It’s amazing how complicated nature really is. There are so many links and interactions and dependencies, more than we might ever fully understand. At first glance, you might think an interaction between several species is quite straightforward. But upon closer inspection it holds more ties with other organisms than you might have expected.
In almost every “simple” interaction that you will encounter, other species or abiotic factors will be influenced as well. It might be just the simple competition for a bit of food, the trampling of grass or the depositing of droppings that changes something for other animals, plants or fungi. But it can be something bigger too.
In the modelling project that I am working on with a friend of mine at the moment, we are looking at one of those bigger effects. We have built a simplified computer model of a savanna ecosystem, including vegetation, several herbivores and a predator. That in itself sounds pretty straight-forward, right?
That is what we thought, too. But then, when you start to add more and more interconnected lines and parameters affecting each other, suddenly the model becomes a whole lot more complicated, and much more fun!
We have been looking at the effect of a predator that can switch between two types of prey on the frequency of savanna fires. At first instance, that might sound a bit far-fetched and Lion King-ish (you know, with the bad lion setting the whole lot on fire and everything), but the results are actually amazing!
It turns out that if the predator prefers grazers over animals that eat shrubs, forest fires occur much more frequently! Which of course is only a theoretical outcome, because there are many, many more parameters to be dealt with before having a whole, representative model. (So don’t go using this for any serious school or study things.) But it does show how simple things can affect other events quite drastically.
And that is still a rather linear effect, as the predators affect the herbivores, which affect the vegetation structure, which affects the occurrence of fires. But if we follow that line of thought for a bit, what other species would be affected by having more fires? And what effect does their decline or increase have on the animals preying on them? I think we can go on and on in that way.
Although this example is of a savanna system, you can imagine that such intertwined relationships exist in every environment. Just think for a moment about an interaction between wild animals that you have witnessed recently, or can imagine to be happening close by.
What is the immediate effect of that interaction? And how do you think that might affect other animals or plants in the close proximity?
If we look at having large grazers in a nature area, for example. Say, we have a grassy field and introduce some cows to keep it open and prevent the trees from taking over. Before the cows were there, it might have been a very good living space for voles, who like to forage and hide between high grasses. If the cows now eat a lot of grass and trample the rest, voles will feel much more exposed and might go looking for another place to live (or be eaten by predators). On the other hand, now that the field is open, rabbits will suddenly find it much more attractive, exactly because of that openness. They like to have a clear view of their surroundings.
You get all that? Right, now the fun begins!
Because with the increased occurrence of rabbits, do you think other predators might be attracted to the area as well? Could it be that they start feeding on other animals apart from the rabbits? What effect would the rabbits themselves have on the vegetation? And so the questions go on and on…
I could probably talk about this for the next few hours, but basically what I’m trying to say is that interactions and relationships in nature are much more complicated than we are often aware. It is something wildlife managers should be aware of and include in their plans. But it is an important realisation for us, normal people, too. Because we are part of that huge network just as well, and we should keep in mind that our actions work through to many, many other species. So try to be conscious of your impact upon nature, try to live sustainable and green, and keep enjoying all the life around you.
What interactions in nature fascinate you most?