Population growth

J-shaped (exponential)

dn/dt=rN, but some factors becomes limiting and effects density. Intrinsic rate of increase (R), but conditions in nature are rarely ideal for long. Cause growth to depart from exponential

S-shaped (logistic)

dn/dt= rN [(K-N)/K]. exponential early but checked by natural factors. describes changes in intrinsic growth rate. Exponential phase, plateau phase, decline phase. The highest rate of increase is the inflection point : n1/2K. Environmental resistance K= carrying capacity.

limits growth

Stochastic processes especially important in small populations (genetic drift, inbreeding, allee effect.)

Density independent factors

'factors that do not tend to increase population size when they are small and decrease it when they are large, have “same” effect on population regardless of its size. (ex: variation in weather, abiotic factors)

Density dependent

have greater effect when the population is large and lesser effect when it is small. Tend to be biotic factors. Result in population regulation.

Population cycles

delayed density dependence, predator-prey dynamics, reproductive time lag, genetic factors.

r-selected

short lived, small body size, rapid development, high r at low densities, type 3 survivorship, no parental care, unstable habitats (semel parous), good colonizers/poor competitors, generalists, usually density independent adult mortality.

K selected

long lived, larger body size, slow development, low r at high densities, type 1 survivorship, extensive parental care, stable habitats (iteroparous), poor colonizers/good competitors, specialists, often density dependent adult mortality mortality. S-shape growth.

populations exist in a patchy habitat

there may be local breeding populations, each of which has a risk of extinction, but recolonization may occur following extinction, the dynamics of the local populations are not synchronized.

Metapopulations

populations are linked by dispersal, may be caused by fragmentation, extinction and colonization rates vary among patches, source (great) and sinks (drains) dynamics. Rescue effect ( help small populations)