Sigmoid Growth Curve

• When small number of individuals in a species are in a habitat, we get a predictable population growth curve pattern (S-curve)
• Lag phase: Population size is very low as individuals acclimatise to habitat; reproduction rate is zero or very low so many species have a breeding season, which must occur before population size can grow
• Log/exponential phase: Reproduction rate is fast (greater than death rate), population size increases rapidly; no limiting factors, plentiful resources, and favourable abiotic factors for growth
• Stationary phase: Population size evolved out at habitats’ carrying capacity; reproduction and death rate are equal so it remain stable with small fluctuations around a mean (k) as environmental factors change (seasons)
• Post-stationary phase: Several things may happen, depending on organism and environmental conditions: wither numbers stay constant for long periods or fall slightly before remaining constant (seasonal conditions)
• Sigmoid is typical of k-strategists: have fewer offspring but heavier investment (increase survival); limiting factors exert more force closer to carrying capacity and deceleration before stationery phase is reached
• R-strategists have different growth, produce lots of offspring, but with little investment (high death rate); log phase has rapid increase exceeding crrrying capacity before limiting factors impact (boom and bust); when capacity is exceeded, lack of resources and increased competition leads to more death, includes spieces with short generation time (e.g. bacteria, algae) and pioneer species