Population
POPULATION
Population growth happens in patterns:
Types of Population Growth
Exponential growth
Happens when food is unlimited
Population increases very fast
Shown as a J-shaped curve
Example: bacteria in a lab
Logistic growth
Food and space become limited
Growth slows and stabilizes
Shown as an S-shaped curve
Stabilizes at carrying capacity
Factors Affecting Population
Birth rate
Death rate
Immigration
Emigration
FOOD SUPPLY
Food is the primary limiting factor.
Effects of Food Supply
Abundant food → early maturity, more offspring
Limited food → starvation, competition, weaker individuals
Poor nutrition → lower immunity → more disease
Competition
Intraspecific: within the same species
Interspecific: between different species
Only the fittest survive (natural selection).
PREDATORS
Predators do more than just kill prey.
Benefits of Predators
Remove weak, old, sick individuals
Prevent overgrazing and habitat destruction
Maintain genetic strength in prey populations
Predator–Prey Graph
Prey population rises first
Predator population rises later
Prey falls → predator falls
This cycle repeats naturally.
DISEASE
Disease acts as a density-dependent factor.
How Disease Controls Population
Spreads faster in crowded populations
Kills vulnerable individuals first
Reduces fertility and growth rate
Types of Disease Spread
Airborne (crowded areas)
Water-borne (poor sanitation)
Vector-borne (mosquitoes, flies)
INTERCONNECTION
Food increases → population rises
Population rises → competition increases
Competition → weaker individuals die
Large population → disease spreads
More prey → predator numbers rise
Predators + disease → population falls
Food recovers → cycle restarts
This is population regulation.
HUMAN POPULATION
Humans reduce natural limits using:
Agriculture
Medicine
Technology
But problems still occur:
Food shortages
Pandemics
Environmental damage