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| Despite two centuries of effort in characterizing environmental
gradients of species richness in search of universal patterns, surprisingly
few of these patterns have been widely acknowledged1–3.
Species richness along altitudinal gradients was previously
assumed to increase universally from cool highlands to warm lowlands,
mirroring the latitudinal increase in species richness from
cool to warm latitudes1,4,5. However, since the more recent general
acceptance of altitudinal gradients as model templates for testing
hypotheses behind large-scale patterns of diversity5–9, these gradients
have been used in support of all the main diversity hypotheses,
although little consensus has been achieved. Here we
show that when resampling a data set comprising 400,000 records
for 3,046 Pyrenean floristic species at different scales of analysis
(achieved by varying grain size and the extent of the gradients
sampled), the derived species richness pattern changed progressively
from hump-shaped to a monotonic pattern as the scale of
extent diminished. Scale effects alone gave rise to as many conflicting
patterns of species richness as had previously been
reported in the literature, and scale effects lent significantly different
statistical support to competing diversity hypotheses.
Effects of scale on current studies may be affected by human activities,
because montane ecosystems and human activities are
intimately connected10. This interdependence has led to a global
reduction in natural lowland habitats, hampering our ability to
detect universal patterns and impeding the search for universal
diversity gradients to discover the mechanisms determining the
distribution of biological diversity on Earth. | |
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