A project undertaken at the Centre for Integrative Ecology, Deakin University, and supervised by Thomas Newsome and Euan Ritchie
Background
Carrion is an important resource that affects many aspects of community ecology. It can influence species diversity and contributes to nutrient cycling. Despite the community-wide effects of this resource, carrion ecology remains understudied, and research is primarily northern-hemisphere based. Our project will address this gap, as it investigates how carrion shapes ecological communities in Australia. Specifically, we will explore how carrion is used by carnivores, and will further examine the effects of carrion on detritivores and soil nutrients. This research will provide insight into the role of carrion in Australian food-webs and will contribute to carrion management in Australia.
Figure 1. Feral pigs scavenging a kangaroo carcass in Kosciuszko National Park, NSW.
Figure 2. Dingoes scavenging a kangaroo carcass in the Simpson Desert, QLD.
Figure 3. Wedge-tailed eagles fighting over a carcass in the Wolgan Valley, Blue Mountains, NSW.
Figure 4. An invasive red fox feeding on a carcass in the Wolgan Valley, Blue Mountains, NSW.
Figure 5. Carrion beetle (Silphidae sp.) larvae on a kangaroo carcass in Kosciuszko National Park, NSW.
Figure 6. Eastern golden-haired blowfly (Calliphora stygia) captured in pitfall traps with mutilation evident in the form of decapitation (i.e. removal of their heads).
Figure 7. PhD student Emma Spencer setting up a carcass site with remote monitoring camera in the Simpson Desert, QLD.
Figure 7. Potential interactions between European wasps, blowflies and native and invasive vertebrate scavengers when European wasps are present in the system. The arrows show the direction of the interactions, and the (−) or (+) signs indicate whether the interaction decreases or increases, respectively, in the presence of wasps. Solid lines indicate direct interactions with the wasp, while dotted lines show the indirect (cascading) effects of wasp presence on other species.
Aims
Because there is little understanding of the role of carrion in Australian ecosystems, our project has the following fundamental and applied scientific objectives:
1) Determine the extent to which different predator guilds use carrion resources within the landscape;
2) Examine the interactions that occur between different predator species at carrion sites;
3) Examine the factors that influence the use of carrion by different predators;
And,
4) Assess the extent to which detritivores use carrion and whether there are any flow-on effects to soil properties (soil fertility and chemistry).
Upon establishing this foundational study, it is our aim that our research will provide capacity for and inform broader and more complex ecological studies into the role of carrion in Australian food-webs.
Outcomes to date
Over the past three years we have monitored over 200 animal carcasses across three spatially distinct ecoregions, the Wolgan Valley, in the Blue Mountains, NSW (a forest ecoregion), Kosciuszko National Park, NSW (an alpine ecoregion) and the Simpson Desert, QLD (a desert ecoregion). We have collected and sorted through over a million camera images, which we are using to determine the incidence of scavenging by vertebrate species, as well as the interactions shared between these different species around carcasses. We have also sorted through hundreds of pitfall traps used to sample insect scavengers and detritivores, to determine how insect assemblages around carcasses change across different landscapes and stages of carcass decomposition. Finally, we have also collected hundreds of soil samples and mapped the longer-term changes in vegetation due to the nutrient influx produced by animal carcasses.
Thus far we have documented several interesting trends in vertebrate scavenging patterns across Australia. Namely, we have observed high activity of invasive animals on the monitored carcasses. This included feral pigs and European wasps in Kosciuszko National park, red foxes in the Wolgan Valley, and red foxes and feral cats in the Simpson Desert. We have produced a peer-reviewed manuscript on our findings around invasive wasp scavenging in Kosciuszko, which was particularly interesting as it appeared that the wasps were excluding key native vertebrate such as the dingo and decapitating the heads of insect scavengers, including the golden-haired blowfly (Calliphora stygia; Spencer et al., 2020a). Another interesting finding was the presence of extensive scavenging by feral cats in the Simpson Desert, with one cat consuming a large part of a kangaroo carcass.
As we anticipated, vertebrate scavenging efficiency differed widely across the study seasons, with invertebrates (e.g. maggots, beetles, ants) generally outcompeting vertebrates in the warm seasons. Because of this, carcasses disappeared rapidly in warmer seasons, generally only lasting a week or two compared to the months they sometimes persisted in the cool seasons. We also found that scavenging by larger animals such as the dingo may play an important role in carcass removal too (an important ecological process that contributes to ecosystem and human health by reducing the spread of pathogens; Spencer et al., 2020b).
Habitat primarily impacted the avian scavengers, as they relied on sight to detect carcasses. Most birds arrived at carcasses more slowly when the carcasses were positioned under tree cover. Mammals such as the dingo, on the other hand, relied on scent and were able to find carcasses with similar efficiency regardless of habitat type. These findings, among others, provide the most comprehensive understanding of the role of carrion in Australian food webs.
In a global context, our data is also contributing to research examining global patterns of vertebrate scavenger assemblages (e.g. Sebastián‐González et al., 2020). This collaborative research has shown that vertebrate scavenger assemblages are driven largely by anthropogenic disturbances (i.e. human activity) and ecosystem productivity worldwide, with reduced functionality of scavenger groups (i.e. carcasses are removed more slowly by scavengers) occurring in more disturbed environments.