Download Interactions within communities

Interactions within Communities
 Populations of different species interact in a community
 Some organisms rely on other organisms within the
community for survival
Ecological Niches
 An organism’s ecological characteristics, including use of
and interaction with abiotic and biotic resources
within its environment
 Think of a habitat being one’s “address” and its ecological
niche as its “occupation”
 e.g. a lion’s niche includes what it eats, what eats it, the way it
reproduces, the temperature range it tolerates, its habitat,
behavioural responses, and all other factors that can describe its
pattern of living
Ecological Niches
 A Fundamental niche is the
biological characteristics of the
organism and the set of
resources individuals in the
population are theoretically
capable of using under ideal
conditions
 Realized niche – the
biological characteristics of the
organism and the resources
individuals in a population
actually use under the prevailing
environmental conditions
Interspecific competition
 Interaction between individuals of different species for
essential common resource(s) that are in limited supply
 serves to restrict population growth
 Can occur in two ways:
 Interference competition –involves aggression
between individuals of different species who fight
over the same resource(s)
 Exploitative competition – involves
consumption of shared resources by individuals of
different species, where consumption by one limits
the resource availability to the other species
Interspecific competition

 Gause’s Principle
o competitive exclusion
o No two species with similar
requirements could coexist in
exactly the same niche
indefinitely
o Population of weaker
competitor can decline
o One species could change its
behaviour to survive using
different resources
o One population could migrate
to another habitat
Resource partitioning
 Avoidance of/reduction in
competition for similar
resources by individuals of
different species occupying
different non-overlapping
ecological niches
Lake Malawi Cichlids
 850 species from one
ancestor!!
Mimicry
 Batesian mimicry
 Palatable / harmless species mimics unpalatable/harmful organism
 Mullerian mimicry
 Several animal species resemble one another and are all poisonous or
dangerous
Predation
 interspecific interaction by which population density of one
species (predator) increases while population density of other
species (prey) declines
 time lags exist between responses to predator – prey
interactions and their population sizes
 sinusoidal curves exist in some predator-prey relationships
Defence Mechanisms - Plants
 plants use both morphological defences
 thorns, hooks, spines, needles
 chemical defences
 the defensive systems in plants act as selective agents
which initiate the evolution of counter-adaptations in
herbivore populations
 these changes brought about by co-evolution between plants
and insets can affect competition
Defence Mechanisms - Animals
 sometimes employ passive defence mechanisms
 e.g. hiding
 others employ active defence mechanisms
 e.g. fleeing
 more costly to prey in terms of energy uses
 other effective behavioural defences exist
 e.g. alarm calls
 e.g. camouflage (cryptic colouration)
 e.g. visual warnings – in terms of chemical defences
Symbiosis
 Some organisms have
obligatory mutualism
 neither organism could grow
or reproduce without each
other
Mutualism
Mutualism – A symbiotic relationship in
which both species benefit.
Mutualism
Examples:
 Cowbirds and Large Animals
 Termites and Trichonympha
 Bees and Flowers
Cowbirds and Large Animals
The cowbird benefits by eating the ticks
and mites off the large animal. The large
animal benefits from have the parasites
removed from them. The birds can also
warn them of danger.
Termites and Trichonympha
You probably think termites eat wood; they
do…in a way.
Termites can’t digest cellulose, which is the
main component of wood.
Therefore, they get help from a protozoan
called trichonympha.
This protozoan lives in the gut of the termite.
It breaks down the cellulose for the termite.
The trichonympha gets a free meal and
shelter; the termite is able to eat and receive
nutrients from the wood.
Termite and Trichonympha
Trichonympha
Bees and Pollen
Bees receive nectar from
the flowers in order to
make honey. As the bees
collect nectar, they collect
pollen on their body. As
they fly to another flower,
they pollinate it by dusting
the pollen on the flowers
stamen.
Commensalism
Commensalism – A symbiotic relationship in which one
organism benefits and the other is not affected.
Examples:
Clown fish and sea anemones
Shark and remora
Clown Fish and Sea Anemones
The clown fish is immune to the stings of the
sea anemones tentacles. The clown fish makes
its home in the tentacles for protection. The
clown fish gets shelter, but the sea anemone
gets nothing.
Shark and Remora
The remora hangs
around the shark picking
up any scraps it may
leave. The remora gets
food while the shark
gets nothing.
Parasitism
Parasitism – A symbiotic relationship in which
one organism benefits but the other is
harmed.
Parasitism
 one organism benefits at the expense of another
organism which is usually harmed
 Parasites can be
 Microparasites – microscopic in size with rapid reproduction rate
(blood protozoans)
 Macroparasites – larger organisms (tapeworms)
 Endoparasites – live inside the body of their host
 Ectoparasites – live and feed on the outside surface of their host (lice)
 Social parasites manipulate the social behaviour of another species so
that they can complete their life cycle
Parasitism
Examples:
 Tapeworm and Humans
 Cuckoo bird and warbler
 Ticks
Tapeworm and Humans
Tapeworms and Humans
Tapeworms and Humans
Tapeworms and Humans
Cuckoo birds and warblers
Cuckoo and Warbler
Ticks
Tick
Even Athletes foot is a parasite
Parasitism
Parasitism
Symbiosis
Disruption of Community Equilibrium
 interspecific interactions help maintain necessary
equilibrium within complex and dynamic natural
systems that sustain communities
 A variety of disturbances affect this equilibrium
 natural disasters
 introduction of nonindigenous species
 human influences
 HOMEWORK P688 #1-7