Chapter 4
Population Biology
Linear growth – increase by the same amount each unit of time. (ex: saving $10 each week) Not the way populations grow!
Exponential Growth – growth at an ever-increasing rate that results in population explosion. J – shaped curve.
Thankfully populations have limiting factors in their environment!
Carrying Capacity – The number of organisms of a population that a particular environment can support for a long period of time. This is shown by an S-shaped curve.
Two types of limiting factors:
1. Density-dependant factors – have an increasing effect as the population increases. (Ex: disease, competition for food or space, parasites)
2. Density-independent factors – devastating affects regardless of population size. (Ex: temperature, storms, floods, drought, habitat destruction)
Interactions between organisms limit populations
1. Predation – populations of predator and prey can show a cycle as they rise and fall almost together. (Ex: Lynx & Hare)
2. Competition – As the population increases & demand for resources exceeds the supply, the population size decreases.
3. Crowding & Stress – Symptoms include aggression, decrease in parental care, decreased fertility, & decrease in resistance to disease.
Demography – The study of human population growth.
- Humans can somewhat alter limiting factors
- Better health care & higher food production
- Some countries in Africa have high death rates but even higher birth rates = very rapid growth.
- Age Structure – a large portion of children indicates rapid growth (Africa). Equal numbers of all ages have a stable population size (Germany). A larger portion of elderly indicates declining growth (China in 25 years)
Rapid Growth
•Africa & India have a large portion of young people = population is growing!
Stable Growth
•Germany & Sweden have relatively equal numbers of all ages = stable population size.
Declining Population
•China has a larger portion of elderly = declining population size.
- Immigration – populations increase due to people moving in. Can put a sudden stress on resources.
- Emigration – populations decrease by people moving out.
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