A resource‐based conceptual model of plant diversity that reassesses causality in the productivity–diversity relationship

Abstract

Biogeographical studies frequently reveal positive correlations between species richness and estimates of environmental water and/or energy. A popular interpretation of this relationship relates the supply of water and energy to productivity, and then, in turn, to richness. Productivity-diversity theories are now legion, yet none has proved sufficiently intuitive to gain broad acceptance. Like productivity, heterogeneity is known to influence diversity at fine spatial scales, yet the possibility that richness might relate to water-energy dynamics at coarse spatial scales via a heterogeneity-generating mechanism has received little attention. In this paper we outline such a conceptual model for plants that is internally consistent and testable. We believe it may help to explain the capacity of environments receiving different inputs of water and energy to support variable numbers of species at a range of spatial scales, the pervasive correlation between productivity and richness, some exceptions to the productivity-diversity relationship, the form of productivity-diversity curves and the link between richness and environmental 'harshness' . The model may also provide an answer to one of the most venerable puzzles in the field of diversity studies: why high inputs of water and energy correspond to more species rather than simply more individuals.

Environmental correlates of avian diversity in lowland Panama rain forests

“…Therefore, our results are consistent with those of Currie & Paquin (1987), Kerr & Packer (1997), Kerr et al (2001) and Rahbek & Graves (2001), which state the importance for biodiversity of topographic complexity and a complex habitat structure. We consider that our study provides better support for the habitat heterogeneity hypothesis, which predicts a positive correlation between species diversity and habitat heterogeneity (see definition in Tews et al, 2004), particularly relevant at local scales (Lavers & Field, 2006). Nevertheless, as mentioned earlier, the relationship between diversity and habitat complexity is also influenced by historical biogeographical events in the region and by habitat area (speciesarea relationship), confirming that species diversity does not result from a single process (Hill & Hill, 2001;Currie et al, 2004;Ricklefs, 2004).…”

Community‐based processes behind species richness gradients: contrasting abundance–extinction dynamics and sampling effects in areas of low and high productivity

“…A number of the mechanisms proposed to generate the species–energy relationship assume a positive association between community size and species richness (Evans et al , 2005a). Our results suggest that these mechanisms may be driving variation in species richness only in low‐productivity areas, where the association between community size and species richness is significant, and thus qualitatively different processes may be determining variation in species richness in high‐productivity regions (Kerr & Packer, 1997; and see Lavers & Field, 2006). This is consistent with the observed decrease in the predictability of species richness for the high‐productivity altitudinal band when modelling with environmental data.…”

“…Environmental models for the whole gradient suggest that productivity and habitat availability are the main factors determining variation in richness over the whole gradient (Wright, 1983; Hawkins et al , 2003b; Lavers & Field, 2006). However, the analyses conducted within altitudinal bands suggest that the dynamics in high‐ and low‐productivity regions differ.…”

Metabolic Theory and Diversity Gradients: Where Do We Go From Here?

“…If predictions of MTE become vague and not subject to falsification, how does MTE differ from other theories (see Lavers and Field 2006)? G&A optimistically interpret our results as promising, despite the extreme range of slopes found.…”