What Is a Keystone Species? 4 Examples to Help Explain • Earth.com
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What Is a Keystone Species? 4 Examples to Help Explain

Our ecosystems are vast networks of nuanced connections. With such expansive intricacy, it can be hard to know where to start. Today, we’re going to focus on keystone species – the definition of the term, 4 specific examples, and projections of keystone species and the ecosystems they inhabit in the future.  In doing so, we might have a better understanding of what work is most needed in the various habitats we each call home – supporting keystone species instead of contributing to their eradication. 

What Are Keystone Species? 

The keystone species concept is defined as “a species whose presence and role within an ecosystem has a disproportionate effect on other organisms within the system.” Often, a keystone species is a top predator. Again and again, we have observed an apex predator disappear from an ecosystem, which results in the proliferation of prey population and can send an entire ecosystem spiraling. We will look at examples of this occurrence later on. 

Sometimes keystone species aren’t the most dominant predator, however. There are instances where keystone species are species that do not prey upon other animals but still significantly alter their environment through their life cycle behaviors. Because of this, they impact a broad swath of other organisms. 

There is plenty of biodiversity within the “keystone” category as well: freshwater swimmers, invertebrates, carnivores and herbivores, amphibians, and more. The intricate food web and delicate balance of an ecosystem can swing in the balance of a single species. 

Another term to be aware of in this realm of study is keystone mutualists. These are examples in nature where two or more species engage in reciprocal actions that are vital to an ecosystem’s balance. Together, and in tandem, species become shared keystones to the broader system. Think about a specific species of bee and the critical plants they pollinate. Both are needed and depend upon each other to support a whole plethora of other species and a habitat at large.  

Examples Of Keystone Species

In studying these ecological concepts, vibrant examples can help us commit relationships and intricacies to memory. Here are 4 examples of keystone species worth remembering:   

Beavers 

Beaver’s are true ecosystem engineers – shaping their wetland habitat to their liking and impacting the organisms around them in dramatic ways. 

Beavers are native to the Northern temperate hemisphere. There are two species living today: the North American beaver (Castor canadensis) and the Eurasian beaver (C. fiber). These creatures are the second-largest living rodent today and are categorized as “semi-aquatic”. 

Here’s a key element to the beaver behavior: beavers build dams. 

They build dams and their own lodges with tree branches, mud, rocks, sand, and vegetation. If one hikes in a beaver-inhabited area, a person will see the evidence of these furry architects – their teeth marks like guilty fingerprints around the trunk of the surrounding trees. 

In a sense, these animals are using elements of their habitat as technology, or infrastructure. And the work they do in turn shapes a landscape into wetlands. Tons of other species depend on these wetlands for seasons, years, or lifetimes. And beavers keep their knack for engineering in the family: mating for life and producing offspring that help to repair and rebuild lodges and dams through the years. 

Clearly, beavers are important to ecosystems. They are also very important to entrepreneurs, historically. Up until recently, people hunted beavers – almost to the point of extinction on both the North American and European continents. And what was it that made these giant rodents so enticing to enterprising Homo sapiens? 

Beavers produce castoreum. This is a substance they secrete from their anal glands that humans use in medicine, perfume, and food flavoring. Additionally, beavers are hunted for meat and were a staple in the fur trade. Our desire for these products, and the hunt for beavers, went unchecked until the early 20th century. Activists and legislators finally provided protections for the animals, and their populations have rebounded – to the benefit of many additional creatures and wetland biomes. Today, both species of beavers are listed as species of “least concern” by the IUCN Red List, a delicately balanced victory for the beavers – and all of us. 

Gray Wolves 

Wolves don’t need much of an introduction for most of us – they are one of the best-known animal species in many cultures. They are prevalent in folklore, fantasy films, and even politics today. 

As the largest canine species in North America and Eurasia, these four-legged predators have enchanted and haunted human society through the eras. They’ve certainly earned their place in our collective imaginations. But what many people don’t realize is that gray wolves are a keystone species and ecosystems depend upon their existence, regardless of what enraged ranchers or scheming politicians might tell you. Why is this the case? 

Wolves specialize in cooperative game hunting. In areas like Yellowstone National Park, they are apex predators designated as a keystone species because of their role in the food chain. While Grizzlies hunt for berries and bison graze the prairie, wolves work together to hunt their prey. 

According to a study from the University of Manitoba Winnipeg “[The wolves] importance… was unknown until they were anthropogenically extirpated in the 1920s. The 75-year absence of gray wolves in Yellowstone led to declines in biodiversity, and habitat quality, all of which is gradually returning upon wolf reintroduction in 1995.” 

The study credits “trophic interactions” as the driving forces behind the gray wolves’ ability to, directly and indirectly, provide benefits for almost all species of fauna and flora. “Trophic interactions” are when one organism feeds upon another. Specifically, wolves prey upon the elk population – and in doing so, weed out weak and sick elk individuals to create more resilient elk herds.

In the 1970s there was no evidence of wolf activity in the park. When wolves were reintroduced to Yellowstone, they catalyzed what ecologists call a “trophic cascade” and a rebalancing of the ecosystem. Many people consider this reintroduction an ecological success story, but a fragile one. There is still heated political debate on the interactions between wolves and farming/ranching enterprises. This debate is currently raging in places like Minnesota and Wisconsin, where wolf hunts take place despite ecological concerns of “over-harvesting” this once nearly exterminated keystone species. 

Prairie Dogs 

Apex predators get a lot of love in pop culture and the news – there’s a certain mystic and glamour that comes along with those large, powerful species that haunt our dreams. But that’s not to say there aren’t keystone species of equal importance but smaller size and notoriety. 

For example, the prairie dog is in fact a keystone species. According to the Great Plains Restoration Council, the prairie dog and the buffalo are the “bookends” of the prairie. And while these rodents of the prairie can seem humorously curious and abundant, they are also creating habitats and influencing massive ecosystems and over 160 other species of birds and animals depend on the niches that the prairie dogs make. A metaphor to keep in mind: prairie dog colonies are the “coral reefs of the sea of grass”. 

Studies have shown that when prairie dog management plans focus too much on eradication, the diversity of the ecosystem plummets. There are calls for ongoing study and necessary funding to understand all the intricacies of their “significant effect on the structure, function, and processes of an ecosystem.”

Kelp Forests

Keystone species are often animals with fur, teeth, and tails, but as it turns out, plant species can be keystone species as well. 

While the redwood forests of California, the mighty Amazon, or the Black Forest of Germany may be the sort of images that come to mind when we talk of forests, that is a limited view. Forests are in the ocean, as well, and in those instances, we call them kelp forests. 

Kelp forests are the keystone to an entire ecological community, a marine environment that determines the health of our planet. Similar to the ways in which an on-land forest provides habitats from the roots all the way up the canopy, a kelp forest does the same from the seafloor to the sea surface. 

The “infrastructure” of these forests is made up of seaweed. The seaweed thrives as both a food source and as the “building” structure of many creatures’ homes. Seaweed will photosynthesize, providing necessary nutrients to other species. The organisms that munch on the kelp are prey to other animals of the food chain. Kelp is the building block of life for many different species including limpets, snails, prawns, octopus, mussels, sea urchin populations, and more. The entire ecosystem is finely balanced. 

Kelp forests are threatened by natural elements as well as human activity. Pollution, El Niño events, and plant competition are just some of the factors that influence a forest’s health. 

Kelp forests are known for their remarkable growth patterns. Because of this, they are generally regarded as resilient ecosystems that can quickly recover from disturbances. 

However, this is true within a certain scale. It becomes harder for even the most resilient species to recover when layers of disturbances and simultaneous threats occur in an ongoing, unrelenting fashion. Even a kelp forest’s health is “proportional to the number of adverse conditions to which it is exposed”. The National Marine Sanctuary, in partnership with the NOAA, designates commercial kelp harvesting as the greatest threat to these forests. Kelp is a product in high demand, and humans prove time and time again to have an insatiable appetite that can only be curbed by aggressively protective legislation. 

Understanding The Nuances Of Ecosystems 

Ecology is a vast area of study – ever more fascinating, the deep you dig. Each ecosystem is specific and still connected to the entire workings of the planet. In exploring the concept of keystone species, we catch glimpses of how these networks function. It is this holistic approach that can inform our research, opinions, and legislation as we shift our gaze towards restoration, conversation, and the climate crisis upon us. We now understand: what works in one place, will be totally different in another. Let’s look at two very different examples – the savanna and the coral reefs. 

Savanna 

A savanna is a grassy plain in tropical and subtropical areas, with very few trees (with the exception of the great, disappearing oak savannas of North America). Today we are going to look at the savannas of East Africa – the keystone species that sculpt and shape the ecosystem and the management response that humans can and are working to implement. 

The beloved Elephant is a keystone species in most savannas in this part of the world. There are areas of these grasslands where elephant populations are denser, and then there are areas where the elephants are absent due to poaching activity. Ecologist David Western explains that “comparably few plants, dominated by one or two species, are located in areas of low to negligible elephant density and in the central park, where elephant densities are exceptionally high (more than 4 per sq. km.). Conversely, two or three times as many species, contributing far more evenly to total plant abundance, are found in areas of moderate elephant density.”

The savannas have enchanted human beings since time immemorial. Archeological evidence suggests that our own species origin takes place in this corner of the globe. From Disney’s Lion King to Ernest Hemingway’s short stories, and to the millions of people that call this landscape home, it is critical that the ecosystem flourishes and thrives. 

In the tall grass zebra, antelopes, and wildebeest roam. Acacia trees stand like lonely scouts, and giant thunderclouds roll overhead. Our human desires threaten this landscape – poaching for ivory, extractive tourist behavior, and the oppression of indigenous, nomadic ways of life congeal into a dire narrative. Protecting the elephants, a keystone species is one small thread in a dense tapestry of interconnections 

Coral Reef

Let’s travel from the dusty grasslands to the coast – and take a closer look at another beloved ecosystem: coral reefs. 

These ecological phenomena are one of the most vivid and strange arrays of structure and habitat on our planet. Their fame and flair draw us like a magnet. There has been a lot of recent talk around the threats to coral reefs and the mass bleaching events that have taken place. We are watching these thriving “metropolises” and “nurseries” go from bustling communities to bone-like skeletons. What’s going on here? And where do keystone species play a role? 

You may not realize this, but coral is not just colorful sediment – it is a living organism and as such, coral itself is one of the keystone species of these marine ecosystems. 

Species diversity is key – though not all marine animals exhibit the same behaviors. Some species have a greater impact on the coral environment than others. For example, the parrotfish of the great barrier reef is the only species of thousands that actually scrapes and cleans the coral. 

While scientists study the resiliency behavior of corals around the globe, there are additional, tangible actions that our species can undertake even while we continue to learn. We know that overfishing and warming oceans contribute to massive disruptions in the coral ecosystem – and we know what we need to do to shift our consumer habits away from the factors that lead to these events. We simply lack the political will and accountability to do so. 

Keystones To The Future 

Climate change is upon us. Indigenous activists and ecologists alike have been ringing the alarm bells of the climate crisis for hundreds of years. This is not new information and will be the challenge of our lifetimes. Sustainability is a buzzword in our popular dialogue, but how many of us are actually shaping our lives and behaviors around the buzz of the honey bee or the whir of the hummingbird as they do their work of pollination? 

Conservation ecologists Maclanahan, Polunin, and Done spell it out clearly in their study on “Ecological States and the Resilience of Coral Reefs“, explaining that our ecological goals must include maintenance of species diversity, protection for keystone species, connectivity, and that “achieving these goals will require unprecedented cooperative synergy between human organizations at all political levels from intergovernmental to local”. 

Following Indigenous Leadership

While these projections and calls to action can be daunting, there is also an exciting momentum behind what is possible and how we as a species move into the future. 

This is especially true in the generous teachings and ancestral practices of indigenous people all over the globe. While less than 10% of the human population is still connected to their indigenous landscape and heritage, 80% of the world’s biodiversity is in the care of indigenous people. That is a striking statistic that speaks for itself: it is beyond time to follow the leadership and vision of native wisdom and embodied behavior and habits. 

Maybe you’re wondering – can humans be considered a keystone species? Well, some scientists identify Homo sapiens as “hyperkeystone species” because of the immense impact we have on all ecosystems, every food chain, and connected species. 

Either way, it is undeniable that human activity will continue to play an important role in the existence of keystone species and the ecosystems they determine. What sort of impact do you want to have?

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