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Community Ecology (Concepts (community (group of species that occur…
Community Ecology
Concepts
community
group of species that occur together
same time/place
boundaries in time and space
succession
predictable sequence of changes
organisms alter their habitat
climax community
community remain the same for many years
community restoration
attempting to reestablish a climax community
reintroduction of plants and animals
habitat loss/fragmentation
loss due to human infrastructure
farms
mines
community ecology
may be able to minimize damage
Predator-Prey Interactions
One Predator, One Prey
simplest system
functional response
feeding rate
how quickly to find new prey
handling time
time taken to consume prey
prey dependent
feeding rate increases with prey available
Lotka-Volterra model
dN/dt is rate of prey pop change with time
r is intrinsic rate of increase of prey species
N is prey individuals in community
a is predator's per capita attack rate
P is predator individuals
zero growth isocline
line indicating population stability
dN/dt=0
prey & predator coexist stably
paradox of enrichment
prey zero growth isocline rises
predator-prey interaction becomes unstable
may lead to predator overexploit of prey
both species will be lost
maximum sustained yield
population's maximum per capita productivity
inflection point
harvest just enough individuals to keep population stable
we do not know enough to determine the inflection point
fixed effort harvesting
alternative way to determine population health
amount of a species that can be harvested with a particular amount of effort
populations healthy=harvest abundant
populations sparse=harvest poor
harvest must stop after particular effort/time
rely on governments to set effort level
fixed quota harvesting
fisherman/hunters allowed harvest particular amount
no matter how long it takes
or how much effort is required
could cause great harm
rely on governments to set quota
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Predator Selection Among Multiple Prey
most animals
vertebrate herbivores
can/will eat variety of plants
omnivores
eat both plants and animals
humans=widest/diverse diet
optimal foraging theory
interaction between three factors:
1) probability that particular prey is encountered
2) decision to attack individual
3) probability that attacked prey successfully eaten
optimal diet model
four predictions:
1) predators prefer prey that yields most energy per handling time
2) if high-yield prey is scarce then, predator more successful by broadening its diet
3) some prey always eaten/ others never eaten even if encountered
4) less profitable prey ignored if more profitable prey is available
Competition Between Species
several species often compete for same resources
exploitation competition
organisms consume shared resource
less available for other organisms
interference competition
one organism restricts access to resource from another
example: leaves blocking light to another organism
invasive species
species increases from low to high population density
even with resource competitors present
resource=substance/factors that increase growth rates
Apparent Competition
prey species share a preditor
if prey population low=predator population low
if prey population increase=predator population increase
larger predator population results in more herbivory on many plant species
increase in one plant species associated with decrease in others
appear to be in competition
not actually competing for resources
Interconnectedness of Species: Food Chains and Food Webs
food chain
direct line of consumption
food web
network of numerous interrelationships
energy flow web
how energy flows through a community
difficult to construct for real communities
keystone species
presence/absence of certain species
dramatically affects structure of the community
reduce population of sea urchins
urchin grazing minimized
kelp spores allowed to germinate
extensive underwater forests
Diversity
checklist
a count of species present in a community
all national parks/wildlife preserves have checklists
always incomplete
impossible/unnecessary to catalog every microbe
not enough trained specialists
Diversity and Scale
scale
larger areas more diverse than smaller
alpha diversity-local small site
beta diversity- differences b/t several small sites in a larger region
gamma diversity-number of species in region
species-area relationship
relationship b/t area and species
S=cAᶻ
S is number of species
A is the area
c & z are constants
species abundance distribution
plot
number of species
in each abundance class
Diversity and Latitude
theories
tropical regions have benign environments
warm
abundant rainfall
hundreds of millions of years to adapt
higher latitudes have more severe conditions
freezing
water stress
only tens of millions of years to adapt
Beneficial Interactions Between Species
mutualism/ mutualistic relationship
two organisms interact and both benefit
facilitation
one organism helps another but does not benifit
first organism facilitates the presence of the other
nurse plants
primary succession
organisms establishing on new substrates
Metapopulations in Patchy Environments
metapopulation
several local populations interconnected
migration
gene flow b/t patches
conservation biology
preserving endangered species
metapopulation crucial
common model makes 4 assumptions:
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
assisted dispersal
aka assisted migration
animals captured in one area then released into an new area
plant seeds or whole plants can be moved
