The Arthur Rylah Institute (ARI) and the Department of Environment, Land, Water and Planning (Victoria) has been highlighting recent research on invasive species as part of National Science Week. The following summarises the research and findings, with the full article published in the Journal of Applied Ecology.
Predators and prey: does rabbit control reduce the abundance of foxes?
It’s long been an important question in ecology – do predators control prey species, or does the abundance of a prey species control the abundance of a predator by influencing its food availability? And what happens when both are invasive species, such as the European Rabbit and Red Fox in Australia?
It’s also a question that has direct relevance to management. Managers often advocate controlling invasive prey in the belief that this will also reduce predator abundance. In practical terms, will control of rabbits reduce the numbers of foxes, and thereby reduce the detrimental effect of both species on farming systems and biodiversity?
This is the issue that Mike Scroggie and colleagues at ARI set out to test, using long-term data (from 1998 to 2015) on the abundance of rabbits and foxes, collected from spotlight surveys at 21 transects in rural locations widely scattered across Victoria. These transects were established to monitor the effects of the RHD virus on rabbit populations. Many of the locations were also targeted for intensive rabbit control via ripping warrens.
As expected, their analysis showed that rabbit abundance was substantially reduced by control measures. There was little response of rabbits to rainfall, but there were higher rates of increase in the autumn-spring interval, and negative density-dependence (i.e. population growth slowed as density increased). But it was the results for foxes that were most surprising! The rate of increase in fox populations was not related to rabbit abundance. Although rabbits are a common prey of foxes, it may be that foxes can effectively ‘switch’ to other prey when rabbit numbers are low. Rather, fox populations increased after high rainfall, and they too showed negative density dependence.
The conclusion from this research is that controlling rabbits to a low abundance does not substantially reduce fox abundance in south-eastern Australia. Rather, if we wish to control fox abundance, it’s necessary to undertake management actions that deliberately target fox populations.
Published in a highly regarded international journal, this work is likely to attract attention worldwide. Managing invasive predators and prey is a global issue.
Reference: Scroggie, M.P., Forsyth, D.M., McPhee, S.R., Matthews, J., Stuart, I.G., Stamation, K.A., Lindeman, M. and Ramsey, D.S.L. 2018. Invasive prey controlling invasive predators? European rabbit abundance does not determine red fox population dynamics. Journal of Applied Ecology (online early).