Optimal conservation strategies in fragmented landscapes: a case study on two forest rodents, Muscardinus avellanarius and Myodes glareolus, in Central Italy

Human-induced fragmentation of ecosystems and natural habitats is considered one of the major threats to biodiversity. Albeit a considerable effort have been invested in research, progresses in conservation measures occur too slowly compared to the current rate of extinction of plant and animal species caused by the fragmentation of habitats. The delay is mainly due to the complexity of the processes involved, which produce a multitude of effects, both direct and indirect, occurring at various spatial scales and levels of biological organization. Recently, it has emerged how conservationists would not only need face and find answers to ecological problems, but their analysis would have to take into account also socioeconomic factors , since the latter could threat the success of conservation actions and determine a waste of limited financial resource. In a world with limited conservation funds, and with a great geographical variability in the conservation costs, efficiency would be better measured in terms of conservation return on financial investment. The scope of this study was to determine the fixed-budget optimal conservation strategies in fragmented landscapes for two forest-dwelling rodents hazel dormouse Moscardinus avellanarius and bank vole Myodes glareolus, by analyzing their demographic parameters, and by evaluating the efficacy and cost-effectiveness of simulated conservation actions. From results emerged that the hazel dormouse vital rates showed a strong relationship with the quality of the fragments (i.e. the complexity of the shrub layer), influencing both the survival rate and the fertility. On the other hand, the bank vole appears to be related to suboptimal quality fragments, with survival rates increasing in smaller fragments and fertility increasing in fragments with lower fruit-bearing shrubs density. Likewise, the analysis, which aimed to predict the species persistence in the fragmented landscape, resulted in opposite trends. While the population viability analysis for the hazel dormouse predicted an important decline in metapopulation abundance and occupancy during the 50-year simulated period, the population viability analysis for the bank vole metapopulation showed a marked increase in abundance within the same time interval. The optimization protocol I elaborated explores which fixed-budget conservation actions would enhance the persistence of the hazel dormouse metapopulation. The protocol allowed to determine that, between the two conservation strategies explored, i.e. habitat restoration and habitat quality improvement, to restore a certain amount of woodlands is the most effective way to increase the metapopulation abundance and to reduce, although slightly, the probability of decline of a given percentage. It is important to note that, however, the optimal conservation strategy would not reverse or prevent the hazel dormouse metapopulation negative trends.