C4.1 :

• Population :

  • Group of individuals of the same species living in the same geographical area and time period & able to interbreed.
• What isolates populations :

  • Restrict gene flow due to reproductive isolation :
  • Temporal - exist in different time periods/reproduce during a different time period.
  • Geographical - physical seperation by geographical barriers.
  • Behavioural - different behaviours in terms of reproduction.
• Sample :

  • Small part of individuals used to model the entire ecosystem.
• Use for sampling populations :

  • Used to estimate the number of individuals in an ecosystem as individually counting is hard to do.
• Sampling error :

  • Difference between estimated population size & actual population size.
• Random sampling :

  • Randomly selecting random sectors in a geographical area to then count the number of individuals present.
  • Then do this & average the value.
  • Multiple the average per area by number of areas to get your estimated size.
• Use of randomness in sampling :

  • Removes any biases from investigators.
  • Obtain a more representative sample to accurately reflect overall population.
• How to capture sessile & motile organisms :

  Motile -> Capture-mark-relase-recapture method.

  Sessile -> Random sampling using quadrats.
• Quadrat :

  • Square with a certain size used to measure a sample.
• Systematic sampling :

  • Where line/grid is set up.
  • Obtain samples at regular intervals (e.g : every 10m).
• Capture-mark-release-recapture method :

  • Used to sample motile organisms.
  • Capture a sample of the population & mark them.
  • Release the individals -> capture another sample from the same geographical area & count the number of marked/unmarked individuals.
• Lincoln index :

  • Population size estimate = initial marked individuals x (recaptured individuals / marked recaptured individuals)
• Limitations to motile sampling :

  • Process may harm the individuals (i.e. pitfall causes limb damage).
  • Marking may lead to lower survivability -> visible to predators.
  • Assumption of closed population -> no im/emigration.
  • Assumption that ratio of marked-unmarked reflects total population.
  • No births/deaths assumed.
• How to increase accuracy of Lincoln index :

  • Increasing sample size.
  • Repeating sampling to create mean value.
• Carrying capacity :

  • Maximum number of individuals that a particular habitat can support.
  • K.
  • Dynamic.
  • Based on combination of limiting factors.
• Examples of limiting factors :

  • Availability of resources (nutrients/land/mates).
  • Disease.
  • Predation.
  • Build up of waste products.
• Population density :

  • Number of individuals per unit area/volume.
• Density dependent factors :

  • Factors that influence a population based on population density.
  • E.g : competition/predation/diseases.
  • Act as negative feedback mechanism to regulate & control population size.
• Density independent factors :

  • Factors that influence a population regardless of its size/density.
  • E.g : climate change/forest fire/volcanic eruption.
• Conditions for exponential population growth :

  • Unlimited food & water.
  • No diseases.
  • No barriers to mating.
  • Unlimited land.
  • No predators.
• Population growth curve :

  • Sigmoid (S) curve used to represent population growth in real-world ecosystem.
  • 1 : Exponential -> number of organisms exponentially increases due to abundant resources (no competition).
  • 2 : Transitional -> growth rate slows down as some factors have competition -> density-dependent factors come into play.
  • 3 : Plateau -> number of individuals stabilises as carrying capacity is reached due to diminishing resources.
  • It fluctuates

  
• Exponential growth curve :

  • Exponential (J) curve used to represent population growth in an ideal ecosystem.
  • Growth continues to happen exponentially due to unlimited resources.
• Intraspecific relationships :

  • Relationships between individuals of the same species.
  • Competition & Cooperation.
• Competition :

  • Individuals of species compete with others for limited resources -> food, water & space.
  • Lead to adaptation to niches, displacement of less competitive individuals & maintain population size.
• Cooperation :

  • Individuals of species work together to increase chances of reproduction & survival.
  • Social animals do this.
• E.g of competition :

  Animal -> bird for mates.

  Plants -> trees extend roots for water.
• E.g of cooperation :

  • Animal -> bee work together in hive.
  • Plant -> Amoeba combine to help with spore distribution.
• Community :

  • Group of populations living & interacting with each other in an area.
  • Coral triangle :
  • Coral polyps build foundation.
  • Fishs inhabit the area.
• Herbivory :

  • Herbivore (organism that consumes plant matter only) feeds on plants.
  • Giraffe -> leaves.
• Predation :

  • When an animal (predator) consumes another animal (prey).
  • E.g : Lion -> Zebra.
• Parasitism :

  • One organism benefits off the other, whilst the other experiences loss.
  • E.g : Tapeworm -> humans
• Pathogenic :

  • Relationship where microorganism causes disease to other organism.
  • Covid -> Human.
• Mutualism :

  • Both organisms benefit off the relationship.
  • Bees -> flowers.
• Competition (interspecific) :

  • Species competes with another species for resources.
  • E.g : Grey vs Red squirrel.
• Root nodules & Fabaceae :

  • Root nodules contain nitrogen fixing bacteria -> provide nutrients to plant (N).
  • Plant photosynthesis -> provide carbon compounds to bacteria.
• Mycorrihiaze & Orchid :

  • Fungi colonise roots of Orchid -> pass on nutrients due to high s.a of roots.
  • Orchids -> provide nutrients from photosynthesis.
• Zooxanthellae in hard coral :

  • Algae photosynthesise to produce nutrients -> give to hard coral.
  • Hard coral produce sheltered environment.
• Interspecific relationship :

  • Relationship between 2 different species.
• Endemic species :

  • Species that is found in the region.
• Invasive/Alien species :

  • Species that is not typically found in region.