Author's Final Manuscript
Nature Ecology & Evolution
Crossley et al. (2020)1 examine patterns of change in insect abundance and diversity across US Long-Term Ecological Research (LTER) sites, concluding “a lack of overall increase or decline”. This is notable if true, given mixed conclusions in the literature regarding the nature and ubiquity of insect declines across regions and insect taxonomic groups2–6. The data analyzed, downloaded from and collected by US LTER sites, represent unique time series of arthropod abundances. These long-term datasets often provide critical insights, capturing both steady changes and responses to sudden unpredictable events. However, a number of the included datasets are not suitable for estimating long-term observational trends because they come from experiments or have methodological inconsistencies. Additionally, long-term ecological datasets are rarely uniform in sampling effort across their full duration as a result of the changing goals and abilities of a research site to collect data7. We suggest that Crossley et al.’s results rely upon a key, but flawed, assumption, that sampling was collected “in a consistent way over time within each dataset”. We document problems with data use prior to statistical analyses from eight LTER sites due to datasets not being suitable for long-term trend estimation and not accounting for sampling variation, using the Konza Prairie (KNZ) grasshopper dataset (CGR022) as an example.
Welti, E.A.R., Joern, A., Ellison, A.M. et al. "Studies of insect temporal trends must account for the complex sampling histories inherent to many long-term monitoring efforts." Nat Ecol 5: 589–591.