SL Content Statements

• C4.1.1

  Populations as interacting groups of organisms of the same species living in an area

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  Students should understand that members of a population normally breed and that reproductive isolation is used to distinguish one population of a species from another.
  

• C4.1.2

  Estimation of population size by random sampling

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  Students should understand reasons for estimating population size, rather than counting every individual, and the need for randomness in sampling procedures.
  NOS: Students should be aware that random sampling, instead of measuring an entire population, inevitably results in sampling error. In this case the difference between the estimate of population size and the true size of the whole population is the sampling error.
  

• C4.1.3

  Random quadrat sampling to estimate population size for sessile organisms

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  Both sessile animals and plants, where the numbers of individuals can be counted, are suitable.
  AOS: Students should understand what is indicated by the standard deviation of a mean. Students do not need to memorize the formula used to calculate this. In this example, the standard deviation of the mean number of individuals per quadrat could be determined using a calculator to give a measure of the variation and how evenly the population is spread.
  

• C4.1.4

  Capture–mark–release–recapture and the Lincoln index to estimate population size for motile organisms

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  AOS: Students should use the Lincoln index to estimate population size.
  Population size estimate = M × (N ÷ R), where M is the number of individuals caught and marked initially, N is the total number of individuals recaptured and R is the number of marked individuals recaptured. Students should understand the assumptions made when using this method.
  

• C4.1.5

  Carrying capacity and competition for limited resources

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  A simple definition of carrying capacity is sufficient, with some examples of resources that may limit carrying capacity.
  

• C4.1.6

  Negative feedback control of population size by density-dependent factors

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  Numbers of individuals in a population may fluctuate due to density-independent factors, but density- dependent factors tend to push the population back towards the carrying capacity. In addition to competition for limited resources, include the increased risk of predation and the transfer of pathogens or pests in dense populations.
  

• C4.1.7

  Population growth curves
  

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  Students should study at least one case study in an ecosystem. Students should understand reasons for exponential growth in the initial phases. A lag phase is not expected as a part of sigmoid population growth.
  NOS: The curve represents an idealized graphical model. Students should recognize that models are often simplifications of complex systems.
  AOS: Students should test the growth of a population against the model of exponential growth using a graph with a logarithmic scale for size of population on the vertical axis and a non- logarithmic scale for time on the horizontal axis.
  

• C4.1.8

  Modelling of the sigmoid population growth curve

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  AOS: Students should collect data regarding population growth. Yeast and duckweed are recommended but other organisms that proliferate under experimental conditions could be used.
  

• C4.1.9

  Competition versus cooperation in intraspecific relationships
  

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  Include reasons for intraspecific competition within a population. Also include a range of real examples of competition and cooperation.
  

• C4.1.10

  A community as all of the interacting organisms in an ecosystem

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  Communities comprise all the populations in an area including plants, animals, fungi and bacteria.
  

• C4.1.11

  Herbivory, predation, interspecific competition, mutualism, parasitism and pathogenicity as categories of interspecific relationship within communities

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  Include each type of ecological interaction using at least one example.
  

• C4.1.12

  Mutualism as an interspecific relationship that benefits both species

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  Include these examples: root nodules in Fabaceae (legume family), mycorrhizae in Orchidaceae (orchid family) and zooxanthellae in hard corals. In each case include the benefits to both organisms.
  

• C4.1.13

  Resource competition between endemic and invasive species

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  Choose one local example to illustrate competitive advantage over endemic species in resource acquisition as the basis for an introduced species becoming invasive.
  

• C4.1.14

  Tests for interspecific competition
  

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  Interspecific competition is indicated but not proven if one species is more successful in the absence of another. Students should appreciate the range of possible approaches to research: laboratory experiments, field observations by random sampling and field manipulation by removal of one species.
  NOS: Students should recognize that hypotheses can be tested by both experiments and observations and should understand the difference between them.
  

• C4.1.15

  Use of the chi-squared test for association between two species
  

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  AOS: Students should be able to apply chi-squared tests on the presence/absence of two species in several sampling sites, exploring the differences or similarities in distribution. This may provide evidence for interspecific competition.
  

• C4.1.16

  Predator–prey relationships as an example of density-dependent control of animal populations

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  Include a real case study.
  

• C4.1.17

  Top-down and bottom-up control of populations in communities

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  Students should understand that both of these types of control are possible, but one or the other is likely to be dominant in a community.
  

• C4.1.18

  Allelopathy and secretion of antibiotics

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  These two processes are similar in that a chemical substance is released into the environment to deter potential competitors. Include one specific example of each—where possible, choose a local example.