Line | There are recent reports of apparently drastic |
| declines in amphibian populations and of extinctions |
| of a number of the worlds endangered amphibian |
| species. These declines, if real, may be signs of a |
(5) | general trend toward extinction, and many |
| environmentalists have claimed that immediate |
| environmental action is necessary to remedy |
| this amphibian crisis, which, in their view, is an |
| indicator of general and catastrophic environmental |
(10) | degradation due to human activity. |
| To evaluate these claims, it is useful to make a |
| preliminary distinction that is far too often ignored. |
| A declining population should not be confused with |
| an endangered one. An endangered population is |
(15) | always rare, almost always small, and, by definition, |
| under constant threat of extinction even without a |
| proximate cause in human activities. Its disappearance, |
| however unfortunate, should come as no great |
| surprise. Moreover, chance events—which may |
(20) | indicate nothing about the direction of trends in |
| population size—may lead to its extinction. The |
| probability of extinction due to such random factors |
| depends on the population size and is independent of |
| the prevailing direction of change in that size. |
(25) | For biologists, population declines are potentially |
| more worrisome than extinctions. Persistent |
| declines, especially in large populations, indicate a |
| changed ecological context. Even here, distinctions |
| must again be made among declines that are only |
(30) | apparent (in the sense that they are part of habitual |
| cycles or of normal fluctuations), declines that take |
| a population to some lower but still acceptable |
| level, and those that threaten extinction (e.g., by |
| taking the number of individuals below the minimum |
(35) | viable population). Anecdotal reports of population |
| decreases cannot distinguish among these |
| possibilities, and some amphibian populations have |
| shown strong fluctuations in the past. |
| It is indisputably true that there is simply not |
(40) | enough long-term scientific data on amphibian |
| populations to enable researchers to identify real |
| declines in amphibian populations. Many fairly |
| common amphibian species declared all but extinct |
| after severe declines in the 1950s and 1960s |
(45) | have subsequently recovered, and so might |
| the apparently declining populations that have |
| generated the current appearance of an amphibian |
| crisis. Unfortunately, long-term data will not soon |
| be forthcoming, and postponing environmental |
(50) | action while we wait for it may doom species and |
| whole ecosystems to extinction. |