Assessment of biodiversity Australia’s biodiversity Species richness Species Diversity Simpson’s Index
Things you need to know • Australia is internationally recognised as one of the 12 countries with major repositories of biological diversity and the only one with a developed economy. • The 12 regions combined account for 75% of the total biodiversity of the planet. • It is estimated that Australia has 450 000 species. This is 9% of all species on Earth.
Assessing biodiversity • Measuring the diversity for comparative purposes requires the ecologist to look at 3 distinct categories. • The number of species • Simply the number of species found in a given area • Species richness • The number of different species present, ranks each species present as equal. A rare species will be counted equally with a common species and even and introduced species. This term and the above are interchangeable. • Species diversity • Takes into account the relative abundance of each species present as well as the number of different species.
Simpson’s Diversity Index • This diversity index estimates the probability of two specimens belonging to the same species and was first developed in 1949 • Where: N= number of species • = sum of • Pi= the proportion of individuals belonging to species i. • The index gives relatively little weight to rare species and more weight to common species. • The higher the value the higher the diversity
Shannon-Weiner Diversity Index • Historically, the index has been used to measure the effects of habitat quality such as effects of pollution effluents. • Recently, this index has fallen out of favor because it doesn’t take into account habitat specific parameters required by specific species. • The symbols used are the same as those for Simpson's index. • The higher the value the higher the diversity
Example • As an example, let us work out the value of D for a single quadrat sample of ground vegetation in a woodland. Of course, sampling only one quadrat would not give you a reliable estimate of the diversity of the ground flora in the wood. Several samples would have to be taken and the data pooled to give a better estimate of overall diversity. How many samples?
Example Results. • Simpson’s index • D= 1-p2 • D= .496 • Shannon’s Index • H = 1.28 • Online calculator used • G:\Unit 3 Environmental Science\aos2 biodiversity\Biodiversity Calculator of the Simpson and Shannon-Wiener Indexes.mht
Endemism as a way to evaluate biodiversity • A species is considered to be endemic if it is restricted to that area only. • Why are the majority of Australian species endemic to this continent? • The endemism of the biodiversity of a region can be expressed as the percentage of endemic species present. • 90% of mammals, 93% of frogs,89% of vascular plants and reptiles are endemic to Australia. • Why would birds be much lower than the figures above, estimated to be at 45%?