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2005-2006
Population Ecology
Changes to population size• Adding & removing individuals
from a population• birth• death• immigration• emigration
2005-2006
Growth rate• Exponential growth • characteristic of a population without limiting factors• ex. introduced to a new environment
2005-2006
African elephantprotected from hunting
Whooping cranecoming back from near extinction
Carrying capacity• Can populations continue to grow
exponentially?• of course NOT!• what sets limit?
• resources, predators, parasites
• Carrying Capacity (K)• maximum population
size that environment can support with no degradation of habitat• not fixed; varies with
changes in resources
2005-2006
Model of growthDecrease in rate of growth as reach carrying capacity
2005-2006
Different life strategies• K-selection• r-selection
2005-2006
K-selection
r-selection
mortality constant
Reproductive strategies• K-strategy• have few offspring & invest a lot of energy in
raising them to reproductive age• primates• coconut
• r-strategy• have many offspring & invest little in their
survival• insects• dandelion & other weeds
2005-2006
Predator – prey interactions• Population cycles
2005-2006
Age structure• Relative number of individuals of each age
2005-2006
What do the data imply about population growth in these countries?
Human populationWhat factors have contributed to this exponential growth pattern?
2005-2006
1650500 million
20056 billion
Is the human population reachingcarrying capacity?
2005-2006
Community Ecology
Inter-species interactions • Symbiotic interactions• competition (-/-)
• compete for limited resource• 2 species cannot coexist in a community if their niches are
identical
• predation / parasitism (-/+)• mutualism(+/+)
• lichens (algae & fungus)
• commensalism (+/0)• barnacles attached
to whale
2005-2006
2005-2006
commensalism (+/0)
(+/+) mutualism
predation (+/-) competition(-/-)
Niche • An organism’s niche is its ecological role
habitat = address, niche = job
2005-2006
Resource partitioning
Niche & competition• Competitive Exclusion
• No two similar species can occupy the same niche at the same time
2005-2006
Predation drives evolution• Predators adaptations• locate & subdue prey
• Prey adaptations• elude & defend
2005-2006
spines, thorns, toxins
horns, speed, coloration
Trophic structure• Food chains• feeding relationships• food chain usually 4 or 5 links =
trophic levels• length of food chain limited by
inefficiency of energy transfer
2005-2006
Energy transfer• Energy in• from the Sun• captured by autotrophs =
producers (plants)• Energy through• food chain
• transfer of energy from autotrophs to heterotrophs (herbivores to carnivores)
• heterotrophs = consumers• herbivores• carnivores
2005-2006
Energy inefficiency
2005-2006
incompletedigestion
metabolism
Pyramids of production• represent the loss of energy from a food chain• how much energy is turned into biomass
2005-2006
Food webs• Food chains are hooked
together into food webs• Who eats whom?• a species may weave
into web at more than 1 trophic level• bears• “there’s always a bigger
fish”
2005-2006
What limits the length of a food chain?
Implications • Dynamics of energy through ecosystems have
important implications for human populations• what food would be more ecologically sound?
2005-2006
Disturbances • Most communities are in a state of
change due to disturbances • fire, weather, human activities, etc.• not all are negative
2005-2006
Disturbances • Disturbances are often necessary for community development
& survival
2005-2006
Different life strategies• K-selection• r-selection
2005-2006
K-selection
r-selection
mortality constant
Reproductive strategies• K-strategy• have few offspring & invest a lot of energy in
raising them to reproductive age• primates• coconut
• r-strategy• have many offspring & invest little in their
survival• insects• dandelion & other weeds
2005-2006
Predator – prey interactions• Population cycles
2005-2006
Age structure• Relative number of individuals of each age
2005-2006
What do the data imply about population growth in these countries?
Human population
What factors have contributed to this exponential growth pattern?
2005-2006
1650500 million
20056 billion
Is the human population reachingcarrying capacity?
2005-2006
Community Ecology
Inter-species interactions • Symbiotic interactions• competition (-/-)
• compete for limited resource• 2 species cannot coexist in a community if their niches are
identical
• predation / parasitism (-/+)• mutualism(+/+)
• lichens (algae & fungus)
• commensalism (+/0)• barnacles attached
to whale
2005-2006
2005-2006
commensalism (+/0)
(+/+) mutualism
predation (+/-) competition(-/-)
Niche • An organism’s niche is its ecological role
habitat = address, niche = job
2005-2006
Resource partitioning
Niche & competition• Competitive Exclusion
• No two similar species can occupy the same niche at the same time
2005-2006
Predation drives evolution• Predators adaptations• locate & subdue prey
• Prey adaptations• elude & defend
2005-2006
spines, thorns, toxins
horns, speed, coloration
Trophic structure• Food chains• feeding relationships• food chain usually 4 or 5 links =
trophic levels• length of food chain limited by
inefficiency of energy transfer
2005-2006
Energy transfer• Energy in• from the Sun• captured by autotrophs =
producers (plants)• Energy through• food chain
• transfer of energy from autotrophs to heterotrophs (herbivores to carnivores)
• heterotrophs = consumers• herbivores• carnivores
2005-2006
Energy inefficiency
2005-2006
incompletedigestion
metabolism
Pyramids of production• represent the loss of energy from a food chain• how much energy is turned into biomass
2005-2006
Food webs• Food chains are hooked
together into food webs• Who eats whom?• a species may weave
into web at more than 1 trophic level• bears• “there’s always a bigger
fish”
2005-2006
What limits the length of a food chain?
Implications • Dynamics of energy through ecosystems have
important implications for human populations• what food would be more ecologically sound?
2005-2006
Disturbances • Most communities are in a state of
change due to disturbances • fire, weather, human activities, etc.• not all are negative
2005-2006
Disturbances • Disturbances are often necessary for community development
& survival
2005-2006
Ecological cyclefire as part of a natural community cycle
2005-2006
Ecological succession• The sequence of community changes after a disturbance• transition in species composition over ecological time
• years or decades
2005-2006Mt. St. Helens
Succession
• From bare soil, then…• bacteria• lichens & mosses• grasses• shrubs• trees
2005-2006
makesoil {
Change in species mix over time
Succession
2005-2006
from mosses & lichens= pioneer species
to shrubs & trees
Climax forest
2005-2006
solar energy levels temperature rainfall fertility & depth of soil
The species mix of climax forest is dependent on the abiotic factors of the region
birch, beech, maple, hemlock
