Interactions within Communities

Populations of different species interact in a community

Some organisms rely on other organisms within the community for survival

Ecological NichesAn 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 NichesA 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 competitionInteraction between individuals of different

species for essential common resource(s) that are in limited supplyserves to restrict population growthCan 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

Resource partitioningAvoidance

of/reduction in competition for similar resources by individuals of different species occupying different non-overlapping ecological niches

Lake Malawi Cichlids850 species from

one ancestor!!

Predationinterspecific 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 - Plantsplants use both morphological defences

thorns, hooks, spines, needleschemical defences

the defensive systems in plants act as selective agents which initiate the evolution of counter-adaptations in herbivore populationsthese changes brought about by co-evolution

between plants and insets can affect competition

Defence Mechanisms - Animalssometimes employ passive defence

mechanismse.g. hiding

others employ active defence mechanismse.g. fleeingmore costly to prey in terms of energy uses

other effective behavioural defences existe.g. alarm callse.g. camouflage (cryptic colouration)e.g. visual warnings – in terms of chemical

defences

SymbiosisSome organisms

have obligatory mutualismneither organism

could grow or reproduce without each other

Mutualism

Mutualism – A symbiotic relationship in which both

species benefit.

Mutualism

Examples:Cowbirds and Large

AnimalsTermites and

TrichonymphaBees and Flowers

Cowbirds and Large AnimalsThe 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 TrichonymphaYou 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.

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.

Parasitismone organism benefits at the expense of

another organism which is usually harmed.

Tapeworm and Humans

Tapeworms and Humans

Cuckoo and Warbler

Ticks

Tick

Parasitism

Disruption of Community Equilibriuminterspecific interactions help maintain

necessary equilibrium within complex and dynamic natural systems that sustain communities

A variety of disturbances affect this equilibriumnatural disastersintroduction of nonindigenous specieshuman influences