| Popis: |
Lucky me to have had the chance of enjoying the barely audible sound of calling spadefoot toads on warm spring nights! Right at the breakthrough of spring they arrive at the breeding ponds, by the time when the air becomes heavy with the promising fragrances of spring and early summer. Lucky me to have experienced the wonders of early summer sunrises in the field - and the joy of thawing out frozen fingers after hours of field work around freezing point. Amphibian populations are declining. This worrying fact is what has initiated this work. Some fifty years ago, the life history of frogs and toads was common knowledge to everybody due to personal experience: amphibians were abundant. Noisy and innumerable in spring when reproducing, silent and even more abundant in late summer with both adults and metamorphs leaving the breeding ponds. Today, experiencing frogs and toads is an event, something to talk about. Fortunately, amphibians are still numerous in certain places and hopefully, we will get to a point when we know enough about the declines and their backgrounds to bring the decline to an end. It is my hope that results of this work will add a piece to the puzzle. This work is the result of my three year PhD study at the National Environmental Research Institute, Kalø, and University of Copenhagen. Funded by NERI, the Danish Research Academy, and the Danish Road Directorate, it has dealt mainly with the effects of traffic and roads on amphibian populations. The Spadefoot toad as described above has been studied most intensively, but the work has included common and crested newt, common toad, common frog and moor frog as well. The work has resulted in three manuscripts which form the main part of the thesis: I Quantification of demographic parameters in a Danish metapopulation of Spadefoot toads (Pelobates fuscus Laur.) II The effect of road kills on amphibian populations III Simulating viability of a Spadefoot toad (P. fuscus) metapopulation in a landscape fragmented by a road The manuscripts are preceded by a synopsis which sums up the work and puts it into a broader perspective. In the synopsis, I describe and briefly review the paradigms behind the work, I review and discuss my most important findings, and finally, I point at gaps in our present knowledge: further work that has to be done to improve our understanding of ecological patterns and processes within this field. Although this thesis is basically one woman's work, several people have improved it substantially by making the work more interesting, more appealing, more correct - and not to forget, more fun. I thank my advisors Aksel Bo Madsen and Gösta Nachman for all kinds of valuable advice along the way. Thank you Helle Clausen, Bente Hansen, Tine Hansen, Klaus Nordvig, Sune Thomsen, and Mikkel Ørsberg for skilled field work, and Jesper Bruun-Schmidt, Thøger Dige, and Susanne Nielsen for allowing me to use data from your masters' theses. Thanks are also due to my Swedish colleagues and friends, especially Per Edenhamn, Johan Elmberg, Andreas Seiler, and Per Sjögren-Gulve, for sharing your knowledge and enthusiasm for science with me. Constructive ideas, different approaches, and elaborate discussions are crucial parts of any scientific process: I thank Lenore Fahrig for dedicated and original teaching and discussions during the PhD-course in Landscape Ecology and Wildlife Management at Grimsö, Sweden, December 1995 and Peter Kareiva for new ideas during my stay in your lab in Seattle, Washington, in the autumn of 1997. I am also grateful to Thomas Bregnballe, Erik Buchwald, and Chris Topping for invaluable discussions and for improving various versions of the manuscripts. Finally, I thank Tove Petersen and Kirsten Zaluski for improving my English, and Bo Bendixen for the front page drawing. |
