But that only makes sense if insectivore populations have in fact, not decreased. Haven’t they? Do you have data on it? Surely human activity has damaged the populations of many species, both over the last few decades and the last few millennia.
My understanding is that they have declined, but in ways that weren’t obviously related to lack of prey species. For example, amphibians have been declining seriously since the 80s, but a lot of that seems to be because herpetologists studying the decline were an infection vector for a fungus that decimated populations. Bat populations are also being decimated by a fungus. Ocean fish populations have halved since the 80s, and freshwater fish populations are down 80%. (One of many culprits here is also a fungus.)
[edit]See another comment, where a decline in bird populations is explicitly linked to a collapse in prey insects.
The Wikipedia link on amphibian decline mentioned the effects of artificial lighting on the behavior of insect prey species as a possible contributor. I suppose it’s possible that that’s a factor in the observations from the German study as well, particularly since they only looked at flying insects. But the observations were apparently made in nature preserves, so one would think that artificial lighting wouldn’t be that common in those habitats. There could still be indirect effects, though.
My understanding is that they have declined, but in ways that weren’t obviously related to lack of prey species. For example, amphibians have been declining seriously since the 80s, but a lot of that seems to be because herpetologists studying the decline were an infection vector for a fungus that decimated populations. Bat populations are also being decimated by a fungus. Ocean fish populations have halved since the 80s, and freshwater fish populations are down 80%. (One of many culprits here is also a fungus.)
[edit]See another comment, where a decline in bird populations is explicitly linked to a collapse in prey insects.
The Wikipedia link on amphibian decline mentioned the effects of artificial lighting on the behavior of insect prey species as a possible contributor. I suppose it’s possible that that’s a factor in the observations from the German study as well, particularly since they only looked at flying insects. But the observations were apparently made in nature preserves, so one would think that artificial lighting wouldn’t be that common in those habitats. There could still be indirect effects, though.