CHAPTER 5: ASSESSING THREAT IN CONSERVATION
Risk: The possibility of suffering some harm as a result of some activity. (Includes: physical damage or injury, economic loss or environmental damage)
Risk Assessment: Using data to estimate the probability of some harmful event occurring. Used in the conservation of biodiversity.
Risk of Extinction
Approaches to estimate the risk of extinction:
Approach 1
o Theory of island biogeography to estimate the number of species that can be maintained in a given area
o Used to predict the effects of habitat loss and fragmentation on species and to estimate the size of reserves necessary to preserve species.
o Have a high level of uncertainty, used with caution
Approach 2
o Uses collections of organisms in herbariums and museums. Classifies an organism as extinct if it has not been collected for some period time. (50 years) – does not consider that some species live in very remote areas.
Data used to calculate the probability a species is extinct (or not) if the fact that they have been collected over time is taken into account.
If not extinct, calculated by considering time since the last collection or sighting, the time since the species was first collected and no. of specimens collected.
• If last collection is recent, high probability species is not extinct
Population Viability Analysis
Technique that assists with risk management in conservation biology. Used to examine how management decisions may produce changes in population numbers and affect the risk of extinction
o Allowing managers to rate different management options and highlight areas where more research is needed.
Used in managing several Australian mammals (e.g eastern barred bandicoot and Leadbeater’s Possum)
o Involves construction of a computer model of population under investigation and incorporates the available demographic and ecological data . + likely sources of variability or threats (e.g environmental variation, demographic variation and fragmentation)
This process fills in gaps and identify what needs to be researched
o Model used to generate a series of population projections and probability of each occurring.
Different management strategies evaluated by comparing outcomes based on different inputs.
o Can also help determine a minimum viable population for a species. i.e the smallest population that has a reasonable probability of surviving for some time into the future.
Useful for estimating the minimum size of a conservation reserve for a species should be.
o Models not a perfect tool for managing rick in conservation biology
As there is no complete data on any species
Conservation Categories
When a species is classifies according to their conservation status, it provides a framework for setting priorities for the allocation of the limited resources available for conservation.
o Classifies plant and animals from ‘extinct’ to varying levels of risk to ‘under no immediate threat.’
Components that contribute to the rarity of a species:
o A species’ rarity depends on the combination of each factor
Population size – density of no. of individuals within a local area (high to low)
Geographic Range – the spatial distribution of the species (restricted to widespread)
Specificity of habitat – the variety of ecological conditions within which a species can survive (wide or general / specific or narrow)
o A population described as rare is not necessarily faced with imminent extinction.
The International Union for the Conservation of Nature (IUCN) has a classification scheme that is widely used in conservation management.
o Extinct – there is no reasonable doubt that the last individual has died
o Extinction in the wild – the taxon is known to survive in cultivation, in captivity or as a naturalised population well outside its past range. Exhaustive surveys have failed to record an individual in the wild.
o Critically Endangered – the taxon is facing an extremely high risk of extinction in the wild in the immediate future.
o Endangered – The taxon is not critically endangered but is facing a very high risk of extinction in the wild in the near future.
o Vulnerable – the taxon is not endangered, but is facing a very high risk of extinction in the wild in the medium-term future.
o Near threatened – the taxon is close to meeting the threatened thresholds or would be threatened were it not for an ongoing taxon-specific conservation program.
o Least concern – has been evaluated to have a low risk of extinction
o Date deficient – there is inadequate info to make a direct or indirect assessment of its risk of extinction based on its distribution or population status.
o Not evaluated – the taxon has not yet been assessed against the criteria.
Threatened taxa: critically endangered, endangered, vulnerable)
Criteria include assessments of the species’ population size, geographic distribution, no. of mature individuals in the population and estimate of probability of future extinction in the wild.
Taxon: A group of one or more populations of an organism or organisms seen by taxonomists to form a unit.
Useful to have these system of conservation categories to determine when species fit into the three categories of threatened taxa. Also helps determine priorities and planning conservation programs.
STUDY DESIGN
Measuring Changes in Biodivserity
Threats to Biodiversity
• predictions of species population survival using probabilities including likelihood of extinction
• conservation classification of species and how this depends on measures including changes in the geographic range and number of individuals within that range, the date the species was last recorded, and the extent of habitat.
• assessment of threat in defining conservation categories for a species and/or ecosystem, including extinct in the wild, conservation dependent, critically endangered, endangered, and vulnerable.