Population Ecology

3 Fundamental Characteristics of a Population Density-number of individuals per unit area or volume Dispersion-pattern of spacing Demographics-vital statistics of pop and how they change over time

Density Count Mark-recapture method Marked recapture =Marked 1 st Total in 2 nd Population size Affected by immigration and emigration

Patterns of dispersion Territorality Most common

Life Tables (cohort)

Survivorship Curves

Reproductive Rates Reproductive table/ Fertility schedule

Life History traits Big-bang reproduction (semelparity) –Often in harsh climate when offspring survival rate low –Many offspring –Often one time –Salmon –Agave-grows for years -then wet year-seeds

Iteroparity Repeated reproduction More common in dependable environments But there are those –Oak trees and sea urchins-many offspring repeatedly

Exponential Growth

Per capita b(per capita birth rate) = births per year/pop size d (per capita death rate) = deaths per year/pop size SO to predict number of births, B= b N

Population growth equation

If r > 0, population is growing. If r < 0, population is declining. ZPG=Zero Population Growth

Exponential Growth Growth under Ideal conditions

Logistic Model A population grows more slowly as it nears it carrying capacity

K selection-sensitive to population density (usually in areas that are close to carrying capacity r selection-maximize reproductive success (usually where environments are below carrying capacity

Density dependent-death rate that rises with density Density independent-rate does not change with density

Density-Dependent Population Regulation Competition for resources Territoriality Disease Predation Toxic wastes Intrinsic factors (psychological)

Population Dynamics-complex interactions between biotic and abiotic factors that affect pop size Stability and fluctuation (Soay sheep) –Weather, parasites

Predator/Prey

Population Cycles

10 year cycles of Hares 3 hypotheses: Food shortage during winter, but why 10 year? Predator-prey interactions-other predators involved? Sunspot activity-when low, less ozone- more UV-plants produces UV-blocking chem and fewer chem that deter herbivores

So Provided food…same cycles Radio collars-predators ate 90%-no hares died of starvation-so eliminated predators and food still seemed to play a part-better fed can escape Low sun spot  rise in hares SO…predators and sunspots play a role, but food less

Metapopulations Local populations linked-occupy discrete patches of suitable habitat in a sea of unsuitable habitats

Global Human Population Not growing exponentially, but still increasing rapidly million billion billion billion Grows by 200,000/day # increasing, but rate is slowing

Demographic transition From: ZPG= high BR - high DR To: ZPG=low BR – low DR

Age Structure Pyramids

Infant Mortality and Life Expectancy

Estimates of Carrying Capacity Needs: food, water, fuel, building materials and other resources-clothing, transportation, etc. Ecological footprint –Add up all ecologically productive land and divide by population= 2 hectares(6 acres)/person –If reserve land for parks, etc. so 1.7 ha/person

But In US, our ecological footprint= 10ha!

Transition Page