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If demand is modest relative to renewable resource supplies, then the classic

supply–demand relationship occurs. There is a single intersection between the sup-

ply and demand curves, defining the economic equilibrium (Fig. 19.16a). Harvests

should build over time and resource prices should fall until the supply meets

demand. Due to the severe non-linearities in the supply curve, however, this ideal

situation can be rapidly transformed into a more troubling scenario. Imagine, for exam-

ple, that economic development leads to slight overall increase in consumer demand

(Fig. 19.16b). This results in a situation in which there are three points of intersec-

tion: at high, moderate, and low prices, and low, moderate, and high harvest levels.

Now the system is poised to flip between dramatically different economic equilibria

with slight changes in resource levels or economic performance. The high price/low

harvest combination is particularly worrisome, because it arises because of a severely

overharvested resource, teetering dangerously near extinction. It is nonetheless

profitable enough to justify the huge effort required to eek out a meager harvest. Further

increase in demand leads to a singular economic equilibrium, this time in the

risky zone.

This scenario is particularly likely when the demand curve descends quite sharply.

An economist would characterize such a demand curve as being “inelastic,” meaning

that it requires quite substantial change in price to suitably alter consumer behavior

(by definition, inelastic means that a 1% change in price achieves less than a 1% change

in demand). For some wildlife products, such as ivory, there is evidence that con-

sumer demand is determined solely by income, regardless of price (Milner-Gulland

1993). Should demand be highly elastic (much flatter in a plot of price versus quan-

tity demanded), multiple economic equilibria become far less likely. Food products,

because there is greater room for substitution, are often highly elastic, which should

offer some comfort. On the other hand, small changes in rural incomes can lead to

substantial changes in diets, with bush meat and other wildlife food products rapidly

becoming highly prized.

Ivory-harvesting presents a fascinating case study (Milner-Gulland and Beddington

1993). Male elephants have substantially larger tusks than females, so any rational

harvesting scheme would be biased towards males (Milner-Gulland and Mace 1998).

WILDLIFE HARVESTING 351

1.5

1.0

0.5

0

1.5

1

0.5

0 20 40 60 80 100 120 00 20 40 60 80 100 120

Harvest Harvest

Price Price

(a) (b)

Fig. 19.16Supply (solid) and demand (broken) curves for a renewable natural resource at (a) low and (b) high levels of
demand.