Environmental ScienceChapter 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.

ExamplesA 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

competitors

predator Pisaster

Barnacles MusselsBalanus Mytilus

Barnacles MusselsBalanus Mytilus

StarfishPisaster

SO………………..Remove the Starfish and……..

time

starfishremoved

%of

inter-tidalzone

mussels

barnacles

- mussels are the dominant competitor- competitive exclusion of barnacles- starfish allow coexistence of competitors

Starfish are picky – they prefer the dominant competitor,which allows the weaker competitor to coexist.

How do starfish promote coexistence?

StarfishPisaster

Barnacles Mussels

ExamplesWhen 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 mantisWhich is the predator?

Click oneDragon flyDragon fly

Praying mantisPraying 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 stability1. 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)

camouflagewarning colorsmimicry

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 dangerousor tastes bad

Mullerian mimicry convergence of several unpalatable species

Mimicry – look like something that is dangerousor tastes bad

Batesian mimicry – palatable species mimics an unpalatable species

model

mimic

model

mimics

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 worm2. Leeches3. Ticks4. Fleas

Tapeworm• Two types that may infect

humans1. beef tapeworm 2. pork tapewormAn 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. 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.

2. 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.

TicksA 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.

TicksTicks 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).

FleasFleas 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 whale2. Clown fish and sea anemone3. Cattle egrets and cattle4. Moss on trees

Mutualism

• Relationship in which both species benefitCan you name examples:1. Ants and acacia tree2. Insects pollinating flowers3. Yucca plant and yucca moth4. Seed dispersal by birds

6.2 Ecological SuccessionLearning Targets:

•Contrast primary and secondary succession•Describe the sequence of ecological succession in a lake and on an island.

Ecological SuccessionOrganisms 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: fireHow 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 BiomesLearning 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 – terrestrialType depends on average temperature and amount of precipitation the area receives.

2. Aquatic – waterType depends on water depth, nutrients, and nearness to land.

Biomes

• Are useful when talking about sets of related habitats………….

Biomes

• Terrestrial ecosystems can be divided into either major biomes……..

1. 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

3. Rain forest

• Covers 6% of Earth’s land mass• Contains 50% of Earth’s biomass• Is the most diverse biome

Biomes

Biomes

• There are three grassland biomes ………..– Steppe– Prairie– Savanna

4. Grassland

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