ECOLOGICAL BIOGEOGRAPHY (Who lives where and why)

The distribution of any species of organism is limited by the distribution of suitable environments. The three main climatic controls of the plant communities are: TEMPERATURE, SOLAR RADIATION, and PRECIPITATION. Each of these factors affects the vegetation directly or indirectly through its effect on the soil. Average intensity and distribution of these factors throughout the year are both important. In turn, the distribution of plant communities, in association with climatic factors, determines the type of animal communities that can live in any area.

Temperature and radiation have a familiar north-south gradient. There is also an obvious east-west differentiation, especially through the Temperate Zone, which is due mainly to changes in precipitation and subsequent evaporation. There are many irregularities in this gradient. These are all HORIZONTAL zones of climate. There are also VERTICAL zonations, such as one finds when climbing a mountain. As one ascends he encounters conditions similar to those at sea level farther north. In general, we find an increase in altitude or elevation of 1 000 feet is roughly equivalent to a loss of one month in time of the growing season.

The physical characteristics of the environment determine the types of organisms that can settle there initially. Winds, temperature, amount, type, and temporal distribution of precipitation, chemical composition of the surroundings, latitude, altitude and soil conditions all contribute. The combination of precipitation and temperature is fundamentally important in determining the distribution of general vegetation, which, in turn, determines the distribution of animal life.

Temperature affects the rate of physiological processes, reproduction, and the survival or death of plants. Soil temperature influences the rate of absorption by the roots and the rate of root growth. In addition, by its very presence, a particular community of organisms gradually alter local conditions.

In the last analysis, it is the climate -- the basic action of wind, rain, temperature -- that molds an environment. In both hemispheres, just beyond the tropics, trade winds blow toward the equator. They carry moisture which falls in tropical areas creating tropical forests. But to the north and the south these same winds leave behind patches of desert and various grassland-shrub areas, such as savannahs. Still farther north and south, winds from polar and subtropical zones mix, forming variable rain patterns that produce temperate forests and grasslands.

These large terrestrial areas, dominated by particular plant communities, are known as biomes. While biomes are repeated around the world, each continent has its own particular version of each as well as the animals that have adapted to it.

Terrestrial Biomes

There are two types: Arctic, which is found above 60 degrees north latitude, and Alpine which is found at elevations over 7 000 feet The major limiting factor is water availability since water is usually in the form of snow, ice, or permafrost.

Climate - cold, ranging from 30-700 F. on average; permafrost; short growing season of about 60 days; frequent winds; soil often wet with poor drainage resulting in boggy areas; rainfall averages 10-17.5 cm (4-7 inches), usually during growing season.

Vegetation - lichens, mosses, dwarf and woody plants, e.g. dwarf willows, heath, birches, cranberry bushes, sedges and rushes

Plant Adaptations - dwarfism; small, hairy leaves for water conservation, ability to survive in frozen condition, vegetative propagation, e.g. runners

Animal life - rodents, arctic hare, caribou, wolf, grizzly bear, polar bear, snowy owl, few invertebrates - mosquitos, black flies; waterfowl may use bog areas for breeding in summer

Animal Adaptations - white coloration, hibernation, burrowing

TAIGA (Coniferous Forest)

These areas tend to circle the northern hemisphere. They are usually found between 50-60 degrees north latitude. The major limiting factor is light, particularly due to dense shade created by the trees.

Climate - cold and severe winter climate, growing season of 3-5 months; below freezing most of the year; 60-700 F. during the summer; rainfall of 25-75 cm (10-30 inches) per year; much of the precipitation is snow

Vegetation - needle or scale leaved evergreen trees (spruces, firs, cedars, pines) poor shrub and herb layer


These areas are common in the eastern United States. The major limiting factor is light availability.

Climate - temperate, long summers, fairly constant temperatures, deep rich soil, moderate rainfall (50-150 cm [20-60 inches]); evenly distributed seasonally

Vegetation - deciduous trees and shrubs, large shrub and herb layer, diverse species; cherry, oak, basswood, maple, beech, birch, hemlock

Plant Adaptations - leafless in winter, heavily foliated in summer

Animal life - all groups represented: mammals, birds, reptiles, amphibians, many insects; white-tailed deer, wild cats, foxes, bears, arboreal birds

Animal Adaptations - sharp claws, movable scales in snakes, hibernation, estivation, migration, various nesting habits


Represented by prairies in North america, savannahs in Africa, and steppes in Russia and Argentina. The major limiting factor is light availability and seasonal distribution of precipitation.

Climate - similar to Temperate Deciduous Forest: major difference is uneven seasonal distribution of rainfall, mostly 25-100 cm (10-40 inches) in the spring

Vegetation - mostly grasses, few trees, some wild flowers; grass species dependent upon location

Plant Adaptations - deep, fibrous root system - sometimes 2 meters deep; creates sod formation

Animal life - jack rabbit, antelope, fox, bison, coyote, wolf, cougar, rodents, reptiles, insects

Animal Adaptations - running, leaping, burrowing


These areas make up about 1/7 of the total land surface. They are found in areas of high pressure. Low altitude deserts tend to be hot, while high altitude deserts, such as the Gobi, can be quite cold. There is a distinct lack of organic material in the soil and high mineral salt concentrations leading to an alkaline pH. Major limiting factor is water availability.

Climate - intense sunlight leading to hot days and cold nights; high evaporation rate, constant winds; low annual rainfall of 2.5-10 cm (1-4 inches) occurring once or twice a year

Vegetation - xerophytic plants, annual plants, succulents, shrubs; drought evaders with seeds that germinate quickly after a rain and have a rapid life cycle and drought resisters with deep root systems

Plant Adaptations - hairy leaves and stems, leaflessness, water storage in succulent stems, accelerated life cycles; phytotoxin and antibiotic production, photosynthetic stems

Animal life - reptiles, rodents, coyote, foxes, insects, burrowing animals

Animal Adaptations - uric acid waste products allow for water retention; nocturnal, protective coloration, estivation, hibernation


Found near equator and in lower section of temperate zones. Dependent upon amount of rainfall, it may be a tropical rain forest or just a tropical forest. Major limiting factor is light.

Climate - high year round temperatures, uniform length of night and day; at least 200 cm (80 inches) of rain per year - may go as high as 1 000 cm (400 inches)

Vegetation - rain forests, woody vines, epiphytes, many species with few dominants; little underbrush, poor leached soil; bamboo, orchids, mistletoe

Plant Adaptations - plants woody and grow as trees; distinct canopies

Animal life - exceedingly varied; ants, mosquitos, frogs, monkeys, birds, few mammals

Animal Adaptations - nocturnal, fruit-feeding, hanging nest


--------------------------------------------------------------------------- |uneven dis-| grasses | deep root |wolf, fox| running, GRASSLANDS |tribution | |systems, sod |bison, | leaping, |of rainfall| |formation |rabbit | burrowing --------------------------------------------------------------------------- |low yearly | succulents, | hairy leaves |reptiles,| nocturnal, DESERTS |rainfall, |annual plants|and stems, |rodents, |water stor- |hot days, |shrubs |rapid germina-|insects, |age, protec- |cold nights| |tion,chemical |birds |tive colora- |winds | |warfare |mammals |tion --------------------------------------------------------------------------
TUNDRA frozen ground, cold
temperatures, short
growing season
lichens, mosses,
small, hairy
mosses, dwarf
& woody plants
small, hairy
white colored
leaves, survival
in frozen state
rodents, hare,
fox, wolf
bees, flies
CONIFEROUS FOREST (TAIGA)3-5 month growing season
cold winter climate
needle or scale shaped leaves;
spruce, fir, cedars
flexible, waxy needles
branches triangular-shape
flies, rodents, bears, birds, fox, hare, elk layers of fat, foot pads, protective color
moderate rainfall
broad leaves leafless in winter,
much foliage in summer
fox, deer, birds, insects, bear hibernation, migration
TROPICAL FOREST high temperature all year , high rainfall rain forest;
woody vines, epiphytes
woody plants; rapid growth; nutrient-rich vegetation insects, birds, all groups found nocturnal; fruit eaters; hanging nests

Email: demmeluth@hotmail.com