Zoogeography – Realms, Theories pertaining to distribution of animals


Table of Contents

What is Zoogeography?

  • Zoogeography is the branch of biogeography that studies the geographic distribution of animal species, both in the present and the past.
  • It incorporates various scientific methods such as molecular biology, genetics, morphology, phylogenetics, and Geographic Information Systems (GIS) to understand the evolutionary events within specific regions.
  • Alfred Russel Wallace, considered the father of zoogeography, proposed the concept and quantified phylogenetic affinities among different zoogeographic regions, shedding light on the geographic distribution and evolutionary relationships of organisms.
  • Advances in molecular biology and evolutionary theory have contributed to unraveling questions about speciation events and expanding our knowledge of phylogenetic relationships among different taxa.
  • Integration of phylogenetics with GIS allows for the visual representation of evolutionary origins through cartographic design. This approach has been applied in research conducted in various oceanic regions, such as the southern Atlantic, Mediterranean, and Pacific Oceans.
  • DNA barcoding techniques have helped explain phylogenetic relationships within specific families of marine venomous fishes, such as scorpaenidae and tetraodontidae, residing in the Andaman Sea.
  • Research in zoogeography has also explored the evolutionary divergence of killifish (Aphanius and Aphanolebias) based on fossil records in the Mediterranean and Paratethys areas, revealing climatological influences during the Miocene.
  • Zoogeography provides ecological and geographic data that contribute to understanding the productivity of South Atlantic ocean regions and the distribution of organisms in similar regions. This knowledge helps establish frameworks for taxonomic relationships and evolutionary branching of benthic polychaetes.
  • Modern zoogeography heavily relies on GIS technology to enhance our understanding and predictive modeling of past, current, and future population dynamics of animal species on land and in the ocean.
  • By analyzing abiotic factors of habitats, such as topography, latitude, longitude, temperatures, and sea level, and their correlations with species distribution, zoogeographers can explain how populations have changed over geologic time.
  • Zoogeography investigates speciation events that may have occurred due to physical geographic isolation or the incorporation of new refugia to survive unfavorable environmental conditions.
  • Ultimately, zoogeography aims to uncover the complex patterns of animal species distribution and their underlying evolutionary processes, contributing to our understanding of biodiversity and the natural world.

What is Zoogeographical realms?

Zoogeographical realms, also known as biogeographical realms or ecozones, are large geographic regions characterized by distinctive combinations of animal species. These realms are defined based on similarities in the composition and distribution of animal taxa within their boundaries. Here are the main zoogeographical realms recognized by biogeographers:

  1. Nearctic Realm: This realm encompasses most of North America, including Greenland, Canada, the United States, and parts of Mexico. It is characterized by a high diversity of mammals, including iconic species such as bears, wolves, and deer.
  2. Palearctic Realm: The Palearctic realm covers Europe, Asia north of the Himalayas, and northern Africa. It is known for its diverse range of large mammals like horses, bovines, and big cats. It also includes many important bird species.
  3. Neotropical Realm: The Neotropical realm includes Central America, South America, and the Caribbean. It is one of the most biodiverse realms, hosting a wide array of species, including monkeys, sloths, toucans, and numerous reptiles and amphibians.
  4. Afrotropical Realm: The Afrotropical realm encompasses most of Africa, excluding the northern regions. It is known for its diverse megafauna, including elephants, rhinoceroses, giraffes, and large predators like lions and cheetahs.
  5. Oriental Realm: The Oriental realm includes South Asia and Southeast Asia, extending from India to the Philippines and Indonesia. It is known for its rich biodiversity, with iconic species such as tigers, elephants, orangutans, and diverse birdlife.
  6. Australian Realm: The Australian realm comprises Australia, New Guinea, and nearby islands. It is characterized by unique and diverse wildlife, including marsupials like kangaroos and koalas, as well as a wide range of bird species found nowhere else.
  7. Antarctic Realm: The Antarctic realm consists of the continent of Antarctica and the surrounding Southern Ocean. While terrestrial animal life is limited, this realm is home to various marine species, including seals, whales, and penguins.
  8. Oceanic Realm: The Oceanic realm encompasses the vast open oceans and islands not included in the other realms. It is home to a wide range of marine organisms, including fish, turtles, dolphins, and migratory species like whales.

These realms are not rigid boundaries, and some overlap may occur at their edges. They provide a framework for understanding the distribution patterns of animal species and the evolutionary processes that have shaped their diversity across different regions of the world.


Theories pertaining to distribution of animals

Theories Pertaining to the Distribution of Animals:

  1. Brown’s theory of centrifugal speciation:
  • Populations of a species are largest in the most favorable areas.
  • Population pressure can force pioneers to venture into less habitable peripheral areas, leading to isolation and speciation.
  • Speciation proceeds from the center to the periphery due to the centrifugal force generated by population pressure.
  • Migration and differentiation of races, clines, or subspecies occur across the species’ range of distribution.
  1. Age and area theory of Willis:
  • The age of a species is proportional to the area it currently occupies.
  • Species slowly enlarge their range of distribution in all directions.
  • Widely distributed species are older, while endemic species are younger.
  • Subdivision into races and subspecies occurs through isolation, mutations, and genetic changes.
  • Assumes that all species spread at the same slow rate throughout evolution, but this is not always the case.
  1. Climate and evolution theory of Matthew:
  • Climate changes throughout the history of evolution have a significant impact on animal distribution.
  • Continental drift, corridors, and filter bridges play no role in distribution.
  • Warm and humid periods allow animals to freely migrate and evolve.
  • Cooler ice ages make northern land masses inhospitable, leading to migration to southern continents or extinction.
  • Major placental mammals originated in northern regions and migrated southwards, while monotremes and marsupials remained confined to southern continents.
  1. P.J. Darlington’s view:
  • Generally agrees with the permanency of continents.
  • Major groups of vertebrates originated in the tropics and subtropics of the old world.
  • Tropics and subtropics still retain the most abundant and varied fauna.

These theories provide different perspectives on the factors influencing the distribution of plants and animals across continents, including population pressure, age, area, climate changes, and the role of different geographic regions in the origin and migration of species.


Plate tectonic and Continental drift theory

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