WEIT Chap4

The Geography of Life

The distribution of species around the world is surprisingly specific. To understand the distribution of species, we must take in account the movement of continents, for example Gondwana which 40 million years ago was a super-continent that joined South America and Australia.
In each place inhabitants live because they are adapted to their land. But also huge changes occurred all along the years since the very first species, due to those geological relations. We name it the biogeography.
Nowadays, we justify biogeography with two important developments:

• Molecular taxonomy is an accumulation of DNA information that can tell us the evolutionary relationship between species and also the approximate times when they diverged from their common ancestors. The change of DNA sequences shapes helps us estimating the divergence times of species in poor fossil records.
• Continental drift, which is the past movements of continents.

We'll notice that natural selection is different on continents and on islands. Every theory-most of them are Darwin's-developed in our chapter contradicts the ideas of creationism, and proves that evolution can be justified by natural selection.

Continents

What is convergent evolution?

Convergent evolution explains how two different species that live in similar habitats can look and behave in the same way, because of similar selection pressures from their environment.
Convergent evolution proves three evolutionary theories.

Not clear enough. Define PRECISELY what convergent evolution is. The main idea is to find similar organism despite the fact that they are NOT link... Such as marsupial and eutherian animal who look similar despite the fact that their development is very different....Pierre.brawand 29 mai 2011 à 22:09 (CEST)

1. Common ancestry, which explains the features shared (or not shared) between two infraclasses of mammals

not clea enoughPierre.brawand 29 mai 2011 à 22:09 (CEST).

1. Speciation is the process by which a common ancestor can generate several different offsprings.

not clear enough. Speciation is the process defining how new species formPierre.brawand 29 mai 2011 à 22:09 (CEST)

1. Natural selection expresses how each spieces adapted to its own environment.

species or individuals?Pierre.brawand 29 mai 2011 à 22:09 (CEST)

How can similar species live in similar habitats but on different continents?

The continental drift explains this particularity. Million years ago, the continents weren't situated as they're now.It was attach into one landmass. Which means that some place in our actual continents contain the same habitats be the descendants of earlier species that lived in the same place. The organisms continued to evolve even if theybut are now in completely different places on earth. It explains the fact that species or plant living in one area should weren't living in the same place anymore. The habitats staid similar in different continents, for example Africa and South America were part of the Gondwana, one continent. To be precise the organisms disperse and colonize a new area and finally can evolve. That's why there should be descendants. The common ancestor is directly link to the explanation of descendants of similar species in similar environment.

Islands

Darwin realized that islands play a very important role in the theory of evolution. Before we got to this evidence, we have to distinguish two types of islands: the continental and the oceanic ones.
not enoughPierre.brawand 29 mai 2011 à 22:09 (CEST)

What is a continental island?

It's an island which was once connected to a continent but was separated from it either with the increase of sea levels which formed a barrier or by moving continental plates. Examples: Madagascar, Great Britain.

What is an oceanic island?

This kind of island was never connected to a any continent. They came out of the seafloor "bereft of life", as for instance growing volcanoes. Examples: Hawaiian Islands, Galàpagos Archipelago.

What are the (main) differences between continental and oceanic islands?

There are two "sets" of facts about oceanic islands:

• Many groups of native species that we can observe on continents and continental islands, which are absent on oceanic islands.

Darwin "noticed" that this was hard to explain from a creationist point of view, because the question would be why would a creator put some species on certain islands and not on others? Moreover, why should the way in which the island was created make a difference? Particularly, on oceanic islands live small flowering plants that can evolve into trees.

Moreover, animals such as mammals, amphibians, freshwater fish, and reptiles, introduced on oceanic islands by humans manage well, so well, that after a certain period of time, they often take over, wiping out native species. For instance, the cane toad of Hawaii (native to tropical America) was introduced in 1932 to control beetles on sugar cane plantations. Now, it has became a pest, because they are too much and they kill the other animals which take them for a meal, such as cats and dogs. This exemple shows that the introduction by humans of non-native species on oceanic islands diplace and destroy the native species.

• The groups that are found in oceanic islands are replete with many similar species

Although the lack of many basic species on oceanic islands, the ones which are present, with other similar species, have enough space to colonize largely the island. Let's take for instance the Galápagos Islands where, we can find twenty-eight species of birds. Among those, the half belong to a single group of closely related birds: the Galápagos finches. It's the only place in the world which is so heavily dominated by those birds. Thus, some absent spieces are, in a way, replace by

These two observations together show that, compared to other area of the world, such as continental islands, life on oceanic islands is unbalanced.

Two other observations are also relevent:

•The oceanic island native species are plants, birds and insects with other artropodes. In "opposotion", the missing species on those islands are land mammals,reptiles, amphibians and freshwater fishes.

The reason is quite simple and obvious. We may remind us that oceanic island come out of the sea floor like volcanoes and bereft of life. Thus, the individual that may come on it would have to go across a natural barrier, which doesn't represent the same difficulty for everybody. The species of the first category would encounter lot less difficulty to reach such an island than an individual of the second category. So, the kind of species that are found on oceanic islands are those whoy can arrive, intetionnally or not, across this sea-barrier from distant island.
Let's take for instance a bird (able to fly) and a cat. To get to an oceanic island, the bird have the possibility to fly, which is far easier than the cat to swim (moreover, cats usually do not enjoy water). We could take an other example. Seeds of plants and freshwater fishes. The seeds would reach the island by floating (if it does, obviously. Here, you may pay attention to the fact that the plants which seeds doesn't float have only one possibility left to reach the island: to have been the last meal of a bird and fall on the island's ground in the guano).
However, an individual from the second category, as a frog for example, would also, ridding on "rafts" (wood logs, masses of vegetation)be able to reach an oceanic island.

• The animals and plants on oceanic islands are, with few exceptions, most similar to the species found on the nearest mainland.

An example is the Galálapagos Islands, whose species resemble to those found on the west coast of South America. The similarity cannot be explained by the fact that the two places have similar habitats, simply because they are't.

• ...

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Pierre.brawand 25 mai 2011 à 22:23 (CEST)
AllanP 5 avril 2011 à 14:37 (CEST)
EstelleV 5 avril 2011 à 14:49 (CEST)
HéloiseD 7 avril 2011 à 11:09 (CEST)

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