# Population Density kendricknovak

Document Sample

```					What kind of plants do we see in a
climax community?
Agenda for Thursday May 26th
1. Communities and populations notes
2. Random sampling lab
Community
• Def. – a group of interacting populations that
occupy the same area at the same time

• Different organisms occupy different biomes
Communities
• Limiting factors – any biotic or abiotic factor
that limits the number, reproduction, or
distribution of an organism
– Sunlight, food, temperature

• Tolerance – ability of an organism to survive
when subjected to abiotic or biotic factors
– Upper and lower limit = range
Recall…
• Populations – members of a single species that
live in once place at a single time
Population Characteristics
• Population Density – # of organisms per area

• Dispersion – pattern of spacing of a population
within an area
– Based on available resources (food)
– 3 types
• Uniform
• Clumped
• Random
Dispersion Pattern: Uniform
Dispersion Pattern: Clumped
Dispersion Pattern: Random
Dispersion
• Smaller animals usually clump
– Larger animals usually independent
– Fish

Q: What advantage do smaller fish (animals)
gain by forming schools (clumped groups)?
Safety, confuses predators
Q: Which type of population distribution allows
you to predict more accurately how many
individuals reside in a given area?
Determine how many oak trees are
in the forest using the random
sampling technique. Use the grid.
7
Agenda for Friday May 27th                   3
1. Quiz                                  5
8       7
2. Population sampling
techniques
1. Mark and recapture
Question
If you were in charge of a team given the
responsibility to determine the number of
sunfish in Horseshoe Lake, discuss with a
partner how would you accomplish this task.
Sampling
• A technique called sampling is sometimes used to
estimate population size.

• Organisms in a few small areas are counted and
projected to the entire area.

• Example: A biologist counts 10 squirrels living in a
200 square foot area, she could predict that there
are 100 squirrels living in a 2000 square foot area.
Questions
1. A biologist collected 1 gallon of pond water
and counted 50 paramecium. Based on the
sampling technique, how many paramecium
could be found in the pond if the pond were
1,000 gallons?

2. What are some problems with this
technique? What could affect its accuracy?
Mark and Recapture
• Biologists use traps to capture the animals alive
and mark them in some way
– Animals are returned unharmed to environment
• Animals trapped and data is taken on how many
are captured with tags
• A mathematical formula is then used to estimate
population size
Formula for Mark and Recapture

• Ecologists marked 20 bears in an area. Over 5
years they captured 100 bears. Of those 100
captured 50 had a tag. What is the population
of the bears?

Population estimate = (total number captured) x (original # with mark)

(Total number captured with mark)
What is mark and recapture?
Agenda for Tuesday May 31st
1. Mark and recapture notes and lab
2. Finish population notes
Mark and Recapture Concerns
• Capturing the animal could injure the animal or scientist
• Disturb animal's normal behavior pattern
• The marks used to track the animals, such as ear punches, may
cause injury to the animals or get lost between captures
• Marked animals may be more or less attractive to predators
because of markings
• Assumes all animals require the same effort to get caught,
– might catch the weaker or younger animals more
• Some animals learn to fear the traps and avoid recapture
– or become trap-happy and attempt to get caught when they
learn there is food involved and that they will be re-
released
Population Ranges Limiting Factors
• Abiotic conditions
– Temperature
– Humidity
– Rainfall
– Sunlight
• Biotic conditions
– Predators
– Competitors
– parasites
Density independent factors
Def. – any factor that does not depend on the
number of organisms in a population in a given
area

• Abiotic
– Weather – drought, flooding, extreme heat/cold,
– Water
– Fire
– Sunlight
Density Dependent Factors
Def. – any factor that depends on the number of
organisms in a population in a given area

• Biotic factors
– Predation, disease, parasites, competition
Predation
• More members of a population = more predators
Disease/Parasites
• Outbreaks of disease tend to occur when
population size has increased
– Disease is transmitted faster
– True for humans as well as animals
• Parasites increase at higher densities
Competition
• When resources become limited animals
compete
– Within a population or between 2 different species
– Lead to starvation – population can decrease
Population Growth Rate
How do we figure out population growth rate?
• Must know birthrate and mortality
• Emigration – moving out of a pop.
• Immigration – moving into a pop.
– Immigration rate = emigration rate

• Calculating growth rate
=(population at end – population at beginning)
Population at beginning
Different Growth Rates
What is a density dependent factor?
What is a density independent factor?
Agenda for Wednesday June 1st
1. Finish notes
2. Human pop. Graphing
3. Biodiversity
Exponential Growth Rate
• Starts slow – few organisms
• Faster because all organisms
are reproducing

• Rarely happens
– WHY?
– Limiting factors – food, space
Logistical Growth Rate
• Logistic growth occurs when a population’s
growth slows or stops following exponential
growth
– Carrying capacity
Carrying Capacity
• Maximum number of individuals that an
environment can support for the long term
– Limited by energy, water, oxygen, nutrients available

• Population grows until carrying capacity
– Births outnumber deaths
– Exceed carrying capacity then deaths outnumber
births
Reproductive strategies
R-strategy (rate strategists)
• Produce as many offspring as possible in a short
time
– Little energy in raising young

K-strategists (carrying capacity strategy)
• Few offspring that have a better chance of living
– Expend a lot of energy raising young
Human Population Growth
Trends in Human Population
Growth
• Was slow and stable

• Recent increase in growth
– Technology – agriculture, medicine, shelters

• Developing countries add more than
developed countries
More trends
• Zero population growth
– birth rate + immigration rate = death rate +
emigration rate

• Age structure
– # of males and females in three age groups
• Pre-reproductive (0-19), reproductive (20-44), and
post –reproductive (45-80+)
Human Carrying Capacity
• Humans have a carrying capacity

• Technology allows an increase in carrying
capacity

capacity
– resources being used
Describe what is happening to the
population in the graph below.
Agenda for Wednesday Jan 26th
1. Finish Notes
2. Human pop. graph

```
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
 views: 7 posted: 10/10/2012 language: English pages: 41