Principles of In-Situ Management of Wildlife Communities

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Remember: “ A species may rehearse its extinction many times before the main event”

Natural History Investigations - It seems trite to warn against tackling conservation problems without a basic knowledge of the species’ natural history — but it happens. For example, the Large Blue butterflies – Phengaris arion. It had been declining in SE England since the 1880s (adverse weather linked to decline). The numbers fell from 100,000 in 1950, to 250 in 1972

and was declared extinct in 1979.

Collecting, pesticides, weather, inbreeding, were all considered as the cause of decline. But ecology is much more complicated than that. In fact the larvae are obligate parasites in ant colonies (Myrmica spp.). They survive best in young M.sabuleti nest within 2m of thyme plant.

A lack of grazing caused a change in microhabitat so that a taller sward grew (taller than 2 cm), so M.scabrinodes replaced M.sabuleti.

However necessary, don’t let such natural history investigations get out of hand (by the time you have calculated the exact age-specific rates of fecundity and mortality it may be too late to save the species)

The Florida Panther (Puma concolor coryi) (P.c.couguar ?) – Not Evaluated? – Management Controversial. What you need is a “feel” for the ecology of the species, which will allow you to construct testable hypotheses as to the cause of the decline — you can add to your knowledge through the testing of these hypotheses.

DIAGNOSING THE CAUSE OF THE PROBLEM

Look for correlations with:

- Environmental variables

- Trends in other species (introductions, competitors, predators)

- Habitat change

- Other human activities

Remember that such causes may act in concert: loss of shelter may increase exposure to predation; such interactions complicate but don’t preclude accurate diagnosis (cf. Bermuda petrel and White-tailed tropic bird)

Remember that if such correlations are found that they are OBSERVATIONS not EXPLANATIONS

- Over harvesting by people is a common cause of decline and can be targeted or unintentional (by-catch of turtles, seabirds)

The simplest way to diagnose this is by demonstrating that harvest exceeds MSY (maximum sustainable yield) for the population/ species but very seldom is there enough data to allow the estimation of MSY (or to accurately determine harvest. A very few countries have accurate harvest statistics and underreporting is common i.e. illegal harvesting not included

Alternative approach is to compare CPUE (catch per unit effort) (cf. whales). If the CPUE is declining, population is being depressed.

- Habitat changes are advanced as the dominant cause of extinctions. It is very important, but “habitat” is often a flustered concept. There is a need to reduce habitat to suite of variables (resources)

Habitat modification - If woodland modified by fire, or felled, it will clearly have an effect wildlife density but we may not know why? Rather than evoking “habitat modification” we need to identify what element is being changed to the species’ detriment.

- May be an abiotic factor (humidity down after clearance)

- May be a food resource (cf. Mauritius kestrel)

- May be loss of “access” to habitat by predation, competition, etc. (cf. Lord Howe Island woodhen, Nene)

Habitat fragmentation - may increase competition from “edge” species, this is a common thing for birds.

The Gull Island vole (Microtus nesophilus) was discovered and described in 1889. It was restricted to the 7 ha Gull Island off Long Island, New York. Fort Michie was built there in 1897, its construction requiring that most of the island (and thus the vole’s habitat) be coated with concrete. The species has not been seen since.

- Impact of introduced Species — implicated in 40% historical extinctions. There is always a temptation to control all alien species. Sometimes this can have detrimental effects on native species. Need to first unequivocally establish the link:

- Coincidence of timing

- Proof of predation/competition

- Response to removal experiments

Remember - the alien may be simply expanding to fill the void left by a species in decline for other reasons. (However: beware expansion to fill temporary voids

cf. Red and Grey squirrels)

- Chains of Extinction— usually a response to extreme specialisation. The clearance of evergreen forests on Mauritius led to the decline of geckos and subsequently the decline of Mauritius kestrel. Likewise the intensification of agriculture in the NA prairies, led to decline of Prairie dogs and thus, decline of Black-footed ferret.

The black-footed ferret once ranged across most of the central plains of North America from southern Canada to Texas. Its lifestyle is closely linked to that of the prairie dog (Cynomys leucurus), a squirrel-like rodent that lived in huge colonies on the plains. The ferret feeds mainly on prairie dogs but can feed also on mice, ground squirrels, and rabbits. However, 90% of its diet comprises prairie dogs. The ferret lives in the warrens or burrow systems of the prairie dogs and hence that species provided the ferret with both its habitat and a large proportion of its food supply. Around the turn of the century there was a concerted effort to eradicate the prairie dog, which was viewed as vermin by ranchers. It was seen as competing with sheep and cattle for grass and its burrow systems made riding a horse most unsafe. The prairie dogs were poisoned, trapped, and shot in their millions by farmers and by government pest controllers. As the prairie dogs went, so did the ferrets. By the middle of the century they were judged to be extinct, but in 1964 a small population was discovered in South Dakota. That colony died out in 1973. In 1981 a colony was discovered in Wyoming. Careful censusing produced an estimate of 129 individuals in 1984, but by the middle of 1985 the population had declined to 58 animals and within a few months was down to 31. Canine distemper was diagnosed in this