UNIT 3
ECOSYSTEM
STRATEGIES
3.1 SPECIALIST AND GENERALIST
SPECIES
The way species utilize their niches can be
broadly grouped as generalists or specialists.
1. The Giant Panda is an
example of a specialist
specie. It has a narrow
niche with no predators
except man.
2. The advantage of
specialist species is that
competition is reduced.
3. However, when food and
habitat are limited,
survival is threatened due
to lack of adaptability.
4. Only about 800 Pandas are alive in the wild and 220
are in zoos. They are more closely related to raccoons
than to bears.
5. The Panda’s habitat is western China where human
population is soaring. It has become endangered
because:
• loss of habitat people are
encroaching
• specialized diet –
Pandas feed only on
bamboo and need to
spend most of the
day eating up to 1/3
of its body weight.
• Bamboo has a natural tendency to
die back and grow slowly.
• low birth rate - one cub every other year; at birth the
baby is blind, without fur, and weighs only 5 oz.
• finicky mating habits - Pandas are usually solitary,
but during courting the males are very
possessive.
6. Mothers must care for
their young for 2 years
- assuming the mother
survives.
Adults weigh about 250 lbs.
7. The American Alligator is an example of a
generalist specie that also has no predators except
8. man.
It became endangered simply from hunting.
9. When hunting alligators became illegal,
• the specie made a huge comeback.
• They showed up in swimming pools, drainage
ditches and retention ponds. People were even
feeding them.
EPA
• Alligators began to
consume ducks,
hunting dogs, pets,
pigs, deer, cattle,
wading birds, and
people!
10. By 1977, alligators were removed from endangered
status to threatened status. Hunting with a permit is
now allowed.
11. The advantage of
generalist species is
their wide niche and
habitat choices.
12. Competition from
other species is their
only disadvantage.
FWS
13. On farms,
reproductive rates
have increased 4 fold,
growth rates have
doubled, and
unplanned mortality
reduced by 34%.
Alligator serve a vital role in the ecosystem and are
tied to a healthy food web.
3.2 KEYSTONE SPECIES
1. The alligator is a keystone specie in the swamps, wetlands, and
river systems of southern states.
2. Keystone specie have a central role in the functioning of an
ecosystem and the existence of other species are closely
tied to them.
3. Alligators are the top carnivores in the food web and feed on
nearly every animal in or around water.
4. Alligators are keystone because they:
• dig holes that fill with fresh water; other animals use
the holes for drinking and habitat
• make nesting
sites that are later
used by egrets
and herons
• eat predatory fish that cause a decrease in bass
and bream
• make pathways to the water, keeping grassy areas
open for drainage and use by other animals
5. Reptiles share these characteristics:
• 3 chambered heart (except the alligator has 4
chambers)
• cold blooded - warm habitats improve metabolism
• integument has scales and some can shed their
skin
• skutes are used for protection and thermoregulation
• bony skeleton
• breathe with lungs
Order Crocodilia is composed of:
1. Crocodiles
• have a pointed snout and lay
eggs in holes.
• They are native to Africa,
India, Indonesia and
southern Australia.
2. Alligators
• have a rounded snout and lay
eggs in above ground nests.
• They are larger and are
darker in color than the
crocodiles.
3. Caimans
• have short, up-turned
snouts and large
eyes.
• They are native to
Venezuela and the
south Amazon basin.
4. Gharials
(gavials)
• have small flat
heads and a very
long, thin,
pointed snout.
• They are native
to the larger
rivers in India.
Alligator
Crocodile
Gharlal
5. The American Alligator is the largest specie in the
Order. Females lay 20-70 leathery eggs in a mound of
vegetation.
6. As the vegetation decomposes it gives off heat. The
incubation temperature determines the gender of the
young.
Reptiles have an amniotic egg with a membrane to
prevent drying out. Eggs below 85oF hatch into
females, while those above 95oF become males. After
65 days the eggs begin hatching.
7. The young signal the mother with chirping sounds.
She will help them crack the shells and will eat the
unfertilized eggs.
The young are transported to the water either in her
mouth or riding on her back. They hide in her mouth
for protection.
8. In 1967, the American Alligator was placed on the
endangered species list. In less than 10 years, it was
reclassified to threatened in Florida, Louisiana, and
Texas where 90% of the alligators live.
By limiting hunting and farming the species for its
meat and hides their populations quickly grew.
The alligators’
return is one of
the most
successful
stories in
wildlife
conservation.
3.3 SPECIE INTERACTIONS
1. Indicator species
serve as an early
warning for
environmental
problems.
2. Birds are excellent
indicator species.
They are found
almost everywhere
and respond quickly
to environmental
changes.
3. Historically, canaries were used to
detect low oxygen levels in mine shafts.
The term is now synonymous with
indicator species.
4. The interaction of species gives a good picture of the
stability of an ecosystem. Species interact in 4
ways:
Competition
•usually leads to adaptations or
new species “survival of the
fittest”. It is a limiting factor.
• interference - limit another’s
access to resources
ex: establishing a territory
NASA
• exploitation - one specie is better at getting resources
ex: lions are better at attacking larger prey than
leopards
• exclusion - similar species can’t occupy the same niche
ex: nutria vs. muskrat’s territory
• Humans have often resorted to exclusion (using one
specie to get rid of another), but the introduction of
non-native species, called exotics, has usually
resulted in disaster.
ex: Kutzu was used
as a ground cover
along highways,
but it is only eaten
by goats.
Avoidance - finding ways to reduce competition
• resource partitioning - limiting themselves to
territories not already used
ex: birds dividing up a tree, nocturnal-diurnal
patterns of reef fish or mammals.
• character displacement - species have special
features that cause different feeding habitats or
locations
ex: bill shape and size on birds
Predation is enhanced by
• speed
• keen eyesight
• sense of smell
• hunting in packs
• ambush
•
•
•
•
•
sharp teeth
flight
chemicals
camouflage
Behaviors
• Predation is harmful to the individual prey but
necessary at the population level to prevent any
NOAA
specie from over-running the habitat and to weed out
sick and injured.
Symbiosis
• living in close association
with others
• parasitism (+ -) one benefits
by harming another
ex: lamprey on fish
Hooks on a lamprey mouth
• mutualism (+ +) both
benefit
ex: tickbird on rhinos;
one gets a meal - the
other gets ticks removed
• commensalism (+ o)
one benefits, other
not affected
ex: bird’s nest in a
tree; tree height
provides protection
- no benefit nor
harm to tree
3.4 BACKYARD BIRDS
Phylum: Chordata
Class: Aves
There are over 8,500 species
of birds in 27 different Orders.
1. A common way to
visually group them is
by:
• waterfowl
• aerialist
• marine birds (both long
and short legged waders)
• birds of prey
• fowl-like birds
• song birds and non-singing land birds
2. Anatomical adaptations:
• Body shape is adapted for flying, hopping, running,
diving, tipping, floating, wading, tearing flesh,
hunting, drilling and for least resistance.
Hummingbirds
and sparrows
are very small
3-7 inches.
Canadian geese and swans are large - over 25”.
• Wing shape is used for identification.
Long wings are common on migratory ducks and
heavy birds.
Short wings are found on woodland birds because
they take up less room in a crowded forest and aid in
lift off from the water.
• Tails may be rounded, forked or squared off.
• Waterfowl bird legs are
positioned behind its center of
gravity; good for swimming but
makes walking slow.
• Wading bird legs are tall and
thin.
• Songbirds have feet that “lock”
so they don’t fall out of trees.
• Bones have hollow spaces to reduce weight in flight.
The neck is flexible but the rest of skeleton is rigid so
they don’t wobble in flight.
• Lungs contain extra air sacs
that may collapse during a
dive; oxygen is stored in the
blood and muscles.
• Heart is 4 chambered, is
warm blooded (around 104107 o F), and beats 135 - 1000
times/minute depending on
the species.
FWS
3. Birds must eat large
quantities of food to get
energy for flight and to
regulate temperature.
Digestive system is
poor; materials pass
through in 2 hours.
4. Their diet may be
• small animals (snails, fish, amphibians, reptiles,
rodents, mollusks, worms, insects, other birds)
• plant products (nectar, sap, grass, roots, leaves,
pollen, seeds, tubers, fruit, and buds).
Some fly by rapid
wing beats,
gliding, soaring,
or hovering.
Some need a
running start to
become airborne
and to land,
others can lift out
of the water.
5. Flying in a V formation reduces air resistance and
conserves energy.
6. Migration in waterfowl and songbirds
• greatly increases the ecological flexibility. They do
not have to adapt - just move. Their range is where
they can be found over the course of a year.
• Internal hormonal clocks regulate
migration in response to climate,
stars, photoperiod and earth’s
magnetism. Unusual weather
may have drastic results.
The Migratory Bird Treaty Act
protects 93% of the 777 species
of birds including wading birds,
birds of prey, shorebirds, sea
birds, and perching birds.
7. Plumage
• Male birds have more colorful plumage to attract
females
• Female birds are camouflaged to blend in with a
nest.
8. Songs and displays are used for sex identification, to
claim territory, and to attract mates.
9. Egg
• The egg is produced in a
single ovary.
• Fertilization takes place at
the junction of the oviduct
and ovary.
• Eggshells
i. are made of calcium and
magnesium salts and
ii. contain channels for the
exchange of respiratory
gases and water vapor.
iii. Albumin (egg white)
and color for the
eggshell are produced
by the oviduct wall.
Some birds will lay one egg per day whether it has been
fertilized or not. Other lay continuously until the clutch
size is reached.
USDA
10. Nesting habits
• brood parasites- lay their eggs in the nests of
other birds. Ex: Cowbird
• Altricial birds - born
blind, without
feathers and
helpless. They hatch
quickly but take
more time in
parental care. (Ex:
song & marine birds)
• Precocial birds
i. hatch more slowly but
fully mature in a few
hours.
ex: waterfowl
ii. Precocial chicks and
waterfowl copy the mother’s
activities in an irreversible
type of learning called
imprinting.
iii. In 1973, Conrad Lorenz won a Nobel Prize for his
work in animal behavior that described the window
of time after hatching for effective imprinting. His
work touched off the “nature vs. nurture” debate.
3.5 SUCCESSION
1. All ecosystems age in a (theoretically)
predictable way called succession.
However, nature is very random.
Often stability is maintained by
change. Older organisms die
leaving younger ones to replace
them.
2. Stability is based on three
parameters, but scientists
disagree whether stability must
include all three.
• inertia (resistance to change)
• constancy (ability to live within
the resources)
• resilience (ability to bounce
back)
3. Rain forests
• High inertia
because of high
specie diversity,
but low resilience.
• nutrients are
stored in the
vegetation rather
than in the soil.
• Once the forest is
cut, recovery is very
slow. This is
another reason why
cutting rain forests
for farming is a bad
idea.
• The soil is very
poor.
4. Grasslands
• low inertia with low diversity - only grass.
• high resilience because nutrients are stored in
the roots, which helps them grow back quickly.
5. The four stages of succession are:
• pioneer - begins with soil formation;
small plants and species with
minimal requirements
• juvenile communities - low diversity
• mature communities - high diversity
• climax communities – stability; some scientists
argue that climax communities don’t exist
This is the way ponds become meadows and meadows
become forests.
The animal populations also change with the environment.