Small changes in an ecosystem can initiate a turbulent chain reaction.
Klassekampen, 10 Feb 2017
I should be talking about Donald Trump, and the unprecedented shift in American science policy. From a president who published in Science only last January, we have gone to one who tries to silence climate researchers, and threatens to take away federal funding for a university because of demonstrations against a right-wing activist. And we’re only three weeks in.
No, I’d rather talk about dramatic transitions that have received less attention in the media. More precisely, those in nature. Changes can also occur rapidly there, whereby ecosystems suddenly shift from one state to another.
When I was a student in Amsterdam and followed classes in ecology, I learned of a classic example. Many lakes in the Netherlands do not have the best water quality, to put it mildly. Because the country is so densely populated, with intensive agriculture, many nutrients and pesticides have entered surface waters. This has caused a chain reaction, whereby many freshwater ecosystems changed dramatically, which strongly affected nature.
Young pikes need a place to hide
This happens as follows: when water flees decline due to pesticides, in combination with a high amount of nutrients, plankton starts to grow explosively, leading to more murky waters. Sunlight doesn’t penetrate murky waters so deep, which leads to poorer growing conditions for water plants, and eventually these disappear.
This disappearance of water plants is detrimental to pike. Adult pike aren’t particularly picky on what they eat. When they encounter a young pike, they will simply gobble them up. Young pike, therefore, need to have the possibility to hide among the water plants. If they can’t, pike disappears from the lakes, and the fishes that were eaten before see an explosive increase in their numbers.
In such lakes in the Netherlands it’s primarily bream that increases in numbers when pike disappears. Bream is a fish that, when looking for food to eat, turns over the lake sediment. The problem is that all this extra sediment makes the weather even murkier than before, and water plants can’t reestablish themselves. Not to mention the pike. Bream therefore enhances the problem, and the ecosystem can’t restore itself. This way, a dramatic shift occurs: from stable ecosystems with clear water, which can support many different types of fish and plants, to monotone, dirty and mirky waters that are dominated by bream. And although this means there’s more of them, individually they’re not better off.
This shift has happened in many lakes in the Netherlands, but luckily there are also solutions. Bream can be caught, river banks can be made more suitable for water plants and as a spawning ground for fishes, and pike can be reintroduced. In many places this has been done, but it takes a lot of work.
This is not the only example of such a chain reaction in an ecosystem. The absence of large predators in the Netherlands, such as the wolf, has led to the staggering amount of 4000 dear in the dunes to the west of Amsterdam, even though it’s only 34 square kilometer in size. Apart from the increased risk for Lyme’s disease, these dear eat everything until a barren landscape is left. There’s simply not enough food in such a small nature area for that many dear, which is why many of them die from starvation during the winter. Feeding them is possible, but that’s more like fighting the symptom rather than an adequate solution. After much debate, it has now been decided that thousands of dear may be shot.
Nature areas in the Netherlands are rather small of course, and therefore more vulnerable. On a larger scale, however, the same processes occur. Since the wolf has been reintroduced in Yellowstone Park, in the US, the dear population has been reduces tremendously, which caused a chain reaction on every level of the ecosystem. Insects and grasses increased, willow and poplar reestablished, the eagle, beaver and foxes returned, grizzly bears had more food, and the previously menacing population of coyotes has been reduced by the increased competition.
Some animal species, especially predators, can be essential for the natural balance in an ecosystem. Ecosystems that are also essential to people – for clean water and air, and food. And although I do not want to downplay the often tense relationship between humans and predators, it must be possible to find a natural balance here as well.
This text first appeared in Klassekampen on 10 Feb 2017