All animals play an integral role not only in taking care of our environment but also maintaining balance. Without a particular species, the rest of the animal kingdom will be affected. Research by Robert T. Paine, an American zoology professor, showed that removing a single species had a huge effect on our planet.
Scientists identified organisms that can help define an entire ecosystem as keystone species. Since they help in holding the system together, ecosystems would look extremely different without them. Previous studies identified keystone species in three types: predators, mutualists, and ecosystem engineers.
Importance of Keystone Species
According to National Geographic, an American pay television network and flagship channel that is owned by National Geographic Partners, there are some predators that can control the distribution and population of large numbers of prey species. For instance, the feeding behavior of prey species as well as where they choose to make their nests and burrows in the Greater Yellowstone Ecosystem (GYE) are largely driven by the presence of gray wolves.
In the late 19th century, governments at the local, state, and federal level eradicated wolves from the GYE because they fear they the predators would heavily impact herds of elk and bison. The removal of the top predator in the ecosystem has negative effects, unfortunately. Reports showed that the populations of elk herds drastically increased. Their food sources such as reeds, sedges, and grasses didn’t have time or space to grow because there are too many elks.
Eventually, this influenced the populations of other species such as fish, beaver, and songbirds. Balance was only restored when the US government started reintroducing wolves in the GYE in the 1990s.
Mutualists, meanwhile, are two or more species that engage in mutually beneficial interactions. One impact on a species would also affect the other, eventually changing the entire ecosystem. A perfect example of this is bees. These pollinators often maintain gene flow and dispersal throughout widespread ecosystems. Another example is a hummingbird known as the green-backed firecrown. Local trees, shrubs, and flowering plants have evolved to only be pollinated by this bird. In turn, these plants provide the food for the hummingbird.
Another keystone species are ecosystem engineers. They are organisms that can create, change, or destroy a habitat. Previous studies have revealed that they contribute to the physical geography of their habitat.
All About Ecosystem Engineers
Ecosystem engineers not only impact the presence of other animals but also shape landscapes. Species who have the ability to do this can alter the distribution and abundance of large numbers of plants and animals. Some of the ecosystem engineers have also contributed to species richness at the landscape level.
According to World Atlas, an educational geography, travel, and current events website, ecosystem engineers are divided into two broad categories: allogenic and autogenic engineers. Those who can modify the environment by mechanically transforming material from one form to another or various forms are considered allogenic engineers. A perfect example of this is beavers. Beavers have the ability to alter their ecosystem extensively through the process of clear-cutting and damming. The dams built by beavers have ecological impacts on other species since they create habitat and control a number of abiotic resources that other animals can use and can also support species not found anywhere. Beavers can also shape landscapes by creating lakes and changing the paths of rivers.
A 2002 study also revealed that beaver engineering increased species richness of plants at the landscape scale. However, not all ecosystem engineers can do this. For them to increase species richness at the landscape scale, they must have an ability to create a patch with a combination of conditions not present elsewhere in the landscape.
On the other hand, autogenic engineers modify the environment they are in by modifying themselves. Trees, for instance, are used by other organisms as habitats including birds, insects, snakes, and other organisms as they grow their trunks, leaves, and branches. As they grow and become larger, both of their living and dead tissues create habitats for other organisms to live on or in.
Another important and unexpected ecosystem engineer is rattlesnakes. Rattlesnakes, like any predator, play a crucial part in a healthy ecosystem. A 2018 study found out that they are important seed dispersers. According to researchers, different types of rattlesnakes found in Arizona munch on rodents, many of which still have seeds in their cheeks or gut. Often, the seeds stay whole because snakes can’t chew them.
Since rattlesnakes don't have the enzymes to break seeds down, they can germinate while in a snake’s colon. “Rattlesnakes should be viewed as more than just predators. They’re actually functioning and providing ecosystem services beyond that, so beyond just the seed thing, they’re taking on the role of ecosystem engineer,” co-author Gordon Schuett said.
Recent research led by Justin Yeakel, an ecologist at the University of California, Merced, revealed that the increasing number of ecosystem engineers have stabilized the entire ecological network against extinctions. To achieve this conclusion, the researchers created an ecological network model to understand the long-term impact of ecosystem engineers.
"We wanted to understand how food webs and interaction networks were established from a mechanistic perspective. To do that, you have to include things like engineering because species influence their environment and there's this feedback between the environment to the species,” Yeakel said.
According to Phys.org, an internet news portal that provides the latest news on science, the ecological network model was created without specific species like beavers or concrete environmental features like rivers. Everything is reduced to interactions: species can eat, need, or make. However, the model has a simple rule that it needs to follow: species have to eat only one thing to survive but they have to obtain all of the things they need.
The model also showed how food webs can be assembled, how species interactions can change over time, and when species go extinct. The findings revealed that many ecosystem engineers led to stability and few extinctions while only a few ecosystem engineers led to many extinctions and instability. "As you increase the number of engineers, that also increases the redundancy of the engineers and this tends to stabilize the system," Yeakel said.