1. Scales of Ecological Organization

2. Distribution and Abundance Relationships between Populations
Population Dynamics
Distribution and Abundance
Relationships between Populations

3. Population – group of individuals of the same species
living in the same area, potentially interacting
Community – group of populations of different species
living in the same area, potentially interacting
What are some ecological interactions?

4. Populations
A population is a group of individuals of the same species living in the same area.
Species features are important to their location

5. Populations
Distribution is the area that one or more members of the same species are found
Three patterns found: uniform, clumped, and random.
Species have a dispersion pattern which indicates where the species are found.
Random
Uniform
Clumped

6. Population Growth
All populations undergo three distinct phases of their life cycle:
growth
stability
decline
Growth - when available resources exceed the number of individuals using them. Reproduction is rapid, and death rates are low, producing an increase in population size.

7. Population stability is often followed by a "crash"
Stability is longest phase
Decline is the decrease in the number of individuals in a population can lead to extinction.
since the growing population eventually outstrips its available resources.

8. Factors Influencing Population Growth
Nearly all populations will tend to grow exponentially if resources are available.
Most populations have the potential to expand at an exponential rate, since reproduction is generally a multiplicative process.
Two of the most basic factors that affect the rate of population growth are the birth rate, and the death rate.

9. The size of a population depends on the rates of birth, death, immigration and emigration
r = (b+i) – (d-e)
Factors that influence population growth as the numbers increase are called DENSITY DEPENDENT eg food supply
Birth rates and death rates may vary regardless of population density. Factors which make this happen are called DENSITY – INDEPENDENT eg environmental changes

10. Types of ecological interactions
competition
predation
parasitism
mutualism
commensalism
symbiosis

12. Competition – two species share a requirement for a
limited resource  reduces fitness of one or both species

13. Predation – one species feeds on another  enhances
fitness of predator but reduces fitness of prey
herbivory is a form of
predation

14. Parasitism – one species feeds on another  enhances
fitness of parasite but reduces fitness of host

15. Mutualism – two species provide resources or services
to each other  enhances fitness of both species

16. Commensalism – one species receives a benefit from
another species  enhances fitness of one species; no
effect on fitness of the other species

17. Symbiosis – two species live together  can include
parasitism, mutualism, and commensalism

18. Organizing ecological interactions
effect on species 1
predation
herbivory
parasitism + -
commensalism
mutualism
effect on
species 2
competition

19. Competition The main density-dependent factor Compete for resources
Can be interspecific or intraspecific

20. Competitive Exclusion Principle
Two species cannot occupy the same niche, in the same place, at the same time
If there are 2 species with very similar requirements there are 2 outcomes:
One species out competes the other
Species undergo evolution and therefore occupy different niches.

22. Two modes of population growth.
The Exponential curve (also known as a J-curve) occurs when there is no limit to population size.
The Logistic curve (also known as an S-curve) shows the effect of a limiting factor (in this case the carrying capacity of the environment).

23. Interaction between Populations can influence population numbers- PREDATION
An interaction where an individual of one species (predator) eats all or most of an individual of another species (prey).
The most thoroughly studied consumptive relationship between species.
Of high ecological and evolutionary significance.
An everyday occurrence in nature.

24. Possible Outcomes of Predation
1. Predator population has little effect on abundance of prey.
2. Predator population eradicates prey population;
3. Predator and prey populations coexist.
this may contribute to extinction of predator population due to lack of food.

25. Prey Population Living Alone
Assume a constant rate of increase in absence of predators.

26. Predator Population Living Alone
Assume a constant rate of decline in absence of predators.

27. A Model Predator/Prey Cycle
This graph shows a limit cycle of predators and prey.

28. The Hare & Lynx Predator/Prey Relationship
Snowshoe hare and Canadian lynx show classic population cycles with a year cycle.
Hare are herbivores and feed on twigs under the snow in winter; lynx feed primarily on snowshoe hare.

29. The Hare/Lynx Cycle Based on Pelt Sales
Similar data is provided in Figure (Freeman, 2005).

30. Human Population Has been 3 population explosions
20 000yrs ago due to tools
6000yrs ago increase in farming
300yrs ago improvement in medicine etc
Humans unlike other species populations have created environmental changes to raise the normal population carrying ability
To what extent can the human species can continue to change the environment to sustain an ever increasing population?