1. Density-Dependent Limiting Factors

2. So what in the world is a density-dependent limiting factor??
Density-dependent: something that depends on the amount of organisms in a unit area. (5 examples to follow)

3. Competition
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

4. Predation
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

5. Herbivory (Predation of Plants)
Plant and herbivore populations fluctuate just like the predator and prey populations

6. Parasitism and Disease
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

7. Stress from Overcrowding
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

8. Density-Independent Limiting Factors

9. So what is it?
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

10. Wait a second…is it really density dependent?
So what would happen after a drought?
No water so species will compete for the water
WAIT A SECOND MR. BLAUVELT! YOU’VE TRICKED US!

11. Sometimes a density independent factor can lead to a density dependent limiting factor like competition
What do you think??

12. Thinking back to logistic growth…
We said that something happens to stop populations from growing.
How do density-independent and dependent factors play into this?

13. Carrying Capacity
These limiting factors contribute to what is called carrying capacity
Defined as: the maximum number of individuals of a species an environment can support

14. On a graph…

15. Exit Ticket
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.