Effects of land‐cover transitions on emerging aquatic insects and environmental characteristics of headwater streams in an agricultural catchment

Abstract

Streams and their adjacent riparian zones are increasingly viewed as interdependent systems linked by reciprocal exchanges of energy, organisms, and materials. We assessed potential associations between the emerging aquatic insect flux and transitions between agricultural land and forest fragments to better understand these stream‐riparian linkages in managed landscapes. We sampled stream environmental conditions and emerging insects at 28 sites distributed along three streams flowing through agriculture‐forest‐agriculture transitions in central Ohio, USA, in the summer of 2012. Ephemeroptera and Trichoptera (ET) taxa had higher flux densities in forests (mean and 95% CI: 0.3 insects m−2 d−1 [0.1, 0.8]) compared to agriculture (mean and 95% CI: 0 insect m−2 d−1 [0, 0.1]; p = .004), and ET taxa were found in 67% of forested sites compared to only 15% of agricultural sites. In contrast, Dolichopodidae were more strongly associated with agricultural land (mean and 95% CI: 0.6 insect m−2 d−1 [0.3 to 1.2]) than forests (mean and 95% CI: 0.1 insects m−2 d−1 [0.1, 0.2]; p = .002). Although Chironomidae were the most numerically abundant, ET taxa were among the larger bodied insects and comprised >30% of the total biomass flux, illustrating the importance of taxonomic traits in mediating flux dynamics. Mechanisms driving emerging insect flux were related to substrate grain‐size distribution, channel width, and nutrient concentrations. Overall, our results demonstrate that small forest fragments are strongly related to the aquatic‐to‐terrestrial insect flux and thus have important implications for terrestrial biodiversity and food webs in agricultural landscapes.

The vulnerability of British aquatic insects to climate change

“…3). This reduction in records may indicate the effects of other pressures such as land use and riparian habitats which are known to be partly important to insect populations in streams (Staponites et al, 2019;Goss et al, 2020) and warrants further investigation. Equally the change may reflect a difference in sampling effort between the two investigation periods within Wales.…”

Niche differentiation, reproductive interference, and range expansion

“…An environmental layer for the presence/absence of flowing water would be useful for generating high-resolution habitat suitability maps but not for studying niche differentiation, because flowing water is a habitat requirement for all calopterygid damselflies in North America (Westfall & May, 1996). Syntopic species of rubyspot damselflies often differ in microhabitat use (e.g., current speed, canopy cover and stream width) (Anderson & Grether, 2011;McEachin et al, 2021), which suggests that microhabitat data would be useful for explaining the distributions and relative densities of species within streams, as has been shown in other aquatic insects (Goss et al, 2020), but microhabitat differences could not account for species range differences at the continental scale.…”