This document discusses various types of biological interactions between organisms including competition, mutualism, commensalism, amensalism, parasitism, and predation. Competition occurs when organisms attempt to use the same limited resources, and can be intraspecific or interspecific. Mutualism benefits both species involved. Commensalism benefits one species without affecting the other. Parasitism benefits one species at the expense of the other. Predation involves a predator consuming another organism, the prey. Examples of each type of interaction are provided.

1. Department of Bioresources
University of Kashmir
By Shariqa Aisha
Biological Interactions
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2.  To understand the concept of ecological interactions.
 To know about the different types of competition .
 To learn about the various types of interactions.
 To acquire the knowledge about parasitism and predation.

3.  An ecological community consists of all the populations of all the different species
that live together in a particular area.
 The populations can be very much affected by the interactions between the
organisms in the ecosystem i.e. Interspecific interactions.
 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
(+/-), mutualism, (+/+), commensalism (+/0), and parasitism (+/-).

4.  Competition is a relationship in which different organisms or populations in the
ecosystem attempt to use the same limited resources at the same time.
 The limiting resource may be water, prey, light, water etc., which is responsible for
the organism’s growth and survival in the ecosystem.
 Competition can occur both within (intra specific) and between (inter specific)
species.
 Competition among the individuals can also be characterized as resource
competition or interference competition.
Resource competition: It is characterized by the organism’s completion directly for the
limiting nutrient in the ecosystem, there by obtaining as much each individual can.
• An example is the competition of fly maggots in a mouse carcass, where few
individuals obtain enough nutrients for their reproduction and survival.

5. Interference Competition: in this case, the individuals harm
each other directly by a physical force. In this case either
the individuals interact with foraging, survival, and
reproduction of others or directly prevent their physical
organization in a part of their habitat.
• Interference competition generally results in the
exclusion of one of the two competitors.
The competitive exclusion principle,sometimes referred to
as Gause's law, stated that two species competing for the
same limited resource cannot coexist at constant
population values. When one species has even the slightest
advantage over another, the one with the advantage will
dominate in the long term.
Competitive Exclusion Principle
1: A smaller (yellow) species of bird
forages across the whole tree.
2: A larger (red) species competes for
resources.
3: Red dominates in the middle for the
more abundant resources. Yellow
adapts to a new niche restricted to the
top and bottom of the tree, avoiding
competition.

6.  Interspecific competition is competition for
resources (such as food, space, water, light, etc.)
between members of different species, and in
general one species will out-compete another
one.
 This can be demonstrated by growing two
different species of the protozoan Paramecium in
flasks in a lab.
 They both grow well in lab flasks when grown
separately, but when grown together P. aurelia
out-competes P. caudatum for food, so the
population of P. caudatum falls due to
interspecific competition.
Case first shows no competition as they are
grown separately, while as in case second P.
aurelia out-competes P. caudatum due to
interspecific competition.

7.  Intraspecific competition is an interaction in population ecology, whereby members of
the same species compete for limited resources. This leads to a reduction in fitness for
both individuals, but the most fit individual survives and is able to reproduce.
 Two basic types have been identified for intraspecific competition:
i) Interference (adapted) intraspecific competition: This occurs in species that establish
hierarchies through aggressive behavior where one or more individuals within the
population hold a dominant status over the others.
ii) Exploitation (contest) intraspecific competition: This occurs between individuals of the
same population exploiting the same resources and reducing or depleting its availability
to others.

8.  Mutualism is an interspecific interaction between two
organisms in the ecosystem with benefit to both the
associating members in the interaction.
 During this interaction, populations of each interacting
species grow survive and reproduce at a higher rate in the
presence of the other interacting species.
 Mutualism is an interaction between two or more species,
where species derive a mutual benefit, for example an
increased carrying capacity.
 One or both species involved in the interaction may be
obligate, meaning they cannot survive in the short or long
term without the other species.
 Pollination is a good example to explain mutualism, where
the plant gets benefit from the dispersal of pollen the
pollinator obtaining a meal of nectar from the flower.

9. The spider crab and the algae. Spider crabs live in
shallow areas of the ocean floor, and greenish-brown
algae lives on the crabs' backs, making the crabs blend in
with their environment, and unnoticeable to predators.
The algae gets a good place to live, and the crab gets
camouflage.
The bacteria and the human. A certain kind of bacteria
lives in the intestines of humans and many other
animals. The human cannot digest all of the food that it
eats. The bacteria eat the food that the human cannot
digest and partially digest it, allowing the human to finish
the job. The bacteria benefit by getting food, and the
human benefits by being able to digest the food it eats.
Mutualism: The algae gets a good place to live
and the spider crab gets camouflage to live.
Bacteria benefits by getting food and
human benefits by being able to digest
food it eats

10.  Commensalism is a type of symbiotic relationship in which one species benefits, while the
other species is neither harmed nor helped.
 The species that gains the benefit is called the commensal. The other species is termed the
host species.
 A commensal species benefits from another species by obtaining shelter, food, or support
from the host species, which (for the most part) neither benefits nor is harmed.
 Commensalism ranges from brief interactions between species to life-long symbiosis.
Example:
Cattle egrets eat the insects stirred up by cattle
when they are grazing. The cattle are unaffected,
while the birds gain food.

11.  Amensalism is an interaction where an organism inflicts harm to another organism
without any costs or benefits received by itself.
 There are basically two types of amensalism: competition and antibiosis.
i) In competition, a larger or more powerful organism excludes another organism from
its source of shelter or food.
ii) In antibiosis, one organism secretes a chemical that kills the other organism, while
the one that secreted the chemical is unharmed.
Example:
Algal blooms can lead to the death of many
species of fishes and other animals, however
the algae do not benefit from the deaths of the
individuals.
Amensalism

12.  Parasitism benefits one species at the expense of
another.
 Parasitism may be regarded as a special form of
symbiosis in which the parasite usually is much smaller
than the prey and remains closely associated with it.
 Parasitism is harmful to the prey organism and
beneficial to the parasite.
 In many cases, the parasite kills its host, and thus the
ecological effects of parasitism can be similar to those
of predation.
 It is in the parasite’s best interest not to be too
detrimental to the host. If the host dies, then the
parasite dies.

13.  Parasites that feed on the exterior surface
of an organism are external parasites, or
ectoparasites.
 Many instances of external parasitism are
known in both plants and animals.
 Parasitoids are insects that lay eggs on
living hosts. This behavior is common
among wasps, whose larvae feed on the
body of the unfortunate host, often killing
it.
Examples:
Hair and body lice (head lice )

14.  Parasites that live within the body of their hosts, termed endoparasites, occur in
many different phyla of animals and protists.
 Internal parasitism is generally marked by much more extreme specialization than
external parasitism, as shown by the many protist and invertebrate parasites that
infect humans.
Example:
Acanthamoebiasis
This tiny ameba can affect the human eye, the skin, and the brain. It exists all over
the world in water and soil. Individuals can become infected if they clean contact
lenses with tap water.

16. Amoebiasis
This is caused by the parasite Entamoeba histolytica. It affects the intestines. It is more
likely in tropical regions and in areas with high population density and poor sanitation. It is
transmitted through the fecal-oral route.

17.  The term predation is defined as the
consumption of one living organism (prey)
by another ( the predator) excluding
scavengers and decomposers.
 It is act of capturing, killing and eating.
 The organism which does the act of
predation is called a predator. The second
organism which is killed and eaten is called
prey.
 Predation is generally linked to carnivorous
animals and predator is generally larger in
size compared to the prey.

18. Examples:
 Spiders spinning webs to trap and kill insects

19.  Rattlesnakes using venom in their bite to kill small animals

20. NAME DESCRIPTION EFFECT
Competition Organisms of two species use the same
limited resource and have a negative impact
on each other.
- /-
Mutualism A long-term, close association between two
species in which both partners benefit. + /+
Commensalism A long-term, close association between two
species in which one benefits and the other
is unaffected.
+ / 0
Amensalism An organism inflicts harm to another
organism without any costs or benefits
received by itself.
- / 0
Parasitism A long-term, close association between two
species in which one benefits and the other
is harmed.
+ / -
Predation A member of one species, predator, eats all
or part of the body of a member of another
species, prey.
+ / -

21. Multiple choice Questions
Q.1 When both partners are affected negatively the nature of interaction is:
a) Competition
b) commensalism
a) predation
b) amensalism
Q.2 The ascaris, entamoeba and plasmodium are considers as an examples of:
a) Endoparasite
b) Ectoparasite
c) Digestion parasite
d) synthetic parasite
Q.3 The organism who kills, attacks and feeds others are called:
a) Prey
b) parasite
c) assimilators
d) predators

22. Q.4 The competitive exclusion principle was first described by Gause for species of:
a) Mice
b) Birds
c) Protozoa
d) Grass
Q.5 Predation and Parasitism are which type of interactions:
a) + /+
b) + / -
c) - / -
d) - / +
Q.6 The interaction shown by rattle snack and rat is:
a) Predation
b) Parasitism
c) Mutualism
d) Cooperation

23. Q.7 A relationship between two organisms in which one organism benefits and the other
is unharmed:
a) Competition
b) Parasitism
c) Commensalism
d) Mutualism
Q.8 Amensalism is an interaction between two species where:
a) One species is harmed and the other is benefited.
b) One species is harmed and the other is unaffected.
c) One species is benefitted and the other is unaffected.
d) Both species are harmed.
Q.9 Cattle egrets and Cattle shows which type of interaction:
a) Amensalism
b) Protocooperation
c) Parasitism
d) Commensalism

24.  http://www.sciencedirect.com
 https://www.britannica.com
 http://www.ncbi.nllm.nih.gov
 http://www.reseacrhgate.net
 https://www.khanacademy.org
 Life sciences_ Pranav Kumar
 Ecology_ Theories and applications by Peter Stiling