Insect community activity patterns on a diel scale: Trophic position and body size

Most arthropods limit their activity to a particular time of the day or night. Arthropod activity times are often determined by changes in temperature, ambient light, predator abundance, or resource availability. Despite long recognized daily patterns of arthropod activity, we know very little about how key characteristics of arthropod communities vary on diel scales. Body size and trophic position structure species interactions within ecosystems, yet, there have been no community-level studies to date investigating when particular trophic levels are active and how large active arthropods are at a particular time of day. The abundance of predators and parasitoids during particular times of day may determine the risk associated with activity of detritivores and herbivores, whereas small arthropods may be less perceptible to visual predators during the day. To characterize how an arthropod community changes with time of day we collected insects within 4-hour intervals for 5 days using pitfall and malaise traps, identified all arthropods to family, measured each individual’s length and width, and assigned family level trophic positions. We found that body size within most orders was on average higher during the night. Overall abundance of arthropods collected was highest during the day. Detritivores were more active during the night, whereas parasitoids were almost entirely day-active. Herbivores and predators made up a relatively constant proportion of the community; however, the identity of active herbivores and predators changes throughout the day. These results suggest that key characteristics of arthropod communities vary on diel scales, including body size and trophic position.