Premium
EXPANSION VS. COMPRESSION OF BIRD ALTITUDINAL RANGES ON A MEDITERRANEAN ISLAND
Author(s) -
Prodon Roger,
Thibault Jean-Claude,
Dejaifve Pierre-André
Publication year - 2002
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/0012-9658(2002)083[1294:evcoba]2.0.co;2
Subject(s) - ecology , endemism , range (aeronautics) , biological dispersal , mediterranean islands , mediterranean climate , habitat , geography , intraspecific competition , altitude (triangle) , pleistocene , mainland , population , biology , materials science , demography , geometry , archaeology , sociology , composite material , mathematics
Habitat expansion is a commonly recognized feature of the insular syndrome. It has been explained either by restricted dispersal, intraspecific spillover resulting from density inflation, benign and predictable climate, or by the ecological release that results from species impoverishment. The latter hypothesis has been frequently invoked to explain shifts and/or broadenings of elevational ranges on islands. In this paper, we compared the elevational distribution of 85 terrestrial breeding bird species on a Mediterranean island (Corsica) with their mainland counterparts in a control area of similar altitude, latitude, and climate (Eastern Pyrenees). We calculated specific altitudinal amplitudes in both areas from the upper and lower limits of the bird ranges in the breeding season. We then calculated Island/Mainland Amplitude Ratio (IMAR) for each species. The ratios we found showed an overall trend in favor of range compressions on Corsica, despite a lower number of species on the island than on the mainland. However the well‐differentiated subspecies‐level endemics are the ones more likely to expand their ranges on the island. Their frequency is highest in the middle of the elevational gradient, in the cool forests situated between 1400 m and 2000 m. The non‐Mediterranean and non‐alpine nature of endemism on Corsica, together with the niche broadening of the endemic forms, can be explained by taking into account Pleistocene glacial–interglacial cycles. The resulting up and down and back again shift of the bioclimatic belts tended, in turn, to eliminate the lower ranging and the higher ranging species from the elevational gradient. The belt that persisted throughout the cycles was the mid‐altitude belt, where differentiation processes had sufficient time to lead to endemism. This mechanism also tended to broaden the species ranges, both by selecting among the colonizers those that already had wide ranges on the mainland and by exerting selective pressures on the residents in favor of the broadening of their ranges. More recently, human activities on the island have favored the immigration of undifferentiated species whose elevational ranges are still relatively low.