Science 10 Evolution: Environment & Organism Changes

Diversity of LifeHumans comprise one branch of life’s fascinating diversity. Evolution results in a vast number of different adaptations for survival and reproduction. Life exists in many different forms & places; in soil, on the surface of land, in the water and in air. All species on earth have not yet been discovered. 1.8 million species are known today. There may be as many as 100 million!

About one million currently unknown species of insects There at least 360 000 green plants Another 75 000 are molluscs (octopi, squids, snails,

mussels ect) Nearly 60 000 fungi have been scientifically described Among the vertebrates roughly 28 500 ray finned fish,

10000 birds, 8000 reptiles and 5000 mammals have been described. There are at least 4000 species of red algae(protists)

Past organisms were very different than those now alive. The fossil record shows key evolutionary changes over large time scales for example: mass extinctions, the emergence of terrestrial vertebrates, the amniotic egg or the origin of flight in birds.

Mass Extinctions: The fossil record shows that most species that have ever lived are now extinct. The extinction of species are sometimes caused by changes to a species’ environment. At times, the rate of extinction has increased dramatically and caused a mass extinction. Mass extinction is the result of disruptive global environmental changes.

Consequences of Mass Extinctions: Mass extinction alters ecological communities and increase the niches available for organisms to fill. It can take from 5 to 100 million years for diversity to recover following a mass extinction. On a smaller scale, individual ecosystems can recover much quicker. The percentage of marine organisms

that were predators increased after the Permian and Cretaceous mass extinctions. Mass extinction can pave the way for adaptive radiation.

1

Science 10 Environmental change:Although global catastrophes will lead to rapid, extensive loss of diversity and provide the opportunity for new species to develop, more often than not the changes to environment happen on a much smaller scale. Charles Lyell was a geologist who’s work influences Charles Darwin on the theory of evolution. Lyell showed that the earth changes (earthquakes, volcanoes, moving continents etc) over time. Change in ecosystem is called ecological succession. This is the process of gradual change that occurs when organisms colonize a habitat, modify it, and are forced out by a new species better adapted to the now altered environment.

Organism Change:Darwin realized if the earth could change so could animals. He proposed this took place through a process he defined as Evolution by Natural Selection where environmental factors favour the selection of fit individuals. When an organism is born, it belongs to a species and possesses a unique set of characteristics. Over time, living organisms have changes in response to changes in the environment. Ex. Marine sticklebacks had to adapt to their fresh water environments when they got stuck in ponds and after the last ice age.

Natural Selection:Natural selection is the process that makes change in living things possible. It is the process where the best adapted members of a species will survive and are better able to reproduce and pass along their traits. Sometimes, organisms are born with unique characteristics that give them an advantage within their niche. Ex. Salmon with a slightly larger tail may be able to swim faster and farther in a river, therefore escape predators and be able to reproduce more.

Those with unfavourable traits have less chance to reproduce and pass along their traits. Ex. A salmon with a smaller tail may never have a chance to spawn because it cannot swim to the correct location.

Darwin’s Finches: An Example of How Organisms Adapt to ChangeThe Galapagos Islands, off the coast of Ecuador, are a famous example of natural selection. Many species on these islands are very similar to each other but different from species on the mainland of South American continent. There are 13 species of finches on the islands that develop from a single species on the mainland. Each species has a unique characteristics for feeding and mating, that allows it to thrive in its own niche and not compete with other finches for resources. This is called adaptive radiation.

2

Science 10

Adaptive Radiation:Adaptive radiation describes the evolution of diversity adapted species from a common ancestor. Adaptive radiations may follow:

mass extinctions natural disasters mutations creating new characteristics colonization of new regions

Worldwide Adaptive Radiations:Mammals underwent an adaptive radiation after the extinction of terrestrial dinosaurs. The disappearance of dinosaurs (except birds) allowed for the expansion of mammals in diversity and size. Other notable radiations include photosynthetic prokaryotes, large predators in the Cambrian, land plants, insects and tetrapods.

Regional Adaptive Radiations: Adaptive radiations can occur when organisms colonize new environments with little competition. The Hawaiian Islands are one of the world’s great showcases of adaptive radiation.

3