The Eurasian Otter (Lutra lutra) in the Alpine Arc: Resource selection and habitat suitability models
Habitat selection is a fundamental aspect in ecology. It affects survival and reproduction of individuals and hence influences population dynamics. Today, most landscapes are modified by anthropogenic activities, resulting in habitat fragmentation, destruction and homogenisation. In such altered landscapes, either species can adapt to the new environmental conditions or they perish. To implement efficient conservation measures, it is crucial to understand how the animals move within a landscape and what habitat requirements they have. The Eurasian otter (Lutra lutra) is a semi aquatic mammal, whose populations have declined strongly during the 20th century. In recent decades, otter populations started to recover in some areas, e.g. at the periphery of the Alpine Arc. Here the riverine landscape has been altered massively due to hydropower, flood prevention and an increase of road networks and traffic following a strong increase of the human population in the last 30 years. Today, the otter is still absent in large parts of the Alpine Arc. But there are a growing population in the Central Alps in Austria and small and isolated occurrences in the French Alps. Understanding habitat requirements of otters in this landscape and predicting habitat suitability to the core of the Alps will contribute to facilitate the recovery and the reconnection of the populations within the Alpine Arc. To investigate these aspects, I radiotracked wild otters in the Eastern Central Alps, in Styria (Austria) Using the data of nine otters tracked from seven to 30 months, I analysed habitat selection at multiple spatial scales. Specific behaviours require different habitats. I thus discriminated between the main daily behaviours of foraging and resting. I analysed foraging habitat selection at three different spatial levels: population, individual and within home range (Chapter 2) At the finest scale, I combined habitat selection with movement by applying a step selection function to the linear system of the watercourses in a novel way. I show that otters adapt well to a landscape interrupted by a multitude of hydropower stations. Indeed, modifications to the riverine landscape by damming provide even new and profitable foraging grounds for the otters. This behaviour may be driven by the traditional fish stocking regime. I conclude that otters are flexible in their selection for foraging habitat, supporting the notion of a successful recovery of the species into the Alpine Arc. Resting is one of the most vulnerable states of an animal. Resting sites provide protection from harsh weather conditions but also from predators. Humans often evoke strong antipredator behaviour, even in apex carnivores. Little is known about general resting site selection of otters and less about the effect of humans on this selection. As a semi aquatic mammal, otters are linked to waterbodies and may seek protection in its immediate surrounding. However, modifications to the watercourses and an intensification of the 3 agriculture have reduced the riparian vegetation. Additionally, leisure activities increase along watercourses. In the third Chapter, I show that resting sites are indeed almost exclusively situated in the riparian vegetation. With data from 284 resting sites, I illustrate that otters are content with small riparian vegetation belts as long as daily human disturbance is low, but that a larger riparian vegetation belt is required as a protective buffer when there are more frequent human activities. I argue that humans are perceived as threats by carnivores and that the intensity of human presence influences resting site selection. I conclude that strips of vegetation cover is a crucial necessity for resting carnivores in anthropogenic altered landscapes and stress the importance of riparian vegetation, a threatened landscape in Europe. Habitat suitability maps can predict occurrence of a species and provide information on the permeability of the landscape matrix. Scale is an important factor because environmental factors can be scale sensitive and because conservation actions often are targeted at different levels e.g. local or national. To predict future otter occurrence at the core of the Alpine Arc and its potential to reconnect the French and Austrian population, I developed two habitat suitability models (HSM) using two different data set at a different scale (Chapter 4) The large scale HSM was built on large scale snowtracking surveys in Styria, Austria at a resolution of 10 km2. For the fine scale HSM I used radiotracking data on resting behaviour, which has higher habitat requirements than foraging behaviour. I demonstrate with both HSMs that there are suitable habitats for otters in the core of the Alps. I show that a recolonization of Switzerland by otters seems possible and a reconnection of the populations within the Alpine Arc is realistic. My results also highlight the importance of scale, which is even more pronounced when environmental data are lacking. In summary, I evaluated key factors for habitat selection of different behaviours, based on radiotracking data of otters in the Eastern Central Alps. I then used this data to develop habitat suitability models at two spatial scales to reveal the potential of re expansion of the species to the core of the Alps. In the last chapter (Chapter 5) I summarize my results based on five years of work and discuss my findings, conclusions and their applications.