Ch. 4 Ecosystems

Biology I

Loulousis

Objectives

• 1.) Define ecology, ecosystem, and succession

• 2.) Identify and distinguish between the levels of organization in ecology

• 3.)Distinguish between primary and secondary succession

KEY CONCEPT

Ecology is the study of the relationships among

organisms and their environment.

Ecologists study everything from single cells to the entire planet

Interactions and Interdependence

Levels of Organization biosphere

biome

ecosystem

community

population

Organism (Species)

INDIVIDUAL ORGANISM Species:

Group of similar organisms that can breed and produce fertile

offspring

Levels of Organization

POPULATION Groups of individuals that belong

to the same species and live in the same area

Levels of Organization

Communities Different populations that live

together in a defined area

Levels of Organization

Ecosystem all the living organisms

(biotic) that live in a particular place, together with nonliving(abiotic) or

physical environment

Levels of Organization

Biome A group of ecosystems that have

the same climate and similar dominant communities

Levels of Organization

The largest “house” is the biosphere.

BIOSPHERE = contains the combined portions of the planet in which all life exists (land, water, air, and atmosphere) • 8 km above earth’s surface; 11 km below surface of the ocean

Levels of Organization

Organism

Organism

Population

Population

Community

Community

Ecosystem

Ecosystem

Biome Biosphere

Terrestrial Biomes

• Two factors that determine biomes: Temperature and precipitation

• Grouped by latitude into

1. Tropical

• Tropical rain forests

• Savannas (tropical grasslands)

• Tropical Deserts

2. Temperate • Temperate

grasslands • Temperate forests • Temperate deserts

3. High latitude • Taiga • Tundra

Aquatic Ecosystems

• Organized into

1. Freshwater ecosystems

2. Wetlands – link between land and fully aquatic habitats

– Moderate flooding

3. Estuaries – Fresh water mixes with salt water from

ocean

4. Marine ecosystems

4.1 What is an Ecosystem?

• We are part of the environment along with all of Earth’s organisms

– Interwoven in a complex web of relationships

• Think of a computer

– If you remove a circuit from a computer, it can change or limit the interactions of the computer’s overall operation

• Similarly, removing one species from our environment can have many consequences

Habitat – where a organism lives or population of species live

Diverse Communities in Ecosystems

• Biodiversity – variety of organisms, their genetic differences, and the communities in which they occur

– # of species living in a ecosystem

• The more biodiversity a community has, the more stable it is

Ecosystem Inhabitants

• Most ecosystems contain a few large animals and some smaller animals

• Ecosystems tend to have more plants than animals

• The most plentiful organism in any ecosystem are usually microscopic bacteria and protists

Ecosystem Boundaries

• Physical boundaries are not always obvious

– Depend on how ecosystem is being studied

– Could be a single rotting log if only interested in the fungi and insects living in log

– Often it is a field, forest, or lake (an isolated area)

• No location is ever truly isolated

Change in Ecosystems over time

• When a volcano forms a new island, a glacier recedes and exposes bare rock, or a fire burns all of the vegetation in an area, a new habitat is created

• Pioneer species – 1st organisms to live in a new habitat

– Typically small, fast-growing plants

– Make the ground more hospitable for other species

Change in Ecosystems

• If a major disruption strikes a community, such as the wipe out of many organisms, the ecosystem reacts in such a way that it is restored to equilibrium

– Return to original state

Succession

• Succession is the regular progression of species replacement

– Primary succession – succession that occurs where life has not existed before

– Secondary succession – succession in areas where there has been previous growth

• Initial conditions and chance play roles in the process of succession

• No two successions are alike

Primary succession-

• New organisms form

• takes place on bare rock

Primary succession-

• New bare rock comes from 2

sources:

–1. volcanic lava flow cools

and forms rock

Primary succession-

• New bare rock comes from 2

sources:

–2. Glaciers retreat and expose

rock

Pioneer organisms-

• the first organisms to live in

new habitat

– Ex: lichens are the first to

colonize lava rocks

Primary succession-

Secondary succession-

• sequence of community changes

that takes place when a

community is disrupted by

natural disaster or human

actions – takes place on

existing soil

Secondary succession-

• Ex:

– A fire levels

portions of a

forest

Secondary succession-

• Ex:

– A farmer

plows his

field

Secondary succession-

Pond Succession

Glacier Bay: Ex. Of Succession

• Receding glacier is good example of succession because land is continually being exposed as the face of the glacier moves back

• Glacier Bay – receded 100 km (62 miles) over the last 200 years

• Seeds and spores of pioneer species carried in by wind – Include lichens, mosses, fireweed, willows, cottonwoods

» At first, grow close to ground – hurt by mineral deficiency

• After 10 years, alder seeds come in and take root – Added nitrogen allows willows and cottonwoods to grow with

vigor

• After 30 years, dense thickets of alder, willow, and cottonwood provide shade

Ecological Succession @ Glacier Bay

At the core of every organism’s

interaction with the

environment is its need for

energy to power life’s processes

4. 2 Energy Flow

Producers

• Sunlight is the main energy source for life on Earth

• Less than 1 percent of all of the sun’s energy reaches Earth

• Autotroph- capture energy from sunlight to produce food

– Plants, some algae, & certain bacteria

– Also called producers

Energy From the Sun

• Best known autotrophs are those that

harness solar energy through photosynthesis

• Water + Carbon dioxide + sunlight Oxygen + Glucose

• Most life depends on photosynthetic organisms – Rate at which organic material is produced by photosynthetic

organisms in an ecosystem = primary productivity

• Determines the amount of energy available in an ecosystem

• On land, plants are main autotrophs

• In freshwater ecosystems, algae are primary producers

• Some wet ecosystems have cyanobacteria (photosynthetic bacteria)

Consumers

• Many organisms cannot harness energy directly from the physical environment

• Only way these organisms can acquire energy is from other organisms

• Heterotrophs: Organisms that rely on other organisms for their energy & food supply

• Also called consumers

Types of Consumers

• Herbivores: Eat only plants

• Carnivores: eat animals

• Omnivores: eat both plants & animals

• Decomposers: break down organic matter

Feeding Relationships

• Energy flows through an ecosystem in one direction… from the sun or inorganic compounds to autotrophs (producers) and then to heterotrophs (consumers)

• The relationships between producers & consumers connect organisms into feeding networks based on who eats whom

Food Chains

• Food chains: a series of steps in which organisms transfer energy by eating and being eaten

• Always starts with a producer

• Arrows show the flow on energy; flows TO the organism that eats another organism

Food Webs

• Feeding relationships are more complex than can be shown in a single food chain

• Food web: links a group of interacting food chains

Tropic Levels

• Trophic level: A step in a food chain or food web shows how energy moves based on organism’s source of energy

Trophic Levels

• 1st trophic level consists of

producers

• 2nd trophic level consists of herbivores

• 3rd trophic level is usually omnivores; can be carnivores

• 4th trophic level would be carnivores

Food Web

Food Web

• In most ecosystems, energy does not follow a simple path

– Animals feed at different trophic levels

Ecological Pyramids

• Ecological pyramids: a diagram that shows the relative amounts of energy or matter contained within each trophic level

Energy Pyramid

• Only 10% of the energy that is stored in one trophic level is passed on to the next level

• Rest of the energy is used by organisms for life processes such as respiration, movement, and reproduction, or loss as heat

• The more levels that exist between

a producer and a top level consumer,

the less energy that remains from

the original amount

Trophic Levels – LOSE 90% at each level

Energy Efficiency

• Adding a trophic level increases the energy demand of consumers by a factor of about 10

Limitations of Trophic Levels

• Usually only 3 trophic levels, too much energy lost at each level to allow for more levels

• Number of individuals may not be accurate indicator of amount of energy

– Some organisms are larger than others and use more energy

• Number of organisms often does not form a pyramid when looking

Biomass Pyramid

• Biomass: total amount of living tissue within a given trophic level

• Usually expressed in terms of grams of organic matter per unit area

• Biomass pyramids represent the

amount of potential food available

for each trophic level in an

ecosystem

Limitations of Trophic Levels

• Most terrestrial ecosystems involve only three or, on rare instances, four trophic levels. Too much energy is lost at each level to allow more levels.

• The number of individuals in a trophic level may not be an accurate indicator of the amount of energy in that level. Some organisms are much bigger than others and therefore use more energy.

• Because of this, the number of organisms often does not form a pyramid when one compares different trophic levels.

Limitations of Trophic Levels

• To better determine the amount of energy present in trophic levels, ecologists measure biomass.

• Biomass is the dry weight of tissue and other organic matter found in a specific ecosystem.

• Each higher level on the pyramid contains only 10 percent of the biomass found in the trophic level below it.

4.3 Cycling http://www.youtube.com/watch?v=hehXEYkDq_Y

• The physical parts of the ecosystem are constantly cycling

• The paths of water, carbon, nitrogen, and phosphorus pass from the nonliving environment to living organisms, and then back to the nonliving environment. – These paths form closed circles, or cycles, called

biogeochemical cycles.

• In each biogeochemical cycle, a pathway forms when a substance enters living organisms such as trees from the atmosphere, water, or soil; stays for a time in the living organism; then returns to the nonliving environment.

The Water Cycle

• In the living portion of the water cycle, much water is taken up by the roots of plants.

• After passing through a plant, the water moves into the atmosphere by evaporating from the leaves, a process called transpiration.

• Transpiration is also a sun-driven process. The sun heats the Earth’s atmosphere, creating wind currents that draw moisture from the tiny openings in the leaves of plants.

Steps of Water Cycle

• Water leaves plants through transpiration and enters atmosphere and becomes water vapor (in clouds)

• Water leaves clouds as precipitations

• Some precipitation can become runoff, meaning the water hits the ground and drains into a local lake, river, or ocean.

• From the lake water can evaporate back into the atmosphere and become water vapor again

• Or it can seep into the soil from the lake through percolation and become groundwater.

• Ground water eventually rejoins a larger body of water from where it will evaporate again.

• The cycle continues on …

The Water Cycle

Terms

• Precipitation: Any form of water, such as rain, snow, sleet, or hail, that falls to the earth's surface

• Transpiration: process of giving off water vapor, especially through openings on leaves

• Evaporation: change of a liquid into a vapor, takes place at the surface of a liquid

• Percolation: water passes through a porous substance, like soil and becomes groundwater

The Carbon Cycle

• In the carbon cycle, carbon atoms may return to the pool of carbon dioxide in the air and water in three ways:

1. Respiration Carbon dioxide is a byproduct of cellular respiration.

2. Combustion Carbon also returns to the atmosphere through combustion, or burning.

3. Erosion As the limestone becomes exposed and erodes, the carbon in it becomes available to other organisms.

Respiration

• Plants use CO2 during photosynthesis to make organic molecules (glucose)

• During this process they give off oxygen as a byproduct

• Then living organism use the oxygen to break down organic molecules to release energy. This process gives off CO2 back to the atmosphere.

The Carbon Cycle

The Phosphorus and Nitrogen Cycle

• Organisms need nitrogen and phosphorus to build proteins and nucleic acids.

• Phosphorus is an essential part of both ATP and DNA.

• Phosphorus is usually present in soil and rock as calcium phosphate, which dissolves in water to form phosphate ions phosphate ions.

Cont.

• The atmosphere is 79 percent nitrogen gas, N2.

• The two nitrogen atoms in a molecule of nitrogen gas are connected by a strong triple covalent bond that is very difficult to break. – However, a few bacteria have enzymes that can break

it, and they bind nitrogen atoms to hydrogen to form ammonia.

• The process of combining nitrogen with hydrogen

to form ammonia is called nitrogen fixation.

Nitrogen Cycle

• The nitrogen cycle is a complex process with four important stages:

1. Assimilation is the absorption and incorporation of nitrogen into plant and animal compounds.

2. Ammonification is the production of ammonia by bacteria during the decay of nitrogen-containing urea.

3. Nitrification is the production of nitrate from ammonia.

4. Denitrification is the conversion of nitrate to nitrogen gas.

Nitrogen Cycle