Unit 2 Environmental Science

demography 

Study of human population statistics 

sex ratio

proportion of males to females

emigration

departure of individuals from a given area +

migration

seasonal movement of organisms into and out of an area

Age Structure Diagrams 

‘pyramids’ which show relative numbers of organisms of each age within a population +

Immigration

Arrival of individuals from outside a given area +

Logistic growth

What kind of growth is when a population’s initial exponential growth is slowed and/ or stopped by limiting factors? it is an S-curve +

Density dependent

Describes a limiting factor whose influence changes with population density +

Carrying capacity 

The largest population size a given environment can sustainably support

Total Fertility rate

Average number of children a female member of a population has in her lifetime; 2.4 worldwide, 1.4 US +

Random

Pattern of population distribution where organisms are arranged in a space with no particular pattern

Clumped

Pattern of population distributions where organisms are arranged in according to the resources available. Most common

Uniform

Pattern of population distribution where organisms are evenly spaced out. There is competition for resources.

Population density 

Number of individuals within a population per unit area ++

Density independent

Describes a limiting factor whose influence is not affected by population density

A demographic transition

A model that explains the change in many societies from high to low birth rates and death rates ++

Replacement fertility

Total fertility rate for a nation that would keep its population size stable; 2.1 for many nations  +

Biotic potential

Maximum ability to produce offspring in ideal conditions +

Limiting factors

Characteristics of the environment that limit population growth

Birth rate

Number of births per 1000 individuals; also known as natality +

Population size

Number of organisms present in a given population at a given time 

Death rate

Number of deaths per 1000 individuals; also known as mortality + 

Exponential growth

What kind of growth is it when a population grows by a fixed percentage each year, resulting in a J-shaped curve

Population

Members of a species that live in the same area at the same time

Survivorship curves 

Graphs that show individuals’ likelihood of dying at certain ages ++

Infant mortality

Number of babies out of 1000 that die in their first year of life

Life expectancy

Average number of years an individual is expected to live

Population distribution

Describes how organisms are arranged within an area

Growth rate

Describes how a population changes in size during a specific period of time +++

birth rate and death rate; immigration and emigration (plus migration)

What two set of factors determine population growth?