Multivariate analysis reveals the impact of habitat fragmentation and intraspecific competition threshold of urban crickets

Insect survival strategies exhibit significant phenotypic plasticity in response to environmental variation, yet the mechanisms driving sex-specific adaptations under habitat fragmentation remain poorly understood. To address this knowledge gap, we employed a multivariate analysis approach in structural equation modeling (SEM) to analyze long-term data collected from urban habitats. The data includes multiple body size parameters, natural environment parameters, and social environment parameters under distinct levels of intraspecific competition. Body size parameters varied significantly with environmental and social parameters. We then conducted SEM analysis to explore the relationships among four body size parameters, competitive aggression, habitat area and isolation. Our results revealed distinct sex-specific responses: males were negatively selected by natural environment parameters below-threshold and by social environment parameters above-threshold. Females were positively selected by both natural environment parameters and social environment parameters below-threshold, but negatively by social parameters above-threshold. Our findings indicate sex-specific responses to environmental changes. Furthermore, despite the higher intensity of intraspecific competition in above-threshold males compared to below-threshold males, the probability of intraspecific competitive behavior was greater in below-threshold males. We propose the Density-Dependent Competition-Alternative Strategy Trade-Off (DCAST) hypothesis to explain this paradox, wherein males reduce aggression above-threshold as the benefits of alternative strategies outweigh competitive costs. These insect science findings demonstrate how competition thresholds shape phenotypic plasticity in urban insects, providing a framework for understanding adaptive responses to anthropogenic habitat fragmentation.