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Yearly Archives: 2017
In a recent paper we explored whether the expansion of golden jackal populations in Europe is linked to the widespread extirpation of the grey wolf.
Below is a copy of the abstract and you can view the open access paper HERE
Top-down suppression by apex predators can limit the abundance and spatial distribution of mesopredators. However, this phenomenon has not been studied over long time periods in human-dominated landscapes, where the strength of this process might be limited. Here, we used a multi-scale approach to analyse interactions between two canids in the human-dominated landscapes of Europe. We tested the hypothesis that the range expansion of golden jackals (Canis aureus) was triggered by intensive persecution and resulting decline of the apex predator, the grey wolf (Canis lupus). To do so, we (1) reviewed literature to reconstruct the historic changes in the distribution and abundance of the two canid species on the continental scale, (2) analysed hunting data patterns for both species in Bulgaria and Serbia, and (3) surveyed jackal persistence in eight study areas that became re-colonized by territorial wolves. The observed trends were generally consistent with the predictions of the mesopredator release hypothesis and supported the existence of top-down suppression by wolves on jackals. We observed inverse patterns of relative abundance and distribution for both canid species at various spatial scales. In most (seven out of eight) cases of wolf re-colonization of jackal territories, jackals disappeared or were displaced out or to the periphery of the newly established wolf home-ranges. We suggest that wolf extermination could be the key driver that enabled the expansion of jackals throughout Europe. Our results also indicate that top-down suppression may be weakened where wolves are intensively persecuted by humans or occur at reduced densities in human-dominated landscapes, which has important management implications and warrants further research.
The arguments focused on two key points:
- That dingo reintroduction proposals have been inspired largely by the reintroduction of wolves into Yellowstone National Park.
- That unstable climates in Australia will make if difficult for dingoes to exert strong effects on ecosystems via trophic cascades.
(see here for a definition of a trophic cascade, and below for an example of a dingo-induced trophic cascade).
In a paper published in the journal Food Webs, we responded to these criticisms and argued that (1) the case for dingo reintroduction has never been solely based on the reintroduction of wolves into Yellowstone National Park, and (2) that the climatic circumstances under which dingoes can provide net positive effects on ecosystems via trophic cascades are those that typically prevail in Australia.
We concluded that the case for dingo reintroduction in Australia remains strong, and urge managers and decision makers to consider the mounting evidence that dingoes can have positive effects on ecosystems before deciding whether or not to reintroduce dingoes into ecosystems where they have been extirpated by humans.
A dingo-induced trophic cascade (solid arrows).
If dingoes suppress large herbivores (e.g. kangaroos and emus), then grass and herb biomass is expected to increase. If dingoes suppress lower order predators (e.g. foxes and cats), then numbers of small mammals (e.g. mice), reptiles (e.g. goannas), and birds (e.g. parrots) are expected to increase. Invertebrates also may respond to improved vegetation conditions and contribute to soil quality. However, the strength of all interactions may be influenced by the extent of rainfall and fires (hashed arrows). Numbers represent the predicted sequence of events based on trophic cascade theory.
Since my last post I have been a co-author on two research papers on feral cats.
1. Legge S, et al (including Newsome TM) (2017) Enumerating a continental-scale threat: how many feral cats are in Australia? (Biological Conservation)
In this paper we found that feral cats cover over 99.8% of Australia’s land area, including almost 80% of the area of our islands.
“Australia’s total feral cat population fluctuates between 2.1 million when times are lean, up to 6.3 million when widespread rain results in plenty of available prey,” explains the lead author Dr Sarah Legge from The University of Queensland.
Furthermore, cat densities were found to be the same both inside and outside conservation reserves, such as National Parks, showing that declaring protected areas alone is not enough to safeguard our native wildlife.
This paper has now become the most heavily ‘e-cited’ paper in the journal Biological Conservation.
A full summary of the media generated can be found HERE
2. Molsher R, Newsome AE, Newsome TM, Dickman CR (2017) Mesopredator management: effects of red fox control on the abundance, diet and use of space by feral cats (PLOS ONE)
In this paper we investigated interactions between red foxes and feral cats in south-eastern Australia.
We used a fox-removal experiment to assess whether foxes affect cat abundance, diet, home-range and habitat use.
The results provide little indication that cats responded numerically to the fox removal, but suggest that the fox affects some aspects of cat resource use. In particular, where foxes were removed cats increased their consumption of invertebrates and carrion, decreased their home range size and foraged more in open habitats.
The results suggest that fox control programs could lead to changes in the way that cats interact with co-occurring prey, and that some prey may become more vulnerable to cat predation in open habitats after foxes have been removed.
The paper was featured in the NRM Research and Innovation Network weekly updates.