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Reptiles and breeding birds on Mt. Hermon: Patterns of altitudinal distribution and species richness

Nathan, R.; Werner, Y., L.

Israel Journal of Zoology 45(1): 1-33

1999


ISSN/ISBN: 0021-2210
Accession: 011287457

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We review and analyze the altitudinal distribution of reptiles (from museum collections) and breeding birds (from literature records and a recent field sampling project) on Mt. Hermon (latitude ca. 33degree30 N), over the range 300-2814 m. Species richness was greater in breeding birds (n = 86-90) than in reptiles (n = 34), declining with increasing altitude in both groups, but more steeply so in birds. We suggest that the simplification of vegetation structure with increasing altitude may explain this difference, because birds probably better use the three-dimensionality of densely-vegetated habitats that dominate low elevations. But in both taxa the overall decline was nonlinear; species richness actually increased from low to mid-elevations, forming a hump-shaped pattern. Standardization of species richness for surface area, across altitudinal belts of 100 m up to 1,900 m, revealed the area effect as both significant and unpredictable. It did not affect the overall decline, but contrary to a general expectation of a linear trend turning hump-shaped, the hump-shaped curve became concave, i.e., from low to mid-elevations the number of species per unit area declined sharply, and at higher elevations it remained fairly stable. In a comparison with other mountains in the Mediterranean Basin (between latitudes 35degree00 and 42degree30 N), the very same reptile species reached higher maximum elevations on Mt. Hermon, while the same bird species reached similar elevations in both areas. This difference may reflect lesser ability of reptiles, compared to birds, to inhabit high elevations at higher latitudes, but their altitudinal distribution on Mt. Hermon showed no evidence for such a physiological difference. In general, in contrast with other reports, we found no positive correlation between the extent of altitudinal range of the species and their position on the altitudinal gradient, as would have been implied by Rapoport s altitudinal rule. Future mapping of local distributions of the Mt. Hermon biota, required for efficient conservation, should derive from planned, extensive field sampling, augmented with museum records for clarification of taxonomic uncertainties.

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