Population growth and carrying capacity — Biology, 14–17
Why populations can grow quickly, then level off when resources and conditions limit them.
Growth has limits
A population rises when births and arrivals outnumber deaths and departures. Its carrying capacity is the largest population that an environment can support over time with its available resources and conditions.
Why use carrying capacity?
A straight-line prediction assumes each generation has unlimited food, space and clean water. Real populations compete for these things, so growth slows as the population approaches what the environment can support.
A rabbit population
A meadow has 40 rabbits. In one season, 12 are born and 4 die, with no movement in or out: 40 + 12 − 4 = 48. If food becomes scarce above 50, the population may grow briefly but cannot keep doubling.
The limit is not a fixed wall
It is tempting to treat carrying capacity as one permanent number. That mistake is reasonable because a graph often shows one line, but rain, temperature, predators and human activity can change the limit.
Managing living populations
Ecologists use these ideas to manage fisheries, forests and wildlife reserves. They can estimate when harvesting is too intense, but predictions remain uncertain because weather and food webs change.
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