This video, we're going to talk about resource partitioning and partial niche overlap between competing organisms. And so what happens to a weaker competitor when its niche only partially overlaps with a stronger competitor's niche? Well, in that case, resource partitioning can occur. And this is when a species actually avoids competitive exclusion by differentiating or changing its niche and partitioning the resources that are available. And so resource partitioning can cause an organism to shift from its fundamental niche to its realized niche.

Now, the fundamental niche is the full or total theoretical niche that a species could potentially occupy without any competition. Whereas the realized niche, on the other hand, is the smaller portion of the fundamental niche that a species actually occupies due to competition. So let's take a look at this image down below where we've got these two graphs very similar to the ones that we saw in our last lesson video. And so notice that we're showing you the same exact stronger competitor here with Paramecium aurelia here with this reddish curve. But this time, we're showing you a different, weaker competitor in Paramecium bursaria with this green curve.

And notice that this time, there's only partial niche overlap between these two competing species, which is what allows for resource partitioning to occur. And so notice that the weaker competitor is shifting from its fundamental niche, this full curve here, over to its realized niche. And the realized niche is the smaller darker green portion of the curve. And this shift in niche is occurring because of competition with the stronger competitor. Now, the weaker competitor, by changing its niche in this particular way, it reduces competition and thereby helps the weaker competitor to avoid competitive exclusion.

Therefore, it can coexist in the same community with this competitor. And we can see this actually happening over here in this graph on the right, where once again we've got time on the x-axis and the number of cells on the y-axis. And we've got P. Aurelia growing alone and growing mixed together with P. Bursaria.

And then we've got P. Bursaria growing alone and mixed together with P. Aurelia. And so notice that when these two species are growing alone, they exhibit those classic sigmoidal logistic growth curves that we expect to see. But when they're mixed together, these two species are going to compete with one another.

And we know that competition is a minus-minus interaction where both organisms are negatively affected. And so we can see that P. Aurelia is negatively affected when it's growing together because its growth is somewhat diminished, and we can see something similar happening here with P. Bursaria when it's growing together. Its growth is diminished.

Now the key difference here is that because these two species only have partial niche overlap, resource partitioning can allow the weaker species to avoid competitive exclusion and coexist with the stronger competitor. And so notice that this time around, the weaker competitor is not driven into local extinction or local exclusion like what we saw in our last lesson video, and that's because of resource partitioning. So it's allowed to coexist with the stronger competitor because of resource partitioning. So this here concludes our lesson on this, and we'll be able to learn more and apply these concepts and problems moving forward. So I'll see you on our next video.