World distribution of Plants and Animals – UPSC

In this article, You will read World distribution of Plants and Animals for UPSC (Biogeography).

The distribution of plant and animal species is a key topic in biogeography, the study of the relationship between geography and living things. While every species is unique, all are in some way impacted by the landforms, resources, and climates they’re exposed to.

World Distribution of Plants

There is a wide range of variations in the distribution of vegetation on the globe. There is a zonal pattern of vegetation from the equator towards the poles and from seal level to vegetation level on the high mountains.

The distribution of plants is affected and controlled by a variety of factors e.g.:

• Climatic factors (sunlight, temperature, moisture and humidity, precipitation, soil moisture, etc.);
• Edaphic factors (soil nutrients, soil texture, soil structure, acidity and alkalinity, nature and properties of soil profiles, etc.);
• Biotic factors (effects of living organisms mainly animals and man of a particular habitat on plants, interactions between different plant species and between plants and animals like natural selection, competition, mutualism, parasitism, etc.);
• Physical factors (reliefs and topography, slope angle, gradient, and slope aspect, etc.);
• Tectonic factors (continental displacement and drift, plate movements, endogenetic forces and movements, vulcanicity and seismic events, etc.)
• Fire factor (forest fire-natural forest fire through lightning, man-induced forest fire both intentional and accidental;
• Dispersion of plants, and
• Human interferences.

Distribution of plants may be attempted in a variety of ways viz.:

• On the basis of habitats as the distribution of terrestrial and aquatic plants,
• On the basis of floral divisions,
• On the basis of latitudinal and altitudinal extents, and
• On the basis of characteristic features of plant communities etc.

The land plant species of the world are grouped into 6 major floristic kingdoms on the basis of their worldwide distribution as given below:

1. Australian Kingdom:

This floristic kingdom includes the plants of whole Australia which is characterized by typical plant species e.g., eucalyptus. The different species of this unique genus of eucalyptus are so dominant in Australia that they represent 75 percent of all Australian plants. There are over 600 species of eucalyptus which greatly vary as regards their general characteristics as they range from tall, giant, and shady eucalyptus trees to dwarf and stunted desert eucalyptus trees. Eucalyptus is said to be related to mimosa which is still found in South America (only a few species).

Eucalyptus has been dispersed and distributed by man (deliberately) from Australia to almost every continent. One can see the extensive plantation of eucalyptus in India particularly along the rail and roadsides and it is being expanded rapidly by deliberate actions of man in all parts of the country irrespective of environmental requirements and suitability of this unique exotic plant. The typical endemic floras of Australia having unique characteristics have developed due to its isolation from other continents of the southern hemisphere because of continental drift.

2. Cape Kingdom:

The floral kingdom has developed in the southern tip of Africa wherein the plants having bulbs and tubers have developed and these represent the typical plant species of this floral kingdom. The plants of this kingdom belong to the category of cryptophytes which bear buds in the form of bulbs and tubers which are buried in the soils. These bulbs and tubers give birth to other plants as new shoots come out from these bulbs and tubers and are developed as plants.

These plants represent most plants of the gradient such as garden flowering plants (e.g., Loplia, Kniphogia, Erica Freesia, etc.). The dispersal of these garden plants became possible when South Africa was colonized by Europeans who distributed these garden flowering plants from South Africa to the gardens of other parts of the world.

There is a gradual decrease in the number and area of these garden flowering plants in their own native areas (southern part of South Africa) because their areas are continuously being replaced by agricultural lands. The untouched areas still have sclerophyllous shrubs that attain a height of a few meters. There is an undergrowth of herbaceous shrubs in the sclerophyllous shrubs. It may be remembered that the native vegetation of this region before the European colonization consisted of temperate evergreen forests which were extensively cleared off by the Europeans for agricultural purposes and thus the sclerophyllous shrubs developed in this region at later date as a secondary succession of vegetation.

3. Antarctic Kingdom:

This kingdom includes a narrow strip in the north of Antarctica which runs from Patagonia and southern Chile of South America to New Zealand. The most important representative plant of this zone is Nothofagus which is also known as Southern Beech. About 100 million years ago temperate grasses developed as the native vegetation of this region (New Zealand).

The most outstanding and typical species of the grasses were Tussock Grasses though a few species of Sedges (plants which grow in water) and dicotyledon shrubs were also developed these original native vegetation have undergone massive modification and transformation since the colonization of New Zealand by the Europeans.

Thus, the present-day vegetation of New Zealand is of the modified type which is still characterized by two types of tussock grasses viz.:

1. Short Tussock Grasslands have two main species e.g., Festuca and poa. The average height of these grasses is up to 0.5 m and the color is yellow-grey,
2. Tall Tussock Grasslands have the main species of Chiomechloa.

Warm temperate areas of New Zealand are characterized by the dominance of the forest of gymnosperms and angiosperms trees. The main species of the coniferous family of gymnosperms are Podcarpaceae, Cupressaceae, and Araucariaceae whereas flowering plants are included in Angiosperms of which Nothofagus is the most important plant.

The sub-tropical forests of New Zealand are of the evergreen type which is characterized by a dense cover of tall trees having different vertical strata of other plants. The original vegetation of New Zealand has been greatly modified and destroyed by human activities and the mammals (mainly grazing red deers and rabbits) brought by them from Europe. This has led to the destabilization of the vegetation communities on a large scale.

4. Palaeotropical Kingdom:

This kingdom includes most of Africa, South West Asia, South Asia, South East Asia, and the southern and middle portions of China. This floral kingdom is further divided into 3 sub-kingdoms e.g.:

1. African sub-kingdom,
2. Indo-Malaysian sub-kingdom, and
3. Polynesian sub-kingdom.

This floral kingdom is also divided into several floral provinces or regions e.g., West African rainforest region, Madagascar region, Iran-Turanian region, East Asian region, etc. There is great variation in plant species from one region to another region but few plants are common to all sub-kingdoms and regions.

5. Neotropical Kingdom:

This region includes the whole of South America except southern Chile and Patagonia. A few genera are common to this kingdom and palaeotropical kingdom mainly Africa because the original flowering plants were developed in South America and Africa during the Cretaceous period when all members of Gondwanaland were united together.

Later on the spreading of the Atlantic sea-floor, disruption of Gondwanaland and westward drift of South America from Africa became responsible for the origin and development of new species at the regional level and therefore variations in the plant species of South America and Africa were introduced.

6. Boreal Kingdom:

This floral kingdom includes the whole of North America except Middle America, Greenland, entire Europe, northern Asia, and the Arctic region.

This is the most extensive kingdom of all the floral kingdoms. This is again divided into several sub-kingdoms and regions or provinces e.g. Rocky Mountainous Region (RMR); Atlantic – North American Region (ANAR, fig.); Arctic and Sub-Arctic Region (ASAR); Europe-Siberian Region (ESR); Mediterranean Region (MR), etc.

World Distribution of Animals

The study of distributional patterns of animals at the global scale is carried out in different ways e.g.:

• A collective study of the distributional patterns of all members of particular species. This involves the division of animals into definite distributional areas on the basis of the abundance of animal species.
• Animal distribution is also studied at the community level which involves the consideration and study of the total population of all individuals of all species of a given region.

It may be pointed out that the distributional patterns of animals at global or regional levels are more complex than the distribution of vegetation because animals are very much mobile. Thus no animal species is universally distributed because several factors distort the uniformity of distributional patterns of animals.

Distribution of Land Animals

The following facts must be taken into account while studying the world distributional patterns of animals:

• Physical environmental conditions determine the number, abundance, and diversity of animals. Maximum diversity is noticed among the vertebrate animals of the land and freshwater habitats of the tropical regions.
• There is a zonal pattern in the world distribution of animals. This zonal pattern of the animal distribution is in two forms viz.: (i) Horizontal zones, and (ii) Vertical zones.
  • Latitudes have maximum control on the horizontal zonal patterns of animal distribution because sunlight decreases from the equator towards the poles, which means there is a corresponding decrease in vegetation and its diversity towards increasing latitudes, and hence species diversity also decreases from the equator towards the poles.
  • It may be further pointed out that the origin and evolution of animals first took place in the tropical or the equatorial regions from where animals were dispersed to other areas. Thus the development of animal zones in the higher latitudes took place because of the dispersal and migration of animals from the animal zones of the tropical regions.
  • Thus the horizontal animal zones of the higher latitudes are the result of the dispersal and migration of animals and various phases of speculation. For example, the development of the temperate animal zone took place due to the subtraction of animals during their migration from the tropical zone.

• The animals have radiated in all directions from the centers of their origin. In other words, the animals have dispersed and migrated in all directions through various routes from the centers of their origin. Consequently, the distributional patterns of the world fauna are found in concentric zones.
• The diversity of animals of any region is the result of several phases of their dispersal and colonization.
• The concentration of animals could be possible only in mammals whereas the distribution of other species of animals is more widespread and is not specific.
• The distributional patterns of all the animal species are not uniform because the distribution of the same animal species is continuous while that of other species is discontinuous or disjunct. For example, the distribution of moose (a type of deer) is found in the continuous zonal pattern in the taiga regions of North America and Eurasia whereas the distribution of Azure-winged maggie, weather fish, and bitterling is discontinuous as their two continuous distribution zones in middle and western Europe and in south-east Asia are separated by an extensive zone devoid of these animals.
• Oceanic islands are characterized by special types of animals because there has been minimum migration and dispersal of plants and animals to the islands because of great oceanic barriers. Hawaii Island, which was never connected with any landmass in the geological history of the earth, lacks in reptiles, amphibians, freshwater fishes, and mammals (except one species of bats).

A.R. Wallace attempted the classification of world animals into faunal regions in 1876. Since then a number of attempts have been made to divide the world animals into faunal regions by several scientists e.g., P.J. Darlington (1957), S.C. Kendleigh (1961), W. George (1962), De Latin (1967), W.T. Neil, and M.D.F. Udavardy (1969), De Laubenfels (1970), J. lilies (1974), etc. but still the division of world animals into faunal regions as presented by A.R. Wallace is the most convincing and acceptable among all the subsequent divisions. Normally, the world is divided into the following 6 major faunal regions:

1. Palaearctic region
2. Nearctic Region
3. Oriental Region
4. Ethiopian Region
5. Australian Region
6. Neotropical Region

1. Palaearctic region

Palaearctic region includes Europe and middle and north Asia which represent 28 chordate families. The important animals of this great faunal region are Russian desmans, dormice of Eurasia, Mediterranean mole rats, saiga and chiru antelope (a type of deer), acentors, crocodiles, lizards etc. Reptiles are found in lesser number. This faunal region is further divided into 5 sub-regions on the basis of vegetation e.g.:

• i. Tundra region represents caribou, lemming, muskox, arctic hare, arctic fox, wolf, polar bear, etc.
• ii. Temperate coniferous forest region– moose, mule, deer, lynx, etc. are the important animals of this region,
• iii. Temperate grassland region represents saiga, wild ass, horse, camel, jerboa, hamster, jackal, etc.,
• iv. Deciduous forest region represents racoons, oppossum, red fox, black bear as important animals, and
• v. Desert region – the important animals of this region are lizards, snakes, hamster, hedgehog, rats, jerboa, cottontail, etc.

The Palaearctic faunal region includes 136 families of vertebrate animals, 100 genera of mammals, and 174 genera of birds. Besides, 3 unique families of vertebrate animals, 35 and 57 unique genera of mammals and birds respectively are also found in the Palaearctic faunal region.

2. Nearctic Region:

Nearctic region consists of the geographical territories of North America and Greenland. It is significant to point out that there is much similarity between the Palaearctic and Nearctic faunal regions. Both the regions were connected through the Bering Land Bridge during Tertiary Epoch and Pleistocene periods. This land bridge enabled free exchange and migration of animals between these two regions which resulted in much mixture of animal species and therefore increase in species diversity.

For example, American and European bisons reproduce after having sexual intercourse between them. Both regions have salmons and trouts. On the basis of such biological similarities between Palaearctic and Nearctic regions, some scientists have grouped these two regions into one single region as Holarctic
region. It may be pointed out that in the beginning, horses, pigs, goats, and sheep were not present in the Nearctic region but later on these animals migrated to North America from N.E. Asia through the land-bridge of Bering Strait.

The Nearctic region is characterized by a few special and typical animals e.g. pocket gophers, pocket mice, pronghorns, wild turkeys, etc. Reptiles are found in large numbers. There are 122 families of all vertebrates, 74 genera of mammals, and 169 genera of birds. Besides, 12 unique families of invertebrates, 24 unique genera of mammals, and 52 unique genera of birds are also found in this region.

Nearctic faunal region is also divided like Palaearctic region into 5 sub-faunal regions on the basis of vegetation:

• i. Tundra region is characterized by the dominance of caribou, musk ox, lemming, arctic wolf, arctic fox, polar bear, etc. It may be pointed out that the genera of the animals of Palaearctic and Nearctic faunal regions are the same but their species vary.
• ii. Temperate coniferous forest region includes moose, mule, deer, wolverine, lynx, etc.
• iii. Temperate grassland region is characterized by bison, pronghorn, jackrabbit, prairie dog, gopher, fox, coynote, etc.
• iv. Deciduous forest region includes racoons, oppossum, red fox, black bear, etc. The genera of animals of deciduous forest regions of the Palaearctic and Nearctic faunal regions are almost the same but their species vary.
• v. Desert region is characterized by lizards, snakes, kangaroo, jerboa, hamster, hedgehog, cottontail, etc.

3. Oriental Region:

The oriental region includes the geographical areas of mainly south and south-east Asia. The Himalayas, Tibetan plateau, and Chinese mountainous regions form transitional zones between Palaearctic and oriental faunal regions. Similarly, East Indies form transitional zone between Oriental and Australian faunal regions. The whole of this faunal region falls under tropical regions and hence this faunal region is associated with the Ethiopian faunal region.

This faunal region represents 164 families of all vertebrates, 118 genera of mammals, and 340 genera of birds out of which there are 12 unique families of vertebrates, 55 unique genera of mammals, and 165 unique genera of birds. This faunal region is characterized by the dominance of Indian elephants, rhinos,
several species of deers, antelopes, pheasants, tigers, lizards, snakes, gibbons, monkeys, sun bears, porcupine, etc. Tree shrews, gibbons, orangutans, and tapirs are the typical animals of the Oriental faunal region.

4. Ethiopian Region

The Ethiopian region incorporates substantial areas of the whole of Africa south of Sahara and far off southwestern Arabia which is separated from the African region by the Red Sea. This faunal region also falls under tropical climatic regions. Unlike other faunal regions, this region is characterized by minimum diversity of animals though there is the complete absence of moles, beavers, bears, and camels in this region. This region represents 174 families (22 are unique) of vertebrate animals, 140 genera (90 are unique) of mammals, and 294 genera (179 are unique) of birds.

This faunal region is further divided into 3 sub-regions:

• i. Desert region is characterized by the dominance of springbok, porcupine, jerboa, rock hyrax, etc.
• ii. Savanna region represents zebra, eland, gemsbok, hartebeest, gnu, giraffe, elephant, ostrich, lion, cheetah, etc.
• iii. Tropical forest region includes important animals like okapi, gorilla, chimpanzee, monkey, forest elephant, etc.

There is a similarity in a few animals of the Oriental and Ethiopian faunal regions like elephants, lions, cheetah, etc. Hippopotamus, aardvark, ostrich and rodents, and a few species of insectivorous animals are exclusively found in the Ethiopian faunal region.

5. Australian Region:

Australian region includes Australia, New Zealand, and islands between S.E. Asia and Australia (such as New Guinea, Soloman, Samoa, etc.). Some scientists do not include New Zealand in the Australian faunal region. There is a difference of opinions among the scientists about the linkage of this region with the oriental faunal region. This region is dominated by placental animals. Marsupials (characterized by pouch attached to the outer part of their abdomen) are the typical animals of the Australian faunal region.

These animals carry their off-springs in their pouch which has feeding mechanisms. There are 141 families (22 are unique) of vertebrate animals, 72 genera (44 are unique) of animals, and 298 genera (1989 are unique) of birds.

This faunal region is further divided into 3 sub–regions:

• i. Desert region is characterized by marsupial, mole, jerboa, parakeet, lizard, etc.
• ii. Savanna region is represented by emu, red kangaroo, bandicoot, wombat, cockatoo, parrot, etc.
• iii. Tropical forest region is dominated by the tree and musk kangaroos, wallaby, koala, oppossum, cassowary, etc.

6. Neotropical Region:

The neotropical region includes the whole of South America which is characterized by tropical environments. This region represents the largest number of exclusive mammals (which are not found elsewhere). About 32 families of marsupials (which are quite different from the Australian marsupials), and several typical and special families and genera of monkeys, birds, and rodents are exclusively found only in this faunal region. There are 168 families (44 are unique) of vertebrate animals, 130 genera (103 are unique) of mammals, and 683 genera (576 are unique) of birds in this faunal region.

This faunal region is further divided into 3 sub-regions

• i. Temperate grassland region is dominated by guanaco, rhea, viscacha, cavy, fox, shunt, etc.
• ii. Desert region is characterized by guanaco, rehea, armadilo, vulture, etc.
• iii. Tropical forest region is represented by monkeys, kinkajou, pygmy ant eater, sloth, tree snakes, parrot, hummingbirds, etc.

Some scientists have assigned the status of minor faunal region to those islands which have been connected with the mainland (though this concept of isolation of some islands from the mainland throughout the geological history of the earth is still debatable). Such islands include Hawaii Island, Greater Antilles, Madagascar, and New Zealand. The solenodons and hutia family of rodents in the Greater Antilles; tenrecs, lemurs, aye-aye, Malagasy mongooses and fossa, Malagasy rats and vanga shrikes in Madagascar and Kiwis, tustara, New Zealand frogs, etc. in New Zealand are some of the important animals of such so-called isolated islands.