Evidence at Higher Level: The same statement as SL. At Higher Level, judge the evidence: how reliable a survey is, and when data from citizen scientists can be trusted.
Practise this as you read
- Discuss citizen science as a source of evidence.
- Compare two surveys using richness and evenness.
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The big idea: Reliable surveys from habitats all around the world show that biodiversity is falling fast: a biodiversity crisis.
The points to remember
- IPBES is the international panel of experts that reviews the evidence on biodiversity for the world's governments.
- Its 2019 global report estimated that about 1 million species of animals and plants are threatened with extinction.
- The Living Planet Index follows thousands of animal populations: on average they have fallen by about 70% since 1970.
- The evidence comes from many habitats, on land, in fresh water and in the sea.
- It must come from reliable surveys: careful methods, repeated over time.
Real example: North American birds: Combining decades of repeated bird counts, scientists estimated in 2019 that North America has about 3 billion fewer breeding birds than in 1970, nearly a third fewer.
Use the evidence the right way:
Evidence, not opinion: Say what the surveys and reports show, with a figure if you can. 'Everyone knows species are disappearing' is not evidence.
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The big idea: Surveys must be repeated, at the same places with the same methods, to show a change in species richness and evenness.
The points to remember
- Species richness: the number of different species in an area.
- Species evenness: how equal the numbers of each species are.
- One survey shows biodiversity at one time only.
- A repeated survey, same sites and same method, shows whether richness and evenness are falling.
- Evenness can fall before any species is lost, when one species takes over.
Real example: reef surveys: Divers count fish along the same lines on a coral reef each year. If one species becomes very common while others vanish, evenness falls even before any species is lost.
Read a single survey with care:
One survey shows no change: A single survey cannot be evidence of a crisis: a change needs at least two surveys to compare.
The big idea: Evidence comes from expert scientists and from citizen scientists. To be trusted, it is published and peer-reviewed so that others can check the methods.
The points to remember
- Expert scientists design surveys, identify species reliably and publish their results.
- Citizen scientists are members of the public who collect data, such as counting birds or insects.
- Benefits: many observers, huge areas, many years, low cost.
- Concerns: misidentified species, different effort or methods, and more records from easy places.
- Evidence is verifiable when it is published after peer review, so others can check the method.
Remember it as: Many eyes, checked by experts.
Citizen data: benefits
- Far more data than scientists alone
- Wide areas and long time spans
- Cheap to collect
Citizen data: concerns
- Species may be misidentified
- Effort and methods vary
- Bias to easy places and species
Real example: eBird: Birdwatchers around the world upload their sightings to eBird, which holds over a billion records. Scientists filter the records, for example removing unlikely sightings, before using them.
Weigh both sides:
Not useless, not perfect: Citizen data are not worthless and not automatically reliable. Say how methods, training and checking make them usable.
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How it is tested: Paper 1B: read survey data and say what changed. Paper 2: outline why surveys are repeated, or discuss evidence from citizen scientists.
IB-style questionDiscuss[3 marks]
Discuss the use of data collected by citizen scientists as evidence of a biodiversity crisis.
Model answer plan
See the answer broken into clear points, with guidance on how each point earns marks.
Name richness and evenness: When you read survey data, say what happened to the number of species and to how equal their numbers are.