POPULATION GROWTH NOTES Module 2 Ecology

Growing rapidly Tripled in size in about 70 years Est. size to day 6 billion+ (approx. 2 billion in 1930) Human Population

Problems cause by humans  Thinning ozone layer – ozone layer protects living things from ultraviolet radiation form the sun  Climatic changes  Greenhouse effect: insulates earth from the deep freeze of space; keep Earth warm  Caused extinction of other species – extinction rate higher today than at any other time  Increased pop. requires increasing amts. of food, energy, space – greater share of Earth’s resources will be required  Burning Fossil Fuels for energy – releases carbon dioxide; excess CO 2 traps too much heat in Earth’s atmosphere

Human Population Growth  Improved by agricultural development, hygiene, diet, and economic conditions improved  Today, population growth is faster in less-developed countries and slower in more developed countries

Population Dynamics  Changes in size and composition over time  Measure include:  birth rate - number of births over time (in US it is 4 million per year)  death or mortality rate – number of deaths in a period of time (in US it is 2.4 million per year)  life expectancy – how long an individual is expected to live (1996: in US it was 72 yrs. for a man and 79 for a woman)

Population Growth Rates  Amount of change within a population’s size in a given time  Four factors that affect growth rates:  Birth  Death  Emigration – movement out of a population  Immigrations – movement into a population  Demographers – scientists who study populations dynamics  Birth rate – death rate = growth rate

 Carrying capacity of a population is the number if individuals the environment can support for an indefinite period of time.  Populations fluctuate over time do to environmental changes.  Small populations are less able to rebound from environmental changes. They are more likely to experience inbreeding and their genetic diversity is low.

Population Growth Curves  Linear – growth occurs along a straight line NOT what we see w/ populations of organisms

Population Growth Curves  Exponential – as population gets larger, it grows faster (population explosion) “J shaped”

Predator-Prey  Predator-Prey – (predation is density dependent limiting factor)  When population grows beyond carrying capacity of environment, density-dependent Limiting Factors reduce population  population grows/shrinks  cycles

Carrying Capacity  What is seen in most populations of organisms. Population growth is limited by factors in the environment such as food supply or habitat.