are species whose male ornaments (horn, tusks, antlers, or other body parts) make
them particularly attractive to humans, regardless of the cost and energy required to
kill them. There are several obvious examples: black rhinos, elephants, and big cats
(lions, leopards, and tigers). When the profit from a rhino horn can exceed a rural
African’s expected income for a decade, it is not surprising that overharvesting occurs.
In many cases, though, the ornaments of interest appreciate in value as animals
get older. When successful breeding depends on having adequate numbers of mature
males, it may make a good deal of conservation sense only to harvest the oldest males,
who have already bred, rather than harvest indiscriminately. This principle is illus-
trated in lions (Whitman et al. 2004). Male lions are attractive as trophies to many
tourist hunters, particularly old males with a full mane. Lions ordinarily live, feed,
and breed in a stable social group called a pride. A typical pride in East Africa com-
prises a group of six or so breeding females, often sisters, and a coalition of two or
three males. Male coalitions come and go, whereas females usually remain within a
given pride for their entire life. Given the short pride tenure (2–3 years) that any
male can expect to hold, rapid breeding is essential to their reproductive success.
Because of this, incoming coalitions often kill all the cubs surviving from their pre-
decessors. This brings all the mothers rapidly into estrous, allowing the new batch
of males a chance to sire offspring. However, if males turn over too quickly, infan-
ticide outstrips successful reproduction and the population declines.
Whitman et al. (2004) developed a detailed, spatially explicit model of individual
lions, each of whom lived, bred, and died within 5–10 computer prides, based on long-
term studies conducted in Serengeti National Park and Ngorongoro Crater (Packer
et al. 2005). They used this model to consider the impact of harvesting of males by
sport hunting. At typical quotas for the East African savanna, their model suggests
that indiscriminate harvesting of all mature males with full manes (those 4 years and
older) is unsustainable. The reason is that removal of males by hunters before they
would ordinarily lose their position at the head of a pride causes new males to come
in and so there is too much infanticide for the lion population to cope with. On the
other hand, the model suggests that hunters couldharvest all the males they might
want that are 8 years old or older. These males have already bred, by and large, so they
are expendable. Since they are also the most attractive as trophies it is a win–win
situation, so long as hunters can tell how old each male is before shooting him. Whitman
et al. (2004) showed that the amount of black on a lion’s nose provides a reliable
indicator of the age of that individual. This simple harvesting strategy, combined with
a reliable clue to age, might prove vital in conserving African lions in the long term.
This kind of enlightened harvest policy might prove useful for other trophy
species as well. For example, harvesting of horns from male saiga antelopes (Saiga
tatarica) is an important source of income for people living around the Caspian Sea.
Recent data, however, suggest that so many male saiga antelopes are now being removed
that breeding by females is compromised (Milner-Gulland et al. 2003). This is an
example of how harvesting can induce an Allee effect (Courchamp et al. 2000a; Petersen
and Levitan 2001), whereby population growth rates begin to decline once a popula-
tion falls below a critical lower threshold.The most serious challenge currently facing most threatened bird and mammal
species is habitat contraction and loss. It is rare that habitat loss would pose a
serious risk for a generalist species, capable of living in a wide range of places. It isCONSERVATION IN THEORY 309
17.8.3Extinction
threat due to habitat
loss