Ecology Chapter 30: Ecology of Population Lecture Notes

Definition of Ecology: Ecology is the scientific study centered on the interactions of organisms with one another and with their physical environment.
The Role of Ecologists: Ecologists are tasked with developing models designed to explain and predict the distribution and abundance of populations. These predictions are based on the complex interactions that occur within an ecosystem.

Organisms: This level focuses on how individual organisms adapt to their specific environments.
Populations: A group of individuals of the same species in a given area.
Community: The level of study that examines the various interactions between different populations existing in the same area.
Ecosystem: This level encompasses all living organisms in an area along with their physical, non-living environment.
Biosphere: This represents the Earth's surface and all the regions of the planet occupied by living organisms.

Global Distribution: The human population is not evenly distributed across the globe.
Regional Concentration: Approximately $60$ % of the world's population resides in Asia. The majority of this concentration is found within China and India.
Historical Growth Trends:
- $1200$ – $1400$ : The population was significantly impacted by the Black Plague.
- Industrial Revolution: This period marked the beginning of a sharp increase in global population growth.
- Modern Science and Medicine: These advancements further accelerated population growth through the $1900$ s and into the year $2000$ .
- Current State: Human population growth is currently categorized as rapid.
- Projections: Data indicates projected annual growth rates for country populations spanning from $2010$ to $2050$ . Historical data points on growth charts include the years $1200$ , $1400$ , $1600$ , $1800$ , $2000$ , and a projection for $2100$ .

Doubling Time: The current estimated doubling time for the global human population is $67$ years.
Resource Access Concerns: There are critical areas worldwide where populations lack access to essential survival resources, specifically:
- Fresh water
- Food
- Shelter
Carrying Capacity:
- Definition: Carrying capacity refers to the maximum number of individuals of a species that an environment can sustain over an indefinite period of time.
- Human Status: The specific carrying capacity of Earth for the human population has not yet been determined, raising questions about how many people the planet can ultimately support.

Country Classifications: Global nations are divided into More Developed Countries (MDCs) and Less Developed Countries (LDCs) based on the Human Development Index (HDI).
Age Structure Groups: Populations are divided into three primary demographic groups:
1. Prereproductive
2. Reproductive
3. Post-reproductive
Demographic Differences:
- MDCs: Typically exhibit a stable age structure.
- LDCs: Characterized by populations that continue to expand rapidly.
Environmental and Resource Disparities:
- Population Size: LDCs maintain a much larger share of the total global population.
- Resource Consumption: MDCs consume a significantly higher percentage of the Earth’s resources compared to LDCs.
- Waste Production: MDCs account for only $22$ % of the world’s population, yet they are responsible for $90$ % of the world's hazardous waste production.

Dependence Factors: Population growth is heavily dependent on the availability of resources and specific demographics.
Abiotic Factors: These are non-living influences on population growth, such as weather patterns.
Biotic Factors: These are living influences, including:
- Competition
- Predation
- Parasitism
Reproductive Metrics: Metrics influencing growth include the reproduction age of individuals and the number of offspring produced per reproduction cycle.
Population Density: This is defined as the number of individuals within a specific unit of area. Density is directly reliant on the resources available in that area.

Competition: Categorized as a density-dependent factor. As the density of a population increases, the percentage of that population affected by competition also increases.
Predation: Also a density-dependent factor. The impact of predation on a population increases as the population density rises.
Predator and Prey Population Cycles: The population sizes of predators and their prey often fluctuate in a synchronized (sync) manner.
- Example: The cycle between the Snowshoe hare and the lynx. When the population of the Snowshoe hare decreases—often due to fluctuations in food availability—the lynx population subsequently decreases as well.

Opportunistic Life Pattern:
- Characterized by exponential population growth.
- Features a short life span.
- The population possesses a high dispersal capacity.
Equilibrium Life Pattern:
- Characterized by logistic population growth.
- Features a long life span.
- The population is slow to reach maturity.
Extinction: Defined as the total disappearance of a species.
- Susceptibility: Species following an equilibrium life pattern are more apt to go extinct than opportunistic species.
- Determinants of Extinction Risk: The danger of a species facing extinction can be determined by three primary factors:
  1. The size of the geographic range.
  2. The degree of habitat tolerance.
  3. The size of the local population.