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64 Amphibians and reptiles are coming to be regarded in Europe as indicator groups for a general decline in species diversity (Thielcke et al., 1983; Blab, 1985, 1986). The decline of these groups has been well documented in Europe and on other continents as a result of numerous surveys (e.g., Lemmel, 1977; Feldmann, 1981; Hayes and Jennings, 1986; Hölzinger, 1987; Osborne, 1990; Carey, 1993; Mahony, 1993). Even in areas little affected by human activity, declines seem to have occurred. However, to date, adequate investigations of the declines and their actual causes are lacking (Pechmann et al., 1991; but see Osborne, 1989). The global decline of amphibians over large land masses is presumed to be attributable to as yet essentially unknown factors (Blaustein and Wake, 1990; Yoffe, 1992), while previously established causes of decline have been neglected. However, the reverse tendency exists for local and regional investigations —in those cases, as a rule, factors are readily identified as causes, but are seldom investigated because the causal relation to observed declines is often difficult to clearly establish (Henle and Streit, 1990). Thus, there is frequently not a clear distinction between potential threats and proven causes, and many opportunities to prove causal connections, or at least to carefully construct foundations for hypotheses, are missed. A scientifically based analysis of causal relations is essential to effective conservation efforts since it leads to the prediction of appropriate countermeasures. The most important type of database for the documentation of the declines of amphibians and reptiles and their potential causes results from regular surveys of a specific geographic area. Surveys will maintain this important role in the future. Therefore, attempts should be made to fully utilize the potential of these surveys for causal analysis of declines within the bounds of permissible conclusions. That is, the limits of herpetofaunal surveys as a tool for determining the causes of decline must be explicitly defined. The available methods for causal analysis are insufficiently known to many people engaged in surveying projects because of inadequate education in statistics and research planning. The goal of this work is to demonstrate the available methods of causal analysis, as well as their limitations, by applying the methods in the analysis of a long-term surveying project (Henle and Rimpp, 1994). Further, remarks on the optimization of surveying projects that will facilitate subsequent causal analyses are presented. By suggesting improvements in the planning and assessment of future surveying projects, I hope to contribute to the technical support of herpetological conservation work, and with that, to the protection of our amphibians and reptiles. Methods for Analysis of the Causes of Species Decline The principles of planning and analysis of experiments furnish three experimental approaches for evaluating causal relations in ecology: (1) laboratory experiments, (2) field experiments, and (3) unplanned or natural experiments (Diamond, 1986; Henle and Streit, 1990). In all three types of experiments the presence of adequate control populations that remain unaffected by the factor in question (e.g., road traffic) is essential. Likewise, it is important to formulate a precise question in the form of a so-called null hypothesis, for example, “Addition of pollutant chemicals to a water body does not lead to increased mortality in comparison to unpolluted water bodies.” The probability that the null hypothesis is correct is then determined statistically. The advantages and disadvantages of the three different experimental approaches are briefly summarized below. Laboratory Experiments Laboratory experiments have the advantage that disturbances are largely eliminated; independent variables (in our case, potential threats) are controlled, allowing the effect of a specific threat to be clearly determined. They have a disadvantage in that their relevance to natural systems is highly questionable because of the stark simplicity of the laboratory system. This problem can be minimized, but not fully eliminated, by the use of experimental conditions that simulate natural TW E LVE Lessons from Europe K. HENLE * Translation by William T. Leja of Möglichkeiten und Grenzen der Analyse von Ursachen des Artenrückgangs aus herpetofaunistischen Kartierungsdaten am Beispiel einer langjährigen Erfassung. 1996. Zeitschrift für Feldherpetologie 3:73–101. conditions as much as possible. There has been considerable investigation in the laboratory of the threat posed to amphibians by predators (e.g., Glandt, 1984; Kats et al., 1988; Semlitsch , 1993). However, in this case the results are frequently of severely limited applicability or are actually inapplicable to field situations because of the generally simplified and artificial laboratory conditions. Field Experiments Field experiments are of far greater relevance. The...

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