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All animals and plants are important to their environment, but are some more important than others? Every ecosystem consists of complex interactions between plants, animals and abiotic (non-living) factors that keep the system in balance. If a very important species has been removed from its ecosystem, is that enough to cause the entire ecosystem to collapse? What happens to other species when a species dies? These are important questions that ecologists and environmental biologists ask when evaluating different ecosystems, especially in light of: climate change. As the natural world is changing at unprecedented rates, it is important to understand the potential consequences. This article will define “keystone species” and explore why they are so important to their environment.
What is a Keystone Species?
Simply put, keystone species have a disproportionate impact on their ecosystems. If they were removed, an ecosystem would change drastically. lay even more concise, keystone species hold entire ecosystems together!
But even that description can raise questions about what keystone species are. Are they just predators, could they be humble plants? Below we will break down the exact nature of keystone species and why they are so important to their ecosystems.
What is an ecosystem?
An ecosystem is a community of interacting organisms, abiotic factors and their environment. Organisms in an ecosystem include all plant and animal species. Abiotic factors include the weather, minerals present, available water, sunlight and other non-living elements of the environment. An ecosystem is ultimately concerned with how all elements of the environment and its inhabitants interact with each other.
Different interactions in an ecosystem include consumption, competition and mutualism.
- Consumption: describes predator-prey interactions, parasitic interactions, and other situations where one organism benefits and one organism at a loss. A complete overview of consumption interactions in an ecosystem is often referred to as a food web.
- Contest: can occur between different species (interspecific) or within a species (intraspecific). For example, interspecific competition can be competition over territory or a food source. Intraspecific competition can be similarly related to resource availability, competition among partners, or other forms of competition within a species. In competition-like interactions, both sides experience negative effects.
- mutualism: describes interactions that benefit all parties. For example, some ants provide acacia plants with protection from other insects in exchange for food and shelter from the plant. In this example, ants and acacia plants have a mutualistic relationship.
What is a trophic cascade?
In an ecosystem, organisms can be organized in a hierarchy. Producers such as plants produce their own food and are at the bottom of the hierarchy. Primary consumers, those who eat plants, come next. Secondary consumers feed on primary consumers, tertiary consumers feed on secondary consumers, and so on. Alfalfa, for example, produces carbohydrates through photosynthesis, moose feed on alfalfa, and coyotes feed on elk. In this example, alfalfa is the producer, elk are primary consumers, and coyotes are secondary consumers.
This community structure can be influenced both bottom-up and top-down. If abiotic factors, such as sunlight or water availability, affect the abundance of producers in an ecosystem, this will in turn affect the abundance of primary consumers, which will affect the abundance of secondary consumers. To continue the earlier example, if there is a drought causing a decline in alfalfa, moose populations will decline due to lack of food. Coyote populations will then decline due to declining moose populations. This is bottom-up control.
Top-down control occurs when a change in the number of secondary or tertiary consumers affects the number of primary consumers, which in turn affects the number of producers. For example, if humans hunted all the coyotes in an ecosystem, moose populations would grow because of decreasing predation. Their growing population would then deplete the alfalfa population. Changes at the top of the hierarchy in this example affect the hierarchy.
Trophic Waterfalls
When changes in control from above cause substantial effects two, three or more links down a food web, a trophic cascade has occurred. Therefore, in simple terms, a trophic cascade is when a change at the top of the food chain has a rippling or cascading effect on the food chain.
Biologist Robert Paine conducted an incredibly important ecological study that revealed this phenomenon. On the Washington coast he observed two tide pools each with: Sea urchins and kelp. When he removed the sea urchins (primary consumers), the kelp population (producers) grew immediately. But why did nothing regulate the sea urchins when they were eating all the kelp?
Paine compared two similar ecosystems with kelp and sea urchins. In one ecosystem, there was a healthy Otter population and in the other ecosystem there were no otters. The ecosystem with otters maintained a balanced population of kelp and sea urchins, while the ecosystem without otters was completely overrun by sea urchins and lacked kelp. This was an example of top-down control because without the secondary consumer (otters), the primary consumer (sea urchins) became overpopulated and the producer population (kelp) became depleted.
What is the concept of the keystone type?
Biologist Robert Paine continued his research and developed the concept of the keystone species. he conducted further research on the Washington coast aimed at starfish. He identified all the coastal species and mapped their interactions. In doing so, he determined that a purple starfish was the predator at the top of the food chain. Paine collected the starfish and threw them into deeper water to remove them from the shoreline ecosystem. He then followed the other species in the absence of starfish. Of the 15 different species cataloged initially, only 8 remained after a year and a half. After seven years, only a monoculture of mussels remained. He came to the conclusion that a single predator can regulate the entire composition of a community.
Robert Paine coined the term “keystone species.” In architecture, the element in the center of an arch where the two sides of the arch meet is the keystone. If you remove the keystone, the arch will collapse. This is true for keystone species in that if they become extinct, their ecosystem is vulnerable to collapse. Keystone species are species that have a disproportionate impact on their ecosystem relative to their population density. In other words, species that affect their environment in very large ways, even if they are not the most populous species.
Why is this important today?
Understanding keystone species and their huge role in their environment is incredibly important. As global warming and man-made habitat destruction threaten an increasing number of species, extinction is likely to occur. Environmentalists and those seeking to conserve vulnerable species need to understand the roles and interactions of organisms in an ecosystem so they can prevent ecosystems from completely collapsing.
A good example of this is the Wolf population in Yellowstone National Park. Wolves are apex predators, meaning they have no natural enemies and are therefore at the top of the food chain. By the middle of the twentieth century, gray wolves had been almost completely eliminated from the mainland U.S. As a result, the moose population exploded. Each overpopulated the area and depleted food resources. After the dispersal of moose, their local food source of young aspen trees declined sharply. The depletion of aspen trees also severely affected other species. This illustrates how one species, such as gray wolves, can have a major impact on an ecosystem. It is therefore imperative that we protect keystone species around the world, as their ecosystems depend on it to maintain balance.
Examples of Keystone Species
Examples of keystone types are:
- beavers
- Wolves
- Jaguars
- otters
- Starfish
- sharks
- elephants
- Brown bears
- bees
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