ED-STEEP: Education Solutions to Environmental
and Economic Problems
Biodiversity of Soil Invertebrates
Subjects
Biological Sciences, Environmental Sciences, Agricultural Sciences
Introduction
Biodiversity refers to the abundance and variety of organisms, genes, and communities in nature,
and is an essential concept for students to understand. In this lesson, students will define
diversity, discuss it’s importance, and conduct an experiment to compare the biodiversity of two
habitats. Students will extract soil invertebrates from litter and soil samples, sort their catches
into groups, calculate diversity, and analyze their data. The Berlease funnels and Baermann
funnels used to extract soil invertebrates are inexpensive and easy to construct. Students will be
fascinated and surprised by the diversity and kinds of animals that live in soil. Related lesson
plans include the following:
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Biodiversity of Ground-dwelling Arthropods
Soil Organic Matter
Soil Organic Matter and Biodiversity
Soil Chemistry and Physics
Relevant STEEP Research Projects
Scientists at University of Idaho have been studying the effects of crop systems on soil
invertebrates. Here are some highlights of their research:
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Earthworms are more prevalent in no-till cropping systems, particularly no-till pea fields
with barley residue.
The abundance of other macrofauna were similar in no-till and conventional tillage cropping
systems.
The greater abundance of earthworms in no-till cropping systems is related to the greater soil
nitrogen and carbon content of no-till soils.
Earthworm populations were higher in the spring in no-till fields, mostly likely because of
better microclimates and food resources.
o Assessing the impact of no-till and conventional-till on crop, variety, soil, insect, and
disease response, S. Guy, N. Bosque-Perez, S. Eigenbrode, J. Johnson-Maynard, and L.M. Dandurand, 2003 STEEP Progress Report.
o Examination of tillage factors, crop type, soils and non-crop habitat upon soil fauna and
ground dwelling predators in a small inland PNW watershed, J. Johnson-Maynard, T.D.
Hatten, N.A. Bosque-Perez, and S.D. Eigenbrode. 2004 STEEP Annual Progress Report.
o Assessing the impact of direct seeding (no-till) and conventional-till on crop, variety,
soil, and insect responses. S.O. Guy, N.A. Bosque-Perez, S.D. Eigenbrode, and J.
Johnson-Maynard, 2004 STEEP Annual Progress Report.
Objectives
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Students will define biodiversity, and discuss its causes, consequences, and importance
Students will discuss the types and function of soil invertebrates
Students will classify soil invertebrates into taxonomic groups
Students will estimate the diversity of soil invertebrates in two different habitats
Students will determine the effect of habitats on biodiversity of soil invertebrates
Major Concepts
Biodiversity, Classification, Invertebrates, Soil Ecology, Terrestrial Ecosystems, Scientific
Method
Standards
AAAS Benchmarks
Idaho State Science Standards
Oregon State Science Standards
Washington State Science Standards
Materials
Print Resources
 Biodiversity Fact Sheet
 Choosing a Sample Site and Preparing Soil Samples
 Soil Invertebrates Fact Sheet
 Soil Organism Picture Guide (MS Word document)
 Soil Organism Picture Guide (PowerPoint document)
 Constructing a Berlese Funnel for Collecting Soil Invertebrates
 Constructing a Baermann Funnel for Collecting Soil Nematodes
 Scientific Experiments and Publication Formats for Lab Reports
 Constructing Bar and Line Graphs
 Student Data Sheet
Collecting soil samples
 Soil and litter samples from 2 or more habitats (1 sample per student group)
 Shovels or trowels
 Ruler
 1-quart plastic baggie per sample
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Markers
Soil Invertebrates
 Trays or large sheets of paper for hand-sorting soil samples
 Berlese funnel (1 per group) and collection vessel with alcohol
 Baermann funnel (1 per group)
 Test tubes (1 per Baermann funnel sample) and Pasteur pipettes
 Water-agar plates for counting and examining soil nematodes
 Plastic petri dishes for examining invertebrates in alcohol
 Forceps, slides, etc., and microscopes for examining invertebrates
 Invertebrate picture key
Web Resources
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USDA National Resource Conservation Service - Soil Biology Primer. An introduction to
the living component of soil, intended as a resource for farmers and ranchers, agricultural
professionals, scientists, students, and educators.
USDA National Resource Conservation Service - Soil Quality Information Sheets. A series
of introductory fact sheets.
o Soil Biodiversity
Ecological and Ecosystem Diversity, National Biological Information Infrastructure
Biodiversity Fact Sheet, Ecological Society of America
General Procedure
The general producers involve collection litter/soil samples, extracting out invertebrates using
Berlese and Baermann funnels, sorting and identifying the invertebrates, recording data and
calculating diversity, and writing a report. Ideally, students should be allowed to collect soil and
litter samples in two or more different habitats. However, this depends on the availability of
suitable and readily available habitats, and the time of year. Many different kinds of habitats can
be used, including old fields, grasslands, alfalfa fields, no-till crop fields, and forests. The more
diverse the habitat and the more soil organic matter, the more abundant and diverse the soil
invertebrates. The time of year is also critical and is best done before November and after April.
Other times will also work depending on the local climate. If habitats are not readily available
and students can’t collect their own insects, then the teacher can easily collect enough litter/soil
samples for students. It takes less than a minute to collect a single sample. Students enjoy
making the Berlese and Baermann funnels for extracting the invertebrates, which should take
only 10-15 minutes. It takes about 3 days to extract nematodes from the soil samples, and it
takes about 1 week to extract other invertebrates with the Berlese funnels.
Procedures
1. Plan on about 2 weeks to complete the activity (actual class time is 1-3 periods).
2. Follow the instructions in Choosing a Sample Site and Preparing Soil Samples for collecting
litter and soil samples.
3. Present students with information on soil invertebrates (Soil Invertebrates Fact Sheet) and
biodiversity (Biodiversity Fact Sheet), or allow them to explore the topics on their own (see
Web Resources).
4. Working in groups, have students write down a testable hypothesis relating habitat to
biodiversity
a. Example 1 - biodiversity of soil invertebrates is greater in more diverse and complex
habitats because there are more food resources available
b. Example 2 – biodiversity of invertebrates is greater in forest soils than crop soils
because there are more plant species in forests to support more soil invertebrates.
5. Have students construct the Berlese and Baermann funnels
6. Have students place their own litter/soil samples in the Berlese funnels and allow 1 week for
the invertebrates to move into the collection vessels
7. Have students place their own soil sample in the Baermann funnel and allow 3 days to extract
out nematodes
8. Have students sort their samples into groups (see Soil Organism Picture Guide), count the
individuals, and record the data on the data sheets (Student Data Sheet )
9. Have the students calculate species diversity and prepare a Bar Graph showing their results
(Constructing Bar and Line Graphs)
10. Have students discuss results and conclusions, or prepare a formal lab report (see: Scientific
Experiments and Publication Formats for Lab Reports)
Assessment
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Student Worksheet
Student Lab Report
Questions:
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What is a “morpho-species” and why is it used instead of real species?
Which habitat had the most and least individuals?
Which habitat had the highest species diversity? Why?
What is the advantage and disadvantage of using species richness as an estimate of
diversity?
What would happen if the diversity of arthropods was suddenly reduced by 50%? 95%?
Does diversity affect soil processes, such as decomposition and nutrient recycling?
What is the function of the different soil invertebrates?
Notes:
Morpho-species are often used in biodiversity studies for two main reasons. First, many
individuals can not be identified to the species level because either experts are not available to
identify the species. Often, paraprofessional taxonomists are trained to recognize distinct
groups. Second, many individuals can’t be identified to the species level because the taxonomy
of many groups has simply not been worked out. In fact, most insects in the world haven’t been
identified to species.
Biodiversity researchers often try to relate the diversity of one group to the diversity of other
groups. Sometimes this can be done, but other times there are not clear relationships. For
example, the diversity of plants in a location or region is often highly correlated with the
diversity of grasshoppers. In contrast, sites with a high diversity of spiders, may not necessarily
have a high diversity of ants.