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Conservation: keeping a species where it lives, or somewhere else

Two ways of stopping a species disappearing, each able to fix what the other cannot, and neither cheap. Underneath the biology sits an argument about why any of it is worth doing, which people answer in four incompatible ways — and a set of case histories in which the numbers went up and the problem did not go away.

Before this Species diversity and genetic diversity · Genetic bottlenecks and the founder effect · Succession and habitat management

Before you start

If a species is in trouble, breed it in a zoo and put it back. Captive breeding has saved species that would otherwise be gone, so this is not a silly thing to think — but as a general plan it fails on arithmetic and on ecology. A zoo can hold a few dozen large animals, which is nothing like enough individuals to keep the alleles a species has, so the population that comes out is already less varied than the one that went in. Animals reared in captivity often cannot hunt, avoid predators or navigate, because those things are learned. And putting an animal back requires somewhere to put it: if the habitat was destroyed, or the poaching continues, or the ant the caterpillar needs has gone, the release is a release into the same problem. Ex situ conservation buys time. It does not, on its own, buy a future.

What you should be able to do

The two places, and what each is for

Conservation is the protection and management of species and habitats so that they persist. It is not preservation, which means leaving something untouched; a great many British habitats exist only because somebody keeps cutting, grazing or burning them.

In situ conservation
Conserving a species in its natural habitat, so that the community and the conditions it is adapted to are conserved with it.
Ex situ conservation
Conserving a species outside its natural habitat — in a zoo, a botanic garden, a seed bank or a captive breeding centre.
Endangered species
A species at high risk of extinction in the wild, as assessed against criteria such as the IUCN Red List's.
Extinct in the wild
A species surviving only in cultivation, captivity or as a population well outside its past range.
The lower half of each card is the part worth learning. Each approach has a set of problems it is structurally unable to reach, and those sets barely overlap.

In situ: the whole community, and the things you cannot fence out

Conserving a species where it lives means conserving a great deal besides. National parks, nature reserves, Sites of Special Scientific Interest and marine conservation zones all protect an area rather than a species, and everything in the area benefits — including the species nobody has got round to studying. Selection carries on operating, so the population stays adapted to conditions that are themselves changing. Populations can be large, which is the only way to keep genetic diversity. And per species conserved it is far cheaper than anything done in captivity.

It also requires management, which surprises people. A chalk grassland left alone becomes scrub and then woodland within a few decades, and the orchids and butterflies it was designated for disappear. So reserves are grazed, coppiced, mown or burned on rotation: succession is held back deliberately, at the stage that suits the species being conserved.

The limitations are the things a boundary on a map does not stop. Poaching continues inside reserves, and in some places a designation concentrates the animals and makes them easier to find. Invasive species walk in. Pollution and climate arrive from outside entirely. Reserves are often too small, or too isolated from each other, to hold a viable population of a wide-ranging animal, which is the argument behind wildlife corridors linking fragments. And a reserve on land somebody was farming or logging has a cost that falls on the people who live there, which is why enforcement fails where local communities get nothing from it.

Two international agreements come up by name. CITES, the Convention on International Trade in Endangered Species, has been in force since 1975 and regulates cross-border trade: species in Appendix I may not be traded commercially at all, those in Appendix II only under permit. It controls trade and nothing else, so it does not touch habitat loss, and it depends entirely on member states enforcing it at their own borders. The Convention on Biological Diversity, agreed at the Rio Earth Summit in 1992, is broader and softer: signatories commit to conserving biodiversity, using it sustainably, and sharing the benefits that come out of genetic resources fairly with the countries they came from. It sets targets rather than prohibitions, and the targets have been missed more often than met.

Ex situ: control, and the arithmetic of small numbers

A zoo, a botanic garden or a captive breeding centre offers things no reserve can. Conditions are controlled — temperature, diet, disease. Veterinary care is available. Breeding can be assisted with artificial insemination, embryo transfer or surrogacy, and, crucially, matings can be chosen. Modern captive breeding runs on a studbook: a record of every individual's ancestry, used to pair the least related animals available and slow the loss of alleles. Animals can be moved between institutions to do it. And for a species already gone from the wild there is no alternative at all.

The problems start with numbers. 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 not there. Inbreeding raises the frequency of homozygous recessive genotypes, and with it the incidence of inherited disease and of reduced fertility. Captivity also selects: over generations, the animals that breed best in enclosures are not necessarily the ones that would survive outside them.

Then behaviour. Hunting, predator avoidance, migration routes and, in many birds and mammals, the details of courtship are learned from other individuals. A hand-reared animal may not have them, which is why release programmes now use puppet feeding, mentor birds, pre-release training pens and soft releases with continued support. It is expensive and it often still fails.

And the cost. Keeping a large mammal in a zoo costs more per animal per year than protecting a substantial area of habitat, which is the sharpest version of the argument between the two approaches: given a fixed budget, how much should go into enclosures and how much into land? Zoos answer that they also do research, breeding science and public education that feeds money and support back into field work. Critics answer that a species whose habitat is not protected is being kept alive as an exhibit. The disagreement is about priorities rather than facts.

Seed banks

For plants, ex situ conservation is far better arithmetic. Seeds are small, they are already a dormant stage, and a single collection can hold tens of thousands of them from hundreds of separate parent plants — so a seed bank can store genetic diversity that a zoo could never match, in a room rather than a landscape.

The freezing is the step everybody remembers and the least demanding of the five. Drying is what makes freezing survivable, and the germination test is what stops the collection quietly becoming a cupboard of dead seed.

Seed is collected in the wild, from many individuals across a population, with the locality, date and habitat recorded — an accession without that information cannot be put back anywhere in particular. It is cleaned and X-rayed so that empty or insect-damaged seeds are discarded. It is then dried slowly, typically at around 15 °C and 15 per cent relative humidity, down to roughly 5 per cent moisture content. Only then is it frozen, conventionally at −20 °C, in sealed containers. Drying first is not optional: water left in the seed forms ice crystals that rupture the cell membranes.

Low temperature and low water content slow metabolism almost to a stop, so respiration barely proceeds, reserves are not used up and enzymes do little damage. Seeds of many species stay viable for decades or centuries this way. But viability does fall, so a sample from each accession is germinated at intervals — every ten years is a common cycle — and if the germination percentage has dropped too far, seed is grown on to produce a fresh batch.

The Millennium Seed Bank at Wakehurst in Sussex, run by Kew, holds seed from tens of thousands of species with a particular emphasis on wild plants rather than crops; the Svalbard Global Seed Vault, cut into permafrost inside an Arctic mountain, exists as a backup copy of the world's crop collections. The advantages over conserving the plants themselves are straightforward: far less space, far less labour, no risk from a fire or a disease outbreak in a living collection, and the storage of many more individuals and therefore many more alleles.

There is one hard limit, and it is worth knowing because it is the obvious exam question. Seeds that tolerate drying and freezing are called orthodox; a substantial minority, the recalcitrant seeds, do not. Acorns, horse chestnuts, avocados, mangoes, cocoa and a large proportion of tropical rainforest trees have seeds that are shed with a high water content and die if dried. They must be kept as living collections, or by freezing extracted embryos in liquid nitrogen, or in tissue culture — all of which are more expensive and less secure. The habitats richest in species are the ones whose seeds a seed bank finds hardest to take.

Why people think it is worth doing

Exam questions ask for 'reasons for maintaining biodiversity' and the expected answer is a list under four headings. The list is fine as far as it goes, but each heading is a position that somebody holds and somebody else objects to, and an answer that shows you know that reads very differently from one that does not.

Each of these is a real argument made by real people, and each has an answer it has to live with. Knowing the objection is how you tell an argument from a slogan.

The economic case. Wild species are a stock of useful material. Vincristine and vinblastine, still used against childhood leukaemia and Hodgkin lymphoma, came from the Madagascar periwinkle; paclitaxel came from the bark of the Pacific yew. Wild relatives of crops carry disease resistance that breeders need — a wild rice from India supplied the resistance to grassy stunt virus that was bred into cultivated varieties. Habitats also do work for nothing: wetlands hold flood water, forests hold soil, insects pollinate crops. The objection is that the argument cuts both ways. If a species is worth conserving because it might be useful, a species shown to be useless is one you may spend, and most species will never be shown to be useful because nobody will ever look.

The ecological case. Species are connected, and removing one takes others with it. Some species have effects out of all proportion to their abundance — sea otters keeping sea urchins off kelp forests is the standard example — and a community that loses species loses the redundancy that lets it absorb a shock. The objection is practical: nobody can say in advance which species those are. Most of the time the answer arrives after the species has gone, which makes this an argument for caution about everything rather than a way of choosing what to fund.

The ethical case. A species is the outcome of a very long history and is not ours to end, whatever use it is to us; and we owe something to people who are not born yet. This is the position held by most people who work in conservation, and it does not depend on the species being useful or charismatic. The objection is that it offers no way to choose. Budgets are finite, and an argument that every species has an equal and absolute claim cannot say which of two species to save when you can afford one.

The aesthetic and cultural case. People value landscapes and animals, travel to see them, write about them and build identities around them; ecotourism turns that into income that can pay for protection. The objection is that this valuation is uneven and known to be so. It favours large mammals and birds over invertebrates, fungi and plants, which is roughly the reverse of where the diversity actually is, and it makes conservation depend on fashion.

None of the four settles the matter, and they conflict with one another in practice. An answer that presents them as four boxes to be ticked misses what the question is about; an answer that says which reason it is leaning on, and why, does not.

Two case histories

The large blue butterfly, and why it needed an entomologist before it needed a reserve. The large blue, Phengaris arion, declined through the twentieth century in Britain despite its remaining sites being protected, and was declared extinct here in 1979. Protection had not worked because nobody knew what the butterfly actually required. Jeremy Thomas established that the caterpillar leaves its food plant of wild thyme after a few weeks, drops to the ground and is carried into the nest of a single ant species, Myrmica sabuleti, where it spends ten months eating ant grubs. That ant needs short, warm turf. When myxomatosis destroyed the rabbit population in the 1950s and grazing stopped, the turf grew longer, the soil cooled by a couple of degrees, the ant was replaced by a related species that will not do, and the butterfly starved inside the wrong nests.

The response was to restore the grazing — sheep, cattle and returning rabbits — and re-establish the sward at the height the ant needs, then reintroduce the butterfly from a Swedish population from 1983 onwards. It now flies at dozens of sites in the west of England in numbers larger than for many decades. The reason it worked is the interesting part: the conservation action that mattered was not protecting the butterfly but managing an ant. The red kite, reintroduced to England and Scotland from 1989 using birds from Spain and Sweden and now breeding in thousands of pairs, has the same structure — the cause of the decline, there persecution and poisoning, had to be dealt with before the birds went back.

The California condor, and a population that cannot yet stand up on its own. By 1982 there were 22 California condors alive anywhere. The decision taken in 1987 was drastic and bitterly opposed: every remaining wild bird was caught, and the species existed only in two zoos. Captive breeding worked better than expected — double clutching, in which the first egg is removed so the pair lays another, roughly doubled the output — and releases began in 1992. The total population passed five hundred in recent years, with more than half of those birds flying free.

On any species-count measure that is a triumph. The complication is that the thing that caused the decline has not gone. Condors are scavengers, and carcases shot with lead ammunition contain lead fragments; lead poisoning remains the leading cause of death in free-flying birds. So the released population is monitored intensively, birds are trapped and blood-tested, and those with high lead levels are treated with chelation therapy. An outbreak of highly pathogenic avian influenza in 2023 killed a substantial part of one flock and prompted an emergency vaccination programme. Without continued releases, trapping and treatment, the free-flying population would decline. It is not, in the technical sense, self-sustaining.

So is the condor programme a success? It depends what you think conservation is for. If the goal is that the species should still exist, it plainly succeeded, and the alternative in 1987 was extinction within a few years. If the goal is a wild population living without veterinary support, it has not got there, and the obstacle is a regulation about ammunition rather than anything biological. The giant panda raises the same question from the other end: the IUCN moved it from Endangered to Vulnerable in 2016 on the strength of a rising count and an enormous reserve network, China's own authorities disagreed with the downlisting at the time, and the wild population remains split into many small groups separated by roads and farmland, several of which are too small to persist on their own. Whether that is a recovery depends on whether you are counting animals or counting populations.

TRY IT — Choosing an approach, and defending it

A tropical island holds an endemic tree that grows nowhere else. Fewer than 200 mature individuals remain, in three fragments of forest separated by plantations. The tree is pollinated by a bat that is itself declining, and its seeds are large, fleshy and die within days of falling. A conservation body has funding for one main programme.

Evaluate in situ and ex situ options for this species, and recommend one, giving the biological reasons.

Check your answer

Start with what the seeds rule out. Large, fleshy seeds that die quickly are almost certainly recalcitrant: they cannot be dried to 5 per cent moisture and frozen at −20 °C, so a conventional seed bank is not available. The ex situ options are therefore a living collection in a botanic garden, cryopreservation of excised embryos, or tissue culture — all more expensive, all holding far fewer individuals and therefore far fewer alleles.

Now the pollinator. The tree depends on a declining bat, and no botanic garden collection will conserve that relationship. Plants grown ex situ would need hand pollination indefinitely, and a population that has been hand pollinated for decades tells you nothing about whether it can still reproduce in the wild. Conserving the tree without the bat conserves half a system.

The fragmentation is an in situ problem. Fewer than 200 individuals in three separated groups means gene flow between them is limited or absent, and diversity is being lost to drift and inbreeding in each fragment independently.

Recommendation: in situ, focused on the fragments and the gaps between them. Protect the three areas legally, manage them for regeneration, and plant corridors of native forest between them so that bats can move and pollen can flow — which conserves the bat at the same time. Hand-pollinate between fragments in the short term to restore gene flow while the corridors grow.

Alongside it, not instead of it: establish a small living collection in a botanic garden, propagated from as many different parent trees as possible, as insurance against a hurricane or disease taking one of the fragments. The reason this is secondary is that it cannot conserve the pollination system, cannot hold enough individuals to preserve the alleles, and does not address why the tree is declining.

The honest caveat: this recommendation assumes the plantations between the fragments can be bought or negotiated for. If they cannot, the ex situ option stops being second best and becomes the only option available, which is how a great many of these decisions are actually made.

In the exam

Check yourself

A national park protects an area of savannah containing a population of about 400 black rhinoceros. Poaching has risen and 30 animals were killed last year. A donor offers enough money either to double the number of rangers patrolling the park, or to establish a captive breeding herd of 40 animals in a fenced sanctuary elsewhere. Discuss the biological arguments on each side.

Answer

The case for the rangers — in situ. The 400 animals in the park are a far larger gene pool than any captive herd could be, so keeping them alive conserves genetic diversity that cannot be recreated once it is gone. They are in the habitat they are adapted to, with the plants they browse and the community they belong to, and natural selection continues to act. Protecting the park protects everything else living in it at no extra cost. The threat here is poaching, which is precisely the threat more rangers address; the habitat itself is intact, so nothing else is currently limiting the population.

The case for the sanctuary — ex situ. Forty animals behind a fence are far easier to protect, and a catastrophe in the park — an escalation in poaching, a disease outbreak, a drought — would not take them with it. Breeding can be managed with a studbook so that the least related animals are paired, and reproduction can be assisted. Rhinoceros are large, slow-breeding and easy to find, which makes them poor candidates for protection by patrol alone.

Against the sanctuary. Forty founders is a bottleneck: alleles present in the other 360 animals are lost at the moment of selection, and inbreeding will raise homozygosity in the herd within a few generations. It costs a great deal per animal. It does nothing whatever about the poaching, so the wild population continues to fall while the herd is established, and any future release goes back into the same danger.

Against the rangers. Patrolling treats the symptom. If the demand for horn and the poverty that supplies poachers are untouched, more rangers raises the cost of poaching without ending it, and the money runs out eventually.

A defensible conclusion. Spend it on the rangers. The habitat is intact and the population is large, so the only thing currently reducing it is killing, and the intervention that stops killing conserves 400 animals and their alleles rather than 40. The sanctuary would be the right answer if the habitat itself were being lost, or if the population had already fallen so low that protection in place could not be relied on. Either answer can earn full marks if it argues from population size, genetic diversity and the nature of the threat rather than from preference.

Questions

Written to the command words the boards use. Try them on paper before opening a scheme: the marks go to points made, not to length.

Question 15 marks

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
  1. 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
  2. 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
  3. 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
  4. 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
  5. 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

Question 24 marks

Describe how seed is collected, prepared and stored in a seed bank, and describe how the collection is checked for viability.

Mark scheme
  1. 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
  2. B1 it is dried slowly, typically at about 15 °C and 15 per cent relative humidity, down to roughly 5 per cent moisture content
  3. 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
  4. 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

Question 34 marks

Explain why a captive breeding population loses genetic diversity, and explain what is done to slow that loss.

Mark scheme
  1. 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
  2. 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
  3. B1 inbreeding raises the frequency of homozygous recessive genotypes, so inherited disease and reduced fertility become commoner in the herd
  4. 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

Question 44 marks

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.

Mark scheme
  1. B1 in situ keeps the species where it lives, so the whole community and the conditions it is adapted to are conserved with it, whereas ex situ conserves the species alone and cannot conserve its habitat or the species it depends on
  2. B1 in situ can support a far larger population, so far fewer alleles are lost to drift and inbreeding, whereas an ex situ population is founded by a handful of individuals and passes through a bottleneck
  3. B1 selection continues to act in situ, so the population stays adapted to conditions that are themselves changing, whereas captivity selects for animals that breed well in enclosures and learned behaviour such as hunting or predator avoidance may never be acquired
  4. B1 ex situ offers controlled conditions, veterinary care, assisted breeding and chosen matings, and is the only option for a species already gone from the wild, whereas a boundary on a map does not stop poaching, invasive species, pollution or a changing climate

Question 53 marks

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.

Mark scheme
  1. B1 the seed cannot be dried to about 5 per cent moisture, and freezing it while wet would form ice crystals that rupture the cell membranes, so the method depends on a step these seeds do not survive
  2. B1 they can be kept as a living collection of plants in a botanic garden, which takes far more space and labour and holds far fewer individuals, and therefore far fewer alleles
  3. B1 embryos can be excised and frozen in liquid nitrogen, or the plants maintained in tissue culture, both of which are more expensive and less secure than a seed store

Question 62 marks

State what is meant by in situ conservation and what is meant by ex situ conservation.

Mark scheme
  1. B1 in situ: conserving a species in its natural habitat, so that the community and the conditions it is adapted to are conserved along with it
  2. B1 ex situ: conserving a species outside its natural habitat — in a zoo, a botanic garden, a seed bank or a captive breeding centre

Worth remembering

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