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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