VARIATION IN POPULATION CHARACTERISTICS

DIFFERENCE IN STRUCTURE, FUNCTION AND BEHAVIOUR BETWEEN INDIVIDUALS BELONGING TO THE SAME SPECIES ARE COMMON. IN FACT, NO TWO INDIVIDUALS BELONGING TO THE SAME SPECIES ARE COMMON. IN FACT, NO TWO INDIVIDUALS, EXCEPT PERHAPS IDENTICAL TWINS, HAVE EXACTLY SIMILAR CHARACTERISTICS. IT IS THE GRADUAL ACCUMULATION OF MANY VARIATIONS OVER MANY GENERATIONS WHICH EVENTUALLY GIVES A POPULATION REPRODUCTIVE ISOLATION AND, CONSEQUENTLY SPECIES IDENTITY.

POPULATION MAY VARY IN CHARACTERISTICS  AS ADAPTATIONS TO LOCAL HABITAT CONDITIONS. AN INCREASE OR DECREASE IN THE FREQUENCY OF A GIVEN CHARACTERISTIC  APPEARS TO BE A RESULT OF VARIATIONS  IN THE SELECTIVE PRESSURE OF THE ENVIRONMENT, PERMITTING INDIVIDUALS WITH CERTAIN CHARACTERISTICS OR GENE COMBINATIONS TO SURVIVE AT ONE TIME OR PLACE; OTHER INDIVIDUALS, AT OTHER TIMES AND OTHER PLACES.

MOST SPECIES DIFFER NOT BY SINGLE GENES BUT BY HUNDREDS AND THOUSANDS OF GENES. WHEN FREE BREEDING, PREVAILS  IN A SPECIES, THESE GENES MAY BE ARRANGED IN ALL SORTS OF COMBINATION TO FORM AN ALMOST INFINITE MIXTURE OF CHARACTER MODIFICATION. HETEROZYGOTE ARE, THEREFORE, MUCH MORE FLEXIBLE IN ADAPTIVELY RESPONDING TO THE ENVIRONMENT  THAN ARE HOMOZYGOTE. THE MORE CHARACTERS FOR WHICH AN INDIVIDUAL IS HETEROZYGOUS, THE MORE ADAPTABLE ITS OFFSPRINGS ARE LIKELY TO BE. THESE POPULATIONS ARE MORE EFFICIENT IN EXPLOITING THE ENVIRONMENT THAN ARE GENETICALLY UNIFORM ONES.

SPECIATION

GENETIC VARIATION LEADS TO EVOLUTION OF NEW SPECIES OR SPECIATION. SPECIATION IS THE PROCESS THAT SEPARATES GENETIC VARIATION INTO DISTINCT UNITS, OR SPECIES. IN SPECIATION, THE ORIGINAL POPULATION OF ORGANISMS WITH SIMILAR GENES, CALLED GENE POOL, IS DIVIDED INTO TWO OR MORE GENE POOLS. EACH OF THIS GENE POOL ACQUIRES A NEW SET OF CHARACTERISTICS THROUGH MUTATION AND SELECTION. SPECIATION FOLLOWS MOST COMMONLY FROM THE PHYSICAL DIVISION OF A GENE POOL. THE SEPARATION INHIBITS INTERBREEDING BETWEEN INDIVIDUALS  IN TWO POPULATIONS. IN TIME, ONE OR BOTH POPULATIONS CHANGE ENOUGH TO PROHIBIT INTERBREEDING.

SPECIATION IS THEREFORE THE PROCESS OF EVOLUTIONARY DIFFERENTIATION BETWEEN POPULATIONS, WHICH MAY RESULT IN ONE OLDER SPECIES BECOMING SPLIT INTO TWO OR MORE NEW ONES.

GENETICISTS DEFINE A POPULATION  OF SPECIES  AS A ' A REPRODUCTIVE COMMUNITY SHARING A COMMON CHARACTERISTIC GENE POOL.' EACH LOCAL POPULATION IS DIFFERENT FROM THE OTHER; THROUGH NOT EASILY DISTINGUISHABLE FROM  ONE ANOTHER, AND THEREFORE ARE GIVEN NO FORMAL NAMES.

MUTATIONS

MUTATION IS THE PROCESS IN WHICH THE GENETIC MATERIAL OF A PERSON, PLANT OR AN ANIMAL CHANGES IN STRUCTURE WHEN IT IS PASSED ON TO THE OFFSPRING. THE RATE AT WHICH ANY ONE GENE MUTATES VARIES GREATLY FROM ONE GENE TO ANOTHER. MUTATIONS OF DIFFERENT SORTS APPARENTLY OCCUR HAPHAZARDLY AND ARE NOT INFLUENCED BY ENVIRONMENTAL CONDITIONS. ADAPTION OF A SPECIES TO A PARTICULAR HABITAT OR NICHE IS AFFECTED THROUGH NATURAL SELECTION OF THE FAVOURABLE MUTATIONS OUT OF THE MANY THAT OCCUR. THE SIZE OF THE POPULATION AND THE RATE AT WHICH A PARTICULAR GENE MUTATES AFFECTS THE ODDS OF MUTATION THAT A GENE ESTABLISHES ITSELF IN A POPULATION. 

BIOMES

A BIOME SYSTEM  IS RECOGNIZED ON THE BASIS OF COMMUNITIES, OF CHARACTERISTIC COMBINATIONS OF ANIMAL AND PLANT SPECIES, OF SUCCESSIONAL  RELATIONS BETWEEN  COMMUNITIES AND THE SUCCESSIONAL RELATIONS BETWEEN COMMUNITIES AND  THE SUCCESSION IN ALL LOCAL HABITATS WHICH EVENTUALLY CONVERT INTO A CLIMAX COMMUNITY PATTERN' AND FORMS THE MOST IMPORTANT  ECOLOGICAL CHARACTERISTIC OF A GEOGRAPHIC AREA.

THE PRINCIPAL GEOGRAPHIC UNIT IN A ECOLOGICAL SYSTEM IS THE BIOME. THE BIOME IS DIVIDED INTO PLANT ASSOCIATIONS, DISTINGUISHED  BY UNIFORMITY IN THE SPECIES COMPOSITION OF THE CLIMAX PLANT DOMINANCE AND BIOCIATIONS, IDENTIFIED BY UNIFORMITY AND DISTINCTIVENESS IN THE SPECIES COMPOSITION OF THE CLIMAX COMMUNITY, PARTICULARLY OF THE ANIMAL PREDOMINANT. SOME NINE TERRESTRIAL BIOMES AND FOUR MARINE BIOMES ARE RECOGNIZED. ON LAND, THE MOST IMPORTANT CLIMAX SPECIES ARE USUALLY PLANT DOMINANTS THAT OCCUR IN DISTINCTIVE VEGETATION AND LANDSCAPE TYPES; IN THE OCEAN, THE MOST IMPORTANT ORGANISM  THAT DEFINE BIOMES ARE USUALLY THE PREDOMINANT  ANIMALS WHICH ARE ALSO SOMETIMES ALSO DOMINANTS.

NUMBER SPECIES IN THE WORLD

WE DO NOT KNOW EXACTLY HOW MANY SPECIES INHABIT THIS EARTH. ESTIMATES RANGE FROM 4 MILLION TO 100 MILLION. THE BEST GUESS IS 10-14 MILLION. MOST OF THE SPECIES IN THE WORLD ARE INSECTS AND MICRO-ORGANISMS NOT VISIBLE TO THE NAKED EYE.

SO FAR ABOUT 1.8 MILLION SPECIES (NOT INCLUDING BACTERIA) HAVE BEEN IDENTIFIED, NAMED, AND CATALOGUED. THESE INCLUDE 270,000 PLANT SPECIES, 45,000 VERTEBRATES,  AND 950,000 INSECTS. ROUGHLY 10,000 NEW SPECIES ARE IDENTIFIED EVERY YEAR.

OVERALL, OUR KNOWLEDGE OF SPECIES AND ECOSYSTEMS IS POOR. EVEN OUT OF THE IDENTIFIED SPECIES, ONLY A ONE THIRD HAVE BEEN STUDIED TO SOME LEVEL. AMONG THESE AGAIN, WE UNDERSTAND THE EXACT ROLES AND INTERACTIONS OF JUST A SMALL NUMBER OF SPECIES.