Class Webpage http://userwww.sfsu.edu/~efc/classes/ 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 Plantae (Multicellular Plants) 248,428 described species Non-insect Arthropoda 123,151 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) 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 Power Spectrum Analysis of Extinction rates Mass extinctions during the history of life have been caused by asteroid impacts occurring very 26-31 myr that reduce the diversity of life.
The fossil record records five to seven mass extinctions. Stability-Time Hypothesis 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 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.
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