Reptile and frog responses to different farm management practices in grazing landscapes

Abstract

Managing agricultural landscapes for biodiversity conservation is increasingly difficult as land use is intensified for agricultural production. Finding ways to mitigate the often negative effects of agriculture on biodiversity is therefore critical: Using reptiles and frogs as focal taxa, my broad aim was to examine the effect of different human-modified land cover types on biodiversity in a grazing landscape. I present my thesis as a series of five conceptually linked journal papers that together address this applied ecological problem. I surveyed reptiles and frogs at 12 sites Box Gum Grassy Woodland grazing landscapes in south-eastern Australia. Each site contained remnant woodland patches and four adjacent paddock types: a) grazed pastures, b) linear plantings, c) coarse woody debris added to grazed pastures, and d) fences between grazed pastures. Each site was either continuously or rotationally grazed. In my first paper, I compared the habitat preferences of reptile and frog species to predictions developed from five conceptual landscape models. Importantly, no one model fully captured the range of species responses to the different land uses, but four of the models provided useful concepts to aid our understanding of faunal responses to human-modified landscapes. It is important that relevant conceptual models are used by researchers as the different models can result in very different outcomes. These types of models can help inform management, but all models have limitations and often cannot provide useful management recommendations. In my second paper, I recorded higher reptile abundance and species richness in areas with more tree cover and leaf litter, and greater abundance and diversity of rare reptiles in sites with high tree cover in the surrounding 3kms. Management recommendations include: protecting existing remnant vegetation, regardless of amount, and promoting key habitat features of trees, leaf litter and shrubs. Establishing plantings and fences in paddocks can also provide habitat in grazing landscapes. In my third paper, I found that frogs were influenced by both land use and the environmental conditions, and often responded to interactions between these variables. Frog abundance decreased with distance to water more strongly in remnants than paddocks, and rare frog richness and the abundance of Limnodynastes tasmaniensis increased with taller ground cover in remnants but not adjacent paddocks. Retaining remnant vegetation, maintaining water bodies such as farm dams, and maintaining taller ground cover within remnant vegetation may therefore benefit frog assemblages. Environmental context and current management must be considered in planning future management actions. In my fourth paper, I found that reptiles and frogs displayed contrasting movement behaviours. For example, recaptured reptiles exhibited greater movement within and out of paddocks than remnants. However, the smooth toadlet (Uperoleia laevigata) moved within remnants more than within paddocks, while the spotted marsh frog (Limnodynastes tasmaniensis) moved out of pasture transects more than other transects. Reptiles and frogs appear to use the whole landscape as habitat and but perceive different land management types as different qualities of habitat. My fifth paper synthesised the state of knowledge of reptiles in woodland agricultural landscapes in south-eastern Australia. I highlight the key factors influencing these reptiles, synthesise the management implications, and outline future research needs. My research has provided new insights into how reptiles and frogs are influenced by land use in grazing landscapes. Importantly, I found that commonly discussed ecological concepts applied to human-modified landscapes did not provide a useful framework for understanding/predicting biodiversity responses to land cover types. Show more