BIO320 Chapter 5

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ENVIRONMENTAL
SCIENCE
A Study of Interrelationships
15th Edition
Interactions: Environments and Organisms
Chapter 5
©2019 McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or
further distribution permitted without the prior written consent of McGraw-Hill Education.

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Outline
5.1 Ecological Concepts
5.2 The Role of Natural Selection and Evolution
5.3 Kinds of Organism Interactions
5.4 Community and Ecosystem Interactions

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5.1 Ecological Concepts
Ecology is the study of ways organisms interact with each
other and with their nonliving surroundings.
Environment means everything that affects an organism
during its lifetime.
• Abiotic factors: Nonliving things that influence an organism, such
as energy, nonliving matter, living space, and ecological processes.
• Biotic factors: All forms of life with which the organism interacts.

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Levels of Organization in Ecology

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Limiting Factors
Limiting factors are any 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.

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Temperature Is a Limiting Factor

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Habitat and Niche (1 of 2)
The habitat of an organism is the space in which an
organism lives; it is defined by the biological requirements
of each particular organism.
• Usually highlighted by prominent physical or biological features.
The niche of an organism is the functional role (profession)
the organism has in its surroundings.
• This term includes all the ways an organism affects the organisms
with which it interacts as well as how it modifies its physical
surroundings.

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Habitat and Niche (2 of 2)
The Ecological Niche of a Beaver The Niche of a Dandelion

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Moss Habitat
The habit of mosses is typically cool, moist, and
shady, since many mosses die if they are
subjected to drying.
Mosses must have a thin layer of water present in
order to reproduce sexually.

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Genes, Populations, and Species
Genes are distinct pieces of DNA that determine the
characteristics an individual displays.
A population includes all organisms of the same kind
found within a specific geographic region.
• A population contains more kinds of genes than any single
individual within the population.
A species is a population of all the organisms potentially
capable of reproducing naturally among themselves and
having offspring that also reproduce.

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5.2 The Role of Natural Selection
and Evolution
Natural selection is the
process that determines which
individuals within a species will
reproduce and pass their genes
to the next generation.
The changes seen in the genes
and characteristics displayed
by successive generations of a
population of organisms over
time is known as evolution.

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Natural Selection (1 of 2)
Several conditions and steps are
involved in the process of natural
selection:
1. Individuals within a species show
genetically determined variation.
2. Organisms within a species typically
produce more offspring than are needed
to replace the parents when they die.
Most of the offspring die.
3. The excess number of individuals
results in a shortage of specific
resources.

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Natural Selection (2 of 2)
4. Due to individual variation, some
individuals have a greater chance
of obtaining needed resources and
therefore have a greater likelihood
of surviving and reproducing than
others.
5. As time passes, the percentage of
individuals showing favorable
variations will increase while the
percentage showing unfavorable
variations will decrease.

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Evolutionary Patterns (1 of 2)
Speciation is the production of new species from
previously existing species.
• It is thought to occur as a result of a species dividing into two
isolated subpopulations.
Extinction is the loss of an entire species.
• Of the estimated 500 million species believed to have ever existed
on Earth, 98-99% have gone extinct.
Coevolution is the concept that two or more species can
reciprocally influence the evolutionary direction of the
other.
• Grazing animals and grass species.

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Evolutionary Patterns (2 of 2)
Speciation Extinction

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Change Resulting from Natural
Selection

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Coevolution
Coevolution is the concept that two or more species of
organisms can reciprocally influence the evolutionary
direction of the other. In other words, organisms affect the
evolution of other organisms.
Since all organisms are influenced by other organisms,
this is a common pattern.

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5.3 Kinds of Organism Interactions
Predation is a kind of
interaction in which one
animal kills/eats another.
• Predator benefits from food.
• Prey adaptation is manifested in
a higher reproduction rate.+

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Competition (1 of 2)
Competition is a kind of
interaction in which two
organisms strive to obtain the
same limited resource.
• Intraspecific competition is
competition between members of
same species.
• Interspecific competition is
competition between members of
different species.

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Competition (2 of 2)
The competitive exclusion principle holds that no two
species can occupy the same ecological niche in the same
place at the same time.
Less-fit species must evolve into a slightly different niche.

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Niche Specialization

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Symbiotic Relationships (1 of 3)
Symbiosis is a 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

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Symbiotic Relationships (2 of 3)
Commensalism is a relationship in which one organism
benefits while the other is not affected.
• Remoras and sharks
Mutualism is a relationship in which both species benefit.
The relationship is obligatory in many cases, as neither can
exist without the other.
• Mycorrhizae

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Symbiotic Relationships (3 of 3)
Parasitism is a relationship in which one organism
(parasite) lives in or on another organism (host), from
which it derives nourishment.
• Ectoparasites live on the host’s surface.
• Fleas, lice, molds, mildews
• Endoparasites live inside the body of the host.
• Tapeworms, malaria parasites, bacteria, fungi

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Parasitism
Source: CDC/James Gathany,
William Nicholson

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Commensalism

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Mutualism
Root nodules containing
nitrogen-fixing bacteria
Oxpeckers removing
parasites

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5.4 Community and Ecosystem
Interactions
A community is an assemblage of all interacting species
of organisms in an area.
An ecosystem is a defined space in which interactions
take place between a community, with all its complex
interrelationships, and the physical environment.

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Major Roles of Organisms in
Ecosystems (1 of 2)
Ecologists have divided organisms’ roles in ecosystems
into three broad categories:
• Producers: Organisms that are able to use sources of energy to
make complex organic molecules from simple inorganic substances
in their environment.
• Consumers are organisms that require organic matter as a source
of food.
• Decomposers are organisms that use nonliving organic matter as
a source of energy and raw materials to build their bodies.

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Major Roles of Organisms in
Ecosystems (2 of 2)
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.

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Keystone Species
A keystone species plays a
critical role in the maintenance of
specific ecosystems.
When bison are present in
American tall grass prairie
ecosystems, they increase the
biodiversity of the site.

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Energy Flow Through Ecosystems
(1 of 2)
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).
Because it is difficult to measure the amount of energy
contained in each trophic level, biomass (weight of living
material) is often used as a proxy.

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Energy Flow Through Ecosystems
(2 of 2)

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Trophic Levels in an Ecosystem

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Food Chains and Food Webs
A food chain is a series of organisms occupying different
trophic levels through which energy passes as a result of
one organism consuming another.
A food web is a series of multiple, overlapping food chains.

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Food Web

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Biogeochemical Cycles—Carbon
Cycle (1 of 2)
1. Plants use carbon dioxide during photosynthesis to
produce sugars. Oxygen is produced as a by-product.
2. Herbivores eat plants, break down the complex organic
molecules into simpler molecular building blocks, and
incorporate those molecules into their structure.
Respiration produces CO2 and water and releases
those compounds back into the atmosphere.

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Biogeochemical Cycles—Carbon
Cycle (2 of 2)
3. The decay process of decomposers involves respiration
and therefore recycles naturally occurring organic
molecules.
4. Carbon sinks are processes or situations that remove
atoms from active, short-term nutrient cycles, such as
sediments, oceans, and bodies of plants.

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Carbon Cycle

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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.

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Nitrogen Cycle (1 of 3)
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.
• Decomposers also break down nitrogen-containing molecules,
releasing ammonia.

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Nitrogen Cycle (2 of 3)
Nitrifying bacteria are able to convert ammonia to nitrite,
which can be converted to nitrate.
Denitrifying bacteria are able (under anaerobic
conditions) to covert nitrite to nitrogen gas (N2) which is
ultimately released into the atmosphere.
The primary sink for nitrogen is the atmosphere.

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Nitrogen Cycle (3 of 3)

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Carbon Sinks and Human Effects

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Human Alteration of 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.”

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Phosphorus Cycle (1 of 2)
Phosphorus is not present in the atmosphere as a gas.
The ultimate source of phosphorus atoms is rock.
Phosphorus compounds are released by erosion and
become dissolved in water.
• Plants use phosphorus to construct necessary molecules.
• Animals gain necessary phosphorus when they consume plants or
other animals.
• Decomposers recycle phosphorus compounds back into the soil.

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Phosphorus Cycle (2 of 2)

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Summary (1 of 2)
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.

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Summary (2 of 2)
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.