Functional Complementarity of Birds and Arthropods in Pest Control: Effects of Habitat Complexity and Seasonal Dynamics in Ethiopian Smallholder Agroecosystems

Understanding how habitat structure and seasonal variation influence natural pest control is crucial for designing sustainable farming systems in tropical landscapes. This study experimentally quantified the contributions of birds and arthropods to pest suppression across tree-rich and tree-poor smallholder agroecosystems in the Kafa Biosphere Reserve, southwestern Ethiopia. Using 3,000 plasticine caterpillar models deployed over six weeks, it was assessed spatial and temporal variation in predation and evaluated how landscape complexity and prey traits shape predator activity. Overall, 33.9% of caterpillars exhibited predation marks, with arthropods responsible for 51.5% of attacks and birds for 46.9%. Total predation was higher in complex, tree-rich habitats (19.7%) than in simplified, tree-poor farms (14.2%). Birds exerted stronger predation pressure in complex landscapes, whereas arthropods dominated in simplified ones, demonstrating functional complementarity between predator guilds. Prey coloration significantly affected avian but not arthropod predation, indicating contrasting sensory foraging mechanisms. Predation activity peaked between the second and fourth weeks, coinciding with favorable microclimatic conditions. These findings reveal that habitat heterogeneity and seasonal dynamics jointly regulate biological control services in tropical smallholder systems. Promoting agroforestry, conserving native trees, and aligning farm management with periods of high predator activity can enhance the resilience of natural pest control. The study provides rare empirical evidence from African biosphere reserves, highlighting the ecological and practical value of maintaining multifunctional predator communities for biodiversity-based pest management.