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Chapter 1 – Classifying Life’s Diversity
1.1 – Identifying, Naming, and Classifying Species
species: a group of organisms that can interbreed in nature and produce fertile offspring
Identifying Species: Using Species Concepts
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Biologists use the morphological species concept, the biological species concept,
and the phylogenetic species concept to define species.
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The morphological species concept focuses on morphology – body shape,
size, and other structural features.
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The biological species concept defines species on the basis of whether two
organisms can produce fertile offspring.
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The phylogenetic species concept examines the phylogeny, or evolutionary
history, of organisms.
Species Concept
Morphological
Concept Is Based On
appearance
Biological
behaviour and ability to mate
and produce fertile offspring
Phylogenetic
evolutionary relationships
Advantages and Disadvantages
simple, but there is often significant
variation in appearance within a
species
widely used, but cannot be used
with many extinct species or
separated species
can be used with extinct species and
makes use of DNA evidence, but
evolutionary relationships are not
always known
Classifying Species
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TAXONOMY is the branch of biology that identifies, names, and classifies species.
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Each species is named using two words. Example: Felis domesticus (house cat). It is
often referred to as the scientific name.
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The system of using a two-word name for each species is called BINOMIAL
NOMENCLATURE and was found nearly 300 years ago by Carolus Linnaeus. The first
word is the name of the genus in which the organism is classified and the first letter is
capitalized. The second word is the name identifies a particular species.
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All species are classified by being in eight nested ranks (taxonomic categories). The
broadest category is the domain, continuing to narrow to kingdom, phylum, class,
order, family, genus, and finally species, which is the narrowest category)
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Domains are the largest taxa (millions of species) and species is the smallest taxa (one
organism).
(TABLE 1.2, pg 15 – Taxonomic Classification of the Grey Wolf)
Rank (Taxonomic
Category)
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Grey Wolf Taxon
Eukarya
Animalia
Chordata
Mammalia
Carnivora
Canidae
Canis
Canis lupus
Number of Species in
Taxon
4 – 10 million
2 million
50 000
5 000
270
34
7
1
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Here’s are a couple of mnemonics to help you remember the correct order of taxa:
“Deaf King Philip Came Over From Germany Swimming.” OR “Does Kim Play
Chess Or Fix Great Sandwiches?”
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Homework:
pg 16 Work on Questions #1 – 11
1.2 – Determining How Species Are Related
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The goal of modern classification is to assign species to taxa so that the
classification reflects both morphological similarities among organisms as well as
hypotheses about their phylogeny (evolutionary history).
It is thought that the more a species shares it evolutionary history with another
species, the more closely related they are.
Evidence of Relationships Among Species
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There are three main types of evidence used to determine how closely related
different species are. These are: anatomical, physiological, and DNA evidence.
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Anatomical evidence includes comparing the structure and form of organisms,
including bones.
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Physiological evidence includes comparing the biochemistry of organisms, including
proteins.
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DNA evidence includes comparing organisms’ DNA sequences.
Phylogenetic Trees
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Once scientists have studied the features of organisms and learned more about
their evolutionary histories, they often use a tool called a phylogenetic tree to
represent a hypothesis about the evolutionary relationships among groups of
organisms. (See Figure 1.5, pg 17 and Figure 1.12, pg 21)
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Like a family tree, the roots or the base of the phylogenetic tree represents the
oldest ancestral species. The upper ends of the branches represent present-day
species that are related to the ancestral species.
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Forks in each branch represent the points in the past at which an ancestral species
split – evolved, or changed over time – to become two new species.
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Understanding phylogeny can help scientists trace the transmission of disease and
develop and test possible treatments.
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Understanding the evolutionary relationships among species and groups of
organisms can also have important consequences in agriculture and in the
conservation of biodiversity.
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Homework:
pg 23 #1 - 10
1.3 – Dichotomous Keys
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Taxonomists use dichotomous keys to make choices between pairs of options to
narrow down identifications.
dichotomous key:
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an identification tool consisting of a series of two-part choices that
lead the user to a correct identification
A dichotomous key is a device used to easily and quickly identify unknown organisms.
The key is a sequence of choices between two statements (couplets) based on
characteristics and lead to couplets indicating progressively specific characteristics. If
the organism falls into one category, you go to the next indicated couplet. By
following the key and making the correct choices, you should be able to identify your
organism.
Constructing Your Own Dichotomous Key
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Start with the most general characteristics and progress to increasingly more specific
characteristics.
Indent each couplet or leave a space between each couplet to make the key easier to
read.
Use constant characteristics rather than variable ones.
Use measurements rather than terms like “large” and “small”.
Use characteristics that are generally available to the user of the key rather than
seasonal characteristics or those seen only in the field.
Make the choice a positive one – something “is” instead of “is not”.
If possible, start both choices of a pair with the same word.
If possible, start different pairs of choices with different words.
Precede the description with the part that is being described – “leaves are red” instead
of “red leaves present”.
SAMPLE DICHOTOMOUS KEY: IDENTIFYING CANADIAN MONEY
1a
1b
Composed of Paper
Composed of Metal
Go to 2
Go to 3
2a
2b
Sir John A. MacDonald is Pictured
Sir Wilfred Laurier is Pictured
$10 Bill
$ 5 Bill
3a
3b
Metals in Coin Appear Uniform
More Than One Type of Metal is Visible
Go to 4
Twoonie
4a
4b
The Edges Have Ridges
The Edges Are Smooth
Go to 5
Go to 6
5a
5b
Smaller than 20 mm in Diameter
Larger than 20 mm in Diameter
Dime
Quarter
6a
6b
Silver in Colour
Colour Other Than Silver
Nickel
Go to 7
7a
7b
Copper in Colour
Brass in Colour
Penny
Loonie
1.3 – KINGDOMS and DOMAINS
The Six Kingdoms
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All plants, animals and other organisms can be organized into groups sharing similar
characteristics.
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Classification is a valuable way of learning how organisms are related to one another.
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Through this we can make sense of the amazing diversity of life on Earth.
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Over 2 000 years ago, Greek philosopher Aristotle, divided all living things into two
Kingdoms, either Plantae or Animalia, based on certain characteristics.
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A problem arose because some organisms had characteristics of both kingdoms (ex.
corals and sponges that are non-motile but do not photosynthesize).
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In the 17th century, when the microscope was invented, classify organisms became
more difficult because a new world of organisms was revealed called microorganisms
(ex: euglena that swim and photosynthesize).
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In 1866, Ernest Haeckel proposed a new kingdom, Protista, one-celled organisms
with a nucleus.
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In the first half of the 1900’s, some single-celled organisms were found to be
extremely small and without a cell nucleus, so a new kingdom, Bacteria, was created
for them, bringing the total to four.
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In the 1960’s, scientists added a fifth kingdom, Fungi because fungi were so different
that they needed their own kingdom.
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During the 1990’s bacteria that live in extreme environments because of their unique
structures were researched and scientists classified these into a sixth kingdom,
Archaea.
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Figure 1.3, pg 24
Two Major Cell Types
- There are two major types of cells: prokaryotic cells and eukaryotic cells.
Prokaryote: organism with cells lacking a true nucleus and most other types of organelles;
bacteria and archaea
Eukaryote:
organism with cells containing nuclei and other types of membrane-bound
organelles; protists, fungi, plants and animals
Differences Between Prokaryotes and Eukaryotes
Prokaryotes
Eukaryotes
(bacteria, archaea)
(protists, plants, fungi, animals)
small (1 – 10 μm)
large (100 – 1000 μm)
DNA circular, not bounded by membrane
DNA in nucleus bounded by membrane
genome made up of a single chromosome
genome made up of several chromosomes
cell division not by mitosis and meiosis
cell division by mitosis and meiosis
asexual reproduction common
sexual reproduction common
multicellular forms rare
most forms are multicellular
mitochondria and other membrane-bound
organelles absent
mitochondria and other organelles present
many are anaerobic (do not require oxygen)
most are aerobic (require oxygen)
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Fossil evidence shows that the first forms of life were prokaryotic organisms similar in
appearance to bacteria. First prokaryotes appear 3.5 billion years ago.
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The first eukaryotes appear 1.5 billion years ago (2 billion years later).
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The first multicellular organisms appear 700 million years ago.
The Three Domains
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There are three domains: Bacteria, Archaea, and Eukarya.
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Organisms in the domains Bacteria and Archaea are unicellular and prokaryotic.
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Organisms in the domain Eukarya have eukaryotic cells and are unicellular or
multicellular. There are four kingdoms in the domain Eukarya: Protists, Plantae,
Fungi, and Animalia.
Table 1.5, pg 29 summarizes some of main characteristics of kingdoms and Figure 1.17,
pg 29 shows examples of organisms in each kingdom.
HOMEWORK:
pg 30 # 1 – 8
1.4 - Classifying Types of Biodiversity
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Biodiversity is the variety of life in the world. It is often used to gauge the health
of biological systems.
Valuing Biodiversity
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Ecosystems that have a high biodiversity tend to be healthier and more resilient to
changes in the environment.
Biodiversity helps to maintain life-sustaining services, conditions, and processes:
 Insects, bats, birds, and other animals pollinate flowering plants and crops.
 Micro-organisms make nutrients available and break down toxic substances in
water and soil.
 Ecosystems cycle carbon, nitrogen, and oxygen.
 Ecosystems clean air, purify water, control erosion, prevent floods, and modify
climate.
Often the presence or absence of a single keystone species can have a dramatic
impact on an ecosystem.
Keystone species are species that have a disproportionately large effect on the
ecosystems in which they live, such as the honeybee.
Discuss role of honeybee (Pearson, pg 5)
Levels of Biodiversity
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There are three levels of biodiversity: genetic diversity, species diversity, and
ecosystem diversity.
Genetic diversity
genetic diversity: the variety of heritable characteristics (genes) in a population of
interbreeding individuals
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The variation among individuals in a population is largely a result of the differences
in their genes.
Genetic diversity within a population is known as the gene pool. In other words,
the gene pool is the sum of all the versions of all the genes in a population.
As genes determine hereditary characteristics, these small differences make each
organism unique. They also allow populations to adapt to changes in
environmental conditions and evolve over time.
Genetic diversity is especially important in disease resistance.
Populations that lack genetic diversity are more susceptible to disease than those
that have high diversity. The entire population could be eliminated which could
eventually lead to the extinction of the species.
Genetic diversity also allows populations and species to survive changing
environmental conditions, such as a change in resource availability, climate change,
a change in a predator population, or the introduction of non-native species.
Species Diversity
species diversity: the variety and abundance of species in a given area
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A greater variety of species in ecosystems allows those ecosystems to survive
environmental changes, such as drought, plagues, or disease outbreaks.
Each species has a certain set of conditions in which it can survive.
Each species also contributes to the whole ecosystem and, without the actions of
each species, the ecosystem and other organisms may not be as successful.
Ecosystem Diversity
ecosystem diversity:
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the variety of ecosystems in the biosphere
Recall that ecosystems are made up of two components – biotic factors (interacting
populations of species) and abiotic factors (altitude, latitude, geology, soil
nutrients, climate, and light levels).
Ecosystems can range in size from a small plant that grows on another plant to an
entire biome, such as a tropical rainforest or Canada’s boreal forest.
Ecosystem services are the benefits experienced by organisms, including humans,
which are provided by sustainable ecosystems.
Earth would lose most of the services that ecosystems provide if there was no
ecosystem diversity.
Wetlands provide several important ecosystem services, including storing water
(reduces the risk of floods), filtering water (removes pollutants) and providing
habitat for commercially important species of fish and shellfish.
Because wetlands are so valuable, government agencies and non-governmental
organizations often work together to preserve and protect them.
Ecosystem Function and Species Diversity
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Ecosystems with greater species diversity have higher resilience.
resilience:
the ability of an ecosystem to remain functional and stable in the presence of
disturbances to its parts
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In experiments conducted at the University of Minnesota from 1982 to 1993,
researchers concluded that greater biodiversity in an ecosystem results in at least
three beneficial patterns: increased plant cover, more resistance to invasive
species, and more disease resistance. (See Fig 1.21, pg 35)
Ecosystem Services and Human Actions
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In Ontario, bass-free lakes have been stocked with smallmouth bass. While this
improves the bass population and recreational fishing, ecologists have noticed a
decline in the number of native fish species such as stickleback and dace.
This has a ripple effect on other species. With fewer small fish, trout must then
consume less nourishing food, resulting in slower growth, smaller fish, and
decreased populations.
This leads to a decline in species diversity and affects the diversity of an
ecosystem.
Homework: pg 37 # 1 - 11