Questions about evolution

[pgrmdave]

But how did they begin - how did we get from self-replicating protein to endoplasmic reticulum?

[Fishteacher73]

Prokaryotes don't have membrane bound organelles. They are essentailly a greasy sack with a bit of DNA strewn about in it. Eukaryotes do have these organelles. I personally have not seen to much about the evolution of the ER, Golgi bodies, etc. Outside of the nucleus and the mitochondria most other organelles are concerned with either houskeeping (cell division, digestion, etc.) or protien synthesis. I would assume that each has its own evolutionary origins (I think I remember the Golgi bodies were a spin off of the ER), but unfortunately I had a tendency to doze off durring cell physiology (two jobs, two kids and a full load at school....oops; and it didn't help that the professor was about as interesting as eating paste... :( )

[bumab]

Chloroplasts are the same if I recall. As for the rest of the organells, they are constructed by the cell.

 

Yeah, they are the same- their own DNA and replication schedual.

[BEAKER]

Sparrows live in the Galapagos. Sometimes for some years at a time the water level is higher. Thus insects are in sections of the rocks that do not have as deep of worn away holes. THis gives sparrows with short beaks an advantage. Thus after a few years, generations of short beak sparrows take over.

 

But as the water level sinks, the deeper holes in the rocks become the homes for the insects. Then longer beaks are required and long beak sparrow thrive and grown in number, short beak sparrows dying of starvation.

 

It would seem to me that the long beaked sparrows would have the advantage in eather case.

 

By the way, what ever happened to the short necked girraff?

[Tormod]

By the way, what ever happened to the short necked girraff?

 

It is happily grazing on African steppes known as the Okapi.

 

http://www.danger-island.com/true/mokapi/okapi.html

[chill]

I recently had an interesting topic for my ecology module on vegetation succession. I know it's quite an old theory. As an example, I'll take the ruins of some old building. At first, weeds and grasses thrive, as they are generalists and good at surviving harsh conditions. After a while, these species alter the soil state, such that other plant species become more suited to living in this environment. This process of taking over and altering continues until the woody trees come about, and depending on the climate, may produce temperate or tropical forests. When this comes about, a climax is reached, where there is no further altering of the soil overall, and the diversity levels stabilise, along with the biomass and productivity. You see this happening all the time in tropical rainforests (which are mostly in the climax stage).

 

My question is why don't the first batch of species (weed, etc.) have to alter the soil? Why can't they evolve a method in which they do not alter it, therefore increasing their survival rate and dominance?

[Fishteacher73]

Many of the first stage reclamation species are short lived fast growing species. They generally alter the sopil by dying and returning nutrioents back to the soil. Perhaps they also will alter the chemistry of the soil for it to be more hosptable to the second wave.They are dispersed wide and far and have no real biological pressure on them to really alter their methods. The change of stage comes when the secondary growth starts and is better able to utilize the resources (light, nutrients, etc.). This shift tends to occur ofter a dormant period (Winter, say) when the first stage plants have been killed off due to seasonal changes).

 

Another way to look at this would be to understand that the second stage growth has also evolved with this idea of reclamation. There is a constant cycle of clearing (through disease or fire for example) that many of these plants depend on. Red woods will not release the seeds unless the cones have been subjected to a reasonable amout of heat (read: a fire). Many other plant have come up with chemical means in which to drive off the first wave after the soil has become good enough. Birch trees secrete toxins that prevent other seeds from germinating. Once the soil is optimal for their growth they begin to sprout. Once they start growing they begin to inhibit the growth of other plant and secure the resources.

[chill]

Why is it that in some cases (take for example the cane toad in Australia), introduced species can dominate over the local species without human intervention (other than actually introducing the species)?

Shouldn't it be that the introduced species are wiped out as they are not as well adapted to that environment as the local species? Therefore, it should be harder for them to compete in getting resources with, say, an indigenous australian tree frog.

[zadojla]

Because species don't exist in a vacuum. For instance, a given species might have predators that don't exist in the new environment, or the new climate may be more conducive to reproduction. Or it could be as simple as the introduced species is more aggressive, or can eat a more varied diet.

There are so many variables that it is impossible to predict accurately what might happen in advance.

[Buffy]

There's nothing that says a species introduced into a new environment won't thrive. Take a species from a really awful environment, not conducive to life at all and put it in a nutrient rich environment with no predators and it will thrive. In San Francisco Bay the biggest ecological threat is the Zebra Mussel which hitched a ride here as ballast in cargo ships, and it has eradicated large numbers of native species that it has squeezed out of existence.

 

Cheers,

Buffy

[Fishteacher73]

Just like most things we only tend to remember the bad things. It is estimated that only 5-10% of introduced species can actually form sustainable populations and only 2-3% form growing populations. Here is an excellent USGS article about how and why : http://biology.usgs.gov/s+t/SNT/noframe/ns112.htm

 

I recently saw that they believe that with the exotic pet trade, people have released enough Burmese pythons in FL to form a stable population in the wild. Looks like Mickey's gonna get ate.... :)