Intraguild relationships between sympatric predators exposed to lethal control: predator manipulation experiments

Abstract

IntroductionTerrestrial top-predators are expected to regulate and stabilise food webs through their consumptive and non-consumptive effects on sympatric mesopredators and prey. The lethal control of top-predators has therefore been predicted to inhibit top-predator function, generate the release of mesopredators and indirectly harm native fauna through trophic cascade effects. Understanding the outcomes of lethal control on interactions within terrestrial predator guilds is important for zoologists, conservation biologists and wildlife managers. However, few studies have the capacity to test these predictions experimentally, and no such studies have previously been conducted on the eclectic suite of native and exotic, mammalian and reptilian taxa we simultaneously assess. We conducted a series of landscape-scale, multi-year, manipulative experiments at nine sites spanning five ecosystem types across the Australian continental rangelands to investigate the responses of mesopredators (red foxes, feral cats and goannas) to contemporary poison-baiting programs intended to control top-predators (dingoes) for livestock protection.ResultShort-term behavioural releases of mesopredators were not apparent, and in almost all cases, the three mesopredators we assessed were in similar or greater abundance in unbaited areas relative to baited areas, with mesopredator abundance trends typically either uncorrelated or positively correlated with top-predator abundance trends over time. The exotic mammals and native reptile we assessed responded similarly (poorly) to top-predator population manipulation. This is because poison baits were taken by multiple target and non-target predators and top-predator populations quickly recovered to pre-control levels, thus reducing the overall impact of baiting on top-predators and averting a trophic cascade.ConclusionsThese results are in accord with other predator manipulation experiments conducted worldwide, and suggest that Australian populations of native prey fauna at lower trophic levels are unlikely to be negatively affected by contemporary dingo control practices through the release of mesopredators. We conclude that contemporary lethal control practices used on some top-predator populations do not produce the conditions required to generate positive responses from mesopredators. Functional relationships between sympatric terrestrial predators may not be altered by exposure to spatially and temporally sporadic application of non-selective lethal control.

Can we save large carnivores without losing large carnivore science?

“…Although such experiments are expensive and difficult to achieve because of the logistical challenges arising from the massive scales that large carnivores utilise, they can and have been done in some places (e.g. Eldridge et al, 2002;Hayes et al, 2003;Hebblewhite et al, 2005;Allen et al, 2013a;Marshall et al, 2013;Allen et al, 2014b;Christianson and Creel, 2014;Ford et al, 2014;Hervieux et al, 2014;Ford et al, 2015b;Mitchell et al, 2015). These have often, but not always, shown support for elements of the MRH, TCH and BMTCH; less so for dingoes (Allen et al, 2014b) but more so for wolves (Winnie and Creel, 2017).…”

More buck for less bang: Reconciling competing wildlife management interests in agricultural food webs

“…Annual rainfall was calculated for the calendar year, January to December. Detailed descriptions of NSA, along with background information on contemporary dingo, kangaroo and cattle management practices are not described here, but can be found elsewhere (Wallis 1997;DEH 2008;Allen 2012;Allen et al 2013a;Allen et al 2014a). Although other means of lethal dingo control (e.g.…”

“…Due to reinvasion, dingo populations usually persist in areas subjected to contemporary control efforts (Allen et al 2013a). However, periods of spatiotemporally intensive control efforts can temporarily suppress dingo population abundances (Fleming et al 2001;Allen et al 2013a). Importantly, dingoes are also thought to suppress kangaroos (Caughley et al 1980;Pople et al 2000;Fillios et al 2010;Letnic and Crowther 2013), one of dingoes' primary prey in arid areas (Corbett and Newsome 1987;Thomson 1992;Allen and Leung 2012).…”

“…Due to reinvasion, dingo populations usually persist in areas subjected to contemporary control efforts (Allen et al 2013a). However, periods of spatiotemporally intensive control efforts can temporarily suppress dingo population abundances (Fleming et al 2001;Allen et al 2013a).…”

Response to Allen ‘An alternative hypothesis to the conclusion of Colmanet al. (2014)’

“…Allen [1] focuses on the activity of dingoes being influenced by the timing of poison baiting campaigns. Allen [1] contends that these only reduce dingo abundance in the short term (less than 1 year) and that rapid invasion of dingoes can occur soon after [3], (but see [4]). Allen [1] inappropriately used paired t-tests to analyse data from the electronic supplementary material of Colman et al [2] to argue that dingo activity and fox activity did not differ between baited and unbaited pairs.…”