Distribution Determinants of Endangered Iberian Spider <I>Macrothele calpeiana</I> (Araneae, Hexathelidae)

Abstract

Little is known about the habitat preferences of Macrothele calpeiana (Walckenaer, 1805), an endangered endemic Iberian spider. In this paper, we seek to identify its distribution determinants and to disentangle their independent from combined effects. Generalized linear models (GLMs) of species presenceÐabsence in southern Iberia were built from available distribution information and a variety of climate, land-use, and vegetation-vigor explanatory variables. Their independent and combined effects were estimated using variation and hierachical partitioning. On the scale of this work, M. calpeiana distribution is determined mainly by climate variables, especially by those related with precipitation; high annual precipitation and high precipitation periodicity favors the spider. Temperature is also important, because the species is not found where temperatures reach extremes. Whereas independent vegetative vigor and land-use effects, not easily separated from climate effects, are negligible, loss of forest to agriculture seems to have a negative effect. The slight positive effect of artiÞcial surfaces cannot be directly attributed to anthropogenized-habitat prefer- ences. Failure of climate model interpolation to predict some core species distribution areas in southern Iberia is discussed. The need for reliable distribution information from which to develop accurate habitat models is highlighted.