Explain how biodiversity can be viewed at different levels.
The St. Lawrence river in Canada contains many aquatic mammal species, especially whales. Each spring, thousands of whales travel from the Atlantic ocean into the St. Lawrence river. Thirteen different whale species have been recorded. One of them is the blue whale, Balaenoptera musculus. Fig. 1.1 shows a blue whale.
State the two sources of phenotypic variation in the blue whale population.
Suggest one reason why determining the actual population size of the blue whale is difficult.
The St. Lawrence river passes through very heavily industrialised areas. It has many ports for cargo ships, a strong fishing industry and numerous tourist whale-watching boat trips. Decades of whale hunting caused a major fall in whale population sizes. Since whale hunting was banned, whale populations have not rebounded. Seven of the thirteen whale species in the St. Lawrence river have been classified as endangered species. Suggest two reasons why the whale populations have not recovered since the ban on whale hunting.
Fat samples from beneath the skin of individual whales from several different species were collected. These were analysed, and the concentrations of the toxins DDT and PCBs were measured. Suggest why whales were found to have built up very high concentrations of DDT and PCBs in their fatty tissues.
Algal blooms sometimes arise in the Atlantic ocean near the St. Lawrence river. They are caused by rapid increases in the population of unicellular algae such as Alexandrium tamarense. A. tamarense produces saxitoxin, a neurotoxin that paralyses muscles by acting on voltage-gated sodium ion channels in neurones. Saxitoxin can kill whales. Suggest how saxitoxin causes the death of a whale.
Algae, such as A. tamarense, used to be placed in the kingdom Plantae but are now assigned to the kingdom Protoctista. State one reason why A. tamarense is classified in the kingdom Protoctista and not in the kingdom Plantae.