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Transcript
2/16/2015 Evolution, Biodiversity and Population Ecology • Chapter 3 After this lecture, you will be able to: • Explain the process of natural selection and cite evidence for this process • Describe the ways in which evolution influences biodiversity • Discuss reasons for species extinction and mass extinction events • List the levels of ecological organization • Outline the characteristics of populations that help predict population growth • Assess logistic growth, carrying capacity, limiting factors, and other fundamental concepts in population ecology Evolution is the wellspring of biodiversity • Evolution simply means change over time – Biological evolution is genetic change in populations over time – These genetic changes lead to changes in appearance, functioning, or behavior over generations Evolution by natural selection Natural selection • Evolution may be random or can be driven by natural selection • Natural selection is the process whereby inherited characteristics that enhance survival and reproduction are passed on more frequently to future generations than those that do not Evidence of natural selection is everywhere • Artificial selection is the process of selection conducted under human direction • It is one of the best-supported and most illuminating concepts in science and is the foundation of modern biology • Evolutionary processes influence agriculture, pesticide resistance, medicine, health, etc. • In 1858, both Darwin and Wallace proposed natural selection as the mechanism of evolution 1 2/16/2015 Natural selection shapes organisms • Premises of natural selection: – Organisms struggle to survive and reproduce – They produce more offspring than can survive – Individuals of a species vary in their characteristics because of genes and the environment – Some individuals are better suited to their environment and reproduce more effectively • Natural selection acts on genetic variation Populations (NOT individuals) adapt to the environment • A parent that produces more offspring passes on more genes to future generations • Over time, characteristics (traits) that lead to better reproductive success become more prevalent • Adaptive trait (adaptation): a trait that promotes reproductive success • Sexual reproduction also leads to genetic variation – Producing new combinations of genes • Environmental conditions determine the pressures of natural selection – Organisms need time to adapt to changing conditions Resolving religion and evolution • Literal biblical account is not compatible with evolution • What we know is not compatible with biblical account – E.g., species are unchanging Many religions accept evolution Speciation • Given enough geographical isolation or selective pressure (from natural selection), members of a population become so different from their ancestors that they may be considered an entirely new species 2 2/16/2015 Speciation produces new types of organisms • The process of generating new species from a single species • Allopatric speciation occurs when species form as a result of physical separation of populations – Main mode of speciation – Populations can be separated by glaciers, rivers, mountains – Each population, with its own set of mutations, diverges Convergent evolution • Phylogenetic trees are branching diagrams that show relationships among species, groups, genes, etc. – Represent life’s history Divergent evolution • Similar conditions lead to similar adaptations • Species look alike even if they are not related • Species evolve into different types to take advantage of opportunities in environment and reduce competition Producers rely on ____________ to capture chemical energy and consumers rely on ____________ to release chemical energy. Respiration produces energy from 1. 2. 3. 4. 5. Speciation results in diverse life forms 100% water, carbon dioxide, and sugar. Sugar and oxygen. oxygen, carbon dioxide, and sugar. carbon dioxide, enzymes, and sugar. oxygen, water, and sugar. 0% 0% 0% 1. 2. 3. 4. 5. cellular respiration; photosynthesis cellular respiration; cellular respiration photosynthesis; cellular respiration photosynthesis; photosynthesis the sun; the sun 0% 0% 1 2 3 4 0% 0% 0% 3 4 0% 5 1 2 5 3 2/16/2015 _______ drives the hydrologic cycle by producing rain and snow from evaporated surface water. 1. 2. 3. 4. 5. Fossil fuels and living trees are known as “carbon sinks” because 1. 2. 3. 4. 5. Lunar tides The Coriolis Effect Hurricanes Solar energy none of the above they have no carbon. they create carbon. they destroy carbon. they store carbon. due to gravity, carbon is found closer to the ground. 0% 0% 0% 0% 0% n. n. .. rb o rb o ca ca ity , ca st or e ey to de s ey gr av rb o rb o ca ca te no e cr ea ha v ey ey du th th th e of ne 1. the discovery of a desirable characteristic in a population. 2. better survival or reproduction rates by individuals with a particular genetic characteristic. 3. an individual’s physiological modification. 4. environmental change that forces modification in a resident species. 5. a population’s physiological modification 1 th ov e ab s er gy an e en la r ur ric H So s id e Ef fe ct rt na or io lis Lu C e Th no Fossils show life’s history Evolution occurs as a result of 0% rb on . n. 0% th 0% e 0% n. 0% tr oy 0% 0% 2 0% 0% 3 4 Extinction • Most species that once lived are now gone • Extinction is the disappearance of a species from Earth – Species last 1–10 million years • Biological diversity is now being lost at an astounding rate – This loss of species is irreversible 0% 5 • A fossil is an imprint in stone of a dead organism • Phylogenetic trees and the fossil record show: – Life has existed on Earth for 3.5 billion years – Life evolved complex structures from simple ones – Life evolved large sizes from small ones – But natural selection can also favor simplicity and small size Some species are vulnerable to extinction • Extinction occurs when the environment changes rapidly • Many factors cause extinction: – Climate change, changing sea levels, severe weather – Arrival of new species, small populations – Specialized species • Endemic species exist only in a certain, specialized area – Very susceptible to extinction – These species usually have small populations • Island species Number of species = speciation – extinction 4 2/16/2015 Earth has had several mass extinctions • Background extinction rate: extinction usually occurs slowly, one species at a time • • Mass extinction events killed off massive numbers of species at once • Occurred five times in Earth’s history • 50–95% of all species went extinct at one time Cretaceous-Tertiary (K-T) event: 65 million years ago • A gigantic asteroid caused dinosaur extinction • End-Permian event: 250 million years ago • 75–95% of species went extinct The sixth mass extinction is upon us • Humans are causing the sixth mass extinction event – Population growth, development, resource depletion – Destruction of natural habitats – Hunting and harvesting of species – Introduction of non-native species • This loss affects humans – We need organisms for food, fiber, medicine, services • Amphibians are disappearing faster than any other group – 170 species have already vanished We study ecology at several levels • Ecology studies interactions among organisms abd their enviroment • Ecology and evolution are tightly intertwined Species to ecosystems • A species is a “type” of organism • A population is all members of a species living in a given area at the same time • A community consists of all of the populations of organisms living and interacting in a particular area • An ecosystem is the biological community and its physical environment 5 2/16/2015 Levels of ecological studies • Organismal ecology examines relationships between individuals and their environment • Population ecology investigates population changes – The distribution and abundance of individuals – Why some populations increase and others decrease • Community ecology focuses on patterns of species diversity and interactions • Ecosystem ecology studies living and nonliving components of systems to reveal patterns – Nutrient and energy flows Each organism has habitat needs • A habitat is the environment where an organism lives – It includes living and nonliving elements • Species use different criteria to select habitat – Soil, topography, vegetation, other species • Species have different habitat needs – Depending on body size, season, etc. • Species survival depends on having suitable habitats The niche • A niche is an organism’s use of resources – Along with its functional role in a community – Habitat use, food selection, role in energy and matter flow, interactions with other individuals • Specialists have narrow niches and specific needs – Extremely good at what they do – But vulnerable when conditions change • Generalists are species with broad niches – They use a wide array of habitats and resources – Survive in many different places Population size • Number of individuals that contribute to a population’s gene pool • Immigration & Births add individuals • Emigration & Deaths subtract individuals Population • Populations can be described by vital statistics or demographics – – – – – Size Age structure Sex ratio Density Distribution Population density • Population density is the number of individuals in a population per unit area • Large organisms usually have low densities – They need many resources and a large area to survive • High densities make it easier to find mates – But increase competition and vulnerability to predation – Also increase transmission of diseases • Low densities make it harder to find mates – But individuals enjoy more space and resources 6 2/16/2015 Population distribution Sex ratios and age structure • Sex ratio is the proportion of males to females • Population distribution (dispersion) is the spatial arrangement of organisms • Random - haphazardly located individuals, with no pattern – Resources are widespread • Uniformn - evenly spaced individuals – Territoriality, competition – In monogamous species, a 1:1 sex ratio maximizes population growth • Age structure (distribution) is the relative numbers of organisms of each age in a population – Helps predict population growth or decline • In species that continue growing as they age – Older individuals reproduce more (e.g., a tree) – Experience makes older individuals better breeders • Clumped - most common in nature – Arranged according to resources Population age structure • Divide population into age categories Four factors of population growth or decline • Natality - the births within the population • Mortality - deaths within the population • Immigration - arrival of individuals from outside the population – Births and immigration add individuals to a population • Emigration - departure of individuals from the population – Deaths and emigration remove individuals Population growth rate • Growth rate is the rate of change in a population’s size per unit time – Equals (birth rate + immigration rate) – (death rate + emigration rate) – Tells us the net changes in a population’s size per 1000 individuals per year • Growth rate is expressed as a percent Exponential population growth • In exponential growth, a population increases by a fixed percent – Graphed as a J-shaped curve • It occurs in nature with: – Small populations – Low competition – Ideal conditions 7 2/16/2015 Limiting factors restrain population growth • Exponential growth rarely lasts • Limiting factors: physical, chemical, and biological attributes of the environment limiting population growth • Environmental resistance is all limiting factors together – Stabilizes the population size at its carrying capacity – Terrestrial animals -space, food, water, mates, shelter, breeding sites, temperature, disease, predators – Plants- sunlight, moisture, soil chemistry – Aquatic systems - salinity, sunlight, temperature, etc. Population density affects limiting factors • Density-dependent factors are limiting factors whose influence is affected by population density – Increased density increases the risk of predation, competition for mates, and disease – Results in the logistic growth curve – Environmental resistance has a stronger effect on larger populations • Density-independent factors are limiting factors whose influence is not affected by population density – Temperature extremes, floods, fires, and landslides Carrying capacity • Carrying capacity is the maximum population size the environment can sustain – Determined by limiting factors • Limiting factors slow and stop exponential growth – Forms an S-shaped logistic growth curve Carrying capacities can change • Environments are complex and ever-changing – The carrying capacity can change • Humans lower environmental resistance for ourselves – Increasing our carrying capacity – Technologies have overcome limiting factors – We have appropriated immense amounts of resources • But by increasing the carrying capacity for humans – We have reduced the carrying capacity for countless other organisms – Calling into question our own long-term survival Conserving biodiversity • Human development, resource use, and population pressure are changing populations and communities • Factors threatening biodiversity have complex social, economic, and political roots – We must understand these factors to solve problems • Millions of people are working to protect biodiversity and to safeguard ecological and evolutionary processes Costa Rica’s protection is paying off • Costa Rica was losing forests at the world’s fastest rate – Now, 25% of its area is under protection • Ecotourism is when tourists visit protected areas – Ecotourism provides thousands of jobs and billions of dollars to Costa Rica’s economy 8