knowledge-22 PAE

• Species- a group of organisms with similar characteristics , which can breed to produce fertile offspring and are reproductively separated from other species.
• population: a group of organisms of the same species occupying a particular space at a particular time.
• Gene pool : the set of all alleles of the same species occupying a particular space at a particular time.
• Allele frequency: the occurrence of a given variety of gene in a given population.
• Environmental conditions that cause variation:

  The conditions in which an organism develops can cause variation.
• Mutation - the random change to the structure of a DNA molecule or the structure or number of chromosomes.
• Meiosis has two main events that cause variation:

  • independent assortment of homologous chromosomes causes variation between gametes.
  • crossing over between the non-sister chromatids of homologous chromosomes.
• Random fertilization of gametes where two gametes meet by chance , contributing to novel combinations of genes.
• in a population , not all organisms survive to be able to reproduce. individuals die or fail to reproduce due to:

  • predation
  • disease
  • competition for resources.
• Organisms with variations that allow them to survive are more likely to reproduce - they have a selective advantage.
• Only favorable alleles are preferentially passed onto the next generation . Those frequencies increase in the gene pool.
• Evolution is the change in allele frequency within a population and if different populations of the same species face different selection pressures this can lead to a new species emerging.
• Stabilizing selection is when phenotypes at the extremes are selected against , this causes the alleles of the middle range to be favored.
• Directional selection is when conditions gradually change , the individual with the adaptive phenotype survives and reproduces , this changes the frequency of the phenotype.
• Disruptive selection is when the two extremes of a phenotypes are favored , this lead to an increase in the frequency of the extreme phenotype.
• Speciation:

  In given population , under certain conditions, a new species can arise from existing species.

  If two populations are reproductively separated , differences in their gene pools can accumulate .

  If these differences make it impossible for the two populations to breed and produce fertile offspring , then they become two species.
• Allopatric speciation has driven the majority of species formed and has been predominant on land masses that experience cycles of geographical fragmentation.
• Sympatric speciation occurs without separation of populations due to geography , but at the generic level.
• Genetic drift - is the random change of allele frequency due to only some of each generation reproducing. This is more apparent in small population, because chance changes can have greater influence.
• Abiotic- non-living parts of the environment
• biotitic conditions involve the living parts of an environment.
• Ecosystem can be very small or large. They are made up of the interactions between the community and the abiotic features of the environment.
• Habitat is the place an organism lives within an ecosystem.
• Community is the total number of all populations living together in a particular habitat.
• Niche is a space within a habitat in which a species survives.
• Carrying capacity is the size of a population an ecosystem can support , which varies due to abiotic factors and interactions between organisms.
• interspecific competitions - organism from different species compete for the same resource.
• Intraspecific competition - organisms of the same species compete for the same resources.
• Predation - the number of predators determine number of prey and vice versa.
• communities change over time by ecological succession
• Primary succession can occur on bare rock , which is first colonized by pioneer species. Over the years , grasses and perennials colonize, followed by small trees and shrubs then larger trees until a climax community stabilizes on the land.
• Some climax communities reduce biodiversity , to maintain habits and biodiversity , succession has to be managed.
• Slow moving and sessile (non-moving) organisms quadrats can be used to sample a habitat and estimate the population size of a species.
• Quadrats can be placed randomly over a given area ( a random number generator can be used) or along a belt transect.
• Measure of abundance of sessile species percentage frequency is the probability is the probability that a species will be found within a single quadrat.
• frequency = number of quadrats in which the species is found / total number of quadrats
• Mark- release- recapture . methods are used for organisms that move around. It involves capturing a random sample using humane traps , marking those captured , releasing them to mix with the population , then some time later setting traps up again. A proportion of marked organisms will be caught and from this the population size can be estimated.
• Population size = (total of first sample x total of a second sample) / marked organisms in second sample.