1. Ecology Biological Communities
NO species exists independently of other species

2. Evolution in Communities
Some interactions among species are the result of a long evolutionary history
Natural selection causes back-and-forth evolutionary adjustments between members of a community
Co-evolution is a result of this history of interaction

3. Interaction By Predation
The act of one organism killing another for food

4. Types of predators Carnivores – kill the prey during attack
Herbivores – remove parts of many prey, rarely lethal.
Parasites – consume parts of one or few prey, rarely lethal.
Parasitoids – kill one prey during prolonged attack.

5. Parasitism
Parasites derive nourishment from their hosts, whether they live inside their hosts endoparasites, or feed from the external surfaces of their hosts- ectoparasites
Tapeworm
Tick

6. Predation
Striking adaptations often characterize predators and their prey
Predators may evolve cryptic morphology (camouflage)

7. Predation
Prey may evolve to blend in too! Camouflage

8. Prey may evolve warning morphology
Aposematism
Prey may evolve warning morphology
Aposematic colors = warning

9. Mimicry Batesian mimicry
Organisms may evolve to look like other organisms
Batesian mimicry
harmless mimic evolves to look like harmful model
looks like something that is dangerous or tastes bad
Viceroy
Monarch
Milk Snake
Coral Snake

10. Interaction By Symbiosis
Where two organisms live together in close association.
Can be mutually beneficial or benefit one organism and leave the other unharmed

11. Mutualism
A symbiotic relationship in which both species benefit

12. Commensalism
One member benefits while other is neither benefited nor harmed
mites hitching a ride on a beetle

13. How Competition Shapes Communities
When two species use the same resource, they participate in a biological interaction called competition

14. How Competition Shapes Communities
Intraspecific – between individuals of the SAME species
Interspecific – between individuals of DIFFERENT species

15. Ecological Niche Niche
Often described in terms of how the organism affects energy flow within the ecosystem, it is a pattern of living
To understand how competition influences the makeup of communities, you must look at the functional role of the species:
Niche
Habitat & microhabitat (Space utilization)
Food “spectrum,” essential nutrients
Reproductive requirements
Nutrition, nest/den sites
Seasonality: When are resources required, used.
NOT TO BE CONFUSED WITH:
Habitat - location where a particular organism lives

16. What is the niche? set of conditions multi-dimensional with as many
within which an organism
can maintain a viable
population
multi-dimensional
with as many
dimensions as their
are limiting conditions
ecological
niche
light intensity
okay
temperature
salinity

17. Size of the Niche Fundamental niche Realized niche
The entire range of opportunity
The organism’s potential (the role it could play) in the absence of biotic enemies
depends on physical (abiotic) conditions.
Realized niche
The actual range of the organism (the role it does play in the community) – in the presence of biotic enemies
depends on biotic as well as abiotic conditions

18. Competition and Limitation of Resources
Barnacles compete for space on rocky intertidal shores
What is the realized niche of each barnacle?
What is the fundamental niche of each?

19. Competition and Limitation of Resources
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

20. Chthamalus realized niche
Competition and Limitation of Resources
How can we determine the realized niche of each barnacle?
Where do they grow when allowed to compete?
Balanus
Chthamalus
growth
rate
Balanus
realized
niche
Chthamalus realized niche
low
middle
high
Location in intertidal zone

21. Competitive Exclusion Principle
Two species cannot coexist if they occupy the same niche
(the barnacles did not coexist where their fundamental niches overlapped)
Competition between two species with identical niches results either in competitive exclusion or the evolution of resource partitioning
Stable coexistence requires niche differentiation,
members of each species compete more strongly among themselves than with members of the other species
(intraspecific > interspecific)

22. Law of Competitive Exclusion
No two species will occupy the same niche and compete for exactly the same resources for an extended period of time.
One will either migrate, become extinct, or partition the resource and utilize a sub-set of the same resource.
Given resource can only be partitioned a finite number of times.

23. Resource Partitioning

24. interspecific competition
A classic interspecific competition experiment
two species of Paramecium
predict the outcome of
interspecific competition
P. aurelia
P. caudata
Competitive exclusion
When forced to compete, one species eliminates other

25. Keystone Species
Keystone Species - the affect on its community or ecosystem is much larger and more influential than would be expected from mere abundance.
Large predators
Critical food organisms (bamboo and pandas)
Often, many species are intricately interconnected so that it is difficult to tell which is the essential component.
Picky predators can promote coexistence among competing prey species.
Competitive exclusion is prevented when the dominant competitor is the preferred prey.

26. How Keystone Species Affect Community Structure
Starfish
Pisaster
preditor
How do starfish promote coexistence?
competitors
Barnacles Mussels
Balanus Mytilus
Starfish are picky – they prefer to eat mussels (dominant competitor), allowing barnacles (weaker competitor) to coexist.

27. Removal experiment - mussels are the dominant competitor
- competitive exclusion of barnacles
starfish
removed
mussels % of
inter-
tidal
zone
barnacles
time

28. GENERALIST VS SPECIALIST
Animals are generally selective and efficient in their food choices
Some animals, such as gulls, are feeding “generalists”
Other animals, such as koalas, are feeding “specialists”

29. GENERALIST VS SPECIALIST
narrow
diet
specialist consumes only one prey type
broad diet
generalist consumes many prey types

30. GENERALIST VS SPECIALIST
Generalists - Broad niche
When generalists and specialists collide, generalists usually win
Specialists - Narrow niche

31. Invasive Species Invasive species competitively exclude native species
Imported fire ant
Kudzu
Purple loosestrife
Zebra mussel
Squirrels

32. Future Evolutionary Flexibility = Biodiversity