WEIT 2012 Chap4

THE GEOGRAPHY OF LIFE

Endemic Spieces

What is an endomic spiece??

An endomic specie is a speci that is unique to a defined geographic location. An organism that is native of a particular place is not endemic if it's find somewhere elese. There is two different subcategories of endemism: paleoendemism and neoendemism. A paleoendemism is an organism which was at the origin widespread but is now restricted to a smaller area.Neoendemism would be a specie that is "recent", like a species that has diverged and become reproductively isolated, like on an island, or one that has formed following hybridization and is now classified as a separate species.--TheoL 16 mars 2012 à 16:04 (CET)

This is absolutely not Okay... Nothing written since March 16... and only one question. BE VERY CAREFUL... Don't make me become mad...--Pierre.brawand 28 mars 2012 à 13:41 (CEST)

Juan Fernandez Islands

Where are these islands located ?

The islands of Juan Fernandez are situated in the South Pacific ocean, off the coast of Chile. There are three of them: Robinson Crusoe (also Isla Más a Tierra) , Alejandro Selkrik Island (alsoIsla Más Afuera) and Santa Clara Island (Isla Santa Clara). They are three volcanic islands and only one of them is inhabited by humans, the Robinson Crusoe island (around 633 people).

Which are the endemic species found on the islands ?

We can count some 5 species of birds present on the different islands. Among these five species of birds is an endangered hummingbird, the Juan Fernandez Firecrown. This hummingbird is endangered because its population is in general decline since years, the male and the female of the species are very different, so much that until the 19th century people thought that they weren’t part of the same species. Two other species endemic to the Juan Fernandez Islands are the Juan Fernández Tit-tyrant, endangered because of the loss of habitat and the Masafuera Rayadito. This last species is mainly threatened by the introduced species which degrade its habitat. The Juan Fernandez Firecrown is mostly found on the Robinson Crusoe Island whereas the Masafuera Rayadito lives on the Alejandro Selkirk Island. 126 endemic species of plants can also be found on the diverse Juan Fernandez islands, within them, we can found many strange members of the sunflower family, also called Asteraceae. This family is one of the two largest flowering plant families with more than 22,750 currently accepted species and it's largely distributed throughout the world. The members of this family are mostly herbaceous plants but we can also find some shrubs, trees and climbers as Asteraceae. Their differentiation seems to have taken place some 42-36 million years ago but the reason why they developed so successfully remains unknown.Some fur seal are also present on the islands, these "Juan Fernandez fur seal" have a particular history because they were discovered in the 16th century and their members were so rare that they were considered as extinct in the mid-20th century until we found some 200 fur seals which were protected so that the population grows up. Now we think that they are at least 10'000 animals spread on and around the Juan Fernandez Islands. And of course a handful of insects can also be found on these three islands.

Why are these islands notable ?

In fact, the islands miss some groups very common on other areas such as the amphibians, the reptile and the mammals. And we can't count any native species from these groups on the islands. This lack of major groups is even more impressive knowing that they are groups widely spread around the world and that are completely absent of these islands which are on the other side the habitat of lots of endemic species. These two characteristics of the Juan Fernandez Islands seem to be repeated on oceanic islands in general, which gives us many informations about evolution.

Biogeography

What is biogeography ?

The biogeography is the study of the distribution of species throughout the world. This tends obviously to also study the evolutionary explanation of the geography of life because we cannot deny that the distribution of species is closely related to their evolution.However, the first theory about biogeography is ironically based on religion. It was trying to connect the Noah'Ark in the Bible with the distribution of species. But the explanation had too obvious problems, that's why an other theory took place. This theory pretended that the distribution of species had been done through multiple creations distributed around the world with the quotation of Louis Agassiz (renowned Swiss zoologist): "not only were species immutable and static but so were their distributes, with each remaining at or near their site of creation. This theory was also proved to be false (by fossils between others) and finally, Darwin's theory was formulated, saying that "the distributions of species were explained not by creation, but by evolution." Even if part of this theory isn't true, the major part was an important discover for all the study of distribution.

What is continental drift ?

The continental drift is the fact that the Earth's continents move. The first hypothesis about continental drift was expressed in 1596 by Abraham Ortelius and Alfred Wegener developped it in more details in 1912. Some time later, the idea of tectonic plates came out and the theory that the Earth is broken into around ten of these tectonic plates containing the continents which move with the sea floor.

What is molecular taxonomy ?

The molecular is the classification of organisms with regard to the distribution and composition of chemical substances in them. This new way of classify the organisms is due to the information taken from DNA and protein sequences that help us understand not only the evolutionary relationships between species but also approximately when they separated from common ancestors.

What is molecular clock ?

The molecular clock is a way to deduce the time in geologic history when there is a divergence between two species or other taxa thanks to the use of fossil constraints and rates of molecular change. And with this method of the molecular clock, we can match the movements of continents that we know but also the movements of glaciers and the formation of genuine and bridges with the evolutionary relationships between species.

What is convergent evolution ?

The convergent evolution is the description of the acquisition of an identical biological trait in unrelated lineages. These traits are called analogous structures in opposition with the homologous structures whose origin is common. The divergent evolution, opposite to the convergent evolution is the fact that related species develop different traits. As an example of convergent evolution, we can take the marsupial and placental mammals. The first ones are mainly found in Australia whereas the second ones are rather located elsewhere in the world and even if they show important anatmocal differneces, they have astonishing similarities in other characteristics. We have for example the sugar glider (marsupial) and the flying squirrel (placental) which both glide in the same way from tree to tree even if they live respectively in Australia and Americas. A second example could be the banded anteater (marsupial)living in Australia and behaving just like the anteater (placental) living in Americas. Finally we can talk about the marsupial mole (marsupial) and the mole (placental) which look and act the same. The theory of creationism cannot explain this particular similarities but the evolution can, by the principle of convergent evolution which defines that species living in similar habitats have to face similar selection pressures from their environment, which leads to similar adaptations, even if the two species aren't directly related. But these species will still show key differences that allow us to deduce their distant ancestry.

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