Abstract
Forest canopy is densely populated by phyto-, sapro-, and microbiphages, as well as predators and parasitoids. Eventually, many of crown inhabitants fall down, forming so-called ‘arthropod rain’. Although arthropod rain can be an important food source for litter-dwelling predators and saprophages, its origin and composition remains unexplored. We measured stable isotope composition of the arthropod rain in a temperate mixed forest throughout the growing season. Invertebrates forming arthropod rain were on average depleted in 13C and 15N by 1.6‰ and 2.7‰, respectively, compared to the soil-dwelling animals. This difference can be used to detect the contribution of the arthropod rain to detrital food webs. Low average δ13C and δ15N values of the arthropod rain were primarily driven by the presence of wingless microhytophages, represented mainly by Collembola and Psocoptera, and macrophytophages, mainly aphids, caterpillars, and heteropterans. Winged arthropods were enriched in heavy isotopes relative to wingless specimens, being similar in the isotopic composition to soil-dwelling invertebrates. Moreover, there was no consistent difference in δ13C and δ15N values between saprophages and predators among winged insects, suggesting that winged insects in the arthropod rain represented a random assemblage of specimens originating in different biotopes, and are tightly linked to soil food webs.
Highlights
Numerous feedback mechanisms link the above- and belowground components of e cosystems[1,2,3]
Approximately 28% of the total mass of arthropod rain is formed by dead animals and exuviae; this fraction can be consumed by saprophages such as collembolans
We further proposed that (2) winged insects in the arthropod rain have on average higher δ13C and δ15N values than wingless invertebrates because the former are likely to have tight trophic connections with soil and detrital food webs
Summary
Numerous feedback mechanisms link the above- and belowground components of e cosystems[1,2,3]. Aboveground consumers of higher trophic levels receive energy subsidies from detrital food webs, which allows for a larger population of aboveground invertebrate generalist predators[4,5,6]. This phenomenon subsequently impacts plant productivity by controlling the populations of phytophages[7]. Our first arthropod rain study in a temperate forest[12] showed that the rain was taxonomically diverse: it comprised approximately 15 orders and more than 60 families of invertebrates Some of these animals are slow-moving and defenseless and can be captured by soil predators. Due to the prevalence of macrophytophages and microphytophages in the arthropod rain, it can be expected to be depleted by 2–3‰ in 13C and 15N content relative to the animals belonging to detrital food webs in soil
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