Download Interactions between Organisms

Eco-interactions between organisms
P.1
Interactions between Organisms
A
n interaction between two organisms may be ben______, ad______ to either side or n______.
Since organisms are continually evolving, it should not be surprising to note that different
types of interaction occurring in nature are sometime difficult to be put into distinct categories.
Type of
A B
Nature of the interaction
Interaction
Mutualism
+ + Interaction is favourable to both and is obligatory
Commensalism
Commensal (A) benefits whereas the host (B) is not affected
Predation
Predator kills and consumes the prey (B)
Parasitism
Parasite exploits the host (B) which is affected adversely
Competition
Organism competing and adversely affecting each other --- (A) and (B)
Summary of the various kinds of interactions that may occur between two organisms
I)
Mutualism
When both populations ben____ from an association that is ob______, we call this mutualism. Why
is it obligatory ? The answer is that the partners has become phy____________ interdependent on
one another.
A)
Autotrophs -- Heterotrophs interaction
a) Symbiotic algae. Many aquatic invertebrates possess symbiotic algae, include the
r___-forming corals.
In the case of invertebrate hosts, perhaps the relationship looks a little more
like ‘internal farming’, e.g. Certain marine molluscs feed on seaweed but incorporate the chloroplasts
into the cells lining their gut. Here the chloroplasts may live and photosynthesise for some days while
releasing carbohydrates to the mollusc.
b) Mycorrhiza.
Roots of most healthy plants are
usually associated with fungus called my_______. This
association is so important that many higher plants fail to
grow in the absence of mycorrhiza.
Characteristically in_______ nutrients are supplied to
the higher plants enabling them to live in low nutrient
status soil, and 'in return' the fungus is supported by the
plant which is the photosynthesising partner.
c) lichens.
Lichens are composed of a f_____ and an a___. But the relationship is more than
the sum of the parts. Lichens show struct____ modifications, and phy_______ activities (such as
the formation of so-called lichen acids) that are found in neither component when isolated.
The fungus, which may make up 95 per cent of the lichen dry mass, obtains or____ compounds from
the photosynthesis of the alga. The alga receives more nut_____, car___ dioxide, it can occupy a
wider range of habitats, and can better withstand des________.
Q. Name the autotrophs in the above interactions. In what ways are they benefited from the association?
Eco-interactions between organisms
Q. Explain the experimental evidences that support that there is nutritional interdependence between the fungus and the
Scots pine
Lichen:
structure and physiology
P.2
Eco-interactions between organisms
P.3
Reference Reading 1: Crops without chemicals
With the world's population increasing at an annual rate of about 2 per cent, improvements in our total crop
production and distribution are essential if we are to avoid a catastrophe of widespread starvation.
In the 1960s, the Green Revolution provided the undernourished world with cereal strains of much improved
yield, but these made heavy demands on the fertility of the soil. So far the only answer to this problem has
been the use of expensive nitrogenous fertilizers. The fertilizers themselves have produced problems when
their application on farmlands has led to the eutrophication of lakes and waterways.
This is one of the reasons why agricultural botanists have been directing their attention for some time towards
the prospect of developing cereal crops which can directly assimilate atmospheric nitrogen and so reduce
the demand for nitrogenous fertilizers. In nature, nitrogen fixation is an ability confined to a few genera of
bacteria and blue-green algae/bacteria. Some associated with host plants while others are free-living.
Perhaps the best-known
nitrogen-fixer is the bacterium
Rhizobium which is found in
the root nodules of
leguminous
Legume crops have long been
used in rotation with
non-legumes to improve the
fertility of the soil.
Rhizobium bacteria enter the
legume roots and invade
cortical cells of the root which
are stimulated into
meristematic activity.
The root nodules which develop
may appear pink because of the
synthesis of leghaemoglobin
by the legume root tissue. This
is the only form of haemoglobin
known in the plant kingdom; like
animal haemoglobin, it has the
ability to bind oxygen.
In nodules which do not
produce leghaemoglobin, it has
been shown that the Rhizobium
bacteria do not fix nitrogen.
This knowledge about nitrogen fixation is now being put to good use in the search for ways of producing
nitrogen-fixing cereal food crops. Much effort has been expended in trying to persuade Rhizobium from
legumes to invade the roots of wheat and other cereal plants, but with little success.
Even if nitrogen-fixing cereal crops can be produced, however, there may be serious drawbacks. Nitrogen
fixation consumes a great deal of energy (up to 24 molecules of ATP for each molecule of nitrogen fixed) and
the presence of nitrogenase in many cereals would turn out to be something less than the economic miracle
anticipated.
a
Give the meaning of the following terms:
1 eutrophication
2
facultative anaerobes
3
obligate mutualist.
Eco-interactions between organisms
b
Describe two ways in which nitrogen fixed by Rhizobium bacteria in leguminous plants may enter the soil.
c
1. Suggest a function of the leghaemoglobin produced in the root nodules of legumes.
2
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Explain how this benefits the Rhizobium bacteria.
d. Give a reason for the comment that ‘the presence of nitrogenase in many cereals could turn out to be less than the
economic miracle anticipated’.
Reference reading 2: The Endosymbiosis theory --- Origin of eukaryotic cells
The endosymbiosis theory postulates that

The mitochondria of eukaryotes evolved from aerobic bacteria living within their host cell.
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The chloroplasts of eukaryotes evolved from endosymbiotic cyanobacteria.
The Evidence

Both mitochondria and chloroplasts can arise only from preexisting mitochondria and chloroplasts. They
cannot be formed in a cell that lacks them because nuclear genes encode only some of the proteins of
which they are made.

Both mitochondria and chloroplasts have their own genome and it resembles that of bacteria not that of
the nuclear genome.
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o
Both genomes consist of a single circular molecule of DNA.
o
There are no histones associated with the DNA.
Both mitochondria and chloroplasts have their own protein-synthesizing machinery, and it more closely
resembles that of bacteria than that found in the cytoplasm of eukaryotes.
o
The first amino acid of their transcripts is always fMet as it is in bacteria (not methionine [Met]
that is the first amino acid in eukaryotic proteins).
o
A number of antibiotics (e.g., streptomycin) that act by blocking protein synthesis in bacteria
also block protein synthesis within mitochondria and chloroplasts. They do not interfere with
protein synthesis in the cytoplasm of the eukaryotes.
o
Conversely, inhibitors (e.g., diphtheria toxin) of protein synthesis by eukaryotic ribosomes do
not — sensibly enough — have any effect on bacterial protein synthesis nor on protein
synthesis within mitochondria and chloroplasts.
Eco-interactions between organisms
P.5
Q. Suggest the possible advantages for such an association between an autotroph and a heterotroph.
a) Advantages to the heterotrophs
b) Advantages to the autotrophs
B)
Autotroph -- Autotroph interactions
Anabaena is a member of the blue-green bacteria, Anabaena is found as an endosymbiont in the
floating fern Azolla. The association allows Azolla to live in very nut_____-poor waters.
Q. Suggest how Anabaena can help azolla to strive in nut_____-poor waters.
C)
Heterotroph -- Heterotroph interactions.
C________-digesting Bacteria and Protozoans in the guts of rumi_____ and ter____. The gut
mutualists receive a constant supply of f___ and, in the case of ruminants, a continuously high
tem______ which is ideal for rapid metabolic activity. The ruminants and termites benefit because
they can absorb the products of digestion of cellulose.
The gut microorganisms may also produce B-vit_____, and convert inorganic nitrogen into a____
acids which are absorbed by the animal. Supplementing protein in the poor diet of the basically
vegetarian animals
Non-obligatory Associations
There are many other interactions that are mutually beneficial but is n___-obligatory and looser than
mutualistic ones.
a)
Pollination and Dispersal
The benefit to the plants is obvious and the animals may feed on nectar or a fleshy fruit, and so on. It
must be said that in some cases the modification of the plants is so extr_____ that only a single
species may be attracted or may fulfill the role as pollinator. In these circumstances, the relationship
has crossed the boundary to mutualism. For example, figs can only be pollinated by certain wasps.
b)
Mullerian mimicry
During the course of evolution, prey species have evolved a number of strategies to reduce the
likelihood of their being eaten. One of these methods is to become unpalatable either by making
toxins or by feeding on plants and concentrating their toxins.
Un_________ or toxic animals then employ wa______ coloration to advertise their distastefulness:
they use red, white, black or yellow. It is to the advantage of the prey (and to the predators) if
unpalatable species sh___ the same warning colours. Thus, unrelated species may bear a strong
superficial resem______ to each other. This is known as Mullerian mimicry.
Eco-interactions between organisms
III)
P.6
Commensalism
It is an interaction in which one species benefits and the other is unaff______. Examples can be
identified into four broad groups in which commensalism may be based on:
a) Cleaning Oxpeckers, removes ticks and fleas from the skin of cattle, zebra, giraffes, and
others, and the Egyptian plover, cleans the teeth of the Nile crocodile.
b) Protection and camouflage. For instance, hermit crabs, may carry on its shell anemones,
which seem to protect it from octopuses.
c) Support
Trees are often covered with individuals of other plants, which grow on their trunks and branches.
These ‘epiphytes’ gain support & grow nearer the light then they would have done on the ground.
Examples of e_______ are lichens, some algae, mosses, ferns & orchids, it seems that the trees are
not greatly affected by their presence.
d) Transport
Where one species may use another to, in effect, hitch a ride! The remora, Remora remora. is well
known. It clings to the underside of sharks using its specially modified dorsal fin.
IV)
Predation
In predation the association is unequal: one population benefits, the other suffers.
A)
The evolutionary race between predator and prey
To be a successful predator, an animal must be adapted to loc____, cap____, ing___ and dig___ its
prey, while the preys also ev____ a number of corresponding adaptations to prevent themselves
from being eaten. There is, in fact, a constant evol_________ race between predator and prey.
Eco-interactions between organisms
Predator vs Prey
Prey location vs
Predator evasion
Capture vs
Escape
Ingestion vs
Resistance &
deterrent
B)
Predator are adapted to capture
and kill
good senses of smell, hearing,
for____-facing eyes with
stereoscopic vision
Well-camouflaged, stealthy and
speedy,
some hunt in group
Spec______ mouth parts, strong
and sharp t____, poi_____
injection for killing prey
P.7
Prey are often equipped to avoid being
captured and killed
good senses of sm___, he____, lat____-placed
eyes with very wide field of v____
prey often find safe h_____ places, cam______,
mimicry, has the speed to r__ away
gain protection by living in l____ groups and
communicating danger to each other
H___ shell, poisonous or foul-tas____ chemicals.
Plants may be protected by t____ chemicals such
as cyanogenic glucosides, silica bodies, sp___
Chemical defence in plants
Plants incapable of locomotion cannot avoid being eaten except by making itself unattractive or
distasteful to predators. They may be phys____ tough, covered with spines and thorns, or
chem_____ harbour chemicals that deter potential predators. These chemical are extremely
interesting because they are often bio______ active in animals.
Herbivory/ plant eating is analogous to parasitism. Since herbivory does not necessarily lead to
the death of the 'prey'. Nevertheless, plants have evolved an enormous array of antipredator devices.
Laurel, some clovers, and bracken all produce cyanide if chewed or otherwise damaged. The cy____
(-CN) group, is attached to a sugar to form a glycoside. Also in the cells, but kept separate, is a
glycosidase enzyme. If the cell is damaged these two substances come into contact and cyanide is
released.
However, there is a price to pay for these selective forces. In order to overcome obstacles presented by
the prey, predators may become increasingly spe______ as they become more adapted. In other
words the range of possible prey may become restricted. Many insects are monophagous, that is
depend on one food species; some are oligophagous and maybe feed on just one family of plants.
Polyphagous insects can feed on a variety of plants.
Q. Which group of insects, monophagus, oligophagous or polyphagous do you think pose greater threats to crops? Why?
Reference reading: The defence mechanism of Bracken (a fern)
Bracken defends itself in the following ways. It produces cyanide like clover and
other harmful chemicals which make it distasteful; these include phenolics,
lignins, tannins, carcinogens and a sheep blindness factor. It also produces a
chemical which mimics insect moulting hormones, an ecdysone. Furthermore,
bracken also has a protective association with ants. The ants feed on sugar
produced at extrafloral nectaries and, in return, they drive off many potential
herbivores. Despite this armory, over 20 species of phytophagous (plant-eating)
insects have been found on bracken in UK. This illustrates the general point that selective forces on the
prey are balanced by those on the predator.
Eco-interactions between organisms
P.8
Reference reading : monarch butterfly, cardiac poisons and Batesian mimicry:
One example of allelopathy involving animals is provided by the monarch butterfly.
Its caterpillar stage feeds on the milkweed plant which produces chemicals that act
as strong cardiac (heart) poisons in vertebrates.
This, or its unpleasant taste, presumably discourages grazing herbivores from
eating the plant. However, the caterpillars can tolerate the poison, and can store it
and carry it into the adult butterfly stage.
The butterfly, in turn, gains protection from predatory birds. The bright
colouration and striking markings of the butterfly therefore serve as a warning to
potential predators and act as a protective device. An incidental consequence of
this is that some butterflies mimic the markings of the monarch, thus also
gaining protection. This is known as Batesian mimicry.
Batesian (non-toxic) mimics are disadvantageous to the species they mimic (the distasteful model)
because potential predators may encounter harmless mimics and thus take longer to learn to avoid the
model.
Generally speaking, many plants subjected to grazing contain toxic chemicals to which only a few
herbivore species are tolerant.
V)
Parasitism
A parasite is an organism that lives on or in its h___ and that nourishes itself at the exp____ of the
host without rapidly destroying it as a predator does its prey, but often inflicting some degree of
injury affecting its welfare'. What distinguishes parasitism is that the prey does not die im_________.
Parasitism is like a weak form of predation and analogous, as we have seen, to herbivory.
Animal parasites come principally from the groups Protozoa, Platyhelminthes and Nematoda.
Outside these groups we might cite leeches, ticks, fleas, mosquitoes and lice.
Eco-interactions between organisms
P.9
A key problem for all parasites is to establish the association in the first place. Commonly parasites
have very complex life-c
involving several h___.
The nature of the host-parasite interaction in animals necessitates a variety of meta___ and
phys_______ adaptations. It may also induce reactions to the parasite by the host which in turn the
parasite must overcome.
Almost all bacterial, viral and fungal diseases are par____ and even angiosperm plants can become
parasites; plants like dodder are wholly parasitic on other plants. Finally, parasitism is not confined to
higher organisms. Bacteria may be parasitised by viruses, called bacteriophages.
Some structural, physiological and reproductive specializations of parasites
Types of specializations
Structural
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Physiological

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Reproductive
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Highly specialised mouth____ as in fluid feeders. Development of ‘suckers’
in some parasitic green plants.
Bor___ devices to effect entry into a host.
Att_____ organs such as hooks or suckers
Resistant outer cov____.
Degeneracy of s____ organs associated with the constancy of the parasite's
environment. Absence or deg______ of feeding and loco_____ organs characteristic of g__ parasites.
Enz___ production to digest host tissue external to parasite.
Anti________ in blood feeders
Chemo-sen________ in order to reach the optimum location in the host's
body.
Production of anti-enz_____ in gut parasites.
Ability to respire adequately in an________ conditions
Hermaphrodite condition thus aiding possible self-fertilisation
Enormous numbers of repro_____ bodies i.e. eggs, cysts and spores.
Highly Res_____ reproductive bodies when external to the host e.g. eggs
with protective shells.
Employment of specialised reproductive phases in life cycle. e.g. asexual
reproduction phases in larval forms -- Malaria plasmodium
Use of sec_______ hosts as vectors.
Eco-interactions between organisms
VI)
P.10
Competition
Competition for res______ may be int___specific or int___specific. In competition, since both
species suffer, avoidance mechanisms tend to evolve, leading to niche spec________.
It is important as a pop_____ regulating factor, it is also a very potent evo________ force.
Example 1 : Specialization / Avoidance through competition
Barnacles are animals (Arthropoda)
covered by a shell. They live fastened to
coastal rocks in the area which is
exposed at low tide, called the intertidal
zone.
Once attached to a rock barnacles are
fixed to the spot until they die. They feed
on zooplankton when they are covered
by the sea.
In Scotland, one species of barnacle,
Balanus balanoides, occurs in the low
part of the intertidal zone. Another
species, Chthamalus stellatus, which is of
a similar size to Balanus, occurs higher
up on the rocks.
Young Chthamalus often attach themselves in the lower shore, but no adults are found there if Balanus is
present in numbers. If there is no Balanus, Chthamalus can easily live in the lower shore. On the other hand,
even if there are no Chthamalus, Balanus cannot establish itself in the upper parts of the shore.
a. List the differences in environment between the upper shore and the lower shore.
b. What possible factors are limiting the upshore limit of Balanus ?
c. Why do you think Chthamalus is restricted to the upper shore?
d. It this is an example of competition, what do you think the two species are competing for ?
e. Design an experiment to determine whether the two species are competing for the resource you named in ‘d’.
f.
Suggest the signficance of the two species of Barnacles specializing on slightly different microhabitats.
Eco-interactions between organisms
Example 2:
P.11
The Avoidance of Competition and Adaptive radiation
Individuals involved in interspecific competition are likely to suffer through lower food intake, less
reproduction and a greater risk of disease. This is true even for the 'winner' of the competitive
interaction. The loser may face starvation, loss of shelter or nesting sites, and death from other causes.
It might, therefore, be expected that natural s_______ occurs in competing individuals leading to
adaptations to av___ competition. Such an adaptation is called character displacement, in which
similar species living together become more dif______ than usual, so they can divide the available
resources without competition.
Adaptive radiation by one or both species may then occur over a period of time with the result that
they come to occupy separate n____, thus min_______ the extent of competition. Thus competition
can be a very potent force of evolution.
Q. State 3 ways in which competition is important ecologically or in evolution of new species:
VII)
Concluding remarks
We have seen how different populations may interact in a variety of ways. We have also seen how
some forms of interaction may create sel____ pressures: the predator-prey relation is a classic
example. The prey species develops a defensive chemical or a modified behaviour and the predator
responds accordingly. We also saw that this may lead to a progressive spec_______ by the predator
leading to a dependence on a few or even one prey species.
Whether we are talking of predator-prey or host-parasite relationships or symbionts, there comes a
point when to understand the evolution of one we need to understand the story of the other. When
evolutionary interactions are interdependent like this we call it co-evolution.
Assignment : Look for a further example of co-evolution resulting from the
interaction between two organisms, collect pictures, write short description
and discuss points of biological interest in the relationship, be ready to present
your assignment in 2 weeks time.. (Don’t write more than one A4 pages!)
END
Eco-interactions between organisms
P.12
Suggested Answers to Study Item:
Crops without chemicals
a. 1. Eutrophication is the enrichment of water with plant nutrients, particularly with nitrates and
phosphates. The nitrates comes mainly from fertilizers & phosphate mainly from detergent & sewage.
Eutrophication results in excessive growth of algae, water weeds and anaerobic condition when
bacteria absorb oxygen when decomposing the dead algae.
2. Those that can live without oxygen if needs arises, but normally live in microhabitats that contain
oxygen.
3. Organisms which must be in partnership with another species in order to survive and reproduce; a
partnership from which both partners benefit.
b. When plants die, diffusion of organic and inorganic nitrogenous compounds from roots. Seed dispersal;
plant eaten by herbivore and egested.
c. i) It seems to prevents large concentration of oxygen from building up in the inner cortical cells.
ii) protect nitrogenase against attack by oxygen.
d. N-fixation is a very energy-demanding process, the constant need to supply glucose to bacteria may
reduce crop production.
In addition, it would also be essential to transfer the leghaemoglobin genes to the cereals so that the
Rhizobium in the cereal roots would be protected against oxygen.
Competition between two species of Barnacles
a.
Upper Shore
Lower Shores
Longer exposure to air, humidity lower
Action of drying effect of wind more pronounced
Less exposure to air
Temperature fluctuation greater
Salinity fluctuation larger
Conditions more stable
Less frequently covered by the sea
receive less splashes from sea water
Danger of
predations from sea-living organisms
Food brought in from sea water
b. Desiccation / Exposure to air / extremes of temperature, salinity fluctuation.
c. Expansion of niche into lower shore restricted by competition from Balanus.
d. Attachment to rock surface.
e. Find stones with both species of barnacles.
Place them in the lower tide level where both species can thrive,
leave half of the stones untouched.
For the other half, chip away the Balanus that are in contact with the Chtlamalus.
Observe some time later if better growth of Chtlamalus occurs where Balanus were removed.
f. This specialization allows the two species to co-exist in a habitat, avoiding competition, exploiting slightly
different niches.