27
3
Identifying the Ecological Correlates of
Extinction-Prone Species: A Case
Study of New Zealand Birds
Brendan Moyle
Introduction
Risk of extinction is a variable used in a number of conservation management
arenas. For instance, the U.S. Endangered Species Act classes species according
to risks of extinction and mandates differing levels of federal protection based on
these classifications. The international agreement on trade in endangered species
(CITES) uses a similar system in which differing levels of trade restrictions are
applied to species for which risk of extinction is an important criterion (Lyster
1985). The IUCN (World Conservation Union) categories attempt a more precise
definition of extinction risks but without any associated policy prescriptions
(Mace and Lande 1991). Nonetheless, these extinction risks are intended to provide species managers with information to aid in decision making.
Although extinction risk is widely recognized as being important and as having
applications for conservation policy, there remains a gap between theory and
application. One problem is that methods for determining extinction risk can be
demanding. For instance, field studies may be necessary to determine whether a
species is in decline. Population viability analysis (PVA) may be used, but this
technique usually requires detailed population data; consequently, relatively few
species have actually been the target of such analysis (Mace and Lande 1991;
Boyce 1992; Beissinger and Westphal 1998).
The impact of the requirements for additional empirical information and PVA
has several adverse effects. If the conservation organization avoids such exercises
(and their associated costs), it may bias conservation policy toward those species
that are already well known. Typically, these are the charismatic fauna (Metrick
and Weitzman 1996). Mammals and birds tend to be popular recipients of recovery effort relative to the less well-known invertebrates or lower plants.
In addition to the substantial costs associated with field studies and data collection exercises for PVA, response lags may occur. There may be significant delays
between the point at which a species crosses some extinction risk threshold and
the point at which this is observed or recognized, compromising recovery efforts.
For example, recovery work on the Little Spotted Kiwi (Apteryx owenii) was
3
Identifying the Ecological Correlates of
Extinction-Prone Species: A Case
Study of New Zealand Birds
Brendan Moyle
Introduction
Risk of extinction is a variable used in a number of conservation management
arenas. For instance, the U.S. Endangered Species Act classes species according
to risks of extinction and mandates differing levels of federal protection based on
these classifications. The international agreement on trade in endangered species
(CITES) uses a similar system in which differing levels of trade restrictions are
applied to species for which risk of extinction is an important criterion (Lyster
1985). The IUCN (World Conservation Union) categories attempt a more precise
definition of extinction risks but without any associated policy prescriptions
(Mace and Lande 1991). Nonetheless, these extinction risks are intended to provide species managers with information to aid in decision making.
Although extinction risk is widely recognized as being important and as having
applications for conservation policy, there remains a gap between theory and
application. One problem is that methods for determining extinction risk can be
demanding. For instance, field studies may be necessary to determine whether a
species is in decline. Population viability analysis (PVA) may be used, but this
technique usually requires detailed population data; consequently, relatively few
species have actually been the target of such analysis (Mace and Lande 1991;
Boyce 1992; Beissinger and Westphal 1998).
The impact of the requirements for additional empirical information and PVA
has several adverse effects. If the conservation organization avoids such exercises
(and their associated costs), it may bias conservation policy toward those species
that are already well known. Typically, these are the charismatic fauna (Metrick
and Weitzman 1996). Mammals and birds tend to be popular recipients of recovery effort relative to the less well-known invertebrates or lower plants.
In addition to the substantial costs associated with field studies and data collection exercises for PVA, response lags may occur. There may be significant delays
between the point at which a species crosses some extinction risk threshold and
the point at which this is observed or recognized, compromising recovery efforts.
For example, recovery work on the Little Spotted Kiwi (Apteryx owenii) was