Download Keystone Species

Keystone Species
Script: Dr. Sukanya Datta
TRSA 70 NPL Colony
New Rajinder Nagar
New Delhi 110 060
Characters (Four)
Father
Mother
Son
Daughter
Mother: I am so glad that Bari didi is coming this evening. Really, the arrangements for
our first Diwali in our new home are simply not going according to plan. But I know that
the moment she comes, everything will fall into place.
Father: I agree. She is so good at managing things; she is worth at least ten of us put
together.
Mother: Yes…laughs…see Rambhuj? All day today, he has been pretending to polish
the banisters…but once he sees Bari didi he will be galvanized into action and the house
will sparkle from top to bottom…in a matter of hours.
Father: Laughs. Why blame Rambhuj? Look at our son…for the last week he has been
working on this school engineering project trying to design a bridge …and till today he
has not got the arch right. His keystone is all wrong…I tried to tell him and he wouldn’t
listen…. Just wait till Bari didi catches him!!! He will work double fast under her gaze
and listen to her every word too.
Mother: Actually, come to think of it…Bari didi is our keystone too…without her, our
family simply falls apart.
Both laugh.
Father: Well said. She is our keystone and our cornerstone too. God bless her.
Girl’s voice: What is this keystone business? Bhaiya was also mumbling about a
keystone. He was looking upset and angry about it. But you two are laughing about a
keystone. What is it? I want to know too…
Father and Mother (simultaneously): Ah! There you are! Come…sit down…
Father: So, your Bhaiya is unhappy about a keystone!! At least now he realizes where he
is going wrong.
Daughter Yeah! But you are laughing about it…that is wrong. You must not laugh at
Bhaiya. He is trying very hard to make the bridge but his arches are falling down.
Mother: Oh my dear…we were not laughing at Bhaiya.
Daughter But I heard you say Keystone…that is also what Bhaiya was
saying…keystone. What is a keystone? Is it a key made of stone? I did not know you
could make keys out of stone!
Mother: No dear. A keystone is a word that is used to mean that some one or something
is very important…you know, fundamentally important.
Daughter I don’t understand.
Father: Let me explain with an example. Your mother and I were talking about how
important my Bari didi …your Aunt is to us. We spoke about her as being our family’s
keystone.
Daughter Yeah…Ok. I get it but how come Bhaiya is so upset about his keystone…that
is something different isn’t it? I mean Aunty is a person and she is our family’s keystone
but what does it have to do with the bridge Bhaiya is designing? The keystone is messing
it up for him and it is not Aunty!!!
Parents laugh: (simultaneously) No dear it is not Aunty.
Father: Ok. Let me explain. You see in bridges there is a wedge-shaped stone to support
the top of an arch. If this is disturbed the bridge will fall down. It is very important to
place the keystone correctly when designing bridges.
Daughter So a keystone can mean a person and it can also mean a part of a building or a
bridge…how strange that this one word can be applied to people as well as things.
Mother: Well…to tell you the truth the word can be applied to both animals and plants
too.
Daughter (surprised tone) What? The word keystone can be applied to people, buildings,
animals and plants as well. It is amazing how much work one word can be made to do!!
What a versatile word. I want to know more.
Father: What do you want to know?
Girl (thoughtfully): We..ll…let’s see. I know how the word applies to people…and I
know how it can be applied to buildings….so tell me how is this word used in the context
of animals and plants?
Mother: Good thinking. But tell me do you know what a community is?
Daughter Ma! We have learnt this is school. Human community is a group of people
who live together in the neighborhood like we do in our Residential complex. In the
context of plants and animals it means a naturally occurring group of different species
that share a common environment.
Father: You are correct. But there is something that you forgot to say.
Daughter Forgot to say something? What?? Oh I know…..community members interact
with each other. One community is usually distinct from another community because of
these interactions.
Parents: Excellent.
Father to Mother: You know, kids these days know so much more as compared to us
when we were kids.
Mother: This is because communication channels are so much more these days. TV,
Radio and Internet are all such powerful mediums in their own right.
Girl (impatiently): So each is a keystone in communication…but please let us get back to
our topic.
Parents laugh: Yes dear.
Mother: OK…as we were saying, keystone species in the context of communities means
that has a disproportionately large effect on the communities in which it occurs.
Daughter What do you mean… disproportionately large (tonal emphasis) effect on the
communities?
Mother: I mean that its influence is much more than what might be expected based
simply on its abundance in the community.
Daughter Oh, so it is not like just counting the number of individuals….but rather on
how much influence the species exerts.
Son: (Suddenly entering the conversation) Like Bari Bua is only one person but the
influence she has on our family and friends… not to mention neighbors and servants… is
simply enormous.
Father: Laughs…See it is always easy to understand when you have examples handy.
Mother: Hello son…are you through with your project? Is your bridge done?
Son: Yes Ma. It was the keystone placement that was wrong…Thanks Papa, your hint
helped. Once I corrected the placement of the keystone my bridge took just minutes to
finish.
Father: Glad to have been of help. Sometimes it helps if a fresh pair of eyes looks at the
situation.
Daughter I wonder whose eyes first recognized the keystone species…that person must
have been really observant.
Mother: The credit for coining the term keystone species goes to American zoologist
Robert T. Paine.
Father: Yes he gave the idea in 1969.
Daughter So according to him…some animals or plants are more important than others
and these are the keystone species!
Mother: That is a generalization, my dear and slightly inaccurate too. You see, the
keystone concept is context dependent. The importance of a species in one community
may be different from its importance in another community. But one fact is common:
Disappearance of such species may lead to significant ecosystem change or breakdown in
its function which may have snowball effect on a broader scale.
Daughter So what would be the best way to define it?
Father: It would be better if you said that a keystone species is a species that plays an
essential role in the structure, functioning or productivity of an ecosystem.
Son: You know, I feel that he saw these species as the keystone of the architecture of
the web of species in a particular ecological space and that is why he used this term.
Afterall, the keystone in architecture is the supporting element of a larger structure.
Father: Perhaps you are right. It is certainly a logical piece of reasoning.
Daughter I wonder what animal or plant actually gave him the idea.
Mother: I donot know what animal Paine studied but I do know that the earliest reported
example was from temperate inter-tidal communities on the west coast of North America.
Father: Yes. And it involved invertebrate animals such as the starfish (Pisaster
ochraceous) and the mussel (Mytilus californianus).
Son: And here I was thinking it would be huge animals. Laughs
Mother: Yes dear…large animals are sometimes keystone species too. The elephant is.
Girl (impatiently): Bhaiya, don’t interrupt. We are talking about how scientist reported
this the first time.
Father: Yes dear…I was talking about the starfish which preyed on the mussels and kept
the population within limits.
Mother: Had that not been so, the mussels, which had competitive superiority over the
other species in the community, would have dominated the community.
Father: However, what really surprised the scientist was that the starfish could not
totally eliminate the mussel from the community because it was not able to predate upon
the largest mussels.
Son: Oh! Oh! That means predation by the starfish on the mussels merely reduced their
numbers so that the prey of the mussels could thrive too.
Mother: Absolutely. This actually meant that the community could maintain a greater
richness of species. It was more complex in structure because the monopoly of mussels
was prevented.
Daughter So keystone species exert influence on biodiversity.
Son: Wow! You know what biodiversity is! I am impressed.
Daughter
Don’t
be.
It
is
on
TV
all
the
time…species
richness
and
biodiversity…everyone knows…but I want to know a little more about keystone species
affecting biodiversity. Mummy, do animal keystone species act only on other animal
species or can animal keystone species impact plants too?
Mother: This is an excellent question dear. The impact of animal keystone species is not
restricted to only other animals. These can, and do, impact plants too.
Father: Yes…the Sea otter is a good example.
Son: Oh! So keystone species are not restricted to land but can be found in aquatic
habitats too!!
Mother: Yes. The sea otter (Enhydra lutris) is a marine mammal that feeds on Sea
urchins. Sea urchins in turn are herbivores and feed on large marine algae known as
kelps.
Daughter I think I can see where this is going…please may I guess? You can correct me
if I am wrong.
Mother…laughing: Go on, guess.
Daughter If the Sea otters disappear, there will be no one to keep the Sea urchin
population in check. The Sea urchin population will grow.
Son: It will not just grow…it will explode.
Daughter Ok…it will explode and all those new Sea urchins will eat up all the
Kelp…which by the way, are like huge forests under the waves.
Parents Clapping : Well done!!!
Father: What you said is absolutely right but not complete.
Daughter I always give incomplete answers, don’t I? What did I miss this time?
Mother: Not much…just that in addition to promoting growth of kelp forests, Sea otters
also influence mussel populations on which they also feed. They remove mussels from
rocky seaside areas, liberating space for competitive species. This leads to increased
species diversity in the area
Father: By the way…it may interest you that when the Sea otters were nearly wiped out
because of trade in their fur in the 18th century; the kelp forests suffered. But now that the
Sea otters are making a slow comeback…so are the kelp forests.
Mother: And if you want a terrestrial example using a large animal…there is the African
elephant (Loxodonta africana). It eats a wide range of herbaceous and woody plants and
in the process it tramples or knocks down woody plants; often killing them.
Daughter But how does that help?
Father: By feeding in a manner that is destructive to shrubs and trees, elephants shift the
balance of the savanna ecosystem toward a greater dominance of herbaceous species.
Daughter Is there an example of a terrestrial animal affecting aquatic systems?
Father: Why not? Everything in nature is interconnected dear. You just have to look
closely enough.
Mother: The beaver (Castor canadensis) has tremendous influence on its habitat. They
create extensive wetlands by damming streams, causing them to flood low-lying areas.
By doing so, they create fertile open-water wetlands for their own use as well as for many
other species that otherwise might not be able to utilize the local habitats.
Son: I remember reading that species that exert a large impact on their ecosystem by
modifying habitat are called “ecosystem engineers.”
Daughter Ecosystem engineers…I like the term. The Beaver is an Ecosystem engineer.
Boy: Yes …although it never ever needed to make a bridge for a school project!!!
Mother: But it did graduate from the school of Mother Nature!
Son: I wonder if there are many such ecosystem engineers.
Mother: You will be surprised at how many there are! And some are so insignificant that
you would never have known about the important role they play if you had not taken the
trouble to study them.
Boy: How so?
Father: The crabs found in mangrove ecosystems tunnel into the soft soil and create a
complex of interconnected burrows mainly to live in. Now, apart from serving as their
shelters these tunnels also serve as a conduit for water; dissolved nutrients and for air.
Mother: Mangrove crabs also drag leaves into their burrows and the uneaten ones get
buried in the soil where these are decomposed by bacteria.
Son: Oh! I see…this impacts the fertility of the soil in a positive manner.
Mother: The absence of burrowing crabs from the mangrove ecosystem would result in
nutrient deficiency in mangrove soils.
Father: If so, then the mangrove trees would not thrive; the plants would be stunted and
populations, sparse.
Daughter Papa, is there any practical importance behind studying keystone species?
Father: Yes of course. The concept is important in conservation biology because the
loss, or even the decline, of keystone species has far-reaching consequences for the
structure and functioning of their ecosystems. For example, if the tiger…a top predator in
terrestrial ecosystems is wiped out…. populations of herbivores such as deer will
explode. Think what will happen to the greenery if the unchecked deer population eats it
all up. And then think what will happen to the deer once there is no greenery left!
Son: You did not mention plant keystone species…aren’t there any?
Father: Of course there are. From Rhododendrons in the Sikkim Himalayas, to Cullenia
tree in the Kalakkad rainforest ecologists have identified a wide variety of keystone
species. These keystone species are pillars of their community. The stability of the entire
ecosystem depends on these species.
Daughter How can a tree be a keystone species…after all it is not a predator to keep
down the population of its prey!
Father: Laughs…my dear child…predation is not the only way to keep a population
under control.
Mother: A tree provides food, dear…food and shelter and safety too.
Father: The Cullenia tree, for example, is a hot bed of activity when in flower because
the sepals of the flowers are edible although nectar quantity is poor. It is a keystone
species for several species of arboreal mammals including the endangered Lion tailed
macaque (Macaca silenus).
Mother: Many Insects come to eat its fruits. Birds and reptiles follow and feed on the
insects. Monkeys eat insects, leaves and fruits. Tigers sleep below in the shade of the
trees …perhaps dreaming about catching the animals that ate the insects that ate the
fruits!
Daughter Oh! This is splendid!!! It is wonderful to see how many different species
benefit from this one tree species.
Mother: It is unfortunate that keystone species are usually noticed when they are
removed or they disappear from an ecosystem, resulting in dramatic changes to the rest of
the community.
Son: My friend recently visited Mukurthi National Park in the Western Ghats mountain
range. He said the park was created to protect its keystone species, the Nilgiri Tahr.
Mother: So, you can see just how important it is to understand which is the keystone
species in the community; and then to take all possible steps to conserve it.
Sound of the car coming close…car door opening…car door closing…footsteps…. door
bell
Everybody: Hooray, our Keystone person is home.
Sounds of running footsteps to greet the visitor.