demographics
advertisement
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 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 Evolution by natural selection Evidence of natural selection is everywhere Artificial selection is the process of selection conducted under human direction Artificial selection 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 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 Speciation results in diverse life forms Phylogenetic trees are branching diagrams show relationships among species, groups, genes, etc. Represent life’s history Convergent evolution Similar conditions lead to similar adaptations Species look alike even if they are not related Divergent evolution Species evolve into different types to take advantage of opportunities in environment and reduce competition Respiration produces energy from • • • • • water, carbon dioxide, and sugar. Sugar and oxygen. oxygen, carbon dioxide, and sugar. carbon dioxide, enzymes, and sugar. oxygen, water, and sugar. Producers rely on ____________ to capture chemical energy and consumers rely on ____________ to release chemical energy. • • • • • • • • • cellular respiration; photosynthesis cellular respiration; cellular respiration photosynthesis; cellular respiration photosynthesis; photosynthesis the sun; the sun _______ drives the hydrologic cycle by producing rain and snow from evaporated surface water. Lunar tides The Coriolis Effect Hurricanes Solar energy • • • • • • none of the above Fossil fuels and living trees are known as “carbon sinks” because • they have no carbon. • they create carbon. • they destroy carbon. • they store carbon. • due to gravity, carbon is found closer to the ground. Evolution occurs as a result of the discovery of a desirable characteristic in a population. better survival or reproduction rates by individuals with a particular genetic characteristic. an individual’s physiological modification. environmental change that forces modification in a resident species. a population’s physiological modification Fossils show life’s history 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 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 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 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 and their environment 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 Species Populations Community Ecosystem 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 Populations can be described by vital statistics or demographics Size Age structure Sex ratio Density Distribution Population size Number of individuals that contribute to a population’s gene pool Immigration & Births add individuals Emigration & Deaths subtract individuals 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 Population distribution 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 Clumped - most common in nature Arranged according to resources Sex ratios and age structure Sex ratio is the proportion of males to females 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 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 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. 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 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 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
