Resource pulses and mammalian dynamics: conceptual models for hummock grasslands and other Australian desert habitats

Abstract

Resources are produced in pulses in many terrestrial environments, and have important effects on the population dynamics and assemblage structure of animals that consume them. Resource-pulsing is particularly dramatic in Australian desert environments owing to marked spatial and temporal variability in rainfall, and thus primary productivity. Here, we first review how Australia's desert mammals respond to fluctuations in resource production, and evaluate the merits of three currently accepted models (the ecological refuge, predator refuge and fire-mosaic models) as explanations of the observed dynamics. We then integrate elements of these models into a novel state-and-transition model and apply it to well-studied small mammal assemblages that inhabit the vast hummock grassland, or spinifex, landscapes of the continental inland. The model has four states that are defined by differences in species composition and abundance, and eight transitions or processes that prompt shifts from one state to another. Using this model as a template, we construct three further models to explain mammalian dynamics in cracking soil habitats of the Lake Eyre Basin, gibber plains of the Channel Country, and the chenopod shrublands of arid southern Australia. As non-equilibrium concepts that recognise the strongly intermittent nature of resource pulsing in arid Australia, state-and-transition models provide useful descriptors of both spatial and temporal patterns in mammal assemblages. The models should help managers to identify when and where to implement interventions to conserve native mammals, such as control burns, reduced grazing or predator management. The models also should improve understanding of the potential effects of future climate change on mammal assemblages in arid environments in general. We conclude by proposing several tests that could be used to refine the models and guide further research.

Ecology and predator associations of the northern quoll (Dasyurus hallucatus) in the Pilbara

“…My results support the hypothesis that rocky habitats represent a refuge from introduced predators for threatened northern Australian mammals and in arid environments, although they are not necessarily the highest quality habitat on other dimensions (Letnic and Dickman 2010;Start et al 2007;Woinarski et al 2011). …”

“…Yang et al (2010) noted stronger responses for primary consumers around the world such as omnivores, granivores, and herbivores. In Australia, Letnic and Dickman (2010) noted that herbivores and omnivores responded more immediately to drought-breaking pulses than did carnivorous marsupials; Rodentia (rodents), Peramelidae (bandicoots), Potoroidae (bettongs and potoroos), and Macropodidae (kangaroos) responded more strongly than Dasyuridae (carnivorous marsupials). Similarly, in the Simpson Desert in western Queensland, Greenville et al (2016) showed that rodent abundance was tightly linked to rainfall because rodents respond opportunistically to rain at any time of year, but this was not the case for dasyurids in the genera Dasycercus, Sminthopsis, and Ningaui.…”

Aboriginal hunting buffers climate-driven fire-size variability in Australia’s spinifex grasslands

“…As ENSOdriven bust periods increase mammalian dispersal distances simultaneously with an increase in fire size, buffering such effects could substantially reduce mortality through both predation and resource limitation, mitigating declines and species extinction among mammals in the critical weight range (50-3,000 g), most of which have occurred in desert regions (17,26). If Aboriginal fire regimes do buffer climate-driven variability in fire size, then the deterioration of Aboriginal fire mosaics following their removal from the desert around the mid-20th century (15) likely explains observed increases in catastrophic fires and subsequent declines and extinctions of many small-to medium-sized mammal populations (27,28), and provides a strategy to mediate these effects in the future.…”

Top‐down limitation of mesopredators by avian top predators: a call for research on cascading effects at the community and ecosystem scale

“…However, bottom-up factors, such as food availability and habitat structure, can also influence predator-prey interactions (Ritchie & Johnson 2009). For example, resource abundance can temporarily allow prey populations to escape predator regulation and decouple interactions between predators (Letnic & Dickman 2010).…”