Concept if keystone species

1. KEYSTONE SPECIES
SUBMITTED BY – MRIDUL
JAMWAL
ROLL No. - CUHP18ZOO14
MSc. ZOOLOGY 3rd SEMESTER

2.  A Keystone species is a species that has a very large effect on the community
through both direct and indirect pathways even though its abundance or
biomass in the community is low .
 The keystone species have huge effect on community structure .
 Term Keystone species was given by Robert T. Paine in 1966 .

3. Effects of keystone species on the structure of the community :
1. Altering the physical structure .
2. By affecting the prey and host population as predators, parasites or pathogens .
3. By supplying essential services and resources as mutualism
4. Affecting energy flow and material resources as producers and consumers .

4. - Robert T . Paine proposed that the keystone species are the species whose feeding
activities have inordinate influences on community structure .
OR
- The feeding activities of keystone species may control the structure of community .

5. Reasons to emerge Paine’s keystone species hypothesis :
1. He proposed that predators might keep prey population below their carrying capacity .
2. The potential for competitive exclusion would be low in populations kept below carrying
capacity .
3. If keystone species reduce the likelihood of competitive exclusion , their activities would
increase the number of species that could co-exist in communities .
In other words Paine predicted that some predators may increase species diversity.

6. Experiment by Paine :
- Paine began his studies by examining the relationship between overall species diversity within food web and proportion of
the community represented by predators .
- Paine describe a food web from the intertidal zone of Mukkaw Bay ,Washington , which lies in the North temperate zone at
49 degree North .
- This food web is typically of the rocky shore community along the west cost of North America .
- The base of this web consists of 9 dominant intertidal invertebrates :
1. Two species of chiton.
2. Two species of limpets.
3. One California mussel.
4. Three species of acron barnacles .
5. One specie of Goose neck barnacle.
He used to remove the predator species from the intertidal zone , Pisaster ochraceous (sea star) to study effect that
the predator has on the abundance and diversity of species in the rock intertidal community .
- Pisaster obtain 90% of its energy from the mixture of chiton (40%), mussels (37%), and barnacle (12%).
- The total number of species found there are 15 .

7. chiton Calliforniamussel Acronbarnacles
limpets Gooseneckbarnacles Pisasterochraceous

8. - He used to study site in the middle intertidal zone that extended 8m along the shore and 2m vertically .
- One site was designated as Control and the other as an Experimental site .
- He removed Pisaster from the experimental site and relocated them in another portion of intertidal zone .
- Each week Paine check the experimental site for the presence of Pisaster and removed any that might have
moved in since his last visit .
- Paine followed the responses of the intertidal community to sea star removal for 2 years .
- Over this interval , the diversity of intertidal vertebrates in the control plot remained constant at 15 , while
the diversity within the experimental plot declined from 15 to 8 , a loss of 7 species .
- This reduction in species diversity supported Paine’s Keystone species hypothesis .
- Reason – The most common limiting source in Rocky intertidal zone is space . So this reduction was due to
competitive exclusion i.e competition for space .
- Within 3 months of removing Pisaster from the experimental plot, the barnacles, Balanus glandula occupies
60% to 80% of the available space.
- One year after Paine removed Pisaster and Balanus glandula then it was crowded by mussels, Mytilus
californianus , and gooseneck barnacles, Pollicipes polymerus .
- Benthic algal population also declined because of a lack of space for attachment .
- The herbivorous chitons and limpets also left, due to lack of space and shortage of food .

9. - Sponges were also crowded out and a Nudibranch(marine gastropod molluscs) that feed on
sponges also left .
- After 5 years; the Pisater removed plot was dominated by two species:
- The mussel, M. californianus .
- The gooseneck barnacle, P. polymerus.
- This experiment showed that Pisaster is a keystone species .
- when Paine removed it from his study plot , the community collapsed .
- To demonstrate this we need more experiments and observations across a wide variety of
communities .
- Paine followed his work at Mukkaw Bay with a similar experiment in New Zealand .
- The top, predator is sea star, Stichaster australis , that feed on a wide variety of invertebrates ,
including barnacles, chiton, limpets, and a mussel, Perna canaliculus.
- After 15 months , Perna dominate the study area excluded nearly all other flora and fauna,
covering 68% to 78% of the space .
- Paine’s studies in north America and New Zealand provide substantial support for keystone species
hypothesis.

10. TYPES OF KEYSTONE SPECIES :
 Keystone species falls into several broad categories :
1. Predators (keystone carnivore, seedpredators)
2. Mutualists
3. Herbivores(ecosystemengineers)
4. Plants
5. prey

11. Keystone Carnivore Predators – The Keystone predators alter the abundance of prey
species which initiates a number of indirect effects .
- Insect – feeding birds often maintain insect diversity in forests by feeding on the most
abundant species and hence , preventing single – species outbreaks, which can be catastrophic .
- Sea otters in the North Pacific feed preferentially on sea urchins that feed voraciously on valuable
kelp (seaweed) species that comprise the productive and diverse kelp beds of the Pacific Coast .
The otters indirectly but greatly benefit the kelps and a highly diverse group of species
that depend on the kelps for food and refuge .
- Alligators in Everglades feed on mid – sized prey (reptiles and mammals) as well as on small prey
(mice, rabbits) , but benefit the smaller prey by consuming the predators of these smaller preys.
Alligators by chance , also benefit a large number of water dependent species by
digging nest holes that contain water throughout the dry season. This includes species
that they prey on.
1.
(i)

12. - Big predatory fish maintain fish diversity in rivers and lakes, by consuming abundant ,
easy to find species, and hence, preventing dominant species from increasing to
their shutout levels .
- The keystone top predators such as panthers, lions, tigers, and leopards in terrestrial
ecosystem have strongly influenced the community by reducing competition
among prey species .

13. Keystone seed predators – In the Chihuahuan desert system (United States) Kangroo rats
are dominant seed consumers and compete with other smaller granivorous rodents .
- Through long term removal experiment , the keystone guilds of the kangroo rats, have been
shown to cause changes in energy flow and species composition in the rodent and plant
community , so much so that desert shrubland was converted into grassland .
- However , colonization by a small exotic rat (Chaetodipus baileyi) has removed the flow of
energy through the rodent community .
(ii)

14. Keystone mutualists - The keystone mutualist species maintain the diversity of organisms in
the community by controlling the abundance of other species through mutualistic interactions
between two or more species .
For example: They serve as essential link in the recycling of nutrients or are major seed dispersers and
pollinators .
They are also known as Mobile links as their foraging movements are critical to other species. Mobile
link pollinators and seed dispersers are essential for the persistence of pant population .
Once identified, keystone mutualists can be managed to ensure the survival of the species dependent
on them .
By increasing the abundance of keystone mutualists for instance, it would be possible to increase the
population of dependent species .
2 .

15. Various species of rats, ants, and humming birds serves as mobile links, which depend on specific
hosts for their food .
Mammalian dispersers: Flying squirrels and red backed voles are the mammalian dispersers of
the mycorrhizal fungi .
The frugivore populations of primates, squirrels, rodents, and birds depend for their food on palm
nuts, figs, and nectar of flowers in tropical forests.
Certain species of tropical figs bear fruits during the season when no other fruit is available for
frugivores (fruit eating animals).
If figs are not available during periods of food scarcity many animals can die .
Some groups of species provide support to vertebrates in the tropical rainforests .
Termites are a favoured food for the chimpanzees .

16. Even microorganisms play a vital role .
In various forest ecosystems mycorrhizal fungi are essential for mineral mobilization
and absorption .
Rather than a single species, mycorrhizal fungi are actually a group of species that, as a
group, fulfil a keystone function.
In keystone mutualists the disruption of one species impacts the other and, ultimately
ecosystem as whole .

17. Keystone Herbivorers : Vertebrate herbivores strongly influence plant species
composition .
Many tropical grasslands owe their origin and perpetuation to grazing animals .
Instead of impacting food supply they create, modify, or maintain the landscape around them .
They influence the prevalence and activities of other organisms and help define the overall
biodiversity of the habitat .
For example : African elephant are known to have transformed woodland into open grass –
savanna .
3 .

18. Keystone plants: Some keystone plants , like the Sonoran desert’s saguaro cactus, are
those that provide a critical source of food and/or shelter for species .
4.

19. Keystone prey : The keystone prey have a big role to play in the ecosystem .
They serves as critical food source for predator population; moreover , they are resilient
creatures , unlike some other types of prey species that are more susceptible to becoming rare
or extinct within an ecosystem .
5 .

20. What Effect do keystone species have on ecosystem:
 Keystone species maintain the local biodiversity of an ecosystem, influencing the
abundance and type of other species in a habitat .
 They are critical component of the local food web .
 They fills a critical ecological role that no other species can .
 Without keystone species , an ecosystem would radically change or cease to exist
altogether .
 It’s important to note that a species role can change from one ecosystem to the
next, and a species that is considered a keystone in one environment may not be
considered the same in another .

21. Examples of keystone species :
1. Sea otter : Native to the northern Pacific Ocean, sea otters play a vital role in the health of coastal
kelp forest .
Dense ecosystems of brown algae towering above the ocean floor, kelp forests provide food, shelter,
nursery habitat, and hunting grounds for an abundance of fish, marine mammals, and other species
but they are vulnerable to predation by marine invertebrates .
Sea urchins in particular graze on kelp and, without predators like sea otters to keep them in check,
grow larger and more abundant.
Whole “herds” of sea urchins have been known to sweep across the ocean floor, gobbling kelp stands
at a rate of up to 30feet per month and leaving barren sea floor in their wake .
Sea otters are voracious eaters with the ability to consume up to 25% of their body weight daily. It’s
the sea otter’s outsize appetite for the spiky marine animals that enables them to control sea urchin
populations and keep forests flourishing .

22. Sea otter :

23. 2. Beavers : Beavers are ecosystem engineers that dramatically reshape the physical environment
around them .
The dams they construct flood the surrounding landscape and form a wetland habitat of ponds and
marshy meadows that can support a rich concentration of animals and plants.
Freshwater fish, insects, amphibians, birds, other animals, and, plants, including threatened and
endangered ones, rely on wetlands for shelter, nursery habitat, and breeding and feeding grounds.
Beaver dams and the water quality in streams, replenish underwater aquifers, reduce flooding, store
nutrients for plants, and reduce erosion of stream banks by slowing the flow of water.

24. Beaver :

25. 3. Wolves : Grey wolves are top predators whose presence has a ripple effect on the rest of its
ecosystem .
Studies show that wolves keep elk population in check, preventing them from over-browsing on
willow and aspen, which in turn helps maintain healthy stands of trees in the landscape.
Wolves are a boon to other predator population as well, with their uneaten food scraps
strengthening the food supply of scavengers like eagles, coyotes, and bears.
The grey wolf remains as endangered keystone species.

26. Wolf :

27. 4. elephants:A keystone species in eastern and southern Africa savanna elephant consumes as much
as 300 pounds of vegetation per day.
By uprooting and eating vast quantities of small trees and shrubs that would otherwise convert to forest
or scrubland, they are ecosystem engineers that preserve sunny, open space where grasses can thrive.
This vegetation supports other herbivores like antelopes, wildebeests, and zebras; it also provides warm,
dry soil for smaller animals like mice and shrews to burrow into.
In turn, these prey species feed carnivores such as lions, hyenas, and cheetahs.
Meanwhile, via their dung, elephants also spread plant seeds to new areas – in fact, some plants have
evolved to the point where they germinate more easily after passing through an elephant’s digestive
tract.
This vital species is under attack from poachers and trophy hunters and at risk of extinction.

28. African elephant :

29. 5. Bees : Like hummingbirds, bees also support the reproduction of as much as 90% of world’s
flowering plants , so called as keystone species .
Not only do they pollinate fruits, vegetables, and other crops that provide humans with everything
from food to clothing to fuel , but they also help produce the seed, nuts, berries, and fruit that
countless other species in ecosystems around the world survive on .
Without bees, there would be a bottom-up cascade of consequences throughout the food chain .
Despite this, bees like the endangered rusty patched bumblebee have failed to receive crucial
protection in the United States .

30. Bees :

31. Keystone species by region :
 Ocean : Sharks which allow the population of herbivorous fish farther down the food
chain to thrive, and these fish, in turn, graze on algae that otherwise degrade coral reef.
 Desert : Native to Sonoran desert of the southwest United States and Mexico the
saguaro cactus is a keystone species that provide critical nesting spot for birds like red-tailed
hawks and woodpeckers and their blooming flowers feed bats, birds, and bees, while their
ripened fruits serves as food for mammals, insects, etc.
 Boreal forest or taiga : Keystone species include trees like aspen and
willow which provide critical habitat for lichens, fungi, insects, and birds.
 Tundra : A prey keystone species like lemming, a small rodent which feed predators
like arctic foxes, snowy owls, and weasels.
 Tropical rainforest : Fig tree, serve as keystone species feeds more that
1,200 types of birds, bats, and other species year around.

32. Shark as keystone species in ocean Saguaro cactus as keystone species in Desert Blooming flowers in saguaro cactus
Aspen as a keystone species in Boreal forest Lemming as a keystone species in tundra Fig tree as a keystone species in tropical rainforests