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SYEFEST Activity: Nature Preserves: Is Bigger Better?
Hope College, 1994
Holland, Michigan
Contributor: Kathy Winnett-Murray
Starter Question: What is the effect of "nature preserve" size on the
diversity and abundance of organisms protected within the preserve?
Elementary Curriculum Objectives: For Michigan Essential Goals and Objectives for
Science Education (K-12): Constructing New and Reflecting on Scientific
Knowledge; Using Scientific Knowledge - Life Science: Organization of
Living Things, Evolution, and Ecosystems.
Ecology Themes:Scale, Communities and Human Impacts on Communities.
Grade Level: All.
Background:
A practical question confronting conservation biologists, politicians, and
the voting public is the design and management of nature preserves -
national parks, wilderness areas, wildlife refuges - any chunk of habitat
that has been set aside with at least one of the intentions being the
preservation of biological diversity. Biological diversity, or
"biodiversity" can be measured at various levels of biological
organization, the two most common being: a) species diversity, that is the
number of different kinds of species and their relative abundances, and b)
genetic diversity (the genetic variety present within a given species, as
well as among different kinds of species). Both kinds of variety are
critical for the maintenance of a healthy, viable population of organisms
and for the long-term health of an entire ecosystem (why?).
This exercise introduces students to the measurement of biological
diversity, the relationship between sampling effort and species diversity
(optional), also known as the "species-area curve relationship", and (most
importantly!) the relationship between habitat patch size and species
diversity. These relationships provide a model from which we will draw
conclusions about the design of nature preserves (habitat patches, if you
will).
How big should a nature preserve be? Most of us would reply intuitively
that "bigger is better" - but can we provide sound ecological reasons why
bigger is better? Challenge your students to think of some of these
reasons. All else being equal, a big preserve can hold more individuals
than a small one, on average. Much less obvious is the prediction that a
large preserve will also contain a greater variety of organisms, on average, than a small one. Why might this be so?
Materials:
- Hula hoops - about 80 cm diameter, 1 per group of students.
- Embroidery hoops - about 16 cm in diameter, 1 per group of students..
- Hand magnifiers (optional) if very small animals are to be included in
the census.
- Data sheets and clipboards - 1 set per student group.
Procedure:
- Locate a schoolyard habitat such as a patchy lawn or a weedy area.
Divide the class into groups and distribute the hoola hoops and embroidery
hoops. If the 80cm and 16 cm varieties are chosen, then you will have big
preserves 5 times the size of small ones and that's convenient for later
analysis.
- Each group throws the hoola hoop at random (throwers CLOSE EYES) and
censuses all living things inside by recording the type of organism and how
many of each. If you have a particularly diverse area, restrict the census
to just plants or just animals.
- Each group does the same thing with the embroidery hoop.
- It is not necessary to correctly identify all species but it is very
important that different groups choose consistent name for the same creatures so that they are recorded under the same name on everybody's data sheet.
- Tally the class results.
- Compare the total number of living things in big vs. little, the
number of different kinds of things in big vs. little, and the number in
each population. Discuss what a "viable" population might be for various
organisms, (e.g., if you have just one caterpillar in a reserve is that
likely to sustain the population over a length of time or are more
caterpillars (in more preserves) needed?
- For advanced students: Plot the cumulative number of species types
found on the y axis, and the number of plots sampled on the x axis. This
is called a species-area curve. It shows the importance of sample size,
among other things. If you get a graph that goes up, then levels off, this
means that at the corresponding number of samples, you are no longer
picking up new species even though you take more samples. This way, you
know how many samples it takes to get a very good notion of how many
different critters/plants are in the entire area. How many hoola hoop
samples does it take to reach this point? How many embroidery hoop throws?
What would you predict? This relationships reinforces the concept that
bigger will hold more variety, on average.
- Still more advanced, sort of: What if the conservationists and other
citizens are faced with the choice below:
- These two preserve "designs" have equivalent area, but one has the area
broken into 5 small chunks and the other has all of the area contained in
one large chunk. Which preserve system would contain the greatest variety
of species? Based on our mathematical intuition alone, we might conclude
that the sum of the species types found in preserve system 1 should equal
the number of species sampled in preserve system 2. However, in the real
world, the answer is: it depends. And what it depends on most, apparently
is a more complex understanding of the ecological ties in the habitats
involved. For example, if the big preserve, by virtue of being big,
contains a greater variety of landscape features (rivers, low areas, high
areas, wet areas, dry areas), then more species may be found there. On the
other hand, depending upon how spread apart the little preserves are, they
may encompass more different types of terrain.
- Still, you are left with the problem of smaller populations that can be sustained in each of the
smaller chunks. Get the picture? The answer may be complex and depends
a lot on the particular situation. Try it on your schoolyard and see what happens. If your school had $500 to buy wildlife preserves, would you spend that money in one big chunk and carefully select it (where would you put it on your schoolyard?) or would you buy 5 small pieces where would you put those?) Here is a good reason for having the hoola hoop measure 5 times
the diameter of the embroidery hoop!
Follow-up:
The same exercise can be done sampling bird species in a neighborhood.
This exercise uses the same 5:1 ratio for area sampled as the
hoola/embroidery hoop technique. A single "yard" can count for one small
preserve and 5 yards constitute a big preserve. Have groups of students
count and identify all of the bird species present in several large and
small preserves. (When I did this I enforced a rule of all census-takers
remaining on the front sidewalk - no walking into backyards, although they
were allowed to count birds that could be seen anywhere in the preserve).
Also, this is more scientific if you make a rule for when to sample large
and small - don't leave it up to the census takers. For example, Yard 1 =
first small, skip 2 houses, next 5 yards = large preserve , skip 2 houses,
then second small preserve, and so on.
References:
K. Winnett-Murray, Biology Dept., Hope College.
Please post any questions or comments in our Nature Preserves forum. We welcome your input.
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