Ecology of populations

Ecology of Populations Reference: Chapter 46

Density vs Distribution
Density: #/area
Distribution
Ecological reasons for each?

Limiting factors
Resource or environmental condition that restricts the abundance or distribution of an organism
Abiotic or biotic
Why is there a
tree line?

Intrinsic Rate of Natural Increase
What increases population size?
What decreases population size?

Intrinsic Rate of Natural Increase, r
Population growth rate
+ natality (birth) rate
- mortality (death) rate
+ immigration rate
- emigration rate
If immigration = emigration
r = birth rate – death rate
Rates expressed per capita
2 out of 50 die = 0.04 death rate

Discrete breeder: one reproductive event in lifetime
Continuous breeder: many reproductive rates through out lifetime

Exponential Growth
Unchecked growth
Unlimited resources
Protection from disease & predators
Biotic potential = MAX growth under ideal conditions
R = net reproductive rate (offspring that survives from one female)
N t+1 = RN t N t = # females present N t+1 = population size the following year

Environmental resistance
Populations don’t grow unchecked forever…
Stopped by …

Logistic Growth
Growth slows or stops as resources dwindle
Carrying capacity
Maximum # of one species environment can support

Logistic Growth

Life History Patterns
Environment may influence reproductive strategies
Density-independent factors
Weather, natural disasters, etc.
Density-dependent factors
Parasitism, competition, predation

Unstable environment
Density-independent factors keep population from getting too high
r -selection
Rate of increase is most important
r -strategists
Many offspring; minimal parental care
Small body size; mature quickly
Good dispersers and colonizers
Get it while the getting’s good!
“Live fast, die young”

Stable environment
Density-dependent factors keep population from getting too high
K -selection
Carrying capacity is most important
K -strategists
Few offspring; extensive parental care
Large body size; mature late
Specialists
“Slow and steady wins the race”

Cohort = all the members of population born at the same time.
Survivorship = probability of newborn individuals of a cohort surviving to particular ages
Survivorship Curves

Survivorship Curves

Human Population Growth
Human population has an exponential growth pattern.
Doubling time currently estimated at 53 years.
Population Size
1800 1 Billion
1930 2 Billion
1960 3 Billion
2000 6 Billion

World Population Growth

Country Development
More-Developed Countries (MDCs)
Slow population growth.
High standard of living.
Completed Demographic Transition.
North America and Europe
Less-Developed Countries (LDCs)
Rapid population growth.
Low standard of living.
Latin America
Africa and Asia

Age Distributions
Age Structure Diagrams divide populations into three age groups.
Pre-Reproductive
Reproductive
Post-Reproductive

More-Developed Countries

Less-Developed Countries

Age Structure Diagrams
Keep your eye on the reproductive ages!

Environmental Impact
Environmental impact of a population is measured in terms of:
Population Size
Resource Consumption Per Capita
Resultant Pollution

Environmental Impact

Echoes of the Boom…

Ecology of populations

by jtwining

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