2.1 Biological diversity includes genetic, species, and community/ecosystem diversity Species diversity Species are defined commonly using two concepts 1. biological species concept -group of individuals that breed among themselves but not among other groups -used by evolutionary biologists and works well for birds and mammals that are well known and have reproductive data 2. morphological species concept -group of individuals morphologically, physiologically, or biochemically distinct from other groups -most commonly used by taxonomists 2.2 (A) Entomologist collecting moth specimens; (B) Natural history collections such as at Harvard Taxonomy is the science of classifying living things into a hierarchial system Kingdom - Monera (eu- and archeabacteria), protista, fungi, plants, animals) Phylum or Division - Magnoliophyta and Chordata Class - Magnoliopsida (dicots) and Liliopsida (monocots) and fishes (Agnatha, Chondryichthyes, Osteichthyes), amphibians, reptiles, Aves (birds), as well as mammals Order Family Genus Species = genus + species epithet - binomial nomenclature developed by Linneaus Ex. Homo sapiens Box 2.1 Blackburnian warblers are related to more and more other animals at successively higher levels of taxonomic organization Difficulties in distinguishing species 1) species concept and problems with taxonomy 2) varietal or subspecific variation Ex. breeds of dogs all belong to one species by a biological definition -difficult to distinguish variation within a single species from that between closely related species Ex. threatened (ivory tusks) African elephant -- Is it a single widespread species or three separate species? 2.3 Dogs are all one species and readily interbreed There are about 600,000 African elephants, and between 30,000 and 50,000 Asian elephants. The Africans dropped by 50%, from 1.3 millions to 600 000, between 1979 and 1989, because of poaching. About 8 elephants an hour (70,000/year) were poached during this period, until the CITES Ivory ban 1989. The CITES (Convention of International Trade In Endangered Species) regard both species as threatened. Indian (Elephas maximus) small ears one lobe at trunk tip five toenails India and SE Asia African (Loxodonta africana) large ears two lobes at trunk tip four toenails widespread in S 2/3 Africa -some advocate dividing it up into a savannah, forest, and desert species Difficulties in distinguishing species (cont.) 3) hybrids -often sterile because chromosomes cannot pair in metaphase I -if fertile they violate the biological species concept -common in plant species -few remaining red wolves (Canis rufus) may all be hybrids with coyotes (Canis latrans) and may lose its status as endangered and go extinct due to hybridization red (Canis rufus) grey (C. lupus) coyote (C. latrans) medium large small (1/2 size of red wolf) more slender face SEUSA Canada widespread Alaska Minnesota Figure 2.4 The hybrid tiger salamander (left) is larger than its parent species (California tiger salamander (right) (an endangered species) and introduced Barred Tiger salamanders) and is increasing in abundance Origin of new species 1. gradual speciation or phyletic evolution -gradual transformation into another species -first described by Charles Darwin and Alfred Wallace (Darwin, C. 1859. On the Origin of Species) Read Pg. 29 of text on mountain rabbits in Canada -usually involves a geographic barrier = allopatric speciation Ex. E and W species of plants and animals in North America 2. rapid speciation -often occurs on islands through a process called adaptive radiation - local adaptation and subsequent speciation Ex. 1) mouthparts of insects, 2) Honeycreeper family of birds originated in Hawaii 10s of 1000s of years ago from a single pair of birds 2.5 The Hawaiian honeycreeper family is a spectacular example of adaptive radiation Rapid speciation may occur in a single generation in the same geographic area (sympatric) because of polyploidy Ex. Parents Gametes 10 chromosomes 5 chromosomes Offspring = 9 chromosomes that do not pair producing a sterile hybrid Parents Unreduced gametes 10 chromosomes 10 chromosomes Offspring = 18 chromosomes that pair producing a fertile polyploid that is intermediate in morphology and reproductively isolated from parents -common mode of speciation in plants and invertebrates X X X X 8 chrom. 4 chrom. 8 chrom. 8 chrom. Species arise all the time but today species extinction is about 100-1000X faster than speciation. Why? 1) much of earth’s surface is occupied by people 2) many of species threatened with extinction are the sole remaining representative of their genus and family Ex. coelacanth, giant panda, ginkgo 3) existing protected areas and national parks may be too small for speciation 2.6 Certain groups of organisms apparently need a minimum area in order to undergo the process of speciation Measuring Species Diversity -no simple relationship between diversity and stability of communities -many diversity indices are used and most incorporate two ideas 1) richness - number of species in a community 2) evenness - number of individuals of each species in a community -mathematical indices of biodiversity have been developed to describe three different geographic scales 1) alpha (local) diversity = richness/small (local) area 2) gamma (total) diversity = richness/region 3) beta diversity = gamma diversity/ average alpha diversity -represents variability of species composition along an environmental or geographical gradient -indicates whether each part of a region has a more distinct assemblage of species than another part 2.7 Biodiversity indexes for three regions, each with three mountains Genetic diversity -observable units are populations- group of individuals in same place and time that mate and produce offspring -individuals within a population are genetically different from each other. They have different forms of genes or alleles that arise from mutations in DNA. All the genes and alleles in a population = gene pool 2.8 The phenotype of an individual is determined by its genotype and by the environment 2.89 Genetic variation at the population and individual. Genetic variation is due to: 1) Mutation a. point- one nucleotide is substituted for another b. frameshift- a nucleotide is added or deleted 2) meiosis and recombination during sexual reproduction a. crossing over in Prophase I b. independent assortment in Metaphase I c. recombination of two genotypes during fertilization -most mating occurs within populations but individuals occasionally move from one population to another allowing for the transfer of new alleles = gene flow Amount of genetic variation is measured by: 1) number of polymorphic genes- genes with more than one allele Ex. 1a1a, 1b,1b, 1c1c 2) number of heterozygotes that result from polymorphisms Ex. 1a1b, 1a1c, 1b1c -individuals that are heterozygous have greater fitness than homozygotes Ex. hybrid vigor in domestic animals Why? 1)having two different forms of an enzyme gives the individual greater flexibility in dealing with the environment 2) nonfunctional or harmful alleles are masked by functioning alleles -sometimes individuals that differ genetically differ in their ability to reproduce. If individuals with certain alleles are better able to reproduce, then gene frequencies in the population will change in subsequent generations -this process where environment causes changes of genes in a group of populations of the same species (evolution) is called natural selection. When man does the selecting, it is called artificial selection Community and Ecosystem Diversity ecosystem = community + environment Community (biota) = species that occupy an area Environment (abiota) = physical habitat and interacts with community to form niches niches= unique set of resources in the environment that each species uses Ex. plant - soil type, pollination ecology, seed ecology, moisture, sunlight, etc. -any component of niche may become a limiting resource when it restricts population size 2.10 In this illustration, each animal species lives at different depths and in association with certain structural features Communities are organized into four trophic levels: 1) Photosynthetic species (primary producers) -obtain energy via photosynthesis from the sun or some type of chemosynthesis - mostly plants in terrestrial habitats and algae/cyanobacteria in aquatic habitats 2) Herbivores (primary consumers) -eat photosynthetic species 3) carnivores (secondary consumers or predators) -eat herbivores or other carnivores -omnivores include plants in their diet 4) detrivores (decomposers) -recycle nutrients through the ecosystem -mostly fungi and bacteria. Also includes animals like worms, dung beetles, and vultures Four trophic levels comprise food chains or webs and the greatest biomass is usually found as primary producers -species at the same trophic level that use approximately the same resources compete with each other = guild 2.12 Field ecosystem showing its trophic levels and simplified energy pathways 2.123 A diagram of a simple food web studied in a traditional agricultural ecosystem. Species interact within communities in ways beyond trophic levels Predation and competition as well as limiting resources determine a habitats carrying capacity = number of individuals at each level that the resources of the ecosystem can support Species in the community often interact as symbionts=species found together in close association and cannot survive without each other Three types of symbiotic relationships recognized: 1. commensalism (+ 0) -two species live in close association (symbiosis) where one benefits and the other is not affected. Ex. epiphytes 2. predator (+ -) -symbiosis where one species benefits and the other does not -parasitism is a subclass of predator symbiosis. Ex. Animals are affected by bacteria, fungi, protozoans, worms, arachnids, and insects. Plants are affected by bacteria, fungi, protozoa (slime molds), other plants, worms, and arthropods 3. mutualism + + -symbiosis where both species benefit. Ex. fruit eating animals, flower pollinators, lichens 2.11 Mutualistic relationships (A) Ant and acacia; (B) Hummingbird and legume Communities change in species composition, community structure, and physical characteristics in response to natural and human caused disturbance = succession Two types of succession 1) Primary - no soil is present Ex. lava fields, sand dunes 2) Secondary - soil is present Ex. cleared field reverting back to Cross Timbers ecosystem Some species have a greater impact on an ecosystem than others = Keystone species -because of their impact on the ecosystem, their protection is a priority -usually have high impact on the ecosystem and low proportional biomas -can be classed according to the following: 1) major predators a. sea stars -one of the best quantified examples and one of first to use the term (Paine, 1966) -removal of sea stars decreased the richness of mussels, barnacles, snails, and other species -one species of mussel dominated and this limited the space for many other species b. sea otters -keep shellfish, sea urchin and kelp in balance c. grey wolves -keep deer and herbs in balance 2.13 Keystone species Box 2.2 Forests of giant kelp provide the starting point and structure for a diverse biological community Read box 2.2 and discuss The sea otter as a Keystone species. 2) ecosystem engineers a. beavers -create wetland ecosystems b. leaf cutter ants -fungal gardens are habitats for 100s of subterranean species 3) food resources a. nectar bearing flowers and certain fruits -comprise less than 1% plant species diversity in the tropical forest yet are essential parts of food webs -Ex. Fig wasps pollinate fig flowers that form fruit that is used by dozens of animals b. flying foxes (bats) -pollination and seed dispersal for hundreds of tropical plants c. some grazing animals -species of fish and sea urchins control of weedy algae on coral reefs 2.14 Flying foxes are vital pollinators and seed dispersers in Old World tropical forest communities 4) decomposers -dung beetles exist in low densities in tropical forests -bury dung for larvae that releases nutrients -seeds in dung germinate into a number of fruiting species used by other animals -kill parasites in dung keeping vertebrate populations healthy -losing a keystone species can create a series of linked extinctions called an extinction cascade 2.15 Dung beetles are important keystone species in many communities Keystone resources -certain resources are vital to the functioning of a ecosystem = keystone resources -these resources occupy only a small portion of the habitat but are crucial to many species in the community Examples of keystone resources: 1) salt licks and mineral pools -greatly affect the abundance of vertebrates 2) deep pools in streams and springs -refuge in dry seasons 3) flowing water -essential for some aquatic species 4) hollow tree trunks and rotting wood -nesting and denning sites for many bird and mammal species Key Ecosystem Processes -influence ecosystem dynamics Include: 1) transfer of energy through trophic levels 2) production of biomass 3) cycling of nutrients 4) movement of water 5) fire ? -key ecosystem processes maintain ecosystem health when stable, resistant, and resilient
