Decline of insects and arachnids driven by nutrient enrichment: A meta‐analysis

Abstract

Recent studies have documented global declines in insects and their relatives, but the exact mechanisms explaining these patterns are not fully understood.A potential driver underlying arthropod population declines is increases in anthropogenic inputs of nitrogen (N) and phosphorus (P). Here, we synthesize the effects of N, P, and combined N + P enrichment on the abundance of hexapods (insects and collembola) and arachnids from 901 experiments reported in 84 studies. We found that N and combined N + P enrichment caused significant decreases in the abundance of these groups overall. While arthropod responses to nutrient enrichment across aquatic and terrestrial habitats and in temperate as well as tropical climatic zones differed in magnitude, our results suggest that arthropods are decreasing similarly in response to nitrogen and phosphorus enrichment. Further, despite previously shown differences in the nutrient demands of different insect metamorphosis groups, we found consistent negative effects of N + P enrichment on all groups. Our results also showed that the negative effects of nutrient additions are stronger for aquatic insects that are considered more sensitive to changes in physical-chemical parameters in their environments, Ephemeroptera, Plecoptera, and Trichoptera (EPT), compared with other aquatic insects. In addition, N + P enrichment reduced the abundance of above-ground and below-ground arthropods, suggesting that a similar mechanism driving arthropod community change is acting on both groups. These findings suggest that changes in elemental cycles are a potential cause of the ongoing global decline of arthropods and underscore the serious effects of nutrient enrichment on ecological systems.

Fluctuation in the diversity of mayflies (Insecta, Ephemerida) as documented in the fossil record

“…The consequences are much more pronounced in standing water bodies compared to rivers, due to greater flow in the latter, which causes nutrient transport rather than settlement 49 . Mayflies have been identified as one of the groups particularly sensitive to the negative effects of nutrient additions 48 and we hypothesise that phenomenon was responsible for the pronounced increase of their extinction rate in the mid-Cretaceous.…”

“…In aquatic environments, an increased input of nutrients (in particular nitrogen and phosphorus) has many effects on the chemistry and biology of water bodies, such as elevation of pH, dissolved oxygen depletion, reduction of water clarity, and increased biomass of freshwater phytoplankton and periphyton 47 . For illustration, the consequences can be compared with the anthropogenic eutrophication caused by the excessive nutrient enrichment of today, recently identified as one of the drivers underlying ongoing arthropod population declines 48 . The consequences are much more pronounced in standing water bodies compared to rivers, due to greater flow in the latter, which causes nutrient transport rather than settlement 49 .…”

A call to expand global change research in LTER coastal wetlands

“…3). As posited in two recent studies (Nessel et al 2021, Nessel et al 2022, the decline in invertebrate abundance and biomass may be due to nutrient enrichment changing the identity of the limiting nutrient, thereby causing elemental imbalances between consumers and their resources. Such mismatches can constrain consumer growth and reproduction, leading to changes in population abundance as well as the structure of the ecological community (Schade et al 2003, Mulder 2010, Gonzalez et al 2014, Lemoine et al 2014.…”