CHAPTER 46Community Structure and Biodiversity: A Summary

AP BiologySpring 2011

WHICH FACTORS SHAPE COMMUNITY STRUCTURE?

Where a species resides is its habitat whereas a niche is its role in the community Factors influencing niche of plant: soil, light,

water, etc.

WHICH FACTORS SHAPE COMMUNITY STRUCTURE?

Species relationships: Commensalism: one species in the relationship

is benefited and the other is unaffected

WHICH FACTORS SHAPE COMMUNITY STRUCTURE?

Species relationships: Mutualism: both species in a relationship

benefit

WHICH FACTORS SHAPE COMMUNITY STRUCTURE?

Species relationship: Predation and parasitism: one species

benefits at the other species’ expense

MUTUALISM

Mutualistic relationships are common in the environment Insects serve as pollinators, while plants provide

nectar for the insect Legumes change nitrogen into a usable form and

plants provide nutrition In lichen, fungi serves to soak up water while

plant again provides nutrition Anemone fish protects the anemone and the

anemone provide defense for the fish in the form of nematocysts

Perhaps mitochondria where bacteria that sought protection in cells while providing energy to the cell

COMPETITION INTERACTIONS

Competition between species may result in evolution by natural selection When two species of

paramecium were in the same environment, one thrived and one died

When two species of salamanders were together in the same area, both populations decreased due to competition

COMPETITION INTERACTIONS

Species may be able to survive together if they partition their resources In a study of finches in the Galapagos Islands,

one species of finch developed a smaller beak so that they could utilize a different sized seed as a food source

Minimize the competition

PREDATOR-PREY INTERACTIONS

The numbers of prey can influence the quantity and types of predators Type 1 response: fairly constant number of

prey are killed Amount of prey killed depends on their density Ex. Spiders, filter feeders

PREDATOR-PREY INTERACTIONS

Type 2 response: number of prey killed depends on the skill level of the predator Initially, there are many more kills, but

eventually it slows down since predators can only eat so much

Ex. Large animals like tigers, wolves, etc.

PREDATOR-PREY INTERACTIONS

Type 3 response: number of prey killed increases at a slow rate, then quickly and finally levels off Could be due to predator switching to a different

type of prey Predator could be learning more effective ways

of hunting prey The rapid rise in kills could involve the prey

running out of hiding places

PREDATOR-PREY INTERACTIONS

EVOLUTIONARY ARMS RACE Prey develop various defenses for survival

Some have natural camouflage to hide from predators Ex. Bittern birds, caterpillars, lithops plants

Some have warning colouration to alert predator to bad taste or possible stinging Ex. Yellow jacket

Some illustrate mimicry where an organism appears like another organism that is dangerous or distasteful Ex. Viceroy butterfly mimicking monarch and other

insects resembling yellow jackets

EVOLUTIONARY ARMS RACE

Predators develop various adaptations Some develop better hunting methods

Ex. Swift cheetah Some utilize camouflage to ambush prey

Ex. Undetectable scorpion fish and polar bear

PARASITE-HOST INTERACTIONS

A parasitic lifestyle benefits the parasite and usually harms the host Parasites may weaken the host or cause sterility A successful parasite should not destroy the host Often parasites utilize a vector to deliver the

parasite to a suitable host organism Vectors include insects and other arthropods

PARASITE-HOST INTERACTIONS

A parasitoid is a parasite that lays eggs in an insect’s body and destroys it

Parasites can be used as biological controls in an attempt to eliminate an undesirable organism

STRANGERS IN THE NEST

Social parasites are those that take advantage of another animal’s behavior Ex. Cowbird who lays its eggs in another bird’s

nest so that the other bird serves as a foster parent

ECOLOGICAL SUCCESSION

Primary succession: when an area lacking soil is originally colonized Lichens and mosses settle first because they can

inhabit an area with little or no soil Soil is developed from plant liter and other

species settle

ECOLOGICAL SUCCESSION

Secondary succession: relates to an area’s recovery from a fire or natural disaster

ECOLOGICAL SUCCESSION

The factors that relate to the organisms that occur during succession are sometimes unpredictable Factors that determine the species population

during succession are soil composition, climate and often chance events

The intermediate disturbance hypothesis states that the number of species inhabiting an area is highest when the disturbances are less drastic

ECOLOGICAL SUCCESSION

SPECIES INTERACTIONS AND COMMUNITY INSTABILITY

Keystone species: one that has an overwhelming effect on the environment Ex. Periwinkle

snails, beavers, sea star

SPECIES INTERACTIONS AND COMMUNITY INSTABILITY

Geographic dispersal: when residents of established communities move out of their home range and successfully take up residence elsewhere Over a number of generations, population might

expand its home range by slowly moving to outlaying regions

Due to jump dispersal, organism may be moved far from its native habitat (rapidly transported across great distances)

May be moved by continental drift, slow pace over long time period

EXOTIC INVADERS

Some exotic imported species may upset the natural balance in the new environment Common algae present in fish tanks can

dominate natural waterways Kudzu plant from Japan is extremely is extremely

fast growing and difficult to control in the US Australia attempts to control a rabbit infestation Hearty grey squirrels introduced to Europe out

survive the native red squirrels

BIOGEOGRAPHIC PATTERNS IN COMMUNITY STRUCTURE

Biogeography: studies the natural location of species The greatest number of species settles close to

the equator This is due to the amount of rainfall, temperature and

the fact that tropical environments are well-established communities

BIOGEOGRAPHIC PATTERNS IN COMMUNITY STRUCTURE

Newly formed islands are an excellent habitat for studying speciation The equilibrium model of island

biogeography attempts to predict the amount of speciation on an island

The amount of speciation can be estimated by the land area of the island and its distance from the mainland