Population Ecology Concepts

Population Ecology

• Population: A group of organisms of the same species living in a specific geographic area and interbreeding. It's a reproductive group. "Population" also refers to the size, the number of individuals.
• Population Density: The number of individuals of a species in a given unit of area or volume.
• Population Dispersion (Distribution): Refers to the spatial pattern of organism distribution in a population.
• Population Growth Rate: An expression of population size increase over a period of time. Calculated by (Birth Rate - Death Rate) / Time. Can be positive, negative or zero.
• Reproductive Potential: The maximum number of offspring an organism can produce. Influences population growth. Some species (like bacteria) have very high reproductive potential.

Population Growth

• Exponential Growth: Logarithmic growth where the population increases by a constant factor over successive time periods. Occurs in nature when food, resources and lack of predators or competition are abundant (e.g., bacteria, mold).
• Carrying Capacity: The maximum population size an environment can sustainably support given limited resources. The limiting resource is the resource that is consumed at the same rate it's produced. The supply of the most severely limited resources determines carrying capacity for a given species at a given time.
• Environmental Resistance: Factors that limit a population’s size (density-dependent factors, density-independent factors, territory, etc.)

Population Regulation

• Density-dependent factors: Factors that affect death rates in proportion to population density. Examples include limited resources, predation, and disease. Death rates are higher in crowded populations because of resource competition, disease prevalence, exposure to predators, and stress.
• Density-independent factors: Factors that affect death rates regardless of population density. Examples include severe weather and natural disasters. They affect all populations in a general or uniform way, regardless of density.

Niche and Symbiosis

• Niche: A species' unique role in an ecosystem comprised of its physical use of its habitat and its interactions within an ecological community. Distinct from habitat, which just describes a location.
• Symbiosis: A close relationship between two different species where one or both species benefit. Examples include parasitism, commensalism, and mutualism.
• Competition: An interaction between 2 or more species where they attempt to use the same limited resource. This can result in negative effects for both species involved. Competition can be direct or indirect, between members of the same species, or different species. If different species occupy overlapping niches, they may compete.
• Predation: One species (predator) feeding on another (prey). Predators may also be prey themselves.
• Parasitism: When one species (parasite) benefits by living on or in another (host) and harms the host.
• Mutualism: A relationship where both species benefit.
• Commensalism: A relationship where one species benefits and the other is neither harmed nor helped.

Demography

• Demography: The study of human populations and population patterns, including size and distribution, characteristics, and population growth factors.
• Survivorship: The percentage of a population born at a certain time that can be expected to survive to a given age. Used to predict population trends.
• Migration: The movement of individuals into or out of an area.

Demographic Transition

• Demographic Transition: A model that describes the changes in birth and death rates in a population. Historically associated with more developed countries.
• Stages:
  • Stage 1: High birth and death rates, stable population size.
  • Stage 2: Death rates fall, birth rates remain high, rapid population growth.
  • Stage 3: Birth rates start to fall, population growth slows, population bigger than before the transition.
  • Stage 4: Birth and death rates are low, stable population size.

Population Growth and Environment

• Overpopulation: A population growth rate that exceeds the environment's ability to support that population.
• Infrastructure: The basic facilities of a country or region—roads, bridges, sewers, power plants, subways, schools, hospitals.

Least Developed Countries

• Least Developed Countries: Countries with low levels of income, human resources, and economic diversity, identified by the UN. These countries are prioritized for development programs.