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Community Ecology (Predator-Prey Interactions (One predator, one prey…
Community Ecology
Predator-Prey Interactions
Competition between species
Species often compete for same resources
Exploitation competition
Organisms consume shared resources
Less available for other organisms
Interference competition
Ex. Leaves blocking light from another organism
Organism restricts access to resource from others
Invasive species
Species increase from low to high
Even with resources, competitors present
Resource=factors that increase growth rates
Predator selection among multiple prey
Most animals
Vertebrate herbivores
Can/will eat variety of plants
Omnivores
Eats both plants & animals
Humans=most diverse diet
Optimal forging theory
Interaction between 3 factors
Decision to attack individual
Probability attacked prey=eaten
Probability that prey is encountered
Optimal diet model
Four predictions
Predators prefer prey that yield most energy
2.Predator is more successful broadening diet
3.Some prey always eaten/others never encountered
4.Less profitable prey ignored
One predator, one prey
Simplest system
Lotka-Volterra model
dN/dt=rate of prey pop change/ time
r=intrinsic rate of increase of prey species
N=prey individuals in community
a=predator's per capita attack rate
P=predator individuals
Zero growth isocline
dN/dt=0
Prey & predator coexist stably
Line indicating population stability
Functional response
Handling time
Time taken to consume prey
Prey dependent
Feeding rate increases w/ prey availability
Feeding rate
How quickly to find new prey
Maximum sustained yield
Infection point
Harvest just enough to keep population stable
Population's maximum per capita productivity
Don't know enough to determine inflection point
Fixed effort harvesting
Alternative way to determine pop health
Populations healthy=harvest abundant
Populations sparse=harvest poor
Species harvested w/ particular amount of effort
Harvest must stop after certain time
Rely on governments to set effort level
Fixed quota harvesting
Hunters allowed certain amount
Or how much effort required
Could cause great harm
Rely on governments to set quota
No matter how long it takes
Paradox of enrichment
Predator-prey interaction becomes unstable
May lead to predator overexploit of prey
Prey zero growth isocline rises
Both species will be lost
Apparent competition
Prey population low=predator population low
Prey population increase=predator population increase
Prey species share a predator
Large predator population=
More herbivory on plant species
Increase in 1 plant associated w/decrease in others
Appear to be in competition
Not actually competing for resources
Interconnectedness of Species: Food Chains & Food Webs
Food web
Network of numerous interrelationships
Energy flow web
#
How energy flows through a community
Difficult to construct for real communities
Food chain
Direct line of consumption
Keystone species
Dramatically affects structure of community
Presence/absence of certain species
Urchin grazing minimized
Kelp spores allowed to germinate
Reduce population of sea urchins
Extensive underwater forest
Diversity
Diversity and scale
Species=area relationship
Relationship b/t area & species
S=cA^z
S=number of species
A=area
C & z are constants
Species abundance distribution
Plot
Number of species
In each abundance class
Scale
Larger areas more diverse than smaller
Beta diversity
Differences b/t small sites in large region
Gamma diversity-number of species in region
Alpha diversity-local small site
Diversity and latitude
Theories
Tropical regions have benign environments
Abundant rainfall
Hundreds of millions of years to adapt
Warm
Higher latitudes have severe conditions
Water stress
Tens of millions of years to adapt
Freezing
Checklist
National parks/wildlife preserves have checklist
Always incomplete
Impossible to catalog every microbe
Not enough trained specialist
A count of species present in a community
#
Beneficial Interactions Between Species
Mutualism/mutualistic relationship
#
Two organisms interact & both benefit
Facilitation
One organism helps another but doesn't benefit
First organism facilitates the presence of the other
Primary succession
Organisms establishing on new substrates
Nurse plants
Metapopulations in Patchy Environments
Metapopulation
Source habitat
High-quality patch
Sink habitat
Low-quality patch
Fugitive species
Survives by colonizing new patches
Flourishing temporarily
Then colonizing new patches
Before it dies out in older patches
Conservation biology
Preserving endangered species
Metapopulation crucial
Assisted dispersal
Animals captured in one area & released in another
Plants seeds or whole plants removed
AKA assisted migration
Several local populations interconnected
Migration
Gene flow between patches
Relationship
Energy
Species
