Defaunation erodes the diversity of rodent personality traits in fragmented forests

Habitat fragmentation is a primary driver of biodiversity loss globally. One impact of habitat fragmentation is the resultant decline and loss of large and medium mammal populations (also known as defaunation). While the effects of habitat fragmentation and associated defaunation on species diversity are well documented, their impacts on intraspecific diversity are less studied. One understudied source of intraspecific diversity is the animal personality traits within populations. As individuals with contrasting personality traits may disproportionately contribute to ecosystem functions, losing diversity of personality traits could thus impair ecosystem functions, even if some individuals of the species still persist. However, it is still unclear how the diversity of animal personality traits changes in fragmented habitats with severe defaunation. Here, we conducted mammal surveys and comprehensive behavioural assessments of Niviventer confucianus (Chinese white-bellied rat)—the most abundant rodent—on 11 forested islands in Thousand Island Lake, China, a fragmented reservoir island system formed by dam construction. We used Bayesian structural equation modelling and a functional diversity framework considering intraspecific variation to disentangle the direct and indirect effects of habitat fragmentation and defaunation on the functional diversity of N. confucianus personality traits. We found that defaunation directly decreased the functional divergence of N. confucianus personality traits. Decreasing island area indirectly reduced the functional divergence of N. confucianus personality traits through intensifying defaunation. We also found that island area directly increased rodent abundance but simultaneously exerted an indirect negative effect via defaunation. However, we did not find an effect of rodent abundance on the functional divergence, nor any effects of habitat fragmentation and defaunation on the functional richness or functional evenness of N. confucianus personality traits. These results indicate that defaunation may play a key role in mediating the negative effects of habitat fragmentation on animal behavioural diversity. The defaunation-resultant declines of intraspecific behavioural diversity highlight the importance of measuring intraspecific diversity to better understand the ecological consequences of human-driven environmental changes on biodiversity.