Chapter 40 Population Ecology and Distribution of Organisms – Part 2

Population characteristics Density- # of individuals per unit of area •counts •sample size estimate •indirect indicators •mark-recapture Dispersion- pattern of spacing •random- unpredictable, pattern less spacing (a) •clumped- patchy aggregation (b) •uniform- even spacing (c)

Demography: factors that affect growth & decline of populations Birthrate (natality, fecundity) - # of offspring produced Death rate (mortality) Age structure- relative number of individuals of each age Survivorship curve- plot of numbers still alive at each age N = population size t = time r = b (births) – d (deaths) = (rate of growth) Pos. r = population growth Neg. r = population decline R = 0 = ZPG (Zero Population Growth)

Survivorship Curves (plot of numbers still alive at each age) Type I Curve - Low death rate early in life (humans). Type II Curve – Constant Mortality (squirrels). Type III Curve – High death rate early in life (oysters/zebra mussels).

Population life history “strategies” r-selected (opportunistic) exponential Short maturation & lifespan Many (small) offspring; usually 1 (early) reproduction; no parental care High death rate K-selected (equilibrial) logistic Long maturation & lifespan Few (large) offspring; usually several (late) reproductions; extensive parental care Low death rate

Population Growth Models Exponential model (blue) • idealized population in an unlimited environment (J-curve); r-selected species (r=per capita growth rate) Organisms exhibit high rates of reproduction and occur in variable environments in which population densities fluctuate well below K Logistic model (red) •carrying capacity (K): maximum population size that a particular environment can support (S-curve); K-selected species Organisms live and reproduce around K and are sensitive to population density

Exponential Growth Population-Whooping Crane

Logistic Models (Paramecium, Daphnia) Vs. Population Affected by Density – Independent Limiting Factors (severe winters)

Population limiting factors Density-dependent factors •competition for resources •predation •parasites and disease transmission •stress/crowding •waste accumulation Density-independent factors •weather/climate •periodic disturbances Population Cycles - Fluctuations in Population size in response to varying effects of limiting factors (Hares & Lynx)