Lecture 22. Ecological Niche

What is an ecological community?

Populations of different species living together in a particular area - have the potential to interact

Intraspecific interactions

Organisms interact with other members of the SAME species

Interspecific interactions

Organisms interact with members of OTHER species

Ecological niche

The full range of environmental conditions (biotic & abiotic) under which a species can exist

Competitive exclusion

Two species which compete for the same limited resource cannot coexist indefinitely - one will always outcompete the other

Examples of factors that can determine ecological niche

Time of day active, prey availability, presence of water, etc.

Niche characteristics of American Dipper (bird)

Fast-flowing mountain streams, streams have cascades & riffles, streams are unpolluted, etc.

Ecological niche is not…

A location or a habitat

Grinnell first used the term “niche” to describe…

An animal’s use of particular resources

Grinnell’s niche concept

Niche = adaptations of organism to its habitat

Hutchinson’s niche concept

Niche = n-dimensional hypervolume

A species’ niche is a…

Set of conditions and resources (ex. temperature & food availability or temperature, elevation, & latitude)

Fundamental niche

Full range of environmental conditions (biotic & abiotic) under which a species can exist

Realized niche

Range of environmental conditions that species actually occupies

Niche overlap between species causes…

Competition

Level of overlap in niches helps determine…

If & how species interact

What is one possible outcome of niche overlap & competition?

Competitive exclusion

What is the importance of competitive exclusion in ecological communities?

Competition helps structure ecological communities

Competitive exclusion in Chestnut-backed & Boreal Chickadees

One will crowd out the other

Resource partitioning

Phenotypic differences evolve that allow species to use different resources → reduces competition

Resource partitioning example (birds)

5 warbler species differed in nesting date & nesting height (height in tree)

Resource partitioning example (bullfrogs)

Adult bullfrogs are carnivores while juvenile bullfrogs (tadpoles) are mostly vegetarian

Character displacement

Form of resource partitioning with a particular geographic context - can occur when two species with high niche overlap live in same area

Character displacement results in…

A particular geographic pattern in the traits related to resource acquisition

Sympatric

Live in same area

Character displacement example (Darwin’s finches)

Character displacement in beak depth occurs between species on islands where they are sympatric