Population Ecology

Population Dynamics Population: All the individuals of a species that live together in an area Demography: The statistical study of populations, allows predictions to be made about how a population will change Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Population Dynamics Three Key Features of Populations Size Density Dispersion Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Size: number of individuals in an area Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Growth Rate: Birth Rate (natality) - Death Rate (mortality) How many individuals are born vs. how many die Birth rate (b) − death rate (d) = rate of natural increase (r) Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Three Key Features of Populations Density: measurement of population per unit area or unit volume Pop. Density = # of individuals ÷ unit of space Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

How Do You Affect Density? Immigration: movement of individuals into a population Emigration: movement of individuals out of a population Density-dependent factors: Biotic factors in the environment that have an increasing effect as population size increases (disease, competition, parasites) Density-independent factors: Abiotic factors in the environment that affect populations regardless of their density (temperature, weather)

Factors That Affect Future Population Growth Immigration + + - Population Mortality Natality - Emigration

Three Key Features of Populations Dispersion: describes the spacing of organisms relative to each other Clumped Uniform Random Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

Population Dispersion

How Are Populations Measured? Population density = number of individuals in a given area or volume Count all the individuals in a population Estimate by sampling Mark-Recapture Method

How Do Populations Grow? Idealized models describe two kinds of population growth: Exponential Growth Logistic Growth

Exponential Growth Curve Figure 35.3A

Logistic Growth Curve

Carrying Capacity (k): The maximum population size that can be supported by the available resources There can only be as many organisms as the environmental resources can support Although several species may share a habitat they each have their own niche. A niche is a very narrow range where a species fits within a habitat.

What keeps a population from growing exponentialy? Limiting factors=Factors that are biotic or abiotic that keep a population from continuing to increase indefinitely 2Types: Density-independent factors Density-dependent factors

Factors Limiting Growth Rate Declining birth rate or increasing death rate are caused by several factors including: Limited food supply The buildup of toxic wastes Increased disease Predation

Density- independent Factors Density-independent factors = Any factor in the environment that does not depend on the number of members in a population per unit area Usually abiotic (natural phenomena) Ex: Weather events (tornadoes, floods, hurricanes) Fire Human alterations of the landscape Air, land, and water pollution

Density-Dependent Factors Density-dependent factor = Any factor in the environment that depends on the number of members in a population per unit area Usually biotic Ex: Predation Disease- (high population density--> disease quickly spreads) Parasites Competition – food, space limitations

“Booms” and “Busts”

Human Population Growth J curve growth Grows at a rate of about 80 million yearly r =1.3% Why doesn’t environmental resistance take effect? Altering their environment Technological advances The cultural revolution The agricultural revolution The industrial-medical revolution

The Human Population Doubled three times in the last three centuries About 6.1 billion and may reach 9.3 billion by the year 2050 Improved health and technology have lowered death rates

History of the Human Population