EcoBeaker Lab #1 - February 10-13
Part A: Oil Spills and Logistic Bacteria
Part B: Competitive Exclusion Principle
Objectives:
Part A:
1. Introduce concept of crude population growth rate and specific
population growth rate
2. Determine experimentally the effect of initial population size
on growth rates.
3. Determine experimentally the effect of varying efficiency of
food use on population growth rates.
Part B:
1. Introduce competitive exclusion principle and determine whether
it holds for an experimental situation.
2. Determine effects of varying initial population sizes of
competitors and resource availability on which competitor survives.
3. Determine conditions under which two or more species with
similar food requirements can coexist.
Procedures:
Part A:
1. Open the situation file Oil Spills and run the situation a few
times to see the response of bacteria (resetting the conditions
each time). Summarize what occurs. Your objective is to try to have
bacteria reduce the oil by 90% within 2 days from time zero. Does
this happen?
2. Compute and record the crude population growth rate (e.g. number
of bacteria at time t+12 minus the number at time t) for times t
near the start of the experiment, in the middle when population
size is the highest and towards the end. When is growth rate
highest?
3. Compute and record the specific population growth rate (e.g.
number of bacteria at time t+12 minus the number at time t divided
by number at time t) for times t near the start of the experiment,
in the middle when population size is the highest and towards the
end. When is specific growth rate highest? Do you get the same
qualtitative information from the specific growth rate as you do
from the crude growth rate?
4. Vary the initial number of bacteria. How does this affect the
time it requires to reduce the oil by 90%?
5. Vary the efficiency of each bacteria (amount of energy a
bacteria gets froma drop of oil). How does this affect the time it
requires to reduce the oil by 90%?
6. Summarize your findings and relate the terms "Intrinsic growth
rate" and "Carrying capacity" to your observations.
Part B:
1. Open the situation file Competitive Exclusion and run the
situation a few times to see the response of rabbits (resetting the
conditions each time). Summarize what occurs. Your objective is to
see if you can develop conditions under which two or more rabbit
species can coexist. Does this happen in these first simulations?
Does one species win each simulation, or do different species win
different times.
2. Vary the amount of resource (Lettuce) available by double-
clicking on Lettuce in the Species Window, clicking on Settlement
Parameters, and modifying the Number of Immigrants/Turn - this
gives the number of Lettuce leaves added each time period. Does
this affect the outcome of competition? Can you get more than one
species to coexist by varying this?
3. Vary the initial number of one of the species of rabbits by
double-clicking on one of the rabbit species, double clicking on
Settlement Parms and changing the initial number of rabbits given
by Number of Immigrants/Turn. Run the simulation a number of times
- compare your results to those obtained in #1.
4. Vary the Action Parameters for one of the rabbit species, such
as Speed, Cost of Living, etc. Rerun the simulations a number of
times. Do two or more species coexist?
5. Add a new food resource (Carrots) by changing its Number of
Immigrants/Turn to something greater than 0. Can you modify the
action parameters of the rabbit species so that two or more species
coexist now?
6. Summarize your findings and state clearly under what conditions
you could get two more species to coexist.
EcoBeaker Lab #2 March 10-13
Part A: Intermediate Disturbance Hypothesis
Part B: Island Biogeography
Objectives:
Part A:
1. Introduce concept of community succession as time course of
change in species present in community and how this is measured by
a diversity index .
2. Illustrate the effect of disturbance on succession.
3. Illustrate interdependence between disturbance frequency and
magnitude in effect on successional patterns.
Part B:
1. Illustrate island biogeography as equilibrium between
colonization and extinction.
2. Allow students to determine the effects of island size and
location relative to mainland on species colonization and
extinction rates.
3. Allow students to determine the effects of island size and
location relative to the mainland on which species are present on
the island.
Procedures:
Part A:
1. Open the situation file Intermediate Disturbance and run the
situation a few times to see the response of the community of
plants (resetting the conditions each time). Summarize what occurs
and how this is measured by the Simpson's Diversity Index. Your
objective is to see how modifications of fire frequency and spread
affect the successional pattern you observe.
2. Vary the chance of a fire starting to something above zero, and
run the simulation a number of times. Each time, does the diversity
index reach some relatively stable value? How does this value
change as you change the chance of a fire starting and how does
this diversity index relate to the bar chart showing the community
composition?
3. Vary the rate of chance of a fire spreading and run the
simulation a number of times. How does this affect the diversity
index?
4. Try to develop values for the two fire parameters that lead to
a community pattern in which all species are present at equal
frequencies (e.g. the bar graph is flat). How does this affect the
diversity index? Is there only one set of fire parameters which
leads to this, or can you get a variety of different ones which
each lead to a community pattern with all species present at equal
frequency?
5. The Intermediate Disturbance Hypothesis says that the highest
community diversity typically occurs at intermediate levels of
disturbance. State your opinion on this based upon your
experimental results and back up your argument using the data you
obtained.
Part B:
1. Load the situation file Island Biogeography and run the
simulation a few times to observe how the species on the island
changes. Your objective will be to analyze how island size and
position affect the number and type of species present.
2. Develop a method you feel is appropriate to estimate the number
of species present on the island. To do this you may want to
average the number present at particular times. Carefully write
down the method you are using and then use it for all the below
consistently.
3. Compute the number of species present on the island for a
variety of choices of island size and location (e.g. distance from
mainland). How does the number of species present depend on the
island size and location? Illustrate your results with appropriate
graphs.
4. Compute immigration and extinction rates for a variety of
different island sizes and locations. These give the number of new
species being added to the island per time period and the number of
species present on the island going extinct each time period. Again
you will need to develop a method to estimate these from the graphs
and do it consistently. Describe your method and summarize how
these rates were afected by island size and location.
5. Consider the species you found on the islands as you varied size
and location. Was there any consistent pattern as to some species
only present for large islands or ones far from the mainland or
some present for small ones or ones near the mainland? Summarize
your results here and give an hypothesis to explain your
observations.