Matthew D. Moran, by Hendrix College
In recent years, the notion of an insect apocalypse has become a hot topic in the conservation science community and has attracted public attention. Scientists who have warned that the catastrophe is exposing those arthropods – which include a large range of invertebrates – to worms – are rapidly declining, perhaps indicating a general collapse of ecosystems worldwide.
Starting around the year 2000, and more frequently since 2017, researchers have documented large population declines among mites, beetles, bees, butterflies, and many other insect types. If verified, this trend will be of serious concern, especially given that insects are important animals in almost all terrestrial environments.
But in a newly published study, in which I co-authored with 11 colleagues, we reviewed more than 5,000 data on arthropods in North America, including thousands of species and dozens of habitats. We found, in essence, no change in population size.
These results do not mean that insects are cured. In fact, I believe there is good evidence that some species of pests are at risk of degradation and extinction. But our findings suggest that overall, the idea of declining pests on a large scale is an open question.
For most scientists, the idea of disappearing insects is a precursor that will have harmful consequences for all aspects of life on Earth, including human welfare.
But some scholars were skeptical about the reported insect apocalypse. Numerous studies focused mainly on Europe, reflecting widespread declines, which were geographically limited. Typically, these studies analyzed only a few species or groups of species.
Insects have developed adaptations that enable them to live in a vast range of environments around the world.
Some particularly long-lasting assessments showed that the decline occurred in the last 30 years when the relevant insect population increased. Many insect populations are known to fluctuate naturally, sometimes dramatically.
Many scientists concluded that while there was a possibility of widespread pest damage, the jury was still out on what was actually happening.
Pointing to north america
Ecologist Bill Snyder and I thought that studies about widespread insect-diseases suggest that an intriguing pattern was produced with significant changes, but that the findings were not strong enough to draw conclusions. We wanted to investigate what is happening in North America, which is quite diverse and surprisingly not a comprehensive analysis of the decline of pests for us.
For our study, we decided to use data from sites in a long-term science research network, supported by the National Science Foundation. The network includes 28 sites across the US that have been intensively studied since the 1980s and includes deserts, mountains, prairies, and forests. With nearly 40 years of data collected, we expected trends at these sites to be a good complement to European insect studies.
We put together a 12-man team, consisting of six graduate students, post-doctoral scholars Michael Scott Crossley and Amanda Maier, and colleagues from the US Department of Agriculture. When we finished compiling our data set, at least some of us expected to see widespread pest degradation.
Instead, the results surprised us. Some species we declined, while others grew. But until now the most common result for the species at a particular site was no significant change. Most of our species had stable numbers.
At first we felt that we were missing something. We tried to compare different taxonomic groups, such as beetles and butterflies, and different types of feeding, such as herbivores and carnivores. We tried to compare urban, agricultural and relatively small areas. We tried to compare different dwellings and different periods.
But the answer remains the same: no change. We had to conclude that the sites we examined did not have signs of an insect apocalypse and, in fact, no widespread decline.
Explain continental differences
We are confident in our analysis and our conclusion, but a more important question is why our results differ so much from other recent studies. I see two possible explanations: location and publication bias.
As I noted, most insect degradation papers came from European data. In fact, Europe has better and more comprehensive long-term data than other parts of the world. It is also one of the most densely populated parts of the world – three times more than North America.
In addition, almost all of Europe’s land has been modified for human use. Agriculture is widespread and intense, and cities and suburban areas comprise large parts of the landscape. It is perhaps therefore surprising that Europe has lost a larger proportion of its wild animals than North America.
Publication bias is not about dishonesty or false results. This refers to the idea that more dramatic results are more youthful. Critics and journals are likely to be interested in species that are disappearing in comparison to species that show no change over time.
Just dismissed from a top magazine because our findings are not surprising enough. “Are there any countermeasures or unexpected conclusions that the author might uncover more? If not, the paper feels like this is documentation of the things we would have already expected.” #publication bias pic.twitter.com/4BuPlWBTaW
– Dr. Rebecca Kritzer (@rebeccakreitzer) November 8, 2019
The result is that over time, falling species can be more heavily represented in the literature. Then, when scholars look for papers on animal populations, they primarily decline what they find.
We selected long-term ecological research sites for their analysis in part because they had “raw” data available that were not peer-reviewed for publication and were not collected in anticipation of degradation. Rather, scientists collected these data to monitor ecosystems and observe trends over time. In other words, it was unbiased data. And because the data sets were so diverse, they covered a wide range of species and habitats.
Future of insects
Our study will not be the final answer. As the human population continues to grow and employ a large portion of the world’s land, water, land, and biomass, other species can only lag behind and survive with fewer resources. I have no doubt that every time a forest is cut, a prairie plowed or a farm is paved, the world loses the lives of some of its animals and plants.
Determining this process will require more monitoring, more conservation biologists working in the field, and greater awareness of how human actions affect the Earth’s biodiversity. But it may be possible that insects that have lived for millions of years through a great many biological catastrophes, are also finding a way to keep our presence alive.
Matthew D. Moran, Professor of Biology, Hendrix College
This article is republished from chit chat Under a Creative Commons license. Read the original article.
Bottom line: Although the recent reports of a dramatic decline in insect populations have raised concerns about the ‘insect apocalypse’. A new analysis of data from sites in North America suggests that the case has not been proven.