Transcript Document
Ecosystems Part 2 Edge effects How the local environment changes along the boundary or edge in a habitat Caused by: natural events (tree fall) humans (deforestation) Results: Changes in species composition and diversity Vocabulary Interior species: can only live in the undisturbed core of a habitat Edge species: can live in edge habitats Open community: edge is gradual or has indistinct boundaries which many species cross over Closed community: community is sharply devided from its neighbors U.S. Roads 3.9 million miles of public roads in the United States. Wildlife and highways Road kill – animals that are killed by being run over by cars each year Millions of animals die each year Have a significant impact on populations Costs $8 billion per year Wildlife crossings: bridges and tunnels Ecosystem diversity Involves: Biodiversity Natural selection Evolution Ecosystem services Biodiversity Attempts to describe diversity of life at three levels: Genetic – range of all genetic traits in a population Species – number of different species that inhabit a different area Estimated between 10 and 30 million species on Earth Named around 1.5 million Ecosystem – the range of habitats that can be found in a defined area Biodiversity Increases Diverse habitats Moderate disturbance in the habitat Environmental conditions with low variation Trophic levels with high diversity Middle states of succession Evolution Decreases Extreme stress Extreme environments Extreme limitations in the supply of a fundamental resource Extreme amounts of disturbance Introduction of species from other areas Geographic isolation Natural Selection The mechanism of how organisms evolve Works on the individual level by determining which organisms survive and reproduce The range of genetic variation in a population determines if the species Natural Selection “Survival of the fittest” Fittest = how many babies you have who go on to have babies New genes enter the population through mutation Natural selection Types of selection Stabilizing Directional Disruptive Stabilizing Selection Selects against the extremes of a population Most common form of natural selection Results: Decreased diversity Maintenance of a stable gene pool No evolution Directional Selection Affects one extreme of a population Gives an advantage to other extreme Results Change in population characteristics Can lead to evolution of a new species Disruptive Selection Acts against the individuals in the middle Favors both extremes Results: Splitting of population into two smaller populations Results in evolution of two new species Evolution Change in the genetic composition of a population over successive generations Supported by evidence from: Fossil record Genetics Homologous traits Embryological similarities Computer models Speciation Results when segments of a population becomes isolated so gene flow stops The isolated populations eventually become new species Maintaining gene flow Some species of spiders balloon to disperse through the environment They let out a long strand of silk which is caught by air currents and transports them over long distances Patterns in Evolution (A) Divergent (adaptive radiation) – similar species become less similar (B) Convergent – Unlike species evolve similar (analogous) traits while evolving in separate ecosystems (C) Parallel – Two independent species evolve at the same time, in the same ecosystem, and acquire similar traits Convergent Evolution Adaptive Radiation Parallel Evolution Gradualism vs. Punctuated Equilibrium Gradualism Views evolution as slow, stepwise development of species over a long period of time Punctuated Equilibrium Proposes some species arose suddenly in a short period of time after long periods of stability Ecosystem services Things the environment does for us for free. Includes but not limited to: Moderate weather extremes and their impacts Disperse seeds Mitigate droughts and floods Cycle and move nutrients Detoxify and decompose waste Purify air and water