The role of habitat diversity in generating the small‐island effect

Abstract

The small‐island effect (SIE) has become a widespread pattern in island biogeography and biodiversity research. However, in most previous studies only area is used for the detection of the SIE, while other causal factors such as habitat diversity is rarely considered. Therefore, the role of habitat diversity in generating SIEs is poorly known. Here, we compiled 86 global datasets that included the variables of habitat diversity, area and species richness to systematically investigate the prevalence and underlying factors determining the role of habitat diversity in generating SIEs. For each dataset, we used both path analysis and breakpoint regressions to identify the existence of an SIE. We collected a number of system characteristics and employed logistic regression models and an information–theoretic approach to determine which combination of variables was important in determining the role of habitat diversity in generating SIEs. Among the 61 datasets with adequate fits, habitat diversity was found to influence the detection of SIEs in 32 cases (52.5%) when using path analysis. By contrast, SIEs were detected in 26 of 61 cases (42.6%) using breakpoint regressions. Model selection and model‐averaged parameter estimates showed that Number of sites, Habitat range and Species range were three key variables that determined the role of habitat diversity in generating SIEs. However, Area range, Taxon group and Site type received considerably less support. Our study demonstrates that the effect of habitat diversity on generating SIEs is quite prevalent. The inclusion of habitat diversity is important because it provides a causal factor for the detection of SIEs. We conclude that for a better understanding of the causes of SIEs, habitat diversity should be included in future studies.

Unravelling the small‐island effect through phylogenetic community ecology

“…If habitat availability is the main driver of small island richness (e.g. Chen et al, 2020;Triantis et al, 2006), we would expect species occurring on small islands (in a given archipelago) to be clustered in the phylogenetic tree, because only a subset of closely related species (e.g. from a limited number of clades) will likely be adapted to the limited habitat types on small islands.…”

“…One possible pattern emerging from such area‐independent extinction rates on small islands is higher temporal species turnover on smaller compared to larger islands (MacArthur & Wilson, 1967). The second hypothesis refers to the primary role of habitat diversity and niche‐based factors in driving the SIE (Chen, Yang, Tan, & Wang, 2020; Chisholm, Fung, Chimalakonda, & O’Dwyer, 2016; Sfenthourakis & Triantis, 2009; Triantis et al., 2006). Here, the idea is that on small islands island area and environmental heterogeneity become decoupled (Triantis, Mylonas, Weiser, Lika, & Vardinoyannis, 2005; Triantis et al., 2006), and that below a threshold of island area the absence of major habitat types is the main constraint on richness (Chen et al., 2020; Sfenthourakis & Triantis, 2009).…”

“…The second hypothesis refers to the primary role of habitat diversity and niche‐based factors in driving the SIE (Chen, Yang, Tan, & Wang, 2020; Chisholm, Fung, Chimalakonda, & O’Dwyer, 2016; Sfenthourakis & Triantis, 2009; Triantis et al., 2006). Here, the idea is that on small islands island area and environmental heterogeneity become decoupled (Triantis, Mylonas, Weiser, Lika, & Vardinoyannis, 2005; Triantis et al., 2006), and that below a threshold of island area the absence of major habitat types is the main constraint on richness (Chen et al., 2020; Sfenthourakis & Triantis, 2009). For example, Niering (1963) postulated that the lack of mature soils on islands smaller than 3.5 acres explained the SIE pattern he observed; it should be noted that Niering did not explicitly use the term SIE.…”

“…Overall then, we predict that, if habitat diversity is a primary driver of island richness, due to the decoupling of island area and habitat diversity on small islands, the relationship between area and diversity (e.g. richness, PD; Chen et al., 2020; Triantis et al., 2006) will differ from that on large islands (i.e. the small island effect), and also that small islands are expected to support a limited subset of closely related species (i.e.…”

Area threshold and trait–environment associations of butterfly assemblages in the Zhoushan Archipelago, China

“…Accumulative evidences show that thresholds exist commonly in nature (e.g. Chen et al., 2020; Wang et al., 2016; Whittaker & Fernández‐Palacios, 2007). For instance, Matthews et al.…”