| 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. |