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| | Food choices of the red imported fire
ant (Solenopsis invicta Buren)
Introduction
Organisms of all types make choices regarding innumerable variables every
moment of their lives. These choices are necessary to maintain the living
condition. In physiological terms this is referred to as homeostasis. The
concept of choice or preference is fundamental in all living systems. Species
constantly make many judgements of which food to eat, where to germinate,
how to grow, when to reproduce, who to eat, when to attack, when to flee,
and countless other decisions. Ants in general are no exception to this
rule (Hölldobler & Wilson 1990). In this laboratory we will examine
the choices seemingly made by red imported fire ants regarding food. We
will consider how many variables this actually encompasses and how to design
an experiment to isolate the variable of interest. The title of this exercise
seems straight forward, but I see it as quite vague. Our experimental design
and thus experiments need to eliminate the vagueness. Our experiment could
proceed along many lines of questioning and we will decide which lines we
will follow. An important reference for the various ways in which types
of data similar to these may be analyzed is Krebs (1998) and included references.
You should be able to find many other references by searching the primary
literature using such search tools as BIOSIS and other online services (UTNetCAT
2000).
Materials and Methods
Field collected ants were maintained in plastic trays the sides of which
were coated with Fluon (ICI Fluoropolymers, Exton, Pennsylvania 19341) to
prevent escape. They had been maintained for several weeks on an unrestricted
diet of crickets, mealworms, and sugar water.
Empty trays are available. Bridges between trays are available. We will
also have several potential food items which may be interesting to test
for ranked preference. Other equipment and supplies may be available upon
request.
In designing our experiment we need
to consider the concerns of pseudoreplication raised by Hurlbert (1984) as they
relate to non-independent experimental units. Indeed, we need to decide
what our experiment unit is.
A variety of analytical tools are
available to quantify preference. Krebs (1998) provides a good overview of
the indices that have been developed. You should consider which of these
indices, such as those proposed or suggested by Williams and Marshall (1938), Ivlev (1961), or Murdoch (1969) might be most relevant to the way we collect our
data.
Results
We need to obtain these. In raw form, they will consist of columns of data
summarizing the number of ants touching the food source at discrete
intervals. These data will be entered into a spreadsheet on a computer.
Literature Cited
Hölldobler, B. and E. O. Wilson. 1990. The
ants. Harvard University Press, Cambridge, Massachusetts.
Hurlbert, S.H. 1984. Pseudoreplication and the design of ecological
field experiments. Ecol. Monogr. 54:187-211.
Ivlev, V.S. 1961. Experimental ecology of the feeding of
fishes. Yale Univ. Press, New Haven, Connecticut, USA.
Krebs, C. J. 1998. Ecological methodology, 2nd ed. Addison-Wesley Educational
Publishers, Inc. Menlo Park, California, 620 pp.
Murdoch, W.W. 1969. Switching in general predators: experiments on
predator specificity and stability of prey populations. Ecol. Mongr.
39: 335-354.
Singer, M.C. 2000. Reducing ambiguity in describing plant-insect
interactions: "preference," "acceptability" and
"electivity." Ecology Letters 3:
Singer, M. C. 1986. The definition and measurement
of oviposition preference in plant-feeding insects. Pp 65-94. In Plant-Insect
Interactions (Ed. by J. Miller & T. A. Miller, Springer-Verlag, Berlin.
Singer, M. C., D. Vasco, C. Parmesan, C. D. Thomas,
and D. Ng. 1992. Distinguishing between "preference" and "motiviation"
in food choice: an example from insect oviposition. Anim. Behav. 44: 463-471.
UTNetCat. 2000. The Web-browsable online catalog of the University of
Texas at Austin. http://dpweb1.dp.utexas.edu/lib/utnetcat
Williams, C.S. and W.H. Marshall. 1938. Duck nesting studies,
Bear River Migratory Bird Refuge, Utah. J. Wildl. Manag. 2:29-48.
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