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.

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