Presentation on

Interspecific Interactions

COURSE INSTRUCTOR: SUBMITTED BY:

Prof. P.S. Singh Sandeep Kumar Sathua
Dept. of Entomology & Agricultural Zoology I.D. No- Z-13062
IAS, BHU M.Sc. (Ag) 1st Year

CONTENTS
 Interspecific Interaction & Their Types
 Symbiosis
 Neutralism
 Competition & Types of Competition
 Commensalism With Examples
 Mutualism With Examples
 Mutualistic Symbiosis
 Predators
 Parasites
 Seasonal & geographical variation in Interspecific interaction
 Concepts of positive interspecific interactions
INTERSPECIFIC INTERACTIONS
 An interspecific interaction is a type of community interaction in which two
different species living together interact.
 Both species may experience positive, neutral, or negative benefits
Types of Interspecific interactions
There are mostly four types of interactions :
1- Predation: harmful to one and beneficial to another
2- Competition: harmful to both
3- Commensalism: beneficial to one and neutral to the other
4- Mutualism: beneficial to both
Types of Interspecific Interactions

SYMBIOSIS

 ‘Sym’ means together & ‘Bio’ means life

 Any relationship that involves two (or more) species living together and
interacting among themselves.

 This is a general term which includes predation, parasitism, commensalism,

mutualism, etc., but often is used to mean mutualism.

NEUTRALISM

§ Neutralism is the most common type of

interspecific interaction in which neither
population affects the other. Any interactions that
do occur are indirect or incidental.

§ Example: The tarantulas living in a desert and

the cacti living in a desert

COMPETITION

§ Competition occurs when organisms have an adverse effect on each other as

a result of requiring the same resource. The resources are space, nutrients,
light and water are limited in nature.

§ Competition occurs between two or more organisms. When these organisms

belong to the same species it is referred to as intraspecific competition.
When it occurs between individuals of different species it is interspecific
competition.
Two dung beetles fighting for a Ants of different species fighting
dung ball together

TYPES OF COMPETITION

§ Exploitation competition – It occurs when individuals use the same limiting

resource or resources, thus depleting the amount available to others.

§ Interference competition – It occurs when individuals interfere with the

foraging, survival, or reproduction of others, or directly prevent their
physical establishment in a portion of a habitat.

Ants Fighting for a Single Food Source Beetles battle for Survival &
(Exploitation ) Reproduction(Interference)

COMMENSALISM

§ Commensalism is an interspecific interaction where one species benefits and

the other is unaffected.

§ Commensalisms are ubiquitous in nature: birds nesting in trees are

commensal.

§ Commensal organisms frequently live in the nests, or on the bodies of the

other species.
 Examples of Commensalism

§ Ant colonies harbor rove beetles as commensals.

These beetles mimic the ants behavior, and pass
as ants. They eat detritus and dead ants.

§ Anemone fish live within the tentacles of

anemones. They have specialized mucus
membranes that render them immune to the
anemone’s stings. They gain protection by living
in this way.

AMENSALISM

§ Amensalism is when one species suffers and the other interacting species
experiences no effect.

§ Allelopathy involves the production and release of chemical substances by

one species that inhibit the growth of another. These secondary substances
are chemicals produced by plants that seen to have no direct use in
metabolism.

§ Black Walnut (Juglans nigra) trees excrete an antibiotic called juglone.

Juglone is known to inhibit the growth of trees, shrubs, grasses, and herbs
found growing near black walnut trees.

MUTUALISM

§ Mutualism is an interspecific interaction between two species that benefits

both members.

§ Populations of each species grow, survive and/or reproduce at a higher rate

in the presence of the other species.

§ Mutualisms are widespread in nature, and occur among many different

types of organisms

Examples of Mutualism

 The yucca moth both pollinates and feeds on the

yucca plant
  Acacia ants live in the thorns of, defend, and are fed
by the acacia tree in which they live.

 Most rooting plants have mutualistic associations

with fungal mychorrhizae. Mychorrhizae increase
the capability of plant roots to absorb nutrients. In
return, the host provides support and a supply of carbohydrates.

MUTUALISTIC SYMBIOSIS

Mutualistic Symbiosis is a type of mutualism in which individuals interact

physically, or even live within the body of the other mutualist. Frequently,
the relationship is essential for the survival of at least one member.

Example:

Lichens are a fungal-algal symbiosis

The mass of fungal hyphae provides a protected habitat for the algae, and
takes up water and nutrients for the algae. In return, the algae (and
cyanobacteria) provide carbohydrates as a source of energy for the fungus.

PREDATORS

 Predators are the organisms those tend to be larger than their prey, and
consume many prey during their lifetimes for growth & development.

 A predator is a species which consumes members of another species.

 Examples - Preying mantid, Dragon fly, Ground Beetles, Tiger Beetle, Giant
water bug etc.

Lady bird Beetle Dragon Fly Praying Mantis

PREDATOR-PREY POPULATION DYNAMICS

§ Predation may be a density-dependent mortality factor to the host

population-and prey may represent a limiting resource to predators.

§ The degree of prey mortality is a function of the density of the predator

population.

§ The density of the prey population, in turn, affects the birth and death rates
of the predator population.

§ i.e, when prey become particularly common, predators increase in numbers

until prey die back due to increased predation, this, in turn, inhibits the
growth of prey.

§ Typically, there is a time lag effect.

PARASITE

 Parasitism is a symbiotic association between two organisms in which one

organism lives & feeds externally or internally on the host during its entire
feeding stage of life. The attacking organism is called Parasite.

 Usually a parasite is considered to be smaller than the host and therefore

capable of parasitizing only one host at a time.

 Example- Many disease causing microorganisms (Bacteria, virus, worms

etc.)

SEASONAL AND GEOGRAPHIC VARIATION IN INTERSPECIFIC INTERACTIONS

 Interactions vary in their probability of occurrence along environmental

gradients (e.g. latitudinal or altitudinal) and under different ecological
conditions or between habitats; and they vary between seasons.

 In general, the tropics contain more species than an equivalent area at

higher latitudes, although exceptions are numerous when specific taxa are
reviewed.

 Not only are species unevenly distributed, but their interactions also vary
spatially and temporally.
  For Example: The structure of ant communities and of interactions between
ants and plants has been studied in different habitats, and it is clear that
neither the spatial nor the temporal dimension can be ignored, because
along with habitats the interspecific interaction also differ.

Ant of different communities

CONCEPTS OF POSITIVE INTERSPECIFIC INTERACTIONS

Recent attention to the cooperative relationships among species shows that

they are important forces in shaping community structure.

Positive interspecific interactions are defined as ‘Cooperative relationships

between different species that result in better growth, reproduction and/or
survival for at least one species involved in the interaction without negatively
affecting the other species’.
Positive interactions can be trophic and nontrophic, can act directly or
indirectly (mediated by a third species) and can be symmetric (species have
equal effects) or asymmetric (species have unequal effects).

Theory and experiments show that positive interactions are more likely to
occur under stressful physical or biological contexts.

Positive interactions should promote species coexistence and thus increase

species diversity.

Positive species interactions are not static but vary in their outcome
depending on the context under which they occur.

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