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Diversity of Life in
the Sea
• It would be virtually
impossible to
consider the breadth
of organisms in the
sea without some
sort of classification
system
Diversity of Life in the Sea
• Fortunately, there is a unifying concept that
helps make this bewildering diversity of life
comprehensible: EVOLUTION!
• Evolution describes the genetic changes in a
population over time
• Organisms are adapted to their
environment; a good fit
(but not perfect!)
Natural Selection and Adaptation
• Evolution is descent with modification
• Evolution occurs because individual organisms
have genetic differences in their ability to find
food, mates, avoid being eaten, in their
metabolism and in countless other attributes
• The best adapted individuals – those most
successful at meeting the challenges of the
environment – produce more offspring (on
average) than those not so well-adapted.
Natural Selection
• Natural selection is the process by which
favorable, inherited traits become more
numerous in successive generations of a
population of reproducing organisms
• Over time, natural selection leads to species
that are well adapted (highly evolved) to their
environments
• Populations either adapt to environmental
changes or become extinct
The Principles of Natural Selection
• Struggle for existence/Competition
– More offspring are produced than can be supported
by resources
King Penguin Rookery © Momatiuk - Eastcott/Corbis
The Principles of Natural Selection
• Variation
– Some individuals, due to heredity or mutation,
possess characteristics which make them better
adapted to their environment
The Principles of Natural Selection
• Inheritance of Traits
– Best-suited organisms will survive to produce
more individuals that share same adaptation
1Population
with varied inherited traits
2 Elimination of individuals with certain traits
3
Reproduction of survivors
Certain
individuals with
a distinct,
inherited
characteristic
will be selected
against, while
others with a
(different)
distinct,
inherited trait
will survive
Classifying Living Things
• The adaptation of various populations to
different environments has produced a
fantastic variety of life forms
• In order to properly study these organisms, it
is necessary to classify them
• Must first identify what a “species” is exactly
What defines a species?
• Biological species concept:
– A species consists of a population whose
members have the potential to interbreed
with one another in nature to produce
viable, fertile offspring, but who cannot
interbreed with other such groups
– Species are based on their ability to
interbreed; not on physical similarities!
Biological Species Concept
• All domesticated dogs are the same species
because they can interbreed; a subspecies of
the gray wolf, Canis lupus
Taxonomy
• Taxonomy is the practice and science of
classification
• Taxonomy uses taxonomic units, or taxon
• A taxon is a taxonomic unit at any level; for
example, Mammalia is a taxon at the Class
level
• Domain  Kingdom  Phylum  Class 
Order  Family  Genus  Species
Domain
Kingdom
Phylum
Subphylum
Class
Order
Family
Diversification
Genus
Species
Scientific names
• Organisms are typically identified by 2 names;
the name of their genus and their species =
scientific name
• No two organisms can have the same scientific
name and this name is the same everywhere
in the world!
• Written as Genus species
Orcinus orca
Taxonomy
• Scientific names are descriptive
• May describe unique characteristic, region
where species is found, etc.
• Ex. Humpback whale Megaptera novaeangliae
= “long-winged New Englander”
• Common names
can be deceiving!!!
– “dolphin”
– “bear”
Phylogenetics
• Many hierarchies are being re-examined
based on the results of molecular analysis
(DNA, RNA)
• Binomial taxonomy does not take into account
evolutionary relationships
• Enter phylogeny and systematics…
• Reconstructs evolutionary relationships by
grouping organisms by their relatedness
Phylogeny and Systematics
• Systematics is the reconstruction and study of
evolutionary relationships
• Phylogeny – an evolutionary tree; species
grouped by how long they’ve shared a
common ancestor
• Evidence for determining these relationships
must come from body structure*,
reproduction, embryological and larval
development, and molecular characteristics
*homologous structures
Homologous structures
http://www.edwardtbabinski.us/mpm/mpm_whale_limb.html
Phylogenetic Tree: The Tree of Life
• Domain Archaea
• Domain Bacteria
• Domain Eukarya
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