Bio I: Darwin question...please help

[NubianPrincess]

I have a question about theory of evolution. According to my textbook,

because habitats are different in their requirements and opportunities, the organisms with characteristics favored locally by natural selection will tend to vary in different places.

But it also says:

Lands with similar climates, such as Australia, South Africa, California and Chile, have unrelated plants and animals, indicating that diversity is not entirely influenced by climate and environment.

This confused me because it seems to suggest that other factors affect diversity, but I thought that natural selection occurs when certain organisms possess favorable genetic traits that contribute to their survival in that environment. Why does the second paragraph seem contradictory to me? What am I missing?

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[Sheri911]

Re-read your question at the bottom, you answered yourself. It states that their are some "genetic" factors (ie:crossing over, etc) that influence species, along with climate and environmental factors....

 

[racergirl]

You're not really missing anything, the book is just pointing out that more goes into diversity than just environment. For instance, starting material. What animals originally colonized the area? This will influence the products of evolution later on. For instance, Australia's large mammals are all marsupials, simply because they were "around", and evolved to fill all the ecological niches. Another examaple is parallel evolution. A shark and a dolphin are not closely related at all, but they look very similat because they have both evolved in similar environments.

 

[tidy_kiwi]

EVOLUTION.

Not all changes will be advantageous or disadvantageous (ie neutral) and in theory it is hard to drop a change once it is established in a population.

Remember - millions of years of evolution will throw up several very different solutions to the same problem.

I need coffee - sorry if I make no cents.
I will think about it and repost.

 

[NubianPrincess]

Thanks, what you all said makes sense. tidy_kiwi, are you referring to genetic mutations in the role of adaptation to the environment and in evolution? I could be wrong, but that would explain why certain species are unrelated although they are adapting to similar conditions.

 

[tidy_kiwi]

Yeah I think that was what I was getting at - sorry just a bit addled this afternoon (no sleep).

For example - different Antarctic animals will have different mechanisms to deal with the same environmental stresses. Similarly, two different species of desert plants may have different mechanisms to prevent dessication.

It is important to remember that organisms don't adapt by choice - adaptation arises through a particular phenotype (caused by random genetic mutation) having an advantage in a particular environment. These individuals then have greater chance of surviving to produce offspring thus increasing the occurence of those traits in the population and so forth.

But am I forgetting behavioural adaptation and learning? I think I am going to go home to bed!

 

[Atlas]

Also, an often overlooked aspect might be that in addition to genetic and environmental factors in adaptation, the organisms may migrate to areas where they are better suited. This idea of moving around is favorable and not as obvious as genetic or environmental factors, but is often a result of these changes.

 

[sunflower79]

Man, sounds like a midterm question I might have had last semester...

Ok, so the second quote talked about sources of biodiversity. There are many factors that affect what kind of biodiversity exists in an area, including historical biogeography, mutations, genetic drift/the founder effect, etc., which as someone suggested will change the starting material even if adaptive mechanisms are pretty similar. Also you have to take into account the different histories each place invariably has, i.e. the different events that shaped that starting material before the areas came to be similar in modern times.

Also, what I think tidy kiwi was alluding to was that organisms can't all adapt the same way simply because they are built differently-- i.e. they have various constraints (e.g. their morphology) that they just can't overcome in spite of natural selection. If you *really* are interested in that I have a cool paper I can cite you.

Hope that makes sense to you!