Chapter 55 Population Ecology

55.1 Environmental factors Temperature Water Sunlight Soil

Survival Techniques Conformers – Bodies adopt the temperature, salinity, and other physical aspects of their surroundings. Ex. exotherms = cold blooded Homeostasis – keeping a constant internal environment. Ex. Endotherms = warm blooded

Population Density # of individuals per unit area US census

Measuring Density 1) Actual count (census) 2) Sampling techniques (mark and recapture method)

Random sampling Lily pads 1) Count population in several squares 2) Ex. 4 squares 1 st =1 2 nd =0 3 rd =2 4 th =0 3) Add up total population counted = 3 4) Average squares counted total/squares 3/4 =.75 5) Multiply avg per square times number of squares on grid 6).75 x 10 7) lily pad population = 8

Patterns of dispersion Different populations disperse differently

Dispersion Random – no pattern Uniform – Even spaced Clumped – aggregated in patches (safty in numbers)

55.3 Population Demography Demography- quantitative study of populations Survivorship Curves - # Survivors vs Age

Type I survivorship Most survive to adult hood and old age Small amount offspring (1-2) High parental care Ex. Human, lion

Type II survivorship Equal chance of death through out life – constant loss Medium amount of offspring (litter) Some parental care early Rodents, birds, jellyfish

Type III survivorship High early death rate Many offspring Little or no parental care Sea turtle, trees, fish

55.5 Population growth Change in population size over time Δ Population size = Births during - Deaths during ΔTime time interval time interval

Zero population growth Births = Deaths

Exponential population growth model Population increase under ideal conditions Theoretical Growth without limits J curve

Logistical population growth model Takes into account the limiting factors Stabilizes at K (carrying capacity) S (sigmoid) curve

Carrying capacity = K Max population size an ecosystem can hold Based on food, room/space, predation, water

Carrying capacity is based on the maximum population surviving each year

Predator prey interactions on populations Predator population lags behind prey population

Ex. Hare vs. lynx Which population follows the other?

Rate of population increase Rate = dN/dt (change in Number of Individuals/time interval) dN/dt = (B – D) + (I – E) B =birth D = death I = immigration E = emigration OR ignore I and D dN/dt = B - D

Calculating rate of change in population near carrying capacity dN/dt = r max N(K – N)/K dN/dt = rate of change r max = maximum rate of increase (usually 1) N = number of individuals in population K = carrying capacity

Biotic potential Growth at the maximum rate due to no predators etc. Extreme growth rate will eventually end as a resource such as food diminishes

55.6 Factors that regulate population Density independent factors Floods and fires

Density dependent factors Determined by population size Resource limitations - food, water, nesting

r-selected populations – Selected by birth rate early reproduction, short life span, high mortality rate, many small offspring, with little or no parental care.

K-selected Selected by limiting factors Reproduce later in life, long life span, low mortality rate, few large offspring, with extensive parental care.

55.7 Human population growth What problems can we expect? We do not know earth carrying capacity Plague

Age structure graphs US has more females at older age