Class Webpage
http://online.sfsu.edu/~jrblair/
biol170/biol170syl.htm
What is an animal?
While there are exceptions, five criteria
distinguish animals from other life forms.
(1)Animals are multicellular, heterotrophic,
eucaryotes.
(2) Animal cells lack cell walls that provide
structural supports for plants and fungi.
(3) Animals have two unique types of
tissues: nervous tissue for impulse
conduction and muscle tissue for
movement.
(4) Most animals reproduce sexually,
with the diploid stage dominating the
life cycle, and they have a distinct
pattern of development that results in
the formation of multiple tissue layers.
(5) The transformation of a zygote to an
animal of specific form depends on the
controlled expression in the developing
embryo of special regulatory genes called
Hox genes which have DNA modules that
are called “homeobox”.
Forms of Diversity
•Taxonomic Diversity
(species, genera,
families, etc.)
•Genetic Diversity
(proteins, DNA sequence
variation)
•Morphological Diversity
(variety of form)
•Biologists often think of Diversity as
the number of different named species.
•At present, biologists have identified and
named about 1.5 million species.
•This includes over 280,000 plants,
almost 50,000 vertebrates, and over
750,000 insects.
•Thousands of newly identified species are
added each year.
•Estimates of the world’s total diversity
of species range from about 5 million to
over 30 million species.
Diversity of Life
Number of described species
Insecta -751,000 described species
Annelida (Earthworms etc.)
12,000 described species
Plantae (Multicellular Plants)
248,428 described species
Aves (Birds)
9,040 described species
Non-insect Arthropoda
123,151 described species
Coelenterata (Jellyfish, Corals,
Comb Jellies)
9,000 described species
Mollusca (Mollusks)
50,000 described species
Fungi - 46,983 described species
Protozoa 30,800 described species
Algae - 26,900 described species
Pisces (Fish)
19,056 described species
Reptilia (Reptiles)
6,300 described species
Echinodermata (Starfish, etc.)
6,100 described species
Porifera (Sponges)
5,000 described species
Platyhelminthes (Flatworms)
12,200 described species
Monera (Bacteria, Blue-green
Algae)
4,760 described species
Nematoda (Roundworms)
12,000 described species
Amphibia (Amphibians)
4,184 described species
Mammalia (Mammals)
4,000 described species
Genomic versus
morphologic rates of
diversification
•Taxa with complex morphology will be
more likely to be distinguished as
separate species, than taxa with simple
morphology – clams versus birds.
•Therefore we are biased to estimate
that taxa with complex morphology will
be diverse, even if taxa with simple
morphology are equally diverse
genetically.
Diversity of Life
How do we estimate
diversity?
T.L. Erwin – estimates that there are 30 million
species of insects in tropical regions alone
(1988)
Conjecture based on the number of new
species detected when he sprayed the
canopies of 19 individuals of a tropical forest
tree species. Claims tropics and inaccessible
habitats undersampled
How do we estimate
Diversity
• Number of described species minus
number synonymized (A)
• Consultation with taxonomic experts
• Ratio of (A)/number of species
conjectured to be undescribed
• Estimates of undecribed species from
the field
Latitudinal
Gradients
•Climatic harshness
•Time
•Competition
•Predation
•Habitat Heterogeneity
What factors determine
diversity?
Ecological – maintenance of
diversity
Evolutionary – origin of
diversity
• The species-area curve quantifies
what may seem obvious: the larger the
geographic area, the greater the
number of species.
The equilibrium theory of Island
Biogeography proposes that two factors
determines the number of species that
eventually inhabit an island.
– The rate at which new species immigrate to the
island.
– The rate at which species become extinct.
• Studies of plants
and animals on
many island
chains are
consistent with,
this hypothesis.
Hypothesis on the
Origin of Diversity
Plate Tectonic and Provincialism
Periodic Extinction
Stability-Time
Pleistocene Forest Refugia
Co-Radiation
New Adaptive Zone
Plate Tectonics and
Provincialism
•Fusion of continents leads to
high extinction rates because the
availability of habitat declines and
novel groups of species interact.
•When continents break-up
distinct provinces arise in which in
isolation new species might form
• The continents drift about Earth’s
surface on plates of crust floating on
the hot mantle.
• The break-up
and the fusion
of the
continents
may have
driven the
diversification
of life over
geologic time.
Periodic Extinction
Mass extinctions during the
history of life have been
caused by asteroid impacts
occurring very 26-31 myr
that reduce the diversity of
life.
Power Spectrum Analysis
of Extinction rates
The fossil record records five to
seven mass extinctions.
Stability-Time
Hypothesis
Geologically old or Environmentally
Stable Habitats should be most diverse
•Deep sea
•Tropcal Rain Forests
Pleistocene Forest Dynamics
Pleistocene Forest
Refugia Hypothesis
•During glacial periods, because of increased aridity,
tropical forests contracted in size to become isolated
refugia. Populations of species became isolated, and
possibly differentiate.
•During interglacial periods, increased moisture
allowed tropical forest to reoccupy the landscape,
breaking down geographic barriers between
populations of a species leading to contact between
isolated populations
Avian Refuges Proposed
for the Amazon Basin
Co-Radiation
Hypothesis
Explosion of Diversity of
insects with the advent of
the evolution of flowering
plants (Angiosperms)
Fossil Record of
Diversification in Insects
New Adaptive Zone
•Evolutionary breakthroughs (key innovations
allow species to occupy habitats or occupy
lifestyles that they have previously been unable
to do (adaptive zones).
•Such key innovations allow species to use
resources that had previously been
unexploited, expanding their abundance and
potentially leading to the formation of new
species
New Adaptive Zone:
Examples
• Invasion of the land by plants and animals
• Evolution of wings in insects, birds, and
mammals
• Plant eating in Insects
•Phylum Mesozoa
•Phylum Porifera
•Phylum Placozoa
•Phylum Cnidaria
•Phylum Ctenophora
•Phylum Platyhelminthes
•Phylum Nemertea
•Phylum Rotifera
•Phylum Gastrotricha
•Phylum Kinorhyncha
•Phylum Gnathostomulida
•Phylum Nematoda
•Phylum Priapulida
•Phylum Nematomorpha
•Phylum Acanthocephala
•Phylum Entoprocta
•Phylum Loricifera
•Phylum Mollusca
•Phylum Annelida
•Phylum Arthropoda
•Phylum Echiurida
•Phylum Sipuncula
•Phylum Tardigrada
•Phylum Pentastomida
•Phylum Onychophora
•Phylum Pogonophora
•Phylum Phoronida
•Phylum Ectoprocta
•Phylum Brachiopoda
•Phylum Echinodermata
•Phylum Chaetognatha
•Phylum Hemichordata
•Phylum Chordata