A common niche lecture 3

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Enger & Smith

Environmental ScienceA Study of Interrelationships

Thirteenth Edition

Chapter 5

Interactions: Environments and Organisms

Interactions: Environments and Organisms

5.1 Ecological Concepts

Environment everything that affects an organism during its lifetime.

• Abiotic factors: Nonliving things that influence an organism

– energy, nonliving matter, living space, and ecological processes

• Biotic factors: All forms of life with which the organism interacts.

5.1 Ecological Concepts

Levels of organization in ecology

Limiting Factors Limiting factors - factors whose shortage or

absence restricts species success.• Scarcity of water or specific nutrients (plants).• Climate, availability of a specific food (animals).

Range of tolerance - indicates a range of conditions in which an organism can survive.

• Some species have a broad range of tolerance, while others have a narrow range of tolerance.

Limiting Factors

5.1 Ecological Concepts

Limiting factors

Habitat—place

The habitat • space in which an organism lives• defined by the biological requirements of each particular

organism

• Usually highlighted by prominent physical or biological features.

Habitat and Niche

Moss habitat: cool, moist, and shady

The niche • functional role (profession) the organism has in its

surroundings• Includes:

– all the ways it affects other organisms – how it modifies its physical surroundings

Niche--role

Habitat and Niche

Ecological niche of a beaver

Populations A population

• all organisms of the same kind found within a specific geographic region.

Species A species

• population of all the organisms

• potentially capable of reproducing naturally among themselves

• and having offspring that also reproduce.

Natural selection • process that determines which individuals within a

species will reproduce and pass their genes to the next generation.

• Mechanism that causes Evolution

Evolution• Changes in genes and characteristics within

successive generations of a population over time

5.2 The Role of Natural Selection and Evolution

Natural Selection Steps in natural selection:

Excess number of individuals

Results in a shortage of specific resources

Some individuals have a greater chance of obtaining needed resources and

have a greater likelihood of surviving and reproducing than others.

Results of Natural Selection

Percentage of individuals showing favorable variations will increase

Percentage showing unfavorable variations will decrease

Individualvariation

Overproductionof offspring

Observations

Natural selection:unequal reproductive success

Conclusion

Figure 13.UN3

Natural Selection in Action• Examples of natural selection include:

– Pesticide-resistant insects– Antibiotic-resistant bacteria– Drug-resistant strains of HIV

– http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

5.3 Kinds of Organism Interactions Predation

• interaction in which one animal kills/eats another.

• Predator benefits from food.

• Prey have higher reproduction rate

– (field mice 10 to 20 offspring/year)

CompetitionCompetition

interaction in which two organisms strive to obtain the same limited resource.

Intraspecific competition- between members of same species.

Interspecific competition-between members of different species.

Symbiotic Relationships

Symbiosis • close, long-lasting, physical relationship between two

different species

• At least one species derives benefit from the interaction.

There are three categories of symbiotic relationships:• Parasitism• Commensalism• Mutualism

Symbiotic Relationships

Symbiotic Relationships

Parasitism • relationship in which one organism (parasite) lives in

or on another organism (host)• which it derives nourishment

Symbiotic Relationships

Commensalism • relationship in which one organism benefits while the

other is not affected. • Remoras and sharks

Symbiotic Relationships Mutualism

• relationship in which both species benefit. • The relationship is obligatory in many cases, as

neither can exist without the other.

• Mycorrhizae

5.4 Ecosystem Interactions

An ecosystem • defined space in which interactions take place

between a community and the physical environment.

• Ecologists have divided organisms’ roles in ecosystems into three broad categories:

– 1. Producers– 2. Consumers– 3. Decomposers

Producers: Organisms that are able to use sources of energy to make

complex organic molecules from simple inorganic substances in their environment.

5.4 Ecosystem Interactions

Major Roles of Organisms in Ecosystems

1. Consumers: Organisms that require organic matter

as a source of food.

They consume organic matter to provide energy, growth and survival.

Major Roles of Organisms in Ecosystems

• Consumers can be further divided into categories based on the things they eat and the way they obtain food.

– Primary consumers, or herbivores, eat plants as a source of food.

– Secondary consumers, or carnivores, are animals that eat other animals.

– Omnivores consume both plants and animals.

Major Roles of Organisms in Ecosystems

Decomposers

use nonliving organic matter as a source of energy and raw materials to build their bodies.

Many small animals, bacteria, and fungi fill this niche.

Keystone Species

A keystone species plays a critical role in the maintenance of specific ecosystems.

Keystone Species: Prairie dogs

Energy Flow Through Ecosystems

Each step in the flow of energy through an ecosystem is known as a trophic level.

As energy moves from one trophic level to the next, most of the useful energy (90%) is lost as heat (second law of thermodynamics).

Energy Flow Through Ecosystems

Categories of organisms within an ecosystem.

biomass (weight of living material) is often used as a proxy.

10%

1%

Discussion

See handout

Food Chains

A food chain series of organisms occupying different trophic levels

through which energy passes as a result of one organism consuming another

Some chains rely on detritus.

Food Web A food web

series of multiple, overlapping

food chains.

• A single predator can have multiple prey species at the same time.

Nutrient Cycles in Ecosystems—Biogeochemical Cycles

Organisms are composed of molecules and atoms that are cycled between living and non-living portions of an ecosystem.

These nutrient cycles are called biogeochemical cycles.

Carbon Cycle

1. Producers: Plants use carbon dioxide during photosynthesis to produce sugars.

Oxygen is produced as a by-product.

2. Consumers: Herbivores eat plantsbreak down the complex organic molecules into simpler molecular building blocks

incorporate those molecules into their structure.

Respiration produces CO2 and water and releases those compounds back into the atmosphere.

Carbon Cycle

3. Decomposers: The decay process of decomposers involves respiration

Release of carbon dioxide and waterDead organisms are recycled

4. Carbon sinks processes or situations that remove atoms

from active, short-term nutrient cyclesEx: long-lived trees, fossil fuels

Carbon Cycle

Carbon cycle

Human Impact on the Carbon Cycle

Burning fossil fuels takes carbon atoms that were removed temporarily from the active, short-term carbon cycle and reintroduces them into the active cycle.

Converting forests (long-term carbon storage) to agricultural land (short-term carbon storage) has increased the amount of carbon dioxide in the atmosphere.

Nitrogen Cycle

The nitrogen cycle involves the cycling of nitrogen atoms between abiotic and biotic ecosystem components.• Producers are unable to use atmospheric N.

– Must get nitrate (–NO3) or ammonia (NH3.)

• Nitrogen-fixing bacteria convert nitrogen gas N2 into ammonia.

– Plants construct organic molecules.– Eaten by animals.

Nitrogen Cycle

Decomposers also break down nitrogen-containing molecules, releasing ammonia.

Primary sink for nitrogen is the atmosphere

Nitrogen Cycle

Nitrogen cycle

Human Impact on the Nitrogen Cycle

If too much nitrogen or phosphorus is applied as fertilizer, or if it is applied at the wrong time, much of the fertilizer is carried into aquatic ecosystems.

• The presence of these nutrients increases the growth rate of bacteria, algae, and aquatic plants.

– Toxic algae can kill fish and poison humans.– An increase in the number of plants and algae results in

lowered oxygen concentrations, creating “dead zones.”

Summary

An organism’s environment can be divided into biotic (living) and abiotic (nonliving) components.

The space an organism occupies is its habitat, and the role it plays is its niche.

Organisms interact with one another in a variety of ways. Symbiotic relationships are those in which two species live in physical contact and at least one species derives benefit from the relationship.

In an ecosystem, energy is trapped by producers and flows from producers through various trophic levels of consumers.

Summary

The sequence of organisms through which energy flows is called a food chain.

Multiple interconnecting food chains constitute a food web.

The flow of atoms through an ecosystem involves all the organisms in a community. The carbon, nitrogen, and phosphorus cycles are examples of how these materials are cycled in ecosystems.