evolutionary bio (consequences of competition)

[nancy9494]

Hi friends!

 

I can't quite decipher this graph. The top portion shows P. aurelia bacteria and the bottom one shows P. caudatum bacteria. My professor said that the bottom graph is an example of asymmetric competition (one is better than the other. In this case, the P. aurelia is better). The decrease in fitness is clear as the graph progresses in time in unit days.

What I don't understand is why if both bacterium are mixed in each graph, does one show decrease why the other doesn't. I know that they are being compared to different bacteria. The only thing I can think of is the units in volume are different for each graph. For the top graph the intervals are in units of 50, while the bottom graph is in units of 40 (and therefore more detailed?).

Any clarification would be much appreciated. Thank you in advance.

 

[Argent]

This is outside my field of expertise (not that I really have one anyway), however this is my reading of it. P.aurelia occupies a niche that overlaps that of the comparison organism. The overlap is small, but it is enough to constrict resources sufficiently that when it comes up against the comparison organism its maximum population level is held to a lower level than when it can access all the resources.

 

In contrast P. caudatum occupies the same niche as the comparison organism. That organism is much more efficient at utilising the resources and so drives P. caudatum towards elimination.

 

As the note on the page says "Identical niches cannot coexist."

[nancy9494]

Seems easy now that's you've cleared it up for me haha. What I gather now is that although we are looking at the mixed pop., we are just focusing on the consequences of competition on the type of bacteria in question for each graph! That makes so much sense. Thank you!

[Argent]

That makes so much sense. Thank you!

You are welcome.