Unit-2-Interspecific and intraspecific interactions.ppt

Population interactions or biological interaction are the effects that a pair of organisms in a community have on one another.
These effects may be short-term, like pollination and predation, or long-term; both often strongly influence the evolution of the species involved.Intraspecific interactions are those that take place among organisms of the same species while interspecific interactions are those which happen among individuals of different species.
A long-term interaction is called a symbiosis.
Symbioses range from mutualism, beneficial to both partners, to competition, harmful to both partners. 
Interactions can be indirect, through intermediaries such as shared resources or common enemies.

1. ELECTIVE COURSE - II ELECTIVE COURSE - II
(B) – (B) – ECOLOGY AND ECOLOGY AND
EVOLUTION (UNIT-II)EVOLUTION (UNIT-II)
Prepared by
Dr. A. Sudha,
Assistant Professor,
Department of Biotechnology,
Dr. Umayal Ramanathan College
for Women,
Karaikudi.

2. Unit - II
Population interaction:
Intra specific interactions –
Aggregation, Social organization,
divisions of labour and Social behavior,
Territorialism, migration.
Inter specific interaction – Neutralism,
commensalism, synergism, mutualism,
symbiosis, commensalism,
Antagonism, parasitism, competition
and predation.

3. POPULATION INTERACTIONS
Population interactions or biological
interaction are the effects that a pair
of organisms in a community have on one
another.
These effects may be short-term,
like pollination and predation, or long-term;
both often strongly influence the evolution of
the species involved.
An organisms interaction with its environment
are fundamental to the survival of that organism
and the functioning of the ecosystem as a whole.
Populations do not exist alone in nature.
The way organisms interact is important for the
survival of a species.
There are two types of interaction: intraspecific
interactions and interspecific interactions.

4. Intraspecific interactions are those that take place
among organisms of the same species while
interspecific interactions are those which happen
among individuals of different species.
A long-term interaction is called a symbiosis.
Symbioses range from mutualism, beneficial to both
partners, to competition, harmful to both partners. 
Interactions can be indirect, through intermediaries
such as shared resources or common enemies.

6. An ecological community consists of all the
populations of all the different species that live
together in a particular area.
Interactions between different species in a
community are called interspecific interactions—
inter- means "between."
Different types of interspecific interactions have
different effects on the two participants, which may
be positive (+), negative (-), or neutral (0).
The main types of interspecific interactions
include competition (-/-), predation (+/-), mutualis
m, (+/+), commensalism (+/0), and parasitism (+/-).
These are distinguished by the degree of benefit or
harm they cause to each partner.
Interspecific interactions

7. Interspecies interactions can be broken into three
main categories: competition, predation, and
symbiosis.

9. 1. Competition
In interspecific competition, members of two
different species use the same limited resource and
therefore compete for it.
Competition negatively affects both participants
(-/- interaction), as either species would have
higher survival and reproduction if the other was
absent.
Species compete when they have
overlapping niches, that is, overlapping ecological
roles and requirements for survival and
reproduction.
Competition can be minimized if two species with
overlapping niches evolve by natural selection to
utilize less similar resources, resulting
in resource partitioning.

10. 2. Predation
It is a kind of short term interaction.
In predation, one organism, the predator, kills
and eats another organism, its prey.
This interaction is beneficial for the
predator, but harmful for the prey (+/-
interaction).
Ex: Leopard killing deer.
Predators are adapted and often highly
specialized for hunting, with acute senses such
as vision, hearing, or smell.
 Many predatory animals,
both vertebrate and invertebrate, have
sharp claws or jaws to grip, kill, and cut up their
prey.
 Predation has been a major driver of
evolution.

11. Predation has a powerful selective effect on prey,
causing them to develop antipredator
adaptations such as warning coloration, alarm
calls and other signals, camouflage and defensive
spines and chemicals.
Predators and prey regulate each other's population
dynamics.
Also, many species in predator-prey relationships
have evolved adaptations—beneficial features arising
by natural selection—related to their interaction.
On the prey end, these include mechanical,
chemical, and behavioral defenses.
Mimicry is another adaptation evolved in some
species to shock the predators.

12. Predation is a method to transfer the energy to higher
trophic levels.
In fact biological control methods of pests are based on the
predator- prey relationship.
Predation may involve two animal species, but it can also
involve an animal or insect consuming part of a plant, a
special case of predation known as herbivory.
Plants have also evolved various defensive mechanisms
to avoid predation.
They are as follows:
i. Thorns in Acacia and Cactus.
ii. Toxic chemicals are produced by some plants that harm
the plants. Calotropis, a weed produces a highly poisonous
cardiac glycosides and are avoided by the grazing animals.

13. 3. Symbiosis
It is a long-term biological interaction.
Symbiosis is a general term for interspecific
interactions in which two species live together in a
long-term, intimate association.
The organisms, each termed a symbiont, may be of
the same or of different species.
Symbiosis is a broader concept and can include close,
lasting relationships with a variety of positive or
negative effects on the participants.
The six possible types of symbiosis are mutualism,
commensalism, parasitism, neutralism,
amensalism, and competition.
Symbiosis can be obligatory, which means that one
or more of the symbionts entirely depend on each
other for survival, or facultative (optional), when
they can generally live independently.

14. When one organism lives on the surface of another,
such as head lice on humans, it is
called ectosymbiosis; when one partner lives inside
the tissues of another, such
as Symbiodinium within coral, it is
termed endosymbiosis.

15. i) Mutualism:
Mutualism describes the
ecological interaction between two or
more species where each species has a net benefit.
Similar interactions within a species are known
as co-operation. 
Mutualistic relationships may be either obligate for
both species, obligate for one but facultative for the
other, or facultative for both.
An example of mutualism is the relationship between
the  clownfish that dwell among the tentacles of sea
anemones. The territorial fish protects the anemone
from anemone-eating fish, and in turn
the stinging tentacles of the anemone protect the
clownfish from its predators. 

16. Mutualism is a common type of ecological interaction.
In a mutualism, two species have a long-term
interaction that is beneficial to both of them (+/+
interaction). 
Other examples include most vascular plants
engaged in mutualistic interactions
with mycorrhizae, some types of fungi form
mutualistic associations with plant roots,  flowering
plants being pollinated by animals, vascular plants
being dispersed by animals etc..
Mutualism plays a key part in ecology. For example,
mutualistic interactions are vital for
terrestrial ecosystem function as more than 48%
of land plants rely on mycorrhizal relationships
with fungi to provide them with inorganic compounds
and trace elements. 

17. Mutualism is thought to have driven the evolution of
much of the biological diversity such as flower forms
(important for pollination mutualisms) and  co-
evolution between groups of species.
However, mutualism has historically received less
attention than other interactions such
as predation and parasitism.
Humans are involved in mutualisms with other
species: their gut flora is essential for
efficient digestion.

18. Evolution of Mutualism
Mutualisms are not static, and can be lost by
evolution. 
Sachs and Simms (2006) suggest that this can
occur via 4 main pathways:
◦One mutualist shifts to parasitism, and no
longer benefits its partner, such as headlice.
◦One partner abandons the mutualism and lives
autonomously.
◦One partner may go extinct.
◦A partner may be switched to another species.

19. POLLINATION PROCESS
One of the most
commonly observed
mutualism is the
pollination of flowering
plants by an insect or
humming bird.
The pollinator benefits
from the interaction by
receiving nectar.
The plant gets its pollen
transferred from one
plant to another.

20. Mutualism-other examples
Mutualism Species 1 Species 2
Ant & acacia Ant – gains secure home, food
supply
Acacia – gains protection
from predation
Coral & AlgaeCoral – gains carbohydrate from
photosynthesis
Algae – protection and
mineral nutrients
Mycorrhizae &
plants
Mycorrhiza – gains
photosynthetic product
Plant – improved mineral and
water absorption
Ruminant herbivore
& bacteria
Ruminant - gets its food digestedBacteria – gains protection,
warmth, moisture & food
Lichen Fungus – photosynthetic productsAlgae – gains water, minerals
and structural support
Rhizobium and
legumes
Rhizobium – gains photosynthetic
product
Plant – gains nitrate for
protein synthesis

21. Proto-cooperation:
When both the species can survive without each other
it is called facultative mutualism or proto-
cooperation.
Best example of this is the association between
hermit crab and sea anemone. Sea anemone
provides camouflage to hermit crab and in turn is
transported to new feeding places.
It is less extreme type of
interaction in which two
species interact favorably with
each other, though both of
them are able to survive
separately.

22. ii)Commensalism
In a commensalism, two species have a long-term
interaction that is beneficial to one and has no positive
or negative effect on the other (+/0 interaction).
It occurs when one organism takes benefits by
interacting with another organism by which the
host organism is not affected.
For instance, many of the bacteria that inhabit our
bodies seem to have a commensal relationship with us.
They benefit by getting shelter and nutrients and
have no obvious helpful or harmful effect on us.
It's worth noting that many apparent commensalisms
actually turn out to be slightly mutualistic or
slightly parasitic when we look at them more closely.

23. It is derived from the English word commensal,
used of human social interaction.  
A good example is a remora living with a manatee.
Remoras feed on the manatee's faeces.
The manatee is not affected by this interaction, as the
remora does not deplete the manatee's resources.
Remora-Sucker fish
Manatees are large, fully aquatic,
mostly herbivorous marine
mammals sometimes known as
sea cows.

24. Examples for commensalism are – sucker fish
is found attached to sharks with their suckers.
Sucker fish gets protection from predators
whereas it has no effect on sharks.
Epiphytes like mosses, orchids, ferns, money
plants grow on the trunk of other trees. They do
not harm the tree but just grow to get better
sunlight .

25. iii)Parasitism
In a parasitism, two species have a close, lasting
interaction that is beneficial to one, the parasite,
and harmful to the other, the  host (+/-
interaction).
Some parasites cause familiar human diseases.
For instance, if there is a tapeworm living in the
intestine, you are the host and the tapeworm is the
parasite.
In the parasitic association, the species which
provides nourishment and support is called
the host and the one which gets support and
nourishment is called the parasite.
Parasitism takes many forms,
from endoparasites that live within the host's
body to ectoparasites.
 Parasitism is an extremely successful mode of life;
about 40% of all animal species are parasites.

26. Examples of endoparasites are tapeworm, roundworm,
threadworm, Plasmodium, etc. and ectoparasites are ticks,
mites, lice, leech, etc.
Cuscuta is a plant parasite and has lost its ability to
photosynthesize since it derives nourishment from the host
plant.
Parasites are host specific in such a way that both the
host and the parasite have coevolved. The parasites have
evolved special adaptations to live successfully in a host.
They are as follows:
Loss of sense organs
Presence of adhesive organs or suckers
High rate of reproduction
Loss of digestive system.

27. Complicated life history with a primary and one
or more intermediate hosts. Eg: The malarial
parasite (Plasmodium) requires a mosquito which is
a vector to spread to other hosts.
Brood parasitism in bird is an interesting example
of parasitism. This is seen in the cuckoo or koel bird.
The cuckoo lays its eggs in the nest of the crow.
These eggs resemble the eggs of crow. The crow
incubates the eggs and takes care of them.

28. Diagram of the six possible types of symbiotic
relationship, from mutual benefit to mutual harm.

29. iv)Amensalism
Amensalism is an asymmetric interaction where one
species is harmed or killed by the other, and one is
unaffected by the other.
Amensalism describes the adverse effect that one
organism has on another organism.
This is a unidirectional process based on the release
of a specific compound by one organism that has a
negative effect on another.
A classic example of amensalism is the microbial
production of antibiotics that can inhibit or kill
other, susceptible microorganisms.
A clear case of amensalism is where sheep or cattle
trample grass. Whilst the presence of the grass causes
negligible detrimental effects to the animal's hoof but
the grass suffers from being crushed.
Amensalisms can be quite complex interactions.

30. There are two types of amensalism, competition
and antagonism (or antibiosis).
Competition is where a larger or stronger
organism deprives a smaller or weaker one from a
resource.
An example of competition is a sapling growing
under the shadow of a mature tree. The mature
tree can rob the sapling of necessary sunlight and,
if the mature tree is very large, it can take up
rainwater and deplete soil nutrients. Throughout
the process, the mature tree is unaffected by the
sapling. Indeed, if the sapling dies, the mature tree
gains nutrients from the decaying sapling.
Competition is often for a resource such
as food, water, or territory in limited supply, or for
access to females for reproduction.

31. Competition among members of the same species is
known as intraspecific competition, while
competition between individuals of different species
is known as interspecific competition.
According to the competitive exclusion principle,
species less suited to compete for resources should
either adapt or die out.
According to evolutionary theory, this competition
within and between species for resources plays a
critical role in natural selection.
Antagonism occurs when one organism is damaged
or killed by another through a chemical secretion. 
An example of antagonism is black walnut,
secreting juglone, a substance which destroys many
herbaceous plants within its root zone.

32. v) Neutralism
Neutralism (a term introduced by Eugene
Odum) describes the relationship between two
species that interact but do not affect each other.
When the presence of one species appears to have
no effect on the second species (i.e., no
interaction), it is a state of neutralism.
Examples of true neutralism are virtually
impossible to prove; the term is in practice used to
describe situations where interactions are
negligible or insignificant.

33. Cost, Benefits & Consequences
INTERACTION Effect on Population Density
Predation
Parasitism
Commensalism
Mutualism
Competition
Predator increases, prey decreases
Parasite increases, host decreases
Commensal increases, host density is
unaffected
Both species in mutualism increase
Both species in competition decrease

34. Intra-specific interactions

35. Territoriality is the behavior by which an animal lays claim
to and defends an area against others of its species, and
occasionally members of other species as well.
The territory defended could be hundreds of square miles in
size, or only slightly larger than the animal itself.
It may be occupied by a single animal, a pair, family, or entire
herd or swarm of animals.
Some animals hold and defend a territory year-round,
and use the territory as a source of food and shelter.
Other animals establish a territory only at certain times of the
year, when it is needed for attracting a mate, breeding,
and/or raising a family.

Territorialism

36. Types Of Territories
Some animals will establish a territory solely for
the purpose of having a place to rest. Such a
territory is known as a roost, and may be
established in a different area every night.
Roosts are often occupied and defended by large
groups of animals, for the protection offered in
numbers.
Individual personal spaces within the roost may
be fought over as well.
Roosting spots nearer the interior of a group of
animals are often the safest.

37. Several species of birds and a few mammals are
known to establish specialized territories during
the breeding season, which are used only to attract
mates through breeding displays. This type of
territory is known as a lek, and the associated
behavior is called lekking.
Leks are generally of little use for feeding or for
bringing up young, and the animals will abandon
its lek once it attracts a mate or mates, or if it
becomes too weak to defend it.

38. Among birds, territories have been classified as six
types.
Type A: An 'all-purpose territory' in which all
activities occur, e.g. courtship, mating, nesting and
foraging
Type B: A mating and nesting territory.
Type C: A nesting territory which includes the nest
plus a small area around it.
Type D: A pairing and mating territory-lekking type.
Type E: Roosting territory.
Type F: Winter territory which typically includes
foraging areas and roost sites.

39. Defending A Territory
Some animals will defend their territory by fighting
with those who try to invade it.
Fighting, however, is not often the best option, since
it uses up a large amount of energy, and can result in
injury or even death.
Most animals rely on various threats, either through
vocalizations, smells, or visual displays.
 The songs of birds, the drumming of woodpeckers,
and the loud calls of monkeys are all warnings that
carry for long distances, advertising to potential
intruders that someone else’s territory is being
approached.

40. Many animals rely on smells to mark their
territories, spraying urine, leaving droppings
or rubbing scent glands around the
territories’ borders.
Approaching animals will be warned off the
territory without ever encountering the territory’s
defender.
When two individuals of a territorial species meet,
they will generally threaten each other with visual
displays.
These displays often will often exaggerate an
animal’s size by the fluffing up of feathers or fur, or
will show off the animals weapons. 

41. Actual fighting usually only happens in
overcrowded conditions, when resources are
scarce.
Serious injury can result, and old or sick animals
may die, leading to a more balanced population
size.
Under most natural conditions, territoriality is
an effective way of maintaining a healthy
population.

42. Advantages of Territoriality:
I. Associated with Reproduction:
1. It helps in securing a nesting site.
2. Aids in the formation of pairs.
3. Reduces the possibility of disturbances from the
competitors.
4. Permits females to select the males.
II. Associated with Habitat and Food:
1. Permits increased inbreeding within a population as a
means of better adaptation to the local habitat.
2. Secures adequate food for the pair and young ones.
3. Makes the animals familiar with the location of food and
water.

43. Divides resources among the dominant and subordinate
individuals with consequent reduction in fighting and
stress.
III. Associated with Predation and Parasitism:
1. Provides knowledge of location of shelter.
2. Dispersion, thus resulting in less possibility of being
detected by the predators.
3. Provides sufficient space to the members of a species,
thereby decreasing the chances of transmission of
diseases and parasites.
IV. To avoid overcrowding:
Prevents overcrowding and over exposition of resources
through natural selection.

44. An aggregation is any form of gathering
of organisms and the process of coming together.
 In some forms, groups of unrelated species might
form, in which interaction between members of the
aggregation might be minimal.
for example herds of
grazing zebra and antelopes might combine both
the better to observe the approach
of predators, and to improve the odds of escape
in the event of attack by predators.
Sometimes there might be some interaction, such
as mixed flocks of birds that observe each
other's foraging behavior in searching for food.
Aggregation

45. A general theory explaining why individuals
should prefer to aggregate was first proposed by
the Briton W.D. Hamilton, one of the most
important evolutionary biologists of the 20th
century.
Hamilton hypothesized that animals might come
together to form a so-called “selfish herd,” where
an individual’s chances of being eaten are
substantially reduced, especially if that individual
remains in the interior of the group.
Eg: school of fish is formed, it cannot be
eaten by predators.

46. A school of fish

47. Living in groups also protects group members
through a dilution effect.
In the simplest example, when a group-living
individual encounters a predator that will eat just
one prey item, his likelihood of being eaten is
reduced from p, the probability when alone,
to p/N, the probability when the individual is a
member of a group of size N.
For example, if a tadpole joins a group with just one
other individual, it reduces its chance of being eaten
by one-half.
Furthermore, if that tadpole joins with 99 others, its
chance of being eaten drops by 99 percent.

48. Alarm calls and other complex signaling behaviour
within aggregations can also reduce the likelihood
of predation.
Calls may coordinate a group’s escape from danger,
confuse a predator, and prompt individuals to seek
protected sites or shelter.
Alarm calls may also convey information about the
type of predator and lead to the appropriate
evasive behaviour.
Alarm calls might even provide information
regarding an individual predator’s identity and
habits.

49. Structured aggregations tend to be longer-term
and of a specific life-cycle function and context.
 Typically, they will be of a single species. Often
they will be of a single age and possibly of a single
sex.
Eg: mature males of elephants, seals, lions and
other animals would begin to compete with the
dominant males of other animals.
Another example is larvae of certain insects such
as Lepidoptera and Hemiptera form a flock and
feed together and may migrate in "processions"
until they are mature after which some kinds get
dispersed.
Most species of migrating birds and mammals
flock on a large scale, partly for protection and
partly for greater reliability of navigation. 

50. The primary functions of aggregation appear to be
feeding and defense.
The important range of functions are security against
predators, success in food location, wide range of mate
choice, with concomitant increase
of outbreeding opportunities, location with other
members of the same species (sometimes adherence to
separate communities can almost amount
to parapatric residence when say, different communities
of rats or chimpanzees have violent mutual antipathy).
There also are various forms of educational function,
such as in some species where the young must learn the
correct mate recognition skills, and in highly intelligent
species such as crows and elephants, must learn the
necessary social skills and the necessary traditional
foraging techniques in their region.

51. Aggregation also takes place, since the animals are mutually
attracted to each other for some resources.
Examples may include aggregations of sea lions or shorebirds for
breeding purposes or a place to take shelter from cold, aridity, or
otherwise rainy weather , as in aggregations of
opilionids-“harvestmen”.
They survive because a big clump of them, won’t dry out and die
as easily as lone individuals.
These spiders will often stick many of their legs straight up from
the cluster to capture condensation from the night and dawn air,
helping to save them from fatal desiccation in the hot part of
the day.

52. Migration, in ecology, is the large-scale movement
of members of a species to a different environment.
Migration is a natural behavior and component of
the life cycle of many species of mobile organisms,
not limited to animals, though animal migration is
the best known type.
Migration is often cyclical, frequently occurring on
a seasonal basis, and in some cases on a daily basis.
Species migrate to take advantage of more favorable
conditions with respect to food availability, safety
from predation, mating opportunity, or other
environmental factors.
Migration

53. Migration is two way mass movement of the entire population.
It involves a periodic departure and return of the individuals of
a population and occurs only in mobile organisms during un-
favourable periods.
It is shown by many birds, fishes and certain mammals.
Through this type of movement the chances of utilization of
resources in the habitats is very high.
However, during migration of population, mortality of numerous
individuals may occur due to various ecological hazards, such as
temperature fluctuation, scarcity of food, predation etc.
Migration has certain benefits for populations as it enables
wider dispersion of populations. It also avoids competition for
food, shelter, etc.

54. Migratory organisms use environmental cues
like photoperiod and weather conditions as well as internal cues
like hormone levels to determine when it is time to begin a
migration.
Migratory species use senses such
as magnetoreception or olfaction to orient themselves or navigate
their route, respectively.
For eg: The pigeon can return to its home using its ability to
sense the Earth's magnetic field and other cues to orient itself.
The factors that determine migration methods are variable due
to the inconsistency of major seasonal changes and
events.
When an organism migrates from one location to another, its
energy use and rate of migration are directly related to each
other and to the safety of the organism.

55. If an ecological barrier presents itself along a migrant’s
route, the migrant can either choose to use its energy to cross
the barrier directly or use it to move around the barrier.
If an organism is migrating to a place where there is high
competition for food or habitat, its rate of migration should
be higher.
This indirectly helps determine an organism’s fitness by
increasing the likelihood of its survival and reproductive
success.
Elk migrate vertically – up the mountains in spring as snow
recedes and down the mountains in fall as winter advances. 
Millions of zebra, wildebeest and antelope in East
Africa migrate each year in what is known as The Great
Migration or the Annual Wildebeest Migration.

56. Types of migration include:
Animal migration, the physical movement by animals
from one area to another.
◦Bird migration, the regular seasonal journey
undertaken by many species of birds.
Reverse migration, a phenomenon in bird
migration.
◦Fish migration, the regular journey of fish.
◦Insect migration, the seasonal movement of insects
Lepidoptera migration, the movement of butterflies
and moths.
Diel vertical migration , a daily migration
undertaken by some ocean organisms.

57. Effects of migration
Migratory species can transport diseases long-
distance from their original habitat.
A species migrating to a new community can affect
the outcome of local competitive interactions.
If the migratory species is abundant in the new
community, it can become a main prey for a
resident predator.
 It can increase the predatory species’ population
size.

58. Ecological Significance of Migration
Migration, has considerable ecological significance.
It enables fast-moving animals to exploit fluctuating
resources and to settle in areas where life would not
be acceptable for animals incapable of rapid travel.
On the other hand, peaks of food production would
be unexploited without the periodic presence of
migratory populations.
The sequence of migratory movement is
closely integrated in the annual cycle of
ecosystems characterized by productivity
fluctuations.

59. Migrant birds avoid equatorial forests where
productivity is constant throughout the year, and food
surpluses do not occur.
They do gather together, on the other hand, in
savannas where productivity varies with the seasons.
In the Arctic, vegetal and animal production is very
high during the summer; ducks and waders nest in
great numbers, exploiting these resources.
As winter comes, food becomes scarce, and water birds
migrate to the tropics, where the rainy season has
caused food production to increase to optimal levels. 

60. Division of labor refers to separation of activities and the
specialized allocation to different individuals.
The division of labor creates specialized behavioral groups
within an animal society which are sometimes called castes.
A colony has caste differences: queens and reproductive
males take the roles of the sole reproducers, while soldiers
and workers work together to create a living situation
favorable for the brood.
Batra, observed the cooperative behavior of the bees, males
and females alike, as they took responsibility for at least one
duty (i.e., burrowing, cell construction, oviposition) within
the colony.
The cooperativeness was essential as the activity of one
labor division greatly influenced the activity of another.
Division of labor

61. Division of labour (DOL)/ Functional specialization within
organisms is not universal but it is a derived feature.
It is common in most multi-cellular, colonial and social
organisms.
DOL evolved at every level of individuality from some
organelles of single-celled eukaryotes, through different cell
types, tissues and organs within multi-cellular organisms,
to polymorphic zooids and castes in colonial and social
animals.
 DOL occurs in at least 10 colonial and social animal phyla.
Without DOL, the ecology of organisms must remain
simple or their physiology must constantly adjust to
any changes in their environments.

62. The expression of DOL is different across various
types of organisms.
Two basic types can be recognized- reproductive
and ‘other’ types of DOL.
Reproductive DOL occurs when some members of
group do not reproduce.
‘Other’ DOL is defined as non-reproductive
functional differences between members (for
example, between feeding and defence).
Two basic mechanisms have been previously
proposed that jointly explain the origin of DOL
within organisms, colonies and societies.
In the first mechanism, functional variants arise
over evolutionary time.
In the second mechanism, DOL arises as a
solution to a functional optimization problem.

63. An organism with extensive DOL could have feeding,
defensive, reproductive and structural specialists,
whereas an organism without extensive DOL may only
have defensive specialists.
Animal division of labor is the division of labor amongst
animals. This can be demonstrated in a number of areas
such as:
◦Animal defensive behavior
◦Animal foraging behavior
◦Animal parental behavior
◦Nest building
◦Eg; In various species of social insects such as ants,
wasps, termites, and bees, DOL is predominant.

64. Eg:1-The degree of social organization in a Hymenoptera
colony is most evident in the division of labour.
In honeybee colonies, the division of labour is achieved in an
especially interesting manner.
 Tasks are assigned according to age.
The first day after the bee’s emergence as an adult, female
workers carry out wastes, clean the cells, and line them with a
disinfectant secretion preparatory to deposition of the egg
by the queen. 
On about the fourth day this young bee advances to brood
nursing, where she provides older larvae with honey
and pollen.
On the sixth day she also provides young, newly hatched
larvae with specific larval food from her pharyngeal glands.

65. At about 16 days the bee becomes active in secreting wax and
using it to build the comb.
Soon afterward, she makes her first orientation flight
outside the hive.
On about the 20th day she becomes a hunter.
She remains at this job until her death.
This activity sequence parallels certain physiological
changes in the bee. 
Eg:2- In the division of labour among some ant,  highly
specialized types of polymorphism have been developed.
The very close relationship between insects that are social
parasites of the Hymenoptera and their hosts is made
possible by the host’s division of labour and by a special
secretion produced by the parasite.

66. https://www.easybiologyclass.com/
biological-interactions-positive-negative-
interactions-ecosystem-ppt/
https://www.britannica.com/topic/animal-
social-behaviour/Aggregation-and-
individual-protection
https://www.britannica.com/topic/animal-
social-behaviour/The-range-of-social-
behaviour-in-animals#ref1045264