The efficacy of species-area relationship to indicate fragmentation effects varies with grain size and with heterogeneity

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

Island species-area relationships (ISAR), relating fragment area with fragment-level species richness, and ‘species density’-area relationships (D-SAR), relating fragment area with the number of species within a standardized sampling area (species density), are both commonly used as indicators of fragmentation effects on diversity. While numerous mechanisms underlie a positive ISAR, only a small subset of these underlies a positive D-SAR; thus, a positive D-SAR can be used as an indicator for the action of these particular mechanisms. Most frequently, a positive D-SAR is interpreted as a support for the habitat heterogeneity hypothesis of ISAR, which relates species richness with habitat heterogeneity. In this study, we examine two often-neglected aspects concerning the application of D-SAR as an indicator for fragmentation effects. First, the detection of a significant D-SAR, and thus its usefulness as an indicator for some underlying mechanisms, is grain-size dependent. Second, the derivation of D-SAR as an indicator of habitat heterogeneity is often implicitly based on a seldom tested assumption of a parallel within-island species-area relationship. We used a grain size-dependent hierarchical uniform sampling of plant species density and species richness in a fragmented semi-arid agroecosystem to address the following questions: a) Can fine-scale heterogeneity account for D-SAR in Mediterranean plant communities?; b) Do the detection of a significant D-SAR and its slope vary with grain size?; and c) Do within-fragment SARs have uniform slope or does the slope vary with fragment size? In a system of fragments with a relatively uniform habitat, we found a significant SAR, but a non-significant D-SAR regardless of the grain size, which varied from 0.0625 m2 to 225 m2. These results contrast with those from a heterogeneous fragmented system where both SAR and D-SAR were significant and where D-SAR was grain size-dependent. We also found that the slope of within-fragment SAR decreased with fragment size, in contradiction to their frequent depiction in the literature as being parallel. Our study supports the notion that D-SAR is mainly generated by the processes considered by the habitat heterogeneity hypothesis. Furthermore, it provides evidence that habitat heterogeneity may account for significant D-SAR even when within-fragment SAR do not share a common slope. Our study emphasizes the need for clarity in matching theoretical prediction with actual empirical measures, while studying fragmentation effects on biodiversity.

Original languageEnglish
Article number105904
JournalEcological Indicators
Volume110
DOIs
StatePublished - 1 Mar 2020

Keywords

  • Habitat fragmentation
  • Scale-dependence
  • Species density
  • Spill-over effect

Fingerprint

Dive into the research topics of 'The efficacy of species-area relationship to indicate fragmentation effects varies with grain size and with heterogeneity'. Together they form a unique fingerprint.

Cite this