Evolution of Biodiversity Chapter 5 Evolution of Biodiversity

Earth is home to a tremendous diversity of species Ecosystem diversity- the variety of ecosystems within a given region. Species diversity- the variety of species in a given ecosystem. Genetic diversity- the variety of genes within a given species.

Species richness- the number of species in a given area. Species evenness- the measure of whether a particular ecosystem is numerically dominated by one species or are all represented by similar numbers of individuals. Shannon-Wiener and Simpson’s Index take both species richness and species evenness into account

Evolution is the mechanism underlying biodiversity Evolution- a change in the genetic composition of a population over time. Microevolution- evolution below the species level. Breeding of agricultural crops to drug-resistant superbugs Macroevolution (Speciation)- Evolution which gives rise to new species or new genera, family, class or phyla.

Creating Genetic Diversity Dusky-headed conure Genes- physical locations on chromosomes within each cell of an organism. Genotype- the complete set of genes in an individual. Two processes that create genetic diversity: Mutation- a random change in the genetic code. Environmental factors, such as UV light, can cause mutations Recombination – occurs as chromosomes are duplicated during reproductive cell division and a piece of one chromosome breaks off and attaches to another chromosome. Does not create new genes, but it does bring together new combinations of genes on a chromosome and can therefore produce novel traits. Phenotype- the actual set of traits expressed in an individual.

Evolution by artificial and natural selection Evolution by artificial selection- when humans determine which individuals breed. Dogs, horses, plants Evolution by natural selection- the environment determines which individuals are most likely to survive and reproduce.

Darwin’s theory of evolution by natural selection Individuals produce an excess of offspring. Not all offspring can survive. Individuals differ in their traits. Differences in traits can be passed on from parents to offspring. Differences in traits are associated with differences in the ability to survive and reproduce.

Evolution by Random Processes Mutation- occur randomly and can add to the genetic variation of a population. Genetic drift- change in the genetic composition of a population over time as a result of random mating. Bottleneck effect- a reduction in the genetic diversity of a population caused by a reduction in its size. Habitat loss, natural disaster, hunting, climate change Low genetic variation – increased risk of disease and low fertility Cheetah Founder effect- a change in a population descended from a small number of colonizing individuals. Genetic composition very different from that of the homeland. Amish http://www.cbsnews.com/2100-500164_162-700519.html

Polydactyly - Mutated hands as a result of Bardet-Biedl Syndrome Polydactyly - Mutated hands as a result of Bardet-Biedl Syndrome. Mutations in Chromosome 11 with the BBS1 gene and in Chromosome 16 with the BBS2 gene

Speciation and extinction determine biodiversity Allopatric speciation- when new species are created by geographic or reproductive isolation. Geographic isolation – individuals from a larger population may colonize a new area of habitat that is physically separated from the rest of the population. Or a large population is split into two by geographic separation over time. Formation of river Different environmental conditions, such as temperature, precipitation or the occurrence of predators, causes natural selection to favor different phenotypes for survival in each habitat. Reproductive isolation – eventually the two populations will become so genetically different that even if the physical barrier were removed, they could no longer interbreed to produce viable offspring. Leads to allopatric speciation

Sympatric speciation- the evolution of one species into two species in the absence of geographic isolation, usually through the process of polyploidy, an increase in the number of sets of chromosomes. Most organisms are diploid – having two sets of chromosomes. In Polyploidy, the number of chromosomes increases to three, four, or even six sets Plant breeders have found several ways to interrupt the normal cell division process. Colchicine is a toxic chemical that is often used to induce polyploidy in plants.  Basically, the colchicine prevents the microtubule formation during cell division, thus the chromosomes do not pull apart like they normally do.  The end result is a cell that now has double the number of chromosomes that it would normally have. ~ http://www.carnivorousplants.org/howto/Propagation/Colchicine.php

The pace of evolution Rate of Environmental Change – abandoned mine drainage causes acidic conditions in streams in only a few decades. Many stream species go extinct Genetic Variation – high genetic variation means some organisms will survive environmental change. North American Whitetail live across vast regions of NA Population Size – larger populations allow detrimental mutations to spread less rapidly. Generation Time – Species that become reproductively mature more quickly will evolve faster. Bacteria will evolve more quickly than humans.

Evolution in Genetically Modified Organisms (GMOs) Genetic Engineering – scientists can now copy genes from a species with some desirable trait, such as rapid growth or disease resistance. Scientists then insert these genes into other species of plants, animals, or microbes to produce – Genetically Modified Organisms Bacillus thuringiensis – soil bacterium that naturally produces an insecticide as a defense against being consumed by insects in the soil Plant breeders identified the bacterial genes responsible for producing the insecticide, copied those genes, and inserted them into the genomes of crop plants. This makes the plant less likely to be eaten by insect herbivores. Bt-corn, Bt-cotton. Inserting genes is a much faster way to produce desirable traits

Evolution shapes ecological niches and determines species distributions Range of tolerance- all species have an optimal environment in which it performs well. The limit to the abiotic conditions they can tolerate is known as the range of tolerance. Temperature, salinity, pH Fundamental niche- the ideal conditions for a species. Competitors, predators and diseases may prevent an organism from inhabiting their actual niche. Realized niche – the range of abiotic and biotic conditions under which a species actually lives

Niches Realized niche- the range of abiotic and biotic conditions under which a species lives. This determines the species distribution, or areas of the world where it lives. Affects a species distribution – areas of the world in which the species lives. Niche generalist- species that live under a wide range of conditions. Niche specialist- species that live only in specific habitats.

Meadow Spittlebug – niche generalist – has a broad diet and wide habitat preferences. Skeletonizing leaf beetle – niche specialist - feeds only on a single species of plant

The Fossil Record Fossils- remains of organisms that have been preserved in rock. Much of what we know about evolution comes from the fossil record.

The Five Global Mass Extinctions Mass extinction- when large numbers of species went extinct over a relatively short period of time. http://www.pbs.org/wgbh/nova/earth/mass- extinction.html

The Sixth Mass Extinction Scientists feel that we are in our sixth mass extinction, occurring in the last two decades. Estimates of extinction rates vary widely, from 2 % to 25% by 2020. In contrast to previous mass extinctions, scientists agree that this one is caused by humans. Cretaceous-Tertiary Extinction – death of the dinosaurs