Habitat heterogeneity determines species richness on small habitat islands in a fragmented landscape

Abstract

Aim The small‐island effect (SIE), as an exception to the species–area relationship, has received much attention in true island systems. However, the prevalence and related patterns of the SIE have not been well evaluated in habitat island systems. Here, we aimed to identify the existence of SIE for habitat islands in fragmented landscapes and determine the key factors influencing species richness on small habitat islands. Location Inner Mongolia Autonomous Region, China. Taxon Vascular plants. Methods Based on 78 grassland fragments in fragmented landscapes of the agro‐pastoral ecotone of northern China, we used piecewise regression, path analysis and null models to investigate the SIE of the species–area relationship. We then used a multi‐model selection to evaluate the impacts of four influencing factors (instability, isolation, habitat heterogeneity and surrounding productivity) on species richness (including habitat specialists and generalists) on small habitat islands within the range of SIE. Results We found an obvious threshold of 5.1 ha in the species–area relationship, below which habitat island area had no direct and indirect effects on species richness. Small habitat islands (<5.1 ha) host a lower percentage of habitat specialists and a higher percentage of generalists. On small habitat islands, species richness was positively affected by habitat heterogeneity while negatively affected by instability and isolation. Habitat heterogeneity had the strongest effect on species richness, positively affecting specialist richness while negatively affecting generalist richness. Main Conclusions There is an SIE in fragmented landscapes of the agro‐pastoral ecotone of northern China, which should be considered in biodiversity conservation. Habitat heterogeneity had a key role in determining the pattern of species richness, especially for small islands. Habitat specialists and generalists had different SIE‐related patterns. Our study highlights the importance of considering different ecological groups of species to improve our understanding of the SIE in fragmented habitats.

Habitat loss weakens the positive relationship between grassland plant richness and above-ground biomass

“…Farmlandd is the dominant matrix type in this area, accounting for about 30.6 % of the total area, with the main crops grown being potatoes and maize. Further background information about the study area is described in our previous papers ( Yan et al, 2022; Yan et al, 2023; Yan et al, 2021; Zhang et al, 2021 ).…”

“…To do so, we first used the moving window method (window size: 500-m radius buffer) to quantify grassland amount and the four landscape indices (patch density, edge density, mean patch area, and mean nearest-neighbor distance metric) surrounding all grassland cells. The 500-m radius buffer was used because our previous studies showed this buffer includes the optimal scale of spatial processes influencing grassland plant diversity in this region ( Yan et al, 2022; Yan et al, 2023; Zhang et al, 2021 ). Second, to quantify the fragmentation per se level, we derived the first principal component (PC1) of the four landscape indices ( Hertzog et al, 2019; Rolo et al, 2018 ).…”

“…The agro-pastoral ecotone of northern China is a typical anthropogenically 6 / 28 fragmented grassland landscape caused by historical agricultural reclamation, especially in the late Qing Dynasty (about 1840Dynasty (about -1912. Due to land policy reforms, the region has experienced a rapid expansion of farmland since the 1960s, converting continuous natural grasslands into smaller and isolated fragments, seriously threatening the conservation of biodiversity and ecosystem functions (Yan et al, 2022;Yan et al, 2023;Yang et al, 2020). Based on 130 landscapes with different fragmentation levels in the agro-pastoral ecotone of northern China, we investigated how fragmented landscape context (habitat loss and fragmentation per se) impact the relationship between grassland plant diversity and above-ground productivity in the community.…”

Non‐linear thresholds in the effect of area on three dimensions of diversity of herpetofauna in the West Indies

“…Recent studies suggest small habitat islands are hotspots of biodiversity conservation in fragmented landscapes (Wintle et al., 2019; Yan et al., 2021). However, within the limits of the SIE, species richness is independent from the direct effects of the usual explanatory variables, such as area and isolation (Triantis et al., 2003; Triantis & Sfenthourakis, 2012; Yan et al., 2023). Thereby, studies of the SIE could shed new light on the exploration of alternative variables to build up a more predictive and process‐based science of species richness variation across true and habitat island systems.…”

“…Since PDARs and FDARs can be explored within the same statistical framework as SARs, where the response variable S is a substitution of phylogenetic diversity or functional diversity (Helmus et al., 2007; Helmus & Ives, 2012; Smith et al., 2013), the exploration of SIEs in PDARs and FDARs is relatively straightforward. However, to date, the majority of SIE studies are focused on taxonomic diversity (Gao & Perry, 2016a; Yan et al., 2023; Yu et al., 2020), but rarely attempted in PDARs (but see Matthews et al., 2020) or FDARs.…”