It hopefully isn’t a surprise to anyone that the natural world is changing. I mean nature changes but as Rachel Carson wrote in Silent Spring nature takes time to change. The rate of human induced change on the other hand happens on much shorter time scales, the consequences of which can be hard to predict.
Not that many decades ago predator eradication programs were pretty common in Western managed landscapes. These programs, intended to protect people and livestock saw the removal of predators like wolves. The consequences were significant. Species like deer and elk didn’t have to worry so they changed their grazing patterns which tended to decimate local vegetation. The video How wolves change rivers discusses some of the far reaching impacts. Realizing the ecosystem level harm, there have been predator reintroduction programs to try to restore natural cycles.
But here’s a less researched concern: what happens if the predators have no prey? As environments change and prey species disappear, predators have to change or they die. We do this in our own kitchens regularly, well hopefully not to the die part. Say I eat macaroni and cheese, every meal, every day. If I run out and I can’t make it to the store, I either go hungry until I get more or I eat something else. And some predators, in the absence of their mac and cheese equivalent are turning to other menu items including carrion (dead animals) and human provided foods such as that found in dumps.
This might seem like a simple change but it can have significant impacts. First, obviously there is a diet change and we know that that can impact health, not always for the better. Parsons, Newsome, and Young (2021) investigated this topic and found that there are social impacts and changes in how predators move or maintain territory.
If food availability can be predicted then larger groups may persist. However, the social structures within these groups can break down. There are also reduced social bonds. Another impact is that different species might be forced together, for example if they’re all feeding at a dump. And while there may be certain breakdowns of traditional boundaries there are still incidents of aggression.
Another effect is that individuals who survive may be bolder and more willing to explore. Great for them, but Parsons et al discuss how bolder predators are more likely to trigger human-wildlife conflict.
Territories can also change. You may not want to sit shoulder to shoulder with someone, but you’ll stand side by side at the buffet table. The same is true on the animal side. Concentrated food sources, like the dump, will motivate animals to stand a little closer together than they would normally reducing territory size.
It makes sense that predators will change without having prey, we all do have to eat. But it is clear from Parsons et al, that we do not fully understand the consequences of this. If we need a current reason to investigate further, the covid-19 pandemic may be it. Consider how many of the changes could lead to greater interaction between humans and wildlife. Bolder predators? Well that sounds potentially risky. Greater diversity and higher numbers of predators living in closer proximity? Also, riskier sounding. Perhaps we should get on it and start doing more research so we might know what to expect.