1. Population Biology

2. What is Population Biology?
Population Biology asks the question:
What factors cause a population
to be the size that it is?

3. Main Idea #1
Given ideal conditions for growth and reproduction, a population of organisms will grow exponentially.

5. Exponential Growth Curve

6. Main Idea #2
Most populations go through a series of growth phases, which can be represented by a logistic growth curve.

7. Logistic Growth Curve
carrying
capacity

8. This Growth Curve Has 3 Phases
Lag Phase – little initial growth.
Rapid Growth Phase
Stable Phase – stabilizing factors limit growth

9.                                                                                                  
Figure 35-6

10. Main Idea #3
Together, all of the limiting factors acting on a population determine how many individuals can be supported.

11. Limiting Factors
Abiotic factors (temperature, humidity, pH, altitude, light/shade, pollution…)
Food supply
Interspecific Competition
Intraspecific Competition
Predation
Parasitism/Disease

12. Density-Dependent/Density-Independent
Density-dependent limiting factor: factor that limits a population more as population density increases (e.g. food supply, disease)
Density-independent limiting factor: factor unrelated to population density that limits a population (e.g. hurricanes, blizzards, ice storms, and droughts)

13. Main Idea #4
A population usually achieves a steady state when it reaches the carrying capacity of the environment.

15. Main Idea #5
Humans have increased our own carrying capacity through agricultural and technological developments, but we have only postponed the environmental limits to our population growth.