POPULATION BIOLOGY

PRINCIPLES OF POPULATION GROWTH

Increase in size of a population over time.Bacteria/yeast may be plated on agar in a petri dish and the colonies counted over time.

Plants or animals may be introduced into a new environment with plentiful resources and their growth observed.

HOW FAST DO POPULATIONS GROW? Population growth is never linear.

S shaped curve

Carrying Capacity

TIME

Number of organisms

POPULATION GROWTH

LIMITS OF THE ENVIRONMENT

Limiting factors such as food, space and water control the size of a population.

“Leveling off” of population results in S-shaped growth curve.

CARRYING CAPACITY (K) is the number of organisms that can be supported in an environment.Population below K births exceed deathsPopulation above K deaths exceed births

PATTERNS OF POPULATION GROWTH

Rapid life history pattern organisms in an unpredictable environment. Mosquito: small body size, mature quickly, reproduce early, short life span. Population fluctuate rapidly depending upon conditions.

Long life history pattern organisms living in stable environments.Elephants: large, mature and reproduce slowly, longer life span. Population size near carrying capacity

ENVIRONMENTAL LIMITS TO GROWTH POPULATION

DENSITY - DEPENDENT FACTORS Effect increases as population increases

Disease, competition, parasites, food

DENSITY - INDEPENDENT FACTORS

Affects all population regardless of size

Temperature, floods, habitat destruction, drought

ORGANISM INTERACTIONS LIMIT

POPULATION SIZE PredationPredator-prey relationship cycles:Ex: lynx and rabbits

Effects of competitionPopulation low, resources are plentiful, no problems, as population increases resources become limited and competition increases.

Effects of crowding and stressOvercrowding leads to stress. Individuals become more aggressive, show less parental care, decreased fertility

HUMAN POPULATION GROWTH

DEMOGRAPHIC TRENDS

Demography: study of human population growth characteristics. Demographers study population growth rate, age structure and geographical distribution.Human population has increased exponentially Humans are able to reduce environmental effects.

EFFECTS OF BIRTHRATES AND

DEATH RATESSlow population growth rate if deaths, exceed births

Fast population growth rate if births exceed deaths

DOES AGE AFFECT POPULATION

GROWTH? A population with more young than old people will grow faster than the reverse.

Age structure is shown on graphs and helps predict growth rate of population Broader base has faster population that is increasing

AGE STRUCTURE GRAPHS

MOBILITY HAS AN EFFECT ON

POPULATION SIZE

Immigration: movement of individuals into an area. Emigration: movement of individuals out of a population International migration does not affect world population National and local populations are affected by internal migrations

http://galen.metapath.org/popclk.html