Photo by Chris Hammond
Dr. David Larson
Might a little insect give a warning if North Americas
ecosystems are under threat? Dr. David Larson of Memorial Universitys
Department of Biology thinks so.
The subjects of his research are predatory diving beetles (Coleoptera:
Dytiscide). According to Dr. Larson, these insects live primarily
in small temporary ponds whose water levels fluctuate a
lot, known as astatic ponds. They are of varying
The results of Dr. Larsons work was recently published
by the National Research Council of Canada in a book entitled
Predaceous Diving Beetles of the Nearctic Region. Dr.
Y. Alarie of Laurentian University and Dr. R. Roughley of the
University of Manitoba also coauthored the book. It treats the
adult and larval stages of all species of predaceous diving beetles
of North America, particularly those of Canada and Alaska.
Dr. Larson has been studying water beetles for most of his academic
career. I got into water beetles simply because I have
always been interested in insects it goes back as far
as the beginning of my PhD research, he remembered. Here
was a group of insects that were diverse and very fascinating
because they had a unique array of adaptations . . . and that
were not well known. Almost nothing had been written about the
habitats they lived in.
Taxonomy, also commonly known as systematics, is Dr. Larsons
field of specialization. The goal of taxonomy is to organize
biological diversity, Dr. Larson explained. In the
narrowest sense, its identifying and classifying organisms
and groups of organisms. You usually look at organisms on the
basis of their gross appearance: their morphology. That is what
taxonomy originally was.
However, taxonomy is now going through some fundamental re-evaluations
of its philosophy and method. Right now, [taxonomy] is
becoming broader in scope. People are using behavioural characteristics,
biochemical characteristics, virtually any characteristic that
you can find in organisms to compare them, looking for similarities
It is not only the inherent interest of such animals, however,
that has motivated Dr. Larsons taxonomic work. Through
his work, biodiversity and climate change can also be gauged.
There is a significance [to the research] related to understanding
biodiversity, he said. This significance is in grasping
the ecological dynamics of the beetles habitat. Astatic
ponds have tremendous biological significance because there is
a lot of productivity: a lot of insect life and plant life grows
there. They are important in nurturing waterfowl, as well as
a whole variety of other organisms.
The astatic pond supplies the beetle with one of its favourite
snacks: mosquitos. These beetles are probably one of the
major predators on mosquitos, Dr. Larson said.
Despite the importance of such insects in maintaining the ecological
balance, Dr. Larson told the Gazette that, We are still
in the process of finding out what species occur within the confines
of [Canada]. Once youve attained a list of whats
there, your next question is: Whats the geographical distribution?
The geographical distribution is interesting because it changes
over time no species has a static distribution. Their
ranges are always changing, they are in a state of flux in relation
to the environment.
With a better understanding of the biodiversity of the diving
beetles home ecosystem, pressures on the environment can
be better determined. Right now we are concerned about
environmental change; perhaps a global warming may be having
an effect, Dr. Larson pointed out. Changes in precipitation
patterns would certainly effect aquatic insects. By knowing the
ranges of these insects, we have a way of getting a fixed picture
in time as to where they occurred and can then use that to detect
changes that may occur.
Gaining this image of the ecosystem, Dr. Larson explained, is
done through studying the community structure of diving beetles
in a particular astatic pond: There are a lot of different
species and sizes [of diving beetle], each having its own particular
niche. You tend to find these species in more or less consistent
patterns that we call communities.
These communities of beetles tend to be quite stable across
areas. The communities tend to be related to features such as
the habitats stability, productivity, salinity, temperature,
etc. Within a given set of these parameters, you tend to find
the same association of beetles over and over again. It has been
found that looking at these associations gives you quite a good
predictor as to just what that habitat type is like. So they
are useful in classifying habitats and determining whether there
is a habitat change.
Unlikely allies in the search for a better understanding of environmental
change, but allies nonetheless.