adaptive radiation

Examples of adaptive radiation in the following topics:

• Allopatric Speciation

  • Typically, environmental conditions, such as climate, resources, predators, and competitors for the two populations will differ causing natural selection to favor divergent adaptations in each group.
  • This is called adaptive radiation because many adaptations evolve from a single point of origin, causing the species to radiate into several new ones.
  • Island archipelagos like the Hawaiian Islands provide an ideal context for adaptive radiation events because water surrounds each island which leads to geographical isolation for many organisms.
  • The Hawaiian honeycreeper illustrates one example of adaptive radiation.
  • The honeycreeper birds illustrate adaptive radiation.

• Loss of Biodiversity

  • The cichlids of Lake Victoria are the product of an adaptive radiation.
  • An adaptive radiation is a rapid (less than three million years in the case of the Lake Victoria cichlids) branching through speciation of a phylogenetic tree into many closely-related species; typically, the species "radiate" into different habitats and niches.
  • The Galápagos finches are an example of a modest adaptive radiation with 15 species.
  • The cichlids of Lake Victoria are an example of a spectacular adaptive radiation that includes about 500 species.

• Post-Cambrian Evolution and Mass Extinctions

  • The post-Cambrian era was characterized by animal evolution and diversity where mass extinctions were followed by adaptive radiations.
  • As animal phyla continued to diversify, new species adapted to new ecological niches.
  • Continual changes in temperature and moisture throughout the remainder of the Paleozoic Era due to continental plate movements encouraged the development of new adaptations to terrestrial existence in animals, such as limbs in amphibians and epidermal scales in reptiles.
  • Plants, too, radiated into new landscapes and empty niches, creating complex communities of producers and consumers, some of which became extremely large on the abundant food available.
  • In the following Cenozoic Era, mammals radiated into terrestrial and aquatic niches once occupied by dinosaurs.

• The Fossil Record and the Evolution of the Modern Horse

  • Early horse ancestors were originally specialized for tropical forests, while modern horses are now adapted to life on drier land.
  • Successive fossils show the evolution of teeth shapes and foot and leg anatomy to a grazing habit with adaptations for escaping predators.
  • The fossil record shows several adaptive radiations in the horse lineage, which is now much reduced to only one genus, Equus, with several species.
  • The species depicted are only four from a very diverse lineage that contains many branches, dead ends, and adaptive radiations.
  • One of the trends, depicted here, is the evolutionary tracking of a drying climate and increase in prairie versus forest habitat reflected in forms that are more adapted to grazing and predator escape through running.

• Characteristics and Evolution of Primates

  • All primates exhibit adaptations for climbing trees and have evolved into two main groups: Prosimians and Anthropoids.
  • All primate species possess adaptations for climbing trees, as they all descended from tree-dwellers.
  • This arboreal heritage of primates has resulted in adaptations that include, but are not limited to: 1) a rotating shoulder joint; 2) a big toe that is widely separated from the other toes and thumbs, that are widely separated from fingers (except humans), which allow for gripping branches; and 3) stereoscopic vision, two overlapping fields of vision from the eyes, which allows for the perception of depth and gauging distance.
  • Due to this reproductive isolation, New World monkeys and Old World monkeys underwent separate adaptive radiations over millions of years.

• Extremophiles and Biofilms

  • Prokaryotes are well adapted to living in all types of conditions, including extreme ones, and prefer to live in colonies called biofilms.
  • These adaptations, along with others, allow bacteria to be the most abundant life form in all terrestrial and aquatic ecosystems.
  • Other bacteria and archaea are adapted to grow under extreme conditions and are called extremophiles, meaning "lovers of extremes."
  • Because they have specialized adaptations that allow them to live in extreme conditions, many extremophiles cannot survive in moderate environments.
  • Other extremophiles, like radioresistant organisms, do not prefer an extreme environment (in this case, one with high levels of radiation), but have adapted to survive in it.

• Plant Adaptations to Life on Land

  • Plants adapted to the dehydrating land environment through the development of new physical structures and reproductive mechanisms.
  • As organisms adapted to life on land, they had to contend with several challenges in the terrestrial environment.
  • The organism is also subject to bombardment by mutagenic radiation because air does not filter out the ultraviolet rays of sunlight.
  • The most successful adaptation solution was the development of new structures that gave plants the advantage when colonizing new and dry environments.
  • Discuss how lack of water in the terrestrial environment led to significant adaptations in plants

• Heat Conservation and Dissipation

  • For example, vasodilation brings more blood and heat to the body surface, facilitating radiation and evaporative heat loss, which helps to cool the body.
  • Some animals have adaptions to their circulatory system that enable them to transfer heat from arteries to veins, thus, warming blood that returns to the heart.
  • This adaption, which can be shut down in some animals to prevent overheating the internal organs, is found in many animals, including dolphins, sharks, bony fish, bees, and hummingbirds.
  • In contrast, similar adaptations (as in dolphin flukes and elephant ears) can help cool endotherms when needed.

• The Origins of Archaea and Bacteria

  • Early earth had a very different atmosphere (contained less molecular oxygen) than it does today and was subjected to strong radiation; thus, the first organisms would have flourished where they were more protected, such as in ocean depths or beneath the surface of the earth.
  • It is probable that these first organisms, the first prokaryotes, were adapted to very high temperatures.
  • Early earth was prone to geological upheaval and volcanic eruption, and was subject to bombardment by mutagenic radiation from the sun.
  • The evolution of Archaea in response to antibiotic selection, or any other competitive selective pressure, could also explain their adaptation to extreme environments (such as high temperature or acidity) as the result of a search for unoccupied niches to escape from antibiotic-producing organisms.

• Introduction to Light Energy

  • The sun emits an enormous amount of electromagnetic radiation (solar or light energy).
  • The electromagnetic spectrum is the range of all possible frequencies of radiation .
  • Each type of electromagnetic radiation travels at a particular wavelength.
  • The sun emits energy in the form of electromagnetic radiation.
  • All electromagnetic radiation, including visible light, is characterized by its wavelength.