In aquatic and terrestrial ecosystems, habitat heterogeneity has been shown to influence species richness. Habitat heterogeneity has also been hypothesized to be the cause of the high richness observed in soils, but no studies have identified the relationship between habitat heterogeneity and richness in soils.
We conducted three studies to investigate the effect of heterogeneity on species richness and diversity within and between habitats, and between sites. We sampled two contrasting habitats known to differ in composition and richness of soil biota: heather moorland and birch woodland. In each habitat, the communities of mites and microbes were analysed to assess richness across several trophic groups. The oribatid and mesostigmatid mites were extracted and identified to species level, whereas bacterial and fungal communities were assessed using the multiple-terminal restriction fragment length polymorphism (M-TRFLP) method.
Results/Conclusions
A large spatial study was used to elucidate the potential for heterogeneity to cause differences in soil species richness between the two habitats. This study showed an increase in the richness of oribatid mites and fungi, and an increase in the diversity of the latter, in birch woodland. Analysis of vegetation and soil chemistry showed a much greater range in birch woodland of all factors measured, suggesting that there are more microhabitats in this habitat. Several species of oribatid mites only occurred in microhabitats provided by birch woodland, indicating that increased habitat variability could influence the species richness of this group.
We tested whether there was a direct relationship between habitat heterogeneity and species richness in a further study. We sampled the same communities and habitats at 12 different sites across an environmental gradient. The results from this study showed a direct relationship between habitat heterogeneity and species richness of several of the biotic groups, but only when we accounted for the effect of differences in abundance.
To be certain that heterogeneity influences soil species richness we established an experiment in which small scale heterogeneity was manipulated in situ. This study aimed to isolate the effect of heterogeneity on soil species richness and the results will be discussed briefly in the final part of the talk.
We conclude that heterogeneity can have a positive effect on species richness, but only when richness is not impaired by other environmental factors.
