1. Interactions Among Species
Section 2.2

2. No two species occupy the same exact ecological niche.
the role or “job” that an organism has in its ecosystem
the organism’s way of life
includes:
habitat
resource consumption
interactions with other species
ecological “services” provided – how it contributes to function and sustainability of the ecosystem
No two species occupy the same exact ecological niche.

3. All of these factors together make up the big brown bat’s niche.
Example: Big brown bat, Eptesicus fuscus
Lifestyle: nocturnal
Habitat: roosts in hollow trees, and man-made structures; hibernates in caves
Range: North, Central, and South America
Diet: insects
Predators: cats, snakes, raccoons, owls
Ecological Service: regulating insect populations
All of these factors together make up the big brown bat’s niche.

4. Types of Species Interactions
predation
competition
interspecific
intraspecific
symbiosis:
mutualism
parasitism
commensalism
Red billed oxpecker eats ticks on impala’s back (mutualism)

5. Predation
occurs when one organism (the predator) feeds on another (the prey)
Classify the lynx and hare in this photo as either predator or prey
From the graph: What happens to the lynx population when the hare population increases?

6. Predator-Prey interactions influence the size of both populations.
Bottom-Up Population Regulation
fluctuation in a resource at the base of a food chain affects the animals at the higher trophic levels.
Top-Down Population Regulation
fluctuation in animals at higher trophic levels causes a change at lower trophic levels

7. Scenario
Type of regulation
DDT causes a decrease in hawk populations. Lizards, rabbits, and snake populations grow.
Abundant rainfall creates favourable growing conditions for grass. Populations of consumers grow.
Rabbit birth rates are higher than normal. More grass gets eaten, but hawks also have more to eat.

8. Competition
occurs when individuals compete with the same limited resource
food, shelter, water, mates
Two types:
interspecific – Two different species compete
intraspecific – Individuals of the same species compete

9. Observation: As population of female song sparrow grows, the number of eggs laid decreases.
Hypothesis: Competition reduces the reproductive output (by limiting energy available for reproduction).
Prediction: If birds are experimentally provided with food, no decrease in number of eggs laid will be observed.
EXPERIMENTALLY-SUPPORTED

10. Making connections: Is competition a biotic or abiotic factor?
Is competition density-dependent or independent?
What type (interspecific vs. intraspecific) of competition was described in the previous example?

11. similar niche similar habitat similar diet similar lifestyle
Competition can influence the niche an organism occupies.
Organisms have to share available resources.
Their realized niches are smaller than their potential niches.
Example: Brook stickleback & Nine-spined stickleback
similar habitat
similar diet
similar lifestyle
similar niche

12. How does competition affect the habitat of brook sticklebacks?
Scenario 1:
Only brook sticklebacks present:
The brook sticklebacks are found at all levels of the lake
Scenario 2:
Nine-spined sticklebacks also present:
The brook sticklebacks are only found at bottom of the lake
Competition for resources requires that the organisms share in order to co-exist in the same space.

13. Symbiosis
Symbiosis is a type of interaction where members of two species live together in close physical association.
can be further classified based on nature of interaction:
mutualism
parasitism
commensalism

14. Mutualism both organisms benefit from the relationship Examples:
Bees and flowers – Bees receive food (nectar), and flowers are pollinated.
Gut bacteria and humans – Bacteria break down food molecules so that humans can absorb nutrients.

15. Parasitism one organism benefits while the other is harmed Examples:
tapeworms in human intestines
fleas live on animals

16. Commensalism
one organism benefits, while the other is not affected in any way
Example:
Remora sharks use a special disk on their heads to attach to other animals, and “hitch rides”

17. Homework
Handout
Pg. 64 #2, 5, 6, 7