AP Biology Community Ecology Part 1

Important concepts from previous units: 1) Producers are responsible for providing available energy, in the form of sugars, for the food chain. 2) Consumers eat the producers to obtain the energy found in their biomass.

Community – The term refers to a collection of interacting populations within the same given area.

Community

– Species Richness – Refers to the number of different species within a given area. – Relative Abundance – Refers to the population size for each species within that given area. Rare – few exist ; common – many exist Species richness is the same, however, relative abundance is not.

– Rivet model is the best way to explain the interaction among species (A.K.A.food web model) It basically is stating that every species is important in the proper functioning of that ecosystem. If you start removing species (extinction) from the system (what we commonly call a food web), it is like removing a rivet from an airplane. It damages the whole system. The more you remove, the more damage done. At some point, you have removed so many that the whole system collapses…the plane crashes killing all or most.

Consider the ecosystem inhabited by the organisms in the food web below. Suppose a disease caused most of the rabbits in the ecosystem to die. #1. Predict what effects this will have on (a) the hawk population (b) the amount of grass available (c) the field mouse population

Interspecific Interactions - These are between two different species. – Competition ( - );( - ) It is considered a negative- negative relationship. Competition exists because a resource is in small supply. Active competition drains energy away from reproduction. So populations are small.

Competition and also predation

Competitive exclusion model - States each species has it’s own niche in an environment. – Two species cannot occupy the same niche… So one is excluded from getting the resource. – Resource partitioning (dividing) occurs due to displacement. This can cause evolution to proceed faster – such as occurred with Darwin’s finches of the Galapagos.

The “excluded” species has three basic options: – 1) Leave the area to look elsewhere for the resource. – 2) Die off or – 3) Find a replacement resource. (This promotes evolution.)

Predation ( + ); ( - ) Considered a positive – negative relationship. 1. Normal predation (Carnivore or Omnivore eats an herbivore.) 2. Herbivory - Eating plants. (Also considered predation…since they are a different species.)

Herbivory (This is also predation.)

Skip to #4 Coming back to #3

Adaptations for being a predator – claws, teeth, poisons, fast locomotion, muscular (All help kill.) Self defense adaptations against predators – long legs, faster, flight, horns, coloration, very good smell

i. Cryptic coloration – camouflage (like encryption) ii. Aposematic (warning) coloration – bright colors like reds or oranges iii. Mimicry Batesian type – A harmless looks like a harmful organism. This becomes an associative learning exercise for the attacking species. They become very scared to attack organisms that look similar to that bad experience. This increases survival rates for the mimickers. Műllerian type – A harmful looks like a another harmful.

Cryptic Coloration (Can you see the bird?)

Aposematic Coloration

Batesian Mimicry (Catapillar and snake)

Mullerian mimicry (Cuckoo bee and yellow jacket)

Back to #3

3. Parasitism – Death does not occur; but harm is done to another species. a. Three types occur 1) Ectoparasites – These attack from the outside. (mosquito) 2) Endoparasite – These attack from the inside. (tapeworm) 3) Parasitoidism – Insects laying eggs on a host that will eventually become food for the larva. “oid” means “like” It is like parasitism in that there is still harm, but it is the larva (secondary) causing the harm and not the insect (primary) that laid the eggs

Parasitism Ectoparasite

Parasitism Endoparasite (Tapeworm)

Mutualism ( + ); ( + ) Considered a positive- positive relationship.) This relationship promotes co-evolution, But remember that co-evolution can either be good or bad, such as the predator/ prey relationship… it is co-evolution too.

"A sea anemone makes an ideal home for a clownfish. Its poisonous tentacles provide protection from predators and a clownfish makes its meals from the anemone’s leftovers." "A clownfish can help an anemone catch its prey by luring other fish toward over so that the anemone can catch them. Clownfish also eat any dead tentacles keeping the anemone and the area around it clean. "

D. Commensalism ( + ); ( 0 ) Considered a positive- no effect relationship. 1. Few exist in nature and it is hard to see if there is no reciprocal effect.

Community Control Models – Essentially what factor is controlling the species composition in an area. – Bottom Up Model (Nutrients in the soil determine community composition.)(Most cases) Nutrients  Plants  Herbivores  Predators – Top Down Model (Predators determine the community composition.) Predators  Herbivores  plants  Nutrients

Stability – A community at equilibrium. Very little disturbance/change occurs over time.

Non-equilibrium Model – Periodic disturbances occur altering the environments species composition over time. – Examples of disturbances: Fire, flood, drought, human actions, storms, hurricanes/typhoons. – These help create new possibilities in an environment by opening up new niches.

Disturbance and harmful effects Without Pisaster (experimental) With Pisaster (control) 1963 ’64’65 ’66 ’67 ’68’69 ’70 ’71 ’72 ’ Number of species present

Disturbance (Beaver Dams)

Fire and Disturbance Before a controlled burn. A prairie that has not burned for several years has a high propor- tion of detritus (dead grass). During the burn. The detritus serves as fuel for fires. After the burn. Approximately one month after the controlled burn, virtually all of the biomass in this prairie is living.

Ecological Succession – Change in community composition due to time and disturbance. – Two types can occur within environments Primary Succession – This is “starting from scratch” using pioneer species – lichens and mosses. – Hawaii going from barren volcanic rock to plush, tropical island. – Pioneers make the dirt needed for the plants & birds bring seeds in their feces as they feed upon lichens. – Lichens  grasses  bushes  gymnosperms  hardwood trees  Climax Climax Community – Hardwood forest exists all over.

Stages of Succession Pioneer stage, with fireweed dominant Dryas stage Spruce stage Nitrogen fixation by Dryas and alder increases the soil nitrogen content. Successional stage DryasPioneer Alder Spruce Soil nitrogen (g/m 2 )

Primary Succession (Remember Hawaii?)

Primary Succession (Pioneer species)

Primary Succession

Primary succession

Primary Succession Climax Community (Hawaii today)

Succession (Mount St. Helens, WA)

Secondary Succession – This is “starting over at the grasses level” not from scratch. (Such as the farming of fields to grow crops.) a. Dirt already exists b. Grasses  bushes  Gymnosperms  hardwood trees  Climax

Secondary succession (Forest fire destroys the forest)

Secondary Succession (Then over time…life returns)

Biodiversity – This measurement includes Species Richness and Relative abundance in the calculation. Primarily looking at the degree of Heterogeneity. (difference)

Size and Location of an environment – Large Area – Usually means more species. – More habitats and niches present  therefor more species can exist. Richness and land area size

Energy, water, and species richness Rates of Evapotranspiration (determined by solar radiation, temperature, and water availability) increases with abundant rainfall…more rainfall results in greater species diversity

Equatorial  Polar gradient (going from equator to north or south pole) Less biodiversity the farther north or south you get from equator. – Temperature and seasons, sunlight for photosynthesis, water availability all change toward a more harsh environment the closer you get to the poles. – Equator  It is summer ALL year… so more plants and animals. – Poles  Winter ALL year… so less plants and animals. – Above the tropics  Seasonal changes occur over the year. – Tropics  desert (More plants and animals in the tropics versus the desert.

Equitorial Gradients and Species

Islands Biodiversity (Defined by E. O. Wilson – 1960’s – He is a native of Alabama.) – Size of Island (Big – usually has much biodiversity; Small usually has less.) » Pygmism – Smaller sizes exist on some islands due to smaller environment. (Smaller amounts of resources tends to lead toward the evolution of smaller organisms and populations.) – Location of island in relation to mainland (Close – less variation; far – more variation exists) » Similarity of the environments – Amount of disturbance can also affects the biodiversity. If there is recurring, frequent disturbances there will be less biodiversity. A calmer environment promotes progression and evolution.

E.O Wilson A Native Alabamian

Richness and Islands

As the number of species on the island increases, immigration rate of new species decreases because any individual reaching the island is less likely to represent a species that is not already present. As more species inhabit the island, extinction rates on the island increase because of the greater likelihood of competitive exclusion.

Pygmy Elephant of Indonesian Islands