Interspecific interactions among the wolf, ungulates, and mesocarnivores in a Mediterranean area

Interactions that apex predators establish with prey and smaller carnivores have a great potential to shape ecosystem-level processes through top-down effects. In the last decades, growing attention has been paid to this topic. However, most knowledge comes from North American ecosystems, and the information is scarce for human-dominated landscapes such as European ones, recently recolonized by apex predators. For my thesis, I analysed the interactions between the wolf, its prey and smaller carnivores within a Mediterranean protected area where the wolf Canis lupus has recently made a stable return, i.e., the Maremma Regional Park, considering a period ranging from 2016 to 2023. This area host abundant populations of wild ungulates, including the wild boar Sus scrofa, the fallow deer Dama dama, and the roe deer Capreolus capreolus. The primary objectives of my study were to investigate the inter-annual variations of food habits and prey selection of this carnivore and to assess its spatio-temporal relationships with both prey and mesocarnivores (red fox Vulpes vulpes, badger Meles meles, stone marten Martes foina, pine marten Martes martes), to evaluate the potential for the occurrence of responses to the presence of the predator based on spatio-temporal avoidance. I used microscopic analyses of food remains in wolf scats and intensive camera-trapping. Additionally, I compared the spatio-temporal responses of the red fox to the wolf between my study area and a natural area from which wolves have never disappeared, i.e., the Białowieża Primeval Forest (Poland). Large herbivores dominated the wolf diet (> 80% occurrence) with mesocarnivores occurring minimally (c. 2%). The wolf showed a clear prey switching throughout the study. Indeed, at the first stage of the wolf resettlement (i.e., 1-2 years), the fallow deer was the main prey and was positively selected by this predator. In the following years, the wild boar replaced fallow deer as the main prey and was positively selected, with a steady decrease in the use of fallow deer throughout the years. Nevertheless, data support that this prey switching was not driven by prey densities. The relationship between selection indices and population density was negative for the wild boar and weakly positive for the fallow deer. Instead, the roe deer showed a < 10% occurrence in the wolf diet, thus it represented a secondary, alternative prey in my study area (Chapter I). Among prey, the wild boar had the highest spatio-temporal overlap with its main predator. Instead, the fallow deer showed crepuscular/nocturnal activity in the first year, with a sharp and rapid switch towards diurnality in the following years. The increase in the fallow deer diurnality was followed by a decrease in its temporal overlap with the wolf which, instead, remained mainly nocturnal and increased its synchronization with the wild boar, thus supporting the prey switching observed in the wolf diet. Conversely, no prey showed a negative spatial association with the wolf (Chapter II). In addition, the fallow deer showed a ‘lunar philia’ behaviour with less activity around the new moon, suggesting that synchronisation with the lunar cycle might play a useful role in foraging, vigilance and predators detection activities, particularly in herbivores that usually live in large herds. Conversely, roe deer showed an avoidance of the brightest nights in particular in the sites most used by wolves. Hence, the lunar cycle and nocturnal brightness may play a role in modulating the prey-predator interactions (Chapter III). Regarding the relationships between the apex predator and other carnivores, my findings showed no support to a negative spatio-temporal association between their detection rates. Conversely, I found a high level of temporal overlap between them. Results showed a high spatio-temporal association among species and, in particular, between red foxes and wolves. This latter result supports recent findings suggesting dietary facilitation by the apex predator to the red fox through the release of carcasses of its prey (Chapter IV). Hence, I wanted to deepen my research on the interactions between these two canids. The literature has shown contrasting outcomes with a range of negative to positive relationships and suggests a role of latitude as a proxy of ecosystem productivity to mediate the competition between them. To assess support to this hypothesis, I set up a comparative study between Maremma Regional Park and Białowieża Primeval Forest (Poland). I based my predictions on the global meta-analysis by Prugh and Sivy (2020) where the authors showed that the negative interactions among carnivores prevail at the higher latitudes. Thus, I expected greater positive association in the southern area (Maremma) than in the northern one (Białowieża). The results partially supported my predictions: in Maremma, the red fox was better synchronized with wolves both spatially and temporally than in the Polish area, even though I did not find support to spatio-temporal avoidance in either area. Thus, red fox responses to wolves may be relatively comparable over large spatial scales (Chapter V). In conclusion, my results indicated a marked species-specificity in the spatio-temporal responses to the presence of an apex predator, with a gradient that ranged from (i) a strong response concentrated on temporal avoidance (fallow deer), to (ii) a weak spatio-temporal response mediated by nocturnal brightness (roe deer), and to (iii) an absent - apparently - spatial and temporal response (wild boar, which likely adopt other tactics). Furthermore, I showed that anti-predator behaviours may trigger prey switching in a generalist predator. As for the interactions between wolves and mesocarnivores, my results did not underlie either component of spatio-temporal avoidance. In particular for the red fox, my data supported what has been observed in a previous study which suggested a positive association related to dietary facilitation. Hence, results strongly support that a rich community/assembly of wild prey can modulate the relationships in a carnivore guild, mitigating the competition, and bearing the resilience of large carnivores and their ecological role, with important ecological, management and conservation implications.