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 speciesInsecta -751,000 described species

Plantae (Multicellular Plants)248,428 described species

Non-insect Arthropoda123,151 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

Platyhelminthes (Flatworms)12,200 described species

Nematoda (Roundworms)12,000 described species

Annelida (Earthworms etc.)12,000 described species

Aves (Birds)9,040 described species

Coelenterata (Jellyfish, Corals, Comb Jellies)9,000 described species

Reptilia (Reptiles)6,300 described species

Echinodermata (Starfish, etc.)6,100 described species

Porifera (Sponges)5,000 described species

Monera (Bacteria, Blue-green Algae)4,760 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.

Plate Tectonic and Provincialism Periodic Extinction Stability-Time Pleistocene Forest Refugia Co-Radiation New Adaptive Zone

Hypothesis on the Origin of Diversity

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