Could controlling mammalian carnivores lead to mesopredator release of carnivorous reptiles?

Abstract

Emerging evidence increasingly illustrates the importance of a holistic, rather than taxon-specific, approach to the study of ecological communities. Considerable resources are expended to manage both introduced and native mammalian carnivores to improve conservation outcomes; however, management can result in unforeseen and sometimes catastrophic outcomes. Varanid lizards are likely to be apex-or mesopredators, but being reptiles are rarely considered by managers and researchers when investigating the impacts of mammalian carnivore management. Instances of mesopredator release have been described for Varanus gouldii as a result of fox and cat management in Australia, with cascading effects on faunal community structure. A meta-analysis showing extensive dietary niche overlap between varanids, foxes and cats plus a review of experimental and circumstantial evidence suggests mesopredator release of V. gouldii and about five other medium to large species of varanid lizard is likely in other regions. This highlights the need for managers to adopt a whole-of-community approach when attempting to manage predators for sustained fauna conservation, and that additional research is required to elucidate whether mesopredator release of varanids is a widespread consequence of carnivore management, altering the intended faunal responses.

Ecological Implications of Reptile Mesopredator Release in Arid South Australia

“…For example an increase in smaller carnivore activity following a reduction in Coyote (Canis latrans) activity in North America resulted in significant declines of a number of bird species (Crooks and Soulé, 1999). Similar relationships have been demonstrated in other terrestrial mammal systems (Elmhagen et al, 2010) and marine ecosystems (Myers et al, 2007;Casini et al, 2008;Baum and Worm, 2009) but until recently have been largely overlooked where reptiles are the mesopredators (Sutherland et al, 2011).…”

An Introduced Competitor Elevates Corticosterone Responses of a Native Lizard (Varanus varius)

“…Weighing up to 14 kg, it is the second-largest native predator (after the dingo [Canis dingo]) in eastern Australia (Weavers 1988;Guarino 2001). Its activity is seasonal, with home range varying from 185 ha in summer to zero in winter, when animals are inactive (Guarino 2002 However, in some habitats there is good evidence for high dietary overlap between native predators and introduced predators (Sutherland et al 2011). Resource overlap could impose resource competition between varanid lizards and introduced carnivores (Sutherland et al 2011;Anson et al 2013).…”

“…Its activity is seasonal, with home range varying from 185 ha in summer to zero in winter, when animals are inactive (Guarino 2002 However, in some habitats there is good evidence for high dietary overlap between native predators and introduced predators (Sutherland et al 2011). Resource overlap could impose resource competition between varanid lizards and introduced carnivores (Sutherland et al 2011;Anson et al 2013). In our study system, adult lace monitors and red fox share extensive dietary overlap in prey, especially for the ringtail possum (Pseudocheirus peregrinus; Triggs et al 1984;Jessop et al 2010).…”

“…In our study system, adult lace monitors and red fox share extensive dietary overlap in prey, especially for the ringtail possum (Pseudocheirus peregrinus; Triggs et al 1984;Jessop et al 2010). Moreover, the approximately eightfold-higher field metabolic rate of the red fox indicates their need to consume a much greater mass of food per capita than lace monitors (Nagy et al 1999;Jessop et al 2010;Sutherland et al 2011). This large energetic disparity further suggests that the red fox can exert very strong resource competition on lace monitors (Sutherland et al 2011).…”

The evolution of jaw mechanism and dental function in heterodont crocodyliforms

“…Significant dietary niche overlap between varanid lizards, foxes and cats has been poited out by Sutherland et al (2011). An interesting example of habitat partitioning has been documented among four extant South American crocodylian species (Caiman crocodylus, Paleosuchus trigonatus, Paleosuchus palpebrosus and Melanosuchus niger; Magnusson 1985).…”