Analysis of ecological data of the arboricolous nephilid spider Clitaetra irenae Kuntner 2006, endemic to Maputaland forests, South Africa, indicates the species' dependence on this highly threatened habitat. We tested C. irenae habitat dependence via GIS analysis by plotting the known distribution against southern African ecoregions. In the southern part of its range, C. irenae inhabits almost exclusively one ecoregion, the Maputaland coastal plain forests; but further north, in tropical southern Africa, it continues inland into Malawi's woodlands. We test and refute the hypotheses that C. irenae inhabits exclusively mature trees, trees of a particular species, trees with a smooth bark, tree habitats at certain height above ground, and only closed canopy forest stands. The ecological niche of C. irenae is flexible as long as suitable trees under at least partially closed canopy are available. We quantify the C. irenae ontogenetic web changes from orb to ladder and the simultaneous hub displacement towards the top frame. Such web allometry allows the web to increase vertically but not horizontally, which enables the spider to remain on the same tree throughout its development and thus the ladder web architecture is an adaptation to an arboricolous life style. Adult hub displacement, common in spiders with vertical webs, is explained by gravity. Clitaetra irenae web orientation on trees correlates with forest closure, and might indicate the Maputaland forest quality. We argue for utilization of the ecology of arboricolous nephilid orb-weaving spiders (Clitaetra and Herennia) in systematic conservation assessments in the Old World tropics.
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