Chapter 53: Community Ecology

Chapter 53: Community Ecology

Trophic Structure, Predation, and Competition

Trophic Structure, Predation, and Competition

Assemblage of populations of various Assemblage of populations of various species living close enough for potential species living close enough for potential

interaction interaction

SymbiosisPredation

Competition Herbivory

Disease

+/- interaction; predator kills & eats prey

+/- interaction; herbivore eats plant, kills it

PredatorPrey Have senses

that enable them to locate prey

Self-defense mechanisms: camouflage, bright coloration, mimicry

Herbivore

PlantHave special sensors to recognize appropriate food

Chemical weapons/thorns protect them

+/- interaction; one organism (parasite) gets nourishment from other organism (host), which is harmed

endoparasite

Live within host’s body

ectoparasiteparasitoidism

Feed on external surface of host

Insect lays eggs in/on living host, leaving the larvae to feed on body, and kill it

Inflict lethal harm, can limit populations

Pathogen: disease-causing agent; unlike parasite: microscopic, lethal; +/- interaction

+/+ interaction; both species help each other

+/0 interaction; 1 species benefits, & the other is not affected; hard to find true example in nature

Total # of different species

Variety of diff. kinds of organisms that make up the community

Proportion each species represents of total individuals in the community

Feeding relationships between organismsFeeding relationships between organisms Food

Chain:

Eventually to decomposers

Energetic Hypothesis: length of food chain is limited by inefficiency of energy transfer along chain Dynamic Stability Hypothesis: long food chains are less stable than short food chains; population fluctuations at lower levels are more profound at higher levels, causing potential extinction of high level predators

Food Web: food chains are linked together; 1 species, such as plant, is eaten by several species

Biomass: total mass of all individuals in a populationDominant

species

Species that: collectively have highest biomass OR most abundant

Keystone species Not necessarily abundant;

exert strong control on community by their ecological roles

Ecosystem engineers

“foundation species”; facilitators; cause physical changes that benefit community, by increasing survival and reproduction

Mineral nutrients control community organization; nutrients control plant #’s, which control herbivore #’s, which control predator #’s

Predation controls community organization; predators control herbivores, which control plants, which control nutrient levels

Model of community organization

Fish Abundant Rare

Zooplankton Rare Abundant

Algae Abundant Rare

Biomanipulation

Polluted State

Restored State

Primary Succession: occurs in virtually lifeless area, with no organisms or soil; only autotrophic prokaryotes are presentSecondary Succession: occurs where an existing community was cleared by disturbance, that leaves soil intact; first plants to recolonize: grow from wind-blown/animal-borne seeds

Geographic Location Size

Tropical habitats have the most species; tropical habitats are older (long growing season), and greatest evapotranspiration

Greater area=more diverse habitats, more species

New Species Immigration Rate

Species Extinction Rate

Influenced By:

Island Size Island’s

Distance from Mainland

# of Species Already Present

new colonizers: unlikely to reach small island = low immigration rate, high extinction rate (less resources)

Islands near mainland: high immigration rate, low extinction rate (new colonizers sustain presence of species)

# Species

Extinction rate (competitive exclusion)

immigration rate (those reaching island are less likely to represent species not already there)

States that species are found in the same area simply because they happen to have similar abiotic requirements

Integrated Hypothesis (Clements)

Individualistic Hypothesis (Gleason)

Describes a community as an assemblage of closely linked species, locked into association by mandatory biotic interactions

These interactions cause the community to function as an integrated unit

**Walker agrees with Gleason

Rivet Model Redundancy ModelSuggests: most of the species in a community are associated tightly with particular other species in a web of life

**the Ehrlich’s agree with Clements

Exact opposite of the rivet model

Suggests: species in a community are redundant; species operate independently, & aren’t affected if one species increases/decreasesEx. – if one pollinator disappears, then another species will do the job

DDT and other toxins, when in tissues and fats of an organism, can accumulate and be passed onto the next level of the food chain, affecting many organisms. Rachel Carson states in Silent Spring that the concentration of DDT in a low level organism’s fat is a lot lower than that of a higher level organism on the food chain

If phytoplankton is infected

Zooplankton & other primary consumers, secondary consumers, etc. are affected

Everything occurring at low food chain levels is magnified at high food chain levels, causing possible extinction of top level predators

Similar effect of DDT; If organism is affected by pollution, it can spread through food chain, greatly affecting top-level predators

If water is polluted and filled with garbage, the fish living there drink bad water and aren’t

getting the right nutrientsMake fish sick, and all those who eat them: fish’s predators, fish’s predators’ predators, and even

human who eat fish for dinner

**If one organism is infected by either DDT, pollution, or by several other possibilities, the harms done to

that animal certainly don‘t stop there**

The spraying will cover the soil and the nutrients it contains.

•The producers absorb the DDT and are eaten by the consumers.

•The predators will continue to consume the DDT laden prey, accumulating the DDT in their body fats.

imbalance of predators to prey will cause the ecosystem to go out of balance

DDT Impacts Predation

The reduction of 4th level predators, for example, will cause:

overabundance of the 3rd level prey, which consume so much 2nd level prey

Decrease 2nd level prey, so there’s not as many organisms to eat primary producers

As the environment becomes increasingly warmer each year, organisms might not be able to adapt or migrate to other areas

The introduction of organisms disrupts and changes the ecosystem of the environment.

This migration will bring new predators and new prey, which would alter the trophic structure.

Altering the trophic structure would change the predator-prey relationships; the top level carnivores may not be the top level carnivores anymore, having an effect like the top-down model

Effects of Global Warming on Predation

If organisms die, their predators would starve, and there would be an increase in the dying organisms’ prey

DDT Affects Competition

• DDT can increase competitionDDT may kill many organisms of a

species that two other species compete for.

Because the resource is in short supply, interspecific competition between the two competing species will increase, hurting both species

eventually eliminating one of the two competing species (competitive exclusion).

•DDT can also lessen competitionBiological Magnification

DDT’s concentration with each link in the food chain. By eating DDT-contaminated food, DDT accumulates in carnivores, which may be enough to kill the carnivores.

Reproduction RatesDDT influences reproduction ratesEx.: Eagles in Silent Spring by

Rachel Carson-DDT stored in eagles’ fatty cells

cause the deposition of calcium in their eggshells to be hindered.

DDT Affects Competition

less competition among remaining

carnivores for resources.

Less carnivores; some organisms’ populations from lower trophic levels (top-down model), providing more of those organisms for the surviving carnivores (more food for them).

Weak eggs, so many parent eagles accidentally crushed the egg during incubation; some eggs also didn’t hatch eagle population; the population of eagles’ prey increased, so competition for those prey isn’t as intense.

Global Warming’s Impact on Competition

Some organisms may not be able to adapt fast enough to the rapidly changing conditions of the world

Species may become extinct; its predators may starve/be eliminated & its prey is more abundant

Some organisms may adapt well to the new conditions caused by global warming

Have edge over other species to get resources, reproduce rapidly; lead to local elimination of interior competitor (not able to obtain resources)

Survivors reproduce, pass genes onto offspring; over evolutionary time, may evolve to new species

If species is extinct or adapts, a competitor is still eliminated, leading to less competition for resources

A.P. Biology Pd. A9/15/08