Population Ecology

Population Dynamics Population: All the individuals of a species that live together 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.

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 #1 - 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 #2- 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

Density-Dependent Factors limiting resources (e.g., food & shelter) production of toxic wastes infectious diseases predation stress emigration

Density-Independent Factors severe storms and flooding sudden unpredictable severe cold spells earthquakes and volcanoes catastrophic meteorite impacts

A graphic way of representing population data is a survivorship curve A graphic way of representing population data is a survivorship curve. This is a plot of the number of individuals still alive at each age. A Type I curve shows a low death rate early in life (humans). The Type II curve shows constant mortality (squirrels). Type III curve shows a high death rate early in life (oysters).

Survivorship Curve

Three Key Features of Populations #3- 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 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.

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

How well does the logistic model fit the growth of real populations? The growth of laboratory populations of some animals fits the S-shaped curves fairly well. Stable population Seasonal increase

Some of the assumptions built into the logistic model do not apply to all populations. It is a model which provides a basis from which we can compare real populations. Severe Environmental Impact

“Booms” and “Busts”

Reproductive Strategies R Strategists Short life span Small body size Reproduce quickly Have many young Little parental care Ex: fish, cockroaches, weeds, bacteria

Reproductive Strategies K Strategists Long life span Large body size Reproduce slowly Have few young Provides parental care Ex: humans, elephants, orcas