Overview
The Chicago Academy of Sciences conducts field studies each year at
selected sites throughout the Chicago region. Data from each sampling
visit is then summarized for each year by both location and species. Graphical
and statistical analysis is then done on data to try and draw some conclusions
What
Data do we Collect?
Each collector collects
the same data at each site. First, transects have been set up at each
location. A transect is an imaginary line though the study area where observers record the number
and species of butterflies at that site. Each site has 5 such transects
(labeled A-E).
How
Often Do We Sample?
Data collection
is conducted by many volunteers, so often the number of visits to a
given site in a given year is irregular. Some years, a site may not
be visited at all, while other years it may be visited 25 or more times.
This is also true for study sites in a given year--some sites may receive
more attention than others. When analyzing data, the number of visits
to that site should be taken into consideration.
At each
transect the number of each species seen is recorded. Unknown species
are also noted when they appear in a transect. Other supporting data,
such as weather conditions, habitat type, and time of day are collected
to help the scientists with any conclusions they might wish to draw about
trends seen in the data.
The data
for each site is combined into an annual summary which includes the
total number of different species seen at the site in that year, the
average number of visits at that site, the highest number of a given
species that was seen in one hour, and the total number of different
species that have been seen at the site since data collection began.
Study
Sites in the Chicago Area
Data
is collected at over 55 different sites in the Chicagoland area.
Data collected
shows the changes in numbers and kinds of species at each site. Not
every site was visited every year during the study period (1987-2000),
though some were.
View Graphs
of the following sites:
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Butterflies
in the Chicago Area
By
now you've learned about the species of butterflies that we focus on
in our butterfly lab. So what have we discoverd about them in the Chicago
area? Click on the links below to see how populations of these species
have changed since 1987. Remember, the data collected represents many
sites in the Chicago area, not just the city itself.
Once
the data is in a graph, you can study the line connecting the dots. Does
it go up? Down? Up and down? When does it go up or down? Why might it
do that? When you graph, you look at the result and try to figure out
why things happened the way they did. Once you have a new hypothesis (or
possible explanations for a trend, you can design new studies to test
your theories.
Conclusions from Data
While
some of the data you will see will show what appears to be a trend (i.e.
the population has increased over time), scientists must be careful
when assigning a cause or reason for the change. Wild animal studies
are often difficult to draw clear conclusions from because they are
not "controlled."
In statistics,
for example, to conclude significant changes have taken place (as opposed
to random chance events) requires a large sample size. Typically, a
sample size over 500. Butterflies at each site tend not to cooperate
in this regard and are often found in much smaller numbers. This makes
it harder to eliminate chance as a possibility.
Also, animals
move. This makes it difficult to determine whether a change is the result
of a true change in numbers (i.e. the population is smaller) or the
fact that some butterflies that were at the site last year traveled
elsewhere this year, but are still alive. Also, eggs may be laid in
one site one year, but those offspring may lay theirs in a different
location the following year.
Lastly, there is no easy way to provide a "control." Many
scientific studies have a control, or an organism that gets the same
treatment as all the others, except for the element being studied. For
example, if you were testing for a plant's toxicity in the lab, every
butterfly would be exposed to the same conditions (light, humidity,
temperature, etc.) except the type of food they would get. Then
the "control" butterflies would get their natural food, while
the test subjects would be fed the unknown, possibly toxic, plant. When
a change occurs in the wild, it could be the result of many different
variables. Without a control it is difficult to determine which one
is truly causing the change.
This is not to say that our data is useless! It just means that any
changes seen need to be carefully considered, and new tests designed
to further verify any conclusion. Without this data, we wouldn't have
any way of knowing if a change was taking place at all.
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