Selective Disadvantage

[sunspot]

Here is a new twist on evolution and selective advantage. It has to do with evolution leading to selective disadvantage. A good example of this is the cute critter called the koala bear. It will only eat leaves from the eucolytus tree. This is all fine and dandy, but if there is a change in the environment due to nature or humans, its narrow range of adaptation will cause it to be at a selective disadvantage. Many people work very hard to resist any environmental change so cute and nice critters, like the koala, will not be put in the position of selective advantage evolution.

 

What I thought might be a good experiment is to see if it is possible to train koala to eat other plants to help decrease its selective disadvantage. I know of no practical reason it can't eat other plants so it can be a more inclusive vegatarian, with more selective advantage. It is possible that the smell of eucolypus is what attracts him to this tree. Maybe we can spray eucolytus oil on bambo or something and see if we can help diversify his selective disadvantage diet. I would still give him his favorite food but with other things added in.

[JustStuit]

The koala (koala bear is incorrect) adapted to eat eucalyptus leaves when Austraila changed from a rainforest to the current arid climate. Eucalyptus forests showed up at this time and it adapted a new digestive track to eat these leaves that no other animals do. They still eat other plants, just not as much.

The main advantage it gained was that the leaves contained enough water that it did not have to drink. Now it could stay up in trees and survive longer (until trees died) in droughts. It comes into less contact with predators this way.

Wikipedia:

The Koala lives almost entirely on eucalyptus leaves. This is likely to be an evolutionary adaptation that takes advantage of an otherwise unfilled ecological niche, since eucalyptus leaves are low in protein, high in indigestible substances, and contain phenolic and terpene compounds that are toxic to most species.

Also, the koala was brought to Kangaroo Island where it reached nuisance level with lack of predators.

It seems like it is pretty well off and the evolving helped it to me.

[Edtharan]

Specialists will usually be able to out compeat generalists for a specific food source. However a specialist will be at a disadvantage if that food source becomes scarce.

 

With the spread of Eucalyptus trees as Australia dried out, this gave the Koala a big advantage to specialise. However When these trees become more scarce they are at a disadvantage as they can not make use of other food sources.

 

The other advantage a specialist has over a generalist is that they become more efficiant at extracting neutient out of their specific food. This means that they can usually survive with food sources that would not be even edible to other species. This is also the case with the Koala. The Eucalyptus leaves have a lot of toxins in them, but because the Koala is a specialist, it has evolved to be able to handle these toxins that would kill other animals.

 

So a specialist can outcompeate generalists for a specific food source and can get more nutiment and access foods that would not be available to a generalist. This is why an organism will evolve to be a specialist.

 

The down side is that if the food source that they rely on becomes scare or extinct then they will have no other food source to move to and they will die out. Generalists are able to move to another food source in this situation.

[sunspot]

Thanks for the info. What is interesting is how the Koala was able to adapt to a toxic food source. Necessity created a genetic potential for the needed changes in the digestive tract. I can see the koala pushed up these tree by preditors afraid to come down, needing to live off the forest floor. They probably felt sick at first, but if one gets hungry or thirsty enough, even marginal things begin to taste good.

[Edtharan]

AFAIK the toxicity of Eucalyptus increased along with the proliferation of Koalas, probaly in response to another herbivore, which if it was a generalist would just move to another food source, and the Koala as it is a specialist would have to adapt to the increased toxicity. The increased amount of food available to Koalas, due to the switching of other herbivores from the Eucalypts to another food source, allowed their population to expand and also to become more specialised (plentiful food source, low competition for it).

[SkepticLance]

Actually, in more recent years, the koala has had other things to worry about.

The main item governing its survival over the past 60,000 years has been predation by humans. The Australian Aboriginee regarded it as food.

 

More recently, with legal protection, it has, in many places, become too bloody successful, and reproduced to the point of overriding its food supply.

The koala has come close to destroying the very forest it depends on. And sometimes has actually done it.

[Dr. Dalek]

Controlled or limited hunting might be necessary to thin the species out enough to preserve it without totally wiping it out. I live in Maine and Turkeys have proliferated in this area and must be hunted in order to preserve them and prevent them from becoming a nuisance.

I've never had Koala before, but I think it would taste good with sweet and sour sauce.

[the tree]

Here is a new twist on evolution and selective advantage. It has to do with evolution leading to selective disadvantage.

How is natural selection new?

What I thought might be a good experiment is to see if it is possible to train koala to eat other plants to help decrease its selective disadvantage.

Of course it would be, but it wouldn't have any evolutionary affect whatsoever because training is not inheritted.

[sunspot]

Selective advantage and disadvantage, as pointed out by Edtharan, can be correlated to generalization and specialization of behavior. The Koala has become a specialist at eating eucalypus. This is good in a controlled environment but may pose a problem if the environment changed too much. The rat or other rodents, are more generalized in their eating habits such that if the environment changed drastically they have already been experimenting and could more easily adapt to change.

 

An analogy betweeen selective specialization and generalization is connected to the contrast between children and adults. Almost all children, especially when they are small, don't like veggies, or will only eat certain foods. In this case, mother nature, or their mother will create a controlled environment for them to make sure they eat something. As the child gets older, their tastes change and their understanding of nutrition will increase and they will migrate toward a generalist eating style. This makes eating more flexible and allows less dependancy on mother nature to maintain a controlled environment. This is not true in all cases. There are many adults that have very specific requirements, based more on infantile specialized subjectivity.