The role of landscape texture in conservation biogeography: a case study on birds in south-eastern Australia

The binary classification of landscapes into suitable vs. unsuitable areas underlies several prominent theories in conservation biogeography. However, a binary classification is not always appropriate. The textural discontinuity hypothesis provides an alternative theoretical framework to examine the geographical distribution of species, and does not rely on a binary classification scheme. The texture of a given landscape is the combination of its vertical structural complexity and horizontal spatial grain. The textural discontinuity hypothesis states that biophysical features in the environment are scaled in a discontinuous way, and that discontinuities in the body size distribution of animals mirror these biophysical discontinuities. As a result of this relationship, a complex landscape texture should be associated with small-bodied animals, whereas a simple landscape texture should be associated with larger-bodied animals. We examined this hypothesis for birds in five landscapes in south-eastern Australia that represented a gradient from simple to complex landscape texture. In landscapes with a complex texture, the number of detections of small birds was higher than expected, and the number of detections of larger-bodied birds was lower than expected. The opposite pattern was found in landscapes with a simple texture. The pattern remained significant when only bird species found in each of the five landscapes were considered, which demonstrated that the association of landscape texture with body size was not an artefact of landscapes differing in their species pools. Understanding the effects of landscape texture on species distribution patterns may be a promising research frontier for conservation biogeography. We hypothesize that the active management of landscape texture may be used to attract or deter animals of certain body sizes. Consistent with other theories, the textural discontinuity hypothesis therefore suggests that managing entire landscapes, rather than only predefined patches, is an important conservation strategy.