Predation and Populations
Introduction:
Predators affect populations by taking out the individuals that do not fit with their environment. Individuals that are too slow, injured or sick, or do not have good camouflage will be removed from the population by a hungry predator. Individuals that blend into their environment and have traits that allow them to avoid predators survive.
If an individual in a population is eaten, their genes will not be passed on to the next generation. In this way, the genetics of the population changes. This is the basis for evolution.
Before we begin, we will need to define some important genetics terminology:
Alternative forms of a gene are called alleles.
The genetic constitution of an individual is called its genotype.
The physical expression of a genotype is called the phenotype.
If two alleles are identical, an individual is said to be homozygous for that gene; if two alleles
are different, the individual is said to be heterozygous.
A dominant allele has such a strong phenotypic effect in heterozygous individuals that it
conceals the presence of the weaker (recessive) allele.
Purpose:
The purpose of this lab will be to learn how the genetics of a population change due to environmental pressures such as predation.
Materials:
Tray with a smaller tray of salt
Beaker of red beads
Beaker of white beads
Beaker of pink beads
A pair of tweezers
A wire net
Procedures:
1. Gather the materials from the teachers desk
2. Choose persons in the group that will act in the following capacities:
1 person to be the predator.
1 person to be the timer.
1 person to be the recorder.
3. The jobs are simple, but you MUST NOT CHANGE JOBS AFTER THE LAB STARTS!
4. As a group, count out 10 white beads 20 pink beads and 10 red beads. These represent animals and the salt represents the environment.
5. Predict what will happen in the hypothesis section of the lab.
6. These beads must be hidden randomly in the tray of salt while the person who is the predator is NOT LOOKING. It is best if the timer and recorder do not "clump" the beads in a particular area so that they will not easily be found. Record the beginning population in the data section of your lab.
Read 6 -10 before beginning predation:
7. The timer will tell the predator to begin "preying" on the population of animals hidden in the salt tray. The predator will have 45 seconds to prey on the animals and remove all that they find from the environment. Place the beads in the larger tray so they don't roll all over the place.
8. The predator will only be able to remove the animals from the environment by using the tweezers. YOU CANNOT USE YOUR FINGERS OR ANYTHING ELSE TO FIND THE ANIMALS!
9. When the timer says, "STOP", the group will use the wire net to get all remaining animals (beads) out of the environment for counting. Make sure to record the totals for the year's predation in the Data Section of the lab. Figure the percentages for each color for each year.
10. The animals that are remaining will be allowed to breed. Each survivor will randomly breed therefore; the percentage of organisms will stay the same. For example, if you have 10 white beads, 7 pink and 2 red, the next year you will double each of these numbers to 20, 14, & 4.
11. Repeat 6-9 for the second year of predation.
12. After recording the information in your Data Section, repeat the steps 6-9 for four more generations to fill the data section.
13. Answer questions 1- X in the Question Section of the lab.
Hypothesis:
_We believe that______
______
Data Section:
Population White% White Pink % Pink Red % Red Total# Total %
1st Year 10 25% 20 50% 1025% 40 100%
Begin second 16148
Begin third20124
Begin fourth26142
Begin fifth26120
Questions:
1. What is the major reason that the numbers changed from the initial year to the last?
______
______
2. Did the total number of animals in your population change? ______If so, in which way? ______. Graph your results of the total of the graph provided.
1 2 3 4 5
3. What would you expect to happen to the total numbers of your population over another 10 years of predation? ______
______
4. How might a population be changed if predation was heightened?______
______
decreased?______
Analyze the following graph and then answer the questions that follow:
100
50
0
0 1 2 34 5 6
5. What happens to the population of the predator as the population of the prey fluctuates from high numbers to low numbers:______
______
______
6. What would you think would happen if the population of predators were affected by an outside thing such as ranchers killing them off?______
7. Conversely, if the prey animals were affected by something like Lime Disease, a disease that affects ruminants such as deer, what would be the effect?______
A population of deer had three distinct colorations dark brown fur and a lighter tan. The dark brown is dominant. If they live in a temperate forest with thickets and clearings, they will have a population with about 32% recessive (tan colored animals). Due to a forest fire that cleared many of the larger thickets the percentage of tan individuals increased to 64%.
8. What is the population of the dark brown deer before and after the forest fire?
DarkLight
Before:______After:______Before:______After:______
9. Does this show evidence for evolution taking place? Why or why not?:______
______
______