PASSAGE 3 The conservation of rare species

READING PASSAGE 3
You should spend about 20 minutes on Questions 27-30, which are based on Reading Passage 3.

The conservation of rare species

When a naturalist says that a bird or a plant is rare, he or she may mean one of several different things (Harper 1981, Rabinowitz 1981). The concept of rarity can refer to one of three characteristics: geographic range, habitat specificity, or local population size, and a classification based on the interplay between these variables yields seven different types of rarity. For example, certain species may be locally abundant over a wide geographic range, but found in only a very specific habitat, whilst others may be found in several habitats, but only in small numbers and in geographically restricted area. We must therefore recognise that the kinds of management which will be appropriate for protecting species threatened with extinction will vary.

Classic rare species are often those which have a small geographic range and narrow habitat specificity. Many plants of this type are restricted endemics, and are often endangered or threatened (Rabinowitz 1981). Other rare species have very large geographic ranges and occur widely in different habitats but are always at low density. These species are ecologically interesting but almost never appear on lists of endangered species. So the important point is that not all rare species are problems for conservationists.

The reasons why a particular species is rare vary. In some cases we can observe a species declining over time: for example, the African elephant population since 1950. This is a direct result of ivory poaching (Caughley et al. 1990). But not all species that have declined to rarity are so well understood. Some plant and animal species undergo bursts of colonisation and decay so that they persist as a mosaic of increasing and declining populations (Harper 1981).

For species with small geographic ranges or narrow habitat specificity we must be concerned with the spatial distribution of the population. The number or size of habitable sites may be too small, and this could be one reason the species is rare. Or, if there are many habitable sites that are not occupied, a species may be rare because of its limited dispersal powers. Within habitable sites, competition from other species, predation, disease or social interactions may restrict abundance. One example that illustrates some of these factors is the red-cockaded woodpecker.

The red-cockaded woodpecker is an endangered species of bird endemic to eastern parts of the United States of America. It was once abundant from New Jersey in the north to Texas in the south, and from the coast inland as far as Missouri, but it is now nearly extinct in the northern and inland parts of its geographic range. The red-cockaded woodpecker is adapted to pine savannas, but most of this woodland has been destroyed for agriculture and timber production. The birds feed on insects and nest in cavities in old pine trees, and because old pines have been mostly cut down, their available habitats have been reduced (Walters 1991).

Designing a recovery programme for the red-cockaded woodpecker has been complicated by the social organisation of the species. The birds live in groups of a breeding pair and up to four helpers, nearly all males. Helpers do not breed but assist in incubation and feeding. Young birds have a choice of dispersing or staying to help in a breeding group. If they stay, they become breeders by inheriting breeding status on the death of older birds. Helpers may wait many years before they acquire breeding status.

From a conservation viewpoint, the problem is that red-cockaded woodpeckers compete for breeding vacancies in existing groups, rather than forming new groups and occupying abandoned territories, or starting at a new site. The key problem is the excavation of new breeding cavities. Because of the energy and time needed, typically several years, birds are better off competing for existing territories than building new ones.

To test this idea, Walters (1991) and his colleagues artificially constructed cavities in trees a: 270 Pit 2, n the were epini far sis ed. YorktaGeanina Tokeresulta were breeding groups were formed only on areas where artificial cavities were drilled. This experiment showed clearly that much suitable habitat is not occupied by this woodpecker because of a shortage of cavities. Therefore management of this endangered species was not directed at reducing mortality of the birds, but instead focused on physical characteristics of their chosen habitat.

The rescue of the red-cockaded woodpecker is a good example of how successful conservation biology depends on identifying and alleviating limiting factors. However, there can be no general prescription for rescuing rare species. Detailed information on resource requirements, social organisation, and dispersal powers are required before recovery plans can be specified.

Questions 27-30
Choose the correct letter, A, B, C or D.

27 What does the writer say about rarity?
A There is more than one criterion for defining it.
B The term is a cause of dispute amongst naturalists.
C It applies to only a very small number of species.
D It is a phenomenon which has been widely researched.

28 What does the writer say about the threat of extinction?
A All types of rarity present a problem.
B Few plant species are known to be vulnerable.
C Low density by itself does not endanger species.
D Lists of endangered species are not reliable.

29 Which of the following makes it difficult for the red-cockaded woodpecker to increase in number?
A A proportion of male birds are sterile.
B Birds leave the parental nest too early.
C There is too much competition for food.
D Individuals may not breed for several years.

30 What was the basis of the recovery programme for the red-cockaded woodpecker?
A Birds were bred in captivity.
B Nesting holes were created.
C Pine forests were planted.
D Food supplements were provided.

Questions 31-37
Do the following statements agree with the information given in Reading Passage 3. In boxes 31-37 on your answer sheet, write
TRUE if the statement agrees with the information
FALSE if the statement contradicts thevinformation
NOT GIVEN if there is no information on this

31 Species with various habitat types are not necessarily widely distributed.
32 The rate of decline of the African elephant has slowed down
33 The causes of rarity are generally easy to establish,
34 The traditional habitat of the red-cockaded woodpecker has been destroyed by human activity.
35 The red-cockaded woodpecker prefers to leave its nest before breeding.
36 It usually takes years for the red-cockaded woodpecker to make a nesting hole.
37 The project to rescue the red-cockaded woodpecker is ongoing

Questions 38 and 39
Answer the questions below.
Choose NO MORE THAN THREE WORDS from the passage for each answer.

38 What does the red-cockaded woodpecker feed on?
39 Which TWO parental tasks do the helper woodpeckers perform?

Question 40
Choose the correct letter, A, B, C or D.

In this article, the writer’s purpose is to
A alert the reader to the plight of the red-cockaded woodpecker.
B explain how Walters’s recovery programme can be applied to other species.
C illustrate the factors that must be considered when dealing with rarity.
D persuade readers that rarity is a neglected ecological issue.