Population: Characteristics | Zoology Optional Notes for UPSC PDF Download

Population Characteristics

• A population is a group of individuals of the same species living together in a specific region.
• Population ecology studies the dynamics and characteristics of populations and their interactions with the environment.
• Population characteristics are attributes of a population as a whole, rather than of individual organisms.
• Various population characteristics can be compared to understand the dynamics of different populations, including density, natality, mortality, growth forms, and distribution.

Population Density

• Population density is a fundamental property representing the size of a population.
• It is defined as the total number of individuals per unit area or volume at a given time.
• There are two types of density: crude density (per unit total space) and specific (ecological) density (per unit of habitat space).

Determining Population Size

• Population size is often estimated by counting individuals in a small sample area and then extrapolating to estimate the size of the entire population.
• The Mark-Recapture technique is a common method where a sample of the population is captured, marked, released, and then recaptured. The number of marked and unmarked individuals in the second sample helps estimate the total population size (N).

Natality

• Natality refers to the birth of individuals in a population.
• The natality rate or birth rate is the number of individuals produced per female per unit of time.
• Natality can be either maximum natality (physiological natality) or ecological natality (realized natality), which accounts for specific environmental conditions.
• Fecundity and fertility are related terms but differ; fecundity represents the potential reproductive outcome of an individual, while fertility is the actual reproductive performance.

Mortality

• Mortality is the death of individuals in a population.
• Mortality rate or death rate is the number of individuals dying in a given period.
• Mortality can be either minimum mortality (constant under favorable conditions) or ecological mortality (loss under specific environmental conditions).
• Survivorship curves are used to visualize population mortality rates.

Dispersion

• Dispersion refers to the spatial and temporal distribution pattern of individuals within a population.
• There are three main patterns of distribution: regular, random, and clumped.
• Regular dispersion involves individuals being evenly spaced from one another, while random dispersion means no relationship between individual positions. Clumped dispersion indicates individuals grouping together.

Age Structure

• Age structure reflects the distribution of individuals into different age groups within a population.
• It significantly influences population behavior, including natality and mortality.
• Age structure is classified into pre-reproductive, reproductive, and post-reproductive age groups.
• Age pyramids, vertical bar graphs, are used to represent age distribution in populations and can be expanding, stable, or diminishing.

Population Dispersal

• Population dispersal refers to the movement of individuals into or out of a population or its area.
• This movement does not affect the size of the population.
• Dispersal includes emigration (outward movement from an area), immigration (inward movement into an area), and migration (periodic departure and return of individuals to the same area).

Understanding these population characteristics is essential for ecologists to study and manage populations in various ecosystems and gain insights into their dynamics and interactions with the environment.