What the windscreen anecdote tells us about science

The windscreen anecdote has been doing the rounds on social media again.

A couple of years ago, I wrote about why this anecdote is not reliable evidence of insect population trends.

If you’re not familiar with the story, it goes a little something like this. “When I was a kid we would drive long distances for holidays and get bugs all over the windscreen. I don’t see any bugs on the windscreen anymore, therefore….” The interpretation, whether implied or stated explicitly, is that this is yet more evidence that a global insect decline is happening.

There are obvious flaws in this assumption, but the anecdote still strikes a chord with so many people, perhaps through some kind of confirmation bias. We know that biodiversity is in trouble, we know humans are having damaging effects on the environment, so it must be true, right?

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Why did the pollinator cross the road?

The concept of the ‘edge effect’ has inspired long and varied discussion in the ecological literature. In essence, an edge effect is a change in animal or plant communities seen at a boundary between two types of habitat.

These changes are most obvious in plant communities, for example where a swamp segues into a savannah. So, historically, research into edge effects and ecotones (the zone surrounding the edge where two plant communities meet, and energy fluxes and dynamics change) was mostly focused on plants.

It wasn’t until the mid-1900s that people started considering how edges affected animals. Vegetation ecologists had already discovered that the zone surrounding habitat edges usually had more plant species than either of the two patches that met at the edge.

Then in 1930 Aldo Leopold noticed that game animals, like deer, were often found more frequently at forest edges than in the interior. These animals loitered at edges, where they could feed on all the extra plants and see danger coming more easily. And so the misconception arose that edges = more animals. Continue reading