CM . . .
. Volume XIV Number 14 . . . . March 7, 2008
The cane toad is one of 25 organisms described in Alien Invaders as an invasive species. These are animals, plants, fungi, bacteria, and viruses that are deliberatively or accidentally introduced into a habitat where they have never before lived yet manage to survive. In fact, they don’t simply survive, they flourish. According to the authors, Jane Drake and Ann Love, alien invaders tend to devour just about anything in sight, grow quickly, reproduce in large numbers, have no predators, no diseases, no parasites, and no competitors, and eventually overwhelm the original species. The natural community, once balanced and diverse, becomes weakened and less varied as habitat populations of organisms are stressed, overrun, and driven toward extinction. In each account, whether it’s the water hyacinth in Africa’s Lake Victoria or the brown tree snake in Guam, the invader and the consequences of invasion are vividly described. Drake and Love also provide information on the size of each invader, the invader’s homeland, where it is in the process of invading a new habitat, and the manner by which it arrived and was introduced. Complementing this written information are Mark Thurman’s clear and subdued colour illustrations which place the alien species in its new habitat.
There are seven examples of alien invaders in Canadian habitats. These are the plants (purple loosestrife, hydrilla, and knapweed) and the animals (stable fly, sea lamprey, zebra mussel and gypsy moth). We are told that all seven of these alien invaders were accidentally introduced, some by early European settlers who arrived with medicinal plants, bags of grains, cattle and horses, some by operators of transatlantic freighters who, at the end of their voyages, emptied their ballast tanks in Canadian fresh waters, and others by aquarium cleanouts, the opening of the Erie and Welland Canals, and a silk entrepreneur from Massachusetts who had several moths from Europe and North Africa escape from his living collection. The consequences for these Canadian habitats, whether aquatic, rangeland, or hardwood forest, have been devastating and costly.
Alien Invaders is an excellent resource for learning about human-caused global changes to habitats and the resulting effects of international travel and trade on the indigenous animal and plant populations. In the Manitoba science curriculum, this is a specific learning outcome for Grade 4. It would be interesting to listen to Grade 4 students talk about humans as an alien species (p. 8) and to help them to live like the ecoguardian described on pages ten and eleven.
Barbara McMillan is a professor of early years science education in the Faculty of Education, the University of Manitoba.
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Copyright © the Manitoba Library Association. Reproduction for personal use is permitted only if this copyright notice is maintained. Any other reproduction is prohibited without permission.