Island Dwarfing..........

[rooters]

I have a question about Island dwarfing:

 

A species becomes isolated on an island with limited resources. Firstly, is it correct to say that the prediction would be that the species would reduce in size.

 

Secondly, how much is genetic mutation actively involved in this process and what is the cause of the physical change in size other than by a gentic mutation.

 

Thirdly, if this makes any sense. I thought dna mutations were born out of luck rarther than a response to specific change in the environment (in this case limited island resources). If mutational change that causes the species to dwarf is luck, how can it be predicted.

 

Regards as always

[CharonY]

A species becomes isolated on an island with limited resources. Firstly, is it correct to say that the prediction would be that the species would reduce in size.

No it is not. In fact, most probably the population level declines if the resources are limited.

 

Your question shows that you have contorted how natural selection works.

So in your example you have to assume that are already individuals in your population that are smaller than the rest (or have an allele combination that results in this phenotype). Further one must assume that your theory that size reductions equals in lower ressource consumption. This means that in the new environment the alleles that result in smalle size confer a fitnees increase (compared to alleles leading to large body size).

Then it is likelier that the smaller individuals procreate more, resulting in more progenies of smaller size (or, in other words, alleles for small size spread).

 

A change in environment will not, as you you implied in your last sentences lead to a targeted adaptation to the environmental changes. It might only look like it with hindsight.

[root]

Thanks for that. I probably should have indicated that I am being specific to current examples such as the dwarthed elephants, mammoths and even the hobbit.

 

I am trying to establish the mechanism by which the species will reduce as per question 2 and 3. If you could clarify points 2 & 3 that would be great....

[CharonY]

Same applies to them. There was always a variation in size. Natural selection "provides" different fitnesses to them. As such especially your 3rd point iskinda weak to discuss.

 

But still:

2) A decrease in size can be the result from genetical factors but also e.g. by nutrient limitation. If they are taken out of the limiting situation and still remain small (or their progenies rather) then it is mostly genetically determined.

 

3) mutations are (mostly) random. as such you cannot expect a mutation for small size to happen.

[rooters]

But still:

2) A decrease in size can be the result from genetical factors but also e.g. by nutrient limitation. If they are taken out of the limiting situation and still remain small (or their progenies rather) then it is mostly genetically determined.

 

Thanks for this.

 

can I now ask, if genetical factors actively work to reduce a species size over subsequent generations is this then a mutational change. else, how does the change occur?

 

many thanks

[ecoli]

sometimes with mutation, but mostly with genetic variation due to recombinant genes, etc.

[rooters]

sometimes with mutation, but mostly with genetic variation due to recombinant genes, etc.

 

so what is the difference, genetic variation is mutation is it not as the below reference points out.

 

Genetic variation refers to the variation in the genetic material of a population or species, and includes the nuclear, mitochodrial, ribosomal genomes as well as the genomes of other organelles. New genetic variation is caused by genetic mutation, which may take the form of recombination, migration and/or alterations in the karyotype (the number, shape, size and internal arrangement of the chromosomes). Genetic drift is a statistical measure of the rate of genetic variation in a population.

 

Source:http://en.wikipedia.org/wiki/Genetic_variation

[AzurePhoenix]

Keep in mind that this typically applies mostly to large warm-blooded species. Reptiles and small mammals often show the opposite trend, increasing in size, such as komodo dragons, giant geckos and tortoises, and giant island rats.

[rooters]

Thanks for that Azure,

 

The only thing I find confusing is that should warm blooded mammals "dwarf" as a result of island isolation, then what is the mechanism as a distiction has been made that it is either natural selection or genetic mutation.

 

My problem here is that is natural selection or genetical mutation for the two are the same are they not in that Natural selection or genetic variation all require mutation?

 

Surely then island dwarfing is mutation driven???

[Skye]

Change in genetic variation can be brought about be mutation, which generates new variation, and natural selection, which selects which of these variations shall propagate. The rate of change is able to happen much faster with natural selection. The rate of mutation is generally fairly stable. The rate at which natural selection can change the genetic variation in a population is highly variable, and there's essentially no limit to it.

 

So under conditions which don't favour any individuals within the population, natural selection will have no effect and mutation will be the driving force of change in genetic variability. Under conditions that greatly favour the survival and reproduction of certain individuals natural selection will become the driving force.

[Mokele]

It's also important to realize that size is governed by a lot of alleles, and is *highly* variable between individuals; it's one of the fastest things to respond to natural selection.

 

So, short and sweet, mutation and recombination create lots of genetic variation in size in all populations. If selection acts against large animals (or for them), then average animal size changes, often quite rapidly.

 

Mokele