CH. 47 – ECOSYSTEMS

By: Vanessa EchevarriaPr: 2

AP Biology

OBJECTIVES Understand the trophic levels in an ecosystem. Learn the highly interacted relationships of a food web. Know the way energy flows through an ecosystem through the

study of biomass and energy pyramid. Realize the way that toxic substances become highly concentrated

in the top carnivores of a food web. Be able to explain how elements are cycled through living

organisms and the environment. Explain how water goes through the cyclical process of travelling

between bodies of water, land, and the atmosphere. Understand how carbon is cycled between the ocean and the

atmosphere. Be able to explain how greenhouse gasses have an adverse effect

by helping to create global warming. Know how nitrogen changes form and travels between the

atmosphere and the land. Explain the phosphorus cycle and how it passes between the ocean

and the land.

THE NATURE OF ECOSYSTEMS

An ecosystem –

is defined as an array of organisms and a physical

environment, all interacting through a one-way flow

of energy and a cycling of nutrients.

Ecosystems are referred to as open systems because they are environments that require ongoing inputs of energy and nutrients.

All ecosystems run on energy captured by primary producers.

- Autotrophs- Obtain energy from a non-living source

(sunlight)- Build organic compounds from CO₂ and H₂O.

Consumers:- Heterotrophs - Get energy and carbon from

feeding on tissues, wastes, and remains of producers and one another.

Ex: - Herbivores: Feed on plants.

- Carnivores: Feed on the

flesh of other animals- Parasites: Live inside or on

a living host and feed on their tissue

- Omnivores: Feed on both flesh from animals and plants

- Detritivores: Feed on small particles. (i.e, earthworms and crabs)

TROPHIC LEVELS AND FOOD CHAINS

The Trophic Structure of Ecosystems…- When one organism eats another, energy is transferred from the eaten to the eater.

A food chain is a sequence of steps by which some energy captured by primary producers is transferred to organisms at successively higher trophic levels.

THE NATURE OF FOOD WEBS

A food web diagram illustrates trophic interactions among species in one particular ecosystem.

Two types of food chains:

- Grazing Food Chains: Energy stored in producer tissue flows to herbivores, which tend to be relatively large animals.

- (Grazers like voles, lemmings, and hares graze on plant parts.)

- Detrital Food Chains: Energy in producers flows to detrivores, which tend to be smaller animals, and to decomposers.

- (Bits of dead plant material sustain nematodes and soil-dwelling insects, and decomposers such as soil bacteria and fungi.)

TRANSFER EFFECTS IN FOOD CHAINS

Note: - Energy captured by producers usually passes through no more than four or five trophic levels.

However large the number of species in an ecosystem, the number of energy transfers is always limited and the loss of energy limits the length of a food chain.

Ex:- Chains tend to be shortest when in habitats with

varied conditions.- Chains tend to be longer when in habitats that are

stable. - A large variety of herbivores makes for a more

complex web.- The more carnivores, the fewer connections in a web.

ENERGY FLOW THROUGH ECOSYSTEMS

Primary Production:- The rate at which producers (photosynthetic

organisms) capture and store energy.

- Gross Primary Production: The amount of energy captured by all producers in the ecosystem.

- Net Primary Production: Portion of energy that producers invest in growth and reproduction.

- Temperature and availability of water and nutrients are factors that affect producer growth and vary among habitats.

BIOMASS AND ENERGY PYRAMIDS

A biomass pyramid:- illustrates the dry weight of all organisms at each

trophic level in an ecosystem.

- Most commonly, primary producers make up most of the biomass while top carnivores make up very little.

An energy pyramid:

- illustrates how the amount of usable energy diminishes as it is transferred through an ecosystem.

-Sunlight energy is captured at the base (primary producers) and declines with successive levels to its tip (top carnivores).

WHEN HARMFUL SUBSTANCES BECOME MORE AND MORE CONCENTRATED…

BIOLOGICAL MAGNIFICATION There are instances where harmful substances become concentrated as they

pass from one trophic level to the next.

DDT and Silent Spring:

- DDT, or dichlorodiphenyl-trichloroethane is a synthetic pesticide invented in the late 1800’s

- Used to kill lice that spread typhus and malaria carrying mosquitoes.

- In the 50’s, many farmers used DDT as a pesticide

- DDT affected non-pest species in the process, like birds, and eventually travelled into streams killing a variety of fish.

- Rachel Carson: Pioneer in fight against the pesticide industry. Published a book in 1962 on her findings on pesticide use called Silent Spring.

- After her death in the early 1960’s, study of DDT impact increased.

- Researchers concluded that like other synthetic chemicals DDT undergoes biological magnification: a process by which a chemical degrades slowly or not at all and becomes increasingly concentrated in tissues of organisms as it moves up in the food chain.

- DDT caused population sizes of certain species of birds to plummet causing eggs to become more fragile and break.

- DDT could have a major effect on women who are pregnant or planning to become pregnant, as it causes premature births and can affect a child’s mental development.

Mercury pollution

- is also a dangerous substance that has spread through populations of fish as a result of run-off and air-pollution that dissolves into rain. Some species of aquatic life are more at risk than others . Mercury can affect the development of the human nervous system.

BIOGEOCHEMICAL CYCLES… SAY THAT FIVE TIMES FAST…

- Biogeochemical cycles describe the continual flow of nutrients between non-living environmental reservoirs and living organisms.

- Environmental reservoirs include Earth’s rocks and sediments, waters, and atmosphere.

- Chemical and geological processes move elements, like O, H, C, N, and P to and from these reservoirs.

- Elements make their way into the living part of an ecosystem by way of primary producers (i.e, land plants take up CO₂ from the air)

- These nutrients move through food webs when organisms eat one another.

- Prokaryotes help speed up the process by decomposing wastes and remains of other organisms so that elements in those materials are available to primary producers.

There are four main types of biogeochemical cycles…

Water, Phosphorous, Nitrogen, and Carbon.

THE WATER CYCLE - In the water cycle, water moves on a global level. It moves from

the ocean (its main reservoir), to the atmosphere, to the land, and back to the ocean.

- A watershed – is an area where all precipitation drains into a specific waterway.

- Some precipitation collects in aquifers – permeable rock layers that hold water.

- Groundwater – is the water in soil and aquifers. - Run off – when soil becomes saturated and flows back into

streams. - Of the fresh water that human populations use, about 2/3

sustains agriculture. - Salinization – is the buildup of mineral salts in soil that can

stunt crop growth. - Aquifers that supply much of the world’s drinking water are being

polluted. - Desalinization is a possible solution but the process takes up an

excess amount of fossil fuels.

THE CARBON CYCLE

In the carbon-oxygen cycle, carbon moves into and out of ecosystems mainly combined with oxygen, as in carbon dioxide, bicarbonate, and carbonate.

Earth’s crust is the largest carbon reservoir, followed by the ocean. Most of the annual cycling of carbon occurs between the ocean and the atmosphere.

Contributors…- Single celled protists like foraminiferans

produce shells rich in calcium carbonate. - Ocean currents move carbon from upper

ocean waters into deep sea reservoirs.

GREENHOUSE GASSES AND CLIMATE CHANGE Concentrations of gaseous molecules profoundly influence the

average temperature of the atmosphere near the earth’s surface and the temperature has effects on global and regional climates.

Radiant energy from the sun passes through the atmosphere and its energy warms the earth’s surface. The energy emitted – infrared energy – radiates back to the atmosphere and some gets absorbed by the greenhouse gasses. This continues to warm the earth’s surface.

If the amount of greenhouse gasses increase, the long-term increase in the surface temperature may lead to consequences.

In the past thirty years, the global surface temperature has increased at a faster rate.

NITROGEN CYCLE The nitrogen cycle starts with nitrogen fixation. ..- Bacteria converts gaseous nitrogen in the air to

ammonia and then to ammonium. (plants easily take this up)

In ammonification…- bacteria and fungi make additional ammonium

available to plants when they break down nitrogen-rich organic wastes.

In nitrification…- bacteria converts nitrites in soil to nitrate. (plants

also easily take this up) The ecosystem loses nitrogen when denitrifying

bacteria convert nitrate and nitrate back to gaseous nitrogen, and when nitrogen is leached from soil.

PHOSPHOROUS CYCLE

The phosphorus cycle is a sedimentary cycle that moves phosphorus from its main reservoir (Earth’s crust), through soils and sediments, aquatic habitats, and bodies of living organisms.

Primary producers require dissolved phosphate for growth and this process can help restore the land’s fertility.

Fine, phosphorous rock is sometimes spread and used for fertilizer.

This poses somewhat of a threat because in some countries, phosphorous in runoff from some heavily fertilized fields can pollute the water supply.

THE END!!!!