The Biological Budget
“The most striking feature of Earth is the existence of life, and the
most striking feature of life is its diversity” (Tilman 2000).
According to E.O. Wilson (1999), one species will become extinct
every 20 minutes. Coral reefs and rainforests are among the most
diverse ecosystems, but habitat loss and rapid environmental
changes are threatening these ecosystems and the Earth’s
biodiversity.
The ecosystems represented in this version of the biological budget
are coral reefs, mangrove forests, and seagrass beds. We start by reviewing the
different players in a food web including predators, herbivores, detritivores, and
autotrophs.
Figure 1. Biological budget worksheet.
Directions
1. The goal of this activity is to construct a balanced ecosystem with a budget of
1,000 energy points by putting together a food web connecting predator with
prey and prey with producer. In other words, the sum of all your organisms must
total 1,000 energy points. The energy amount is listed underneath each
organism on the critter information sheet (Figure 3). The object of the activity is
to make your ecosystem as diverse as possible while making sure everything in
the ecosystem is sustained (fed). On your poster, use markers, crayons, and
other materials to create a habitat for your organisms.
2. Points will be awarded for number of organisms (diversity), number of different
interactions between organisms, how well you use your budget (you want to use
all of your budget), and the sustainability of the food web (ecosystem)—meaning
everything should be fed the correct food source and amount.
3. Each organism has an energy amount associated with it, for example,
zooplankton = 10 energy points and jellyfish = 20 energy points. Therefore, you
will need to purchase two zooplankton to support one jellyfish. Each
zooplankton will then need one phytoplankton (1 phytoplankton = 10 energy
points).
4. Start with a simple food chain. Decide whether you are going to start from the
bottom of the food chain or the top of the food chain. If you are going to start
from the bottom of the food chain, you will need to pick out an autotroph. If you
are going to start from the top of the food chain you will need to pick out a
predator.
5. If you are starting from the bottom of the food chain, find out what eats your
organism. If you are starting from the top of the food chain, find out what your
organism eats. Read the critter information sheets (Figure 3) carefully to find out
your organism’s food source and its energy amount.
6. After you have put together your food web, add up your energy points on a
separate sheet of paper. You will need to turn this in, so make it neat and
legible. If you are under budget, you will need to add more organisms to their
ecosystem. If you are over budget, you will need to remove organisms.
Remember, you want to use as much of your budget as possible—Don’t waste
any energy!
Note: Make your ecosystem as diverse as possible. For example, if a fish requiring 60
energy points feeds on crabs (20 energy points), lobsters (20 energy points), and clams
(20 energy points), then have that fish eat all of those things rather than just eating
three crabs (3 x 20 energy points = 60 energy points).
Scenario #1: Energy transfer throughout the food web
Looking at your food web, what types of organisms are necessary for the rest of the
food web to exist? __________________________________
Label these organisms in your food web.
Scenario #2: Importance of biodiversity
There is a large die-off in seagrass due to changes in water quality. What would happen
to the rest of your organisms?
Count and write down the total number of different organisms (species richness) found
in your ecosystem. ______________
Remove every individual of one type of organism (e.g., all seagrass) from your
ecosystem by circling them and then record what will happen to the rest of their
ecosystem. Be specific.
Scenario #3: Interaction of organisms
In this scenario, there is a rapid die-off of coral due to mass bleaching and disease. Every
organism has an essential role in an ecosystem, and changes in one part of an
ecosystem often result in changes in other parts of the ecosystem. Some organisms are
considered specialists (e.g., long-nose butterflyfish only feed on live coral) and other
organisms are generalists (e.g., grouper eat a variety of organisms). A specialist is highly
adapted to a specific food source and can usually out-compete other organisms for their
prey. However, because they are dependent on that organism for food, if their prey
decreases in abundance, the specialist may have trouble finding food. Generalists, on
the other hand, may not be able to compete with other organisms for certain prey
items, but they can choose from a variety of organisms.
Label an animal in your ecosystem that they consider to be a generalist and one that
you consider a specialist.
Explain which one of your labeled organisms would have a better chance of survival.
Scenario #4: Impact of humans on marine habitats
We, as humans, affect the structure of food webs in many ways (e.g., removing top
predators, introducing invasive species, decreasing water quality, destruction of
habitats, climate change, and so on). In this scenario, overfishing of a habitat has
resulted in the removal of all groupers and snappers. What has happened to your
ecosystem?
Scenario #5: Diversity of marine habitats
Marine habitats (e.g., coral reefs, mangroves, seagrasses) are interconnected. For
example, animals that live on the reef (e.g., parrotfish) may find some of their food on
seagrass beds. Therefore, nutrients are transferred between ecosystems. Also, detritus
from mangroves or seagrasses can be transported to other ecosystems. In this scenario,
mangroves have been removed due to coastal development. Mangroves are essential
nursery habitat for numerous marine invertebrates and fish. The removal of mangroves
results in the loss of fiddler crabs, blue crabs, spiny lobsters, horseshoe crabs, and
snook. The loss of mangroves also results in an increase of runoff, lowering water
quality in the local seagrass habitat and consequently reducing the amount of
seagrasses. Mangroves and seagrasses are the major contributers to detritus production
so there is also a reduction in detritus.
Eliminate one contributor to detritus (e.g., seagrass, algae, dead fish, or a bird) and
explain what happens to their ecosystem.
Calculating Diversity
The number of species in a community is always considered to be the species richness,
however different scientists and mathematicians have used different formulae to
calculate species evenness and diversity. The most common indices are Pielou's species
evenness and Shannon-Wiener's species diversity.
1. Count the total the number of species from your completed food web. This is
the Species Richness (S). Enter this value here: S = ___________. Take the
natural log of this number. ln S = ____________.
2. Total the number of individuals for all species. Enter this value here for Total
Number of Individuals (N). N = ____________.
3. Calculate the Relative Abundance (Pi) for each species. To do this, take the
number found for that species (abundance) and divide it by the Total Number of
Individuals (N). Repeat for each species.
4. Take the natural logarithm of the Relative Abundance. Repeat for each species
and write in column D.
5. Multiply the Relative Abundance, Pi, by the natural logarithm of Relative
Abundance. Write answer in column E and repeat for each species.
A
B
C
D
E
Species
Abundance
Relative abundance (Pi)
ln(Pi)
6. Species diversity is a measure of the number of different species in an
ecosystem. High diversity means that there is a high degree of uncertainty in
predicting the next organism you will see in the ecosystem. A low ShannonWiener Index of Diversity means a high degree of certainty in predicting the
next organism, meaning there are few chances of crossing paths with anything
else. Shannon-Wiener Index of Diversity ranges from 0.0 to approximately 4.6
A value of 0.0 means that every organism in the sample is the same species and
4.6 means the number of individuals are evenly distributed among numerous
species. The values in the middle are not terrifically descriptive and must be
interpreted with care.
Add all of the numbers in Column E and multiply by -1. This is the Shannon-Wiener
Index of Diversity (H'). Enter this value here: H’= __________________.
7.
Species evenness is a measure of biodiversity which quantifies how equal the
populations are numerically. So if there are 40 foxes, and 1000 dogs, the
population is not very even. But if there are 40 foxes and 42 dogs, the population
is quite even. The evenness of a population can be represented by Pielou's
evenness index:
Pi *ln(Pi)
Where H' is the number derived from the Shannon-Weiner diversity index and H' max is
the natural log of the total number of species found. The less variation in populations
between the species, the higher E is.
Divide the Shannon-Wiener Index of Diversity (H') by the natural logarithm of
Species Richness (S) that you calculated in 1. This is the Pielou's Species Evenness
(E). Enter this value here: E = ______________.
Assessment
Your assignment will be assessed based on project participation, as well as scenario
responses and your final food web.
Food web criteria
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Sustainability—All animals in the food web are fed the correct food source and
amount (i.e., have the correct number of energy points).
Diversity—The number of different organisms in their food web (species
richness).
Interactions—The number of interactions between organisms (i.e.,
predator/prey).
Presentation—Organization and appearance of food web
Budget—the sum of all their organisms should total 1,000 energy points
Diversity— The Shannon-Wiener Index of Diversity will be evaluated for
maximum diversity of your ecosystem.