Population Ecology

Population Essential Questions

What factors influence populations in ecosystems? How do human population dynamics affect the world we live in?

What is a population?A group of the same species living in a

geographic area

Important Note: So a population is made up of individuals. But, multiple populations make up a community.

Quantifying Population

• Three key features:– Population size– Population density– Population distribution

Population Size

• Number of individuals in an region

Population Density• Number of individuals within a population per

unit area

Population Distribution• The spatial arrangement of organisms within

an area

clumped

uniform

random

Population Distribution

Unregulated populations increase by exponential growth

Quick Think: In this model, a population will get bigger and bigger forever! Do you think that is really possible?

Logistic Growth Model

Carrying Capacity (K)

Quick Think: What are some things that may cause population growth to slow down?

Limiting factors prevent endless population growth

• Limiting factors: physical, chemical, and biological characteristics of the environment that restrain population growth

• Limiting factors are also referred to as “environmental resistance”

• Carrying capacity: maximum population size that the environment can sustain

Quick Think: Is the carrying capacity the same for all populations? Why or why not?

Examples of limiting factors

• Space• Sunlight• Availability of:– Food– Water– Mates and breeding sites– Shelter

• Temperature• Nutrients• Pollutants

The influence of some factors depends on population density

Density-dependent factors

DiseaseCompetitionFinding matesParasites

Density-independent factors

TemperatureStormsHabitat DestructionDrought

Reproductive strategies• Biotic potential – ability to produce offspring