Physical variability,diversity gradients and the ecology of temperate and tropical reefs

Traditionally, compared with the tropics, temperate systems are believed to: (i) have environments which are less favourable (i.e. harsher, more variable and less predictable); and (ii) support communities which are less diverse. Explanations for differences between temperate and tropical communities, including differences in diversity, generally rely on the former notion. The evidence for these ideas is, at best, equivocal. Organisms are subjected to physical stresses and disturbances on both temperate and tropical reefs. Communities on temperate reefs are not invariably less diverse than those in the tropics, at least at small spatial scales. Finally, there is as yet little evidence of genuine differences between the ecology of temperate and tropical communities. There is, however, much small-scale, spatial patchiness in the structure of reef communities and their physical environment. This patchiness in structure may result from patchiness in biological factors (e.g. recruitment) or in the physical environment. This small-scale variation in environmental factors may prove to be a more important determinant of community structure than the large-scale, latitudinal trends some ecologists have been obsessed with.