# Populations - Growth and Demography

**Introduction phenomenon**: How do scientists determine the size of a population?

Why do we need to know a population's size?

## How Populations Grow

Geographic distribution – the area a pop lives(range)

Population Density – the number of individuals in an area

Population Growth

Number of births

Number of deaths

Emigration (out) & Immigration (in)

For example, In Springfield, 45 babies are born in the year 2008. 15 people died that same year. What is the growth rate for the city?

Positive Growth rate = population increase

Negative Growth rate = decrease

Exponential Growth –reproduce at a constant rate. Occurs under ideal conditions (no limits)

**J-shape curve **

Logistic Growth – resources become less available, growth slows or stops

**S-shape curve **

Carrying Capacity – the number an environment can support

## Limits to Growth

Limiting Factor – causes population growth to decrease

**Density-Dependent Factors **–depends on population size

competition

predation

parasitism and disease

**Density-Independent Factors** – does not depend on population size

Unusual weather

Natural disasters

Some human activities

**Predator Prey Relationships**

As prey population goes up, so does predator population. What happens when the prey population goes down?

## Demography: The study of human populations

Demographic Transition – a dramatic change in birth and death rates

- United States, Japan, and Europe population growth has stopped
- ZERO POPULATION GROWTH
- In order to achieve ZPG, each couple has only 2 children

**Age Structure Diagrams** can be used to evaluate populations

## Activities on Populations

Estimating Population Size – use bags filled with “animals” to mark and recapture and estimate the population size in the bag

Case Study – Loggerhead Turtles and Population Models – explore the number of eggs hatched and survivorship

Ecology Case Study – The Wolves of Isle Royale – population decline and reintroduction of wolves

Predator Prey Graph – graph data on deer and wolf populations (growth curves)

Random Sampling – estimate a population of “sunflowers”