Biodiversity notes and exam questions

Biodiversity is a measure of three things: The variety of species in an ecosystem The variety of habitats in an ecosystem The genetic diversity of an ecosystem Species diversity can be measured by Simpson's index of diversity, a measure of the probability that two randomly selected individuals will be of the same species.The formula for Simpson's index of diversity is:d=  N(N-1)        Σn(n-1)Where N is the total number of organisms, and n is the number of organisms of each species.What does the value for the index of diversity mean? An ecosystem with a high index of diversity probably has the following features: Complex food webs Stable ecosystem, not likely to be damaged by environmental change Many successful species Accommodating environment Large variety of habitats and food sources The exact opposite is true of an ecosystem with a low index of diversity.Clearly, an index of diversity is a better measure of species diversity than just counting the number of species. For example, two ecosystems could each have 12 different species, but in one of them there may be a roughly similar number of each, while in the other there could be large numbers of one species but very small numbers of others. The second ecosystem would have a low index of diversity because it's dominated by a single species. (Examiners love asking this question!)Humans have a large and usually adverse impact on the biodiversity of ecosystems. In particular, agricultural practices often significantly lower the species diversity of an area. There are four agricultures in particular  which do this: Monoculture Deforestation Fertilisers Culling of predators       You need to be able to explain why each of these practices lowers biodiversity. Monoculture means devoting large areas of land to the production of a single crop. This means that an area will be dominated by one species, and other species are likely to be controlled by pesticides. Wetlands may be drained and hedgerows cut down to create more agricultural land, meaning that there is less habitat diversity and fewer food sources available for animals. Therefore, fewer animal species will be able to flourish.  Deforestation directly results in a reduction in the number of plant species, as well as fewer habitats and food sources for animals, so once again fewer animal species will succeed. It may also be the case that machinery used in clearing woodland could kill some animals, especially small insects. Fertilisers run off into ponds and lakes, where they cause the water to become anoxic (a process called eutrophication). Under such conditions most aquatic organisms will die and only those most tolerant to water pollution will continue to thrive, thereby reducing the species diversity of aquatic ecosystems.4. Foxes and badgers may be culled by farmers due to their effect on livestock, directly reducing species diversity.Always remember in ecosystems that the loss of one species has a knock-on effect as any animals which eat it will no longer be able to survive in the area unless they can find another food source. This impact is more profound in areas with low indices of diversity, as the food chains are simple and each consumer may only consume one species.It is in our interest to conserve biodiversity. Why? There are both ethical and economic reasons:=> To prevent extinctions/loss of populations=> To conserve species which may be of use to future generations=> Plants as yet undiscovered may have important medical and pharmaceutical uses=> Tourism=> Agriculture=> Commercial products

1. a) Scientists investigated the diversity of plants in a small area within a forest. The table shows their results.

Use the formula to calculate the index of diversity of plants in the forest. Show your working. (2)b) The forest was cleared to make more land available for agriculture.  After the forest was cleared the species diversity of insects in the area decreased.  Explain why. (3) 2. a) There are ethical and economic arguments for maintaining biodiversity.(i) Suggest one ethical argument for maintaining biodiversity. (1)(ii) Suggest one economic argument for maintaining biodiversity. (1)Ecologists calculated the percentage of bird species that have become extinct on six islands in the last one hundred years. They also calculated the percentage of original forest area remaining on each island after the same time period. The graph shows their results.

1.a) Answer in range 6.97-7 gains both marks. If your numerator was 6320 and/or denominator was 906, but you didn't get the answer 6.97-7, you would get one mark.b) Any three of: Decrease in variety of plants/fewer plant species Fewer habitats/niches Decrease in variety of food/fewer food sources Machinery/pesticides/other aspect of clearing forest could kill insects 2. a) (i) (We should maintain biodiversity to) prevent extinction /loss of populations/reduction in populations /loss of habitats / save organisms for future generations (ii) A suitable example of how some species may be important financially e.g.  1. medical / pharmaceutical uses;  2. commercial products / example given;  3. tourism;  4. agriculture;  5. saving local forest communities;b) Any two of:1. Fewer plant species / decrease in  plant diversity;  2. Fewer habitats/nesting sites;  3. Fewer niches;  4. Fewer food sources/varieties;  5. Less protection from predators/  hunters/environment;c) 1. Number of (individuals/birds of) each  species;  2. Total number of birds;d) Larger birds have a lower SA:vol ratio;So less heat lost;3. a) Removes bias b) Answer in range 1.28-1.3c) Diversity index would be lower (not a marking point in itself) as any two of: Fewer/only three species Mostly/dominated by one species/bird-cherry aphid Fewer plant species d) Data/evidence supports claim;Only wheat field / only comparing with wood / one type of habitat /only insects considered;e) Any two of:1. Greater variety of plants;  2. Another habitat / more habitats /  places to live / niches;  3. Another food source / more food  types;

b) Explain the relationship between the percentage of original forest area remaining and the percentage of bird species that have become extinct. (2)c) What two measurements would the ecologists have needed to obtain to calculate the index of diversity of birds on each island? (2)d) The ecologists noted that the species of birds surviving on the coldest islands had a larger body size than those surviving on warmer islands. Explain how a larger body size is an adaptation to a colder climate. (2)3. a) Scientists investigated the species of insects found in a wood and in a nearby wheat field. The scientists collected insects by placing traps at sites chosen at random both in the wood and in the wheat field. The table shows the data collected in the wood and in the wheat field.

a) The scientists collected insects at sites chosen at random. Explain the importance of the sites being chosen at random. (1)b) Calculate the index of diversity for the insects caught in the wood. (2)c) Without carrying out any further calculations, estimate whether the index of diversity for the wheat field would be higher or lower than the index of diversity for the wood. Explain how you arrived at your answer. (2)d) A journalist concluded that this investigation showed that farming reduces species diversity. Evaluate this conclusion. (2)e) Farmers were offered grants by the government to plant hedges around their fields. Explain the effect planting hedges could have on the index of diversity for animals. (2)

Biodiversity

exam questions

answers