Messing with nature is fraught with unintended consequences
by Bob Bancroft
Years ago, pest control officers in Borneo began using the chemical insecticide DDT to control mosquitoes and reduce the threat of malaria. Wasps were also killed by the spray. These wasps had previously eaten most of the local caterpillars that were unaffected by the DDT because of their normal eating habits. Consequently, not long after the spraying began, the caterpillar population boomed. They devoured the thatched roofs of everyone’s homes, opening them to the skies.
Then the spraying moved indoors to control houseflies. Previously, small lizards called geckos had consumed fly populations. The geckos ate the poisoned flies and died. Now cats could catch and eat the poisoned geckos. They died too. With cats gone, rats moved into the houses. Rats carry many diseases that can be transmitted to humans. In the end, cats had to be flown to Borneo to restore some balance in this ecological upheaval.
Scientists have discovered that nature’s food chains can be altered by changes at all levels—the bottom with micro-organisms and plants, by changes in the middle of the food chain, and when adjustments occur at top predator levels.
Control efforts in the massive Yellowstone National Park in the US eliminated wolves there in the 1920s. The elk population increased as a result. Freed from the fear of a major predator, elk began to browse aspens along mountain sides and willows along rivers, sites they had previously avoided due to the presence of wolves. Soon, stream banks were no longer being held in place by tree roots. Erosion increased. Streams became wider, shallower and the water became warmer during the summer. Cold water fish populations suffered.
Amid much debate, wolves were reintroduced to Yellowstone in 1995 and 1996. Elk numbers declined, their behaviour changed again to avoid wolves, and positive plant effects became evident. Willows once again began to grow along stream banks. The trees stabilized shorelines, reduced rates of erosion, and provided shade and cool water. Many species, from songbirds to beavers, are returning to these renewed habitats.
In Saltscapes country, early settlers encountered mature forest habitats that offered only small amounts of food that moose and deer could reach. Wolves and cougars traditionally preyed upon moose and deer, but were exterminated by humans after they began to kill domestic livestock.
With the exception of areas of forests subjected to herbicides, which promote softwoods, there is generally more vegetation available to deer in young forests that now dominate the landscapes. For this and other reasons, deer populations have increased in many parts of eastern Canada. Lyme disease is carried by black-legged ticks, which depend upon deer, deer mice and some migratory birds for their dispersal. Recent research suggests that the spread of the ticks and the Lyme disease to humans may have been facilitated by the extirpation of wolves and their natural replacement by coyotes. Unlike wolves, coyotes kill the foxes that eat deer mice. Increasing numbers of deer and deer mice are unwitting hosts for the tick.
Photo Credit: Nick Hawkins
On the west coast of North America, the killer whale (orca) population along Alaska’s Aleutian archipelago traditionally hunted large whales. Commercial whaling removed those whales in the early 1900s. Then the orcas switched to preying upon Steller sea lions, which can weigh as much as 2,500 pounds.
Soon the sea lion population plummeted, possibly already stressed by an intensive fishing industry and climate change. The killer whales began to target sea otters. By 1997, scientist James Estes found that “in some areas, 98 per cent of the (sea) otters disappeared.” The Aleutian sea otter population fell from in excess of 100,000 before 1990 to roughly 3,000 to 5,000 in 2013. It is quite possible that ocean pollution also may have added to the decline.
The absence of sea otters meant that their favourite food, sea urchins, exploded in numbers. The sea urchins began devouring the coastal kelp forests that formed important habitats for fish and other sea creatures. Fish became scarce for bald eagles, which had also preyed upon sea otter pups. With fish and otter pups gone, eagles began feeding on seabird populations.
The loss of the whales at the top of the food web trickled down through many members of the ecosystem, forcing shifts that were difficult to predict.
Forests have complex ecosystem interactions that scientists are only beginning to comprehend. Besides nutrients, forest soils harbour vast numbers of interconnected life forms. Trees have needles or leaves that convert solar energy into sugar food-energy through a biochemical process called photosynthesis. In the soil around each tree, roots interact with species of fungi. Fungal threads called mycelium grow around the root tips of large trees. These fungi feed nutrients like nitrogen, potassium, phosphorus from the soil to the tree roots, in exchange for sugars that the fungi need, but do not have.
Larger trees studied by forest ecologist Suzanne Simard in British Columbia act as healthy “hub” trees, often capturing more sunlight than they need to produce food for themselves. Simard found these trees somehow share resources with other trees. This sharing can be with younger trees of the same species, or with other tree species.
Water is also shared in times of drought, and there is a stress monitoring function within the communication system. Chemical messages can be sent that prompt neighboring trees to raise their defenses against impending insect infestations. For example, when budworms attack fir trees, the infected firs send stress signal alerts to neighbouring pine trees.
Simard also found that during the spring and autumn periods, firs share their sugars with leafless birch trees. When the birches have functioning leaves in the summer, they return the sugar favour to the firs.
To function well, the forest ecosystem must maintain lush, leafy forest canopies and the shady, damp soil conditions under them. This ensures the survival of young trees as well as the fungi and many other inhabitants collectively called “decomposers” that break down dead woody vegetation, and, by that recycling process, make nutrients available for living trees and fungi.
Flying squirrels nest in holes in older trees during daylight hours, coming out nightly to search for fruiting mycelium bodies that we call mushrooms. Then the squirrels glide away, scattering their feces, which contain mushroom spores, throughout the forest floor. In this way they spread healthy fungi through the forest to assist its trees.
Many other wild animals and plants have key roles in maintaining healthy forest ecosystems that we are only beginning to understand. To paraphrase Aldo Leopold, considered the father of wildlife ecology in the United States, “the first rule of intelligent tinkering is to save all the pieces.”
Understanding and respecting these interconnections and workings of nature can avoid much wasted energy and destruction. With the looming effects of climate change, we need to mitigate further human impacts on nature’s balances.