Community-wide body size differences between nocturnal and diurnal insects

Examining community-wide patterns for the most diverse animal group, insects, is fundamental to our understanding of the ecological and evolutionary factors that maintain tropical diversity. Using several sampling techniques (malaise traps, pitfall traps, visual searches, and social spider nest captures), we investigated the day-night community composition of active insects to reveal differences in body size at three elevations in eastern Ecuador. We show that insects active at night are, on average, larger than those active during the day. Even though insect size decreased with increasing elevation, the observed diel pattern was consistent across elevations, and for most insect orders. All sampling techniques consistently detected day-night differences in insect size, except for social spider captures at the two higher elevations, probably due to the reduced range of colony sizes at the higher elevations and possibly lower spider activity at night. We suggest that the observed diel patterns in insect size may be driven by a combination of factors, including increased risk imposed on large insects by diurnal visual predators, mainly insectivorous birds, and physiological responses to diel changes in abiotic conditions.