Biogeography

Biogeography

 Biogeography studies all aspects of the adaptations of an organism to its ENVIRONMENT, considering systematically the origins, migrations and associations of living things. Hence, it aims for a synthesis of data from nonbiological and biological disciplines: GEOLOGY, PHYSICAL GEOGRAPHY, GEOMORPHOLOGY, CLIMATOLOGY and METEOROLOGY, on the one hand; BIOLOGY, taxonomy, GENETICS and physiology on the other. Biogeographical relationships cannot be understood except from an ecological perspective which tries to explain the exchanges between an organism and its environment.

Ecology is subdivided into 3 fields of study: autecology (relations of individual species or populations to their milieu), synecology (composition of living communities) and dynecology (processes of change in related communities). Therefore, in its widest compass, biogeography concerns itself with the EVOLUTION of species, with changes in their ranges and with their extinctions. The principal factors influencing evolutionary development are climatic and edaphic (ie, soil-related) constraints, genetic adaptation and social integration.

Nested Environments

 Ultimately, biogeographic phenomena are explicable only as resolutions of conflicts between heredity and environment. The macroenvironment must contain resources that meet the requirements of individual organisms. Hence, the living population must be viewed as existing in nested environments of increasing magnitude that contain the positive and negative forces that act upon it. From smallest to largest these environments may be designated niche, ecotope, community, ECOSYSTEM, landscape and bioclimate.

The defining of orders of magnitude in the environment permits the identification of providers of resources and factors of constraint. At its lowest spatial level, the niche, the organism encounters an accumulation of all environmental impacts. Such impacts can usually be traced to larger spatial units and to higher orders of control. For example, the 3 organisms of a plant (trillium), an animal (thrush) and a human (young girl), carry out metabolic exchange in a narrow niche, are interactive with other forces in an ecotype, share available resources in a community that is submitted to the regime of an ecosystem, which, in turn, occupies part of a landscape and is finally subjected to the stresses of a regional bioclimate.

Fitness

 The ultimate explanation of plant and animal behaviour and of the fitness of an individual population to its habitat must be sought at each level. Questions concerning the relative importance of, for example, climate/soil, acidity/alkalinity (of soil), sun/shade, may be irrelevant if not set in a frame that will allow the assessment of cumulative effects. For example, climatic effects are most significant in determining the range limitations of many species. Consequently, present-day climatic limitations and knowledge of past circumstances can provide information about the place of origin of species and the migrations that have resulted in their present adjustment.

The principle that must be kept in sight is that each kind of plant and animal (including humans) has an individual ecological strategy that makes it more or less fit to survive in its environment. An estimation of fitness depends on 3 factors (requirements, tolerance and efficiency) that can be ranked under 3 degrees of dependency (high, low and variable). Marginal notations give an overall estimation.

Two species having the same requirements and tolerance do not necessarily have the same efficiency. Thus, where sugar maple and beech grow together (eg, in the eastern Canadian FOREST), the maples seed more regularly and abundantly and usually far outweigh the beeches in the total biomass. Several nesting birds share cattail marshes with the red-winged blackbird, but do not equal its numbers or stability. Inuit populations in contact with southern Canadians rapidly increase their efficiency by applying their ability to learn new technology and move into a storage-exchange economy.

Geological Influence

The study of all existing species of plants and animals in a given area (a forest stand, a lake, a region) often reveals the presence of units that have come there from many diverse areas. Thus, some very old geological events have left closely related species very far apart: northeastern Asia and eastern North America have very similar pairs of deciduous trees (eg, birches, maples, beeches, walnuts, tulip trees); the plains and deserts of North and South America harbour similar species long isolated from one another; Argentina and New Zealand have forests and grasslands dominated by closely related units (eg, Nothofagus, Podocarpus); the mammals and fishes of northern Europe and Canada show many affinities (eg, moose, pike).

Undoubtedly, the geological episode that has cast its stamp most visibly on Canada's landscape is the Pleistocene ICE AGE, the last million years or so. Several successive vegetation sequences followed the retreat of the ice sheet (from 18 000 years ago to the present).

The living flora of southern Québec contain many species that originated in the Tertiary (from 65 million to 1.65 million years ago) eastern deciduous forest (sugar MAPLE, BEECH, white TRILLIUM, bloodroot, woodland frog, ovenbird, white-tailed DEER, etc); other species are closely linked to the boreal transcontinental spruce-fir (or Canadian) forest (white SPRUCE, bunchberry, twinflower, feather mosses; brook TROUT, MOOSE, purple FINCHES, etc). Some have midwestern affinities (creeping FERNS, rock ELMS, mud pickerel, evening GROSBEAKS, etc). Atlantic-coastal-plain elements are rarer (grey BIRCH, candleberry, broom crowberry, etc). Truly arctic-alpine species (eg, purple SAXIFRAGE, MOUNTAIN AVENS) are generally restricted to higher altitudes.

There are, of course, many widespread organisms (ASPENS, raspberries, CROWS), and some that have a nearly worldwide range (bracken ferns, reeds, CATTAILS, etc). None of the above include the introduced WEEDS (eg, dandelion, crabgrass, galinsoga) or pests (eg, STARLINGS, rats) that are completely naturalized (capable of fulfilling their life cycle unaided).

Regional Fluctuations

Similar regional units in Canada or elsewhere, if analysed floristically, would also reveal a composite picture reflecting the history of past fluctuations. Plants of the southern prairies belong to several units that witness more or less unresolved conflicts. The tall-grass prairie (big bluestem), mixed-grass prairie (blue grama, wheatgrass) and short-grass prairie (fescue) have repeatedly moved north and south and left traces. The spotty occurrence of North American halophytes (plants that grow in salty soil, eg, samphire, atriplex, greasewood) and of Great Basin desert plants (umbrella plant) also points to fluctuation of drought and high temperatures.

Western BOREAL FOREST elements (jack and prince'sPINE, black spruce, devil's PAINTBRUSH) and eastern ones (twinflower, bunchberry, BEARBERRY) come together in the cooler highlands. Some eastern deciduous forest species (American elm, false Solomon's seal, sweet cicely) migrate far west along the bluffs and floodplains.

The patterns of geographic distribution of plants and animals are, therefore, very revealing of past fluctuations in the displacement of the communities that harboured them, and indeed of whole bioclimatic areas that have shifted across continents. The biogeography of Canada must be seen as a whole, not solely as patterns of key species of plants and animals. This perspective requires the broader framework of world units.

Global Perspective

Worldwide, 20 bioclimatic formation-classes have been identified, based on the 2 more or less independent variables, heat and moisture: tropical rain forest, temperate rain forest, tropical deciduous forest, summer-green deciduous forest, needle-leaved evergreen forest, evergreen hardwood forest, tropical woodland, temperate woodland, tropical savannah, temperate and cold savannah, thornbush, tropical scrub, temperate and cold scrub, tundra, prairie, steppe, meadow, warm desert, cold desert and crust vegetation. These classes are very unevenly distributed on the planet.

An extreme combination of heat and moisture favours the development of tropical rain forest; an extreme combination of heat and drought, warm desert. Extreme cold (almost always very dry as well) allows only snow or bare rock, or at best crust or tundra. The order in which one formation class will replace another is predictable and depends on warming or cooling trends, changes in moisture, or both (seeCLIMATE; CLIMATE CHANGE).

During the last million years, the unglaciated parts of Canada have undergone periodic shifts from summer-green deciduous forest through needle-leaf evergreen forest, temperate woodland, temperate savannah and meadow to tundra and back again, depending on warmth; from needle-leaf evergreen forest through temperate savannah, temperate woodland and prairie to steppe and back again, depending on moisture; and from steppe through temperate scrub to warm desert and back, depending on both factors.

The extreme north has experienced relatively stable conditions of cold desert and crust during the entire period. Hence, when the temperate rain forests of BC are included, modern Canada contains 12 of the 20 possible bioclimatic formations.

As a Discipline

Biogeography operates with broadly based working hypotheses that have been variously tested. It provides an essential background to cultural geography and to human ecology. In earlier stages of its development, it was more concerned with the impact of landscape on human beings. Fortunately, in recent years the ever-swinging oscillation of physical/cultural anthropology and the emergence of human ecology as an increasingly autonomous discipline have rendered the notions briefly outlined above more relevant to human studies, environmental planning and landscape management. Human activity is proving to be a very significant factor in the distribution of plant and animal species.

In Canada the historical regression of many important animal species is well documented, eg, WAPITI and COUGAR that were once present in the east, and salmon that used to reach Lake Ontario. On the other hand, the white-tailed deer has extended its range greatly; the beaver has made several comebacks. But extinction of the GREAT AUK is forever, and there are many endangered species.

See alsoENDANGERED ANIMALS; ENDANGERED PLANTS; and PLATE TECTONICS.