Competition between microbes
Why compete?
Bacteria and every other every organism need resources, like space to grow. As they spread out, this often also gives them access to food.
The problem is that every other bacterial species also needs those things, and space is limited, so they have to compete.
Imagine an ecosystem that contains two bacterial species. They are identical except for their color, and they have a limited space to grow.
Q: What do you think will happen if they start out with roughly equal populations?
Competing for space
One way we can attempt to answer questions like that is by simulating each individual bacteria and observing how the populations change over time.
The image here shows the results of a simulation where both bacteria species are exactly the same and start out in roughly equal proportions.
Q: What do you observe?
Q: Can you think of a better way to display what's happening?
Graphing Populations
We can graph the total population of each species across time to get a better idea of what's happening.
Here, time is on the X-axis and abundance of each species at that time is on the Y-axis. You can move your mouse over each data point for more information.
Q: What do you see? Are both species growing at similar rates? Are the rates constant?
Grow faster!
It looks like in that situation, neither species was going to outcompete the other.
One strategy that a lot of bacteria use is to grow faster than others. Sometimes they can only grow faster in specific conditions. Other times, they sacrifice other abilities to grow faster (like antibiotic resistance).
Let's imagine the orange bacteria, for whatever reason, grow 50% faster
Q: What do you think will happen? Try to picture, or sketch, the relative and absolute abundance graphs you expect, then go to the next slide.
Grow faster - Results!
Q: Did your predictions match what happened?
Q: Does it look like growing faster helped the orange bacteria compete successfully?
Competition self check
Let's review: (hover your mouse over 'answer' to check yourself)
Q: What are two things bacteria might compete for? AnswerSpace and access to food
Q: What's one strategy bacteria might use to compete for those resources? AnswerGrowing faster.
Q: Are there drawbacks to that strategy? AnswerThey might only grow faster in specific situations and they might have to give up other traits to grow faster.
Q: What is one way to visualize how an ecosystem community changes over time? AnswerWith a population abundance graph.
Q: What is the difference between absolute and relative abundance? AnswerAbsolute abundance shows total counts. Relative abundance shows ratios.
Please proceed to the Poison Tipped Spears section.