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(June 28, 2001, Gazette)

Unlikely allies

Dr. David LarsonPhoto by Chris Hammond


Dr. David Larson

By Alexander Dalziel
SPARK Correspondent


Might a little insect give a warning if North America’s ecosystems are under threat? Dr. David Larson of Memorial University’s 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 size.

The results of Dr. Larson’s 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. Larson’s field of specialization. “The goal of taxonomy is to organize biological diversity,” Dr. Larson explained. “In the narrowest sense, it’s 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 or differences.”

It is not only the inherent interest of such animals, however, that has motivated Dr. Larson’s 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 you’ve attained a list of what’s there, your next question is: What’s 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 beetle’s 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 habitat’s 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.

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