How Far Can We Take the Recovery Process?
Although the status of large carnivores across Europe is heterogeneous and dynamic there are grounds for increasing (though still cautious) optimism concerning their future status. Apart from a few small populations that are clearly still threatened (such as bears in central Italy and the Pyrenees), the main task for the future is more one of sustaining their recovery than of saving them from extinction (Swenson et al.
Fig. 4.3 Distribution of lynx and their populations in Europe in 2012. Dark cells permanent occurrence, Grey cells sporadic occurrence. (From Kaczensky et al 2013)
1998). This leads to asking how far the recovery may go. In other words, what level of conservation ambition should we hope for (Linnell et al. 2005)? While the shortterm recovery goals have always been about achieving “population viability” to safeguard against population and species extinctions, the present conservation discourse is now increasingly moving to one of “ecological functionality”. Although the rewilding movement offers many diverse points of view (Donlan et al. 2006; see Chaps. 1 and 9), it has been placing a lot of emphasis on the restoration of “natural processes” with the often stated understanding that this excludes human activity.
So far these ideas have been mainly directed towards restoring herbivory, although they have met with considerable debate (Hodder et al. 2005; Kirby 2009). There is an increasing trend to also extend them to predation and we feel it is also important to raise some questions concerning whether it is possible, or even desirable, to restore “natural predation processes” (Andersen et al. 2006). It is important to ask what this term means, and even ask if it should be the benchmark goal for large carnivore conservation strategies from strategic and value based points of view.
What are the Characteristics of “Natural Predation Processes”?
Describing the nature of predator—prey dynamics for large carnivores and large herbivores has been an ongoing theme in ecological research for the last 60–70 years at least. From the early writings of Aldo Leopold through to the on-going long-term predator-prey studies of wolf—moose relationships on Isle Royale and other parts of North America and Africa, there has been much speculation about the relative importance of top-down and bottom-up factors in regulating densities of predators and prey (e.g. Skogland 1991; Mech and Peterson 2003). The discussion has also spilled over into discussions in modern conservation biology about the pervasiveness of trophic cascades and the role of predators as ecological keystones (Ray et al. 2005; Terborgh and Estes 2010). Reviewing this vast literature is beyond the scope of this chapter, but it is possible to extract some findings relevant for our discussion. Firstly, predators have been shown to have a diversity of behavioural and demographic effects on their prey and on other aspects of ecosystem function through trophic cascades. However, the strength of these impacts varies considerably across space (Melis et al. 2009, 2010) and time (Mech and Peterson 2003) and with the behaviour of the predator and the anti-predator strategy of the prey. Secondly, the impact of predators on prey is very much dependent on the numerical response of predator density as well on the functional responses of kill rates to changes in prey density (Andersen et al. 2006). Moreover, large carnivore populations operate at very large scales, with home ranges spreading across hundreds of square kilometres (Nilsen et al. 2005) and dispersal distances covering hundreds of kilometres (Samelius et al. 2012). This implies that spatial dynamics of large carnivores can only be measured on such large scales, making it hard to predict impacts at local scales. Additionally, many fine-scaled factors such as variation in habitat structure or snow depth can introduce micro-level modifications to the larger scale processes (Gorini et al. 2012), which introduce uncertainties in predicting larger scale dynamics. Furthermore, both large carnivores and large herbivores are influenced by external factors such as climate and disease that have the potential to induce dramatic changes in population sizes and predator prey relationships. Finally the empirical data underpinning our understanding of predator-prey systems is very limited, especially for systems with multiple predators and multiple prey, and time series are almost entirely rather short.
The present state of knowledge is sufficient to have a good qualitative idea of the impacts of predation and the types of predator-prey dynamics that can occur. However, it is very hard to predict in a quantitative way what will occur in any given location. This is especially true for Europe, where there have been very few long-term predator-prey studies. Therefore, it is rather difficult to speculate about what “natural predation processes” will actually be in any given location.