The intrinsic rate of increase, written r_m, is the exponential growth rate a population reaches when food is unlimited and nothing eats it, at one temperature and host. Birch set out the modern method in 1948: combine age-specific survival and egg-laying from a life table and solve for r. It is the best single number for comparing how fast pests explode.
In practice
An r_m of 0.25 per day means the population grows by e^0.25, about 28%, every day and doubles in ln 2 / 0.25 = 2.8 days. Ten mites become 10 x e^(0.25 x 21), about 1,900, in three weeks. Values come from lab leaf discs or single host plants, so treat them as an upper bound for a cannabis room with predators, crowding and plant defences. Temperature changes r_m more than anything else a grower controls.
Don't confuse with
- Net reproductive rate (R0): offspring per female per generation, not per day.
- Finite rate of increase (lambda): e^r_m, the daily multiplication factor.
- Fecundity: eggs per female, one input to r_m.
