BIOLOGY 281 Final

• Why are invasive species so successful?

  • Enemy release hypothesis: introduced species escape their coevolved enemies (like deer) which had kept their populations in check
  • EICA hypothesis: Evolution of Competitive Ability, wherein invasive species that shed their enemies can redirect biomass and energy to growth and reproduction
  • Resource hypothesis: more favorable environment than their native environment
• Lab experiments allow for control of all variables, but conclusions are possibly reductionistic.
• Field experiments allow for manipulation of variables, but conclusions may not be completely “natural”.
• Natural experiments may have confounding factors that go unaccounted for.
• Proper replication allows for an experiment to produce samples that are statistically independent from each other.
• Proper randomization allows for an experiment to eliminate possible confounding variables.
• Categorical variables: have a finite number of categories or distinct groups.
• Discrete variables: numerical variables that have a countable number of values b/w any 2 values
• Continuous variables: numerical variables with an infinite number of values between any two values
• A type I error (false-positive) occurs if an investigator rejects a null hypothesis that is actually true in the population.
• A type II error (false-negative) occurs if the investigator fails to reject a null hypothesis that is actually false in the population.
• Photons are denser in latitudes closer to the sun because the curve of the Earth is less. Therefore, locations at the equator receive the most solar energy.
• At higher latitudes, photos are filtered by the longer distance through the atmosphere, so they receive even less solar energy at those points.
• Tropical rainforests: temperature does not vary, but rainfall does
• Temperate forests: temperature and rainfall exhibit covariance
• Biomes change dramatically as the Earth’s climate changes.
• Genetic drift: chance events or disturbances determine which alleles are passed on to the next generation (mostly occurs in smaller populations)
• Gene flow: alleles are transferred from one population to another via movement of individuals or gametes
• Adaptive radiation: common ancestor gives way to multiple different species depending on different environmental adaptations
• Directional selection: type of natural selection in which one specific phenotype is favored over any others, resulting in a shift towards its expression

  • ex: thicker bills found in subsequent generations of finch offspring produces a shift in mean trait value
• Allopatric speciation: occurs when populations become physically separated from each other and eventually develop other reproductive barriers
• Sympatric speciation: evolution of a new species from a surviving ancestral species, in which the two species continually occupy the same geographical area

  • can arise through changes in food resources within the area, sexual selection, etc.
•  Living Dead study (research talk):

  • Study asked if rain forest trees isolated from the greater forest area experienced gene flow
  • Determination: Africanized honey bees “rescued” the trees by providing pollination, thereby connecting the trees to the forest via gene flow
• Microsatellite DNA markers are short sections of repeated non-coding DNA that are useful for parentage analyses, or determining the parents of an offspring, based on whether their genomes contain matching sequence repeats.
• Around 600 million years ago, photosynthesis had produced close to modern atmospheric oxygen and conditions for respiration and multicellular life.
• Plants can undergo photosynthesis when their stomata are open, but the leaf then loses water through transpiration.
• Photorespiration: enzyme rubisco acts on O2 instead of CO2 (oxygenation), which forms a toxin and wastes CO2 and energy
• C3 photosynthesis: standard type, uses Rubisco as carboxylase 

  • less water-efficient and has higher photorespiration susceptibility
• C4 photosynthesis: uses PepC as carboxylase, separates CO2 fixation and the Calvin cycle into 2 cell types
• CAM photosynthesis: CO2 fixation processes occur at night while Calvin cycle occurs during the day
• Both C4 and CAM photosynthesis evolved to minimize photorespiration waste.
• Ecological stoichiometry is the study of ratios of essential elements (C, N, and P) in organisms

  • Most organisms have different ratios that must be maintained
• Acclimatization is different from adaptation because it occurs on the basis of changing an individual’s physiology in response to environmental conditions; adaptation marks changes in a population’s traits over time.
• At the thermal neutral zone, endotherms expend little energy to maintain body temperature.
• Although ectotherms cannot function outside of a narrow range of thermal environments, they do not need complex regulatory machinery in their bodies and do not need to eat as much to maintain temperature.
• Saguaro cactus features that allow for temperature regulation:

  • Widespread but shallow root systems to draw up fleeting amounts of rain
  • Large mass and pleated skin to store large amounts of water
  • Contain spines: modified leaves that provide shade and reduce water loss
  • Perform CAM photosynthesis
  • Have columnar shape and perpendicular orientation that exposes relatively little surface area to the sun at midday
• Marginal value theorem is the optimal amount of time an organism should spend foraging at a given foot area to maximize its resource consumption/use, before traveling to a different area.
• Birds demonstrate “leaky” monogamy to increase their fitness (some female birds will have extra pair copulations)

  • It may protect against possible male infertility, increase genetic diversity in offspring, increase what the female recognizes as “genetic quality”, or create incentive for cooperation with males of neighboring territories.
• Hamilton’s model of indirect selection posits that an individual can support their own fitness by making contributions that enhance the survival of genetic relatives, as long as B* r > C

  • B is the benefit of a given behavior, C is the cost of that same behavior, and r is the coefficient of relatedness between the organism and the recipient
• Typically currencies of life history:

  • number of offspring
  • size of offspring
  • number of reproductive events
  • parental care
  • age at first reproduction
  • pre or post-reproductive dispersal