Populations and communities

• define population 


  population is a group of individuals of same species in same area at the same time
• Outline factors that affect population size

  abiotic factors

  biotic factors

  intrinsic factors
• Assumptions of Lincoln Index 


  • closed system of populations, no immigration
  • time between samples are small compared to lifespan
  • the marked organisms must mix again completely
• Define carrying capacity


  amount of population that an environment can support without habitat degradation
• Outline factors that limit growth

  • interspecific and intraspecific
  • competition for resources
• Outline Density dependent limiting factors, with named examples


  competing for food mates and nesting sites

  examples: predators, parasites and pathogens
• Outline the density independent limiting factors 


  Abiotic factors: Sunlight, temperature, rainfall
• Explain what happens if carrying capacity is exceeded?


  Increased d-d factors such as competition & predation for the resources as theres a large population with limited resources
• Explain what happens if populations are below the carrying capacity?


  can lead to higher reproduction and decrease in death eventually, only occurs when d-d factors will take into action
• Outline the models used for quantifying population growth

  • exponential
  • logistic
  • demographic representations (humans mostly)
• Define community 


  community refers to all the organisms that live together in a place
• Key features of an intraspecific competition 


  • The ultimate effect is a decrease in reproduction or survival
  • the effects are density dependent
• Outline examples of intraspecific competitions


  plant= more complex root structure for spatial and temporal partitioning

  animal= mates for reproduction purposes
• Outline all Interspecific Interactions


  1. Herbivory
  2. predation
  3. interspecific competition
  4. mutualism
  5. parasitism
  6. pathogenicity
• Root nodules in legumes form in the roots offer a place with plenty of sugars for rhizobium bacteria so that nitrogen can be fixated
• Mycorrhizal fungi attach to plants by penetrating the orchid root and provide nutrients for the plant
• Zooxanthellae are photosynthetic organisms and attach to corals and produces carbon dioxide, the corals allows the zooxanthelae to use carbon diozide and water
• Endemic species= occur naturally in an area
• Alien species= introduced by humans deliberately or accidentally
• Competitive exclusion theory


  they will not exist with the same amount of population, one of them should reduce while the other increases
• Chi squared is used to test for association between species (positive, negative, no association)
• when predation increases, prey decreases(vice versa)
• Top down: top predator controls population dynamics via an oscillating cascade effect and is related to food supply of prey
• bottom up: plants are consumed too rapidly by prey for replacement to keep up (lead to crash from herbivore to predators)
• Allelopathy: release secondary metabolites to gain a competitive advantage over other plants (i.e. CHEMICALS)
• Sage (allelopathy) releases benzoxazinoid compounds to inhibit germination and growth of annual plants