Unit 1 Interdependence between Organisms within their Environment
Key Unit Competence
To be able to explain complex relationships between organisms within their environment.
LEARNING OBJECTIVES
At the end of this unit, learners should be able to:
• Explain the various interactions of organisms in nature.
• Appreciate the relationships existing among the organisms within their environment.
• State the significance of organisms’ interactions in nature.
• Explain the terms interspecific and intraspecific competition.
• Compare interspecific and intraspecific competition.
• Describe the adaptations of predators to catch and kill prey and adaptations of prey to
avoid
• predators.
• Interpret graphs for predator-prey relationships.
• Classify examples of species interactions, e.g., competition, predation, parasitism,
commensalism, and mutualism.• Recognise the role of saprophytes in mineral recycling.
INTRODUCTORY ACTIVITY
• Have you ever visited Akagera national park?
• Any visitor is impressed by the organization of wildlife Akagera National park. Wen
lions come they alert one another.
• Analyze the photograph below from Akagera national park to see a community ofherbivores grazing.
• At what extent can you say that there is interdependence among these organisms?
1.1 INTERRELATIONSHIP AMONG THE ORGANISMS AND THEIR EFFECTS
ACTIVITY 1.1
Watch a movie on wildlife.
1) What interactions are there among organisms observed?2) State why biological interactions are important and how they help the ecosystem.
No organism exists in an absolute isolation. Every organism interacts with other organisms
within a community. Thus, different organisms interacting with one another within a community
forms a concept called biological interactions or interrelationship among organisms. These
interactions among the organisms can be beneficial or harmful or even neutral. They have the
potential to influence and mould the structure, growth, and maintenance of populations within
a community. Moreover, in some cases, these interactions may result into long-term ecologicaland evolutionary changes among the individuals participating in these interactions.
S5 Biology
These interactions may involve individuals of the same species or different species. When
the interactions involve individuals of the same species, it is called intraspecific interaction.
On the other hand, when the interactions involve individuals of different species, it is called
interspecific interaction.
Biological interactions can be generally classified into different categories based on whether the
effects of interactions are beneficial, harmful or neutral for each of any two species. Thus based
on these criteria, biological or population interactions may be divided into basic interactions
and relationships. All the interactions are indicated by signs such as +, + or –,–, or +,–, even
0, 0. The sign (+) indicates that a particular species is benefitting from the interactions. The
sign (–) indicates that a particular species in the interactions is being harmed, While sign (0)
indicates neutral position where it is neither benefited nor harmed in the interactions. The
important species interactions are:Table 1: Interrelationship among the organisms
APPLICATION 1.1
1. Epiphytes are any plants that grow upon another plant or object merely for physical
support. Can you conclude that epiphytes are parasitic plants? Give reason2. Herbivory can be separated from the predation. Discuss
1.2 INTER AND INTRASPECIFIC RELATIONSHIPS AMONG THE ORGANISMSAND THEIR SIGNIFICANCES
ACTIVITY 1.2
You are now familiar with the words intra and interspecific. Can you cite some examples of
interactions from your surroundings distinguishing these terms? Discuss and note down howmany examples you can point out. Also discuss the severity of types of competition.
1.2.1 Competition (–,–)
Competition refers to the interaction of two organisms striving for the same resource. Generally,
competition is of two types: intraspecific and interspecific competition. In both types of
competitions,
the two or more species competing for the same resource inhibit one another
directly or indirectly. That is why they are denoted as (–,–) signs.
(a) Intraspecific Competition
Intraspecific competition is a competition where individuals of the same species compete for
the same limited resources in an ecosystem. The resources could be food, water, space, light,
mates or any other resource which is required for survival.
Significance of Intraspecific Competition
Intraspecific competition acts as an important regulator of population size, meaning
successful individuals will survive while unsuccessful individuals will die. It can also be
called population density dependent regulator. Moreover, since intraspecific competition
results individuals with different reproductive success, it can be a selective factor inevolution.
(b) Interspecific Competition
Interspecific competition is a type of competition in which individuals of different species
compete for the same limited resources in an ecosystem. The resources could be food, space,
light, water, etc. In this kind of interaction, populations of the two or more species are affectedadversely.
Significance of Interspecific Competition
Structuring ecological communities
Gause’s exclusion principle states that the species with identical ecological requirements cannot
coexist over a long period of time. The less-fit species in the competition will be replaced by
the better-fit species. Thus, in such situations, where interspecific competition is intense, the
competition acts as one of the most important factors in structuring ecological communitiesand also as an agent of natural selection.
Character displacement
Competition can cause species to evolve differences in traits. The characteristics that enable
an organism to reduce competition will function to improve fitness; therefore, influencing the
evolution of characteristics related to the acquisition of resources.
Example: Two Darwin finches of the Galapagos Islands. The medium ground finches
Geospizafortis and the small ground finches G. fuliginosa. When both the species live on
separate isolated islands, they possess similar but overlapping beak size. However, when they
live on the same island, the beak size of the medium ground finch is much larger than that of
the medium ground finches that live on isolated island. Similarly, the beak size of ground finch
is smaller than that of the ground finches that live on isolated island.
Under the pressure of competition for food on the same island, selection favours medium
ground finches to have a large beak size to eat larger seeds; and selection favours small
ground finches to have small beak size to eat smaller seeds. Therefore, when the shift involves
changes in features of the species’ morphology, behaviour, or physiology, it is referred to as
character displacement.
Studies of character displacement are important because they provide evidence that competition
plays a very important role in determining ecological and evolutionary patterns in nature. Thisis also known as the evolution of specialization.
Difference between Intraspecific and Interspecific Competition
1.2.2 Parasitism (+,–)
Parasitism describes a relationship between two organisms where one benefits and the other
is harmed. A parasite is an organism that benefits from the relationship, while a host is the
one which is harmed in the relationship. Parasites can be a number of things, including plants,animals, and even viruses and bacteria.
Types of Parasitism
Parasites are classified by how they interact with their host. Overall, parasites are much smallerthan their hosts and reproduce at a faster rate.
(a) Ectoparasites
The term “ecto” in Greek means outside. Therefore, parasites that live
on their host are termed ectoparasites. Examples of ectoparasites
are fleas, ticks, and mites (Figure 1.1). These parasites live on largeranimals, like cats, dogs and deer.
(b) Endoparasites
Similarly, the term “endo” in Greek means inside. Parasites that live inside their host are termed
endoparasites. These include the things like parasitic worms,
bacteria, and viruses. Tapeworms are endoparasites. They live in
human intestines where they feed on the partially-digested food in
their host’s intestines. It is a fully protected environment and they
grow and thrive in these conditions.
The tapeworms have no digestive system of their own, but absorb
nutrients through their skin from partially digested food as they pass
through the host (Figure 1.2).
Tapeworms are parasitic worms and are most often referred to as just parasites. They literallysurvive through their host’s nutrients. Parasites need hosts to survive.
Significance of Parasitism
1. Parasitism alters the behaviour and morphology of their hosts. This alteration increases
the chance of being preyed by the predators thereby assisting the parasites to move from
one host to another to complete their life cycle.
2. Parasitism promotes coexistence in biodiversity. Usually in an ecosystem, a competitively
dominant species out-competes a competitively inferior species and doesn’t allow
coexistence with this species. However, parasites reduce the competitive ability of the
dominant species in a biodiversity and, thereby, allow a competitively inferior species to
exist together with a dominant species.
3. Parasitism affects the keystone species and modifies the structure of the ecosystem.
In an ecological community, the effect of parasitism is the strongest when the hosts arekeystone or dominant species with crucial functions in an ecosystem.
4. Parasitism leaves parasite with no responsibility. A social parasite is a parasite that takes
advantage of the interaction of other organisms. The best example of a social
parasitism is brood parasitism. This is an interaction where the parasite, typically
a bird, deposits its eggs in the nest of another species (Figure 1.3). The host
(another species) then ‘babysits’ the egg in place of the parasite (bird), allowing
the parasite to deposit eggs in other nests instead of spending time hatching theirown young.
This therefore leaves the parasite with no responsibility of rearing their young. And it gives
them more time to focus on other things such as producing more offspring. Most species of
cuckoo bird are brood parasites, and there is even one species of fish (spotted catfish) whichparasitizes the ‘nest’ of another fish species!
APPLICATION 1.2
1. Complete the blanks with correct missing terms:
(a) ................ is the competition where individuals of the same species compete.
(b) .................... states that two species requiring same ecological requirements cannot
occupy the same ecological niche.
(c) .................... is a parasite that takes advantage of the interaction of other organism.
(d) Parasites that live ............................ are called ectoparasites.
2. Differentiate between carnivores and herbivores.3. Discuss the significance of predation
1.3 PREDATION
ACTIVITY 1.3
Look out for predator and prey relationships in wildlife channels. You can also watch movies
exhibiting these relations on the following link:.
Observe and discuss the following questions while you watch:
• Why is predation important?
• Giving examples of food chain, name predators and prey.• Why does different predators have different preys?
Predation is an interaction between the two species, i.e., predator and prey, in which one
species (predator) uses another species as food (prey). In other words, one organism kills and
consumes another. Predation influences the distribution, abundance and diversity of species
in ecological communities.
Types of PredationGenerally, predation can be divided into:
(a) Carnivory
Carnivory takes place when a predator consumes meat,
rather than plants, and consequently kills its prey.
Organisms that prefer meat to plants are accordingly called
carnivores. The example of the lion hunting the buffaloesis called carnivory (Figure 1.4). In this type of predation
a predator kills its prey more or less immediately. Other examples are a shark eating a tuna or
a Venus fly trap consuming a fly.
(b) Herbivory
Herbivory is the act of animals eating plants. Or when an animal uses
a plant as food, it is called herbivory. Example, when a deer eats grass,
the plant is the prey and the animal the predator (Figure 1.5). Additionally,
organisms do not have necessarily to be larger than their prey to be successful
predators. Venomous snakes are able to take advantage of a variety
of large prey items because an injection of venom can be quite fatal.
Predation can also occur as parasitism, in which the
prey is a host that supports a parasite, such as a virus. In
this case, the prey may be harmed but not killed outright like the antelope. Unlike carnivory, a
parasite feeds for an extended period on a living host. For example—a tapeworm living in thebody of a deer or a mistletoe “feeding” on a mesquite tree.
Not all predators are animals. Carnivorous plants, such as the Venus fly trap and the pitcher
plant, consume insects. Pitcher plants catch their prey in a pool of water containing digestive
enzymes, whereas the Venus fly trap captures an insect between the two lobes of a leaf and
seals the insect inside with digestive enzymes. These plants absorb nutrients from the insectsas they become available during digestion.
Predation and Adaptation
Adaptation in Predator Species
Based on their experience, predators also undergo certain adaptations to be an efficient hunter
or killer. These adapted traits are passed down from generation to generation. Predators exhibit
traits such as sharp teeth (Figure 1.6), claws, and venom that enhance their ability to catch
food. They also possess extremely acute sensory organs that help them to find potential prey.
Depending upon the requirement that arises, predators also adapt themselves to become much
more efficient. Examples of some adapted animals are:
(a) The ability of raptors to spot potential prey from over a kilometre away.
(b) The acute sense of smell of moles.
(c) The ability of owls to locate mice by sound.
(d) The ability of pit vipers to sense body heat while tracking prey.(e) The ability of bats and dolphins to echolocate.
Predators catch their prey either by pursuing potential prey or by ambushing them. Organisms
that give chase are capable of short bursts of speed like Cheetah (Figure 1.7). Those that lie inwait tend to be camouflaged to avoid detection.
Adaptation in Prey Species
In the same way, as much as predator adapts itself to capture prey, preys also adapt as much
as possible to escape from the predators. Many, such as leaf insects, moths, a variety of frogs
and small lizards, and herbivorous mammals, are cryptically coloured to make them moredifficult to see.
Behaviourally, they freeze after detecting the presence of a predator. This lack of movement
helps them better blend in with their background and inhibits the ability of the predator to
find them. But when the predators venture too close, prey will take flight, running or flying
to escape. When a chase ensues, prey will typically survive if they stay out of reach until the
predator gets tired.
Some species take extra time by distracting the predator. Examples include moths that flash
brightly coloured hind-wings, lizards that drop their tails, and insect larvae that dischargeslime. Such actions surprise the predator and give the prey a few extra moments to escape.
Mimicry
Some prey exhibit bright colouration signalling as poisonous individuals. Such aposematic
colouration helps prevent predation by signalling to potential predators that the vividly-coloured
individual is toxic. Toxins may be manufactured within the body, as with the red-spotted newt
(Figure 1.8), or they may be acquired passively via consumption of toxic plants, as with the
monarch butterfly (Figure 1.9).
Not all the species that exhibit vivid colouration are truly toxic. Some have evolved patterns
and colours that mimic those of toxic species. Examples of such Batesian mimicry include
the extraordinarily polymorphic Papiliodardanus swallow tail butterfly in southern Africa and
Madagascar. Females of this species occur in a wide variety of physical appearances, nearly all
of which mimic distasteful species of the Danaeus and Amauris genera with which they co-occur(Figure 1.10).
Figure 1.10: Batesian mimicry—Non-toxic Papiliodardanus swallow tail butterfly
females occur in a variety of forms, each of which mimics the physical appearance
of toxic species. Palatable butterflies (middle column) mimic the warningcolouration of poisonous butterfly species on the left and right butterflies
Adaptation in Herbivory
Herbivory is the consumption of plant material by animals, and herbivores are animals adapted
to eat plants. As in predator-prey interactions, this interaction drives adaptations in both theherbivore and the plant species it eats.
Adaptation in Plants
Though plants cannot move like animals, they also
develop certain mechanism to escape from herbivores. For
example, plants have evolved defences, including thorns
(Figure 1.11) and chemicals, to keep themselves away
from being eaten by herbivores. Scientists have identified
thousands of plant chemical defense compounds,
including familiar compounds such as nicotine andcocaine.
Adaptation in Herbivores
To counteract the adaption of plants and maximize the nutrient intake, herbivores also
have adapted themselves that allow them to determine which plants contain fewer defensivecompounds and more high-quality nutrients.
Some insects, such as butterflies, have chemical sensors on their feet that allow them to taste
the plant before they consume any part of it. Mammalian herbivores often use their keen sense
of smell to detect bitter compounds, and they preferentially eat younger leaves that containfewer chemicals.
Predator-Prey Relationships (Cycle)
Predator-prey relationships are characterized by oscillation of both predator and prey populations
over a period of time. By oscillation, we mean there is a regular pattern of increase and decrease
of populations of both predator and prey (Figure 1.12). Generally, the predator is a carnivore,
while the prey is a herbivore. However, this general truth may vary depending upon the kind
of predator-prey interactions. For example, parasites become predator when they feed on theirhost (prey); herbivores become predator when they feed on plants (prey).
The main reason of oscillation is that as the predator population increases, it progressively
consumes larger number of prey until the prey population starts to decline. Then the declining
prey population no longer supports the large increasing predator population. As the prey
population declines, the predator now faces a food shortage, and many of them starve or fail to
reproduce. As a result, the predator population declines sharply to a point where the reproduction
of prey more than balances its losses through predation. Eventually, the population of prey
increases, which is followed by an increase in the population of predators. In this manner, there
is a regular pattern of increase and decrease in the population of both prey and predator overa time period (Figure 1.12).
Significance of Predation
Predation Prevents a Single Species from Becoming Dominant
A keystone predator is a species that reduces the density of the strongest competitors in a
community. These keystone predators may feed on the dominating prey species and prevent it
from becoming dominant. Thus, they are tied up to the balance of organisms in a particular
ecosystem. Addition or removal of these keystone predators can have drastic cascading effects
on the equilibrium of many other populations in the ecosystem. For example, in grassland,
herbivores (grazers) may prevent as single dominant species from taking over.
Predation can Either Increase or Decrease Species Richness
In an ecological community where predator and prey exist together, predator has the ability to
either increase or decrease the number of prey species. The predator to change the number of
prey depends on the favourability of the environment and also on whether prey is a competitively
dominant species or competitively inferior species in a community. When keystone predator
feeds on dominant prey, it generally promotes species richness by releasing the inferior prey
species to coexist with the dominant species.
Experiment: In an experiment, Paine and others introduced keystone predator Pisaster, a sea
star, in a community (Figure 1.13). This sea star feeds on mussel. In due course of time, they
found out that this predator helped in maintaining species diversity by preventing competitive
exclusion of weaker competitors. Moreover, predation by Pisaster was a key factor in maintaining
populations of at least seven other species. In fact, it was Paine and others who have generatedthe concept of keystone predators.
Predation as Source of Natural Selection
Predation is an important factor of moulding evolution of traits for both predators and prey
species. Natural selection favours the fittest individuals in a community. Thus, the process of
natural selection favours predators that are more efficient in capturing prey than the less efficient
predators. In the same way, the process of natural selection favours prey species that are more
efficient in escaping or deterring predators than the less efficient prey species.
On the one hand, predators impose strong selective force on their prey to evolve into the most
efficient prey against the predators. On the other hand, prey species also counter-impose strong
selective pressures on their predators to evolve into the most efficient predator against the prey.
Since these selection forces are working side-by-side on both predator and prey, these two parties
evolve together. Thus, coevolution is evident. The process of evolution taking place side-by-side
on two closely associated species is called coevolution.
For example: Natural selection process selects faster foxes that can hunt rabbits efficiently.
Simultaneously, natural selection process also selects faster rabbits that can run fast to escape
efficiently from the foxes. The process of selecting the most efficient predator and prey can go
on and on.
APPLICATION 1.3
1). Complete the sentence with the correct assertion:
a) . Thorn is an adaptation of plant against ................................. .
b). Process of evolution taking place side-by-side on two closely associated species is called
a ........................................ .
c) . ................................. prevents a single species from becoming dominant.
d) . Some ................................. exhibit bright colouration signalling as poisonous individuals2) . You are provided with the following Predator-prey data (Snowshoe hare and lynx).
a) Plot the above predator-prey data on a graph paper.
b) Discuss and interpret your graph whether it follows the predator-prey pattern
(oscillation).
c) In the year 1863, the snow hare population was high. What can you say about lynx
population?
d) In 1845, the predator lynx population was more than the prey but gradually it
reversed. What inference can you draw from the change?1.4 MUTUALISMS, COMMENSALISM AND SAPROPHYTISM
ACTIVITY 1.4
Observe the following picture and answer the questions that follow
a) For each animal from A and B, say if it gets benefit (-), it is harmed (-) or remains neutral
(-)
b) What is the name appropriate to each of the relationship A and B above?
c) It is found that mushrooms often develop on decaying manure of cow and Impala.What is the name appropriate to that type of relationship?
1.4.1 Mutualism (+, +)
It is an interaction of two or more species where the interacting species mutually benefit
from each other. And these interacting species mutually benefit from each other so much
that they become completely dependent on one another. They cannot survive and thrive
without each other. That is the reason why this interaction is termed as mutualism or obligate
symbiosis. Mutualism seems to replace parasitism as ecosystems evolve towards maturity,
and it seems to be especially important when some aspect of the environment is limiting(such as water or infertile soil).
Examples:
Bees and flowers: Bees depend on flowers for food in the form of nectar and pollen. And
the flowering plants depend on bees or other pollinators to carry their male reproductive cells
specifically to the female parts of other flowers of the same species. In this way, bees depend
on flower for food, while flower depends on bees for pollination (Figure 1.14).
Humans and E.coli: Inside our own bodies, there are hundreds of different types of bacteria
that live just in our large intestine. Most of these are uncharacterized, but we do know a
lot about E.coli, which is one of the normal bacteria found in all human large intestines
(Figure 1.15). Humans provide E.coli with food and a place to live. In return, the E.coli produce
vitamin K and make it harder for pathogenic bacteria to establish themselves in our large
intestine. Whether or not most of the other species of bacteria found in our digestive tract aid
in digestion, absorption, or vitamin production isn’t completely known, but they all make itharder for invasive pathogens to establish a foothold inside us and cause disease.
Significance of Mutualism
Mutualism is a type of symbiosis, which means living together. The most important impact
of mutualism is that the species which cannot survive individually, can survive by partneringwith other individual species. By living together and depending upon each other, they could
overcome harsh and unfavourable conditions and thrive in the ecosystem. Mutualism thus helps
in moulding or structuring community towards better species interactions.
As seen in the above example, E.coli alone might not be able to survive efficiently in the other
environment like they do in the stomach of human beings. In the same way, we humans
might not get the same benefits that we get from E.coli if instead, we harbour other pathogenic
organisms. Thus, in a situation where an individual species cannot survive by itself, mutualism
gives a better chance of survival and reproduction.
1.4.2 Commensalism (+, 0)
It is an interaction of two or more species in which one species is benefited while the other
species is neutral or is not benefited. The species which is benefitted is designated with “+” sign,
while the species which is neutral is designated as “0”. In commensalism, the species which
is unaffected is the host. The species that benefit from the association is called commensal.
Commensal may obtain nutrients, shelter, support or locomotion from the host species. Normally,
commensal relation is often between a larger host and a smaller commensal. Moreover, during
the interaction, the host remains unchanged, whereas the commensal species may show greatmorphological adaptation.
Examples:
Oysters sometimes have a small, delicate crab (Figure 1.16) in the mantle cavity. These crabs
are usually commensal, although sometimes they overdo their guest status by partaking of the
host’s tissues.
Another example is, the cattle egret follows cattle (Figure 1.17), water buffalo, and other
large herbivores as they graze. The herbivores flush insects from the vegetation as they move,
and the egrets catch and eat the insects when they leave the safety of the vegetation. In thisrelationship, the egrets benefit greatly, but there is no apparent effect on the herbivore.
Significance and Criticism of the Concept
The associations between two populations of species that result in positive effects are exceedingly
widespread and are important in determining the function and structure of populations and
communities.
Some biologists argue that the commensal in commensalism must be likely mutualistic or
parasitic in a small scale which is undetected. And it is unlikely that the host is also completely
not harmed or neutral. Example: Epiphytes intercepting substantial amounts of nutrients from
the host plant must be affecting the host in some other way which might be unnoticed.
1.4.3 Saprophytism
In Greek, sapro-(“putrid matter”) + phyte (“plant, growth”). The condition of certain living
organisms feeding and living on dead organic matter is simply called saprophytism. It is generally
exhibited by saprophytes. Saprophytes are living organisms which feed on dead organic matter
such as dead plant or animal tissue. In this regard, they are detrivores. They break down organic
matters in simpler forms that can be taken up and recycled by plants. Thus, they play a very
important role in soil biology. Examples include most fungi (Figure 1.18 (a and b), bacteria,and some orchids.
The term “saprophyte” is a misnomer. By definition, “Phyte” means a plant, and bacteria and
fungi are not categorized as plants. Most of the saprophytes lack chlorophyll, and therefore,
cannot perform photosynthesis. Thus, they depend on the food energy they absorb from the
decaying organic matters. This means that they are heterotrophs and are considered consumers
in the food chain.
They are characterized by their use of a particular kind of digestion mechanism, called extracellular
digestion. In this process, they secrete digestive substances into the surrounding
environment through which they break down organic matter into simpler substances. The
nutrient-rich broken organic substances are then directly absorbed through the membrane of
the organism’s cells and are metabolized.
One of the most common saprophytic fungi belongs to Rhizopus family. These fungi have an
extensive network of hyphae, similar to tiny roots, which grow through the organic matter.
They grow in a network called a mycelium. Mycelium helps the fungus to penetrate into the
organic matter where the hyphae secrete digestive enzymes and absorb the resulting nutrients.
The most common form of Rhizopus is bread mold, R. nigricans (Figure 1.19). These fungi
can also be seen in fruits, especially stone fruit, and vegetables, faeces and the soil. The fungus
grows very rapidly, maturing within four days, though some fungi might take longer period. The
fungus needs a warm, moist environment to thrive. People can prevent or save from Rhizopus
infection by keeping food under refrigeration or in the freezer so that the spores never get a
chance to grow.
Significance of Saprophytism
Many micro saprotrophs and other decomposers, involving insects, snails and beetles help in
recycling valuable nutrients from dead organic matter which is released back into the soil to be
reabsorbed by plants. For example— in a rainforest ecosystem, to promote healthy rainforest,
nutrients such as iron, calcium, potassium and phosphorous are essentially required. The
decomposers derive these essential nutrients from decaying organic matters and then releaseinto the soil where the plants reabsorb it again.
APPLICATION 1.4
Complete the sentence with the correct assertion
(i) Mutualism ........................ both organisms.
(ii) (+, 0) sign exhibits ............................
(iii) ..................... helps in nutrient recycling.(iv) Cattle egret follows water buffalo and exhibits .....................
1.5 SUMMARY
• The basic species interactions are competition (direct interference type), competition
(resource use type), commensalism, parasitism, predation, mutualism and saprophytism.
♦ Competition
• Competition is an interaction of two organisms striving for the same resource. It is of
two types: Interspecific competition is a competition of individuals of the same species
competing for a limited resource, while intraspecific competition is a competition of
different species competing for a limited resource.
• Competition helps in structuring ecological communities and also plays an important
role in character displacement.
♦ Parasitism
• Parasitism is a relationship between two organisms where one benefits and the other
is harmed. The two types of parasitism are: Ectoparasite and endoparasite. A social
parasite is a parasite that takes advantage of the interaction of other organisms.
• Parasitism alters the behaviour and morphology of their hosts; it promotes coexistence
in biodiversity; it affects the keystone species and modifies the structure of ecosystem.
♦ Predation
• Predation is an interaction between species in which one species (predator) uses another
species as food (prey). It can be divided into: Carnivory, parasitism, cannibalism, herbivory.
• Predation prevents a single species from becoming dominant; it also either increases or
decreases species richness; and it acts as a source of natural selection.
♦ Mutualism
• Mutualism is an interaction of two or more species where the interacting species mutually
benefit from each other so much that they become completely dependent on one another.
Example: Bees and flower.
• Mutualism helps in moulding or structuring community towards better species interactions.
♦ Commensalism
• Commensalism is an interaction of two or more species in which one species is benefited
while the other species is neutral or is not benefited. Example: Cattle egret and cattle.
• It helps in determining the function and structure of populations and communities.
♦ Saprophytism
• Saprophytism is a condition of certain living organisms feeding and living on dead organic
matters. Example: Mold (mushroom).
• Many micro saprotrophs and other decomposers, involving insects, snails, beetles, etc.,
help in recycling valuable nutrients such as iron, calcium, potassium and phosphorous
from dead organic matter which is released back into the soil to be reabsorbed by plants.
1.6 GLOSSARY
• Biological interactions: It is a process of different organisms interacting with one another
within a community.
• Brood parasitism: This is an interaction where the parasite, typically a bird, deposits its
eggs in the nest of another species. The host (another species) then ‘babysits’ the egg in
place of the parasite (bird), allowing the parasite to deposit eggs in other nests instead
of spending time hatching their own young.
• Carnivore plants: Not all predators are animals. Carnivorous plants, such as the Venus
fly trap and the pitcher plant, consume insects. Pitcher plants catch their prey in a pool
of water containing digestive enzymes, whereas the Venus fly trap captures an insect
between the two lobes of a leaf and seals the insect inside with digestive enzymes.
• Commensalism: It is an interaction of two or more species in which one species is
benefited while the other species is neutral or is not benefited.
• Competition: It refers to the interaction of two organisms striving for the same resource.
Generally, competition is of two types: intraspecific and interspecific competition.
• Gause’s exclusive principle: It states that two species with identical ecological requirement
cannot occupy the same ecological niche.
• Herbivory: It is an act of animal eating plants. Or when an animal uses a plant as food,
this is called herbivory. Example, when a deer eats grass, the plant is the prey and the
animal the predator.
• Interspecific competition: It is a type of competition in which individuals of different
species compete for the same limited resources in an ecosystem.
• Interspecific interaction: The interaction which involves individuals of the different
species.
• Intraspecific competition: It is a competition where individuals of the same species
compete for the same limited resources in an ecosystem.
• Intraspecific interaction: The interaction which involves individuals of the same species.
• Keystone predator: A keystone predator is a species that reduces the density of the
strongest competitors in a community.
• Mutualism: It is an interaction of two or more species where the interacting species
mutually benefit from each other.
• Oscillation: It is a regular pattern of increase and decrease populations of both predator
and prey.
• Parasitism: It is a relationship between two organisms where one benefits and the other
is harmed.
• Predation: Predation is an interaction between species in which one species (predator)
uses another species as food (prey); one organism kills and consumes another.
• Saprophytism: The condition of certain living organisms feeding and living on dead
organic matters is called saprophytism. In Greek, sapro-(“putrid matter”) + -phyte (“plant,growth”).
END UNIT ASSESSMENT 1
I. Choose whether the given statements are True (T) or False (F)
1. Organisms’ interaction does only harm.
2. Commensalism harms both species.
3. Competing for food is an example of interspecific competition.
4. Herbivory is the act of predation.
5. Predation never promotes species richness.
6. There is a regular pattern of increase and decrease population in oscillation.
7. Parasitism doesn’t promote coexistence of biodiversity.
II. Multiple Choice Questions
1. Both species are denoted by (+, +) in
(a) Mutualism (b) Saprophytism(c) Commensalism (d) Protocooperation
2. When two species compete for a shared resource, it is called
(a) Predation (b) Exploitative competition
(c) Interference competition (d) Apparent competition
3. Adaptations of a predator are
(a) Sharp teeth of lion
(b) Acute sense of smell of moles
(c) Echolocation of bats
(d) All the above
4. Mineral recycling in a rainforest is done by a
(a) Saprophyte (b) Commensal
(c) Predator (d) Ectoparasite
5. Brood parasitism is an interaction where
(a) A parasite kills the host
(b) A parasite lives in the host
(c) A parasite deposits its sperms to the other species’ nest
(d) A parasite deposits its eggs to the other species’ nest
6. In sexual cannibalism, normally
(a) Males eat females (b) Males eat the younger males
(c) Females eat males (d) Females eat the younger females
7. A flea on a dog is an example of
(a) Parasitism (b) Commensalism
(c) Predation (d) Coevolution
8. Saprophytes are
(a) Predators (b) Plants
(c) Parasites (d) Detrivores
9. A commensal is
(a) species that benefits association
(b) species that benefits from the association
(c) species that is negatively affected from the association
(d) species that negatively affects the association
10. The interaction of bees and flowers is an example of
(a) Protocooperation (b) Commensalism
(c) Mutualism (d) None of theseIII. Long Answer Type Questions
1. Giving suitable examples, explain the various interactions of organisms in nature.
2. Giving examples, describe in your own words, the adaptations of predator species
to catch and kill prey and the adaptions of prey species to avoid predators.
3. What are saprophytes? With one example, describe how saprophytes help in recycling
minerals.
4. Briefly compare interspecific and intraspecific competitions with suitable examples.
5. Draw a predator-prey relationship graph and interpret it.
6. Give two examples of the following:
(a) Predation (b) Parasitism
(c) Commensalism (d) Mutualism
7. How does interrelationship among organisms commit for a sustainably developed
environment? Cite examples to support your answer.
8. With examples, state in your own words, the significance of organisms’ interactionsin nature.