Experimental trial of Australian arid zone reptiles as early warning indicators of overgrazing by cattle

Abstract

The value of reptiles as bioindicators of the initial effects of heavy cattle grazing in a South Australian chenopod shrubland was assessed in an experimental trial. Reptiles were sampled in three different subhabitats within two replicate treatment paddocks and a control region. A total of 30 sites was sampled in two sessions before grazing and four sessions after the commencement of intensive pulses of grazing. Capture rates of most common reptile species, fecundity of abundant gecko species and reptile species composition within different subhabitats were largely resilient to the initial effects of overgrazing. However, agamids in general, and particularly Ctenophorus nuchalis, increased at grazed sites relative to controls following grazing. Most changes observed in the reptile assemblages were predictable based upon species response to alteration in vegetation cover. Because vegetation cover can be rapidly and efficiently monitored, the use of reptiles as early warning indicators of unsustainable pastoralism in the study region was not supported.

Small Australian desert vertebrate responses to grazing intensity during La Niña

“…The agamid C. gibba responded positively to greater grazing intensity possibly because of grazinginduced reductions in vegetative cover, which increase opportunities for basking and, therefore, activity associated with higher temperature (Read 2002). While agamids may respond positively to grazing-induced structural changes in habitat in the short term, the longer-term consequences of over-grazing (e.g., potential reductions or other changes in food resources) may be detrimental to their reproduction and survival.…”

“…Consequently, we expected that the assemblage of native small vertebrates would consist mostly of species with a low tolerance to increasing livestock grazing intensity. We expected that dragon lizards (agamids) would increase and skinks (scincids) decrease in abundance based on previous work in the region (Read 2002;Read and Cunningham 2010). Limited information exists for mammalian species and taxa that occur in the area, but we postulated that native rodent and dasyurid species abundance would most likely decrease at more intenselygrazed sites (Read and Cunningham 2010;Frank et al 2013).…”

“…It has been suggested that the ecological consequences of grazing, particularly in north-western America, are substantial, and include changes in the composition of communities and in ecosystem structure, and disturbance to ecosystem function (Fleischner 1994). However, relatively few published studies have examined the effects of livestock grazing on small vertebrate communities in Australian deserts (but see : Read 2002;James 2003;Read and Cunningham 2010), particularly in wet years (see Frank et al 2013). This paucity of knowledge is peculiar considering that Australia supports the largest area (4.4 M km 2 ) of managed grazing land worldwide (Asner et al 2004), and has experienced the largest global mammal extinction rate in the past 200 years (Woinarski and Fisher 2003;Woinarski et al 2015).…”

“…Grazing can have indirect and direct effects on small vertebrates, facilitated by various causal mechanisms. Indirect effects can include habitat modification over time through browsing (Suominen and Danell 2006), which may be particularly detrimental for habitat specialists (Smith et al 1996), but advantageous for some taxa (e.g., agamids; Read 2002). Direct effects can include activities such as destruction of shelter or burrows (e.g., through trampling; Fleischner 1994) and competition for food resources (Evans et al 2006).…”

Herpetofauna da Estação Ambiental de Peti, um fragmento de Mata Atlântica do estado de Minas Gerais, sudeste do Brasil

“…O papel dos répteis como bioindicadores de alterações ambientais não está demonstrado tão definitivamente como no caso dos anfíbios, um grupo mais uniforme em termos de características úteis para a bioindicação. Embora Pianka & Vitt (2003) forneçam exemplos de lagartos como bons indicadores, Read (2002), por exemplo, trabalhando com 43 espécies de Squamata (27 lagartos e seis serpentes), demonstrou que os lagartos não são bons indicadores precoces de alterações impostas ao ambiente pelo pastoreio não-sustentável.…”