The area‐independent effects of habitat complexity on biodiversity vary between regions

Abstract

Potential explanatory variables often co‐vary in studies of species richness. Where topography varies within a survey it is difficult to separate area and habitat‐diversity effects. Topographically complex surfaces may contain more species due to increased habitat diversity or as a result of increased area per se. Fractal geometry can be used to adjust species richness estimates to control for increases in area on complex surfaces. Application of fractal techniques to a survey of rocky shores demonstrated an unambiguous area‐independent effect of topography on species richness in the Isle of Man. In contrast, variation in species richness in south‐west England reflected surface availability alone. Multivariate tests and variation in limpet abundances also demonstrated regional variation in the area‐independent effects of topography. Community composition did not vary with increasing surface complexity in south‐west England. These results suggest large‐scale gradients in the effects of heterogeneity on community processes or demography.

Piddocks (Mollusca: Bivalvia: Pholadidae) increase topographical complexity and species diversity in the intertidal

“…This is most likely due to the size distribution of the species observed on the shore. Johnson et al (2003) noted similar area-independent effects on rocky shores in the Isle of Man but not in southwest England, while Kostylev et al (2005) reported that changes in surface area alone accounted for the increase in species diversity on rocky shores in Hong Kong. Similar area-dependent results were obtained for Lyme Regis in the current study.…”

“…Similar area-dependent results were obtained for Lyme Regis in the current study. Johnson et al (2003) concluded that regional differences in the effect of topographical complexity on biodiversity were related to environmental conditions, citing variation in crevice microclimate as the most likely explanation; crevices maintained a microclimate on the Isle of Man, whereas in the warmer southwest England, crevices dried out completely during the tidal cycle and so did not provide any effective form of refuge. At the centimetre topographical scale, piddock burrows are relatively deep (maximum recorded depth = 8.1 cm; Pinn et al 2005b).…”

“…However, this may be due to increased area of substratum or as a result of increased habitat diversity (Johnson et al 2003). The effects of topographical complexity and habitat diversity on biodiversity are difficult to separate.…”

“…For example, increasing topographical complexity on rocky shores can create mosaics of microclimate (Johnson et al 1998) and provide refuges from physical and biological disturbances (Menge et al 1985, Bergeron & Bourget 1986. A few studies have successfully managed to separate the effects of topographical complexity and habitat diversity; examples include Pennycuick (1992), Johnson et al (2003) and Kostylev et al (2005).The overall aim of this study was to assess whether ecosystem engineering by piddocks has an affect on intertidal species richness. We hypothesised that their rock-boring activities would significantly increase topographical complexity, in turn influencing species richness.…”

Investigating habitat value to inform contaminant remediation options: Approach

“…Biodiversity has been closely associated with habitat structural complexity by many researchers (Crowder and Cooper, 1982;Downes et al, 1998;Benton et al, 2003;Johnson et al, 2003). For example, the diversity of prey of bluegill sunfish (Lepomis macrochirus) was lower at low macrophyte density than at intermediate or high macrophyte density (Crowder and Cooper, 1982), though very high macrophyte density can lead to hypoxia (Miranda and Hodges, 2000).…”