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Chapter 4

Chapter 4- Evolution, Biodiversity, and Population Ecology.docx

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Monika Havelka

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Chapter 4- Evolution, Biodiversity, and Population Ecology Evolution as the Wellspring of Earth’s Biodiversity  Evolution- Genetically based change in the appearance, functioning, and/or behaviour of organisms across generations, often by the process of natural selection  Natural Selection- The process by which traits that enhance survival and reproduction are passed on more frequently to future generations of organisms than those that do not, thus altering the genetic makeup of populations through time; act on genetic variation and is primary driver of evolution  Evolutionary theory is indispensable; foundation of modern biology and is important to understand for a full appreciation of environmental science Natural Selection Shapes Organisms and Diversity  Natural selection is mechanism for evolution and as a way to explain living things  Darwin and Wallace recognized that:  Organisms produce more offspring than can possible survive, and that some offspring may be more likely than others to survive and reproduce  Whichever characteristics give certain individuals an advantage in surviving and reproducing might be inherited by their offspring  Adaptive Trait/Adaptation- A trait that confers greater likelihood that an individual will reproduce  Maladaptive- A trait that reduces success Natural Selection Acts on Genetic Variation  For organism to pass trait along to future generations (heritable), genes in organism’s DNA must code for that trait  Mutations- An accidental change in DNA that may range in magnitude from the deletion, substitution, or addition of a single nucleotide to a change affecting entire sets of chromosomes; provide the raw material for evolutionary change (can be deadly or beneficial)  Recombination- Process that produces novel combinations of genes, generation variation among individuals  Natural selection acts on genetic variation in three ways: 1. Directional Selection- Selection that drives a feature in one direction rather than another; toward larger or smaller, or faster or slower 2. Stabilizing Selection- Selection produces intermediate traits, in essence preserving the status quo 3. Disruptive Selection- Trail diverges from its starting condition in two or more directions Selective Pressures from the Environment Influence Adaptation  Divergent Evolution- The process whereby two species with a common genetic ancestor evolve different traits over time as a result of adaptation to selective pressures from different environments/habitats; characteristics of populations eventually become so different that they are no longer the same species  Convergent Evolution- The process whereby two completely separate and distinct species evolve similar traits, as result of adaptation to selective pressures from similar environments  Environments change over time as well and organisms move around; successful trait at one time may not be successful in another time Evidence of Natural Selection is all around us  Selective Breeding- Breeding species we like while not breeding those with variants we dislike; able to exaggerate particular traits we prefer; crop plants, pets, and livestock  Artificial Selection- Trait selection conducted under human direction Evolution Generates Biological Diversity  Biological Diversity/Biodiversity- The sum total of all organisms in an area ,taking into account the diversity of species, genes, populations, and their communities  Species- A population/ group of populations of a particular types of organism, whose members share certain characteristics and can breed freely with one another and produce fertile offspring  Population- A group of organisms of the same species that live in the same area; often composed of multiple populations Speciation Produces New Types of Organisms  Speciation- The process by which new species are generated; can occur in many ways:  Allopatric Speciation- the emergence of a new species as a result of the physical separation of populations over geographic distance Populations can be Separated in Many Ways  Natural mechanisms of population isolation that can give rise to allopatric speciation:  Glacial ice sheets advance  Mountain chains are uplifted  Major rivers change course  Sea level rises, creating islands  Climate warms, pushing vegetation up to mountain slopes and fragmenting it  Climate dries, dividing large single lakes into multiple smaller lakes  Ocean current patterns shift  Islands are formed in the sea by volcanism  If geological/climate process that isolated populations reverses itself, then populations can come back together  Sympatric Speciation- Another way of speciation where species form from populations that become reproductively isolated, occupying a new ecological role/niche within the same geographic area We Can’t Infer the History of Life’s Diversification by Comparing Organisms  Cladograms/Phylogenetic Trees- A treelike diagram that represents the history of divergence of species or other taxonomic groups of organisms; one can trace how the traits themselves may have been evolved The Fossil Record Teaches us About Life’s Long History  Fossil- The remains, impression, or trace of an animal or plant of past geological ages that has been preserved in rock or sediments  Fossil Record- The cumulative body of fossils worldwide, which palaeontologists study to infer the history of past life on Earth; which shows that:  Life existed on Earth for at least 3.5 billion years  Earlier types of organisms changes/evolved into later ones  The number of species existing at any one time has generally increased through time  The species living today are a tiny fraction of all species that ever lived  There have been several episodes of mass extinction Speciation and Extinction Together Determine Earth’s Biodiversity  Extinction- The disappearance of an entire species  The number of species in existence at any one time = number added through speciation – number removed by extinction  Species extinction brought about by human impact – single biggest environmental problem because loss of species is irreversible Earth has seen Several Episodes of Mass Extinction  Background extinction rate- rate at which gradual extinction (one species at a time) occurs  Mass Extinctions- The extinction of a large proportion of the world’s species in a very short time period due to some extreme and rapid change; 5 mass extinction events in past half billion years (refer to table 4.3 on page 101) Human Activities have Initiated Another Mass Extinction  Sixth mass extinction event- humans are the cause  Changes in natural systems by human population growth, development, and resource depletion have driver species extinct Levels of Ecological Organization Study Ecology at Several Levels  Life occurs in a hierarchy of levels; hierarchy of matter within organisms: 1. Atoms + molecules 2. Organelles + cells (basic functional units of life) 3. Tissues -> organs -> organ systems 4. = Individual living organism  Levels of ecological organization: 1. Organisms 2. Population- a group of individuals of a species that live in a particular area  Population Ecology- investigates quantitative dynamics of how individuals within a species interact with one another 3. Community- A set of populations of diff
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