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| Scale is widely recognized as a fundamental conceptual problem in
biology, but the question of whether species-richness patterns var)
with scale is often ignored in macro-ecological analyses, despite the
increasing application of such data in international conservation
programmes. We tested for scaling effects in species-richness gradients
with spatially scaled data for 241 species of South American
hummingbirds (Trochilidae). Analyses revealed that scale matters above
and beyond the effect of quadrat area. Species richness was positively
correlated with latitude and topographical relief at ten different
spatial scales spanning two orders of magnitude (ca. 12 300 tu ra. 1
225 000 km(2)). Surprisingly, when the influence of topography was
removed, the conditional variation in species richness explained by
latitude fell Precipitously to insignificance at coarser spatial
scales. The perception of macro-ecological pattern thus depends
directly upon the scale of analysis. Although our results suggest there
is no single correct scale For macro-ecological analyses, the averaging
effect of quadrat sampling at coarser geographical scales obscures the
fine structure of species-richness gradients and localized richness
peaks, decreasing the power of statistical tests to discriminate the
causal agents of regional richness gradients. Ideally the scale of
analysis should be varied systematically to provide the optimal
resolution of macro-ecological pattern. | |
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