body size (rainfall, pasture components, and predator control), interpret factors in the failure of the bridled nailtail wallaby reintroduction, and rangeland recovery after grazing removal.