Challenges in Measuring Global Insect Decline

By Clive Hambler. He is Lecturer in Biological and Human Sciences at Oxford University.

"Global rates of insect decline will be very hard to measure. Conclusions regarding drivers and rates of declines can be unreliable due to biases - including sampling location and omission of relevant publications through narrow search terms. Extrapolation of global species declines from a few regions or a sample disproportionately including population loss at range-margins is indefensible, and the projected global rate of loss can be seriously overestimated. Samples of insect declines (e.g. reviewed publications) must not overlap in space and time, which would violate observation independence. The threat from climate change can be inflated if declines are not separated from the effects of seasonality and activity. Measures of density, not activity-abundance, are most valuable. No extinction can be firmly attributed to anthropogenic climate change unless the climate trend can also be attributed to humans. The role of pesticides will be inflated if developed nations dominate in the samples. We suggest some minimal methodological requirements when reviewing declines and extinctions. Given these strictures, we reaffirm that declines in most non-marine invertebrate groups will have to be estimated using previously calibrated indicators such as birds and freshwater fish."