Population Ecology Review

Exponential Growth
- Formula: dN = 1.0N rac{dt}{dt}
- Description: Population growth where resources are unlimited resulting in a rapid increase in population size (N).
- Example: N reaches 2000.
Logistic Growth
- Formula: dN = 1.0N rac{(1500 - N)}{dt}
- Description: Population growth that begins to slow as it approaches carrying capacity.
- S-shaped growth curve illustrated with population size rising rapidly at first, then stabilizing around the carrying capacity (K = 1500).
Carrying Capacity (K): 1500 is the maximum limit of population size an environment can sustainably support.

Competition for Resources
- In crowded populations, increasing density intensifies resource competition, leading to a lower birth rate.
- Example: Farmers use fertilizers to enhance nutrient availability in crowded populations.
Disease
- High population density affects health and survival.
- Pathogens spread more rapidly in dense populations.
- Real-world Examples: Common cold, flu, COVID-19, and animal parasites.
Predation
- High prey population densities attract predators, increasing predation rates.
- Examples: Lemmings and snowy owls, aphids and ladybugs, kelp perch and kelp bass.
Territoriality
- Limit population density when individuals compete for space, reducing breeding opportunities.
Intrinsic Factors
- Physiological factors can regulate population size.
- Example: In crowded environments, white-footed mice reduce reproduction rates despite abundant food; stress and aggressive interactions can disrupt hormonal balance affecting maturation.
Toxic Wastes
- Accumulation of waste products can limit population growth.
- Example: Yeasts produce ethanol as a waste byproduct, which increases with population density.

Definition: Study of population dynamics examines interactions between biotic (living) and abiotic (non-living) factors causing population size variation.

Both biotic and abiotic factors affect large mammals' population size over time.
Example: Moose population on Isle Royale experienced collapses due to harsh winters and predator increases.

Some populations, like lynx, exhibit regular boom-and-bust cycles (10-year cycle with hares).
Hypotheses Regarding Hare Population Cycles:
- First Hypothesis: Cycles correlate with winter food supply availability. Experimental addition of food led to population growth without stopping cycles, weakening this hypothesis.
- Second Hypothesis: Predation pressure drives cycles. A study showed 95% of hares are killed by various predators (lynx, coyotes, etc.), supporting this hypothesis.

Emigration and Crowding: Increased competition may lead to higher emigration rates.
Metapopulations: Groups of populations connected by immigration and emigration; consist of local populations within suitable habitats.
- Losses due to extinction can be replenished by nearby populations.
Example: Glanville fritillary butterfly populations on the Åland Islands.

An individual's ability to migrate between populations depends on genetic traits.
- Example: Heterozygous Glanville fritillary butterflies at the Pgi gene can fly further at colder temperatures than homozygous ones.
- Pgi (phosphoglucoisomerase): An enzyme in the second stage of glycolysis.

Human population growth has slowed since exponential growth peaks in the 1960s but is still increasing rapidly.
- As of 2023, the global population exceeds 8 billion.

Significant growth was observed post-1650 due to the Industrial Revolution, improved agricultural methods, and medical advancements.

Graph showing population increase from 8000 BCE to present, noting growth spurt starting in 1650.

The annual growth rate began to decrease around the 1960s.
Projected growth rates for future years illustrate a continuing trend of slowing growth.

Population stability achieved under two configurations:
1. Zero Population Growth with high birth/high death rates.
2. Zero Population Growth with low birth/low death rates.
Demographic Transition: Shift from high birth/death rates to low birth/death rates, linked to industrialization and health advancements.

Age structure (distribution of individuals across different ages) is critical in understanding population growth.
Age-structure diagrams help predict future growth and illuminate social conditions.
- Factors influenced: employment, education, retirement age, healthcare.

Infant mortality and life expectancy vary significantly globally.
Global averages show increases in life expectancy but issues remain in regions facing social and health challenges.

The global carrying capacity prediction ranges from 8.1 to 10.6 billion people.
Ecological footprint: A measure of land and water area required to sustain a population or individual.
- U.S. citizens have an ecological footprint 4-5 times larger than global averages.

Potential limiting factors include food, space, nonrenewable resources, and waste accumulation.
Humans uniquely can regulate growth through social changes.

Average per capita energy use varies across regions; U.S. uses 30 times more energy per person compared to some African regions.