Option C.1 Species & Communities

IB Biology

R. Price 2015

Allott 603

The distribution of species is affected by limiting factors

• A limiting factor is the factor that is most scarce in relation to an organism’s needs

• Plant distributions are affected by abiotic variables: temperature, water availability, light intensity, soil pH, soil salinity, and availability of mineral nutrients.

• Animal distributions are affected by temperature, water, breeding sites, food supply, and territory.

The distribution of species is affected by limiting factors

• Every plant species has a range of tolerance for each limited factor. Excluded from areas outside their “range.”

• Tropical plants are adapted to limit transpiration and photosynthesis is efficient in hot weather.

• Plants from the far North have anti-freeze like chemicals to protect their cells

Allott 604

Allott 605

Allott 605, 606

Allott 606

Allott 607

Allott 607, 608

Each species plays a unique role within a community because of the unique combination of its spatial habitat and interactions with other species

• Within an ecosystem, each species fulfills a unique role, called its ecological niche.

• Niche includes: habitat, how obtain food, interactions with other species.

• Abiotic variables: Must be within zone of tolerance

Competitive exclusion principle: two species cannot survive indefinitely in the same habitat if their niches are identical

• P. aurelia thrives by itself in ideal laboratory conditions

• P. caudatum thrives by itself in ideal laboratory conditions

• When cultured together, both species are reduced. P. caudatum reduced far more than P. aurelia

Allott 608

Competitive exclusion principle: two species cannot survive indefinitely in the same habitat if their niches are identical• The Yellow-rumped warbler &

Bay-breasted warbler occupy the same niche.

• These species typically forage in different parts of the same tree.

• Avoid competition with each other.

Allott 609

Allott 609

Allott 609

Allott 610

Interactions between species in a community can be classified according to their effect

• Competition: when two species require the same resource, and the amount needed by one reduces the amount available for the other.

• Herbivory: primary consumer feeding on producers.

• Predation: consumer feeding on another consumer.

• Parasitism: one organism feeds off of another, but does not necessarily kill it.

• Mutualism: two organisms live in close association, and both benefit

• Commensalism: one organism benefits, the other is neither helped nor harmed

Allott 611

Allott 611

Allott 612

Keystone species: Community structure can be strongly affected by keystone species

• A keystone species has a disproportionate effect on the structure of an ecological community.

• Robert Paine removed the sea star Pisaster from one area and compared the results where Pisasterwas allowed to stay.

• In the “removed” area – the other members of the food web immediately began to compete with each other.

• Succession of dominant species, some species wiped out, others emigrated.

• Within a year of Pisaster’s removal, species diversity had decreased from 15 to 8 species.

Sources

ContentAllott, Andrew, and David Mindorff. Biology: Course Companion. 2014

ed. Oxford: Oxford UP, 2014. Print. Oxford IB Diploma Programme.

Walpole, Brenda. Biology for the IB Diploma. 2nd ed. Cambridge: Cambridge UP, 2014. Print.

Images

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