Some interesting syntheses of long-term insect data have been published in the last few months. These synthesis studies attempt to provide an answer to the big question mark raised by the recent insect apocalypse narrative.
This is how much of an impact a single study that gets lots of attention can have on the direction of science. The insectageddon opinion piece that started this ball rolling had fundamental flaws that are now well-documented (unfortunately it is still being widely cited in scientific literature and popular media as supposed evidence of decline). Sure, one could argue it got people talking about an important issue that we already had decades of evidence for.
This meta-analysis, led by Roel van Klink, collated time-series datasets on insect abundances from multiple countries, including studies found through a literature search, and some long-term monitoring databases. The authors explore trends across a number of different contexts, including climatic zones, continents and biomes, highlighting how much variation there is at different scales.
More recently, this study led by Michael Crossley analysed a set of publicly available datasets from LTER stations across the United States. The datasets cover a range of arthropod taxa across multiple ecoregions and again highlight what we already know: trends vary widely across taxa and locations.
These studies got some media attention; most likely this was partly because they were published in the celebrity journals, and partly because they add more clickbait to the insect apocalypse narrative. They also got a lot of criticism on social media, some fair, some not so fair.
Both of these studies have limitations and caveats. Every scientific study does, particularly meta-analyses and big data syntheses. Any attempt to collate and analyse ‘all the data’ on a particular ecological phenomenon, especially something as complicated as insect population dynamics, will face the common challenges of missing data, overlooked data, unpublished data, and misinterpreted data. The recent big data analysis quantifying the effect of last summer’s catastrophic bushfires on Australian biodiversity got huge global media attention, but no one seemed to care that it completely ignored invertebrate biodiversity.
These synthesis studies don’t represent all insects and are skewed toward data from the northern hemisphere. These are inherent flaws in the insect decline narrative that we can’t do anything about (historical data simply don’t exist for most countries and most taxa).
For time series analyses like these, there are plenty of other headache-inducing challenges, especially when the datasets aren’t standardised in sampling methods or timeframe. Trends are only ever relevant to the start and end point of the dataset, the environmental context of the data, and the analysis technique used.
These problems are not new, or even newsworthy. The issue is not that these studies have limitations, but that their simplified overall trends were assumed to be another ‘global fact’ in the insect apocalypse narrative (or at least a US-wide fact, in the case of the second study). Personally, I think the overall trend is the least interesting part of these studies.
Some people have criticised the US study for including data on pest groups, like aphids and mosquitoes. But this is an inconvenient truth of the flawed insect apocalypse narrative. We can’t have it both ways – we can’t promote the generalisation that all insects are in decline to get conservation attention, but then exclude the annoying ones from the conversation. (In reality, most aphids and mosquitoes aren’t pests, you’d have to drill down to species level to really understand those trends.)
Others have pointed out another obvious error: that the article title (and the journal’s social media posts) uses the word insect, but the study includes data on multiple arthropod taxa, including ticks, crabs and crayfish. The paper was originally titled “No Evidence of an “Insect Apocalypse” Across U.S. Long-Term Ecological Research Sites” (the peer review history is published with the paper); in that version, the authors used the term to refer to the existing popular lexicon connoting general biodiversity decline. (I think it’s great that non-insect taxa were acknowledged. Insects have been the focus of the decline narrative, but most other invertebrates are overlooked in conservation). I’m not sure why the authors decided to change the wording, but the current title is a lot more misleading than the original. It sounds pedantic, but this is how simple attempts to ‘be relevant’ can completely change the message of a study.
We can expect to see more of these type of studies, because the insect apocalypse narrative built an open doorway for sexy soundbite science. It’s easy to think we need to find a neat overall trend to answer the big question mark, but this isn’t really how science works.
Are we expecting too much of the limited data we have on insect populations? These synthesis studies do have value by highlighting what a complicated mess it is to try and understand global insect population trends.
This is why the EntoGem project (aiming to synthesise all the available data on insect abundance and diversity) is still ongoing, because it takes huge time and effort to collate these data in the first place.
Another great long-term project, the Swedish malaise trap study, published some of its preliminary results this year (they’ve identified about 700 new species!). The papers didn’t get much attention, probably because the authors didn’t analyse time trends; in one paper they discuss the operational perspective of the study and in another they assess a preliminary inventory of species. The papers are worth a read, especially to understand how much time and cost is required to collect and analyse long-term insect data, long before you get to the point of identifying trends over time.
What will we gain from proving or disproving that populations of all 1 million plus insect species around the globe are in decline? It’s an impossible goal, and we are missing the more important issues by focusing on nitpicking common technical limitations of claimed global trends.
Studies that focus on specific taxa and environmental contexts reveal much more nuance and provide much more detailed evidence that can inform new research, conservation policies and actions.
Understanding how interactions are changing is really important (like this study, led by Danielle Salcido, which found declines in diversity of caterpillars and their parasitoids in a Costa Rican forest associated with climate change and local land use). Interactions between species are what structures ecosystem, not the number of species per se, so it is vital that we understand more about how global change impacts interactions.
Understanding the link between global climate change and changes in resources, such as plant nutrients, and the subsequent effects on insects that depend on those resources to survive, is definitely worth greater exploration (a hypothesis that this study, led by Ellen Welti, explored with data on grasshoppers in a North American prairie).
Studies showing the positive effects of ecological restoration on invertebrates (e.g. these recent studies on natural enemies of forest pest beetles, pollinator, and herbivore communities) provide a clear path forward to achieve the conservation outcomes we seek.
These type of studies don’t get as much attention as they should.
© Manu Saunders 2020