Landscape effects on biodiversity are context dependent – insularization drives physiological condition of amazonian dung beetles

Abstract

The degradation and fragmentation of natural landscapes into isolated fragments threaten species survival in anthropogenic ecosystems. Insularization, caused by human activities such as the construction of hydroelectric dam reservoirs, leads to habitat loss and fragmentation, negatively impacting biodiversity. In this study, we focus on the physiological approach as a key tool to understand the impact of insularization on organisms. We evaluated the effects of insularization on the physiological condition of assemblages, using dung beetles as model organisms. We investigated the physiological condition and body size of dung beetles at the Balbina Hydroelectric Reservoir in the Central Amazon region. The reservoir comprises numerous islands of varying size, shape, and distance from continuous forests. We collected dung beetles from multiple islands and continuous forest areas using pitfall traps. We analyzed the effects of various landscape variables, including size, shape, isolation, proximity, forest cover, and habitat type (island or mainland), on dung beetle physiological condition (muscle mass, lipid mass, and body dry mass) and body size. We used two approaches to assess the impact of insularization on dung beetles: at the individual and assemblage levels. At the assemblage level, the results indicated that forest cover positively influenced dung beetle body size. However, habitat type did not affect the size or body dry mass of the beetles. When analyzing the effects at the species level, contrasting responses were found depending on the species analyzed. Larger islands tended to harbor larger individuals of certain dung beetle species, such as Deltochilum aspericolle, while mainland individuals, such as Dichotomius lucasi and Canthon triangularis, had larger body sizes than those on islands. The proportion of closed-canopy forest also influenced physiological attributes, with C. triangularis exhibiting larger lipid masses in landscapes with a higher proportion of closed-canopy, while D. aspericolle and Dichotomius boreus showed smaller lipid masses in such landscapes. This study sheds light on the impact of insularization on the physiological condition and body size of dung beetles in the Amazon region. The findings contribute to a better understanding of how habitat fragmentation affects biodiversity in island landscapes. Such information can help develop effective conservation strategies to mitigate the adverse consequences of dam construction and habitat fragmentation on Amazonian biodiversity