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Species distribution patterns are based on biotic and abiotic factors and their influences during the very long periods of time required for species evolution; therefore, early studies of biogeography were closely linked to the emergence of evolutionary thinking in the eighteenth century. Some of the most distinctive assemblages of plants and animals occur in regions that have been physically separated for millions of years by geographic barriers. Biologists estimate that Australia, for example, has between 600,000 and 700,000 species of plants and animals. Approximately 3/4 of living plant and mammal species are endemic species found solely in Australia ( [link] ab ).

 Photo (a) depicts a wallaby, a member of the kangaroo family. The wallaby is brown with white flecks on its fur and a light brown underbelly. Its hands are clasped together. Photo (b) shows an echidna. Like a porcupine, the echidna has a compact body covered with brown and white quills. It has a long, slender snout.
Australia is home to many endemic species. The (a) wallaby ( Wallabia bicolor ), a medium-sized member of the kangaroo family, is a pouched mammal, or marsupial. The (b) echidna ( Tachyglossus aculeatus ) is an egg-laying mammal. (credit a: modification of work by Derrick Coetzee; credit b: modification of work by Allan Whittome)

Sometimes ecologists discover unique patterns of species distribution by determining where species are not found. Hawaii, for example, has no native land species of reptiles or amphibians, and has only one native terrestrial mammal, the hoary bat. Most of New Guinea, as another example, lacks placental mammals.

Check out this video to observe a platypus swimming in its natural habitat in New South Wales, Australia.

Plants can be endemic or generalists: endemic plants are found only on specific regions of the Earth, while generalists are found on many regions. Isolated land masses—such as Australia, Hawaii, and Madagascar—often have large numbers of endemic plant species. Some of these plants are endangered due to human activity. The forest gardenia ( Gardenia brighamii ), for instance, is endemic to Hawaii; only an estimated 15–20 trees are thought to exist ( [link] ).

The photo shows a white flower with seven smooth, diamond-shaped petals radiating out from a yellow center. The flower is surrounded by waxy green leaves.
Listed as federally endangered, the forest gardenia is a small tree with distinctive flowers. It is found only in five of the Hawaiian Islands in small populations consisting of a few individual specimens. (credit: Forest&Kim Starr)

Energy sources

Energy from the sun is captured by green plants, algae, cyanobacteria, and photosynthetic protists. These organisms convert solar energy into the chemical energy needed by all living things. Light availability can be an important force directly affecting the evolution of adaptations in photosynthesizers. For instance, plants in the understory of a temperate forest are shaded when the trees above them in the canopy completely leaf out in the late spring. Not surprisingly, understory plants have adaptations to successfully capture available light. One such adaptation is the rapid growth of spring ephemeral plants such as the spring beauty ( [link] ). These spring flowers achieve much of their growth and finish their life cycle (reproduce) early in the season before the trees in the canopy develop leaves.

 This photo shows a white flower with five diamond-shaped petals radiating out from a green center. Faint purple lines radiate out from the center of each petal toward the tip. Five stalk-like stamens with pink-tipped anthers extend from the flower’s green center.
The spring beauty is an ephemeral spring plant that flowers early in the spring to avoid competing with larger forest trees for sunlight. (credit: John Beetham)

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Source:  OpenStax, University of georgia concepts of biology. OpenStax CNX. May 28, 2013 Download for free at https://legacy.cnx.org/content/col11526/1.2
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