understanding the food chain and natural...

Understanding the Food Chain andNatural Selection

EVERY MORNING in Africa, a lion wakes up and

knows that it must run faster than the slowest

gazelle or it will starve. Every morning in Africa, a

gazelle wakes up and knows it must run faster than

the fastest lion or it will be eaten. This African proverb

illustrates the food chain and natural selection.

Objective:

� Describe food energy reliance and adapta-

tions for survival.

Key Terms:

�

Food and Survival

The food chain and natural selection are important forces in biology. The food chain can

be described as the relationships between organisms in which energy is transferred from one to

another. For example, plants harness energy from the sun. Rabbits consume plants and are

then eaten by predators (e.g., fox). Energy flows from the producer to the consumer. Natural

E-unit: Understanding the Food Chain and Natural Selection

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anatomy

asexual reproduction

biotic pyramid

circulatory system

class

cover

digestive system

excretory system

family

food chain

genus

integumentary system

invertebrates

kingdom

muscular system

natural selection

nervous system

nutrients

order

phylum

physiology

respiratory system

scientific name

sexual reproduction

skeletal system

space

species

vertebrates

selection is the process in

which inheritable traits that favor

species survival are passed on to

succeeding generations; unfavor-

able traits are less likely to be

passed on. The plants, animals,

and people that are better adapted

to the environment are more

likely to pass on their genetic

material.

SCIENTIFIC

CLASSIFICATION AND

NAMING

Scientific classification is based on carefully obtained information about organisms. A sys-

tem of taxonomy is used consistently worldwide. Modern classification uses seven divisions or

stages: kingdom, phylum, class, order, family, genus, and species.

The kingdom is the first and broadest classification. All living things belong to one of five

kingdoms: animalia, plantae, fungi, monera, and protista.

The phylum is the second division in classification. The three most important phyla in

studying wildlife are chordate phylum, arthropoda phylum, and mollusca phylum.

The class is the third division in classification. Some important classes in the chordate

phylum of animals are mammalian, reptilian, and aves.


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FIGURE 1. The grizzly bear is at the top of the North American food chain.

(Courtesy, U.S. Fish and Wildlife Service)

EXPLORING OUR WORLD…

SCIENCE CONNECTION: Natural Selection

The term “natural selection” was introduced by Charles Darwin in his 1859 book The Origin of

Species. In the book, he described natural selection as the process by which species adapt to

their environment. In the process, favorable heritable traits become more common in successive

generations of a population of reproducing organisms. At the same time, unfavorable heritable

traits become less common.

Natural selection leads to evolutionary change. Some individuals have certain characteristics

that give them a greater survival or reproductive rate than other individuals in a population.

These characteristics are passed to their offspring.

Natural selection influences an organism’s physical characteristics or phenotype, which is

determined by its genetic composition and the environment in which the organism lives. Over

time, natural selection of certain characteristics may result in specialized adaptations that allow

organisms to occupy ecological niches. It can also result in the emergence of new species.

The order consists of organisms that are more alike than the class. Orders are based on

feeding characteristics.

The family is composed of organisms that are more alike than the orders and are often

based on anatomical features.

The genus is made of similar groups that do not naturally breed with each other.

The species contains very similar creations within the same genus. They are capable of

breeding with each other and are sometimes divided into subspecies.

Scientific Names

Every identified organism has a scientific name. Scientists use these names worldwide

based on information about a species. The scientific name of an organism is a combination of

the genus and species. The genus is the first capitalized word followed by the species name.

The scientific name is always written in italics or underlined. Scientific names are not changed

unless information results in a new name for the species.

LIFE-SUSTAINING PROCESSES

All organisms have body systems that carry out life processes. Anatomy (the study of the

form, shape, and appearance of organisms) and physiology (the study of the functions of

parts of the anatomy) influence how organisms live and experience life processes. The differ-

ences are obvious to our eyes and make it possible for each species to sustain itself in its envi-

ronment.

Organ Systems

The way in which functions are carried out is

influenced by the form of the organ systems. Ani-

mal organ systems include skeletal, digestive, respi-

ratory, muscular, circulatory, excretory, nervous,

and integumentary.

The skeletal system is the body framework

that gives the body shape and protects the organs.

Wildlife animals have skeletal systems made of

bone, cartilage, or chitin. Animals with backbones

are vertebrates, and animals without a backbone

or an internal skeleton are invertebrates.

The digestive system prepares food for use

by the body. The major parts of the digestive system

are the mouth, esophagus, stomach, intestines, and

anus.

The respiratory system is responsible for taking in oxygen and giving off carbon diox-

ide. Many animals have lungs to breathe, but fish have gills to filter oxygen from the water.

The muscular system creates bodily movement and support with special tissues called

muscles that are attached to the skeletal system by ligaments.


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FIGURE 2. Bears are categorized as vertebrates.

The circulatory system is a network of vessels that move blood throughout the body.

The major organ in the circulatory system is the heart.

The excretory system rids the body of wastes (e.g., carbon dioxide, water, nitrogen, and

undigested solid food materials).

The nervous system conducts impulses back and forth from the brain to the muscles.

Vertebrates have a spinal column that contains a spinal cord.

The integumentary system is the skin, which protects the internal organs and gives

shape to the body. It helps regulate temperature. Hair, fur, and scales are part of the

integumentary system.

WILDLIFE REPRODUCTIVE PROCESS

Reproduction is the process by which a species produces new organisms to perpetuate the

species. The process of reproduction is accomplished sexually or asexually.

Sexual Reproduction

Sexual reproduction involves the union of the sperm (the male sex cells produced in the

testes) with the eggs (the female sex cells produced in the ovaries). Mating involves a male and

a female joining together for the male to release sperm on or near the egg(s) of a female. Fertil-

ization may occur internally or externally.

Asexual Reproduction

Asexual reproduction is producing new organisms without the sexual union of male and

female cells. Asexual reproduction is common in plants, not in animals. Cloning is an approach

to producing identical offspring.

MAJOR NUTRIENT

NEEDS

Animals need food to grow

into healthy organisms and to live

a long life. Nutritious food pro-

vides nutrients—chemical sub-

stances in food that support life.

Types of Nutrients

Nutrient types are essential,

energy, protein, minerals, and

vitamins. Essential nutrients are

needed to properly provide for an


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FIGURE 3. This egret obtains nutrients by eating fish. (Courtesy, U.S. Fish

and Wildlife Service)

organism, depending on the life stage. Energy nutrients are needed for an animal to be active

and carry out life processes (e.g., starches, sugars, and plant oils). Protein is needed for growth,

maintenance, and reproduction; it is used to build strong, new tissue and to repair old tissue.

In addition, minerals are needed for growth, reproduction, bones, shells, hooves, teeth, and

horns. Vitamins are present in many foods and are needed to regulate body functions. The

health of an animal depends largely on adequate vitamins (e.g., vitamins A, D, E, K, and B

complex).

Food Sources

Most animal food comes from plants and other animals. Plants are eaten by herbivores,

which are at the bottom of the food chain. Animal food sources are consumed by carnivores

and omnivores. These animals tend to be at the middle to the top of the food chain.

HABITAT REQUIREMENTS

Wildlife animal species have life requirements that must be met by the habitat for a healthy

existence. A habitat is a physical area in which members of a wildlife species live. The habitat

supports life processes.

All organisms require food, and a key component of food is energy. The sun is the source of

energy for all living things. The biotic pyramid is a series of transfers of food energy from

one organism to another; it is a graphical way of showing a food chain.

Water is a basic need to sustain life. It is not a food nutrient because it does not supply

energy. The amount of water, or lack thereof, determines the species of plants that will grow in

an area and, therefore, determines the wildlife species that reside there. Some examples of

water sources for wildlife animals are lakes, streams, rivers, and creeks.

Cover is the vegetation or other material that provides safety in a habitat. Animals use cover

for nesting, resting, and escaping dangerous predators. Cover needs vary throughout the year.

Space is the area or territory

around an organism. Space pro-

vides air, food sources, and cover.

Space requirements vary from

year to year and according to the

habitat quality.

Summary:

� The food chain is therelationship betweenorganisms in whichenergy is transferredfrom one to another.Natural selection is the


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FIGURE 4. Habitat for these elk must include food, water, space, and cover.

(Courtesy, National Park Service)

process in which inheritable traits that favor species survival are passed on to suc-ceeding generations and unfavorable traits are less likely to be passed on.

A system of taxonomy uses seven divisions: kingdom, phylum, class, order, family,genus, and species. The scientific name is composed of the genus and species.

Anatomy is the study of the form, shape, and appearance of organisms. Physiologyis the study of the functions of parts of the anatomy. Organ systems include skele-tal, digestive, respiratory, muscular, circulatory, excretory, nervous, andintegumentary.

Reproduction is accomplished sexually and asexually.

A nutrient is a chemical substance in food that supports life. Nutrient types areessential, energy, protein, minerals, and vitamins.

Wildlife animal species have life requirements that must be met by the habitat.

Checking Your Knowledge:

� 1. What is a food chain?

2. What is natural selection?

3. How do organisms reproduce?

4. What role do nutrients play in the food chain and in natural selection?

5. How does habitat relate to the food chain and to natural selection?

Expanding Your Knowledge:

� Diagram a food chain for an ecosystem in your area. Include as many species as pos-sible. Indicate the flow of energy within the chain.

Web Links:

� Food Chain

http://en.wikipedia.org/wiki/Food_web

Food Chains

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html

Natural Selection

http://en.wikipedia.org/wiki/Natural_selection

Natural Selection

http://evolution.berkeley.edu/evolibrary/article/evo_25


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http://en.wikipedia.org/wiki/Food_web

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/F/FoodChains.html

http://en.wikipedia.org/wiki/Natural_selection

http://evolution.berkeley.edu/evolibrary/article/evo_25

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