Population Ecology

Population: All individuals of one species in a defined area.
Population Density: Number of individuals in an area.
Population Dispersion: The spatial distribution of individuals within a population.
- Clumped Dispersion: Individuals are grouped in clusters with space between clusters.
- Uniform Distribution: Individuals are evenly spaced, as observed in some nesting birds.
- Random Dispersion: Individuals are arranged without any predictable pattern.

Type I Curves: Characterized by low death rates in early and middle life, with an increase in death at older ages. Common in large animals with few offspring and good parenting (e.g., humans).
Type II Curves: Exhibits a constant risk of death throughout life, seen in many rodents, lizards, and some annual plants.
Type III Curves: High mortality rates in early life, but those that survive have a low risk of death later, typical of marine invertebrates, long-lived plants, and many fishes.

Key factors:
- Births and Immigration: Add individuals to a population.
- Deaths and Emigration: Remove individuals from a population.
Population growth formula: (Birth rate + Immigration rate) - (Death rate + Emigration) = Growth curve.
Growth can be exponential when resources are abundant.

Biotic Potential: The maximum growth rate of a population determined by species biology, such as age of sexual maturity and number of offspring.
Limiting Factors: Can restrict population growth such as availability of food, nesting sites, and presence of predators.
Carrying Capacity: The maximum population size that an environment can sustain; populations can exceed this and face die-off.

Density-Dependent Factors: Factors that intensify with population density increase (e.g., competition for resources, disease, predation, territoriality).
Density-Independent Factors: These factors impact population regardless of density and include natural disasters.
Intrinsic Factors: Changes within the species' reproductive strategy affecting population growth.
Toxic Waste: The accumulation of waste can affect reproduction frequency.

Key factors influencing life histories: timing of reproduction and lifespan, number of offspring, investment per offspring, and survivorship traits.
Strategies are shaped by trade-offs influenced by natural selection.

Nazca Booby: Example of investment in reproduction; lays an extra egg as a contingency.
Seralparous Strategy: Species that reproduce only once in a lifetime (e.g., salmon and agave).
Iteroparous Strategy: Species that reproduce multiple times in their lifetime but with lower investment per offspring.

R-Selected Species:
- High reproductive rates with many offspring produced.
- Minimal parental investment, leading to high mortality but potential to colonize quickly (e.g., rats, dandelions).
K-Selected Species:
- Operate near carrying capacity.
- Produce fewer offspring with significant parental investment; typically found in stable habitats (e.g., bears, oak trees).

Historically, humans maintained their population near carrying capacity until recent advancements.
Overcoming Limiting Factors: Technological and agricultural advancements have allowed human populations to grow.
Disparity in Resource Usage: First-world countries consume more resources than those in third-world nations.
Ethical Considerations: Questions arise regarding the morality of advising populations to reduce consumption based on resource availability.