Population Ecology

Chapter 4

GPS

• SB4 Students will assess the dependence of all organisms on one another and the flow of energy and matter within their ecosystems.

• d. Assess and explain human activities that influence and modify the environment such as global warming, population growth, pesticide use, and water and power consumption.

A biological community is a group of interacting populations that occupy the same area at the same time.

A desert oasis

• Organisms within a community adapt to the conditions in which they live.

• These conditions are often abiotic factors

• Communities are often stable but may evolve and change over time.

Keeps a population in check.

Doesn’t allow unlimited growth.

Limiting factors include:

Food, water, shelter/ habitat, mates

Organism compete for these limited resources

Population Dynamics

Populations of species are described by density,

spatial distribution, and growth rate

Population Characteristics

Population Density

The number of individuals per unit area

Spatial Distribution

The pattern of spacing of a population

Population Ranges

• Populations can not live in all environments

• Abiotic conditions effect the range of environments in which a population can live

• A species might not be able to expand its population range because it cannot survive the abiotic conditions found in the expanded region.

Population Limiting FactorsThere are two categories of limiting factors

1. density-independent factors Any factor in the environment that does not depend

on the number of members in a population per unit area

2. density-dependent factorsAny factor in the environment that depends on the

number of members in a population per unit area

Disease

Temperature

Competition

Parasites

Storms

Food

Habitat disruption

Drought

Environmental limits to population growth

Density-dependent factors

disease, competition, parasites, and food

Density-independent factors

temperature, storms, floods, drought, habitat disruption

• An upper limit and lower limit that define the conditions in which an organism can survive

• The ability of any organism to survive when subjected to abiotic factors or biotic factors is called tolerance.

Population Growth Rates

Exponential growth

As the population gets large it also grows faster

Reasons this occurs:

1. Initial increase is slow because few breeding individuals

2. As individuals mature, reproducing individuals increases.

Time

Pop

ulat

ion

size

Exponential growth is not realistic

Populations tend to grow until some environmental condition stops growth

Time

Pop

ulat

ion

size

This is called Logistic Population Growth!!

Carrying capacity and Limiting factors

Keeps a population in check.

Doesn’t allow unlimited growth.

Limiting factors include:

Food, water, shelter/ habitat, mates

Organism compete for these limited resources

Reproductive patterns

Species of organisms vary in:

the number of births per reproduction cycle

the age that reproduction begins,

the life span of the organism

What causes a population to grow

Number of births is greater than the number of deaths

Immigration exceeds Emigration.

What causes a population’s numbers to decrease?

Number of births is less than the number of deaths

Emigration exceeds immigration.

2 Reproductive Patterns• K-strategist

– Little environmental change– Generally large organisms– Long life spans– Few offspring with extended parent care

• R-strategist– Fluctuating abiotic factor occur– Generally small organisms– Short life span– Many offspring

Elephants

Bacteria

Mice

Humans

Cows

Termites

Lions

Rabbits

• Demography- the study of human population growth characteristics.

• Age structure-proportions of a population that are at different age levels.

Predator prey relationships