Module 13: Community Ecology

what is a community?

a group of populations living together and interacting with each other

how a trophic structure organized?

feeding relationships (who feeds on whom)

what are producers?

organisms that obtain atoms and energy and convert them into essential carbon-based molecules of life

make their own food

what are consumers?

organisms that feed on producers and other consumers to survive

they cannot make their food so they must consume it from other animals or plants

what are decomposers?

organisms that feed on dead organisms or waste to renew the raw materials for life by breaking down decomposing organic matter

how are community interactions classified?

by whether they help, harm, or have no effect on the species involved

what are the two main types of interactions?

1. intraspecific
2. interspecific

what is an intraspecific interaction?

interactions between organisms within the same species, typically competition for resources, mates, shelter, etc.

what is interspecific interactions?

interactions between organisms of different species?

what are some types of interspecific interactions?

1. competition
2. predation
3. herbivory
4. parasitism
5. mutualism
6. commensalism

what's an +/+ interaction?

interaction is beneficial for both species

what's an +/- interaction?

interaction is beneficial for one species, but negative for the other

what's an -/- interaction?

interaction is negative for both species

what's an +/0 interaction?

interaction is beneficial for one species and doesn't effect the other species at all

what's an example of an -/- interaction?

when individuals of different species compete for a resource that limits the survival and reproduction of each species

what's two examples of an -/- interaction?

weeds growing in the garden compete with garden plants

different animals trying to eat the same food source

what is competitive exclusion?

two species competing for the same limiting resource cannot coexist permanently in the same place

one species will use the resources better and the inferior competitor will be eliminated

what is the evolutionary result of competitive exclusion?

an ecological niche

what is an ecological niche?

the specific set of biotic and abiotic resources that an organism uses in its environment

what does an organism's role in the ecosystem include?

1. habitat in which an organism lives
2. activity patterns of the organism (time of day it's active)
3. resource it obtains from the environment
4. interactions that occur with other species in the community

what can evolution by natural selection lead to?

resource partitioning and niche differentiation

how can similar ecological species coexist?

if one or more significant differences arise in their niches

how may a difference occur in two organism's individual niches?

one population may adapt to use an alternative resource or similar resources at different times of the day

what is resource partitioning?

the differentiation of niches that enables similar species to coexist in a community

what is a fundamental niche?

the niche which could potentially be occupied

what is a realized niche?

the niche is actually occupied

what is an example of niche partitioning in space?

seven species of Anolis lizards live close, and all feed on insects and other small arthropods

competition for food is reduced because each lizard species occupies a distinct zone

what is an example of niche partitioning in time?

common spiny & golden spiny mouse live in similar areas and share food resources

they coexist because the common spiny mouse is nocturnal, while the golden spiny mouse is diurnal

what is character displacement?

The tendency for characteristics to be more divergent in sympatric populations of two species than in allopatric populations of the same two species.

which species would be in direct competition: sympatric or allopatric?

sympatric species because they are geographically overlapping while allopatric species are geographically separated

what is an example of character displacement?

galapagos finches

how is a predation interaction cataloged?

+/-

how is a herbivory interaction cataloged?

+/-

how is a parasitism interaction cataloged?

+/-

how is a mutualism interaction cataloged?

+/+

how is a commensalism interaction cataloged?

+/0

what are some mechanical adaptations that animals have to defend themselves?

thorns, shells, quills

what are some chemical adaptations that animals have to defend themselves?

toxins or bad odors

what is aposematic coloration?

bright warning coloration

what's an example of aposematic coloration?

poison dart frogs

what is cryptic coloration?

camouflage

what's an example of cryptic coloration?

canyon tree frog

what is batesian mimicry?

a palatable or harmless species mimics an unpalatable or harmful species to which is not closely related (deception)

what's an example of a batesian mimicry?

hawmoth larva or mimic octopus

what is müllerian mimicry?

two or more unpalatable species resemble each other (not deceptive, true signals)

what are some mechanical plant defensive mechanisms?

spines, thorns

what are some chemical plant defensive mechanisms?

toxins, bad taste

what is the food chain?

linear sequence of organisms through which nutrients and energy pass

what is the apex predator?

top-level carnivore, no natural predators

why isn't there a lot of trophic levels?

energy is lost as the food chain escalates which means that at a certain point there is no more energy to give

what is the food web?

a web of interdependent feeding relationships within a community

what do food webs represent?

complexity in feeding relationships because they demonstrate how organisms can have more than one food source or predator

what is species richness?

number of different species in the community

what is relative abundance?

the proportion each species represents of all individuals in the community

why is biodiversity important for a healthy ecosystem?

1. diverse communities are generally more productive

2. diverse communities are better able to withstand or recover from environmental stresses

3. diverse communities are more stable -to-year to year

4. diverse communities are more resistant to invasive species

what is an invasive species?

organisms that become established outside of their native range; they can become dominant because they lack natural enemies and can negatively impact the native biodiversity

what is a foundation species?

dominant species that are the most abundant or that collectively have the highest biomass

what are some effects of foundation species?

1. strong effects on communities as a result of their number or size

2. loss can allow other species to take over, but this negatively impact species that rely on this dominant species; they can control population of other species

what are some examples of foundation species?

trees, desert shrubs, kelp

what is a keystone species?

one whose presence is key to maintaining biodiversity within an ecosystem and upholding its structure

keystone species are not ____________ in a community

abundant

what's an example of a keystone species?

sea otters

what are the ecosystem engineers?

species that dramatically alter their physical environment

what's an example of ecosystem engineer?

beavers

what are the two models of community organization?

1. bottom-up model
2. top-down model

what is the bottom-up model?

a unidirectional influence from low to higher trophic levels

what's an example of a bottom-up mode?

altering biomass at lower levels will cause changes through the food web

what is the top-down model?

a unidirectional influence from higher to lower trophic levels

what's an example of the top-down model?

altering biomass at higher levels will cause changes in the food web

moves in alternating +/- effects

what model did ecologists apply to improve water quality in lakes with high algae levels?

top-down model

what is biomanipulation?

application of the top-down model or bottom-top to affect population density within a community

what is disturbance?

an event, such as a storm, fire, drought, or human activity, that changes a community by removing organisms from it and altering resource availability

what is the nonequilibrium model?

most communities are constantly changing after disturbance

what is the intermediate disturbance hypothesis?

moderate levels of disturbances foster greater species diversity than do high to low levels of disturbance

what is ecological succession?

a disturbed area may be colonized by a variety of species which are replaced by other species which are replaced by other species

what is primary succession?

recovery/colonization in an area that is virtually lifeless

what are some characteristics of primary succession?

1. soil has not yet formed
2. typically prokaryotes, protists, lichens, and mosses colonize first

what is a lichen?

a symbiotic mutualism between a fungus and a green algae pr photosynthetic bacteria

what is an example of primary succession?

the glacier bay in alaska

what is secondary succession?

occurs when existing communities has been cleared by disturbance that leaves the soil intact

what's an example of secondary succession?

Yellowstone fires

what occurs to nutrient content during primary succession?

nutrients change in the soil

bare soil exposed after glacier retreat is low in nitrogen content

almost all pioneer plant species have poor growth and yellow leaves

soil nitrogen content increases too quickly due to dryas and alder plants hosting nitrogen-fixing bacteria

what occurs to nutrient content during secondary succession?

nutrient-rich soil is left behind from the organic debris

pioneer species are those resistant to fire

area may return to original state eventually

how does human disturbance affect biodiversity?

1. agricultural development
2. lumber, cattle grazing, farmland
3. overgrazing and agriculture
4. ocean trawling