Population
What is Population in Biology
A population is a group of individuals of the same species that live in the same geographical area at the same time and are capable of interbreeding.
Example: All deer in a particular forest form a population.
Key Characteristics of a Population
1. Population Size (N)
The total number of individuals in the population.
Small populations are more vulnerable to extinction.
Large populations are more genetically diverse.
2. Population Density
Number of individuals per unit area or volume.
High density → more competition, disease spread.
Low density → harder to find mates, less social interaction.
3. Population Distribution (Dispersion Patterns)
How individuals are spaced:
Clumped — most common; resources patchy (e.g., herds, schools of fish)
Uniform — competition for resources, territoriality (e.g., penguins)
Random — rare; resources evenly available (e.g., some plants)
Factors Affecting Population Size
Birth Rate (Natality)
Higher birth rate → population grows.
Death Rate (Mortality)
Higher death rate → population decreases.
Immigration
Individuals moving into a population → increases size.
Emigration
Individuals leaving → decreases size.
Population Growth Models
1. Exponential Growth (J-shaped curve)
Occurs when resources are abundant.
Population grows rapidly.
Rare in nature for long periods.
2. Logistic Growth (S-shaped curve)
Growth slows as resources become limited.
Reaches a carrying capacity (K) → maximum population an environment can sustain.
This is the typical real-world pattern.
Carrying Capacity (K)
The environment’s limit on how many individuals a population can support.
Controlled by:
Food supply
Water
Space
Predators
Disease
Population Regulation
Density-Dependent Factors
Effects increase with population density:
Competition
Predation
Disease
Resource scarcity
Density-Independent Factors
Affect population regardless of size:
Natural disasters
Climate events
Pollution
Population Genetics
Populations are also studied genetically to understand:
Gene pools
Genetic variation
Evolutionary changes
Natural selection
Allele frequency changes in populations are the basis of evolution.
Population Structure
Age Structure
Proportion of individuals in different age groups:
Pre-reproductive
Reproductive
Post-reproductive
Determines growth potential.
Gender Ratio
Number of males vs females. Affects reproduction and growth.
Population Interactions
Populations interact with other populations:
Competition
Predation
Mutualism
Commensalism
Parasitism
These interactions shape ecosystem dynamics.
Applications of Population Biology
Used in:
Conservation biology (saving endangered species)
Wildlife management
Agriculture and pest control
Epidemiology (studying disease spread)
Ecology and evolution research