First, let me get one thing straight. This term doesn’t have the same meaning as the term keystone species, even though a keystone species usually is an ecosystem engineer. An ecosystem engineer is an organism, that has a crucial role in creating, destroying, modifying and/or maintaining habitat. With their specific behavior, they influence the availability of abiotic and biotic materials, on which other organisms highly depend. As engineers, they can be autogenic or allogenic. Being an autogenic engineer means, that you change the environment by changing yourself. A good example of this would be a tree, changing through seasons or through the years. Allogenic engineers, on the other hand, are the ones, who are changing the environment with their behavior. In this article, I will talk about beavers and Zebra mussels as allogenic engineers.
Related article: What are keystone species?
Beavers are a good example of both, ecosystem engineers and keystone species. On the areas they influence, they vastly contribute to changes in their behavior. They tend to cut down trees in order to build dams and lodges. With all this, they directly increase the habitat richness and indirectly increase the species richness. The trees they choose to cut down are usually on their preferred species or size list. When a tree is cut down it provides an empty space, that immediately allows more sunlight and rain to touch the soil. This enables better living conditions and awakens the dormant seeds. With the right amount of love from nature, the seeds begin to sprout and grow, and a new *succession cycle starts.
A succession cycle is a process, that follows the changes of plant species in the community over time. There are four stages of succession and there are some specific plant species present in every one of them. The succession stages are used in order to better define, how much time has passed since the last interruption.
With building dams, they slow down the water flow and enable a formation of an accumulation. The accumulation has similar living conditions as a lake so it comes as no surprise to find species from lakes here. Beavers work contributes to the overall rise of species diversity. It influences the lives of many fish, birds, turtles, frogs, plants, and others species.
When their lifelong project (the dam) finally brakes, there are large amounts of sediment being allocated along the river. Sediment, that stays in the area of the accumulation is usually full of nutrients and provides an empty and fertile land. This land is usually quickly occupied by new plant and animal species, and again, a new succession cycle starts.
Okay.. but beavers build dams and we can’t because it’s bad for the environment? What is going on here?
Yeah.. about that… I already published an article about our ideas of water accumulations. I need to add that our ideas are a lot different from beavers.
- Beavers constructions are built to last about a decade and ours are built to last for 100 years. Because of the same reason, the amount of sediment behind beavers dams is uncomparable smaller than behind our dams.
- Beavers allow some water from different depths to escape from the accumulation. This prevents high temperatures of water as well as bigger algal blooms in the accumulation.
- Their accumulations are a lot shallower than ours and therefore enable living conditions for many lake species.
Related article: The truth behind hydropower plants
Zebra mussel is an invasive species, native to lakes of Ukraine and south Russia. This species is also one of the strongest ecosystem engineers. They are capable of altering the structure as well as functions of an ecosystem. They can produce crazily high numbers of eggs (like 40.000 to 1 million in a year!). The eggs first develop into free-swimming larvae and later attach to a place, they find nice enough. They literally don’t care where they live as long as the surface is solid. They were found attached to shells of other mussels and bodies of their predators (what an irony). The unfortunate organisms are usually native species, that have no protection and are slowly being suffocated. The decreasing numbers of native organisms are very well visible.
But hey, I’m not finished yet! These mussels are filter feeders and they can filtrate about a liter of water a day. By filtrating, they take all of the yummy stuff out and leave none for the other filtrators. Since they are unable to live without food, they disappear from the food chain which affects other organisms, that feed on them. With so many nutrients removed from the water, processes of nutrient mineralization, oxygen availability and sedimentation rates are being affected. Their impressive filtrating skills are also responsible for moving the photic zone. This is a zone that tells us how deep the light is able to penetrate and therefore support the life of macrophytes. When there are many particles present, the photic zone is shallower than when there are none or very little. The changes of this zone also influence on presence and behavior patterns of some other organisms that are sensitive to light.
In a forest, we usually come across many species. Some of them can be keystone species but the whole forest is functioning as an ecosystem engineer. Trees tend to grow (in height as well as in width) through the warmer part of the year. Through the years, they are able to develop specific features that species like bats and birds use for nesting and living. Every autumn some (or all) leaves fall off as well as some twigs and branches. The organic material from trees is very important in many ways. It plays a huge role as a food source as well as living habitat for many organisms.
When the organic material lands on the forest floor, the material slowly begins to decompose. For the proper decomposition, many organisms living in soil need to play their part. When the process is finished, we get hummus. Humus is not soil, but organic matter, that is broken down into basic nutrients. These nutrients are being moved to lower layers of soil by many different species. There, they get reabsorbed by plant roots during the growing process. The organic matter that ends in the stream is making many changes in the stream itself. Here I am not only speaking about increasing nutrient levels but also of decreasing oxygen levels. The decomposition process also affects the changes in pH, conductivity levels, and many other factors.
I believe you mostly only heard about the ”trees give us oxygen” speech and I really hope this last paragraph gave you a bit more depth. Let me know if you know of some other ecosystem engineers that would in your opinion deserve a space on this site!