Correlation between endemism and local ecoclimatic stability documented by comparing Andean bird distributions and remotely sensed land surface data

Relationships between large-scale patterns of biodiversity and ecoclimatic variability were examined using distributions of 789 Andean birds; recorded in 15' x 15' grid cells, and interannual differences in Normalized Difference Vegetation Index and Brightness Surface Temperature, calculated month by month and resampled to 15' cells. Following the east Andean treeline from 1 degrees N to 18 degrees S; there is no evidence of a latitudinal gradient in species richness, but a considerable local variation reflecting the habitat complexity in individual cells. The mean endemism (inverse range-size for all species present in a given cell) shows well marked peaks. Pairwise comparisons of 'peaks' and adjacent 'lows' of endemism provide strong evidence for linking peaks of endemism with local ecoclimatic stability. The most important single factor responsible for this correlation could be orographic moderation of the impacts a south polar winds. Presently manifested as occasional winter freezes in the southern part of the tropical zone, these winds may have been a major determinant of vegetational changes during Pleistocene glacial periods. The correlations suggest that most endemics are relict populations which survived periods of global climatic change in places where these impacts were moderated. It is suggested that, by retaining relict populations, these places play a significant role in the recruitment to the regional species pool. The stable places were also centres of Andean cultures and have dense human populations. The current conservation strategy of reserving areas with few people therefore needs to be supplemented with actions to secure sustainable landuse in certain densely populated areas.

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