Chapter 6

Ecosystem Balance

Ecosystem Balance 6.1 Relationships in the Ecosystem 6.2 Ecological Succession 6.3 Stability in the Ecosystem 6.4 Land Biomes

6.1 Relationships in the Ecosystem Objectives

1. Explain the relationship between the population sizes of predator and prey.

2. Define symbiosis and describe several symbiotic relationships.

Relationships in the Ecosystem A complex web of relationships exist

among all the species in an ecosystem. Scientists study these relationships by:

Studying how two populations interact with one another.

Expanding the knowledge they have gained to other parts of the ecosystem.

Predator and Prey One of the relationships ecologists study is

that of predator and prey. Define Predator. Define Prey Examples

Predator and Prey

Predator and Prey The sizes of predator and prey populations

are closely linked. Figure 6.1 p. 89 Prey experience populations cycles. A predator’s populations cycle mimics that

of its prey.

Parasitism Some animals do not kill the prey they feed

on. Parasitism-an organism that feeds on the

tissue or body fluids of another organism Host-the organism the parasite feeds off of Examples

Parasites-Tapeworms and Roundworms

Symbiosis Symbiosis-a relationship in which two species

live closely together Three types:

Parasitism-one is helped and the other is harmed (typically)

Commensalism- one organism benefits and the other is neither helped or harmed Examples

Mutualism-both organism benefit Examples

Commensalism

Mutualism

Questions What is the relationship between the

population sizes of predator and prey. Define Symbiosis What are some examples of symbiotic

relationships?

6.2 Ecological Succession

Objectives1. Contrast primary and secondary

succession.

2. Describe the sequence of ecological succession in a lake and on an island.

Ecological Succession Organisms affect their environment Example: Plants Soil Changes are not always beneficial Old niches are replaced by new niches. Other forces can cause change in the

environment. Example: Forest Fire

Ecological Succession As environment change the communities

living in that environment change as well. In many cases different communities

follow one another in a definite pattern, this is called succession.

Volcano Eruption A volcano erupts

leaving the land covered in bare black rock…it is lifeless.

Does it stay this way?

Volcano Eruption (cont) No Almost immediately

organisms begin to inhabit the area.

Primary Succession Define Primary

Succesion Examples: Cooled

lava fields and exposed rock from retreating glaciers.

                                                                                                                    

                            

Primary Succession Primary succession is an orderly process. Follows the same general pattern in most

ecosystems.

Step 1 Colonization by new

organisms and formation of soil from exposed rock.

On land this is done by lichens.

Define lichens. Lichens can live on

bare rock.

                                                                                                                     

                           

Step 1 (cont) Lichens secret acids that break down the

rock and form organic material by photosynthesis.

Weathering also breaks down rocks. Soil is formed by the actions of the lichens

and weathering.

Pioneer Community Lichen Community First community to colonize the

area.

Step 2 Once soil is formed, grasses and other

small plants begin to grow. Root growth and accumulation of dead

leaves Soil formation Plants grow dense lichen disappear

Grass Community Survives for many generations and makes the soil

deeper and more fertile. Soil is deep enough Growth of nonwoody

plants with deep roots (Heath Mat). These plants are taller and shade out the grasses. Since the grass/shrub community is not diverse a

small disturbance may cause drastic change.

Pines and other tress Pines or other trees

with shallow roots are next.

Trees shade out the heath mat.

                

      

Broadleaf and Hardwood Trees As the soil deepens

even further broadleaf and hardwood trees take over.

Hardwood forest in the final stage of succession in many areas.

               

       

Climax Community A community that does not undergo further

succession. Climax communities are usually highly

diverse and can often survive even severe local disturbances.

Primary Succession

Primary Succession Only occurs on freshly exposed rock or in

places where a severe disturbance has occurred.

However most disturbances are not this drastic.

Secondary Succession A fire may kill many plants but leave the

soil in place. Living things can quickly colonize these

types of areas. Define Secondary Succession. Examples: Storms, Fires and human

activity

Deforestation

Secondary Succession Secondary succession resembles the later

stages of primary succession. 1st to colonize are: Next to colonize: Final to colonize:

Secondary Succession Research has shown that many habitats

never develop climax communities. Why? Example

Secondary Succession

Aquatic Succession Newly formed mountain lake.

Low nutrient levels Supports few organisms.

1. Reeds and other aquatic plants.2. Organic matter builds up and lake fills with sediment.3. Nutrient rich water4. Increase in wildlife5. Water plants cover the surface.6. Lake fills with sediment Marsh7. Land plants begin to colonize8. Finally Fertile Meadow (possibly a forest)

Island Succession Similar to succession on the continents. Any organisms found on an island must

have ancestors that were: Carried by water Carried by wind Carried by other organisms

Many islands have large bird populations.

Island Succession There are many unfilled niches on islands. Organisms can evolve to fit many niches. When a population of organisms adapted to

their new niches new species are formed. Example: Figure 6.9 p. 95

Review1. How does primary and secondary

succession differ from each other?

2. What is a climax community?

3. What is a pioneer community?

4. Describe the sequence of ecological succession in a lake and on an island.

6.3 Stability in the Ecosystem

Objectives1. Explain the concept of ecosystem

stability.

2. Characterize the effects of disturbances on the ecosystem

Stability is a measure… …of how easily an ecosystem is affected

by a disturbance. …how quickly it returns to its original

condition after a disturbance. Conditions include: biotic and abiotic factors,

patterns of energy flow and nutrient cycling.

More stable ecosystem Will return steady pattern of energy flow Experience fewer food web changes. Fewer evolutionary changes Fewer changes in the abiotic environment.

Stability in the Ecosystem Determined by the complexity of food web

Manages the system’s energy flow and nutrient cycles.

More connections=stability Impact of disturbance is less.

Equilibrium State of balance Changes counteract other changes.

Weather cooling is counteracted by the evolutionary adaptation to cold weather.

Disturbed ecosystem returns to a state of equilibrium (balance).

Ecosystem Function Scientist do not understand every detail of

how even simple ecosystems function. They do understand that a change in one

part of triggers a change in another. Scientists are trying to apply the chaos

theory.

Chaos Theory A type of mathematics Suggests that ecosystem may be sensitive

to even small changes The beginning state of an ecosystem is

crucial to its later development.

Species Extinction Species are becoming extinct at an

alarming rate. Fastest since the extinction of dinosaurs. Possible causes:

Human Growth Habitat destruction Introduction of foreign species Pollution of fresh water

Thought It is difficult for scientists to predict the

long-term effects of humans on the biosphere.

And for them to predict the ability of the biosphere to support human population.

Review1. What makes an ecosystem stable?

2. What happens to a stable ecosystem when a disturbance occurs?

3. What happens to a ecosystem that is unstable when a disturbance occurs?

6.4 Land Biomes

Objectives1. Explain the concept of the biome, and

name the eight major land biomes.

2. Name an area in which each type is located.

Biomes Earth is very large and diverse Environments range from the ice of

Antarctica to the heat and rain of the Amazon.

Difference in temperature and rainfall create a vast array of conditions.

Life has adapted to almost all of these conditions.

Biomes Definition-major type of ecosystem with

distinctive temperature, rainfall and organisms.

Either terrestrial or aquatic.

Biomes Biome is the largest general category used to

classify ecosystems Conditions may vary from place to place Smaller ecosystems within a biome may have

different habitats with different conditions and organisms.

Every habitat on Earth is different. Term Biome is useful when discussion related

habitats.

Aquatic Biomes Determined by:

Water depth Nutrients Nearness to land

Terrestrial Biomes Determined by:

Average temperature Amount of precipitation 8 major types of land biomes

1.Desert2.Tundra3.Coniferous forest4.Deciduous forest5.Rain forest6.Steppe7.Prairie 8.Savanna

Desert Low humidity High summer temperatures Low annual rainfall Supports only a small amount of biomass Deserts cover 25% of Earth’s land surface Deserts contain only 1% of Earth’s biomass Plant life is scarce in a desert due to lack of water

Desert in Australia

Tundra Cold Windy Dry South of polar ice caps in Alaska, Canada,

Greenland, Iceland, Norway and Asia Very little plant life due to lack of water

Tundra

Forest Biomes Contains 75% of Earth’s Biomass Three types:

Coniferous forest- containing conifers. Deciduous forest – containing deciduous

trees. Rain forest –dense canopy of evergreen,

broadleaf trees that receives at least 200 cm of rain each year.

Deciduous Forest

Coniferous Forest - Yosimite

Amazon Rain Forest

Rain forest Covers only 6% of Earth’s land surface. Contains more than 50% of all Earth’s

biomass. Most diverse biome. Destruction of the rain forest is a HUGE

environmental problem

Grasslands Cover 22% of Earth’s land surface Contain 8% of Earth’s biomass. Grasslands receive less precipitation than do forests

and may have long dry seasons. May experience frequent fires Home to large herds of migrating herbivores Three types:

Steppe Prairie Savanna

Steppe Grassland Biome Receives less than 50cm of rain per year Characterized by short bunchgrasses.

Steppe

Prairie Grassland Biome Characterized by:

Rolling hills Plains Sod-forming grasses

Prairie

Savanna Grassland Biome Tropical Ranging from dry scrubland to wet, open

woodland

Savanna - Africa

Review What is a biome? What are the 8 major types of land biomes? What type of land biome covers the largest

land area? What type of land biome contains the most

biomass?