Biodiversity and conservation practice questions.

Two woodland sites each contain 100 beetles belonging to four species. At site A the individuals are spread evenly across the four species; at site B a single species accounts for 91 of them. Compared with site A, the Simpson reciprocal index for site B will be

• higher, because one species is clearly dominant
• the same, because both sites contain exactly four species and 100 individuals
• lower, because the individuals are unevenly distributed among the species
• impossible to calculate without knowing the total area sampled

Answer: lower, because the individuals are unevenly distributed among the species

The reciprocal index combines richness with evenness; richness is identical at the two sites, so the strong dominance at site B enlarges the sum of n(n-1) and drives D down, from about 4.1 to about 1.2.

A river permanently changes course and divides a population of ground-dwelling lizards into two groups that can no longer interbreed. Over many thousands of generations the groups become separate species. This process is

• genetic drift, because the two groups are of different sizes
• sympatric speciation, because the lizards remain within one region
• artificial selection, because the physical barrier selects which individuals survive
• allopatric speciation, because a geographical barrier isolated the gene pools

Answer: allopatric speciation, because a geographical barrier isolated the gene pools

Allopatric speciation requires physical separation of gene pools followed by independent mutation and selection in each; sympatric speciation produces new species without any geographical barrier, and artificial selection requires a human breeder.

A crop pest population is sprayed with the same insecticide for several years and becomes largely resistant to it. The best account of what happened is that

• individual insects developed resistance in response to being sprayed
• resistant variants were already present and left proportionally more offspring
• the insecticide caused new resistance mutations to appear in every insect
• the insects learned to avoid the insecticide and passed this on to their young

Answer: resistant variants were already present and left proportionally more offspring

Selection acts on variation that already exists in the gene pool, so the spray is the selection pressure rather than the source of the resistance allele. Individuals do not adapt during their lifetime; allele frequencies shift between generations.

An island bird population falls from several thousand to about 30 individuals after a cyclone, then recovers in numbers over the following 50 years. The most likely lasting consequence is

• reduced genetic diversity, lowering the population's ability to adapt
• increased genetic diversity, because the survivors were the fittest ones
• no change in genetic diversity, because population size has recovered
• immediate speciation, because the surviving birds were reproductively isolated

Answer: reduced genetic diversity, lowering the population's ability to adapt

A population bottleneck removes every allele the few survivors did not happen to carry, and rebuilding numbers does not rebuild that lost variation. A narrower gene pool leaves the population less resilient to new diseases or climatic stress.

Madagascar has been separated from other landmasses for tens of millions of years and a very high proportion of its plants and animals occur nowhere else. The main reason for this pattern is that

• island species are always more diverse than mainland species
• the island's climate is far more variable than that of the nearby continents
• isolated gene pools evolved independently, producing many endemic species
• species from the mainland colonise islands faster than they go extinct

Answer: isolated gene pools evolved independently, producing many endemic species

Long isolation prevents gene flow, so mutation and natural selection act independently and lineages radiate into the niches locally available. Endemism is therefore highest on old, isolated islands, which is also what makes those species irreplaceable if lost.

A new motorway is built through a continuous area of forest, splitting it into two blocks with no crossing points. Twenty years later the resident deer population shows reduced genetic diversity. The most likely cause is

• an increase in the total area of suitable habitat
• a rise in the carrying capacity of each forest block
• the loss of gene flow between the two subpopulations
• a shift of the population from K-strategist to r-strategist

Answer: the loss of gene flow between the two subpopulations

Fragmentation does not only remove habitat; it isolates what is left, so breeding individuals can no longer move between patches and each small subpopulation drifts towards inbreeding. Total area may be almost unchanged while connectivity, the property that matters for gene flow, collapses.