Factors determining the distribution of the spur‐thighed tortoiseTestudo graecain south‐east spain: a hierarchical approach

Abstract

This work represents the first attempt to model the habitat‐species relationships of a species of terrestrial tortoise on a large scale. We applied hierarchical variance partition methodology to Generalised Lineal Models (GLMs), with the presence of the tortoise in 1 km2 cells as the response variable. We posited the existence of a hierarchical scheme of factors (including climate, relief and lithology, and land‐use) that determine the distribution of Testugo graeca in southeastern Spain. We also identified the environmental variables within each factor with the greatest explanatory power and decoupled local vs landscape effects. Climate, followed by relief and lithology, and then land‐use, turned out to be the most important factor shaping the distribution of T. graeca in south‐east Spain as well as determining the presence of the species within its range. Univariate models showed that the main climate constraints were related to rainfall and extreme minimum temperatures, two factors which could be related to constraints imposed by the length of the annual activity period and productivity. Finally, multi‐scale decomposition suggested that neighbouring habitat and local dynamics may also be important in the distribution of the species at the landscape scale.

Distribution of Testudo graeca in the western Mediterranean according to climatic factors

“…In order to obtain a first description of the niche of the species, occurrence data were characterized in relation to basic climatic descriptors (mean annual precipitation and temperature) plus the mean minimum temperature of the coldest month, that has been indicated as an important limiting factor in the species (Lambert, 1983;Anadón et al, 2006). Climatic variables were obtained from WorldClim.…”

“…For the remaining countries of North Africa, the range is only superficially known, being described as a wide strip along the coast in Algeria and Tunisia with a small isolated area in the Cyrenaica Peninsula (Libya). In the same vein, the environmental factors controlling the distribution of the species in North Africa at a large scale have only been tackled for Morocco in the pioneering work of Lambert (1983) and in more depth for southeast Spain (Anadón et al, 2006(Anadón et al, , 2007(Anadón et al, , 2010. These studies indicate a meridional limit of the species related to rainfall (aridity) and a septentrional (or altitudinal) limit related to minimal extreme temperatures.…”

Exurban sprawl increases the extinction probability of a threatened tortoise due to pet collections

“…70 ha and the study area covered 35 ha. The reserve contains the optimum habitat for the species in terms of climate, relief and lithology , and has a high density population of spur-thighed tortoise (20 indv/ha; Anadón et al, 2006Anadón et al, , 2009.…”

Large‐scale human effects on an arid African raptor community

“…We performed deviance-partitioning analyses to explore the relative influence of human population, land-uses and productivity on the richness patterns at the two spatial scales (Anad´on et al, 2006;Carrete et al, 2007). This analysis allowed us to separate the pure from the joint effects of the three groups of explanatory variables on raptor richness.…”

“…HS+H+P). Lastly, we calculated the pure and joint effects (deviance explained) of human settlements, land-uses and productivity using basic algebra (Anad´on et al, 2006;Carrete et al, 2007). Once deviance-partitioning analyses assessed the relative influence of population, land-uses and productivity on the raptor richness at the two spatial scales, we identified the variables relevant within each group and their relationship (i.e.…”