Tropical and Temperate Regions:

Tropic is region of earth surrounding equator. It is restricted in latitude by Tropic of Cancer in northern hemisphere at about 23° 26' 16" (or 23.4378°) N and Tropic of Capricorn in southern hemisphere at 23° 26' 16" (or 23.4378°) S. Tropics are also referred to as tropical zone and torrid zone. Tropics comprise all areas on Earth where sun reaches point directly overhead at least once during solar year. Approximately 40 percent of world's human population lives within tropical zone (by 2008 statistics), and by 2060, 60% of the human population will be in tropics, owing to high birth rates and migration.

Some regions inside tropics may well not have tropical climate. There are alpine tundra and snow-capped peaks, comprising Mauna Kea, Mount Kilimanjaro, and Andes as far south as northernmost parts of Chile and Argentina. In biogeography, tropics are divided in Paleotropics (Africa, Asia and Australia) and Neotropics (Caribbean, Central America, and South America). Together, they are at times referred to as the Pantropics.

Temperate or tepid regions of globe lie between tropics and polar circles. Changes in these regions between summer and winter are usually comparatively moderate, rather than extreme hot or cold. Though, in certain areas, such as like Asia and central North America, variations between summer and winter can be extreme as these areas are far away from sea, causing them to have Continental climate. In regions traditionally considered tropical, localities at high altitudes (like parts of Andes) may have a temperate climate.

North Temperate Zone extends from Tropic of Cancer (at approx 23.5 degrees north latitude) to Arctic Circle (at about 66.5 degrees north latitude). South Temperate Zone extends from Tropic of Capricorn (at about 23.5 degrees south latitude) to Antarctic Circle (at about 66.5 degrees south latitude).

Tropical and Temperate Flora:

a) Common features of tropical trees: Tropical plant species often have one or more of the given features not seen in trees of higher latitudes.

• Buttresses: Several species have broad, woody flanges at base of trunk. Initially believed to help support tree, now it is believed that buttresses channel stem flow and its dissolved nutrients to roots.
• Large leaves are common among trees of C layer. Young individuals of trees destined for B and A layers may also have large trees. When reach canopy new leaves will be smaller.

b) Examples of Temperate Plants Dominant plants comprise trees such as Maple (Acer spp.), Elm (Ulmus spp.), Beech (Fagus spp.), Basswood (Tilia spp.), Oak (Quercus spp.), Hickory (Carya spp.), Cottonwood (Populus spp.), and Willow (Salix spp.).

c) Differences between Tropical and Temperate Flora

Features that differentiate tropical species of trees from those of temperate forests comprise:

• Exceptionally thin bark, frequently only 1-2 mm thick. Generally very smooth, though at times armed with spines or thorns.
• Cauliflory, development of flowers directly from trunk, rather than at tips of branches.
• Large fleshy fruits attract birds, mammals, and even fish as dispersal agents
• Branches may be heavily weighed by birds nest ferns and orchids growing on them.

Tropical and Temperate Fauna:

Tropical animals:

1) Toucans: Their large, colorful beaks are almost half the size of their short bodies. They possess small wings as they do not need to fly long distances.

2) Red-Eyed Tree Frogs: Most frogs hop, but these frogs like walking or climbing in trees. These tree frogs live in areas near ponds, streams and rivers. They like to eat insects found in tropical climates

3) Gorillas: They move around by walking on knuckles. Like chimps, gorillas are very smart.

4) Bengal Tigers: These tigers are good swimmers and climb trees. There are lots of trees in the rainforest making it a great place for them to live.

5) Boa Constrictors: These huge snakes can grow longer than 10 feet. They are generally pinkish or tan in color with dark bands. Boa constrictors aren't poisonous, and they eat small animals e.g. bats and lizards

6) Chimpanzees: They are the closest living relatives to people. Chimpanzees are very smart, and at times make hunting tools out of twigs or sticks. Chimps eat plants and small animals.

7) Monarch butterflies: These are the species of poisonous butterflies which feed on milkweed plant. They are mostly found in North America. They seem beautiful and have bright-colored scaly wings.

Dispersal of Plants:

Agents of Plant Dispersal: These comprise water, animals, wind, and force because of gravity.

Animals can serve as dispersers of seeds by:

• eating fruit and seed and passing seeds undamaged in faeces
• eating fruit but discarding seed
• transporting seeds that get caught or stick to body of animal.

Plants have also developed character traits that protect immature fruits from being eaten, comprising camouflage (like unripe fruits are frequently green), spines and chemicals that make unripe fruits unpalatable or poisonous to potential consumers.

Wind dispersal: Seeds that glide in still environment are well represented amongst trees and lianas of tropical rainforests. Though wind dispersed seeds are general among canopy and emergent trees where both wind and height improve potential dispersal distance, it is also found in some tree species of sub-canopy. Wind dispersed seeds are generally grey or brown, mimicking color of dead plant tissue.

Water dispersal: Dispersal of seed by water is essentially confined to rainforest trees fringing watercourses. Woody material surrounding seed of some tree species can float while actual seed remains feasible for significant periods.

Gravity dispersal: While rolling down slopes may appear trivial, it is perhaps the only means of dispersal for some species with large seeds. Usually, only a select few animals with the large gape can disperse large seeded species that highlights significance of cassowary as dispersal agent.

Means of Dispersal of Animals:

Some means of dispersal are given below:

1. Land bridges: They are land connections between 2 large land masses that are separated by sea which may have existed in past and facilitated movement of animals across them. Theory of land bridges was formulated to explain away discontinuous distribution of animals in continents which are presently separated by thousands of kilometers of oceans. They are of two kinds, that is, Corridor bridges and Filter bridges.

a) Corridor bridges: They are land connections of continent size stretching across oceans and connecting 2 continents. When the single continental mass known as Gondwanaland existed in Mesozoic, all southern continents, that is, South America, Africa, Australia and Antarctica were connected by huge corridors across that animals could freely migrate.

b) Filter bridges: Filter bridges are series of islands between 2 land masses which permit some animals to spread across but stop others. Animals could spread by island hopping, crossing small stretches of sea by flying, swimming, rafting or through wind. Two lines, that is, Wallace's line and Weber's line were suggested as boundaries and they surround the area known as Wallacea which has large number of islands which serves as Filter Bridge between Oriental and Australian regions.

2. Sweepstakes: Rafts, driftwood, icebergs and other floating objects in sea can carry small animals, their eggs and other stages to long distances. But this is one-way transport, uncertain and extremely dangerous.

3. Winds and storms: Wind is utilized by several plants for dispersal of their seeds for which they have specialized aerodynamic structures to keep them airborne and drift to long distances. Flying insects can also be carried by air current to long distances across oceans.

4. Human agency: Rats, cockroaches, houseflies and grain feeding insects have been steady companions of man in habitation and in travel. They are fairly common in cargo ships and have spread to all places visited by man. Pets like rabbits, dogs, sheep, cats, and goats have travelled with man to all parts of world and have at times become wild as in Australia where otherwise placental mammals were unknown.

Factors Affecting Dispersal of Animals and Plants:

There are four main factors because of which animals and plants are prevented from spreading to every possible area:

1. Climate: Animals are adapted to combination of temperature and humidity which is affected by rainfall. Lower temperature prevents most of the reptiles from migrating northwards in temperate areas. Polar bear, penguins and large number of mountain inhabiting species are adapted to cold climate and can't come down to tropics and subtropics. Amphibians required high humidity not only for their survival but also for reproduction and therefore can't venture in areas of low rainfall. Low temperature of mountains prevents certain animals like parrots from spreading to these areas.

2. Vegetation: Like animals plants are also sensitive to temperature and rainfall and they influence dispersal of animals as the latter depend on vegetation for food. Tropical areas support broadleaved dense forests while in temperate areas only cold tolerant conifers can survive, each kind harbors its distinctive fauna. Desert climate can support few plants and thus few animals.

3. Other animals: Different animals at different tropic levels make food chains that are interwoven in the complex food web. Such interactions among animals frequently limit particular species to migrate alone to other areas. Interaction between predator and prey, parasite and host and among commensals and competitors pose complex problems in the ecosystem and any immigrating exotic species can upset balance in the native population. Dingo dogs, placental cats and foxes are in danger of exterminating native carnivores in Australia.

4. Physical barriers: Barriers like mountains, deserts, rivers and oceans physically stop animals from invading new areas even when environment is conducive to survival. For land animals water is barrier and for aquatic animals land. Fresh water fishes and amphibians can't cross seas but amphibious reptiles like tortoises, lizards and snakes, owing to thick and impervious skin have crossed seas to reach distant islands far away from the mainland.

Principles of Animal Distribution:

• Animal species are distributed in areas where they are most adapted. Different barriers act in the different way for different species depending on modes of locomotion and dispersal.
• Poikilotherms usually spread slowly as compared to homeotherms (birds and mammals).
• Food, temperature, water etc. limit animals to the area even without barriers. For instance, penguins are limited to Antarctica, giant panda to bamboo forests in China and Koala to eucalyptus forests of Australia.
• Parasites usually disperse with hosts and predators along with prey.
• Majority of birds don't face any physical barriers because of their skill to fly over them.
• Low temperature prevents tropical animals to migrate northwards and polar and temperate animals to migrate southwards.
• For aquatic animals land is barrier while for terrestrial animals sea, rivers and lakes are physical barriers.
• Oceans serve as barriers for freshwater fishes and amphibians because of osmotic problems.

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