Edexcel IGCSE Biology 复习笔记 4.1.3 Biodiversity

• Biodiversity is the range and variety of different species of organisms on Earth, or within an ecosystem
• It considers not only the species richness but the variation within each species, its distribution and population size
  • E.g. a high biodiversity would be found in an environment with lots of different species which show a lot of variation and are living in, all evenly distributed across the study area

   

• Many human activities are reducing biodiversity in individual ecosystems and on a global level
  • E.g. waste production, deforestation and global warming

   

The importance of biodiversity

• Different species depend on each other for:
  • Food
  • Shelter (eg. birds nesting in trees)
  • Maintenance of the physical environment (eg. tree roots provide stability for soils, ensuring they do not get washed away. This in turn provides a stable habitat for other plant species)

   

• High biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for these three things
• Populations with high levels of diversity are also more likely to be resilient to sudden environmental impacts or disease
• Consider the food web below:
  • If the mouse population was suddenly wiped out, the fox and the hawk populations might decrease but would not be wiped out as mice are not their only food source
  • This example ecosystem has sufficient biodiversity to support the fox and hawk populations
  • The fox population can still depend on the rabbit and frog populations for food
  • The hawk population can still depend on the frog and sparrow populations for food

   

A food web demonstrates the importance of biodiversity within an ecosystem

We can investigate biodiversity with quadrats using a similar method to the one used when investigating population size

Apparatus

• 2 tape measures
• Quadrat
• Random number generator
• Species key

Method

• Use 2 tape measures to lay out your first survey area (e.g. 10m X 10m)
• Use a random number generator to create a set of coordinates to place your first quadrat
  • E.g. for coordinates 4,5, you would place your quadrat 4m along on the x-axis and 5m along on the y-axis

   

• Count the number of different species found within that quadrat
• Repeat this process until you have collected the data for 10 quadrats
• Repeat these steps for the second survey area

The method for how to investigate biodiversity using a quadrat

Results

• The simplest indicator of biodiversity in this investigation is simply to compare the number of different species found in each survey area
• A higher level of biodiversity would be indicated by a larger number of different species found in that area
• However, this measurement of biodiversity is very simplistic as it doesn't tell us about the distribution or population size in either survey area
• As with species abundance, the biodiversity is likely to be influenced by biotic factors such as:
  • Competition
  • Predator-prey relationships
  • Interactions with other organisms within the food chain or food web

   

• Biodiversity will also be influenced by abiotic factors such as:
  • Light intensity
  • Mineral availability
  • Water availability
  • pH
  • Temperature
  • Salinity

   

Limitations

• As with the previous investigation (comparing abundance in 2 study areas), it can be easy to miss individual organisms when counting in a quadrat, especially if they are covered by a different species
  • Solution: Use a pencil or stick to carefully move leaves out of the way to check if there is anything else underneath

   

• Identifying species or distinguishing between species may be tricky
  • Solution: Use a species key to identify the species

   

Applying CORMS to practical work

• When working with practical investigations, remember to consider your CORMS evaluation

CORMS Evaluation

• In this investigation, your evaluation should look something like this:
  • C - We are changing the study area where we are collecting the data
  • O - We will count plant species each time (not animal, fungi etc)
  • R - We will repeat the investigation several times to ensure reliability
  • M1 - We will count the number of different plant species found across all quadrats
  • M2 -  this isn't really relevant in this scenario
  • S - We will control the size of the quadrat, the random way that quadrats are placed on the ground, the day that the results were collected