Studying Populations  Geographic Range – varies greatly by species  Density and Distribution-number of individuals per unit area  Growth Rate – depends on deaths, births, immigration and emigration  Age Structure-males, females, old, young, babies,

Sampling Populations  Random Sampling – count a random distribution of individuals/species  Why random- to avoid human influences  Count a certain number of grids and apply to entire area  Population density 85 plantains in 24 square feet- how many in one foot  85 plantains/24 = ?

Practice – Population Density  An ecologist determines the population of spotted knapweed to be 10,000. The area under study is 14 square kilometers. What is the population density?  A small town in Texas covers 14 square kilometers. There are 420 individuals who live within town limits. What is the population density of this town?

Mark and Recapture  Used for animals that move  portion of the population is captured, marked, and released.  Later, another portion is captured and the number of marked individuals within the sample is counted.  Marked is assumed to be proportional to population

Practice  15 deer are caught and marked. Over time biologist capture and count 100 deer, of those deer five have a mark  Total captured (total originally marked)  Total with a mark upon recapture  What is the answer-  Ten years later the biologist repeat the study- again 15 deer are caught and marked. 100 deer are recaptured and 15 have a mark.  What is the answer?  What happened to the population?

Types of Growth  Exponential Growth – under ideal conditions with unlimited resources, a population will grow exponentially (doubles)

Rapid Reproduction One of the fastest growing bacteria is Bacillus cereus, which divides approximately every 11 minutes- Even slower can divide every 20 minutes. A bacterial population can grow to 4,720,000,000,000,000,000,000 in one day!

Logistic Growth- why would growth slow down?

Carrying Capacity  Maximum number of individuals an environment can support.

Limiting Factors

Density-Dependent Limiting Factors  Operate when the population density reaches a certain level.  Predation, herbivory, parasitism, disease, and stress from overcrowding

Density Independent Limiting Factors  Density does not influence  Affects all populations in similar ways  Examples – wildfires, hurricanes, droughts, cold, cold, cold winters

World Population Growth  7 billion in the World  300 million in the United States  1 million in Montana  30,000 in Helena, Montana

Patterns of Human Population Growth  Follow Development-  Initially high birth and death rates  Advances in sanitation/nutrition/healthcare – results in lower death rate  Education and living standards generally decrease birth rate.

Examples India  Second most populous country in the world  China is first  Experiencing Exponential growth Japan  Actually losing population –

Population Age Structure  Used to predict how it can grow- Uses-  # of people of reproductive age  # of people nearing death (old)  Birth rates and death rates  Immigration and emigration  Why would this be important for humans to know the age structure?