Meta-analysis reveals declines in terrestrial but increases in freshwater insect abundances

Abstract

Recent case studies showing substantial declines of insect abundances have raised alarm, but how widespread such patterns are remains unclear. We compiled data from 166 long-term surveys of insect assemblages across 1676 sites to investigate trends in insect abundances over time. Overall, we found considerable variation in trends even among adjacent sites but an average decline of terrestrial insect abundance by ~9% per decade and an increase of freshwater insect abundance by ~11% per decade. Both patterns were largely driven by strong trends in North America and some European regions. We found some associations with potential drivers (e.g., land-use drivers), and trends in protected areas tended to be weaker. Our findings provide a more nuanced view of spatiotemporal patterns of insect abundance trends than previously suggested.

Comparing the success of active and passive restoration in a tropical cloud forest landscape: A multi-taxa fauna approach

“…These three groups have different ecological traits, are highly sensitive to modifications in their habitats [22], and perform important ecological functions, such as seed dispersal, insect population control, and nutrient cycling [23][24][25]. Also they are taxa of conservation concern, as amphibians are the most threatened group of terrestrial vertebrates worldwide [26] and terrestrial insects are undergoing marked population declines [27]. We compared species richness, abundance/occurrence, and community composition of these groups in a 23-year-old actively restored forest, a 23-year-old passively restored forest, a cattle pasture (degraded ecosystem), and a mature cloud forest (reference ecosystem).…”

Insect threats and conservation through the lens of global experts

“…Due to the extent and severity of threats that insects are facing worldwide (Cardoso et al, 2020; Wagner, 2020), it was somehow expected that respondents would identify a mainly decreasing trend in parameters reflecting the status of insect populations. However, it is noteworthy that in almost one third of the answers, respondents selected unknown trends, which indicates that, even with the recent rise in the number of papers tackling insect declines, the most diverse class of organisms on the planet is still severely understudied, hence a nuanced view of insect declines or increases according to taxon and region is needed (van Klink et al, 2020). Functional and phylogenetic diversity had more neutral answers, which might reflect the fact that unique functions or branches in the tree of life are not necessarily lost at the same pace as other metrics, not necessarily that they are not lost at all.…”

“…However, all studies quantifying and assessing long-term global trends in insect abundance or diversity to date (e.g. van Klink et al, 2020) are biased, both spatially and taxonomically, often leading to misinterpretation (Simmons et al, 2019; Didham et al, 2020; Montgomery et al, 2020).…”

Flower power in the city: Replacing roadside shrubs by wildflower meadows increases insect numbers and reduces maintenance costs

“…A remarkable decline in the number of insect species and in the abundance of insects is currently reported from many places around the world [1][2][3][4][5][6]. In addition to the considerable loss of organisms that are valuable per se, the loss of insects is considered to harm species-interactions [7,8] and related ecosystem processes [9][10][11].…”