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UT ENS 112 - Chapter 3: Evolution, Biodiversity, and Population Ecology

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Environmental Science 112FALL SEMESTER 2018INSTRUCTOR: DR. Adrienne [email protected] 3: Evolution, Biodiversity, and Population EcologyEvolution: The Source of Earth’s Biodiversity● A Species is a classification of organism whose members can interbreed and produce fertile offspring● A population is a group of individuals from the same species that live in the same area at the same time● Population ecology is the study of how and why the numbers of individuals in a population changes over time● Populations change over multiple generations as genetic changes alter their physical and behavioral characteristics, a process called evolution (change over time).○ Evolution originates in genes and often leads to modifications in appearance or behaviorNatural Selection Shapes Organisms● Evolution is driven by natural selection (Darwin & Wallace), a process the favors certain inherited characteristics over others, causing them to be passed on more frequently● The idea of natural selection is based on three observations:○ Organisms face a constant struggle to survive and reproduce■ Goal of any living thing○ Organisms tend to produce more offspring than can survive to maturity○ Individuals of a species vary in their attributes● Attributes are passed from parent to offspring through genes○ Genes that lead to better reproductive success will eventually evolve through the 1entire population. This is called adaptation.● The concept of natural selection was first proposed in 1850 by Charles Darwin and AlfredRussel WallaceUnderstanding Evolution is Vital for Modern Society● A working knowledge of evolutionary processes has enabled us to:○ Selectively breed crops and livestocks○ Avoid antibiotic resistance in livestock○ Avoid pesticide resistance in crop-eating insects○ Determine how infectious diseases spread and gain or lose potencySelection Acts on Genetic Variation● Accidental changes in DNA, called mutations, give rise to genetic variation in individuals● The mixing of genetic material through sexual reproduction also generates variation○ Natural selection can drive a feature in a particular direction● Closely related species that live in different environments tend to diverge in their traits○ Different selective pressure leads to different adaptations as certain individuals ina population will survive and reproduce at greater rates● Unrelated species living in similar environments may independently acquire similar traits,in a process called convergent evolution.○ Similar selective pressures favor similar traitsEvidence of Selection is All Around Us● Humans have conducted selection under our own direction, called artificial selection.○ Domesticated dogs, cats, and livestockEvolution generates Biodiversity● Biodiversity or biological diversity refers to the variety of life across all levels● About 1.8 million species have been identified, the the actual amount may be 3 to 100 million2● The process by which new species are generated is called speciationSpeciation produces new types of organisms● Allopatric Speciation: populations become physically separated over a geographic distance● When a mutation arises in an organism of one of the populations, it does not spread to the others○ Eventually, the populations grow so different that they cannot mateWe can infer the history of a life’s diversification by comparing organisms● Scientists represent the history of divergence with phylogenetic trees○ Constructed by analyzing genes and external traits of organisms● Taxonomists group species into categories meant to reflect evolutionary relationships○ RElated species are groups into a genus, related genera are grouped into families■ Domain, kingdom, phylum, class, order, family, genus, speciesFossils reveal lifes long history● A Fossil is an imprint of a dead organism● By dating the rock layers that contain fossils, paleontologists can learn when the organisms lived○ The body of fossils worldwide is called the Fossil Record● The vast majority of species that once lived have disappeared due to extinction● The deeper in Earth a fossils lives, the longer ago the organism lived on EarthSome species are especially vulnerable to extinction● Extinction occurs when the environment changes more rapidly that the species can adapt● Small and narrowly specialized populations are the most vulnerable○ For example, Hawaii’s native birds and plants did not evolve defenses against mammal predatorsEarth has seen several episodes of mass extinction3● Most extinction happens gradually, at a rate called the background extinction rate● The earth has seen at least five mass extinction events that wiped out 50-95% of Earth’s species each time○ The most catastrophic was the Permian extinction, 250 million years ago○ Causes can include volcanism, asteroid impact, methane releases, and global warmingThe Sixth Mass Extinction● Many scientists propose that life on Earth is on the verge of the sixth mass extinction○ Today’s extinction rate is 100-1000 times higher than the background extinction rate● This event is precipitated by human impacts such as○ Habitat loss, pollution, overfishing, invasive species, climate changeEcology and the Organism● Ecology is the study of the interactions among organisms and with their environments● An organism is a single living thing● A population is a group of individuals of the same species that live in the same area● A community includes all the populations of species that live and interact within an area○ Community ecology studies these interactions● Ecosystems include communities and all of the abiotic, or nonliving, parts of the environment ○ Ecosystem Ecology studies the flow of energy and nutrients between the living and nonliving parts● The Biosphere is the sum total of all living things and habitats on the Earth○ Landscape Ecology examines how ecosystems, communities, and populations are distributed across the EarthEach Organism has Habitat Needs● Each organism has a relationship with its habitat, the environment in which it lives○ Rock, soil, leaf litter, plant life, etc.4○ DEpending on the species, a habitat may be a square meter of soil or many miles of land● Organisms thrive in certain habitats and not others, creating patterns of habitat use● Mobile organisms are able to choose where they live, a process called habitat

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