Community Ecology

Campbell & ReeceChapter 54

a group of populations of different species living close enough to interact

Community

interactions with individuals of other species

includes: Competition Predation Herbivory Symbiosis Facilitation

Interspecific Interactions

interspecific competition is a +/- interaction that occurs when individuals of different species compete for a resource that limits their growth & survival

Competition

grown separately, both show logistic growth

when compete Paramecium caudatum became extinct in the culture

2 species competing for same limiting resource: 1 will have advantage in either using resources or in reproduction

Competitive Exclusion

is the sum of a species’ use of the biotic & abiotic resources in its environment

Eugene Odem: “If an organism’s habitat is its “address”, then niche is the organism’s “profession,”

Ecological Niche

not just where an organism lives but also what it eats, when it eats, who eats it, how many resources it uses, how much & what type of wastes it produces, what its parasites are, etc

Niche

3 birds live in spruce tree: each lives in different level so there is no competition even though all live in same trees

Niches: Resource Partitioning

closely related species may have populations that are sometimes allopatric (geographically separate) & sometimes sympatric (geographically overlapping)

Character Displacement

allopatric populations will be morphologically more similar & use similar resources

sympatric populations more likely to show differences in body structures & in the resources they use

Character Displacement

refers to the +/- interaction between species in which 1 species, the predator, kills & eats the other, the prey

Predation

acute senses claws, teeth, fangs, stingers, or

poison those that have to chase their prey

have adaptations that make them fast & agile

those that lie in ambush have adaptations that disguise their position

Feeding Adaptations of Predators

hiding, fleeing, forming herds or schools

active self-defense less common except for mothers protecting young (especially in larger, grazing mammals)

alarm calls mob the predator

Adaptations of Prey

Cryptic Coloration

Defensive Coloration in Animals

Camouflage makes prey difficult to

see

warning coloration often used by

animals that have effective chemical defenses

Aposematic Coloration

Defensive Coloration in Animals

Batesian mimicry: a palatable or harmless species mimics an unpalatable or harmful one

Defensive Coloration in Animals

Mullerian mimicry: 2 or more unpalatable species resemble each other; the more unpalatable prey there are the more quickly predators learn to avoid anything that resembles them

Defensive Coloration in Animals

refers to a +/- interaction in which an organism eats parts of a plant or alga

most herbivores are invertebrates specialized adaptations:

some insect have sensors on feet to detect toxins, or to detect nutritious & less nutritious plants

Herbivory

feature toxins, spines, thorns some toxins:

Strychnine: produced by tropical vine Nicotine: tobacco Tanins: variety of plants Selenium: found in “locoweeds” because

sheep & cattle that eat them found wandering aimlessly, some die

Plant Adaptations

produce chemicals their predators find distasteful: Cinnamon Cloves Peppermint

Plant Adaptations

when 2 or more species live in direct & intimate contact w/each other

some: helpful, harmful, or neutral

Symbiosis

Ecologists estimate that 1/3 of all species are parasites

many have complex life cycles requiring multiple hosts

some change behavior of their host to increase probability of it being transferred

Parasites

leads their crustacean host to leave shelter increasing chances it will be eaten by a bird, its next host

Parasitic accanthcephalan

a +/- symbiotic interaction in which 1 organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process

Endoparasites: live w/in body of their host ex: tapeworm

Ectoparasites: feed on external surface of their host ex: ticks, lice

Parasitism

small wasps that lay their eggs in living hosts that feed on the body, killing it

Parasitoid Insects

an interspecific interaction that benefits both species, +/+

Acacia trees & stinging ants: ants feed on nectar & protein-rich

swellings on tree tree protected by thorns (ants live

inside) & stinging ants that attack any herbivores & ants clip vegetation that grows near the tree

Mutualism

Mutualism

an interaction between species that benefits one of the species but neither harms nor helps the other +/0

in reality may have some slight + or - affect

Commensalism

species can have +/+ or +/0 effects on the survival or reproduction of other species w/out living in direct, intimate contact with each other

this type of interaction = facilitation common in plant ecology

Facilitation

Black rush increases # of plant species that can live in upper middle zone of salt marshes

variety of different kinds of organisms that make up a community

Species richness: # of different species in community

Relative abundance: proportion each species represents of all individuals in community

Species Diversity

Which is Which?

Ecologists use different tools to compare the diversity of different communities over time & space.

Shannon diversity is an index of diversity based on species richness & abundance

Shannon Diversity

Shannon diversity = H

ni = # of 1 species n = # of all species In = natural

logarithm

Shannon Diversity

Which Forest is More Diverse?

higher diversity communities generally are more productive & better able to withstand & recover from environmental stresses

Diversity & Community Stability

higher diversity communities more resistant to effects of invasive species

Invasive Species

layers in food chains/ pyramids

Trophic Structure

summary of trophic relationships of a community

tells whom eats whom

Food Webs

Why are they short?1. Energetic Hypothesis

length limited by inefficiency of nrg transfer

2. Dynamic Stability Hypothesis longer food chains less stable population fluctuations @ lower trophic

levels magnified @ higher levels

Limits of Food Chain Length

the more abundant species in a community

are highly competitive

Dominant Species

1 way to measure effect is to study what happens when a dominant species is removed:

ex: tree, American Chestnut was dominant tree in deciduous forests before 1910

fungal disease chestnut blight introduced: killed almost all of them didn’t bother maples, beeches, oak, or hickories, or birds, or mammals, but 7 species of moths & butterflies became extinct

Dominant Species

not usually abundant in community exert strong control by their pivotal

ecological role or niche

Keystone Species

species that dramatically alter their physical environment

aka: foundation species effect on other species can be + or –

depending on needs of other species

Ecosystem Engineers

proposes a unidirectional influence from lower to higher trophic levels presence or absence of mineral nutrients

(N) controls plant (V) #s which in turn controls herbivore (H) #s which in turn controls predator (P) #s

N V H P adding or removing #s of P will not effect

lower trophic levels but adding or removing N will affect biomass of all higher trophic levels

Bottom-Up Model

postulates #s of predators mainly controls community organization because predators limit herbivores, herbivores limit etc: N V H P aka: trophic cascade model used to improve water quality in

polluted lakes (approach called biomanipulation)

Top-Down Model

an event (storm, flood, fire, drought, overgrazing, or human activity) that changes a community by removing organisms from it or altering resource availability

Disturbance

evidence suggests that disturbance & lack of equilibrium not stability & equilibrium, are the norm for most communities

Nonequilibrium Model

type of disturbance, their frequency & severity vary among communities’

high level of disturbance is generally the result of a high intensity & high frequency disturbance

Characterizing Disturbance

says moderate levels of disturbance can foster higher species diversity than can low or high levels of disturbance

Intermediate Disturbance Hypothesis

the sequence of community & ecosystem changes after a disturbance

Primary Succession: type of ecological succession that occurs in an area where there were originally no organisms present & where soil has not yet formed

Ecological Succession

Primary Succession

type of succession that occurs where an existing community has been cleared by some disturbance that leaves the soil or substrate intact

Secondary Succession

early arrival species may facilitate the arrival of late arriving species by making environment more hospitible

sometimes the early species inhibit establishment of later species so the later species succeeds in spite of the presence of early species

early species may be completely independent of later species which tolerate conditions created by early species

Succession

humans are the most widespread agents of disturbance

man‘s effects usually reduce species diversity

humans also interfere with natural disturbances like fires which can be important disturbances to some communities

Human Disturbance

large-scale factors that influence the diversity of communities

Biogeographic Factors

species richness generally declines along a latitudinal gradient from the tropics the poles

tropics are much older which may contribute to species richness but it is also affected by climate (amt heat, sunlight, water)

Latitudinal Gradients

the biodiversity pattern that shows that the larger the geographic area of a community is, the more species it has

Species-Area Curve

Species richness of North American trees increases most predictably with actual evapotranspiration (evaporation of water from soil + transpiration of water from plants) which is a function of solar radiation, temp, & water availability

Energy, Water, & Species Richness

explanation for this phenomena: the larger areas offer greater diversity if habitats & microhabitats

Species-Area Curve

are generally isolated, limited size so ideal for studying biogeographic factors that affect biodiversity

“islands” = oceanic islands + habitat islands ex: mountain tops Lakes woodland fragments

Island Equilibrium Model

Immigration & Extinction Rates: equilibrium # of species on an island

represents a balance between the immigration of new species & extinction of established species

Island Equilibrium Model

Effect of Island Size: larger islands may ultimately have a

larger equilibrium # of species than smaller islands because immigration rates tend to be higher & extinction rates lower on larger islands

Island Equilibrium Model

Near islands tend to have larger equilibrium #s of species than far islands because immigration rates to near islands are higher & extinction rates are lower

Island Equilibrium Model

are disease causing microorganisms Viruses infectious RNA molecules: viroids infectious RNA proteins: prions

Pathogens

can quickly & extensively alter community structure especially when introduced into new

habitats new hosts have not had chance to

become resistant thru natural selection

Pathogens

pathogens transferred from other animals humans

cause of largest class of emerging human disease

community ecology provides framework for identification of key species interactions ass’c with such pathogens & for helping us track & control their spread

Zoonotic Pathogens

can be transferred by direct contact thru intermediate species called a

vector

Zoonotic Pathogens

often parasites Ticks Lice Mosquitoes

Vectors

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