Don't jump to conclusions on arthropod abundance dynamics without appropriate data
Controversy over the decline of arthropods: a matter of temporal baseline?
Recommendation: posted 19 May 2022, validated 24 May 2022
Humans are dramatically modifying many aspects of our planet via increasing concentrations of carbon dioxide in the atmosphere, patterns of land-use change, and unsustainable exploitation of the planet’s resources. These changes impact the abundance of species of wild organisms, with winners and losers. Identifying how different species and groups of species are influenced by anthropogenic activity in different biomes, continents, and habitats, has become a pressing scientific question with many publications reporting analyses of disparate data on species population sizes. Many conclusions are based on the linear analysis of rather short time series of organismal abundances.
There has been particular interest in how arthropods are impacted by environmental change, with several recent papers reporting contradictory results. To investigate why these contradictions might arise, Duchenne et al. (2022) conducted an analysis of four published data sets along with a series of experimental analyses of simulated time series to examine the power of widely used statistical analyses to gain inference on temporal trends. Their important paper reveals that accurate inference on dynamics, particularly of species that exhibit large temporal fluctuations in abundance, requires time series that are substantially longer than are typically collected, as well as careful thought as to whether linear models are appropriate. Linear analyses of short time series are susceptible to providing unreliable inference as trends can be strongly influenced by points at either end of the time series.
Duchenne et al.’s paper provides important insight on the conditions when strong inference on temporal trends of arthropod (and other species) abundances can be made, and when they should be treated with caution. They do not doubt that many insect and arachnid species are changing their abundances, and that patterns in these changes may vary spatially. What their results do say is that we should treat grand claims of population recovery or rapid declines apparently to extinction with caution when they are based on short time series, particularly of species that show significant boom and bust dynamics. In many ways, these results are not unexpected, but it is nice to see such careful and thoughtful analyses and interpretation. More data are required for most arthropod species before clear assessments of abundance trends can be made. Given our reliance on many arthropods for food, pollination, and numerous ecosystem services, and the ability of other species to spread devastating human diseases such as dengue and malaria, it is advisable that we slow our modification of their habitats while additional data are collected to allow us to better characterise the trajectory of arthropod populations to understand what the consequences of our actions on the natural world are likely to be.
Duchenne F, Porcher E, Mihoub J-B, Loïs G, Fontaine C (2022) Controversy over the decline of arthropods: a matter of temporal baseline? bioRxiv, 2022.02.09.479422, ver. 3 peer-reviewed and recommended by Peer Community in Ecology. https://doi.org/10.1101/2022.02.09.479422
Tim Coulson (2022) Don't jump to conclusions on arthropod abundance dynamics without appropriate data. Peer Community in Ecology, 100098. https://doi.org/10.24072/pci.ecology.100098
The recommender in charge of the evaluation of the article and the reviewers declared that they have no conflict of interest (as defined in the code of conduct of PCI) with the authors or with the content of the article.
Evaluation round #1
DOI or URL of the preprint: https://doi.org/10.1101/2022.02.09.479422
Version of the preprint: 1
Author's Reply, 18 May 2022
Decision by Tim Coulson, posted 23 Mar 2022
Both reviewers, and I, consider this to be an excellent preprint. The analyses that are conducted across four impressive datasets reveals several important results. In particular, the analyses reveal that a lack of good baseline data make it close to impossible to assess long-term abundance trends, and this is particularly the case with short-time series exhibiting non-monotonous dynamics.
One reviewer has very few comments, stating that, for them, this was a rare occassion to read such a well-produced, and important paper that requires little modification. The suggested changes are minor. The second reviewer has a number of suggested edits, all that seem sensible, and none that will impact the results or conclusions. Given this, I am asking the authors to revise their manuscript to address these minor issues. Once that is done, I do not consider it necessary to seek re-review. Instead I will read the revised manuscript, and will recommend.
I would like to finish by congratulating the authors on a very impressive, and important, piece of work.