1. POPULATION
BIOLOGY

2. Ecosystem  Communities  Populations  Organisms
4.1 Population Dynamics
Ecology can viewed through several hierarchical "levels of organization.
Ecosystem  Communities  Populations  Organisms

3. Groups of organisms of the same species that live within a given area
Populations
Groups of organisms of the same species that live within a given area
Key characteristics:
Dispersion patterns
Population density
Growth rate

4. Limiting factors—biotic or abiotic factor that prevents population growth
A. Physical factors -- temperature, water, light, soil acidity
B. Biological interactions --competition, predation, symbiosis
C. Geographical barriers – Mountains, deserts, oceans (Humans sometimes transport species past these barriers)

5. Population Density
Population density is total population size per unit of area.
Population densities depend on:
Interactions within the environment
Quality of habitat
Density dependent factors
Density independent factors
Carrying capacity is the maximum number of organisms that can be supported in a given habitat.

6. Limits on Population Growth
Density Dependent Limits
Food
Water
Shelter
Disease
Density Independent Limits
Weather
Climate
Water and shelter are
critical limiting factors in
the desert.
Fire is an example of a
Density independent
Limiting factor.

7. Density dependent factors – The effect increases as the population increases. a. Predation b. Disease c. Intrinsic influences
· Physiological stress from overcrowding
· Abnormal behavior (aggressive behavior, kill young, etc.)
· Competition for resources

8. Density independent factors -- Affect populations regardless of size.
a. Abiotic – Environmental factors that effect population size. (rainfall, temperature, hurricanes)
b. Biotic – Biological factors. An organisms predator or prey species population changes.

9. Growth Rate is the change in population size over time.
Birth rate--number of births
Death rate--number of deaths
Immigration & Emigration—numbers that leave or join the population

10. Logistic growth (S-shaped curve)—Has a carrying capacity (K)– maximum number of individuals that can survive due to limited resources (food, light, space, water). Logistic growth often has an "overshoot" phase, followed by fluctuations in population.

11. Exponential growth (J-shaped curve)-- Assumes no limitations on resources.
Some species have brief periods of exponential growth, followed by population crashes.

12. Population Growth
Exponential vs. Logistical Growth