Ch 35 Population/
Community Ecology
35.1 Population Density
Population density is the number of
individuals of a particular species per
unit area or volume.
Examples:
 35 alligators per square km of a swamp
 1,000,456 bacteria per cm2 of an agar plate
 120 earthworms m2 of soil
Population density problems
On rare occasions you can count all the individuals in
a population, such as the number of beech trees in a
forest measuring 50 square kilometers (km2).
Population density = Individuals = 1000 trees = 20 trees
Unit area
50 km2
km2

Population density is a helpful measurement for
comparing populations in different locations.
Population Dispersion
35.2 There are limits to a population’s growth
 Exponential
growth: growth of a
population that multiplies by constant
factor
 Limiting factor:condition that restricts a
population’s growth, such as space,
disease and food availability.
 Carrying capacity: number of
organisms in a population that an
environment can maintain.
Exponential Growth
Figure 35-5
This table shows how
many bacteria are in a
population that doubles
every 20 minutes. The
graph is another way to
show the same data.
CARRYING CAPACITY

Figure 35-6
Figure 35-6
Before the early 1900s, hunting
kept this population of fur seals
below the carrying capacity of
the environment. Then, after
hunting was reduced, the
population grew almost
exponentially for two decades.
The population began to level
off as it reached the carrying
capacity.
Changes in Population Size

Growth factors (increase in pop.)



Immigration: individuals moving into a population
Births
Shrinking factors (decrease in pop.)


Emigration: individuals moving out of a population
Deaths
Exponential Growth= J curve




Early phase of growth
High availability of resources
Little competition
Little predation
Logistic Growth= S curve
represent Carrying capacity

Limits on growth
appear




Competition for
resources
Predation
Parasitism
Illness
35.3 Human
Population Growth

The human population is now
growing at a rate of about:
3 people/second or
260 thousand/day or
1.8 million per week or
93 million/year
Earth’s Carrying Capacity
about 50 Billion
Human Population Growth
Are humans in exponential or logistic growth?
35.4 Interactions in Communities
Competition Between Species
An elephant, cannot survive without other
organisms.


elephant herd of elephants (population) an elephant’s community
An elephant’s community = gazelles, giraffes, birds, ants, beetles, fungi,
bacteria, grasses, trees
Members of a population compete for limited resources
in the environment.

-Competition within a single species limits
the growth of the population.
Interspecific competition: when two or more
species rely on the same limited resource
(competition between 2 different species)
example:during times of drought in an African savanna community, grasses may
be in short supply, and competition becomes intense.
Competitive Exclusion
Competitive
exclusion: One
species succeeding
over another, when
the growth of both
species is limited by
the same resource.
Figure 35-14
Two similar species may each thrive in
separate locations, but one may exclude
the other when they are placed together.
The results of an experiment with two
Paramecium species demonstrate this
principle of competitive exclusion.
NICHE
Niche: a unique living arrangement of
an organism defined by its living
place (habitat), its food sources, the
time of day it is most active, and
other factors



The local loss of a species is likely to occur if 2 species have niches that
are very similar
niches are rarely identical.
Example: one lizard in a tropical forest feeds on insects in low shrubs,
while a similar lizard may eat insects high in the trees.
Predation
Predation: an interaction in which one organism eats
another.

The lion attacks and eats an injured zebra or an
egret catches and eats a fish.
Predator: the organism that kills/ eats the prey.
Prey: the organism that gets eaten.

eating and avoiding being eaten are important to
survival,

many effective adaptations have evolved in both
predators and prey.
Predator/ Prey
Predator Adaptations
fast and agile
 camouflage
 teaming up in packs acute senses
 claws, teeth, fangs, and stingers

Ex. Rattlesnakes locate their prey with heat-sensing organs located
between each eye and nostril.
Prey Adaptations

retreat to safe locations

flee from predators

camouflage to hide

"warning coloration" is a caution to
predators.

mimicry -look like organisms that are
poisonus or dangerous.

Plants have poisonous chemicals and
structures such as spines and thorns.
Warning Coloration
Monarch w/ warning coloration
Viceroy Butterfly- mimics Monarch
Symbiotic
Relationships
Symbiotic relationship is a close interaction between
species in which one of the species lives in or on the
other.

3 main types of symbiotic relationships: parasitism,
mutualism, and commensalism.
1.) Parasitism is a relationship in which the parasite
obtains its food at the expense of the host.

Usually the parasite is smaller than the host. (blood-
sucking mosquitoes and tapeworms)
Ticks
Mutualism: both organisms benefit from the
symbiotic relationship.

Your large intestine is inhabited by millions of
bacteria.

The bacteria benefit by having a warm, moist
home and food.

Intestinal bacteria produce vitamin K.
Vitamin
K is essential for blood clotting.

Both you and the bacteria benefit from this
relationship.
Mutualism
Manta
with Remoras
Pair ofRay
Coleman
Shrimp on fire urchin
Commensalism is a relationship in which one organism
benefits, while the other organism is neither harmed
nor helped significantly.
Example:
A spider crab may place seaweed on its back. The crab
benefits by being camouflaged from its predators. The
seaweed is not affected.

commensalism in nature is rare, since most interactions
harm one species (parasitism) or help both species
(mutualism) to some degree.
Commensalism
35.5 Disturbances are common in
communities
Ecological Succession
Ecological succession. Series of changes in
the species of a community, often followed
by a disturbance.
Primary Succession- process by which a
community arises in a lifeless area that has
no soil
barren ground lichen/mosses grass shrubs pine trees  hardwood trees
Examples:
 Forest devastated by a fire, or volcano
 new islands created by erupting volcanoes
 bare rock left behind a retreating glacier.
Primary Succession

The establishment and development of an
ecosystem in an area that was previously
uninhabited
Lichens
and
mosses
Grasses
And
small
shrubs
Large
shrubs and
small trees
Large
trees
Primary Succession
Surtsey: A Case Study

The island of Surtsey formed by volcanic
eruption off of the coast of Iceland during the
period from 1963 - 1967
Surtsey – Post Eruption
Surtsey Today
Secondary Succession
Secondary succession when a disturbance
damages an existing community but
leaves the soil intact

Grasses  shrubs trees similar to the original forest.
Example: when a forested area is cleared for farming and then
abandoned.
Secondary Succession

The recovery of a damaged ecosystem in an
area where the soil was left intact
Fireweed
Sequoia seedling
Case Study: Yellowstone National Park
1988 – Devastating forest fires burn much of
Yellowstone National Park.
Photo: National Parks Service
Yellowstone
National
Park
1988 – Park map
showing areas
(1.6 million acres)
burned by the
series of fires.
Yellowstone National Park
1988 fires – The immediate aftermath.
Photo: National Parks Service
Yellowstone
National Park
One year after the
fires
 Note the appearance of
fireweed

Photo: National Parks Service
Yellowstone National Park

Ten years after the fires (1998)
Photo: National Parks Service
Yellowstone National Park

Twenty years after the fires (2008)
Case Study - Chernobyl

In April, 1986, a nuclear
power plant in the former
USSR experienced a core
meltdown and a
catastrophic release of
radioactivity into the
environment.
Chernobyl

Surrounding towns
and villages had to
be immediately,
permanently
abandoned.
Chernobyl – Twenty Years Later
Chernobyl – Twenty Years Later
Pripyat town square.
Chernobyl – Twenty Years Later
Pripyat Soccer Stadium opened in 1986.
Chernobyl – Twenty Years Later
A local highway.
Secondary succession: trees are colonizing
uncultivated fields and meadows
Human Activities and
Species Diversity
humans have had the greatest impact on
communities worldwide.
 60 % Earth's land is used by humans, mostly
as cropland or rangeland.

Human disturbances have a negative effect on
species diversity
Clearing the Land
 for lumber
 land for farming
 Land for building.
 paved over or eventually recolonized by weeds and
shrubs, as in abandoned city lots.
Invasive Species
Courtesy www.lab-initio.com
Invasive Species
 Introduced species: any
organism that was brought
to an ecosystem as the
result of human actions
 Invasive species: A
species that takes
advantage of an unoccupied
niche, or that successfully
out-competes native
species
Kudzu:
an invasive vine
Introduced Species
Introduced species are organisms that
humans move from the species' native
locations to new geographic areas, either
intentionally or accidentally (exotic
species).

Kudzu, a Japanese plant planted widely in the American South (1930s) to
help control erosion. especially along irrigation canals. But kudzu soon
grew out of control, taking over vast expanses of landscape.

Some introduced species gain a foothold and may disrupt
their new community.
Some introduced species prey on native species or
outcompete native species

Invasive species
Invasive species
are "alien”
species whose
introduction
does or is likely
to cause
economic or
environmental
harm or harm to
human health"

U.S. Invasive Aquatic Plants
Partial list:
Brazilian Waterweed
Caulerpa,
Mediterranean Clone
Common Reed
Eurasian Watermilfoil
Didymo
Giant Reed
Giant Salvinia
Hydrilla
Melaleuca
Purple Loosestrife
Water Chestnut
Water Hyacinth
Water Lettuce
Water Spinach
Hydrilla
U.S. Invasive Aquatic Animals
Partial list:
Alewife
New
Zealand Mud Snail
Northern Snakehead
Asian Carps
Nutria
Asian Swamp Eel
Quagga
Mussel
Bullfrog
Round
Goby
Chinese Mitten Crab Rusty Crayfish
Eurasian Ruffe
Sea
Lamprey
European Green Crab
Sea
Squirt
Flathead Catfish
Spiny
Water Flea
Lionfish
Veined
Rapa Whelk
Zebra Mussel
Zebra Mussel
U.S. Invasive Invertebrates
Partial list:
Africanized Honeybee
Asian Citrus Psyllid
Asian Long-Horned Beetle
Asian Tiger Mosquito
Cactus Moth
Emerald Ash Borer
European Gypsy Moth
European Spruce Bark
Beetle
Formosan Subterranean
Termite
Giant African Snail
Glassy-Winged
Sharpshooter
Hemlock Woolly Adelgid
Light Brown Apple Moth
Mediterranean Fruit Fly
Mexican Fruit Fly
Pink Hibiscus Mealybug
Red Imported Fire Ant
Russian Wheat Aphid
Silverleaf Whitefly
Sirex Woodwasp
U.S. Invasive Vertebrates
Partial list:
Widespread
At Risk of
Brown Tree Snake
Intrusion
Cane Toad
snakes
European Starling
snakes
Wild Boar
rat
House Sparrow
Nutria
Constrictor
Boiga
Gambian pouch
European Starling
Cane Toad
U.S. Invasive Plants
Autumn Olive
Beach Vitex
Canada Thistle
Chinese Tallow
Cogongrass
Common Teasel
Dalmatian Toadflax
Diffuse Knapweed
Downy Brome
Garlic Mustard
Giant Hogweed
Hairy Whitetop
Houndstongue
Japanese
Honeysuckle
Japanese Knotweed
Johnsongrass
Kudzu
Leafy Spurge
Medusahead
Mile-A-Minute Weed
Multiflora Rose
Musk Thistle
Old World Climbing
Fern
Oriental Bittersweet
Purple Star Thistle
Quackgrass
Russian Knapweed
Russian Olive
Saltcedar
St. Johnswort
Scotch Broom
Scotch Thistle
Spotted Knapweed
Tree-of-Heaven
Tropical Soda Apple
Whitetop
Yellow Star Thistle
Yellow Toadflax
Yellow Star Thistle
U.S. Invasive Microbes
Animal Pathogens
Avian Influenza
Exotic Newcastle Disease
Fowlpox
Viral Hemorrhagic Septicemia
West Nile Virus
Whirling Disease
Plant Pathogens
Citrus Canker
Citrus Greening
Plum Pox
Southern Bacterial Wilt
Soybean Rust
Sudden Oak Death
West Nile Virus
Citrus Canker
Kudzu vines
Zebra Mussels clogging pipes
Zebra mussels clogging pipe
35.5 DISTURBANCES
Definitions


Bioaccumulation: is the process by which
substances not readily broken down or
excreted can build up and be stored in living
tissue (usually in fatty tissue.)
Biomagnification: is the process by which
substances become more concentrated in the
bodies of consumers as one moves up the food
chain (trophic levels).
Case Study:
PCBs




PCBs, or polychlorinated
biphenyls, are a group of manmade chemicals.
Introduced in 1929 and widely
used in electrical transformers,
cosmetics, varnishes, inks,
carbonless copy paper, pesticides
and for general weatherproofing
and fire-resistant coatings to
wood and plastic.
The federal government
banned the production of
PCBs in 1976
PCBs can effect the
immune system, fertility,
child development and
possibly increase the risk
of certain cancers



DDT is a pesticide that was
widely used until being
banned in the U.S. in 1972
DDT accumulates in living
tissue, particularly in fat
tissue
High concentrations in some
bird species caused failure
of eggs by thinning the shells
Case Study:
DDT
Case Study:
Methyl Mercury
What makes methylmercury so
dangerous?
Methylmercury is rapidly taken up but
only slowly eliminated from the body by
fish and other aquatic organisms, so each
step up in the food chain (bio)magnifies
the concentration from the step below.
Bioaccumulation factors (BAF's) of up
to 10 million in largemouth bass have
been reported for the Everglades.
Fish-eating birds, otters, alligators, raccoons and
panthers can have even higher bioaccumulation factors.
U.S. Department of the Interior, U.S. Geological Survey, Center for Coastal Geology
This page is: http://sofia.usgs.gov/sfrsf/rooms/mercury/achilles_heel/cause.html
Mercury Health Effects