1. Population Ecology

2. I. General Info A. A population includes all the members of the same species that live in one place at one time B. Population density is the # of individuals/unit area (ex. 180 tree frogs in 9 km 2 = ?)  Factors Affecting Population Size  Deaths  Births  Immigration – movement of individuals into an area  Emigration – movement of individuals out of an area

3. Birth Immigration EmigrationDeath Population size

4. II. Population Growth A. Organisms will reproduce and populations will increase when: 1. Abundant space and food is available 2. Protected from predators and disease 3. Adequate mates B. Two Types of Population Growth:

5.  Exponential Growth  Occurs under ideal conditions with unlimited resources ex:  Constant doubling of the population  Not sustainable WHY?

6. Growth of Aphids Exponential growth Steady population size Peak population size Rapid decline Steady population size

7.  Logistic Growth  As resources become scarce, a population’s growth slows or stops Where do you see this on the graph? Number of Yeast Cells Time (hours) Carrying capacity

8. b. When an organism is introduced into a new environment it takes a while to establish itself (lag phase)  Once the population is established, growth accelerates.  When the population approaches the carrying capacity, various biotic and abiotic factors keep the population in balance.  Carrying capacity is the maximum number of individuals an ecosystem can support (Draw this graph) Carrying Capacity Lag phase *

9. Population Growth can be represented bycharacterized by represented by which cause a Exponential growth Logistic growth Falling growth rate S-shaped curve Limits on growth No limits on growth J-shaped curve Constant growth rate Unlimited resources

10. III. Limits to Growth A. Limiting factors are ecological factors that cause population growth to decrease B. Two Types of Factors: 1. Density Dependent Factors a. Operate strongly on large, high density populations b. Include competition for limited resources, predation, crowding, parasitism and disease c. Oh Deer! Lab

11. 60 50 40 30 20 10 0 195519601965197019751980198519901995 2000 1600 1200 800 400 0 2400 MooseWolves

12.  Density Independent Factors a. Affect all populations regardless of size b. Include human activities and natural disasters like fire, volcanic eruptions, severe storms, drought, or other climate conditions.

13. IV. Human Population Growth

14.  Background Info  Earth is approximately 4.6 billion years old  Modern humans have only been on Earth ~150,000-200,000 yrs 3.For most of human history, limiting factors kept population levels low (scarce food, disease, etc.); high death rates and high birth rates 4.In the last 500 years, improved agriculture, medicine, and sanitation increased population growth

15. Agriculture begins Plowing and irrigation Bubonic plague Industrial Revolution begins

17. B. Future Population Growth 1. Current human population is ~7 billion 2. Overpopulation = when the # of people in an area exceeds the resources and capacity of the environment necessary to sustain human activities 3. Scientists estimate that the Earth’s carrying capacity for humans is 7.7-12 billion people 4. More people = more competition for resources  more human conflicts

18. 5.If the growth rate does not slow down, resources will be depleted, the environment will be degraded and people’s standard of living will be greatly reduced