Presentation for DP Biology Option C.1 Species and Communities

1. Option C.1 Species & Communities
IB Biology
R. Price 2015

2. Allott 603

3. 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.

4. 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

5. Allott 604

6. Allott 605

7. Allott 605, 606

8. Allott 606

9. Allott 607

10. Allott 607, 608

11. 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

12. 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

13. 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

14. Allott 609

15. Allott 609

16. Allott 610

17. 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

18. Allott 611

19. Allott 611

20. Allott 612

21. 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 Pisaster
was 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.

22. Sources
Content
Allott, 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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