Keystone species
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As we all know this Earth we find ourselves on is fragile; all that we see in
nature is just a series of delicately balanced interactions between species
(including us). But sometimes certain species have a linchpin role in such
balances.
Keystone species are crucial species in an ecosystem. If they were to be removed
from an ecosystem, there would a drastic impact on most of the species and the
environment within that ecosystem.
The term "keystone species" was coined by zoologist Robert T. Paine, and defines
species which have a disproportionate effect on their environment relative to their
abundance. Meaning they keep entire ecosystems in check, sometimes in very
indirect ways.
Fosa
Photo Credit: Flickr | Rod Waddington
The Fosa are impressive, odd looking animals endemic to Madagascar and, being
the largest member of the carnivorous Eupleridae family, is in fact the apex predator
of the island. Capable of hunting both on the ground and in the trees Fosa have an
indiscriminate diet, preying on rodents, lemurs, snakes and even insects.
Without the Fosa the populations of these animals would boom. Now, that may sound
like a good thing to begin with, seeing as the majority of lemur species are
endangered, however with nothing to keep them from overpopulating it would
eventually lead to the overexploitation of their food resources. And with the increase
in arboreal habitat loss through deforestation and fragmentation, competition for food
would be exacerbated further.
Snake and lizard numbers would also rise and the birds and small mammals they
prey on would face the same overexploitation, causing the same eventual demise.
These knock-on effects are referred to as cascade effects and are especially
prominent in island ecosystems, even more so in endemic species food chains such
as these.
This is a very worrying notion as the forests that support all of these species are
under threat, and has even forced the Fosa to depredate village chickens, leading to
their persecution. Fosa numbers are low already, and given the fragility of endemic
island ecosystems, further habitat loss could trigger these events.
If you would like to help conserve these crucial habitats check out our Madagascar
Conservation project.
Tiger Sharks
Photo Credit: Flickr | tobze
Another example of the importance of apex predators is the Tiger Shark. Found in
the Torrid Zone’s tropical oceans these sharks have a huge range, spanning the
world's equatorial coastlines from Australia to The Americas and everywhere in
between. It is because of this range, and their tendency to eat anything, that they are
defined as an apex predator.
In fact keystone species are more often than not the animals at the top of the food
chain as they keep their prey populations healthy. By preying on the slowest, injured
or weakest individuals, Tiger Sharks ensure only the fittest survive.
They also directly ensure the vitality of sea grass beds by altering the behaviours of
their prey. Left unchecked, sea turtles and Dugongs would intensively graze sea
grass, overexploiting the resource. Yet with Tiger Sharks present the Dugongs and
turtles are forced to move around or face predation, giving the sea grass chance to
regenerate.
Tiger Sharks have been persecuted for their shallow swimming habits and
occasional human attacks, and have been hunted so much for their fins, meat and
skins that they are currently declared as Near Threatened on the IUCN Red List.
If you would like to see many species of shark whilst contributing to a better
understanding of shark ecology, see our Fiji Shark Conservation project.
Ochre Sea Star Pisaster ochraceus
Photo Credit: Flickr | National Marine Sanctuaries
This makes the top 5 because it was in fact the first species to be classed as
Keystone. In 1966 Robert T. Paine had an idea that not all species have the
equivalent impact on their environments. To prove this he began the gradual removal
of an apex predator species from an ecosystem, in this case the Ochre Sea Star.
This experiment was carried out over 3 years in Makah Bay on the coast of
Washington State, and found that even with the removal of a few individuals the
affects were considerable. Ochre Sea Stars feed on sea snails and barnacles but
their main prey is mussels. These sea stars were so effective at keeping mussel
populations down that when they were removed vast mussel beds established,
overcrowding the rocky surfaces that limpets, barnacles, algae and sea snails
depend on.
This was the first documentation of Cascade Effects.
Robert T. Paine's experiment was highly unorthodox and unethical by today's
standards; however it did provide us with this invaluable knowledge, which is still
used to define many other species’ vital roles in ecosystems. This discovery shifted
the paradigm from ineffective species-specific conservation to management
practises considering the overall protection of ecosystems.
You can see these delicate ecosystems, and help to protect them on our Marine
Conservation and Diving projects in Fiji and Belize.
Grey Wolf
Photo Credit: Flickr | U.S. Fish and Wildlife Service Headquarters
So far we've seen what the absence of a single species could do to an ecosystem,
but keystone species can also be used as a conservation tool. By considering the
cascade effects of a lack of such species, logically the introduction of one into a niche
would reverse these effects and benefit the ecosystem.
In Yellowstone National Park, researchers discovered the park's Quaking Aspen tree
population was in decline. Large, sprawling root systems make aspen one of the
fastest growing and regenerating trees in the world, so this decline didn't make
sense.
The data showed aspens had been under duress for almost 70 years, with a severe
lack of regeneration since the 1920s. It was found that the beginning of this decline
coincided with the extirpation of Grey Wolves, wiped out by human hunting around
1926.
With the lack of a niche predator Yellowstone's Elk population grew to be the largest
in the world, and the park almost reached its Carrying Capacity; the ecological
threshold between population size exceeding food resources, meaning that with the
Elk over-browsing the new tree shoots, the aspens couldn't produce faster than they
were being eaten.
Grey Wolves were thankfully reintroduced in the mid 90's and changed a whole lot
more than just Elk population. To avoid predation the remaining Elk were constantly
moving around the park into less favourable habitats, ensuring the annual recovery
of the forests. The Quaking Aspens naturally recovered, as did Yellowstone's willow
trees, and with more willows came more Beaver colonies (a keystone species in its
own right because of their effect on hydrological systems).
Photo Credit: Flickr | AllAroundTheWest
Wolves also preyed on Coyotes which led to the increase of rodents, and therefore
smaller predators. Also bear, Raven and raptor populations also increased due to
carrion leftover from wolf kills.
This case demonstrates the level of interconnectedness in nature, because not only
did the reintroduction of wolves benefit these species, but as the forests could mature
and establish, there was less soil and riverbank erosion; actively changing the
geography of Yellowstone.
Bees
Photo Credit: Flickr | Paul Rollings
There are around 20,000 species of bee worldwide, spreading across every
continent except Antarctica, and they fall into just 9 taxonomic families. As a
collective they make one of the biggest keystone species in the world, responsible
for a third of plant pollination worldwide, and over 70% of the crops we all eat.
If bees were to disappear there would be a catastrophic cascade effect, more severe
than any other single species. However this cascade would start from the bottom of
the food chain.
Without the necessary cross-pollination many wild and crop plants would die off and
subsequently send ripples all the way up the food chain, similar to the
overexploitation mechanics of Madagascar, but on a global scale.
Some other species may be fine in the long run as "life finds a way", but our
population is so dependent on their service that humans would face major
consequences; huge reductions in food, textiles and even livestock farming to name
a few.
Photo Credit: Flickr | Archangel12
Bees are currently in decline all over the world, threatened by natural parasites,
climate change and anthropogenic pressures such as habitat loss and the use of
harmful pesticides. The parasitic varroa mites which attach to honeybees are a
natural process, and would probably be an ecologically stable trade-off if it wasn't for
the added pressure we pile on.
The UK has seen an alarming 97% loss of its wildflower meadows, mostly due to
making way for arable farmland. The irony being that we then spray these crops with
harmful pesticides, such as neonicotinoids, that directly link to Colony Collapse
Disorder (CCD).
Thankfully neonicotinoids have been banned almost worldwide but they are still
sometimes used for "emergency" pest situations in the UK. The advocacy of such
substances and continued unsustainable land use is most likely to set these
cascades into effect unless we do something.
Elephants
Elephants are among the most intelligent of
the creatures with whom we share the
planet, with complex consciousnesses that
are capable of strong emotions. Across
Africa they have inspired respect from the
people that share the landscape with them,
giving them a strong cultural significance.
As icons of the continent elephants are
tourism magnets, attracting funding that
helps protect wilderness areas. They are
also keystone species, playing an important
role in maintaining the biodiversity of
the ecosystems in which they live.
During the dry season, elephants use their
tusks to dig for water. This not only allows
the elephants to survive in dry environments and when droughts strike, but also
provides water for other animals that share harsh habitats.
When forest elephants eat, they create gaps in the vegetation. These gaps allow
new plants to grow and create pathways for other smaller animals to use. They are
also one of the major ways in which trees disperse their seeds; some species rely
entirely upon elephants for seed dispersal.
On the savannahs, elephants feeding on tree sprouts and shrubs help to keep the
plains open and able to support the plains game that inhabit these ecosystems.
Wherever they live, elephants leave dung that is full of seeds from the many plants
they eat. When this dung is deposited the seeds are sown and grow into new
grasses, bushes and trees, boosting the health of the savannah ecosystem.
There are hundreds of different species that depend on elephants for their survival.
If elephants go extinct – so do they. In the 1950’s wildlife conservationist David
Sheldrick was given the daunting task of transforming Tsavo East National Park in
Kenya into a tourist retreat. However, he soon realized that illegal poaching was
rampant. The few animals that were left were either too scared or too shy to make
themselves known. How could he possibly make a tourist destination if there were
no animals?
Elephants were reintroduced back into the park and to his surprise…hordes of
other animals soon followed. It wasn’t long before the once barren scrubland was
transformed into a grassland oasis that became home to hundreds of animal
species. David was one of the first to question the important role the African
Elephant played in the habitat that surrounded them.
Elephants can turn a barren scrubland into a grassland oasis
Elephants tear down trees and drastically change the environment they live in.
Initially this became a great concern to scientists watching the park go through a
dramatic transformation. Instead of killing them, as had been proposed, David
fought to keep them alive and instead simply observe. He felt there was more at
play than what any of them could see.
Greater Kudu
As elephants tore down the trees David noticed that African
wild grass began to grow where trees once stood. Seeds
inside elephant dung served not only as a nutritious food
source for smaller animals but whatever didn’t get
consumed sprouted into new vegetation. An assortment of
medium-sized plant species sprung up for animals that
weren’t able to reach into the tops of trees such as the
Greater Kudu.
An elephant pushing down a tree
The Balanite tree (Balanites aegyptiaca) is considered a
very valuable resource in Africa. This native tree is solely
dependent on elephants for the dispersal of its seeds
through elephant dung. Many parts of this tree are used
as famine foods in Africa and the wood is one of the
primary sources of charcoal; a heat source for many
homes. Elephants are not just the bulldozers of society
but they are the gardeners as well.
David was amazed at how many animals began to
flourish in Tsavo after the elephants had returned. The elephants had
merely transformed the landscape…not destroyed it. Today Tsavo East National
Park is considered one of the most beautiful tourist safari destinations in the world.
With safari tourism as the backbone of Kenya’s entire economy it doesn’t take
much to think what would happen if elephants went extinct.
Sea Otter
The sea otter (shown below) is considered
a keystone species as their consumption of
sea urchins, preventing the destruction of
kelp forests caused by the sea urchin
population. Kelp forests are a critical
habitat for many species in nearshore
ecosystems. In the absence of sea otters,
sea urchins feed on the nearshore kelp
forests, thereby disrupting these nearshore
ecosystems. However, when sea otters are present, their consumption of sea
urchins restricts the sea urchin population to smaller organisms confined to
protective crevices. Thus, the sea otter protects the kelp forests by reducing the
local sea urchin population.
Sea otters are an iconic
species, representing the
beauty and diversity of marine
life found along California’s
coastline. They’re also
considered a keystone
species because of their
critical importance to the
health and stability of the
nearshore marine
ecosystem. They eat sea
urchins and other
invertebrates that graze on
giant kelp. Without sea
otters, these grazing animals
can destroy kelp forests and
consequently the wide
diversity of animals that
depend upon kelp habitat for
survival. Additionally, kelp
forests protect coastlines from
storm surge and absorb vast amounts of harmful carbon dioxide from the
atmosphere. Sea otters are also considered a sentinel species because their
health reflects that of California’s coastal waters.