Transcript - ILM.COM.PK

Environmental Science
Chapter 6
Ecosystem Balance
6.1 Relationships in the Ecosystem
Objectives:
1. Explain the relationship between the population sizes of
predator prey.
2. Define symbiosis and describe several symbiotic
relationships.
Animal Relationships
When learning from animals, people need to
understand how the animals relate to one another.
All animals live in an ecological system, where they
have a role.
What is a “gator hole?”
Some are keystone species such as
Alligator, who makes ‘gator
holes’ which provides food and
homes for other animals.
Located in marshes with long hydroperiods throughout the Everglades,
alligator holes result either from fire burning an area of rich peat soil or
from alligator activity. Alligators form holes by using their feet and snouts
to clear muck from holes in the limestone bedrock. Water remains in
these holes throughout the year except during severe drought
conditions. As the dry season approaches and water dries up from other
areas within the Everglades, alligator holes retain water and become
refuges to a variety of wildlife. Alligators prey on the animals that
frequent gator holes in search of refuge, food, and water.
•
•
Stag Beetle eats dead trees to make soil.
“Negative” animals such as Leeches have a role,
too. They kill their host and help keep the animal
population in balance.
Ratel and Honeyguide
Although the ratel can locate bee
nests on its own, it has developed
an interesting relationship with
small birds called honeyguides.
A honeyguide alerts the ratel to its
presence by calling repeatedly,
displaying the white markings on
its tail and making short, swooping
flights from tree to tree.
The ratel follows the bird, answering
its calls with guttural growls until
the nest is reached.
The ratel sniffs around until it locates the nest.
It emits smelly, almost suffocating
secretions from its anus glands to fumigate
the hive, much in the same way that human
honey-hunters use smoke.
The ratel rubs the secretions around the hive,
causing most of the bees to flee, and
stunning or killing those that remain inside.
The ratel bites or claws into the nest and
scoops out the honeycomb.
Meanwhile, the honeyguide waits in the tree.
When the ratel leaves, the bird eats the
remaining dead bees, grubs and pieces of
honeycomb.
This relationship between two very different species
indicates their behavior has been learned and
developed to increase food supplies for both.
Though shy and retiring, the ratel is extremely
aggressive and fearless in certain circumstances.
There may be a basis for the legends, as adult male
buffalo, wildebeest and waterbuck have died from
loss of blood after being attacked by a ratel.
One aspect of predator prey relationship is that they
keep each other in check.
For example, prairie dogs would breed uncontrollably
unless the black-footed ferret ate them. Crudely
speaking, the number of prairie dogs determines the
numbers of ferrets.
Mata Mata, a side-necked
turtle, resembles a pile of
leaves. Living at the
bottom of the Amazon
River, this turtle wiggles
his tongue to entice
unsuspecting fish to come
near.
Examples
Observations of prickly pear cactus and the cactus moth in
Australia support this lab experiment. This South American
cactus became a widespread nuisance in Australia, making
large areas of farmland unusable. When the moth, which feeds
on this cactus, was introduced, it rapidly brought the cactus
under control.
Some years later both moth and cactus were
rare, and it is unlikely that the casual observer
would ever think that the moth had
accomplished this.
Once the cactus became sufficiently rare, the
moths were also rare, and unable to find and
eliminate every last plant.
Inadequate dispersal is perhaps the only factor
that keeps the cactus moth from completely
exterminating its principal food source, the
prickly pear cactus.
Examples
Bats capture moths in flight, using sonar to detect them; some
moths are able to detect incoming sonar, and take evasive
action.
Able to find their way and hunt in complete darkness, insect bats
employ ultrasound (inaudible to the human ear) to navigate by
echo-location. A call or chirp is made and then "read" as it is
reflected back to the animal's highly sensitive ear receptors.
Scientists are able to identify and classify bats on the basis of
their calls, by using ultrasound equipment, as each has a
particular "signature". A distinction is made between
"shouters" and "hummers". "Shouters" call through the mouth
and "hummers" project sound through their nostrils via nose
leaves of various shapes.
Examples
A starfish is the top predator upon a community of invertebrates inhabiting
tidally inundated rock faces in the Pacific Northwest.
The rest of the community included mollusks, barnacles and other
invertebrates, for a total of 12 species.
The investigator removed the starfish by hand, which of course reduced the
number of species to 11.
Soon, an acorn barnacle and a mussel began to occupy virtually all available
space, out competing other species.
Species diversity dropped from more than 12 species to essentially 2. The
starfish was a keystone predator, keeping the strongest competitors in
check.
Although it was a predator, it helped to maintain a greater number of species
in the community. Its beneficial impact on species that were weak
competitors is an example of an indirect effect.
Predators can allow coexistence of
competing prey
Starfish
Pisaster
predator
competitors
Barnacles
Balanus
Mussels
Mytilus
SO………………..Remove the Starfish and……..
Starfish
Pisaster
Barnacles
Balanus
Mussels
Mytilus
- mussels are the dominant competitor
- competitive exclusion of barnacles
- starfish allow coexistence of competitors
starfish
removed
mussels
%
of
intertidal
zone
barnacles
time
How do
starfish
promote
coexistence?
Barnacles
Starfish
Pisaster
Mussels
Starfish are picky – they prefer the dominant competitor,
which allows the weaker competitor to coexist.
Examples
When non-native species (exotics) invade an area, they often create "domino"
effects, causing many other species to increase or decrease.
The rainbow trout, beautiful, tasty, and beloved by anglers, has been
purposefully spread to virtually all parts of the world where it can survive.
In New Zealand, it has out-competed the native fishes, which now are found
only above waterfalls that act as barriers to trout dispersal.
Because it is a more effective predator than the native fish species, the
invertebrates that are prey to the trout are reduced in abundance
wherever trout occur.
Algae, which are grazed by the invertebrates, increase because of reduced
grazing pressure.
Great White Shark and Elephant Seals
To learn more about the dynamics of predator-prey
relationships, pick a pair of animals to study. See how
they interact.
For example, Great White Shark’s favorite food is
Elephant Seal. On the surface, this seems strange
since Elephant Seal is himself noted for his strength
and ferocity.
However, study the animals together to see what
wisdom they impart in their relationship.
Great White Shark is an apex predator
in the ocean; only Orca (Killer
Whale) can kill her.
For some unknown reason, when
Great White Sharks reach a certain
size and age, they become female.
Swimming in the oceans since the time
of the dinosaurs, Great White Shark
is acclaimed for her speed and
efficiency.
During that time, She developed her
well-known torpedo-shaped body
and eight senses. Great White Shark
is aptly called “Queen of the Seas.”
Meanwhile, Elephant Seal lives in a
male dominant society.
He fights with other Bulls, to the
death, to possess an Elephant
Seal Harem.
This massive animal’s roar can be
heard long distances away.
The only animals that prey on
him are Orca and Great White
Shark.
Study the interaction between these two animals.
How does Elephant Seal defend himself against Great
White Shark’s sneak attacks?
What lessons do they have to teach?
For one thing, Great White Shark and Elephant Seal
balance each other out.
One is male; the other is female.
Great White Shark lives in a matriarchy, with Queen
Mother Shark eating first.
Elephant Seal lives in a patriarchy with his harems.
Consider that both swim in the ocean, but Elephant
Seal lives on land.
How does that relate to Great White Shark?
Elephant Seal can escape since he is a mammal, not a
Fish.
Great White Shark counters that advantage with her
eight senses.
One of which is being able to sense a beating heart at
long distances.
As you delve into learning about these animals, you
discover how they interact with each other, as well
as, the important lessons they impart.
Attack strategy consists of a swift, surprise attack from
below, inflicting a large, potentially fatal bite.
The shark carries the seal underwater for a distance before
removing a bite and releasing the carcass which then floats to
the surface.
Sharks immobilize prey by decapitation or biting off the hind
flippers.
Then, a waiting period of two to five minutes ensues prior to the
consumption of the prey.
This may be to ensure the prey is incapacitated, to prevent injury
to the shark from pinniped teeth and claws.
White sharks are unbelievably methodical and
controlled in their feeding behavior, swinging
around and around, taking bites from the prey until it
is consumed.
The pinniped often dies from massive trauma or blood
loss (exsanguination).
The many inches of fat between the skin and vital
organs protect them in the event of predatory
attacks.
• If bitten, injured seals go into a deep dive, where
automatically its blood is shunted to its vital organs, slowing
bleeding. If bites are not too deep, elephant seals can survive.
• When the juvenile elephant seals come ashore for the
first time in months, just a few feet off shore, the
sharks are waiting for them.
• The seasonal concentration of young, naive seals draws white
sharks like a magnet.
• Hauling out on a rocky ledge is a struggle, especially at high
tide. Huge waves can wash the seals right back into the surf.
Just a few feet off shore, the sharks are waiting for them.
Predators and Prey
• Consumers that actively hunt other living organisms are
called: predators
• The organism eaten by a predator is called the:
prey
Predators and Prey
Example: dragon fly and praying mantis
Which is the predator?
Click one
Dragon fly
Praying mantis
The Predator Prey Relationship
• This includes predator-prey, herbivore-plant, and
parasite-host interactions.
• These linkages are the prime movers of energy
through food chains.
• Predation is an important evolutionary force: natural
selection favors more effective predators and more
evasive prey.
The Predator Prey Relationship
• Its an “Arms Race”
Example: Some snails, which over time become more
heavily armored prey (thicker shells), and their
predators, crabs, which over time develop more
massive claws with greater crushing power.
• Easily captured prey are eliminated, and prey with
effective defenses (that are inherited) rapidly
dominate the population.
The Predator Prey Relationship
•
Although these relationships are never in balance, they tend
to be stable.
•
Stability is always in question…………
•
Three factors promote stability
1. Some prey are likely to persist in local "pockets" where they
escape detection.
2. Prey evolve behaviors, armor, and other defenses that reduce
their vulnerability to predators.
3. Alternative prey may provide a kind of refuge, because once a
prey population becomes rare, predators may learn to
search for a different prey species.
The Balance of Nature
There is a degree of balance in nature; the numbers of
plants and animals, while not stable, tend to remain
within certain limits, becoming neither too great nor
too small.
But predators are not the sole controlling factor.
In most cases, a variety of things influence the
abundance of a species, including predators, food
availability, competition with other species, disease,
and even the weather.
Predator and Prey Population Cycling.
World predator and prey populations can cycle in
size.
Nature’s Pest Control
Consider the insect-eating capabilities of bats. These tiny
mammals may eat up to one half their body weight in insects
each night.
A bat, weighing only half an ounce, could eat over six pounds of
insects in one year.
A colony of one million free-tailed bats may consume over 12
tons of insects every night.
Barn owls are excellent mousers and, as
their name implies, often nest in
farmer's barns.
Since a family of barn owls can consume
about 1300 mice and rats in a year's
time (about two dozen rats a week),
both the owls and the farmer benefit
from this arrangement.
How has predation influenced evolution?
Adaptations to avoid being eaten:
spines (cacti, porcupines)
hard shells (clams, turtles)
toxins (milkweeds, some newts)
bad taste (monarch butterflies)
camouflage
warning colors
mimicry
Camouflage –
blending in
Aposematic colors – warning
Is he crazy???
Mimicry – look like something that is dangerous or tastes bad
Mimicry – looks like something that is dangerous
or tastes bad
Mullerian mimicry
convergence of several unpalatable species
Mimicry – look like something that is dangerous
or tastes bad
Batesian mimicry – palatable species mimics an
unpalatable species
model
mimics
mimic
model
Symbiosis
• Any relationship where two species live closely together.
There are several types:
• Parasitism
• Commensalism
• Mutualism
Parasitism
•
Harms one organism and benefits the other
Can you give examples:
1.
Tape worm
2.
Leeches
3.
Ticks
4.
Fleas
Tapeworm
• Two types that may infect humans
1. beef tapeworm
2. pork tapeworm
An organism must ingest the eggs or
the tapeworm to become infected
As adults in the host's small
intestine, tapeworms
rarely cause problems; in
exceptional cases the
tapeworms might
physically block the
intestinal tract, due to
their large size, or
proglottids (contain eggs)
might become lodged in
the appendix and result in
appendicitis.
Leeches
The bodies of all leeches are divided into the same
number of segments (34), with a powerful clinging
sucker at each end.
Leeches usually have three jaws and make a Y-shaped
incision. The Australian land leech has only two jaws
and makes a V-shaped incision. Australian leeches can
vary in size from about 7 mm long to as much as 200
mm when extended.
Leeches feed
1.
2.
Leeches are grouped according to the different ways they feed. One
group (the jawed leeches) have jaws armed with teeth with which they
bite the host. The blood is prevented from clotting by production of a
non-enzymatic secretion called hirudin.
A second group (the jawless leeches) insert a needle-like protrusion
called a proboscis into the body of the host and secrete an enzyme,
hemetin which dissolves clots once they have formed. Leeches which
live on body fluids of worms and small freshwater snails possess such an
apparatus.
3.
A third group, (the worm leeches) have no jaws or teeth and swallow
the prey whole. Its food consists of small invertebrates.
Ticks
A tick has a one-piece body.
The harpoon-like barbs of its mouth attach to a host for feeding.
Crablike legs and a sticky secretion help hold the tick to the
host.
When attempting to remove a tick, to prevent the mouth part
from coming off and remaining embedded in the skin, grasp
the mouth close to the skin with tweezers and pull gently.
Ticks
Ticks are not insects like fleas, but arachnids like mites, spiders
and scorpions.
While ticks need a blood meal at each stage after hatching, some
species can survive years without feeding.
The United States has about 200 tick species. Habitats
include woods, beach grass, lawns, forests, and even
urban areas.
Ticks
Ticks may carry various infectious organisms that can transmit
diseases to cats and dogs, including the following (listed with
possible symptoms):
• babesiosis--lethargy, appetite loss, weakness, pale gums
• ehrlichiosis--high fever, muscle aches
• Lyme disease--lameness, swollen joints, fever, poor appetite,
fatigue, and vomiting (some infected animals show no
symptoms)
• tick paralysis in dogs--gradual paralysis, seen first as an
unsteady gait from uncoordinated back legs (some infected
dogs don't develop paralysis).
Fleas
Fleas are obligatory blood feeders parasitizing warm-blooded
invertebrates. More than 94% of known species are parasites
of the mammals and only about 5% of them occur on birds.
Commensalism
•
that benefits one species and neither helps nor harms the other.
Can you give examples:
1. Barnacles on a whale
2. Clown fish and sea anemone
3. Cattle egrets and cattle
4. Moss on trees
Mutualism
•
Relationship in which both species benefit
Can you name examples:
1.
Ants and acacia tree
2.
Insects pollinating flowers
3.
Yucca plant and yucca moth
4.
Seed dispersal by birds
6.2 Ecological Succession
Learning Targets:
•Contrast primary and secondary succession
•Describe the sequence of ecological succession in a lake and on an
island.
Ecological Succession
Organisms affect the environments in which they live.
For example, plants help form soil by breaking down
rocks and making organic matter. The changes a
species causes in its environment may not be helpful
to that species. The environment may change so
much that the species’ niche disappears. Old niches
are replaced by new niches to which different species
are adapted. A species can be the cause of its own
destruction.
Ecological Succession
Other forces also change the environment. A forest formed slowly over
hundreds of years can be destroyed in minutes by fire. Change is a fact of
life in all ecosystems, and living things have evolved in response to change.
As an environment changes, the community living in that environment
changes as well. In many cases, different communities follow one another in
a definite pattern.
SUCCESSION IS ABOUT CHANGE…….
Primary Succession
• Is the sequence of communities forming in an originally lifeless
habitat
– Examples include:
• New volcanic island just formed
• Cooling lava field
• Bare rock exposed after a glacier retreats
Primary Succession
• First step – colonization by new organisms and formation of soil from
exposed rock
• Remember!!! soil formation occurs through the processes of mechanical
and chemical weathering
Primary Succession
• First organisms to colonize rocks are lichens.
– Lichens – a fungus and algae living a mutualistic relationship. Lichens
secrete a weak acid that breaks rock into soil.
– A lichen community is a pioneer community since it is the first to
colonize a new area.
Succession Progression
• Once soil begins to form, grasses and small shrubs begin to grow
from seed.
• Root growth and accumulation of dead leaves accelerate the
process of soil formation.
• Eventually plant growth is so dense that lichens can not get
enough light.
• Lichens disappear
• Grass community surviving many generations making the soil
deeper and more fertile.
Succession Progression
• Soil becomes deep enough to support non-woody plants with deeper
roots.
– Grass and shrub communities are not diverse
• Pines and white birch or other trees with shallow roots.
– Trees shade out the grasses and shrubs
– Soil continues to deepen
• Broad leaf and hardwood trees replace pines
Succession Progression
•
Hardwood forest is the final stage and will change little over time.
– Process many take 100s of years
•
A community that does not undergo further succession is called a climax
community.
Secondary Succession
• Succession that occurs where a disturbance eliminates most
organisms but does not destroy the soil.
– Example: fire
How is this an example of secondary succession?
Secondary Succession
• Progression is the same except that you start at grasses and
shrubs
• Many habitats never reach climax stage
– Disturbances reoccur in less time than is require to reach the climax
stage. EX: GRASSLANDS
Aquatic Succession
Start with a newly formed glacial lake.
• Reeds and water plants grow in the thin sediments near the
shore supporting other organisms
• Organic matter collects in the lake
• Water becomes richer in nutrients
• Water plants begin to cover the surface of the lake
• Lake eventually fills in and becomes a marsh
• Land plants colonize the marsh
Aquatic Succession
• Lake becomes a fertile meadow with land plants and
eventually becomes a forest.
Island Succession
• New islands form quickly through volcanic activity
– Seagulls can be found nesting in these islands before the volcanic
activity stops
• Any organism found on an island must have ancestors that
were carried there by, wind, water, or by other organisms
Island Succession
• Islands tend to have large bird populations.
Why?
• Organisms that arrive tend to fill “open” niches.
• Their offspring will fill even more niches because
there is no competition.
Island Succession
• Populations of organisms adapt to their new
niches and several new species form.
– Example: Galapagos Island finches
Surtsey Island, Iceland
Surtsey Island, Iceland
6.3 Stability in the Ecosystem
Learning Targets:
•Explain the concept of ecosystem stability.
•Characterize the effects of disturbances on ecosystems.
Ecosystem Stability
• Stability is a measure of how easily an
ecosystem is affected by a disturbance and
how quickly it returns to its original condition.
Ecosystem Stability
Original Condition includes:
• Biotic factors
• Abiotic factors
• Patterns of energy flow (food web)
• Nutrient cycling (CO2, H20, and N2)
Ecosystem Stability
• May be related to the complexity of the food web that
manages the system’s energy flow and nutrient cycles
• More connections in a food web may decrease the overall
impact if a single species is lost or a part of the system is
disrupted.
• An ecosystem in balance is in equilibrium.
Ecosystem Stability
Try to solve this little problem.
What actually caused the dinosaurs to become extinct? Think into
the question…. Was it really an asteroid hitting the Earth? Did
all the plants die? Did all the reptiles die? Was the ecosystem
changed? If so what was the result of the change? Write a
decent paragraph explaining your answer……………..
Ecosystem Stability
• Once the dinosaurs were gone, mammals began to fill the available niches
once occupied by the dinosaurs.
• Ecosystems may be sensitive to small changes.
• At present species are becoming extinct at a faster rate since the
extinction of the dinosaurs.
• Extinction may be related to
– Population growth
– Habitat destruction
6.4 Land Biomes
Learning Targets
•Explain the concept of the biome, and name the eight major land
biomes.
•Illustrate where each of the eight major land biomes occurs.
Biomes
• Ecosystems of Earth are divided into several
broad categories.
• Biome – a major type of ecosystem with
distinctive temperature, rain fall, and organisms
Two types of Biomes
1.
On land – terrestrial
Type depends on average temperature and
amount of precipitation the area receives.
2. Aquatic – water
Type depends on water depth, nutrients, and
nearness to land.
Biomes
• Are useful when talking about sets of related
habitats………….
Biomes
•
1.
Terrestrial ecosystems can be divided into
either major biomes……..
Two biomes receive little rain fall and
support a small amount of biomass they are:
desert & tundra
Biomes
2. Forest biomes contain 75% of Earth’s biomass.
There are three forest biomes……….
•
•
•
Coniferous forest
Deciduous forest
Rain forest
Biomes
3. Rain forest
• Covers 6% of Earth’s land mass
• Contains 50% of Earth’s biomass
• Is the most diverse biome
Biomes
4. Grassland
• There are three grassland biomes ………..
– Steppe
– Prairie
– Savanna
Grassland Biomes
•
•
•
•
•
Cover 22% of Earth’s land surface
Contain 8% of Earth’s biomass
Receive less rain than forest biomes
May be disturbed by fire
Large herd of herbivores are common
Owl Pellet Grading Criteria