Population Dynamics and Growth Pre AP Biology Spring ‘12.

Population Dynamics and Growth

Pre AP Biology

Spring ‘12

Competition

• Competition occurs when 2 or more species use the same resource.

• Examples of the resource are:– Food– Light– Space– Shelter– Water– Nesting sites

Limiting factors

• Limiting factors are the biotic and abiotic factors in an ecosystem that limits the existence, numbers or reproduction the organisms in that environment.

Popu l a t i on Low ENVIRONMENTAL FACTOR High

Zone of stress optimum conditions stress zone of Intolerance intolerance

Limiting Factors• Examples of limiting factors:• Temperature: organisms have an optimum

temperature range in which they can survive.• CO2 levels• O2 levels• Humidity• Amount of sunlight• Prey availability• Mineral availability

Kinds of Limiting Factors

1. Density-dependent – has an increasing effect as population increases. Usually biotic.

ex: disease, parasites, competition for food

2. Density-independent – has an effect on all populations regardless of their population. Usually abiotic.

ex: sunlight, temperature

How Predation Helps

• Predators help keep population size within the limits of available resources.

Limiting factor graph (example)

• Graph the temperature tolerance for 2 species of plants (aloe vera and ivy). The data is in sets of three:

A, B, C A = temperatureB = number of aloe veraC = number of ivy

Use 2 different colors. Remember every graph needs a title, x and y axis labeled, and a legend

Data• 0,0,0;• 10,0,0;• 20,0,2;• 30,0,10; • 40,2,20; • 50,5,40; • 60,10,60; • 70,12,70; • 80,30,60 • 90,50,30;• 100,40,10;• 110,20,2• 120,5,0• 130,0,0• 140, 0,0

Population Growth

• Population growth is a change in population with time

• 3 kinds of growth graphs:– Linear growth– Exponential growth– Logistic growth

Logistic is most common

• Linear growth almost never occurs. It assumes the exact same rate of growth. (If every 2 people had 3 children…we’d replace ourselves + 1)

• Population growth is sometimes exponential if resources are unlimited

• Logistic growth is the most common because it represents exponential growth until resources limit growth and it levels out.

Carrying capacity

• Carrying capacity – number of organisms of a population that an environment can support

2 kinds of strategists or patterns of population growth:

r-strategists

k-strategists

R-strategists

• Have a rapid period of population growth• The rapid growth far exceeds carrying

capacity• Rapid growth followed by a crash• After the crash there is another period of

rapid growth, etc.• This organisms have many offspring, don’t

care for their young, and have short life• Examples: bugs and fish

K-strategists

• Have a long period of slow growth

• Then they reach the carrying capacity.

• At that point they have minor fluxuations in growth around carrying capacity.

• They have few young, a long life, and tend to take care of their young.

• Examples: most mammals

Homework

• Answer the following questions about the graph.

1. Give the zones of intolerance for aloe vera and for ivy?

2. What is the optimum temperature for aloe vera?

3. Which plant grows better outside in South Texas?

4. How could a person who owns a gardening store use this information?

Pre AP homework

• 5. Read page 370 and answer question #2 and #3 on page 370. I expect more than a sentence answer. Your answers should fill more than a half a page.