Community InteractionsCommunity Interactions

Community InteractionsCommunity Interactions

• Powerfully affect an ecosystem

• Include:– Competition– Predation– Symbiosis– Herbivory– Disease

Interspecific CompetitionInterspecific Competition

• When organisms of the same or different species attempt to use an ecological resource at the same place and the same time– Resource any necessity to life– Plants and animals compete– Winner and losers– Grass hoppers and bison– Lynx and fox

Rules, rules, rulesRules, rules, rules

• Fundamental rule in ecology– Competitive Exclusion Principle

• No two species can occupy the same niche in the same habitat and the same time• Prevents competition

– Paramecium caudatum and Paramecium aurelia

• Fundamental Niche (potentially occupied)• Realized Niche (actually occupied)• P 1160

How can species coexist in How can species coexist in same community?same community?

• Realized Niche

• Resource portioning

– Differentiation of niches that enables species to coexist

– Different perches

• Character displacement

– Tendency for characteristics to be more divergent in sympatric (geo overlapping) populations of two species that allopatric (geog sep) populations of two species

– Two species with similar niches will make slight changes in body structure and resources they need so they do not compete for resources

• Finches living on island that are usually very similar have different beaks, one for bigger seeds, one for smaller seeds

PredationPredation

• Interaction where an organism captures and feeds on another organism (+/-)

• Predator– Organism that does the killing and eating

• Prey– Organism that is being killed and eaten

(victim)

Defenses p. 1162Defenses p. 1162• Cryptic coloration

– Camouflage

• Aposematic coloration

– Warning coloration for organisms with effective chemical defenses

• Batesian mimicry

– Harmless imitates dangerous

• Mullerian mimicry

– 2 or more unpalatable have similar appearance

– Cukoo bee and yellow jacket

– Coral snakes and yellow jackets…yellow

• Predators also use mimicry

– Turtle tongue

HerbivoryHerbivory

• When a herbivore eats plant or algae (+/-)• Large mammals, small invertebrates (insects), marine organisms

(sea urchins, snails, fish)• Toxic and nontoxic plants

– Chemical sensors– olfactory

• Specialized teeth and digestive systems

• Plants defenses– Toxins: tannins, nicotine, strychnine– Not harmful to humans

SymbiosisSymbiosis

• Any relationship where two species live closely together

• Symbiosis literally means “living together”

• 3 main types– Parasitism– Mutualism– commensalism

What type of relationship is this?What type of relationship is this?• Who is helping who?

MutualismMutualism

• Both species benefit from the relationship (+/+)

• A Happy couple• Flowers and bees

– Flowers need bees for pollination, bees need flowers nectar

CommensalismCommensalism

• One member of the relationship benefits while the other is neither harmed nor helped (+/0)

• One-sided

• Food or shelter

• Barnacles on whale

What type of relation ship is going What type of relation ship is going on here?on here?

• Who is helping who?

What type of interaction is going on What type of interaction is going on here?here?

ParasitismParasitism• One organism lives on or inside another organism and harms it (+/-)

– Endoparasitism– Ectoparasitim– Parasitoidism

• Usually large and multicellular• Parasite obtains all or part of its nutrients from the other organism• Host

– Organism that is harmed in relation ship; the one that provides the nutrients to the parasite

• Parasite– Organism that gets its nutrients from the host

• Do they want to kill their host?– No, because they need them…mostly annoying

DiseaseDisease

• Disease causing agents (+/-)

• Bacteria, viruses, protists, sometimes fungi and prions

• Most are microscopic

• Inflict harm on host

• Not many studies, but they do have an ecological impact

– Sudden oak death: Phytophthora ramorum

• 1994-2004

• Fungus-like protist

• killed thousands of oak trees from CA to Oregon

– West Nile virus• 1999-2003

• Killed thousands of birds in US as it spread

RecapRecap

• What are the three types of interactions in a community?– Competition– Predation– Herbivory– Disease– Symbiosis

• What types do we have?– Mutualism– Commensalism– Parasitism

Interspecific Interactions and Interspecific Interactions and AdaptationAdaptation

• Coevolution

– Reciprocal evolutionary adaptations of 2 interacting species

– Genetic change in one sp. influences genetic change in another sp.

• Ex. Gene-for-gene recognition in plant and pathogen

– Aposematic coloration and predators reactions NOT coevolution

• Across multiple species, not 2 linked population

• Current hypothesis is that Predation and competition are key factors that control community structure and drive community dynamics

– Base on temperate and not tropical communities

• Hypothesis is being challenged

Species DiversitySpecies Diversity

• Variety of different organisms in a community…dependent on both:

– Species richness

• Total # of diff. sp in comm.

– Relative abundance

• Portion each sp represent of the total individuals in comm.

• Example

– Forest 1 and forest 2, 100 individual

– Forest 1• Tree A 25%• Tree B 25%• Tree C 25%• Tree D 25%

– Forest 2• Tree A 80%• Tree B 5%• Tree C 5%• Tree D 10%

• Forest 1 is more diverse, even thought both contain 4 types of trees…

Limits on Food WebsLimits on Food Webs

• Charles Elton 1920 Oxford Biologist– Food chains are not isolated units but linked

in food web

• Each food chain in food web is only a few links long…most hardly more than 5 links from any producer to top-level consumer

Why are they short?Why are they short?• 2 hypotheses

– Energetic Hypothesis • Food chain limited by inefficiency of energy transfer along chain

(10%)• Longer in habitats of high photosynthetic productivity

– Dynamic Stability Hypothesis• Long chains less stable than short ones

– Longer chains have harder time recovering from setbacks like harsh winter, especially at the higher-level

• Shorter chains in unpredictable environments• Another possibility for short food chains

– Animals tend to be larger at successive trophic levels (except parasites)– Size of animal and feeding mechanism put limit on food it can put in its mouth – Mostly, large carnivores cannot live on small organisms because they cannot get sufficent

energy from them• Exception is baleen whales

Important Types of SpeciesImportant Types of Species• Dominant species

– Most abundant or highest biomass

– Powerful control over occurrence and distribution of other species• Ex, sugar maple in North American forest: so big and abundant that affects shade and soil, therefore, influence what o other species can be in forest

– Why?• Hypothesis: dominant sp are most competitive at exploiting resources• Hypothesis: dominant sp. Best at avoiding predation and disease

– Explains success of invasive species

– Removal of dominant species has impact on community

• Keystone species– Discovered by ecologist Robert Paine of U of Washington

– Not really abundant, but rather have strong control on community structure because their pivotal ecological roles, or niches

– Identify with removal experiments

– Sea star and musselsremove sea star and decrease species diversity b/c mussels take over space

– Sea otter and sea urchinsremove sea otter, sea urchins eat all the kelp and destroy kelp forest

• Ecosystem engineers (foundation species)– Cause physical changes to environment that affect structure of community

– Alter through behavior or large biomass

– Foundation species are FACILITATORS that have positive effects on the survival and reproduction of other species

• Beavers change areas of forest into flooded wetlans

• Certain trees provide shade that enable salt marshes to floursih

Ecological SuccessionEcological Succession

• Do all ecosystems stay the same all the time?

• What are some things that cause changes to ecosystems?– Natural and unnatural– Quickly and slowly

• Ecosystems are constantly changing in response to human and natural disturbances.

• As an ecosystem changes, older habitants die out and new organisms move in, causing more change

Ecological SuccessionEcological Succession

• Series of predictable changes that occur in a community over time– Physical environment– Natural disturbance– Human disturbance

Intermediate Disturbance Intermediate Disturbance HypothesisHypothesis

• Moderate levels of disturbance can create conditions that foster greater species diversity than low or high levels of disturbance – High levels wipe out species that are

intolerable– Low level enable dominant species to take

over

Primary SuccessionPrimary Succession• Succession on land

that occurs on surfaces where no soil exists

• Volcanic eruptions• Glaciers melting

leveling moraine (bare rock)

Stages of Primary SuccessionStages of Primary Succession

• Start with no soil, just ash and rock

• First species to populate this area– “pioneer species”– For example, pioneer species on volcanic

rock are lichens (LY-kunz)• Lichens made up of fungus and algae that can

grow on bare rock• When lichens die, they for organic material that

becomes soil…now plants can grow

Secondary SuccessionSecondary Succession

• Succession following a disturbance that destroys a community without destroying the soil

• Natural – hurricane– fires

• Human disturbances– Farming– Forest clearing

Succession in Marine EcosystemsSuccession in Marine Ecosystems

• Deep and dark

• Can succession happen?

• 1987 dead whale off of California– Unique community of organisms living in

remains– Represents stage in succession in an

otherwise stable, deep-sea ecosystem– Whale-fall community

Whale-Fall SuccessionWhale-Fall Succession• Begins when large whale dies

– Sinks to barren ocean floor– Scavengers and decomposers flock to carcass , our first community

• Amphipods• Hagfish• sharks

• After a year, most tissues have been eaten– Now, second small community of organisms live here– Body is decomposing, releasing nutrients into the water

• Small fishes• Crabs• Snails• worms

• Only skeleton remains…– Third community moves in

• Heterotrophic bacteria• Decompose oil in bones release of chemical compounds• Who uses these chemical compounds?

– Chemoosynthetic autotrophs• In come the crabs, clams, and worms that feed on this bacteria

Teacher,

Study Chemical reactions, enzymes,

and Chapters 3

and 4