Sirvi Kuupäev , alustades "2009-10-21T13:54:59Z" järgi

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Impacts of habitat loss and restoration on amphibian populations
(2009-10-21T13:54:59Z) Rannap, Riinu
Currently amphibians have the higher proportion of threatened species among higher taxa in the world. One of the main reasons for global amphibian decline is the loss and degradation of their habitats. However, their impacts on amphibians are known in surprisingly general terms only. This thesis focuses on two threatened amphibians – the natterjack toad (Bufo calamita) and the crested newt (Triturus cristatus). Concerning the natterjack toad, the population-level effects of habitat loss on Baltic coastal meadows were studied. The extinction rates of local populations exceeded habitat loss rates, and this pattern appeared at the advanced stage of habitat loss. The large areas of managed meadow and sand were essential for the survival of natterjack toad populations. As this species is at the northern edge of its distribution range in Estonia, the geographical context and a mechanism behind breeding-habitat requirements were explored at different latitudes (in Estonia and Denmark). Despite the 10 days later onset of breeding in Estonia, the natterjack toad tadpoles caught up the growth and development of their Danish conspecifics and the metamorphoses took place synchronously in two countries. Importantly, the toads in Estonia selected significantly shallower ponds for breeding than the toads in Denmark. Thus the habitat qualities critical for the growth and development of natterjack toad tadpoles varied geographically. To explore the habitat-related explanations to the rarity of species, the habitat requirements of two coexisting newt species, having contrasting population trends ¬– the smooth newt (T. vulgaris) and the crested newt ¬– were compared. Importantly, the species had similar breadths of their ecological niches but different key demands. Thus, instead of a narrower habitat demand, the crested newt’s rarity and declining trend could be related to its niche position in relation to the currently prevailing conditions. The knowledge gained from above mentioned studies were put into the practice in aquatic-habitats restoring project in southern Estonia. This practical study demonstrated that habitat restoration for threatened pond-breeding amphibians can be successful indeed if it is biologically based, implemented at the landscape scale, taking into account the habitat requirements of target species and the ecological connectivity of populations.