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Conservation: keeping a species where it lives, or somewhere else questions
In situ conservation through protected areas, legislation and habitat management, and ex situ conservation in zoos, botanic gardens and seed banks, with the trade-offs of each; how a seed bank stores and tests seed and which seeds it cannot take; CITES and the Convention on Biological Diversity; the economic, ecological, ethical and aesthetic cases for conservation and the objections to each; and two case histories, the large blue butterfly and the California condor.
6 original questions · 22 marks · the conservation: keeping a species where it lives, or somewhere else notes · Classification, biodiversity and conservation
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A captive breeding programme has raised a large scavenging bird from 22 individuals to more than 500, over half of them flying free, but released birds are trapped and blood-tested for lead every year and treated when concentrations are high. Evaluate the claim that the programme has been a success.
Mark scheme
- B1 for: the species still exists, and the alternative when the last wild birds were taken into captivity was extinction within a few years, so on any count of individuals the outcome is a success
- B1 for: the captive breeding worked better than expected. Removing the first egg so that a pair lays another roughly doubled the output, and more than half the birds now fly free rather than being held in enclosures
- B1 against: the cause of the decline has not gone, since carcases shot with lead ammunition remain the leading source of poisoning, so without continued releases, trapping and treatment the free-flying population would fall again
- B1 against: the population is therefore not self-sustaining in the technical sense, and a disease outbreak in one flock can still remove a substantial part of it, so the programme is a permanent commitment rather than a finished task
- B1 judgement: whether this counts as success depends on the goal. It plainly succeeded in keeping the species in existence, and it has not produced a wild population living without veterinary support, with the remaining obstacle being a rule about ammunition rather than anything biological
Describe how seed is collected, prepared and stored in a seed bank, and describe how the collection is checked for viability.
Mark scheme
- B1 seed is collected in the wild from many individuals across the population, with locality, date and habitat recorded, then cleaned and X-rayed so that empty or insect-damaged seeds are discarded
- B1 it is dried slowly, typically at about 15 °C and 15 per cent relative humidity, down to roughly 5 per cent moisture content
- B1 it is then sealed in containers and frozen, conventionally at −20 °C, and the drying has to come first because water left in the seed forms ice crystals that rupture the cell membranes
- B1 a sample from each accession is germinated at intervals, commonly every ten years, and if the germination percentage has fallen too far, seed is grown on to produce a fresh batch
Explain why a captive breeding population loses genetic diversity, and explain what is done to slow that loss.
Mark scheme
- B1 a captive population is founded by a handful of individuals and held at a few hundred at most, so it passes through a bottleneck by construction and alleles that were not in the founders are simply absent
- B1 in a small population the alleles passed on each generation are a small sample of those present, so frequencies drift by chance and alleles are lost altogether, and only mutation or migration restores them
- B1 inbreeding raises the frequency of homozygous recessive genotypes, so inherited disease and reduced fertility become commoner in the herd
- B1 a studbook records every individual's ancestry so that the least related animals available can be paired, and animals are moved between institutions to widen the choice of mates
Compare in situ with ex situ conservation, referring to genetic diversity, to the rest of the community and to the problems each approach cannot solve.
The seeds of many tropical rainforest trees are shed with a high water content and die if they are dried. Suggest why such species cannot be held in a conventional seed bank, and suggest two other ways of conserving them outside their habitat.
State what is meant by in situ conservation and what is meant by ex situ conservation.
Practise conservation: keeping a species where it lives, or somewhere else one question at a time
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