Ecology of populations
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Ecology of Populations Reference: Chapter 46
Transcript of 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 = emigrationr = birth rate – death rate
Rates expressed per capita2 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)
Nt+1 = RNt
Nt = # females present
Nt+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 capacityMaximum # of
one species environment can support
Logistic Growth
Life History Patterns
Environment may influence reproductive strategies
Density-independent factorsWeather, natural disasters, etc.
Density-dependent factorsParasitism, competition, predation
Life History Patterns 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”
Life History Patterns 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 Billion1930 2 Billion1960 3 Billion2000 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-ReproductiveReproductivePost-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 SizeResource Consumption Per Capita Resultant Pollution
Environmental Impact
Echoes of the Boom…
