The highest count is not carrying capacity
- The idea
- Predict
- See it
- Why
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The idea
“Carrying capacity is the biggest the population ever got.”
Carrying capacity sounds like a maximum, so the top of the graph looks like the answer. A population can climb past what its habitat supports, though, and then fall back.
The short version
The mistake: Carrying capacity is the biggest the population ever got.
What's actually true: Carrying capacity is the size where births and deaths balance, the level a population settles around over time.
- Carrying capacity, K, is the largest population the habitat's resources can support over time. It belongs to the habitat, not to any one count.
- Below K, births outnumber deaths and the population grows. Above K, deaths outnumber births and it shrinks. At K they balance.
- A population can overshoot K. Births keep coming for a while after food per individual has dropped, so the count climbs past K before deaths catch up.
- To find K, look for the level the count returns to from above and below, or the size where births equal deaths.
On the exam: K is where births equal deaths, the level the count comes back to. A peak can sit above it.