Lecture_21_-_Population_Ecology_2024
Population Ecology
Definition: Ecological study focused on a population.
Population: All individuals of one species inhabiting the same geographic area.
Example: Percentage of a sockeye salmon population that can be harvested by humans annually without causing long-term declines in numbers.
Long-term Human Population Change
Research Questions:
What is the long-term pattern in global human population change and associated ecological changes?
How can we predict population change over time while considering environmental limits?
Human Population Growth Over Time
Growth Timeline:
1804: 1 billion
1927: 2 billion
1960: 3 billion
1974: 4 billion
1987: 5 billion
1999: 6 billion
2011: 7 billion
(Data displayed graphically over time)
Ecological Changes Associated with Human Growth
Declining Resource Availability:
Overconsumption and unsustainable use.
Ecosystem destruction.
Degradation of the Biosphere:
Resulting from pollution.
Climate Change:
Increased greenhouse gases raise temperatures and intensify droughts/storms.
Reduced Ecosystem Services:
Decline in biological production, species diversity, and ecosystem services like air and water purification.
Predicting Population Change
Logistic Growth Model:
Presumes small initial populations with abundant resources.
Formula: ( Nt+1 = rmax Nt[(K - Nt)/K] + Nt )
Where:
( Nt ): population size at the start of the interval.
( rmax ): intrinsic growth rate based on reproductive potential.
( K ): carrying capacity of the environment (maximum population the ecosystem can support).
( Nt+1 ): population size at next time interval.
Population Growth Example (Logistic Model)
Table displaying generation, population size (Nt), growth rate (rmax), carrying capacity (K), and subsequent population size (Nt+1).
Initial generation size: 10
Carrying capacity: 100
Population sizes increase incrementally leading to:
Generation 10 calculation using logistic model.
Density Dependence and Growth
Growth Dynamics:
Density-dependent factors:
Growth rate slows at high population density.
Relates to carrying capacity limitations.
Logistic Growth Graphs:
Illustrates population growth slowing as density increases.
Factors Regulating Population Change
Density-independent Factors:
Effects are unrelated to population density.
Examples include abiotic stressors (e.g., extreme temperatures) and physical disturbances (e.g., fires).
Density-dependent Factors:
Effect magnitude increases with population density.
Includes competition for resources, predation, and parasitism.
Life History Strategies:
r-selected Strategy:
High reproduction rate, low survival probability.
K-selected Strategy:
Low reproduction rate, high survival probability.
Life History Strategies and Population Dynamics
r-selected:
Characterized by rapid population growth and fluctuations due to density-independent factors.
K-selected:
Exhibits slow growth rates and stability near carrying capacity influenced by density-dependent factors.
Carrying Capacity Considerations
Can populations exceed carrying capacity (K)?
If K is exceeded, potential long-term consequences for the population include resource depletion and increased mortality.
Example of St. Paul Island reindeer population illustrates food supply decline due to overconsumption.
Applications of Population Ecology
Sustainable Harvest Practices:
Optimal population management in fisheries and wildlife.
K = maximum population support by the environment; maximum sustainable yield (MSY) is K/2.
Metapopulation Theory:
Preserves populations in fragmented habitats and prevents extinction.
Enhances migration among smaller populations.
Maintaining Genetic Diversity:
By connecting isolated populations, managed landscapes enable gene flow and increase resilience against extinction.
Wildlife corridors facilitate movement and connectivity to sustain biodiversity.