Animal Distribution

by

Nutan Kumari, Adhoc Faculty

Department of Zoology

J.D. Womens College,Patna

Bsc Part - III

METHODS OF DISTRIBUTION

Basically two theories explain the spreading of animals all over the globe:

1 Continental Drift hypothesis 2 Centre of Origin hypothesis

1.Continental Drift hypothesis: Proposed by Wagner, accordingto him the earth was one whole mass when it was originated, butabout 135 million years ago (Cretaceous Period) the land massfragmented in to continents. With the fragmentation of landmass animals were also distributed in their respective continents

2.Centre of Origin hypothesis: According to this theory theindividuals of a species spread out from the centre of their originbecause of their high reproductive capacity.

CLASSIFICATION OF ANIMAL DISTRIBUTIONThere are three aspects of distribution of animals on earth, two of which are distributed in space(land and water) and one in time.

In space:(a)Geographical Distribution : Horizontal or Surfacial Distribution(b)Bathymetric Distribution : Vertical or Attitudinal Distribution

In TimeGeologic Distribution : Durational Distribution

(a) Geographical Distribution :There is no place on earth’s surface where life is not existing.All over the earth’s surface organisms are distributed. The densetropical forest, high mountains, hot and drought place likedessert, very cold polar regions life is existing. On these placeslife is present but not in uniform one.

Dispersal of AnimalsAnimals dispersed because of following reasons:

Struggle for Existence – rapid multiplication, scarcity of food and shelter and mate.

Changing in climatic condition : in search of favourableclimate animals migrated or become extinct . e.g. Horses andelephant.

Barriers to Dispersal

1.Topographic Barriers: Alps (High and extensive Mountains) –ranges the limit of distribution of some terrestrial forms. e.g. Thereis marked differences b/w the species of northern and the southernslope of the Alps.2. Climatic Barriers: Temperature has a marked influence on limitingthe animal dispersal, particularly on cold blooded animals e.g.Reptiles and amphibians are tropical and temperate in theirdistribution.

3. Vegetative Barrier: The forest become barrier for larger terrestial animals because they can’t penetrate the forest.

4.Large water bodies: Extensive water bodies form barriers foranimals living in water. e.g. Fresh water fishes also prevented tomigration, although certain fish such as Salmon, Sturgeon and Smelt(anadromous fishes) migrate from sea water to fresh waterannually. While in Eel (catadromous fish) reverse migration occurs.

5.Impurity and lack of salinity of sea water: An effective barrier tothe dispersal of certain kinds of marine animals starfishes,squids(cepahlopods), sponges and corals because these animals require amaximum purity and salininity of water.

Means for Dispersal1. Land Bridges2. Natural Rafts and Driftwood3. Favouring Gales4. Land Bridges : Panama (a country that links central and south

America; in map it shows like a bridge) opens up the avenuefor migration of many animals horses, wolves ans cats.

5. Natural Ratfs and Driftwood: Terrestrial animals also takes liftupon drifting (floating) materials which enable them toaccomplished over water journeys.

e.g. Polar bear are also carried by floating shore ice.Mass of driftwood creepers and leave and other natural rafts also

helps in dispersal of animals .3. Favouring Gales : Many animals like insects, bird, and bats

dispersed by strong wind and they get their favorabledestinations. e.g. European birds transported to America byway to Iceland and Green land

Bathymetric Distribution

Bathymetric distribution concern itself with the vertical range oforganisms in space i.e. from the highest Alpine peak to the abyssaldepth of the seal. A series of variations can be easily see in animalsfrom height to depth –

➢Breathing: If animal is completely terrestrial and breath in air, itcan not live in water and those who are completely aquatic andbreath in water can not survive outside the water.

➢Substratum: Animals differs from one another having or nothaving substratum – Some animals are not able to walk they canonly swim, some animals have not complete walking capability(Aves).

➢Animals living in water have several limiting factors like – fresh water or salty water, water pressure with depth.➢On the basis of distribution of animals marine water has beenclassified in to two zones :

(1)Pelagic Zone: It includes the water mass laying above the ocean floor. Thus, the animals live here called Pelagic. Ex-Planktons (microscopic) and necton (large swimming animals).

(2)Benthic Zone: It includes all the sea bottom. Thus, the animals live in the bottom of the sea is called Benthonic.

Three Organic Realms

There are three realms are recognized for bathymetric as wells for geographic standpoint

1.Geobiotic or Terrestrial2.Limnobiotic or freshwater inhabiting (lakes and rivers)3.Halobiotic or Marine or slatwater inhabiting (sea)

1.Geobiotic or Terrestrial – it ranges from alpine (high mountains) to low land.

2.Limnobiotic or freshwater inhabiting (lakes and rivers) –limited to terrestrial water such as pond lake and river and contain very limited fauna.

3. Halobiotic or Marine or saltwater inhabiting (sea)- It is veryimportant realm as we find here all the contrastingcharacteristics abundantly that is why –

Halobiotic realm is divided in to four sub-realms

(a) Strand: It is tidal zone or transitional area between marine andterrestrial realm. In this realm those animals are living those whoare capable to breath both in air and in water. Ex- molluscs.

(b) Flat Sea: it the area of sea up to 200 meter depth, rich both inlight and vegetation. Because of light, vegetation and food someanimals are limited to this area. Ex- Coral, Calcarious Sponges,Zooids (Coelenterates), Sea Anemones etc

(c) Pelagic Realm: It includes the water mass laying above theocean floor. Thus, the animals live here called Pelagic. Ex-Planktons (microscopic) and necton (large swimming animals).

(d) Abbysal Realm: Sea ares below depth of 200 meter, wherethere is no substratum, low temperature, high pressure. Ex –Large carnivorous marine animals, feed on dead organicmaterials.

Geological Distribution: Durational Distribution

Geologist dividedearth’s past history into numberof major divisions called Eras

Eras : Name of duration of time thatindicate the degree of

evolutionary advancement of life

Archeozoic and Proterozoic Era•Called as eras of age of unicellular life .•Animals having low organization.•Also called as ‘Age of Primitive Marine Invertebrates’•Ex- Sponges, Marine Algae

Paleozoic Era (Age of Fishes)Cambrian Period: Vertebrates like fishes evolved from invertebrates.

Ordovician Period: Cephalopods, Tribolites , and fishes evolved.

Silurian and Devonian Period: Scorpion, Amphibian and terrestrial vertebrates evolved.

Mississippian, Pennsylvanian, Permian Period : Shark were dominantfishes during Mississippian period. Insects, Snails & Amphibians wereevolved

Mesozoic Era (Age of Reptiles)

Triassic and Jurassic Period•Fishes, Amphibians, reptiles, bird and mammals were evolved, but reptiles were more dominant .•Flying reptile and reptile like birdswere recorded in this period.

Cretaceous Period•Rise of flowering plants.•Mammals were numerous, but small .•Birds were modern with teeth

and had been replaced by

Cenozoic Era (Age of mammals)Paleocene EpochDinosaurs were apparently

extinct mammals.

Eocene Epoch: Warm blooded mammals evolved.

Oligocene, Miocene and Pliocene Epoch•Glacial age•Evolution of mammals, first man like apes.•Placental mammals diversified.•Formation of new land bridges•Many migrations occurred all over the world.

Pleistocence and Psychozoic Epoch (Age of Man)Some animals evolved in warmer interglacial areas .Age of man began with the greater perfection of man’s mentality

Patterns of Animal Distribution

Animals are not uniformly distributed on land andwater. They are restricted to certain areas by severalfactors such as climate, food, shelter etc.

On the basis of above said restriction factors animalsdistribution is classified into four categories –

(i)Continuous Distribution(ii)Discontinuous Distribution(iii)Bipolar Distribution(iv)Isolated Distribution

(i) Continuous Distribution➢ Wide range of animals are distributed throughout the world in all

climatic zones or in all the confinements is called ContinuousDistribution and such type of animals are called Eurytopic Animals.

➢ Eurytopic animals are adapted to a wide variety of environmentalconditions.

➢ They are not specific to any particular type of food.

➢ Many have special power to cross barriers by flight or rafting orswimming.

Ex- Rats, Bats, Hawks, Cockroach, Flies, lizards, Mosquitoes, Snakes and man

➢ Many of eurytopic animals have continuous distribution because theyare companions of man and have travelled to long distance with him

Continuous distribution has following types –

(A) Cosmopolitan Distribution: Animals or Species occurring in allclimatic zone. Ex- Falco pereginus (Hawk)

(B) Circumpolar Distribution : Animals or species found in aparticular pole of the globe. Ex- Polar Bear

(C) Circumboreal and Circumanstral Distribution: Animal or specieswhich are distributed in a near continuous belt in thetemperature region of northern or southern hemisphere are saidto have circumboreal* and circumanstral* distributionrespectively

*Circumboreal – Throughout Northern Hemisphere*Circumanstral - Throughout Southern Hemisphere

(ii) Discontinuous DistributionWhen continuity of distribution of aspecies is broken by uninhabited areawhich are sometime very large stretchesof oceans.

ORA species distributed in twoseparated geographical areas

or more widelyis called

discontinuous distribution

There are four reasons for why animals are distributed in widelyseparated areas –(1)Animals reach distant areas by different routes – insects, snail,and rats by rafting, turtles by swimming, and birds by favouringgales (storms).

(2)The species was earlier distributed continuously but the landmasses in the intermediate areas submerged, breaking the speciesinto widely separated populations.

(3)Continental drift separated the continents and carried theisolating animals to long distance

(4)A widely distributed species can become extinct in theintermediate areas due to change in the climate to which thespecies is unable to adapt

Examples of Discontinuous Distribution

➢Peripatus has 75 species distributed in Southeast Asia, East Indies,Australia, New Zealand, Africa, and Central America.

➢Alligators occur in America (Alligator mississipiensis) and Asia(Alligator sinensis).

➢Two Species of elephants are surviving today – Loxodontaafricana in south Africa while another elephant , Elephas maximusfound in India, Burma, Thailand and Sri Lanka

(iii) Bipolar DistributionSpecies that can survive only in cold arctic

climate can not migrate to the warmer areas and hence restricted to the polar regions

Ex – Polar Bear, Arctic For, Lemmings are restricted in northern pole

while Penguins are restricted to Antarctica regions

(iv) Isolated Distribution

such forms➢ Some animals found only in certain isolated areas, are said to have isolated distribution.

Ex. Sphenodon (living fossil) - Reptile - New ZealandPrototheria – Egg laying Mammal (Playpus [Duckbill]) – AustraliaMetatheria – Pouched Mammals (Kangaroo) – Australia

Factor Affecting Animal Distribution

Animals spread out in the biosphere through migration. Migration and dispersal of animals are controlled by many factors or barriers

(1)Physical Barrier: It includes mountains, rivers, lakes, saes, vegetations or forests and long distance.

(2)Climatic Barrier: Temperature, moisture, light and pH.

(3) Biological Barrier: Food, predators and enemies

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