2. 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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4. What is a population?
A population is a group of individuals of the same
species occupying the same general area.
Characteristics of a Population
1. Geographic distribution
2. Density
3. Dispersion
4. Growth rate
5. Age structure
5. 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
6. 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
7. 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
8. 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.
9. 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
10. types of growth
» Exponential vs.
» Logistic Growth
» Interrelationships among biotic potential, environmental
resistance, and carrying capacity
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11. factors that limit population growth
– density-dependent:
competition, predation, parasitism and disease,
crowding and stress
– density-independent:
natural disasters, human disturbances
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12. 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
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13. 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
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[3]
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