Principles of Population Ecology
Population ecologists ask:
1) How many are in the population?
2) Are its numbers increasing / decreasing?
3) What is its pattern of reproduction?
4) What is its pattern of mortality?Significance of understanding this?1.Manage domestic and wild populations2.Manage pests3. Save Endangered Species4.Understand our own population changes
Principles of Population Ecology
How Do Populations Change in Size?
On a global scale (closed system):
Principles of Population Ecology
How Do Populations Change in Size?
On a local scale (open system):
Principles of Population Ecology
How Do Populations Change in Size?
Global scale:
r = b – d
Growth rate
Birth rate
Death rate
Principles of Population Ecology
How Do Populations Change in Size?
Local scale:
r = (b – d) + (i – e)
Growth rate
Birth rate
Death rate
Immigration rate
Emigration rate
Rule of 70: 70/Growth Rate% = Doubling Time
Biotic Potential
Maximum Population Growth-
under ideal conditions = intrinsic rate of increase
J-shaped curve (exponential growth)
Carrying Capacity
Environmental Resistance-
Exponential growth cannot occur forever.
What factors prevent it from doing so?
S-shaped curve (logistic growth)
Principles of Population Ecology
Overshooting the carrying capacity can lead to a population crash.
Positive & NegativeFeedback Loops
Population Crash
Population 1910= 26 / 1935= 2K / crash / 1945=8
Reproductive Strategies
Life History Strategies
r-selected K-selectedvs.
high growth rate slow growth rate
small body size large body size
early maturity late maturity
short life span long life span
large broods small broods
little / no parental care high parental care
Which are we? How do we apply this knowledge?
Survivorship & Reproduction
Density Dependent Factors
• Factors that influence population growth when its density is high.
• Predation, competition, disease, parasites, food availability.
Locust
Lemmings
Factors that Affect Population Size
Density-Dependence and Boom-or-Bust Population Cycles
Predator birth timing?
Predatory Prey Dynamics
Wolves Established 1949 - Moose 1900 approx. 1980’s parvovirous hits wolves1995 & 96 harsh winters and overgrazingTick numbers increase with warm spring & fallIsle Royal southern limit of Moose
Ticks
Density-Independent Factors:
• Regardless of population density, influences population growth.
• Weather, fire, earthquakes, etc…
