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Niche The niche of a species consists of: Its role in the ecosystem (herbivore, carnivore, producer etc) Its tolerance limits (e.g. soil pH, humidity) Its requirements for shelter, nesting sites etc etc, all varying through time © 2008 Paul Billiet ODWS Competition • In all environments, organisms with similar needs may compete with each other for resources, including food, space, water, air, and shelter. Feeding relationships • • • • • Predators & prey Herbivory Parasite & host Mutualism Competition Large blue butterfly (Maculinea arion) © 2008 Paul Billiet ODWS Symbiotic Relationships symbiosis: living together with another organism in close benefits at the expense of the host Types of (symbiosis): commensalism: : one organism is benefited and the other is unharmed (+,0) ex. barnacles on whales, orchids on tropical trees mutualism: both organisms benefit from the association. ex. nitrogen-fixing bacteria on legume nodules parasitism: the parasite benefits at the expense of the host. ex. athlete's foot fungus on humans, tapeworm and heartworm in dogs THE COMPETITIVE EXCLUSION PRINCIPLE G.F. Gause (1934) If two species, with the same niche, coexist in the same ecosystem, then one will be excluded from the community due to intense competition © 2008 Paul Billiet ODWS The niche as a two-dimensional shape Species A Niche represented by a 2-dimensional area © 2008 Paul Billiet ODWS Separate niches Species B Species A No overlap of niches. So coexistence is possible © 2008 Paul Billiet ODWS Overlapping niches Species B Species C Interspecific competition occurs where the niches overlap © 2008 Paul Billiet ODWS Specialisation avoids competition Species C Species B Evolution by natural selection towards separate niches Species B’ © 2008 Paul Billiet ODWS Species C’ Specialisation into two separate niches This niche is not big enough for the both of us! Species A Species D Very heavy competition leads to competitive exclusion One species must go © 2008 Paul Billiet ODWS Total exclusion Species A has a bigger niche it is more generalist Species E has a smaller niche it is more specialist Specialists, however, do tend to avoid competition Here it is total swamped by Species A © 2008 Paul Billiet ODWS Example: Squirrels in Britain The Red Squirrel (Sciurus vulgaris) is native to Britain Its population has declined due to: • Competitive exclusion • Disease • Disappearance of hazel coppices and mature conifer forests in lowland Britain © 2008 Paul Billiet ODWS Isle of Wight Tourist Guide The Alien The Grey Squirrel (Sciurus carolinensis) is an alien species Introduced to Britain in about 30 sites between 1876 and 1929 It has easily adapted to parks and gardens replacing the red squirrel © 2008 Paul Billiet ODWS Bananas in the Falklands Today’s distribution Red squirrel © 2008 Paul Billiet ODWS Grey squirrel