Week 7

Week 7

• Tuesday: Complete G1 Guided notes worksheets

• Wednesday – Data Collection outdoors!• Friday – COMPUTER LAB IN MONTICELLO –

EXCEL AND DATA ANALYSIS

COMPLETING G1

• COMPETITION• NICHE CONCEPT• COMPETITIVE EXCLUSION• NICHE PARTITIONING

What is ‘competition’ in Ecology?

Competition occurs when individuals use a shared resource in short supply: There may not be enough of the resource for any given individual to survive, or to reproduce, as well as when more resource is present. Competition does not necessarily involve competitors ever meeting (if the competitors are mobile organisms, such as many animals), or being adjacent to each other (if sessile organisms, such as plants or fungi).

As a result of competition:

• Birth rates are lower, death rates higher, or both. • In ecological terms, population growth rates

decrease and population size is lower at equilibrium

• In evolutionary terms, an individual's fitness is lower.

• Competition is a density dependent effect on population dynamics

Competition can be intraspecific or interspecific

Interspecific CompetitionCompetition

between different species which

depend on the same resource:• Food• Water

• Nesting Sites• Breeding Sites

Intra-specific competition• Example: Adaptive Radiation

in Darwin’s Finches• Example: Competition for

mates

LET’S REVIEW OUR INTER-SPECIFIC RELATIONSHIPS

• PBS marine interactions• Marine Mutualism

The Niche Concept: Definition

• ‘Nicher’ – to Nest:• A term describing

the way of life of a species:

The specialised habitat of an organism:• space and territory• Nutrition and feeding

habits• Interactions with other

organisms• Its reproductive habits• Its role in the community

The Niche concept: A Working Analogy

In 1927, Charles Sutherland Elton, the British Ecologist, stated: ‘When an ecologist states ‘There goes a badger’, he should include in his thoughts a definite idea of the animal’s role in the community, just as if he had said ‘There goes the vicar’

Niche Concept: The Boundary conditions

Two species that use exactly the same resources cannot

occupy the same nicheOnly one species or

population can occupy the same niche for an

extended period

Fundamental and Realised Niches

Fundamental NicheA species’ fundamental niche is the full range of environmental and social conditions under which it

could potentially survive and reproduce

Realised Niche

The realised niche is the specific set of conditions in which it survives in a given habitat or ecosystem, given the other species or limitations present.These are the conditions to which the species is best adapted.

The Competitive Exclusion Principle

Aka ‘Gause’s Law’‘No two species can occupy the same

niche for a prolonged time’

The Competitive Exclusion Principle• If two species share a

niche, there must be inter-specific competition for resources

• The best adapted species will survive

• The loser will struggle to survive and reproduce, and will eventually become extinct OR migrate (if its niche is broad enough)

Examples are abundant• Invasive species• Red versus Grey

Squirrel in Western Europe

• Gause’s Paramecium

Competitive Exclusion: Squirrels

Competitive Exclusion: Squirrel Distribution

The Classic Example of Competitive Exclusion: Paramecium

Georgy Gause cultured 2 species of the protist Paramecium:• P. Aurelia• P. Caudatum• Grown together under ideal

conditions, both populations reach a higher maximum

• Grown together, one species rapidly becomes extinct…

Does Competitive Exclusion work in the real world?....

The competitive Exclusion principle is actually rarely observed in natural ecosystems:• ‘spatial heterogenity’ (niche partitioning)• Niche sharing associated with availability of

multiple resources• ‘The paradox of the plankton’: Why do so

many plankton species exist in a small, limited, homogenous habitat?

Niche Partitioning

1. Spatial: Two different species use the same resource by occupying different areas within the range of the resource2. Temporal: Two species eliminate direct competition by using the same resource at different times 3. Morphological: Two different species evolve different morphologies in order to use a resource in different ways