Testing the Water–Energy Theory on American Palms (Arecaceae) Using Geographically Weighted Regression

Water and energy have emerged as the best contemporary environmental correlates of broad-scale species richness patterns. A corollary hypothesis of water–energy dynamics theory is that the influence of water decreases and the influence of energy increases with absolute latitude. We report the first use of geographically weighted regression for testing this hypothesis on a continuous species richness gradient that is entirely located within the tropics and subtropics. The dataset was divided into northern and southern hemispheric portions to test whether predictor shifts are more pronounced in the less oceanic northern hemisphere. American palms (Arecaceae, n = 547 spp.), whose species richness and distributions are known to respond strongly to water and energy, were used as a model group. The ability of water and energy to explain palm species richness was quantified locally at different spatial scales and regressed on latitude. Clear latitudinal trends in agreement with water–energy dynamics theory were found, but the results did not differ qualitatively between hemispheres. Strong inherent spatial autocorrelation in local modeling results and collinearity of water and energy variables were identified as important methodological challenges. We overcame these problems by using simultaneous autoregressive models and variation partitioning. Our results show that the ability of water and energy to explain species richness changes not only across large climatic gradients spanning tropical to temperate or arctic zones but also within megathermal climates, at least for strictly tropical taxa such as palms. This finding suggests that the predictor shifts are related to gradual latitudinal changes in ambient energy (related to solar flux input) rather than to abrupt transitions at specific latitudes, such as the occurrence of frost

To what extent does Tobler's 1^stlaw of geography apply to macroecology? A case study using American palms (<it>Arecaceae</it>)

Abstract Background Tobler's first law of geography, 'Everything is related to everything else, but near things are more related than distant things' also applies to biological systems as illustrated by a general and strong occurrence of geographic distance decay in ecological community similarity. Using American palms (Arecaceae) as an example, we assess the extent to which Tobler's first law applies to species richness and species composition, two fundamental aspects of ecological community structure. To shed light on the mechanisms driving distance decays in community structure, we also quantify the relative contribution of geographic distance per se and environmental changes as drivers of spatial turnover in species richness and composition. Results Across the Americas, similarity in species composition followed a negative exponential decay curve, while similarity in species richness exhibited a parabolic relationship with geographic distance. Within the four subregions geographic distance decays were observed in both species composition and richness, though the decays were less regular for species richness than for species composition. Similarity in species composition showed a faster, more consistent decay with distance than similarity in species richness, both across the Americas and within the subregions. At both spatial extents, geographic distance decay in species richness depended more on environmental distance than on geographic distance, while the opposite was true for species composition. The environmentally complex or geographically fragmented subregions exhibited stronger distance decays than the more homogenous subregions. Conclusion Similarity in species composition exhibited a strong geographic distance decay, in agreement with Tobler's first law of geography. In contrast, similarity in species richness did not exhibit a consistent distance decay, especially not at distances >4000 kilometers. Therefore, the degree to which Tobler's first law of geography applies to community structure depends on which aspect hereof is considered – species composition or species richness. Environmentally complex or geographically fragmented regions exhibited the strongest distance decays. We conclude that Tobler's law may be most applicable when dispersal is a strong determinant of spatial turnover and less so when environmental control predominates.</p

To what extent does Toblers law of geography apply to macroecology

Loess fits with automatic span selection (S-PLUS 7.0). Data points are only shown for the Amazon subregion.<p><b>Copyright information:</b></p><p>Taken from "To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()"</p><p>http://www.biomedcentral.com/1472-6785/8/11</p><p>BMC Ecology 2008;8():11-11.</p><p>Published online 22 May 2008</p><p>PMCID:PMC2424035.</p><p></p

To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()-3

Loess fits with automatic span selection (S-PLUS 7.0). Only every 2000th data point is shown.<p><b>Copyright information:</b></p><p>Taken from "To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()"</p><p>http://www.biomedcentral.com/1472-6785/8/11</p><p>BMC Ecology 2008;8():11-11.</p><p>Published online 22 May 2008</p><p>PMCID:PMC2424035.</p><p></p

To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()-5

Ween one single grid cell in the center of each subregion and all other grid cells within the study area. The subregions are indicated on the individual maps.<p><b>Copyright information:</b></p><p>Taken from "To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()"</p><p>http://www.biomedcentral.com/1472-6785/8/11</p><p>BMC Ecology 2008;8():11-11.</p><p>Published online 22 May 2008</p><p>PMCID:PMC2424035.</p><p></p

To what extent does Toblers law of geography apply to macroecology

Ween one single grid cell in the center of each subregion and all other grid cells within the study area. The subregions are indicated on the individual maps.<p><b>Copyright information:</b></p><p>Taken from "To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()"</p><p>http://www.biomedcentral.com/1472-6785/8/11</p><p>BMC Ecology 2008;8():11-11.</p><p>Published online 22 May 2008</p><p>PMCID:PMC2424035.</p><p></p

To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()-4

Loess fits with automatic span selection (S-PLUS 7.0). Data points are only shown for the Amazon subregion.<p><b>Copyright information:</b></p><p>Taken from "To what extent does Tobler's 1law of geography apply to macroecology? A case study using American palms ()"</p><p>http://www.biomedcentral.com/1472-6785/8/11</p><p>BMC Ecology 2008;8():11-11.</p><p>Published online 22 May 2008</p><p>PMCID:PMC2424035.</p><p></p