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How does early reproduction affect the rate at which a population can grow?

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Common wildebeest — population ecology A herd of common wildebeest (*Connochaetes taurinus*) migrating across a dusty savanna in Africa. The animal is a keystone species (i.e., a species with a disproportionately large effect on its biological community) in plains and acacia savanna ecosystems from southeastern Africa to central Kenya.

In population ecology, the age at which an organism first reproduces is a critical factor in determining how quickly a population can grow. Populations where individuals reproduce at an earlier age generally have the potential to grow much faster than those where individuals delay reproduction.12

This relationship is mathematically linked to the mean generation time ( $T$ ), which is the average interval between the birth of an individual and the birth of its offspring. The intrinsic rate of natural increase ( $r$ ), which measures how fast a population grows, is calculated by dividing the natural logarithm of the net reproductive rate ( $R_{0}$ ) by the mean generation time:3

$r \approx \frac{\ln (R_{0})}{T}$

Because $T$ is in the denominator, a shorter generation time—resulting from earlier reproduction—increases the value of $r$ , leading to a faster population growth rate. For example, species like mice exhibit higher intrinsic rates of increase compared to elephants primarily because they reach reproductive maturity much sooner.3