Email updates

Keep up to date with the latest news and content from BMC Ecology and BioMed Central.

Open Access Research article

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

Stine Bjorholm1, Jens-Christian Svenning1, Flemming Skov2 and Henrik Balslev1*

Author Affiliations

1 Department of Biological Sciences, University of Aarhus, Build. 1540, DK-8000 Aarhus C., Denmark

2 Department of Wildlife Ecology and Biodiversity, National Environmental Research Institute, University of Aarhus, Grenaavej 12, Kalø, DK-8410, Denmark

For all author emails, please log on.

BMC Ecology 2008, 8:11  doi:10.1186/1472-6785-8-11

Published: 22 May 2008

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.