1. Interactions in Ecosystems
Chapter 14

2. Competition occurs when two organisms fight for the same limited resource.
Intraspecific competition
Interspecific competition
What is the difference
between these?

3. Interspecific or intraspecific?
Two red squirrels race up a tree to find a hidden pile of nuts.
A hyena chases off a vulture to feast on an antelope carcass.
Shrubs and grasses on the forest floor compete for sunlight.
Brown bears hunting for fish on a river’s edge fight over space.

4. Fundamental niche : entire range of conditions an organism is potentially able to occupy. Realized niche the part of the fundamental niche that a species occupies.

5. Competition between two species of barnacles.
Is this the realized niche or fundamental niche?

6. Chthamalus realized niche
How can we determine the realized niche of each barnacle?
Observe where they grow when allowed to compete.
Balanus
and
Chthamalus
growth
rate
Balanus
realized
niche
Chthamalus realized niche
low
middle
high
Location in intertidal zone

7. Chthamalus fundamental niche
How can we determine the fundamental niche of each barnacle?
Removal experiments – remove each species and see
where the other grows
Balanus alone
Balanus
fundamental
niche
growth
rate
Chthamalus alone
Chthamalus fundamental niche
low
middle
high
Location in intertidal zone

8. What are the fundamental and realized niches for each species?
Streams with only
Planaria species A
Streams with only
Planaria species B
Streams with both
Planaria species
What are the fundamental
and realized niches for
each species?

9. interspecific competition
Competitive exclusion keeps two species from occupying the same niche.
Two species of Paramecia
predict the outcome of
interspecific competition
P. aurelia
P. caudatum
Gause (1934)

10. Types of Interactions Interaction Species A Species B Mutualism
Benefit (+)
Commensalism
No Effect (0)
Parasitism
Benefit (+)
Harm (-)
Predation
Competition
Amensalism
No Effect (0)

11. What is symbiosis?
How are predators of animals different from predators of plants?
What is the difference between ectoparasite and an endoparasite?

12. A black rhinoceros grazes on the African plains
A black rhinoceros grazes on the African plains. As it forages, the rhino disturbs multitudes of insects in the grass, crushing some and inadvertently eating others. Birds known as egrets forage on the ground near the rhino, eating insects flushed out by the hooves. Other birds known as oxpeckers
eat ticks from the
skin of the rhino.