Download Populations - Helena High School

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 studyagain 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
Japan
 Second
 Actually
most
populous country
in the world
 China is first
 Experiencing
Exponential growth
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?