1. Understanding populations
ECOLOGY
Understanding populations

2. Features that determine the future of a population:
Population size- the # of individuals in a population
Population density- the # of individuals in a given area
Dispersion-the way individuals are arranged in space

3. How many populations?

4. How many different populations can you see?

5. What is a population?
A population refers to all the members of one species, in one place at one time.

6. DISPERSION:
How members of a population are arranged in a given space.

7. Patterns of dispersion
Individuals in a population may be distributed according to 3 basic patterns of dispersion
Random
Uniform (also known as Even)
Clumped

8. Random Dispersion Scattered, not uniform Why? Environment is uniform
Individuals are solitary
They live independently
Pine trees in a
random distribution

9. Birds in an even distribution
Uniform Dispersion
About equal distance apart, forming a pattern
Why?
Resource competition
Birds in an even distribution

10. Buffalo in a clumped distribution
Clumped Dispersion
Grouped in some places, absent in others irregular pattern
Why?
Resources are patchy
Search for food
Buffalo in a clumped distribution

11. Why do you think scientists study population dispersion?
How individuals are arranged within a population can affect...
Protection
(from predators)
Hunting patterns
(if carnivorous)
Reproduction

12. Can you name the 3 patterns of dispersion?

13. Clumped
Uniform
Random

14. Population density:
The number of individuals in a population that live within a given area.

15. Population Density
Scientists study the population density because it helps determine how the individuals of a population interact.
Reproduction
Protection
Eating patterns
Social hierarchies, if any

18. Which population of wildebeest has the greatest population density?

19. An extremely dense population of wildebeest:

20. Modeling Population growth
Population success = reproduction of species
We can study how and why the number of individuals change over time
Populations grow when more individuals are born than die in a given period. A simple population model describes the growth rate as shown:
(r) = birthrate – death rate

21. Describe what is happening to the population in this graph
AGE
# of Individuals
A small # of the
youngest-decrease
Middle age population
is constant, secure,
not changing
The older population
decreases, faster

22. Exponential Growth
Exponential growth-the rate of population growth stays the same and the population size increases steadily.
This model displays a J-shaped curve which indicates a steady increase of population size.

23. What if the population size kept growing and growing and...
carrying capacity (K)- the population size that an environment can sustain
What factors do you think contribute to an environment's carrying capacity???

24. Factors that
can affect a
population

25. Density-dependent
factors
Resources that are limited because the rate at which they become depleted depends on the density of the population that uses them.

26. Density-dependent
factors
Shelter
Food
Water

27. LOGISTIC GROWTH MODEL
Once again, exponential growth is a steady increase in the population size.
Now we must consider the carrying capacity (K) and density-dependent factors when modeling population growth.
logistic model- a population model in which exponential growth is limited by a density-dependent factor. This model considers carrying capacity.

28. LOGISTIC MODEL

29. Density-independent
factors
Factors that do not depend on the size of the population, but can affect it nonetheless.

30. Density-independent
factors
Weather
Climate

31. Remember...
(r)= rate of growth, birthrate – death rate
(K)= carrying capacity, the population size an environment can sustain
There are 2 types of populations,
(r)-strategists and (K)-strategists

32. r-strategist: Species that grow exponentially when the environment allows for it. Results in temporarily large populations.
When the environmental conditions are no longer suitable for the species, the population size quickly decreases.

33. K- strategists- organisms that grow slowly
K- strategists- organisms that grow slowly. Population sizes are usually small and kept near the carrying capacity of their environment.
K-strategists are characterized by a long life span, a slow maturing process, and reproduction late in life.