SKILL FOCUSInitiating and planningHypothesizingIdentifying variablesPerforming and recordingAnalyzing and interpretingInvestigation
DESIGN YOUR OWN
13 • B458 MHR • Unit 5 Population Dynamics
Problem
How are model ecosystems used to investigate the
impact of various environmental factors on the
production of biomass at various trophic levels of an
energy pyramid?Hypothesis
Devise a hypothesis about how one or more specific
environmental factors may affect the productivity and
biomass of each trophic level within a specific type of
ecosystem.CAUTION: Treat all of the organisms you have
selected with care and respect. Wash your hands
after handling the organisms.Materials
From your procedure, develop a list of required
materials. Be sure to include an appropriate number of
equal-sized containers for your ecosystem simulations.The ecosystem in this aquarium shows three trophic
levels (primary producer, consumer, and detrivore). There
is also an invisible fourth trophic level. Can you identify it?Experimental Plan
1.For this investigation, organize yourselves into small
work groups. Each group will be responsible for
investigating how a specific variable (such as light
intensity) affects some aspect of its model
ecosystem. Groups may wish to co-ordinate their
efforts by testing different ranges or values of the
same variable. This approach will generate a wide
range of data for analysis regarding the impact of a
single variable. Alternatively, work groups may
choose to investigate different variables —
generating a variety of data about the impact of
different variables. Whichever organizational strategy
you select, each group will prepare one control
set-up and a minimum of two experimental set-ups
for the investigation.
2.Use containers to set up terrariums or aquariums
that will serve as simulated ecosystems for your
investigation (each set-up should be identical).
Select organisms (such as phytoplankton,
zooplankton, snails, aquarium plants, and small fish
species) that will inhabit the ecosystems. A typical
ecosystem consists of three to four trophic levels.
3.Identify the organism(s) in each trophic level and
draw a food web of your ecosystems. Include less
obvious organisms (such as bacteria and fungi) that
form important links in the food web.
4.Identify a specific limiting factor or variable, such
as the intensity of light, temperature, fertilizer, or
specific nutrient that will impact the productivity
of your model ecosystems. Make this your
independent (manipulated) variable.
5.Identify the other factors or variables to be
controlled; that is, those that must remain the
same in each of your ecosystem set-ups.
6.Design a procedure to test the effect of the selected
experimental variable on productivity and biomass.
This procedure should allow for quantitative
measurement of changes in biomass production in
each ecosystem. Select an appropriate parameter
to be measured, such as transparency of water, pH,
CO 2 concentration in aquarium water, population
samples of micro-organisms, and so on.Ecosystem Productivity
Various vital environmental factors (such as sunlight, water quality, nutrient
availability, and temperature) influence the variety, distribution, and productivity
of autotrophs within an ecosystem. In this investigation, you will devise model
ecosystems and use them to study the impact of specific environmental factors
on the productivity of various trophic levels of a food web. You will also investigate
how energy flows through the various trophic levels in these ecosystems.