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 1st

Total in 2nd Population size

• Affected by immigration and emigration

Patterns of dispersion

Territorality Most common

Life Tables(cohort)

Survivorship Curves

Reproductive RatesReproductive 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 spotrise 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

• 1650- 500 million• 1850- 1 billion• 1930- 2 billion• 1975- 4 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