Plasticity in daily activity patterns of a key prey species in the Iberian Peninsula to reduce predation risk

Abstract ContextSome prey species can shift their daily activity patterns to reduce the risk of encountering predators, and, in turn, predators develop strategies to increase their chances of meeting prey. European rabbit (Oryctolagus cuniculus) is a key species in Iberian Mediterranean ecosystems. It is the main prey for many vertebrate predators. It is also a game species and is often the target of management measures such as translocations. AimsTo test whether rabbits adjust their activity patterns in response to differing predation regimes in a management context. MethodsRabbits were translocated from a donor area, with a high rabbit density, to a release area in central Spain, with a semi-permeable fenced plot and an unfenced plot, which had no rabbits before the translocation. We estimated daily activity patterns and relative abundance index (RAI) for mesocarnivores and rabbits by using camera-traps, and calculated Jacobs selection index (JSI) to classify each species in a diel period. Additionally, we calculated the activity overlap between prey and mesocarnivores in the different areas. Key resultsRabbits were nocturnal in the donor area, where only two mesocarnivore species were detected, red fox (Vulpes vulpes, with a high RAI) and Egyptian mongoose (Herpestes ichneumon, with a low RAI). However, in the unfenced area, where five mesocarnivore species were present, rabbits showed a crepuscular trend with two activity peaks, around sunrise and around sunset. In contrast, rabbits showed a nocturnal activity in the fenced plot, where four mesocarnivore species were detected but where only the Egyptian mongoose (strictly diurnal) had a high RAI value. Conclusions and implicationsThe results suggest that rabbits in the fenced plot adapted their activity to avoid the diurnal mongooses. Conversely, rabbits in unfenced areas showed a trend towards day/twilight activity patterns as an adaptation to a diverse community of mesocarnivores. Rabbits can adapt their daily activity patterns to reduce predation risk depending on the pressure exerted by different predator species, with conservation and management implications. These adaptations would allow higher success of rabbit translocations despite the risk of predation by carnivores and could help in the management design of future translocations of this key species.

Effects of myxoma virus and rabbit hemorrhagic disease virus on the physiological condition of wild European rabbits: Is blood biochemistry a useful monitoring tool?

Myxomatosis and rabbit hemorrhagic disease (RHD) are the major viral diseases that affect the wild European rabbit (Oryctolagus cuniculus). These diseases arrived in Europe within the last decades and have caused wild rabbit populations to decline dramatically. Both viruses are currently considered to be endemic in the Iberian Peninsula; periodic outbreaks that strongly impact wild populations regularly occur. Myxoma virus (MV) and rabbit hemorrhagic disease virus (RHDV) alter the physiology of infected rabbits, resulting in physical deterioration. Consequently, the persistence and viability of natural populations are affected. The main goal of our study was to determine if blood biochemistry is correlated with serostatus in wild European rabbits. We carried out seven live-trapping sessions in three wild rabbit populations over a two-year period. Blood samples were collected to measure anti-MV and anti-RHDV antibody concentrations and to measure biochemical parameters related to organ function, protein metabolism, and nutritional status. Overall, we found no significant relationships between rabbit serostatus and biochemistry. Our main result was that rabbits that were seropositive for both MV and RHDV had low gamma glutamyltransferase concentrations. Given the robustness of our analyses, the lack of significant relationships may indicate that the biochemical parameters measured are poor proxies for serostatus. Another explanation is that wild rabbits might be producing attenuated physiological responses to these viruses because the latter are now enzootic in the study area.

A case of low success of blind vaccination campaigns against myxomatosis and rabbit haemorrhagic disease on survival of adult European wild rabbits

Vaccination campaigns against myxomatosis and rabbit haemorrhagic disease (RHD) are commonly used in translocation programs conducted for the purpose of recovering wild European rabbit populations in Iberian Mediterranean ecosystems. In most cases rabbits are vaccinated 'blind' (i.e. without assessing their prior immunological status) for economic and logistic reasons. However, there is conflicting evidence on the effectiveness of such an approach. We tested whether blind vaccination against myxomatosis and rabbit haemorrhagic disease improved rabbit survival in a rabbit translocation program where wild rabbits were kept in semi-natural conditions in three enclosures. We conducted nine capture sessions over two years (2008-2010) and used the information collected to compare the survival of vaccinated (n=511) versus unvaccinated (n=161) adult wild rabbits using capture-mark-recapture analysis. Average monthly survival was no different for vaccinated versus unvaccinated individuals, both in the period between release and first capture (short-term) and after the first capture onward (long-term). Rabbit survival was lower in the short term than in the long term regardless of whether rabbits were vaccinated or not. Lower survival in the short-term could be due to the stress induced by the translocation process itself (e.g. handling stress). However, we did not find any overall effect of vaccination on survival which could be explained by two non-exclusive reasons. First, interference of the vaccine with the natural antibodies in the donor population. Due to donor populations have high density of rabbits with, likely, high prevalence of antibodies as a result of previous natural exposure to these diseases. Second, the lack of severe outbreaks during the study period. Based on our findings we argue that blind vaccination of adult rabbits in translocation programs may be often mostly ineffective and unnecessarily costly. In particular, since outbreaks are hard to predict and vaccination of rabbits with natural antibodies is ineffective, it is crucial to assess the immunological status of the donor population before translocating adult rabbits.

Multi-event capture-recapture modeling of host-pathogen dynamics among European rabbit populations exposed to myxoma and Rabbit Hemorrhagic Disease Viruses: common and heterogeneous patterns

Host-pathogen epidemiological processes are often unclear due both to their complexity and over-simplistic approaches used to quantify them. We applied a multi-event capture-recapture procedure on two years of data from three rabbit populations to test hypotheses about the effects on survival of, and the dynamics of host immunity to, both myxoma virus and Rabbit Hemorrhagic Disease Virus (MV and RHDV). Although the populations shared the same climatic and management conditions, MV and RHDV dynamics varied greatly among them; MV and RHDV seroprevalences were positively related to density in one population, but RHDV seroprevalence was negatively related to density in another. In addition, (i) juvenile survival was most often negatively related to seropositivity, (ii) RHDV seropositives never had considerably higher survival, and (iii) seroconversion to seropositivity was more likely than the reverse. We suggest seropositivity affects survival depending on trade-offs among antibody protection, immunosuppression and virus lethality. Negative effects of seropositivity might be greater on juveniles due to their immature immune system. Also, while RHDV directly affects survival through the hemorrhagic syndrome, MV lack of direct lethal effects means that interactions influencing survival are likely to be more complex. Multi-event modeling allowed us to quantify patterns of host-pathogen dynamics otherwise difficult to discern. Such an approach offers a promising tool to shed light on causative mechanisms.