Does forest loss affect body condition and individual ranging patterns in radiated tortoises (Astrochelys radiata, Shaw 1802)?

William Ronto, Daniel Rakotondravony

Abstract


Over the last four decades, nearly half of the Mahafaly Plateau has been deforested. Here presented are findings of how radiated tortoises, Astrochelys radiata, responded to this habitat degradation. The differences in radiated tortoises’ body condition (residual index from a regression of mass on body length) and individual ranging patterns (Minimum convex polygons, n = 10 locations, monitoring period = 20 days) from two populations were examined in: (1) degraded forest resulting from slash and burn agriculture (n = 16/ season), and (2) intact forest (n = 16/ season), within Tsimanampetsotsa National Park in south-western Madagascar during the wet and dry season. We assumed that tortoises in disturbed habitat would either increase their individual range size to maintain a certain body condition, or they would maintain similar individual range size at the expense of their body condition. Despite largely different environmental conditions, we found no habitat specific effect on body condition or on ranging patterns. Constant body condition and comparable individual range size observed at both habitats could be explained by food availability - the different vegetation mosaics in degraded habitat might provide food resources that tortoises exploit due to their generalist food requirements. This study provides insight of the flexibility of A. radiata towards habitat changes, and might be of vital importance for the species conservation. Higher sampling efforts and additional site replications, however, are needed to test these findings on larger scales and to determine the tolerance limit of A. radiata in terms of degradation.

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