Keeping the Bees by Laurence Packer

Author:Laurence Packer [Packer, Laurence]
Language: eng
Format: epub
ISBN: 9781443400398
Publisher: HarperCollins Canada
Published: 2003-04-06T05:00:00+00:00

Several of the patterns we see in bee biodiversity we know with greater certainty from studying other living things. The most impressive of the patterns we have discovered is the latitudinal gradient in species richness—that is, the gradual increase in the number of species as you move towards the equator from either the North Pole or the South Pole. This pattern has been attributed to everything from average temperature, variance in temperature and the surface area of the land to whether the area was once glaciated. The problem is that many of these explanations are interrelated, and teasing apart the various potential causes is complicated.

Despite the controversies, some explanations seem unequivocal. For most organisms over much of the surface of the earth, the amount of available energy is a major determinant of the number of species an area can maintain. There are numerous ways of measuring available energy, but for our purposes, we’ll consider it to be a combination of warmth and sunshine. Warm, sunny weather works very well as an explanation of patterns in both plant and animal diversity for most of northern North America (in practice, this means Canada plus a strip of land just south of the Canada-U.S. border). It is the best explanation of variation in species richness of organisms as divergent as trees, butterflies and birds. This means that if you were to count the number of tree or butterfly or bird species in the squares of an imaginary grid placed across the surface of Canada and Alaska, you would find that the species richness increased as the amounts of heat, sunshine or any other energy-related variable increased. In the comparatively cooler regions of North America, the number of species found in an area is limited by available energy, which on average increases as you move south.

We can understand why by using an economics analogy. It is easier for people to specialize in comparatively obscure jobs in a rich economy than in a poor one. In a well-off part of the world, individuals can earn their living as abstract painters, fruit fly geneticists, brain surgeons or melittologists. In a poorer economy, it is more difficult to earn a living in any of these endeavours. Similarly, greater specialization may be possible in a region of the globe where there is lots of energy for creatures to use than it is in regions with less. The result is that a greater number of species can coexist in parts of the world where there is more warmth and sunshine.

The problem with this hypothesis is that it breaks down completely in warmer parts of the world. In North America, energy seems to be a limiting factor only for the number of species north of a line joining Boston to Seattle. So what determines variation in warmer areas in most of the continental United States?

Throw a grid over a relief map of North America and count the number of different colours found in each of the squares. For a square

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