1. Communities
biodiversity, issues
keystone species
habitats, niches
Interactions:
competition, predation,
mutualism
co-evolution

2. Wasps and Pieris caterpillars form an unusual three-step food chain
Dining In
Wasps and Pieris caterpillars form an unusual three-step food chain
Wasp eggs layed inside caterpillar
Caterpillar eaten up by larvae

3. A second wasp can detect wasp larvae inside these caterpillars
and will deposit her own eggs inside of the first wasp’s larvae

4. Finally, yet another wasp, a chalcid, may lay its eggs inside the second wasp’s larvae
Only the chalcid wasp’s larvae emerge from the caterpillar carcass

5. Community = All the organisms in a particular area
Description includes:
Biodiversity
-- Vegetation
Response to disturbances
Trophic structure (feeding relationships)
Figure 36.1

6. A TERRESTRIAL FOOD CHAIN
TROPHIC LEVEL
Quaternary consumers
What’s for lunch?
Carnivore
Carnivore
Tertiary consumers
Carnivore
Carnivore
Secondary consumers
Carnivore
Carnivore
Primary consumers
Herbivore
Zooplankton
Producers
Plant
Phytoplankton
Figure 36.9A
A TERRESTRIAL FOOD CHAIN
AN AQUATIC FOOD CHAIN

7. Food webs often more real than food chains
Tertiary and secondary consumers
Wastes and dead organisms
Food webs often
more real than
food chains
Secondary and primary consumers
Primary consumers
“Follow the money” becomes Follow the food” to detect energy flow win community.
Producers
Detritivores
(Plants, algae, phytoplankton)
(Prokaryotes, fungi, certain animals)
Figure 36.10

8. Energy supply limits the length of food chains
170 billion tons of biomass per year
10% conversion
to biomass
at next level
Tertiary consumers
10 kcal
Secondary consumers
100 kcal
Primary consumers
1,000 kcal
Producers
10,000 kcal
1,000,000 kcal of sunlight
Figure 36.11

9. Consequence: a field of corn can support more vegetarians than meat-eaters
TROPHIC LEVEL
Secondary consumers
Human meat-eaters
Primary consumers
Human vegetarians
Cattle
Corn
Corn
Producers
Figure 36.12

10. Biodiversity is the variety of organisms that make up a community
Components:
Species variety: total number of different species in the community
relative abundance of different species
Genetic variation within each species

11. Biodiversity - current issues
Another mass extinction in progress?
Wildlife preserves - do they work?
Biodiversity hot spots: Should conservation efforts focus only on areas of high biodiversity?
4. Alien species

12. Communities Habitat is the environment in which an organism lives.
A population's niche is its role in the community
How it uses the biotic and abiotic resources of its habitat

13. Community interactions
There are four main types of relationships among species within communities
Competition
Parasitism, predation
Commensalism
Mutualism

14. Community interactions
Interspecific competition occurs between
two populations if they both require the same
limited resource
Resources include food, water, nesting sites
Plants compete for sunlight, water, soil nutrients, space

15. The competitive exclusion principle
Populations of two species cannot coexist in a community if their niches are nearly identical
High tide
Chthamalus
Barnacle expt shows two outcomes possible:
Remove blue barnacles, brown ones grow down and cover entire rock.
Ther4, blues outcompeting brown for low space on rock.
Remove brown ones, blue ones do NOT grow up. Ther4, resource (space on rock) has been divided and only brown are adapted to drier upper zones of rock.
Balanus
Ocean
Low tide
Figure 36.2

16. Competition between species with identical niches has two possible outcomes
One population will eventually eliminate the other
Natural selection may lead to resource partitioning (division)

17. Predation is an interaction where one species eats another
consumer = predator
food species = prey
Parasitism is a form of predation
Parasite, host
Not immediately lethal
Predation is severe form of natural selection. Leads to many diverse adaptations designed to escape predation and to make more successful predators.
Explains why the most successful parasite is not a fast killer.
Examples: mistletoe on oaks, dodder on phosyn plants, fungal hyphae on nematodes

18. This reciprocal adaptation = coevolution
As predators adapt to prey, natural selection also shapes the prey's defenses.
This reciprocal adaptation = coevolution
Example: Heliconius and the passionflower vine
Eggs
Sugar deposits
Figure 36.3A

19. Prey gain protection against predators through a variety of defense mechanisms
1. Mechanical defenses, such as the quills of a porcupine

20. 2. Chemical defenses
Animals are often brightly colored to warn predators
Example: the poison-arrow frog
Many interesting chemicals from amphibs. Antibiotic megainan, anithestic.
Figure 36.3B

21. 3. Camouflage
Example: gray tree frog
Figure 36.3C

22. 4. Batesian mimicry occurs when a harmless species mimics a harmful one
mimicry can involve behavior
hawkmoth larva puffs up its head to mimic the head of a snake
Figure 36.3D

23. What are effects of predation?
Eliminates weaker individuals
keystone predator maintains diversity by reducing numbers of the strongest competitors in a community
- Ex. sea star is a keystone predator
Figure 36.4A

24. Predation by killer whales on sea otters, allowing sea urchins to overgraze on kelp
Sea otters represent the keystone species
Figure 36.4B

25. Commensalism - one partner benefits and the other is unaffected
Examples
- Algae that grow on the shells of sea turtles
Barnacles that attach to whales
Birds that feed on insects flushed out of the grass by grazing cattle

26. - Nitrogen-fixing bacteria and legumes
Mutualism:
both partners benefit
Examples:
- Nitrogen-fixing bacteria and legumes
Acacia trees and the ants of the genus Pseudomyrmex
Figure 36.5B

27. Disturbance is a prominent feature of most communities
Disturbances include events such as storms, fires, floods, droughts, overgrazing, and human activities
damage biological communities
remove organisms
alter the availability of resources
Figure 36.6