The latest issue of Insect Conservation & Diversity is out, a special issue on insect population trends. I’m really happy I was able to contribute to a few papers in this issue as both editor and author (obviously not the same papers in each case!).
Thanks to Editor in Chief Raphael Didham for pulling together a great collection of papers, as well as rallying the editorial team to contribute to the issue with this really useful peer-reviewed paper summarising the key challenges involved in measuring insect population trends. This paper is really timely, as it highlights some of the potential pitfalls involved in estimating population changes over time.
Ecological data (e.g. long-term data on animal population trends) are not like simplified stock market trends or sports team stats. They are confounded by numerous complex environmental and measurement factors, many of which an observer may not be aware of. Nature isn’t simple and we’re kidding ourselves if we want a quick and easy answer to sum up everything, everywhere.
This special issue highlights some of these complexities, with a collection of great papers analysing complex data trends and discussing complex issues around how we interpret insect decline and support insect conservation.
The data papers are, unfortunately, all from the northern hemisphere – six from Europe and the UK and two from North America. One of the major limitations of the ‘global decline’ narrative is that most of the published evidence is from Europe and North America. While this shows that there is clearly a problem for insects in those countries, we can’t be certain what is happening in the rest of the world because of lack of data. So if you have access to long-term datasets from other countries, particularly in the southern hemisphere, please publish them!
Despite this limitation, the papers in this special issue all highlight key points that we need to acknowledge when we interpret insect population trends, whether they show declines or otherwise.
Different types of insects can respond differently to the same environmental factors. Separate papers show this trend for aphids vs. moths in the UK, and for macromoths, caddisflies and beetles vs. true bugs and mayflies in the Netherlands.
This is why measuring population and community-level trends in the field, in relation to environmental factors, is so important. Not only does it provide important context for the trends, it also provides some valuable insight into how different environmental attributes influence insect populations in different contexts. In this special issue, separate papers show how water quality parameters influence aquatic insect communities, and how changes in the plants and vegetation structure at a particular location (e.g. through land use change and land clearing) affects butterfly communities in Spain and longhorn beetles in Germany.
Data from locally-specific observation programs can be really valuable in providing long-term information on populations of particular species. For example, analysis of data from a citizen science program monitoring a glow-worm (Lampyris noctiluca) population in south-east England showed a decline from 2001-2018.
Occurrence data, e.g. observations of a species’ presence from citizen science or museum records, don’t tell us about abundance or population dynamics. But these observations do provide really important information on how land use change influences wildlife populations. This study of Poweshiek skipperling occurrences in eastern Minnesota and western South Dakota shows a decline in occurrence since 1985, partly because the butterfly is dependent on prairie habitats, which are one of America’s most threatened biomes.
But understanding insect population trends isn’t all about field data. Laboratory experiments can provide valuable complementary knowledge on how specific factors affect insects in isolation. This study used controlled laboratory experiments to show that zinc levels tended to decrease survival of monarch butterfly larvae, but increase survival of cabbage white larvae, although there were some developmental effects in the cabbage whites. Zinc is a widespread pollutant in the environment, but there is still very limited understanding of how heavy metal pollution affects insects and other animals in different environmental contexts.
The last two papers in the issue provide some more philosophical points of discussion. My paper with Jasmine Janes and James O’Hanlon builds on our recent discussion of the insect apocalypse narrative to highlight the communication pitfalls when we use the term ‘insect decline’ too generally, and provides some semantic recommendations for using the term ‘decline’ in relation to insects – it’s not always the most accurate or appropriate term, nor is it always the most effective term to engage audiences with insect conservation.
Another opinion paper, from Adam Hart and Seirian Sumner, includes an interesting proposal for promoting insects using a commercial marketing framework. I think the paper raises some valuable points about why we need to have a thoughtful discussion about how we engage with insects generally. But, as an ecosystem services scientist, I don’t think it gives enough credence to the existing ecosystem services framework that provides a comprehensive evidence-based framework for promoting the many values (economic and non-economic) of different ecosystem components.
Please do take some time to read all these great papers in this special issue. One of the wonderful things about insects is that we will never run out of things to talk about – here’s to many more engaging and nuanced discussions about how and why insects do what they do, and why we should care when we’re losing them.
© Manu Saunders 2020