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Density-Dependent Limiting Factors
Get yourself into 6 groups of 4-5 students per group
Once you find your group, sit at a table You have 30 seconds
Activity
Food Station◦ You will have one piece of “food” to share equally
between you and your group members◦ 3 stations to go to A,B,C-Rotate through them all◦ Make notes on your worksheet
Shelter Station◦ On the ground you will see 3 “shelters”◦ You must stay in the “shelter” for 3 minutes◦ If you are loud, you’re out◦ NO SHOVING! You will be out if you shove anyone◦ Rotate through all 3 stations◦ Make notes on your worksheet
Activity!
So what in the world is a density-dependent limiting factor??
Crowded populations mean the individuals have to compete for food, water, space, sunlight, or anything else necessary for survival and reproduction
Some may have enough to survive, but can’t raise offspring
Some may die of starvation The more individuals in an area, the faster
resources are used up Could be between individuals of the same
or different species
Competition
Predator-prey relationships tend to fluctuate (go up and down)
If there is a lot of prey, the predator can eat more, increasing the number of predators
If the prey decreases too much in population, there won’t be enough food for predators and so the population of predators decreases
Predation
Plant and herbivore populations fluctuate just like the predator and prey populations
Herbivory (Predation of Plants)
Parasites and disease causing organisms feed at the expense of the host
This can weaken or kill the host The larger the population the easier it is for
the parasite or disease to travel through hosts
Parasitism and Disease
Some species will fight amongst each other if they are overcrowded
This fighting can cause stress leaving individuals susceptible to disease
In a few species, overcrowding can cause females to neglect or kill their own offspring
Stress from Overcrowding
Organize the following words into 3 categories◦Density Dependent◦Density Independent◦I’m not sure
Word Splash
A hurricane Famine A disease kills half of
the population A forest is cleared by
a logging company The plants that one
species really likes has only grown half as much as usual
An early frost kills cherry trees
There is an unusually large population of wolves that eat a lot of rabbits
Territorial lions start fighting each other for habitat space
The weather has been unusually dry so the watering hole has dried up
So what did your density-independent factors have in common?
Density-Independent Limiting Factors
A factor that affects all populations in similar ways, no matter the population size or density
It includes things like: Hurricanes Droughts Floods Natural Disasters
So what is it?
So what would happen after a drought?◦ No water so species will compete for the water
WAIT A SECOND MS. JOHNSON! YOU’VE TRICKED US!
Wait a second…is it really density dependent?
Sometimes a density dependent factor can lead to a density independent limiting factor like competition
What do you think??
We said that something happens to stop populations from growing.
How do density-independent and dependent factors play into this?
Thinking back to logistic growth…
These limiting factors contribute to what is called carrying capacity
Defined as: the maximum number of individuals of a species an environment can support
Carrying Capacity
On a graph…
On a sheet of paper, write a paragraph explaining whether or not you think that density independent factors should be considered separate from density dependent factors.
Explain your answer using information from today.
Exit Ticket
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