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| Aim The water–energy dynamics hypothesis posits that species diversity is cor-
related with water availability and temperatures; diversity is lowest when water
availability is reduced at low temperatures because few species can persist
under such conditions. However, the relationship between water and energy
availability and diversity likely varies geographically along environmental gradi-
ents. Here, we examined the drivers of such variability, using a global-scale
data set on oaks.
Location Global.
Method To quantify spatial variation in both species diversity–water relation-
ships and species diversity–energy relationships, we performed geographically
weighted regressions (GWR) of (1) species diversity against energy availability,
measured as potential evapotranspiration and temperature, and (2) species
diversity against water availability, measured by precipitation and an aridity
index. We then regressed the local slopes of these GWR models against water
and energy separately, and water 9 energy combined to assess whether the
regional-scale relationships among oak diversity, water and energy depended
on climatic conditions at larger spatial extents.
Results We found that the effects of low water availability and cold tempera-
tures on oak diversity varied geographically. In particular, the effects of water
and energy availability on oak diversity increased as water and energy availabil-
ity decreased. Furthermore, the interaction between water and energy availabil-
ity in?uenced regional-scale oak diversity–energy relationships but not oak
diversity–water relationships.
Main conclusion Our results suggest that the relationship between climate
(and potentially climatic change) and oak diversity varies geographically, and
that the effects of limiting water and temperature are likely to be most severe
in arid environments. | |
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