1. Populations, Communities, and Species Interaction
Chapter 3

2. Outline:
Critical Factors and Tolerance Limits
Adaptation and Natural Selection
Speciation
Ecological Niche
Species Interaction
Population Growth
Community Properties and Structure
Succession

3. SPECIES INTERACTION
Predation - antagonistic
Any organism that feeds directly on another living organism is termed a predator.
Predation Influences:
All stages of predator and prey life cycles.
Specialized food-obtaining mechanisms.
Specific predator-prey adaptations.
Predation can exert selective pressures.
Coevolution

4. Competition - antagonistic
SPECIES INTERACTION
Competition - antagonistic
Intraspecific - Competition among members of the same species. They cope by:
Dispersal
Territoriality
Resource Partitioning
Interspecific - Competition between members of different species. Best suited will have advantage.

5. SPECIES INTERACTION
Symbiosis - Intimate living together of members of two or more species (can be non-antagonistic).
Commensalism - One member benefits while other is neither benefited nor harmed.
Cattle and Cattle Egrets
Mutualism - Both members benefit.
Lichens (Fungus and cyanobacterium)
Parasitism - One member benefits at the expense of other.
Humans and Tapeworms

6. Defensive Mechanisms
Batesian Mimicry - Harmless species evolve characteristics that mimic unpalatable or poisonous species.
Mullerian Mimicry - Two unpalatable or dangerous species evolve to look alike.
Avoidance - camouflage

7. Keystone Species
Keystone Species - A species or group of species whose impact on its community or ecosystem is much larger and more influential than would be expected from mere abundance.
eg, Top Predators or?
Often, many species are intricately interconnected so that it is difficult to tell which is the essential component. Perhaps ‘keystone set’.
Multiple Key Players

8. Keystone species - species that play essential community roles & not just from abundance (examples: mycorrhizae, giant kelp)

9. Community-level Interactions
Keystone species???
(Botkin & Keller 2003)

10. POPULATION DYNAMICS
Population Growth
Exponential Growth – unrestricted growth. Growth as a percentage of the whole.
dN/dt=rN
Biotic Potential - Potential of a population to grow in the absence of expansion limitations.

11. Boom and Bust Cycles
Exponential growth is graphed as a J curve.
Carrying Capacity - Number of individuals that can be indefinitely supported in a given area.
Overshoot - When a population surpasses the carrying capacity of its environment.
Dieback
Oscillations

12. Population Oscillations

13. Population Oscillations

14. Abiotic & Biotic Controls
Changes in pop:
* No predators & lots of vegetation so moose increase,
* Vegetation heavily eaten & decreases so moose crash,
* Wolves arrive and moose decrease,
* Wolves decrease w less genetic variation and canine virus introduced by dogs so moose increase….
* Moose decrease due to lack of food, poor reproduction, severe winter and tick infestation so crash…. Moose and wolves stabilize
Abiotic & Biotic Controls
Miller 2002
Isle Royal on Lake Superior

15. Growth to a Stable Population
Logistic Growth - Growth slows as the population approaches carrying capacity.

16. Limiting Factors
Environmental Resistance
Density-Independent Factors - Effect on mortality rate is independent of population density.
Abiotic conditions.
Density-Dependent Factors - Mortality rates increase as the density of the population increases.
Disease, Stress, Predation

17. COMMUNITY PROPERTIES
Primary Productivity - Rate of biomass production. Used as an indication of the rate of solar energy conversion to chemical energy.
Net Primary Productivity - Energy (amount of biomass) left after respiration.

18. Abundance and Diversity
Abundance -Total number of individuals of a species in an area.
Diversity - Number of different species, or ecological niches, or genetic variation in an area.
Abundance of a particular species often inversely related to community diversity.
As general rule, diversity decreases and abundance within species increases when moving from the equator to the poles.

19. Community Structure
Random - individuals live wherever resources are available
Ordered - often the result of biological competition
Clustered - individuals of a species cluster together for protection, mutual assistance, reproduction, or to gain access to a particular environmental resource

20. Edges and Boundaries
Ecotones - Boundaries between adjacent communities.
Edge Effects - Important aspect of community structure is the boundary between one habitat and others.
May extend for 100s of meters
May produce differently-shaped habitat patches.

21. Edges and Boundaries
Ecotones- the boundaries between adjacent habitats
Often rich in species diversity
Example: boundary between a forest and a meadow

22. Preserve Shape

23. COMMUNITIES IN TRANSITION
Ecological Succession
Primary Succession - A community begins to develop on a site previously unoccupied by living organisms.
Pioneer Species
Secondary Succession - An existing community is disrupted and a new one subsequently develops at the site.
Ecological Development

24. Primary Succession – development of a community in an area previously unoccupied
(vs disturbed community, then secondary succession)

25. Mature forest
Lichens (fungi+algae)

26. Ecological Succession
Climax Community - Community that develops and seemingly resists further change under a given climate.
Clements – relay of plant species
Individualistic Community - Species become established according to their ability to colonize and reproduce in a given area.
Gleason

27. Lodgepole Pine
Once thought of as ‘climax’
Now considered ‘fire adapted’

28. Introduced Species
If introduced species prey upon, or compete more successfully than, native species, the nature of the community may be altered.
Human history littered with examples of introducing exotic species to solve problems caused by previous introductions.
Mongoose and Rats in Caribbean

29. Introduced Species and Community Change

30. Key Points
Communities consist of an assemblage of populations (a population being a group of individuals of the same species that interbreed).
Individuals with adaptations that improve their reproductive fitness are selected for.
Natural selection works through inter- and intra-specific interactions (mutations & selective pressure).
Populations oscillate before reaching equilibrium at the carrying capacity of the system.
Communities often have repeatable structures and properties that exhibit parallel chronosequences following disturbances (primary and secondary succession).