Wild boar and feral swine number and range are increasing worldwide in parallel with their impact on biodiversity and human activities. The ecological and economic impact of this species include ...spread of diseases, vehicle collisions, damage to crops, amenities and infrastructures and reduction in plant and animal abundance and richness. As traditional methods such as culling have not contained the growth and spread of wild boar and feral pigs, alternative methods such as fertility control are now advocated. We used empirical data on two isolated wild boar populations to model and compare the effects of different regimes of culling and fertility control on population trends. We built a Bayesian population model and applied it to explore the implications for population control of various management options combining culling and/or contraception. The results showed that, whilst fertility control on its own was not sufficient to achieve the target reduction in wild boar number, adding fertility control to culling was more effective than culling alone. In particular, using contraceptives on 40% of the population to complement the culling of 60% of the animals, halved the time to achieve our target reduction compared with culling only. We conclude that, assuming the effort of adding fertility control to culling was found to be cost-effective in terms of population reduction, these two methods should be used simultaneously if a rapid decrease in wild boar number is required for a closed population.
The use of camera traps to estimate population size when animals are not individually recognizable is gaining traction in the ecological literature, because of its applicability in population ...conservation and management.
We estimated population size of synthetic animals with four camera trap sampling-based statistical models that do not rely on individual recognition. Using a realistic model of animal movement to generate synthetic data, we compared the random encounter model, the random encounter and staying time model, the association model and the time-to-event-model and we investigated the impact of violation of assumptions on the population size estimates.
While under ideal conditions these models provide reliable population estimates, when synthetic animal movements were characterised by differences in speed (due to diverse behaviours such as locomotion, grazing and resting) none of the model provided both unbiased and precise density estimates. The random encounter model and the time-to-event-model provided precise results but tended to overestimate population size, while the random encounter and staying time model was less precise and tended to underestimate population size. Lastly, the association model was unable to provide precise results. We found that each tested model was very sensitive to the method used to estimate the range of the field-of-view of camera traps. Density estimates from both random encounter model and time-to-event-model were also very sensitive to biases in the estimate of animals’ speed. We provide guidelines on how to use these statistical models to get population size estimates that could be useful to wildlife managers and practitioners.
Pulsed resources influence the demography and evolution of consumer populations and, by cascading effect, the dynamics of the entire community. Mast seeding provides a case study for exploring the ...evolution of life history traits of consumers in fluctuating environments. Wild boar (Sus scrofa) population dynamics is related to seed availability (acorns/beechnuts). From a long-term monitoring of two populations subjected to markedly different environmental contexts (i.e., both low vs. high frequency of pulsed resources and low vs. high hunting pressure in Italy and in France, respectively), we assessed how pulsed resources shape the reproductive output of females. Using path analyses, we showed that in both populations, abundant seed availability increases body mass and both the absolute and the relative (to body mass) allocation to reproduction through higher fertility. In the Italian population, females equally relied on past and current resources for reproduction and ranked at an intermediate position along the capital-income continuum of breeding tactics. In contrast, in the French population, females relied on current more than past resources and ranked closer to the income end of the continuum. In the French population, one-year old females born in acorn-mast years were heavier and had larger litter size than females born in beechnut-mast years. In addition to the quantity, the type of resources (acorns/beechnuts) has to be accounted for to assess reliably how females allocate resources to reproduction. Our findings highlight a high plasticity in breeding tactics in wild boar females and provide new insight on allocation strategies in fluctuating environments.
Hepatitis E virus (HEV) is an RNA virus causing an acute generally self‐limited disease in humans. An increasing number of autochthonous cases linked to zoonotic transmission of HEV genotype 3 have ...been reported over the last 10 years in Europe. Pigs and wild boars are considered the main reservoirs. The principal route of transmission in Europe is food‐borne, linked by direct or indirect evidence to the consumption of raw or undercooked pork products and wild boar meat. In this study, we sampled 92 wild boar (Sus scrofa) livers during active surveillance in five municipalities in Central Italy throughout the hunting season 2016–2017. HEV RNA was detected in 52.2% of liver sampled with prevalence ranging from 0.0% to 65.7%. HEV‐positive wild boars were detected in all but one area of hunting. Phylogenetic analysis showed that strains clustered within the two subtypes HEV‐3c and HEV‐3f and displayed a wide range of phylogenetic diversity. Several strains were circulating in the areas investigated; animals possibly belonging to the same family group hunted by the same team were infected with a unique strain (100% nucleotide identity). As wild animals are a proven source of HEV transmission to humans and pigs, the high prevalence observed (mean 52.2%) poses a question on the risk of consuming raw or undercooked wild boar meat, and thus, this subject deserves further investigations.
Mast seeding is a well‐known example of pulsed resources in terrestrial ecosystems. Despite the large literature available so far on the effects of mast seeding on the dynamics of seed consumer ...populations, it remains unknown whether heterogeneity in demographic responses to mast seeding exists both within a population of consumers and among consumer populations. Here, we fill this knowledge gap by assessing the effects of acorn production (i.e., oak mast) on all stage‐specific demographic rates (i.e., survival, growth, reproduction) in several consumer populations. From long‐term capture–mark–recapture data collected in three wild boar populations in Europe and detailed information on annual acorn production, we quantified the effects of acorn production on body mass‐specific demographic rates in these populations. We then built a body mass‐structured population model for each population and assessed the effect of acorn production on generation time—the mean age of mother at childbirth—and population growth rate using a combination of prospective and retrospective demographic analyses. Within populations, acorn production had a positive effect on reproduction (proportion of breeding females) and growth of small‐sized females. Survival remained buffered against environmental variation, in accordance with the demographic buffering hypothesis. Thus, all stage‐specific demographic rates were not influenced in the same way by acorn production. In turn, higher reproduction and growth probabilities involved higher population growth rates and shorter generation times. Despite these common demographic responses to mast seeding among populations, we highlighted marked among‐population variation in the magnitude of these responses. Also, while populations inhabiting resource‐rich environments took advantage of current acorn conditions, populations under resource‐poor environments stored and allocated acorns produced the preceding year to reproduction indicating contrasting breeding tactics along the capital–income continuum. Our results suggest heterogeneity in demographic responses to mast seeding, within and among populations. This is an important finding for our understanding of the effects of mast seeding on the dynamics of seed consumer populations.
The wild boar is one of the most invasive species among large mammals in both its native and introduced ranges. This species represents a main threat for crops and biodiversity and a pest for the pig ...industry due to the rapid expansion of the African swine fever. Because of its peculiar life history traits, population control programmes and recreational hunting are usually unable to effectively reduce the number of wild boars. Therefore, a reliable approach based on appropriate, cost-effective, monitoring methodologies is urgently required. Effective monitoring should adopt effective sampling strategies, otherwise the detection of population trends can be erroneous and resulting in a mismatch of appropriate management actions. First, we review the status-of-the-art of wildlife monitoring with a special focus on wild boar and feral pigs. Then, we show that nocturnal distance sampling, carried out using thermal cameras, can be an effective monitoring technique for wild boar population assessment regardless of the characteristics of the sampled area. Using data from multiple surveys performed in four study areas in Italy, characterised by contrasting topography, habitats and level of environmental visibility, we found that the estimate of precision is generally good and almost independent of landscape conditions. A simple method to estimate visibility, which may empirically help wildlife managers to design effective nocturnal distance sampling surveys, is proposed. The bias of our population estimates is evaluated using simulations showing that in some areas the estimate is unbiased, while in others there is the tendency towards a negative bias. Based on reported results, we provide guidelines to perform nocturnal distance sampling of wild boar populations.
The use of line transect methodology and portable thermal imaging for ground survey of wildlife should require a good knowledge of the behavioural response of the animals to the presence of an ...observer, in order to take into account the potential bias in density estimate caused by deviation from the assumption that distances are recorded at the initial position. We used ten fallow deer and eight wild boar fitted with radiocollars to investigate animals’ response during simulated nocturnal line transect surveys, carried out in a Mediterranean plain forest. The experiment consisted in radiolocating a focal animal before and after an observer walked a transect nearby (<100 m). Each transect line was followed using a Global Positioning System (GPS) navigator. We carried out a total of 64 trials on fallow deer and 57 on wild boar. Results showed that despite most of the animals moved significantly in response to the observer (mean ± standard error, wild boar—95.3 ± 10.0 m; fallow deer—149.6 ± 14.2 m), the flying patterns were different in the two species: the reaction of fallow deer turned out to be more intense and directional with respect to that showed by wild boar. Although these results sound explorative, the experiment attempted here, for the first time, is relevant for an appropriate design of nocturnal distance-sampling surveys and gives information about potential bias arising from animal’s behavioural response. We believe that these first results may foster more in-deep analyses which are now made possible with the adoption of GPS technology for animal location.
Actuarial senescence is widespread in age-structured populations. In growing populations, the progressive decline of Hamiltonian forces of selection with age leads to decreasing survival. As ...actuarial senescence is overcompensated by a high fertility, actuarial senescence should be more intense in species with high reproductive effort, a theoretical prediction that has not been yet explicitly tested across species. Wild boar (Sus scrofa) females have an unusual life-history strategy among large mammals by associating both early and high reproductive effort with potentially long lifespan. Therefore, wild boar females should show stronger actuarial senescence than similar-sized related mammals. Moreover, being polygynous and much larger than females, males should display higher senescence rates than females. Using a long-term monitoring (18 years) of a wild boar population, we tested these predictions. We provided clear evidence of actuarial senescence in both sexes. Wild boar females had earlier but not stronger actuarial senescence than similar-sized ungulates. Both sexes displayed similar senescence rates. Our study indicates that the timing of senescence, not the rate, is associated with the magnitude of fertility in ungulates. This demonstrates the importance of including the timing of senescence in addition to its rate to understand variation in senescence patterns in wild populations.
Wild boar and feral swine number and range are increasing worldwide in parallel with their impact on biodiversity and human activities. The ecological and economic impact of this species include ...spread of diseases, vehicle collisions, damage to crops, amenities and infrastructures and reduction in plant and animal abundance and richness. As traditional methods such as culling have not contained the growth and spread of wild boar and feral pigs, alternative methods such as fertility control are now advocated. We used empirical data on two isolated wild boar populations to model and compare the effects of different regimes of culling and fertility control on population trends. We built a Bayesian population model and applied it to explore the implications for population control of various management options combining culling and/or contraception. The results showed that, whilst fertility control on its own was not sufficient to achieve the target reduction in wild boar number, adding fertility control to culling was more effective than culling alone. In particular, using contraceptives on 40% of the population to complement the culling of 60% of the animals, halved the time to achieve our target reduction compared with culling only. We conclude that, assuming the effort of adding fertility control to culling was found to be cost-effective in terms of population reduction, these two methods should be used simultaneously if a rapid decrease in wild boar number is required for a closed population.
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