Transcript Human Ecology and Succession

Population Dynamics
Populations
A
population is a group of organisms of
the same species that live in a particular
place at one time.
 A population could be a species of plants,
animals, bacteria, or people, living in a
given area (for example, bass living in an
isolated pond).
Population Dynamics:
 Populations
are constantly changing and
we need to keep up with the changes. The
study of human population is demography.
Some measures are:
 Birth Rate – Number of births in a given
time. (U.S. – 4 million per year)
 Death Rate – Number of deaths in a given
time. (U.S. – 2.4 million per year)
 Life Expectancy – how long the avg.
person lives. (U.S. men – 77, women – 80)
Age Structure Diagrams


Distribution of people of different ages (shown: histogram)
Also Shows Sex Ratio – number of males to females.
Other histograms:
Population Growth Rate
Amount by which a pop. changes over a period of
time, depends on 4 processes: birth rate, death
rate, immigration, and emigration.
BR + immigration - DR + emigration = growth
Growth of a population is usually exponential,
only contained by limiting factors (food, water,
space,density…)
Exponential Growth – J-shaped
curve. Unlimited growth
ex. Humans
Logistic Growth – S-shaped curve.
Pop’s growth slows because of a
limiting factor (at carrying capacity) ex.
Rabbits in the wild
Exponential and Logistical Growth
Graph
Density Factors
Density-independent – affect all populations
in similar ways regardless of size. Fires,
deforestation, dams, floods, hurricanes
etc…
Density-dependent factors – a limiting factor
that depends on the size of a population.
The more crowded = more competition,
predation, parasitism, and disease.
CYCLIC