Biodiversity and evolution practice questions.

A seed bank sets out to keep as many different traditional varieties of one crop species in store as it can. The kind of diversity it is conserving is

• habitat diversity
• species diversity
• genetic diversity
• functional diversity

Answer: genetic diversity

All the varieties belong to a single species, so species richness is unchanged; what is being preserved is the variation in alleles within that species. Genetic diversity is the level that determines whether a crop can be bred to meet a new disease or a drier climate.

A region is designated as a biodiversity hotspot only if it satisfies two criteria together. These are

• a large total number of species and a large area already protected
• many endemic plant species and heavy loss of original habitat
• high net primary productivity and a large total land area
• many endemic species and a low resident human population

Answer: many endemic plant species and heavy loss of original habitat

The designation combines irreplaceability with threat: species found nowhere else, in a region that has already lost most of its natural vegetation. A region rich in species but largely intact does not qualify, because the point of the label is to direct scarce conservation money to where loss would be permanent and is imminent.

Invertebrates from two river sites are scored with a biotic index built on the pollution tolerance of the families present. Site B returns a much lower score than Site A. This indicates that Site B

• holds more individuals in total than Site A does
• was sampled with a smaller net than Site A was
• holds fewer pollution-sensitive families and is more polluted
• has a higher dissolved oxygen concentration than Site A recorded

Answer: holds fewer pollution-sensitive families and is more polluted

A biotic index weights families by their sensitivity, so the score falls as the sensitive families such as stonefly and mayfly nymphs disappear and tolerant worms remain. Reading a high index as 'polluted' is the standard error, and it inverts every conclusion drawn from the survey.

A student estimates the plant diversity of a hay meadow with five quadrats, all of which she places on the parts of the field that look most flower-rich. Compared with a set of randomly placed quadrats, the Simpson reciprocal index she calculates will be

• too high, because the sampled patches are richer and more even than the meadow as a whole
• too low, because concentrating all five quadrats in one part of the field reduces the number of individuals counted
• unaffected, because the index corrects for the number of individuals recorded in the sample
• unaffected, because the index depends only on which species are present and not on where the quadrats were placed

Answer: too high, because the sampled patches are richer and more even than the meadow as a whole

Placing quadrats where the vegetation looks interesting biases the sample towards the richest and most even patches, so D comes out above the true value for the field. The formula has no correction for a biased sample; only the sampling design can remove that bias.

A student writes: 'Site P has a Simpson reciprocal index of 6.2 and site Q has 2.4, so site P must contain more species than site Q.' Identify the fault in this reasoning.

• The index cannot be compared between two sites unless exactly the same number of individuals has been counted at each of them
• The index combines richness with evenness, so Q could hold more species with almost all individuals in one of them
• The index falls as diversity rises, so the conclusion drawn here is the wrong way round
• The index applies only to animal communities, so it cannot be used for the plants recorded at these two sites

Answer: The index combines richness with evenness, so Q could hold more species with almost all individuals in one of them

A high D can come from few species spread very evenly, and a low D from many species with one of them dominating. Richness has to be counted separately; the index never reports it, and reading D as a species count is the standard error.

A reservoir built across a valley has held one beetle population apart in two blocks of habitat for about eighty years, and the two groups now differ in colour and body size. Identify the observation that would show that speciation has actually occurred.

• The two groups differ in colour and size by more than any two individuals within either group
• The two groups live on opposite sides of the reservoir and are never found together in the wild
• Individuals from the two groups placed together do not produce fertile offspring
• The allele frequencies of the two groups have drifted apart since the reservoir was filled

Answer: Individuals from the two groups placed together do not produce fertile offspring

Visible divergence, geographical separation and drifting allele frequencies all appear long before a species boundary forms, and all three are present in populations that are still one species. The test is reproductive isolation.