We talk often here at CPAWS-SK about umbrella species like the woodland caribou: species whose prosperity is a good indicator of the overall health of the ecosystem, and the protection of which would mean the protection of an entire ecosystem.
A keystone species, in contrast, are often not missed until they are already gone. They can be something as small as a moss or lichen that grows on the rocks in a forest, to the large and magnificent apex predators ruling over a landscape.
“ In many cases, the vital role of a keystone species in an ecosystem is not fully appreciated until that species is gone.”National Geographic
WHAT IS A KEYSTONE SPECIES?
A keystone species are organisms that hold disproportionate influence over the abundance and type of other species in a given ecosystem. The biodiversity of a habitat nearly always falls upon them as a critical component of the food chain. A keystone species always fills a critical role in their environment that cannot be occupied by any other species.
Big or small, if a keystone species was removed from its habitat, the ecosystem that surrounds it would be significantly changed— and may even fall into collapse. Removal would result in a chain reaction where there was a sudden surge in numbers of some species, and a huge decline in the prosperity of others.
There are different types of keystone species.
Predators are perhaps the most obvious category of keystone species. They are the ones who control the population of prey species, impacting the entire rest of the food chain. If the keystone predator of an ecosystem is removed, there will be a sudden increase in all varieties of prey, which then results in a huge decline of prey food sources (often plants), which in turn will result in land erosion, carbon sequestration, and water evaporation— contributing in the long run to the alteration of the climate on a global scale.
Just as predators play a large role in their food webs, so do prey. A keystone prey species is one that serves as a critical food source for the carnivores in their ecosystem, sustaining them when no other elements of the landscape can. Prey keystone species are uniquely susceptible to extinction in a landscape because their most important role is to be eaten— leaving them vulnerable to over-hunting and eventual scarcity.
These keystone species are organisms who work to create, change, or destroy a habitat in a way that is necessary to all the other plants and animals in their ecosystem. They are creatures whose lasting impacts on a landscape are what make way for the easy habitation of that space by many other plants and animals who have evolved to live in exactly the spots that the ecosystem engineers have made for them.
When it comes to mutualist keystone species, we usually talk about them in pairs. They are deeply interconnected organisms whose interactions are each vital to the survival of the other, and to the ecosystem as a whole. Often, these pairs are pollinators like the birds and the bees whose hard work is beneficial not only to them, but also to the plants that rely on them for reproduction.
Just like keystone prey species, keystone plants are often organisms that provide a major food source within their ecosystems. They also occupy a position of significant importance when it comes to land erosion and shelter for other organisms. Without keystone plants, the habitat would quickly become unliveable for most if not all other species living there.
What sort of animals are keystone species in Saskatchewan?
These cute and cuddly rodents are more than just a prey species— they act as ecosystem engineers for native grasslands ecosystems all across North America! Their burrows make the homes for many other species, including the endangered burrowing owls, black footed ferrets, jackrabbits, and for snakes or other ground-dwelling rodents. Their burrows also act as drainage, aeration, and fertilization on the wide open plains, ensuring that water is not left to stagnate and that grasses will flourish in healthy soil.
Prairie dogs act as a keystone species upon whom more than 130 other species depend for their continued survival— while also acting as a food source for coyotes, eagles, and black footed ferrets. Meanwhile, the vegetation that they keep healthy allows greater ecosystem viability for large grazers like elk and bison. When prairie dogs are removed from a landscape, woody plants can take over, changing the shape of the habitat significantly.
Bees are the quintessential mutualist keystone species. As the primary pollinator in many if not all Saskatchewan ecosystem, bees are what fertilize plants and ensure the propagation of many species. In fact, bees are responsible fro the fertilization of as much as 90% of the planet’s flowering plants!
Without bees, most landscapes would be faced with a bottom-up wave of extinction— one where food sources would dwindle first for prey species, then predators, and eventually the very decomposers that break down dead plants and animals and return them to the soil.
Just like the Canadians that the beaver often represents, beavers are hard workers who reshape the world around them. You already know what these ecosystem engineers do— bringing down trees to build dams and lodges that divert waterways and change the drainage and water storage within large tracts of the habitats that they occupy.
The dams that beavers create turn riverbeds and streams into wetlands (ponds and marshy areas) that then support a rich diversity of plants and animals. These include fish and amphibians, insects and algae, and a wide range of aquatic plants that are also they themselves endangered in other landscapes. Their dams also alleviate water shortages and droughts, reduce the risk of flooding, and slow the flow of water in streams, which in turn lessens the slow erosion of riverbanks.
It may surprise you to learn that the plains bison that once numbered in the millions across the prairies of Saskatchewan are also ecosystem engineers. Just by walking around in their herds on stretches of wide open prairies, bison compact the soil and aerate the top layers, fertilizing as they move along. An adult male can weigh more than 2,000 lbs (which is as much as a car)!
It is through their unique grazing patterns that natural grassland vegetation is fertilized and cropped to a length where new plants can receive the sunlight and nutrients that they need to survive. This in turn helps other large grazing animals like deer and elk, who also need to eat the grasses that the bison have tended to.
Bison are also wallowers— they roll in the soil to scratch the itchy bug bites on their backs. The depressions that are left behind (called bison wallows) form pools of water, and enhance seed distribution for native grasses, creating the perfect environment for healthy plant growth. The wallows can also be turned into the start of a den for other grasslands animals in a pinch.
As a highly capable predators, grey wolves both control the populations of large fauna while leaving the scraps of carrion that are necessary for the nutrition of scavenger species. Without wolves, large ungulates like deer and elk would over-graze on young trees like willow and aspen– so keeping their populations in check in turn ensures the healthy growth of trees and other plantlife on the landscape.
WHAT IS A CULTURAL KEYSTONE SPECIES?
A cultural keystone species is one whose continued existence has a significant impact not on its landscape, but on the cultures that formed hand-in-hand with the species. Here in Saskatchewan, we live on land that falls under treaties 2, 4, 5, 6, 8, and 10— traditional homeland of a richly diverse collection of First Nations and Métis communities. Many of these Indigenous nations have a historical and ongoing connection to the land and to the animals that they once depended on completely for food, shelter, clothing, and spiritual wellbeing.
The connection between the Plains Cree of the Saskatchewan grasslands and the bison that once roamed here in the millions are one such example of a cultural keystone species. To this day, the cultural connection between many Nehiyawak (Cree peoples) and the bison is strong— and the Buffalo Treaty of 2011 is just one way that First Nations all across North America are working to restore bison populations to sustainable numbers and to return this crucial cultural element back to the communities and landscapes that once depended on them completely. Learn more about what CPAWS is doing to help.
Another cultural keystone species in Saskatchewan is the barren ground caribou that live in the boreal and taiga shield of the Athabasca Basin— and the Denesuline people that rely on them still for food, shelter, and spiritual connection. While the barren ground caribou have seen nowhere near the population decimation that the plains bison did during colonization, their numbers are still on the decline and their plight indicative of a dangerous climate change trend. Read about what CPAWS is doing to help caribou in Saskatchewan here.