Biodiversity

Biodiversity is an abbreviation for biological diversity and is the variety of living organisms in an area. It can be measured at different levels.

Genetic diversity: refers to variation of genetic types within a species
Species diversity: refers to number of different species
Ecosystem diversity: refers to the variety of different types of habitats or ecosystems available

Methods of determining the diversity of species

Species richness. This is the number of different species in an ecosystem. It takes no notice of abundance and gives as much weight to those species which have very few individuals as to those who have thousands.

Species evenness. This is a measure of the relative abundance of the different species. A community dominated by one or two species is considered to be less diverse than one in which several different species have a similar abundance.

Percentage cover. If we want to know what kind of plants are in a particular habitat, and how many there are of each species, it is usually impossible to go and count each and every one present. Therefore, we use a quadrat and estimate percentage cover.

Percentage frequency. This is the probability that a species will be found within a single quadrat.

Percentage frequency = (number of quadrats in which the species is found/total number of quadrats) x 100

Simpsons Diversity Index (D). This measures the probability that two individuals randomly selected from a sample will belong to the same species. If you need extra help on calculating this, then head to the Simpsons Diversity page.

∑ = sum of

n = number of individuals

N = total number of individuals

The value of Simpsons Diversity Index ranges between 0 and 1. What does an index closer to 1 represent?

The greater the index value, the greater the sample diversity.

What are some problems associated with the percentage cover method of determining species diversity?

Very subjective. One drawback of this method is that plants in flower tend to be over-estimated while low-growing plants are under-estimated.

Comparing ecosystems across spatial and temporal scales

Ecosystems can be compared across spatial and temporal scales.

To understand how an ecosystem will respond requires accounting for the myriad interactions between biological and physical processes across spatial scales ranging from very local to global, and temporal scales ranging from within a day to decades.

Wikle, 2017

A spatial scale refers to the size of the ecosystem being considered. Ecosystems can be studied at a number of different sizes. Broadly:

Large scale: for example, an entire continent or ocean.

Medium scale: for example, a mountain range or desert.

Small scale: for example, a single local area such as a specific forest, paddock or mountain.

A temporal scale considers an ecosystem over a particular timeframe.

This can range from very small scale (i.e. hours to days) to medium scale (seasonal) to very large scale (years). A good example of this is succession, where pioneer species are the first to populate an area, but over time, a climax community will develop.

We can use a number of different factors to compare ecosystems.

Species diversity indices

This includes Simpsons Diversity Index (D), but there are a number of different indices that can be used. For example, the Menhinick Index:

D = species diversity

s = number of different species (i.e. species richness)

N = total number of individuals

On a walk in the Daintree rainforest, we saw 1 cassowary, 2 tree frogs, 2 golden orb spiders, 1 feral pig and 3 rufous owls. a) What is the species richness? b) Calculate D using the Menhinick Index.

a) Species richness = 5; b) D = 5/3 = 1.67

Ecologists studied the process of succession in an area of wasteland over a period of fifteen years. They calculated the index of diversity of the area every year. After three years, the index of diversity was 1.7. After ten years, it had risen to 4.6. What information concerning the organisms present in the area is suggested by the increase in the index of diversity?.

  • Increase in number of species
  • Increase in numbers of some species

Species interactions (biotic factors)

Predation: a species interaction where one species kills and eats another. These interactions can differ temporally. For example, certain predators will only hunt at night. Or one study found that some avian predators will match the activity patterns of songbirds, indicating predators can evolve temporal hunting strategies to exploit temporal patterns in prey behaviour.
Spatially, predator numbers are dictated by prey numbers in the local area, which are in turn affected by ecosystem resources.
Symbiosis: this is any type of a close and long-term biological interaction between species. This can be mutualistic, amensalistic, commensalistic or neutralistic. One study found that there is temporal variation in the algal symbiosis and growth of Astrangia poculata, that was related to seasonal temperatures.
Spatially, differences in mycorrhizal symbiosis between the same species of fungi and plant in two different ecosystems have been observed due to differences in precipitation levels.
Competition: where two or more species compete for the same resource. Can be between members of the same species (intraspecific competition) or different species (interspecific competition).
These interactions will differ dependent on the time of year (for example, males competing for mates around breeding season), and on the available resources of each habitat (for example, a nutrient-poor paddock compared with a nutrient-dense forest).
Disease: a pathogenic condition of a host that is sometimes caused by a pathogen or parasite. Temporal and spatial factors will affect how these pathogens or parasites can be spread. Organisms living in close proximity to each other to each other will allow the spread to occur faster. Seasonal variations can also affect the ease at which a pathogen or parasite can be spread. For example, in Queensland, dengue fever is most likely to be caught in Autumn.

Abiotic factors

Climate: We can compare the climate of different areas. For example, the tropics vs the poles, or even looking at how microclimate changes as you move from the tide line up the beach.

Substrate: We are able to compare the substrate of two areas. The beach is a good place to imagine this. We can have sand, rock, wood or soil substrate here
Size/depth of area: We can easily compare the size of an area. For example, we could look at the size of different rainforests in completely different countries, or the size of two paddocks next to each other. Similarly, we can compare the depth of any aquatic environment, from rock pools which may be only a few cm deep, to the Mariner Trench at nearly 11km deep.

Remember that all of these abiotic factors can be considered both spatially (i.e. considering the substrate of a forest near Brisbane vs a forest near Mount Isa) or temporally (i.e. considering the climate of a forest near Brisbane in June; or 2009 vs 2020).

Tolerance Limits

Environmental factors can limit the distribution and abundance of species in an ecosystem. This is because each organism has their own specific tolerance limit or range that restricts where that organism could potentially live.

  • Available area/size of habitat
  • Climate
    • Precipitation
    • Temperature
    • Wind direction and/or speed
    • Cloud cover
    • Sunshine
  • Soil structure
    • Thickness
    • Structure and porosity
    • pH
    • Nutrient content
    • Salinity
  • Aquatic factors
    • Light level
    • Depth
    • Turbidity (i.e. ‘cloudiness’ of the water)
    • Salinity
    • Oxygenation
    • Temperature
    • Water flow
    • pH
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Created on By QCE Biology

3.1.1 Biodiversity

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SpeciesNumber of quadrats containing speciesTotal number of quadrats sampled
Pikachu2020
Squirtle1920
Eevee1520
Charmander1420
Celebi620
Snorlax320

Identify the percentage frequency of Celebi.

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What is the species richness in the photo?

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The number of different species in an area.

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A country with many different types of ecosystem is said to have a high degree of what?

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If you were to measure the degree of difference between all of the ibis on the Gold Coast, what would you be measuring?

6 / 13

If you were to take a count of the diversity of species in Brisbane, what would you be measuring?

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Genetic diversity of a population can be measured by determining the number of

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Species richness is measured by

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Species diversity in an ecosystem is best determined by measuring

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Genetic diversity of a species is best described as

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The abundance of possums was measured in five randomly located survey sites, each 10

m2

in area. The numbers of possums counted in each area were 12, 29, 32, 10 and 17. The total area of the remnant vegetation was 250

m2

.

What is the best estimate of the total number of possums in the area?

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Ecosystem diversity is the variety of

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Species richness is measured by the

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