population ecology

Population Ecology

Core Concepts

1. Five important characteristics of a population are its

geographic distribution, density, dispersion, growth rate,

and age structure.

2. Three factors can affect population size: the number of

births, the number of deaths, and the number of

individuals that enter or leave the population.

3. The biotic potential of an ecosystem is affected by

environmental resistance, thus resulting in a maximum

carrying capacity.

4. Factors that limit population growth include both

density-dependent (ex. competition) and density-

independent (ex. natural disasters) factors.

5. Understanding patterns in human population growth is

important in addressing population problems around the

world.

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Keywords

• geographic distribution/range

• population density

• population dispersion

• immigration

• emigration

• logistic growth

• exponential growth

• biotic potential

• environmental resistance

• carrying capacity

• density-dependent factors

• density-independent factors

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Characteristics of a Population

1. Geographic distribution

2. Density

3. Dispersion

4. Growth rate

5. Age structure

What is a population?

A population is a group of individuals of the same species occupying the same general area.

Geographic distribution

- geographical range of a species or a group of species

- the suitability of habitats influences the distribution of a species (each species is adapted to a rather limited range of abiotic and biotic conditions)

Population density

- the number of individuals per unit

area or volume

Population dispersion

- pattern of spacing among individuals in a habitat

Types of dispersion:

RANDOM

- habitat conditions are uniform / resource availability is steady

- individuals neither attract nor avoid each other

- rare in nature

UNIFORM

- individuals are evenly spaced in a habitat

- due to competition or territorial behavior

CLUMPED

- species are aggregated in patches

- most common in nature because:

cluster around patchy resources

live in social groups

species has limited dispersal powers

http://www.bioedonline.org/slides/slide01.cfm?q=dispersion+patterns&pg=1



Growth rate

- increase in the size of a population of organisms

population size the number of individuals that contribute to a

population’s gene pool

Estimating Population Size:

CAPTURE-RECAPTURE Method

For mobile animals

Individuals are captured and marked in some way, then the marked animals are released.

Later, animals are captured and checked for marks.

In the later sample, the proportion of marked individuals should be representative of the proportion marked in the whole population.

Growth rate

- increase in the size of a population of organisms

population size the number of individuals that contribute to a population’s gene pool

Factors that affect population size:

1. Number of births

2. Number of deaths

3. Immigration/Emigration

Immigration – the arrival of new residents from other areas

Emigration - individuals permanently move out of the population

types of growth

» Exponential vs.

» Logistic Growth

» Interrelationships among biotic potential, environmental

resistance, and carrying capacity


factors that limit population growth

– density-dependent:

competition, predation, parasitism and disease,

crowding and stress

– density-independent:

natural disasters, human disturbances


Patterns of and problems with

human population growth

population growth through the centuries with important

historical events:

(ex. industrial revolution, bubonic plague) illustrate

factors that limit/boost human population growth

effects of human population growth on society and on

the environment

age-structure diagrams

concepts of ecological footprint and ecological

capacity; compare across countries


Ecological Footprint and Ecological Capacity

• The ecological footprint is a measure of human demand on the Earth's

ecosystem in terms of the amount of biologically productive land and

sea area needed to regenerate the resources a human population

consumes and to absorb and render harmless the corresponding

waste.

• It compares human demand with planet Earth's ecological capacity to

regenerate.

• It estimates how much of the Earth (or how many planet Earths) it

would take to support humanity if everybody lived a given lifestyle.

• For 2006, humanity's total ecological footprint was estimated at 1.4

planet Earths – in other words, humanity uses ecological services 1.4

times as fast as Earth can renew them.[1]

• Every year, this number is recalculated — with a three year lag due to

the time it takes for the UN to collect and publish all the underlying

statistics.

• While the term ecological footprint is widely used,[2] methods of

measurement vary. However, calculation standards are now emerging

to make results more comparable and consistent.[3]7/28/2011 Free PowerPoint Template from www.brainybetty.com 13


Education

population ecology