Factors Affecting Population Numbers

Carrying capacity: the largest population of a species that an environment can support.

• 4 factors that determine the carrying capacity:

1. materials and energy (energy, water, carbon, and other essential nutrients

2. food chains: the population size is limited by the size of the populations at lower trophic levels. (Prey

are limited by their predators and their food supply).

3. competition: each organism has the same need as any other. They compete for resources such as food, water, mates, space.

4. density: depending on their size, environment and way of life, different species have different needs for space.

Competition:

Two types of competition:

1. intraspecific: among members of the same species

2. interspecific: between different species

Density:

• Two types of density factors can limit population sizes.

1. density-dependent factors: these are factors that increase as the population gets bigger and then eventually lead to a decrease in the population size by increasing death rate and lowering birth rate.

* overcrowding

*parasites/disease

*aggression amongst members

* neglect of offspring

• 2. density-independent factors:

can limit a population regardless of its original size.

* forest fire

* flood

* volcano

Population Growth• Since all organisms

reproduce, populations tend to grow over time

• If unlimited resources are present, growth will be exponential

• It will increase very quickly for rapidly reproducing organisms and more slowly for slowly reproducing ones

• The curve will be a “J” curve or an exponential growth curve

Generation # of bacteria time1 1 02 2 15min3 4 30min4 8 45min5 16 1hr6 32 75min7 64 90min8 128 105min9 256 2hrs10 51211 102412 204813 4096 3hrs14 819215 16,38416 32,76817 65,536 4hrs18 131,07219 262,14420 524,28821 1,048,576 5hrs22 2,097,15223 4,194,30424 8,388,60825 16,777,216 6hrs

Population Growth 2• Resources are never unlimited in

real life! • As population rises, resources

decline.• If the growth is too rapid,

resources are rapidly depleted and a population crash can occur

• This pattern occurs often with many populations (including humans)

Gypsy moth caterpillar

Population Growth 3• More often what happens

is that the resources slowly decrease, the growth rate slowly decreases, and they meet.

• This results in an S - shaped curve

• This sustainable population number that they keep returning to is the carrying capacity of the environment for that particular organism

Predator Prey Populations

• Predator Prey Populations means that the two populations are linked- a change in one population causes a change in the other population.

The Rabbit - Wolf Example • Year 1- 3000 rabbit and 5 wolves- the wolves have lots

of food so majority of their offspring survive• Year 2- 2000 rabbits and 15 wolves- many rabbits were

eaten by the wolves and more young wolves survive. (This is the closest we get to a perfect system- wolves are fed and keeping the rabbit population in check.)

• Year 3- 2000 rabbits and 25 wolves- not enough rabbits to feed the wolves. Rabbit population continues to drop and wolves begin to starve. Wolf population also drops.

• Year 4- Rabbit population begins to recover.• Year 5- Whole process repeats again.

Rabbit - Wolf Populations

As the population of rabbits grows, so does the population of wolves, until there are so many wolves that they overeat the rabbits, whereupon the wolf population begins to diminish. But once the wolf population diminishes, the rabbit population is able to begin growing again, and of course as it does so does the wolf population, in a cycle that never ends.

Human Growth Patterns

What are the causes of the rapid growth of human populations?What are some possible consequences of this growth pattern?What will our future look like? (Remember the Reindeer?)

Succession…Changes in the structure of a community of organisms; the

replacement of existing species by more recently arriving species.

Before

After

Primary Succession :

After a major disturbance such as an ice age, the rocks are bare, there isn’t even soil, so it is with great difficultly that the plants return and re-establish themselves.

Pioneer species:Pioneer species: the organisms that come first…

they will establish themselves on bare rock and start to change the

ecosystem!

Secondary Succession…

• This type of succession begins after a disturbance which doesn’t remove all of the vegetation. (Not down to the bare rocks)

Examples: forest firesdeforestationconstructionvolcanos