The Argent and Sable is a nationally scarce moth which feeds on the Bog Myrtle plants that grow on peatland sites. This moth's dramatic decline is largely due to habitat destruction. 

The Red List process developed by the International Union for Conservation of Nature (IUCN) plays an important role in biodiversity conservation, both as the global standard for assessing extinction risk and in (indirectly) catalysing action to protect threatened species1. Recent population trend is a key measure used in this process, with declines of 30% or more over the last 10 years (or three generations, whichever is longer) qualifying for Red List threat categories. However, for species, such as many insects, with populations that vary greatly in abundance from one generation to the next, this short-term trend may be an unreliable measure of true extinction risk. Ten-year trends may be heavily skewed by particular boom or bust years, leading to Red List classifications that depend more on the start year of the trend than on the true, underlying situation faced by each species.

 

A new study1, led by Butterfly Conservation, quantified this effect using data on butterflies and moths from the UK Butterfly Monitoring Scheme and the Rothamsted Insect Survey2. Large discrepancies were revealed between Red List classifications produced using 10-year population trends that differed by just a single start year. For example, 15 butterfly species met the Red List threshold using population trends for 2002-2011, but 29 did so for the period 2003-2012. In the most extreme example, the difference of a single year reduced the number of qualifying moth species from 62 to just 20.

 

While the IUCN Red List guidelines do acknowledge population variability as an issue3, using population trends over just the last 10 years is likely to lead to biased Red Lists for species with high population variability.

Richard Fox

Associate Director Recording and Research

 

  1. Mace, G.M., Collar, N.J., Gaston, K.J., Hilton-Taylor, C., Akçakaya, H.R., Leader-Williams, N., Milner-Gulland, E.J. & Stuart, S.N. (2008) Quantification of extinction risk: International Union for the Conservation of Nature’s (IUCN) system for classifying threatened species. Conservation Biology 22:1424–1442. doi:10.1111/j.1523-1739.2008.01044.x

 

  1. Fox, R., Harrower, C.A., Bell, J.R., Shortall, C.R., Middlebrook, I. & Wilson, R.J. (2019) Insect population trends and the IUCN Red List process. Journal of Insect Conservation 23:269–278. doi:10.1007/s10841-018-0117-1

 

  1. IUCN. (2017) Guidelines for Using the IUCN Red List Categories and Criteria. Version 13, IUCN Species Survival Commission, Gland. www.iucnredlist.org/documents/RedListGuidelines.pdf