CHAPTER 46
Community Structure and Biodiversity: A
Summary
AP Biology
Spring 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


Some have warning colouration to alert predator
to bad taste or possible stinging


Ex. Bittern birds, caterpillars, lithops plants
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
