Populations

• Population is a group of interbreeding same species organisms occupying a particular habitat. Ecosystems are dynamic and always subject to change.
• Factors to population change:

  Birth/cell division rate: The reproductive capacity of a population.

  Death rate: Mortality rate

  Immigration: The movement of individuals into a population of the same species.

  Emigration: The movement of individuals out of a population of the same species.
•   Population growth curve for an equilibrium species (controlled within a stable habitat through competition)

  If conditions of temp & nutrients are favourable the usual pattern of growth is sigmoidal.

  E.g. rabbits newly introduced into a not well established area

  or bacteria placed into a fresh nutrient solution.

  
• Lag phase- Slow rate of reproduction. Enzyme synthesis. Lagged time for individuals to reach sexual maturity in sexual reproducing organisms. For yeast in nutrient broth it is the time taken to hydrate.
• Log phase- Maximum rate of reproduction rate > death rate. There are no factors limiting growth. However, environmental resistance (all factors limiting growth of population)occurs at end of log phase e.g. Glucose availability, intraspecific comp for food, predation, disease, toxc waste build up.
• Stationary phase - Growth stops due to environmental resistance. Birth rate equals death rate. Population has reached carrying capacity (maximum no. of individuals a population can sustain within a particular environment. Actual no. will fluctuate due to environmental change. Yeast change from asexual to sexual reproduction as they reach stationary phase & some survive as spores.
• Decline phase - Death rate exceeds birth rate. Environmental factors fully take over. E.g. glucose run out of nutrient broth.
• Density dependent factors:

  Factors have a greater effect the larger population size (more likely to slow down population growth rate).

  • Disease
  • Food availability
  • Toxic waste build up
• Density independent factors:

  Factors that have an effect regardless of the size of the population (more likely to cause a population crash).

  • Floods
  • fires
  • Sudden temperature changes
• Intraspecific comp- comp of same species

  Interspecific comp-comp of diff species.
• Niche- One species can occupy a particular niche within an ecosystem.

  Specific role & position a species plays within an ecosystem.
• In area where abiotic variables are uniform-

  Sampling techniques:

  1.10m x 10m tape measurer

  2. use random coordinates to determine where to place 1m2 quadrat.

  3. Count percentage cover (if it is difficult to count individual plants).

  4. Repeat at 10 random coordinates.

  5.Calculate a mean for each species.
• In an area where there is a change is abiotic factor:

  Random placement of quadrats are unsuitable if there is an environmental gradient like light intensity. A transect along gradient should be used.
• If you wanted to sample the change in species over time within an area:

  1.10m x 10m tape measurer 2. use random coordinates to determine where to place 1m2 quadrat.3. Count percentage cover (if it is difficult to count individual plants).4. Repeat at 10 random coordinates.5.Calculate a mean for each species.

  Set a permanent area within the habitat. Grid would be visited periodically. to gain comparison.
• Ecosystem is a characteristic community of interdependent species interacting with abiotic components in their habitat.

  Habitat is place where organism lives.
• Community is a population of different species living in the same habitat.
• Photosynthetic efficiency:

  energy incorporated into photosynthetic products/ total light energy falling onto plant x 100
• Why isn't all light energy that falls into a plant absorbed by photosynthetic pigments?

  1.Wrong wavelength can't be absorbed by chlorophyll pigment. e.g. UV, infrared light.

  2.Green light is reflected by chlorophyll pigment.

  3.Light is transmitted straight through the leaf not absorbed by chlorophyll pigment.
• Gross primary productivity- Rate of production of chemical energy into organic chemicals by photosynthesis.(kjm-2year-1).

  Net primary productivity-Energy in plant biomass (dry weight of organic matter)& potential energy available to heterotrophs in ecosystems.

  NPP= GPP- Respiration.
• Why don't consumers take all of this potential energy?

  Some parts of a plant are inedible- roots & bark, bones, fur etc.

  Some parts are egested- cellulose.

  Some parts are lost as metabolic heat.

  Some parts are excreted- urea.
• Biological productivity is rate at which biomass accumulates in an ecosystem.
• Describe how ecologists would be confident that all water had been removed but none of organic matter had been lost- Repeatedly heat dry mass in oven until constant mass is recorded & ensure no combustion occurs.
• Gross ecological efficiency (measure of energy transfer)= Energy in trophic level/ energy in previous trophic level x 100
• Secondary productivity: rate at which consumers accumulate energy from assimilated food in biomass in their cells.

  NSP= Ingested- (egested +excreted+ respiration) NSP=I(E+R).
• Why do carnivores have more efficient energy conservation than herbivores?

  Protein is more rapidly/easily digested than cellulose.

  A lot of cellulose is lost in faeces of herbivore.
• Why do farmers keep animals in barns in winter?

  Won't need as much energy maintaining core body temperature so more energy is available for biomass.
• Aquatic organisms are ectothermic so don't regulate their body temp so save lots of energy relative to warm blooded animals so have higher ecological efficiency.
• Pyramids of energy- quantitative account of feeding relationships in a community.

  Can't be inverted as energy is lost at each trophic level to next & can't be produced.

  Pyramids of energy are better than pyramids of biomass/numbers because it can't be inverted and accounts for efficiency of energy flow in an ecosystem.