Examining the Impact of Habitat Fragmentation on Mammalian Genetic Diversity in Biodiversity Hotspots: A Meta-Analysis

Habitat fragmentation is among the foremost threats to global biodiversity, yet its genetic consequences for mammalian populations within biodiversity hotspots remain poorly quantified. These regions, characterised by exceptional species richness, endemism and disproportionate habitat loss, represent the highest-priority targets for conservation worldwide. To address this gap, we conducted a meta-analysis of the genetic effects of habitat fragmentation on mammals in biodiversity hotspots. Fifteen peer-reviewed studies published between 2009 and 2024 were assessed, and effect sizes (Hedges’ g) were pooled under a random-effects model with Hartung–Knapp adjustment for five microsatellite-based genetic metrics: observed heterozygosity (Ho), expected heterozygosity (He), number of alleles (NA), allelic richness (AR), and inbreeding coefficient (FIS). The main analysis included the six studies in which both the fragmented and the control populations were located within hotspots. In this analysis, pooled differences between fragmented and control populations were not distinguishable from zero for any metric (Ho: g = −0.04, 95% CI −0.54 to 0.46; He: −0.10, −0.43 to 0.23; NA: 0.21, −0.25 to 0.67; AR: −0.14, −0.57 to 0.30; FIS: −0.12, −0.78 to 0.54), and confidence and prediction intervals were wide because only four to six studies contributed to each estimate. In a sensitivity analysis of up to twelve studies that relaxed the hotspot criterion, He was lower in fragmented populations (g = −0.26, 95% CI −0.42 to −0.09, k = 11), whereas Ho, NA, AR and FIS did not differ significantly. Egger’s test did not indicate funnel-plot asymmetry in the sensitivity analysis, but its power was low. The evidence from studies located entirely within hotspots is currently too limited to determine the direction or size of fragmentation effects on mammalian microsatellite diversity. More primary studies with explicit comparisons of fragmented and continuous populations within hotspots are needed.