Insect abundance changes over time

Special Issue: Spotlight on insects: trends, threats and conservation challenges (Insect Conservation and Diversity, march 2020)
“In this special issue of Insect Conservation and Diversity, we present new empirical evidence on insect populations trends, address interacting drivers of change, and identify key challenges for the future.”
Papers:
Interpreting insect declines: seven challenges and a way forward
Are insects declining and at what rate? An analysis of standardised, systematic catches of aphid and moth abundances across Great Britain
Declining abundance of beetles, moths and caddisflies in the Netherlands
Long‐term monitoring reveals decreasing water beetle diversity, loss of specialists and community shifts over the past 28 years
Vegetation encroachment drives changes in the composition of butterfly assemblages and species loss in Mediterranean ecosystems
Glowing, glowing, gone? Monitoring long‐term trends in glow‐worm numbers in south‐east England
Factors contributing to the decline of an endangered flightless longhorn beetle: A 20‐year study
Landscape‐level environmental stressors contributing to the decline of Poweshiek skipperling (Oarisma poweshiek)
Assessing zinc tolerance in two butterfly species: consequences for conservation in polluted environments
Semantics of the insect decline narrative: recommendations for communicating insect conservation to peer and public audiences
Marketing insects: can exploiting a commercial framework help promote undervalued insect species?

Complex and nonlinear climate‐driven changes in freshwater insect communities over 42 years (Baranov et al. 2020)
“These changes were accompanied by an 81.6% decline in insect abundance, but an increase in richness (+8.5%), Shannon diversity (+22.7%), evenness (+22.4%) and interannual turnover (+34%).”

Arthropod decline in grasslands and forests is associated with landscape-level drivers (Seibold et al. 2020)
“Overall gamma diversity in grasslands and forests decreased over time, indicating loss of species across sites and regions. In annually sampled grasslands, biomass, abundance and number of species declined by 67%, 78% and 34%, respectively.” … “In 30 forest sites with annual inventories, biomass and species number—but not abundance—decreased by 41% and 36%, respectively.”

Worldwide decline of the entomofauna: A review of its drivers (Sánchez-Bayo & Wyckhuys, 2019)
“Our work reveals dramatic rates of decline that may lead to the extinction of 40% of the world’s insect species over the next few decades.”

Parallel declines in abundance of insects and insectivorous birds in Denmark over 22 years (Møller, 2019)
“The abundance of flying insects was quantified using a windscreen resulting in reductions of 80% and 97% at two transects of 1.2 km and 25 km, respectively, according to general additive mixed model.”

Widespread losses of pollinating insects in Britain (Powney et al. 2019)
“Here we show substantial inter-specific variation in pollinator trends, based on occupancy models for 353 wild bee and hoverfly species in Great Britain between 1980 and 2013. Furthermore, we estimate a net loss of over 2.7 million occupied 1 km2 grid cells across all species. Declines in pollinator evenness suggest that losses were concentrated in rare species. In addition, losses linked to specific habitats were identified, with a 55% decline among species associated with uplands. This contrasts with dominant crop pollinators, which increased by 12%, potentially in response agri-environment measures.”

Climate-driven declines in arthropod abundance restructure a rainforest food web (Lister & Garcia, 2018)
“We compared arthropod biomass in Puerto Rico’s Luquillo rainforest with data taken during the 1970s and found that biomass had fallen 10 to 60 times. Our analyses revealed synchronous declines in the lizards, frogs, and birds that eat arthropods. Over the past 30 years, forest temperatures have risen 2.0 °C, and our study indicates that climate warming is the driving force behind the collapse of the forest’s food web.”

More than 75 percent decline over 27 years in total flying insect biomass in protected areas (Hallmann et al. 2017)
“Our analysis estimates a seasonal decline of 76%, and mid-summer decline of 82% in flying insect biomass over the 27 years of study. We show that this decline is apparent regardless of habitat type, while changes in weather, land use, and habitat characteristics cannot explain this overall decline.”

Influences of extreme weather, climate and pesticide use on invertebrates in cereal fields over 42 years (Ewald et al. 2015)
“Of the 26 invertebrate groups examined, eleven proved sensitive to extreme weather events. Average abundance increased in hot/dry years and decreased in cold/wet years for Araneae, Cicadellidae, adult Heteroptera, Thysanoptera, Braconidae, Enicmus and Lathridiidae.” … “Some long‐term trends in invertebrate abundance correlated with temperature and rainfall, indicating that climate change may affect them. However, pesticide use was more important in explaining the trends, suggesting that reduced pesticide use would mitigate the effects of climate change.”

Ermittlung der Biomassen flugaktiver Insekten im Naturschutzgebiet Orbroicher Bruch mit Malaise Fallen in den Jahren 1989 und 2013 (Sorg et al. 2013)
English version: “Our data confirms, that in the areas studied, less than 25% of the original number of flying insects collected in 1989, were still present in 2013.”

Large carabid beetle declines in a United Kingdom monitoring network increases evidence for a widespread loss in insect biodiversity (Brooks et al. 2012)
“We found substantial overall declines in carabid biodiversity. Three‐quarters of the species studied declined, half of which were estimated to be undergoing population reductions of > 30%, when averaged over 10‐year periods.”

Long‐term changes in the abundance of flying insects (Shortall et al. 2009)
“There was a significant decline in total biomass at Hereford but not at three other sites: Rothamsted, Starcross and Wye.”

Odonata enter the biodiversity crisis debate: The first global assessment of an insect group (Clausnitzer et al. 2009)
“We have found that one in 10 species of dragonflies and damselflies is threatened with extinction. This threat level is among the lowest of groups that have been assessed to date, suggesting that previous estimates of extinction risk for insects might be misleading.”

Long-term population trends in widespread British moths (Conrad et al. 2004)
“The percentage of species displaying significant decreases (54%) was more than double that displaying increases (22%).”

Rapid responses of British butterflies to opposing forces of climate and habitat change (Warren et al. 2001)
“These insects might be expected to have responded positively to climate warming over the past 30 years, yet three-quarters of them declined: negative responses to habitat loss have outweighed positive responses to climate warming.”

Population Trends of Common British Butterflies at Monitored Sites (Pollard et al. 1995)
“Populations of the species which have expanded in range, monitored for varying periods during 1974-92 have, overall, shown significantly more increases than declines in abundance, as have the species with ranges which already occupy most of Britain.”

Reports:

Monitoring of ecosystem function at landscape‐scale demonstrates temporal difference in invertebrate abundance in Kent and South‐East England (Tinsley-Marshall et al. 2020)
” Between 2004 (n=3838) and 2019 (n=667) there was a statistically significant differece in ‘splat density’ of the order of approximately 50%, from an average of 0.2 splats per mile to 0.1 splats per mile.” … ” We found a small but statistically significant positive relationship between vehicle age and splat density, suggesting that modern cars squash more invertebrates that older cars (Figure 3b). This suggests that the signal from the difference in insect abundance is strong enough to be apparent inspite of more efficient sampling by newer vehicles.”

The State of Britain’s Larger Moths 2013 (Fox et al. 2013)
“Across Britain, the total abundance of larger moths declined significantly, by 28%, during the 40-year period from 1968 to 2007.”

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