Measures of Abundance
Various approaches can be used to summarize the abundance
of mosquitoes in an area. The number of mosquito eggs laid
within a trap of the sort we use in this study is an
example of the use of a relative measure of abundance. We
obtain a number that is useful in comparing different areas
or habitats, or for tracking changes through tim, but it
does not tell us the number of mosquitoes per unit area or
volume of habitat, because we don’t know how many
mosquitoes within the habitat were actually drawn to the
trap, and how many were not. Nonetheless, we can still talk
about density of eggs within the traps themselves, so using
the trap as our habitat, the mean density, or average
number of eggs per trap, gives us a way to describe each
site relative to the others.
The choices made by our students could have a strong
influence on mean density. Mosquitoes use environmental
cues to make decisions about how permanent a container of
water is likely to be, as well as whether it is likely to
have enough food to support her offspring through their
development. A trap in the middle of the parking lot of an
apartment complex is not going to attract as many female
mosquitoes looking for good habitats for their offspring as
a trap set in a damp, dark forest. So, locations of traps
can affect the mean density.
A way to avoid this possible problem is to let the
mosquitoes determine which habitats are suitable, and to
try to measure the degree of crowding that the mosquitoes
experience. If we count, for each individual, the number of
neighbors they share their habitat with, and average this
for all the individuals, then our measure is not affected
by traps that are laid in places that mosquitoes cannot
reach or that they may find unacceptable. This measure of
mean crowding may actually provide a better description of
the conditions experienced by the typical developing
mosquito larva, and it is at the larval stage that
mosquitoes are most likely to experience competition for
food. We provide sample calculations for mean density and
mean crowding here.
