In Paper II, I examined the influence of management and environmental variables on reptiles in grazing landscapes. Here (Paper III), I examine how
management and environmental variables influence frogs. Frogs are poorly studied in these agricultural environments and there has been little research exploring the influence of terrestrial habitat on frogs.
Pulsford, S.A., Barton, P., Driscoll, D.A. & Lindenmayer, D.B. (Under Review) Interactive effects of land use, grazing and environment on frogs in an agricultural landscape. Biological Conservation.
Improved management of human-modified landscapes must be part of the global effort to combat biodiversity loss. We aimed to identify which land management types and
environmental factors influenced the use of grazing landscapes by frogs. We surveyed frog assemblages in remnant vegetation, four different paddock types (pasture, linear planting, coarse woody debris addition and fence), and two grazing regimes (continuous and rotational). Frogs were surveyed using pitfall and funnel traps in twelve grazing properties in south-eastern Australia.
We found frog assemblages were often influenced by interactions of management type and environmental variables. Total frog abundance decreased with distance to water more strongly in remnants compared to paddocks. This difference in response may be due to different traits and behaviours of frogs in remnants compared to open paddocks altering their desiccation risk.
Rare frog species richness and abundance of a common species (Limnodynastes
tasmaniensis) increased with taller ground cover in remnants but no such relationship occurred
in paddocks. Different types of predation risk in remnants compared to paddocks may result in greater ground cover shelter requirements in remnants, as vegetation structure can strongly influence predation.
Total frog species richness increased more rapidly with higher average annual rainfall in continuously grazed versus rotationally grazed properties. Higher rainfall was associated with taller ground cover. Continuously grazed properties had shorter average ground cover than rotationally grazed properties and the increased ground cover height associated with more rain may bring ground cover to a height better able to provide shelter and reduce desiccation risk for frogs.
Our study highlights the importance of both land management practices and environmental conditions and their interaction in shaping frog assemblages. Improved frog biodiversity conservation may be achieved in grazing landscapes by retaining patches of remnant vegetation, maintaining water bodies such as farm dams and maintaining tall ground cover within vegetation remnants.
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4.2 Introduction
Agriculture is one of the largest threats globally to biodiversity (Garnett et al. 2013; Maxwell et al. 2016), placing increasing pressure on many species as the human population expands (Cunningham et al. 2013). Better understanding of the influence of human-modified environments on native biota is needed to improve management and reduce biodiversity loss in agricultural landscapes.
The matrix is the dominant land cover type that surrounds native and remnant vegetation, and does not provide habitat for viable populations of patch-dependent species (Driscoll et al. 2013). The matrix can influence species by changing the abiotic environment, providing foraging and other resources (Kennedy et al. 2010), or
influencing the ability of animals to move through landscapes (Driscoll et al. 2013). Land cover that is perceived as the matrix for some species might in fact be suitable habitat for other species (Kennedy et al. 2011; Prevedello and Vieira 2010). Therefore, agricultural landscapes can possess a variety of habitat types from different species’ perspectives.
Farming practices and different kinds of land management can have a large influence on how the matrix affects native biota (Irizarry et al. 2016; Perfecto and Vandermeer 2010). The more similar the matrix is to remnant vegetation, the higher quality the matrix, and the more likely the matrix will enable movement of individuals (Eycott et al. 2012; Pedro and Simonetti 2015; Prevedello and Vieira 2010). Therefore, management actions that reduce contrast between remnant vegetation and the matrix may promote greater movement throughout the landscape, particularly for largely ground-dwelling taxa such as amphibians (Burel et al. 2004; Prevedello and Vieira 2010).
Grazing by livestock is a major cause of habitat modification in agricultural landscapes and can result in deforestation, woody encroachment, and altered vegetation structure and soil characteristics (Eldridge et al. 2016a; Fleischner 1994). A range of grazing effects on amphibians has been observed from neutral (e.g. McIlroy et al. 2013) to negative (e.g. Jofre et al. 2007) and occasionally positive (e.g. Moreira et al. 2016). In addition to the direct impacts of grazing, there can be interactive or additive effects between grazing and other land management practices, or environmental conditions (Buckley et al. 2014; Davis and Roberts 2011). Few studies, however, have directly compared the influence of different types of grazing regimes on amphibians (but see Kay et al. 2016b).
influence the extent to which frogs can use grazing landscapes? We quantified frog responses to three different land management types: 1) four paddock types (pasture, linear planting, coarse woody debris addition, and fence), 2) remnant vegetation, and 3) two different grazing regimes (continuous and rotational). We expected capture rates of frogs to be higher in remnant vegetation, rotationally grazed properties, and in paddock types with higher levels of vegetation structure such as plantings. Question 2 Do environmental variables interact with management types? We expected frogs to respond significantly to environmental variables such as vegetation, climate and distance to water, and that these responses might interact with the land management types.
A suite of strategies to enhance biodiversity conservation is needed in human- modified landscapes (Chappell and LaValle 2011; Kremen 2015). The research reported here contributes to the understanding of how agricultural landscapes influence frog distributions, with this information helping to better combine agricultural and conservation priorities (Glamann et al. 2015; Wittman et al. 2016).