Chapter 15: Ecosystems and Communities

Organisms and their environmentsby Mark Manteuffel, St. Louis Community College

Learning Objectives

• Be able to explain the following:

What are ecosystems?

How do energy and chemicals move

through ecosystems?

Learning Objectives

• Be able to explain the following:

How do species interactions influence the structure of communities?

How do communities remain stable or change over time?

15.1–15.2 Ecosystemshave living and nonlivingcomponents.

15.1 What are ecosystems?

A community of biological organisms plus the non-living components with which the organisms interact.

Take-home message 15.1

An ecosystem is a community of biological organisms plus the non-living components in the environment with which the organisms interact.

Ecosystems are found not just in obvious places such as ponds, deserts, and tropical rainforests but also in some unexpected places, like the digestive tracts of organisms or the shell of a beetle.

Take-home message 15.1

15.2 A variety of biomes occur around the world, eachdetermined by temperature and rainfall.

Biomes

What is the average temperature? What is the average rainfall (or other

precipitation)? Is the temperature relatively

constant or does it vary seasonally? Is the rainfall relatively constant or

does it vary seasonally?

Biomes

Temperature and precipitation dictate:• Primary productivity levels

the amount of organic matter produced

The numbers and types of primary producers:• are the chief determinants of the amount

and breadth of other life in the region.

Take-home message 15.2

Biomes are the major ecological communities of earth, characterized mostly by the vegetation present.

Different biomes result from differences in temperature and precipitation, and the extent to which they vary from season to season.

15.6–15.8 Energy and chemicals flow within ecosystems.

15.6 Energy flows from producers to consumers.

First Stop: Primary Producers

Second Stop: Primary Consumers—the Herbivores

Third Stop: Secondary Consumers—the Carnivores

Fourth Stop: Tertiary Consumers—the “Top”

Carnivores

Chains or Webs?

Food chain• Pathway from photosynthetic producers

through the various levels of animals

Food web• Involve harvesting energy from multiple

stops in the food chain

Food ChainE

nergy Flow

Food Web

Energy Flows

Losses at every “step” in a food chain

Inefficiency of energy transfers

Take-home message 15.6

Energy from the sun passes through an ecosystem in several steps known as trophic levels.

First, primary producers convert light energy to chemical energy in photosynthesis.

Take-home message 15.6

Herbivores then consume the primary producers, the herbivores are consumed by carnivores, and the carnivores, in turn, may be consumed by top carnivores.

Take-home message 15.6

Detritivores and decomposers extract energy from organic waste and the remains of organisms that have died.

At each step in a food chain, some usable energy is lost as heat.

15.7 Energy pyramids reveal the inefficiency of food chains.

10% efficiency

Biomass

10% rule

Where does the rest go?

Expended in cellular respiration or lost as feces

In humans, why is vegetarianism more energetically efficient than meat-eating?

The 10% rule in application

Why are big, fierce animal species so rare in the world?

Take-home message 15.7

Energy pyramids reveal that the biomass of primary producers in an ecosystem tends to be far greater than the biomass of herbivores.

Take-home message 15.7

Similarly, the biomass transferred at each successive step along the food chain tends to be only about 10% of the biomass of the organisms consumed.

As a consequence of this inefficiency, food chains rarely exceed four levels.

15.8 Essential chemicals cycle through ecosystems.

The recycling of molecules

Chemical Reservoirs Each chemical is stored in a non-living

part of the environment.

Organisms acquire the chemical from the reservoir.

The chemical cycles through the food chain.

Eventually, the chemical is returned to the reservoir.

The Three Most Important Chemical Cycles

1. Carbon2. Nitrogen3. Phosphorus

Why are global CO2 levels rising?

Fossil fuels

Global CO2 levels are rising in general, but they also exhibit a sharp rise and fall within each year.

Why?

Nitrogen is like a bottleneck limiting plant growth.

Fertilizers

Take-home message 15.8

Chemicals essential to life—including carbon, nitrogen, and phosphorus—cycle through ecosystems.

Take-home message 15.8

They are usually captured from the atmosphere, soil, or water by growing organisms; passed from one trophic level to the next as organisms eat other organisms; and returned to the environment through respiration, decomposition, and erosion.

Take-home message 15.8

These cycles can be disrupted as human activities significantly increase the amounts of the chemicals utilized or released to the environment.

15.10. Each species’ role in a community is defined by its niche.

More than just a place for living, a niche is a complete way of living.

No two species occupy the same niche.

Take-home message 15.10

A population of organisms in a community fills a unique niche, defined by the manner in which they utilize the resources in their environment.

Take-home message 15.10

Organisms do not always completely fill their niche; competition with species that have overlapping niches can reduce their range.

15.11 Competition can be hard to see, but it still influences community structure.

Take-home message 15.11

Populations with completely overlapping niches cannot coexist forever.

Competition for resources occurs until one or both species evolve in ways that reduce the competition, through character displacement, or until one becomes extinct in that location.

15.15–15.16 Communities can change or remain stable over time.

15.15. Many communities change over time.

Secondary Succession

Much faster than primary succession• life and soil are already present

Take-home message 15.15

Succession is the change in the species composition of a community over time, following a disturbance.

In primary succession, the process begins in an area with no life and no soil.

Take-home message 15.15

In secondary succession, the process occurs in an area where life is already present.

In both types, the process usually takes place in a predictable sequence.

THREATS TO BIODIVERSITY & THE ENVIRONEMNT

BIODIVERSITY

• Biodiversity is the variety of different types of life found on earth. It is a measure of the variety of organisms present in different ecosystems.

~ UNITED NATIONS ENVIRONMENT PROGRAM

Invasive Species

• A non-native species that is imported or introduced to a native habitat.

• Problems:– No natural predators– Outcompete native species for

resources• Examples:

– Zebra mussels (animal)– Purple Loosestrife (plant)

Examples

Habitat Destruction• Through land development, habitats

can be completely destroyed or fragmented.

Both lead to a decrease of habitats for native species.

Habitat Fragmentation

PollutionTwo types of pollution:1.Point source: a specific point of polluting air or water (ex: pipe draining into a river from a factory)

2.Non-point source: no specific point is located but many widespread points (ex: car exhaust)

Point source

Non-point Source

Bio magnificationBio magnification

the accumulation of toxins through the trophic levels of a food chain.

Ecological “HOT SPOT”

Areas in the world with large amounts of biodiversity but the

habitats and species are endanger of extinction due to

human impact.

NO MORE NOTES EVER!!!