ecology exam 3: communities

community

all populations of various species living together in a particular area that interact or could potentially interact (boundaries are not always rigid and may cover small or larger areas, geographically in the same place)

community apporach

understands the diversity and interactions of organisms living together in the same place

is type of interaction static

no could have 2 species competing for a long time and living conditions change, a species can be introduced or resources change that competition can turn to predation

how are communities often characterized

dominant organisms or by physical conditions that affect the distribution of species 

how are aquatic habitats defined

the structure of the aquatic habitat (lake or stream) and physical conditions than organism expect for coral reefs

when there are definite differences in environmental conditions on one side of something vs the other the division is what

ecotone (treeline of a forest, interior difference from the medow)

ectone

boundary created by sharp changes in environmental condition over a relatively short distance, accompanied by a major change in the composition of species 

ecological transition zones 

talking about ecotone 

what do ectones generally support

a larger number of species than in either adjacent community (constitutes the fundamental niche of both species)

ecological release

ability of individuals to exploit broader niches

why is niche bigger in new areas 

new habitat and other small critters can rapidly adapt because changing how much melanin to produce is not a big stretch 

how is community defined in ecology

an assemblage of species found together in a specific place at a specific time. they interact or have the potential to interact and scale varies widely with species within it being or not being interdependent  

scale of ecological communties

can have one tree or take a portion of the united states

how much of australia is a threat in ecological community

1/3

interdependence 

reliance on another species to exist in a community 

what did Fredric Clements propose

most communities are interdependent and act as a superorganisms (organisms within the community all have a role and all work together)

what did henry gleason propose

most communities consist of species with independent distribution (no dependency every thing in the community was independent)

which biologist was right

it depends typically on abiotic conditions but is typically not interdependent 

what guidelines wound there be if species distributions are independent

they should depend only on individual habitat requirements and there should be gradual changes in species along a line transpect (rise and fall in abundance based on conditions not species)

you will see a gradual change over indepedent species expect for when

ecotone which is a larger change

based on Robert Whittaker’s plant species in the Great Smoky Mountains was it interdependent or independent

independent: different tree species appeared and disappeared at different elevations corresponding to changes in moisture (elevation)

problem with observational studies

cohorts of species may also be evidence for similar biotic or abiotic requirements, and species may be linked by correlations with a 3rd(4th or 5th) variable and not have any interdependencies with one another at all

what can experimental manipulation provide evidence for

support causation

experiment test of interdependency 

if species are interdependent then removing a species should cause other species to decline, if changes are neutral or positive species are independent 

what conditions do species frequently exhibit interdependence

species living under harsh environmental conditions (high elevation)

why might harsher environments result in greater facilitation

neighboring plants reduce stress by buffering wind, cold, and herbivory and by creating more favorable microhabitats

species richness 

the number of spcies in a community 

relative abundance

the proportion of individuals in a community represented by each species

species evenness

a comparison of the relative abundance of each species in a community

rank-abundance curve

a curve that plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species

what communties have higher diversity 

communities with higher species richness and greater evenness 

diversity

implies high number of species and abundance of species

flat abundance curve

high evenness 

titled abundance curve

low evenness 

Two communities each have four species. One community is dominated by a single species, while the other has all species at similar abundances. What does this tell you about their diversity?

Both communities have the same species richness (4 species), but they differ in evenness.The community dominated by one species has low evenness.The community with similar abundances has high evenness.

Which stream has the highest species richness? Eveness?

blue has the highest species richness (goes further down the x axis and blue is flattest so most evenness

what does species diversity depend on

resources available, habitat diversity, influential species, frequency or intensity of disturbances

to understand the influnece of resources ecologist examined what relationship 

productivity and species richnness 

productivity

approximation of available resources

Research can conduct a meta-analysis to identify broad patterns what is meta-analysis

 statistical technique in which data from many studies are combined to test a particular question

what is the curve that might be the general pattern that we are looking for across all different communties 

hump shape curve because at very low levels and high levels of productivity going to see fewer species 

Why lower species at lower level productivity

each propulation probably has lower carrying capacity meaning population smaller

why few species at high level

some species are just really good competitors they finish resources up very quickly leaving nothing for other species in the community 

CSR triangle

idea of how species specialize and jacks of all traits 

competitors in CSR triangle

throw all their available resources into traits that allow them to be good competitors

stress tolerators in CSR

some species throw all their resources and developmental efforts into becoming really good stress tolerators (low water, low resources)

ruderal 

needy, species that put all their life history strategy effort into being really good reproducers, they reproduce really quickly and can recover well after disturbance 

most species exist where in the CSR triangle

center, combination of those things but when talking about a limited number of resources in the lifetime (life history trade offs) have to figure out how to allocate stuff

hump shape curve

high level of productivity: competitors, no stress in the environment, implying things are great because no other species are left, low level of productivity: component of the population more likely to go extinct but also have ton of stress and so stress tolerators will be seen, middle of curve are species that have a combination of traits because environments are not so extreme

which community is most species rich

medium productity 

park grass experiment showed what

An area already starting with some resources adding resources caused a decline in species richness (diversity) of producers so not hump shape (rare)

what does fertilization do

make competitors more competitive

habitat diversity and species richness

not a situation where you see a hump shape curve (tree height)

influential species and species richness

influential species often increase species richness by preventing competitive dominance or by creating habitat that supports more species

keystone species

a species that substantially affects the structure of communities although species might not be particularly numerous

example of keystone species

starfish keep muscles in check without them muscle take over and nothing else can use substrate

ecosystem engineers 

A keystone species that affects communities by influencing the structure of a habitat 

difference in ecosystem enginners

impact on their community because building structures that other species will use

disturbance and species richness

based on intermediate disturbance hypothesis

intermediate disturbance hypothesis 

more species are present in a community that experiences occasional disturbance than in a community with either frequent or rare disturbances (mowing lawn, forest fires or landslides)

Why do you not see many species if the disturbance are not very frequent or intense

those species that are good competitors or ruderals tend to do well

where do you see high level of diversity

at the intermediate of disturbances, whether the intensity of frequency, no one has an advantage and lots of species can coexist

food chain

a linear representation of how different species in a community feed on each other

food web

a complex and realistic representation of how species feed on each other in a community

tertiary consumers

eat secondary consumers

primary consumers

eat producers

secondary consumer

eat primary consumers

what does the trophic levels (level in a food web) start off as

primary producers 

Communities can be organized by guilds which are

based on specifically what/how they eat (leaf eaters, root chewers, nectar sippers)

how can communities also be organized

when the abundance of trophic groups is determined by the existence of predators at the top of the food web or the energy available from producers

direct effect

an interaction between 2 species that does not involve other species but can set off a chain of events affecting other species in the community

indirect effect

an interaction between 2 species that involves one or more intermediate species

trophic cascade

indirect effects in a community that are initiated by a predator (cod→herring→zooplankton→phytoplankton→water quality)

density-mediated indirect effect

indirect effect caused by changes in the density of the intermediate species

trait-mediated indirect effect

indirect effect caused by changes in a trait of the intermediate species 

community stability

the ability of a community to maintain a particular structure

resistance

how much a community changes when disturbed

resilience 

the time it takes after a disturbance to return to its orginal state 

a more diverse community means what

it is more stable

alternative stable states

when a community is disturbed so much that the species composition and relative abundance of populations in the community change, the new community structure is resistant to further change