William A Gardner

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15

January
2018

Chronicles

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Squirrels, Crabapples and Population

Memes and Adaptation in the Natural World


The crabapple tree in the yard dresses itself each spring in a voluptuously self-indulgent display of colour and scent, welcoming the delicate touch of bees on its pink flowers. It is a hedonistic display of nature's wealth and reproductive capacity. Then, as spring dampness morphs into the long dry summer days, the tree gets down to the business of producing a bounteous crop of crabapples from all those blossoms. It is a ritual repeated yearly much to our delight.

The neighbourhood has a generous population of squirrels which provide much amusement as they scurry around the trees either searching for food or chasing one another for love or territory. Their acrobatic prowess is always on display as they jump from branch to branch, fly from branch to roof, or race along overhead wires. They are a constant reminder of the evolution of species as they adapt to particular environments. There are both greys and the blacks (but no reds) in the population and it reminds one of Stewart James and Anthony of Port Wenn fame. Iā€™m sure that with enough time and observation one could start to identify individuals by their habits and markings. One thing noticeable is an apparent increase in population.

Each year as winter starts to relinquish its power the crabapple tree has traditionally dropped the unharvested thawed apples onto garden and lawn resulting in a squishy cleanup. It never happens all at once and many little apples hang on the tree well into spring. Like so often in nature the extra apples, most in fact, went to waste. This occurred for years. But no more. A couple of years ago the squirrels discovered that the crabapples were a good source of food throughout the winter. You could see them from the kitchen window as they crouched on snowy branches and picked and ate the fruit. The following spring there were significantly fewer apples to litter the garden and lawn. It was a win-win situation. The following year ā€“ the year before last - by the time May appeared the tree was essentially bare of crabapples ā€“ no cleanup required. Now this was progress. In fact it was rather surprising just how fast the squirrel population had adapted to this new food source. It was an example of the speed at which wild animal populations adapt to changing circumstances and opportunities.

This last year we watched during the fall as the crop of crabapples slowly disappeared. By Christmas a considerable number had been eaten. Evidently word had spread in the squirrel population like a meme within an online group. The first apples to go were those close to the main tree branches which were easy to access. As time went on the squirrels needed more and more of their innate acrobatic agility to access the apples further out on the smaller branches. It is amazing to watch a squirrel creeping out on a branch so small it can hardly bear the weight of the tiny creature, or hanging from one hind leg upside down as it reached for another tasty fruit. They are fearless about falling. We expected that the crabapples further out on the smaller branches would not be harvested. We were wrong. By the middle of January the tree was bare ā€“ completely stripped of the little apples. The squirrel harvesting culture had gone from zero to where the available crabapples would not last half the winter. Was this just an example of successful adaptation spreading within a population or was it an increase in population?

Nature provides a great deal but not an infinite amount. Biological populations, including humans, have a habit of increasing in number until the tree is stripped bare. Studies have traced increases and collapses of populations in a number of animal species. With humans it may not present as a population collapse but rather a steady decrease in our standard of living as the demands of an increasing population outstrip the available supply of ecological services. When intellect meets biology, biology usually wins in the end.


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