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

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!!

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.

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.

Tapeworm and Humans

Tapeworms and Humans

Cuckoo and Warbler

Ticks

Tick

Parasitism

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