Wild Boar Sus Scrofa Populations Research Articles

Resource‐driven changes in wild boar movement and their consequences for the spread of African Swine Fever in the Russian Far East

Knowledge of animal movement patterns is invaluable to understanding the spread of diseases among wildlife populations. One example is the recent African swine fever (ASF) outbreak among wild boar Sus scrofa populations across East Asia, where there is a lack of information on movements of this species. During a wild boar tracking project to inform abundance estimation methods in the Russian Far East's Sikhote‐Alin Biosphere Zapovednik, the combination of high variability in pulsed resources of acorns and pine nuts between fall 2019 and fall 2020, and the outbreak of ASF during the latter year, offered the unique opportunity to investigate the relationship between wild boar movements to exploit pulsed resources and the potential for disease spread. We analyzed relocation data from GPS‐collared wild boar in fall 2019 and 2020 and compared them to reference data in Belgium, representative of western Europe. We found remarkable differences in movement patterns, with Far East wild boar travelling large distances in fall 2020 (maximum observed of 77 km in four days) when the availability of acorns was low. In our resource selection analysis, we found clear selection for mast‐producing forest types that corresponded with the species of greater mast production (oak or pine) for that year. Comparing the displacement of individual wild boar along a moving window of 1–7 days (time between infection and the onset ASF symptoms) highlighted the potential of rapid ASF spread over long distances when wild boar are in search of pulsed resources. This work demonstrates the capacity of wild boar to move long distances to exploit resources and emphasizes the need to consider resource availability when predicting the speed and extent to which diseases such as ASF can spread.

An inbreeding perspective on the effectiveness of wildlife population defragmentation measures – a case study on wild boar (Sus scrofa) of Veluwe, The Netherlands

Pervasive inbreeding is a major genetic threat of population fragmentation and can undermine the efficacy of population connectivity measures. Nevertheless, few studies have evaluated whether wildlife crossings can alleviate the frequency and length of genomic autozygous segments. Here, we provided a genomic inbreeding perspective on the potential effectiveness of mammal population defragmentation measures. We applied a SNP-genotyping case study on the ~2500 wild boar Sus scrofa population of Veluwe, The Netherlands, a 1000-km2 Natura 2000 protected area with many fences and roads but also, increasingly, fence openings and wildlife crossings. We combined a 20K genotyping assessment of genetic status and migration rate with a simulation that examined the potential for alleviation of isolation and inbreeding. We found that Veluwe wild boar subpopulations are significantly differentiated (FST-values of 0.02-0.13) and have low levels of gene flow. One noteworthy exception was the Central and Southeastern subpopulation, which were nearly panmictic and appeared to be effectively connected through a highway wildlife overpass. Estimated effective population sizes were at least 85 for the meta-population and ranged from 31 to 52 for the subpopulations. All subpopulations, including the two connected subpopulations, experienced substantial inbreeding, as evidenced through the occurrence of many long homozygous segments. Simulation output indicated that whereas one or few migrants per generation could undo genetic differentiation and boost effective population sizes rapidly, genomic inbreeding was only marginally reduced. The implication is that ostensibly successful connectivity restoration projects may fail to alleviate genomic inbreeding of fragmented mammal populations. We put forward that defragmentation projects should allow for (i) monitoring of levels of differentiation, migration and genomic inbreeding, (ii) anticipation of the inbreeding status of the meta-population, and, if inbreeding levels are high and/or haplotypes have become fixed, (iii) consideration of enhancing migration and gene flow among meta-populations, possibly through translocation.

Natural habitats for the stable existence of wild boars (<em>Sus scrofa</em>) in the North

Wild boar Sus scrofa populations are actively expanding northwards. Their presence in the North is closely tied to anthropogenic activities, as wild boars are either fed, or find food and suitable habitat at farmlands. However, the nature reserves of the northern part of Russia show that wild boars are able to survive on their own even in a completely natural environment. In the taiga zone, there are habitats providing for their survival in winter: wetlands in mires and around large water bodies, and dense spruce forests. Continued northwards expansion of wild boar range is likely if pressure from hunting is reduced. Modelling based on climatic variables also shows that they could potentially inhabit vast areas in the North. The existence of wild boars in the North is interrelated with other species of relatively large mammals (beavers and roe deer) and partly supports the idea of “Pleistocene rewilding” in a boreal environment, i.e., the potential to increase the variety and numbers of megafauna representatives.

Associating Metrics of Hunting Effort with Hunting Rate: A Case Study with the Wild Boar Sus scrofa

Wild boar Sus scrofa populations have increased dramatically in recent decades throughout Europe. While hunting is widely used in management activities; it rarely has an important role in regulating and reducing wild boar populations. Therefore, increasing the efficiency of hunting is a compelling issue. In this study, we used a three-year dataset (2016–2018) on a wild boar population living in Campania (southern Italy) as a case study to explore how the hunting effort made in collective drive hunts affected the hunting rate, estimated as the number of individuals culled per day. We fitted a Linear Mixed Model, in which we included the number of wild boars culled per drive hunt as the dependent variable, and the number of beaters, shooters and dogs and the month during which hunting occurred as the predictors. A mean of 1.81 wild boars were culled per drive hunt. The number of culled animals per hunt increased with the increasing number of hunting dogs and with the progression of the hunting season (i.e., from October to December), whereas the number of beaters and shooters had no effect. Overall, we observed a low hunting rate. We suggest that adjusting the hunting calendar and reorganising wild boar collective hunts, e.g., through an appropriate management of the number and training of hunting dogs, are essential to increase the hunting rate. Our results can be useful for wildlife managers to enhance hunting contribution in counteracting the negative impact of wild boar.

Clear phylogeographic pattern and genetic structure of wild boar Sus scrofa population in Central and Eastern Europe

The wild boar Sus scrofa is one of the widely spread ungulate species in Europe, yet the origin and genetic structure of the population inhabiting Central and Eastern Europe are not well recognized. We analysed 101 newly obtained sequences of complete mtDNA genomes and 548 D-loop sequences of the species and combined them with previously published data. We identified five phylogenetic clades in Europe with clear phylogeographic pattern. Two of them occurred mainly in western and central part of the continent, while the range of the third clade covered North-Eastern, Central and South-Eastern Europe. The two other clades had rather restricted distribution. In Central Europe, we identified a contact zone of three mtDNA clades. Population genetic structure reflected clear phylogeographic pattern of wild boar in this part of Europe. The contribution of lineages originating from the southern (Dinaric-Balkan) and eastern (northern cost of the Black Sea) areas to the observed phylogeographic pattern of the species in Central and Eastern Europe was larger than those from the regions located in southern France, Iberian, and Italian Peninsulas. The present work was the first mitogenomic analysis conducted in Central and Eastern Europe to study genetic diversity and structure of wild boar population.

The Relationship between Hunting Methods and the Sex, Age and Body Mass of Wild Boar Sus scrofa.

Simple SummaryWild boar Sus scrofa is a widely distributed species, the global population of which is continuously growing and its ecological impact is substantial. The increasing number of wild boars results in many conflicts with people, as they cause serious crop damage and are reservoirs of many epidemiologically and economically important diseases. That’s why in many countries to reduce these pressure, hunting for wild boars is carried out. Different methods of hunting and individual preferences of hunters may influence the effectiveness of such population control. We analyzed hunting data from the survey area in Western Poland from the years 1965–2016 and showed that individual hunters and team hunters usually hunt wild boars of different sex and age. Understanding these differences may help future planning of hunting operations, which will ensure an effective reduction of the number of wild boars, without causing untoward changes in the age- and sex structure of the population.Increases in the wild boar Sus scrofa population create many conflicts that must be managed, especially because hunting represents a major cause of mortality in this game species. However, hunting effort is not distributed randomly and is influenced by many factors, including hunting methods. This can be especially important in understanding the nature of hunting pressure for both theoretical (ecological and evolutionary) and applied reasons (for management purposes, especially during infectious diseases, for example, African swine fever, outbreaks). We analyzed hunting data from the survey area in Western Poland from the years 1965–2016. In this period a total of 2335 wild boar were culled using two hunting methods: by individual hunters (43.8%) and by teams of hunters (52.0%). During the study period, the number of wild boars increased significantly but in a non-linear manner. More adult males and yearlings of both sexes were shot during individual hunts; more adult females were culled during team hunting. Moreover, the body mass of culled wild boars was positively influenced by the distance to a forest and during the team hunts heavier females and males were shot. To effectively control populations of wild boars, programs to reduce the number of individuals should be better planned and ensure the maintenance of proper age- and sex structure in the wild boar population.

Influence of seasonality, environmental and anthropic factors on crop damage by wild boar Sus scrofa

In recent decades, wild boar Sus scrofa populations have increased both in number and distribution in Italy, thus enhancing problems of cohabitation with humans. Crop damage represents one of the main sources of conflict; understanding the spatiotemporal variation of damage events and which factors increase the risk of damage is crucial to the development of effective management strategies. The aims of this study were to determine the impact of wild boar on croplands in the Special Protection Area “Risaie della Lomellina” (western Po Plain, northern Italy) and to formulate a risk prediction model through a binary logistic regression analysis. Damage events almost exclusively involved maize, and were concentrated in spring and summer. Sporadic cases of damage concerned rice, soybean and sorghum fields. The risk of damage was higher in fields close to forests, far from main roads, urban areas and continuous hedgerows, and in areas with low human population densities.

Seasonal spatial ecology of the wild boar in a peri-urban area

The parallel expansion of anthropogenic environments and wild boar Sus scrofa populations has favoured the intrusion of the species into many European metropolitan areas, including Rome. In this study, we used Maxent to analyse the seasonal spatial ecology of the wild boar in Marcigliana natural reserve, a rural area located in the northeastern suburbs of Rome. The wild boar avoided urban settlements year-round. In the growing season, it had a higher probability of occurring with an increasing presence of turkey oak Quercus cerrioides woods, but seemed to be partially adapted to the presence of arable lands, which had a marked negative effect only when very abundant. These results lead us to hypothesise that the species in this part of the year adopts a spatial strategy which optimises the trade-off among the need for thermal cover and food resources. In autumn and winter, the species avoided meadows and pastures. The analysis of wild boar spatial ecology in metropolitan areas is essential to provide important information contributing to the development of effective plans for managing peri-urban populations and mitigating conflicts with humans.

Invading or recolonizing? Patterns and drivers of wild boar population expansion into Belgian agroecosystems

Native species can also exhibit invasive-like spreading patterns, and identifying mechanisms driving spread of native species is a recent but essential challenge in ecology. In Europe, wild boar Sus scrofa populations and range increased for decades. While patterns of population growth are well studied, those related to range expansion are still poorly understood. In this study, we aimed to understand patterns and mechanisms that promoted wild boar population expansion in agricultural landscapes of Southern Belgium between 1981 and 2010. Using hunting-based knowledge on colonization history and an information-theoretic approach, we evaluated support to four a priori hypotheses explaining mechanisms of wild boar colonisation in an agro-ecosystem: natural forested landscape as recolonization mechanism, and cultivated landscape, propagule pressure and climate change as invasion mechanisms. We found that wild boar population expansion in Belgian agroecosystems was a relatively slow process driven by the natural landscape, propagule pressure, and climatic changes. This suggests a combination of invasive and recolonization mechanisms was in play in the expansion of wild boar over the last three decades. Our study provides insights in the mechanisms that enable the species’ recovery in Europe since the mid-20th century, and underline the need for adapted management strategies taking into account the invasive components of wild boar population expansion.

Next of kin next door – philopatry and socio‐genetic population structure in wild boar

AbstractDispersal patterns can have vital consequences for the transfer of genes in a population, thus shaping its genetic make‐up and structure. Genetic relationships between individuals can, in turn, affect their social behaviour and the emergent social organization of the population. Using combination of behavioural and genetic data from the wild boar Sus scrofa population in Białowieża Primeval Forest (eastern Poland), we evaluated the socio‐genetic structure of wild boar groups, the spatial genetic structure of the population and dispersal patterns. We found that wild boar post‐weaning movements were largely spatially limited to the vicinity of maternal range, with female boars showing a tendency to settle in the direct neighbourhood of the kin and male boars dispersing further away from the natal area. Consequently, such dispersal patterns were reflected in the kin‐based social organization and the spatial genetic structure of the population, which was manifested at a spatial scale corresponding to the size of a few home ranges (<5 km). A negative relationship between geographic distance and genetic relatedness, which was particularly strong in female boars, indicated a presence of local kin clusters dominated by female boars and the importance of female philopatry in shaping the structure of wild boar population. This was confirmed by the genetic profile and composition of social groups. This study showed the role dispersal decisions can play in the emergence of the kin‐based and matrilineal social system of wild boars.

Long-lasting, kin-directed female interactions in a spatially structured wild boar social network.

Individuals can increase inclusive fitness benefits through a complex network of social interactions directed towards kin. Preferential relationships with relatives lead to the emergence of kin structures in the social system. Cohesive social groups of related individuals and female philopatry of wild boar create conditions for cooperation through kin selection and make the species a good biological model for studying kin structures. Yet, the role of kinship in shaping the social structure of wild boar populations is still poorly understood. In the present study, we investigated spatio-temporal patterns of associations and the social network structure of the wild boar Sus scrofa population in Białowieża National Park, Poland, which offered a unique opportunity to understand wild boar social interactions away from anthropogenic factors. We used a combination of telemetry data and genetic information to examine the impact of kinship on network cohesion and the strength of social bonds. Relatedness and spatial proximity between individuals were positively related to the strength of social bond. Consequently, the social network was spatially and genetically structured with well-defined and cohesive social units. However, spatial proximity between individuals could not entirely explain the association patterns and network structure. Genuine, kin-targeted, and temporarily stable relationships of females extended beyond spatial proximity between individuals while males interactions were short-lived and not shaped by relatedness. The findings of this study confirm the matrilineal nature of wild boar social structure and show how social preferences of individuals translate into an emergent socio-genetic population structure.

Contemporary Genetic Structure, Phylogeography and Past Demographic Processes of Wild Boar Sus scrofa Population in Central and Eastern Europe

The wild boar (Sus scrofa) is one of the most widely distributed mammals in Europe. Its demography was affected by various events in the past and today populations are increasing throughout Europe. We examined genetic diversity, structure and population dynamics of wild boar in Central and Eastern Europe. MtDNA control region (664 bp) was sequenced in 254 wild boar from six countries (Poland, Hungary, Belarus, Ukraine, Moldova and the European part of Russia). We detected 16 haplotypes, all known from previous studies in Europe; 14 of them belonged to European 1 (E1) clade, including 13 haplotypes from E1-C and one from E1-A lineages. Two haplotypes belonged respectively to the East Asian and the Near Eastern clade. Both haplotypes were found in Russia and most probably originated from the documented translocations of wild boar. The studied populations showed moderate haplotype (0.714±0.023) and low nucleotide diversity (0.003±0.002). SAMOVA grouped the genetic structuring of Central and Eastern European wild boar into three subpopulations, comprising of: (1) north-eastern Belarus and the European part of Russia, (2) Poland, Ukraine, Moldova and most of Belarus, and (3) Hungary. The multimodal mismatch distribution, Fu's Fs index, Bayesian skyline plot and the high occurrence of shared haplotypes among populations did not suggest strong demographic fluctuations in wild boar numbers in the Holocene and pre-Holocene times. This study showed relatively weak genetic diversity and structure in Central and Eastern European wild boar populations and underlined gaps in our knowledge on the role of southern refugia and demographic processes shaping genetic diversity of wild boar in this part of Europe.

Mortality rates of wild boar Sus scrofa L. in central Europe

In many parts of Europe, wild boar Sus scrofa population increase, and thus, high densities and dispersal into new areas are accompanied by economic problems. Due to many factors like insufficient hunting strategies as well as underestimation of population densities and reproduction rates, harvest rates seem to be insufficient. Thus, we calculated mortality rates of several wild boar populations from 1998 to 2009, to show the efficiency of hunting within several studies distributed over eight European states. For calculating mortality rates, the daily probability of survival of radio telemetrically observed wild boar was analysed according to Mayfield (Wilson Bull 73:255-261, 1961) and with survival analysis in R for three age classes (0, 1, ≥2 years) and both sexes. The mortality rates of wild boar per annum, especially piglets, were comparably low (about 0.5 for piglets and similar for total population). About three third of all observed animals survived at least until the next period of reproduction. Mortality rates differed between some study areas, the sexes and age classes. The sex ratio of the shot piglets equals the sex ratio of captured piglets; there seems to be no sex-biased hunting in this age class, but in an older age. Shooting was the main cause of death; only very few animals died by natural causes, e.g. diseases. The comparative analysis of all studies reflects a low mortality of wild boar in highly productive populations. Our results certified the findings of several studies that predation, natural mortality, and road mortality have only small impact on wild boar populations, whereas especially, nutrition or hunting are mainly decisive. Assuming net reproduction rates of more than 200 % according to literature data, our results indicate that harvest rates are not sufficient at our study sites. In all our studies, mortality rates and, thus, harvest rates are less than the assumed total net reproduction. Especially, the harvest rate of piglets seems to be insufficient. Thus, the population will increase further. High reproduction has to be counteracted by regulating mainly the reproductive animals. For regulating a population, combined and effective hunting methods have to be conducted to harvest at least the net reproduction. Thus, we recommend higher hunting rates of piglets (80 % of the offspring should be harvested) and of adult females. Intensified hunting of piglets by drive hunts and at an early age as well as intensified single hunt on adult females might help regulating wild boar populations.

Forecasting the range expansion of a recolonising wild boar Sus scrofa population

Recolonising native mammals have the potential to cause environmental and agricultural damage. However, if their future distribution can be predicted, effective control measures can be scheduled beforehand to prevent the onset of damage. In this study, we predicted the future range expansion of recolonising wild boar Sus scrofa populations in the Chiba Prefecture, Japan, using simulations. Wild boars were extinct in the Chiba Prefecture until the 1970s, but since then, a new naturalised population has spread, probably due to release for hunting. Recently a small, isolated, naturalised population was found in the northern part of the prefecture, which was considered to be a new release. We divided the Chiba Prefecture (5,156 km2) into 3‐km grids and, based on nuisance control records, we examined the ‘presence’ of wild boar populations from 2002 to 2007 and in 2010. We simultaneously estimated habitat suitability and dispersal probability of the source population via range‐expasion modelling. We predicted the future distribution by the use of stochastic simulations for 20 years after 2010. According to the simulations, the wild boar populations will expand into the southern and northern regions of the Chiba Prefecture at a rate of 2,153 km/year, and crop damage should be expected in these areas in the future. Range expansion into the northern region of the prefecture will be completed by around 2025. If the northern isolated population is removed, it will be possible to delay the range expansion for about five years. The eradication of a small isolated population in the northern Chiba Prefecture may have significant economic benefits because the crop production in this area is relatively large.

New perspectives on managing wildlife diseases

New perspectives on managing wildlife diseases

Erratum to: Reproductive and demographic parameters in two Iberian wild boarSus scrofa populations

Erratum to: Reproductive and demographic parameters in two Iberian wild boarSus scrofa populations

Potential ecological and epidemiological factors affecting the persistence of classical swine fever in wild boarSus scrofapopulations

ABSTRACTClassical swine fever has increased in economic importance since it has become endemic in some wild boarSus scrofapopulations in Europe. The mechanism of disease persistence is still not well understood, and several aspects of both the ecology of boar and the virus are claimed to be responsible for disease persistence.We review literature on the spread and persistence of the disease in free‐ranging wild boar. We determine whether the available knowledge can explain the observed patterns via mechanistic processes and their interactions, and assemble knowledge in a conceptual model.We speculate that the most important factor explaining disease persistence is an alteration in disease outcome, resulting in individual courses with prolonged infectiousness or a sustained reproductive population through immunity. This effect is reinforced by high wild boar numbers either within sites or scattered over larger areas.We highlight the sparse knowledge of disease transmission between wild boar. We derive management suggestions for different phases of an outbreak based on the conceptual model and advocate the use of model‐based investigations to test alternative management options.

Population structure variations of wild boar Sus scrofa in central Italy

The study has been carried out on a wild boar Sus scrofa population in southern Tuscany (Italy). We aimed to estimate the trend in population structure and productivity of a harvested and high‐density population. From 1990 to 1996 we examined 2773 harvested wild boars, assessing age, sex, and number of foetuses per females. We highlighted an increase of the proportions of yearling following a season with a peak of two‐year individuals. Neither significant differences in mean foetus numbers among age classes nor among seasonal variations have been pointed out. Productivity peaks seemed to be related to peaks in sub‐adult females in previous seasons, while food availability and harvest could have been responsible for fluctuations of sub‐adult females. Fluctuations seemed more likely linked to an alternation of high and low frequency in the recruitment of females in the breeding pool than to individual differences in prolificity. Massive harvesting could bring sub‐adult females and males to reproduction when adult individuals are scarce, incrementing the overall productivity, but young individuals are possibly more sensitive to environmental variations. We suggest that these studies should last longer and be strictly associated to a contemporary monitoring of trophic resources.

Variation in ranging and activity behaviour of European wild boar Sus scrofa in Sweden

The present wild boar Sus scrofa population in Sweden mainly originates from animals that have escaped from enclosures. At some locations wild boars have evidently been released deliberately. Whatever their origin, rapid increases in both number and distribution of free‐ranging wild boars have occurred. As wild boars are considered exotic in the Swedish fauna, sportsmen very often provide supplemental food in varying degrees, partly to facilitate and secure hunting possibilities, partly to keep wild boars out of farmed crops. In this paper we describe wild boar activity behaviour and intend to show how wild boar adjust their activity behaviour under different ambient conditions. The aim of our study was to increase the knowledge of managers to improve hunting effectivity and risk assessment concerning crop damage. The wild boars were, almost without exceptions, active during night. The mean time for an activity bout was 7.2 hours and the wild boars in the study area were only to a minor degree adjusting their activity bout to the prevailing night length. However, the hour of sunset seemed to be the cue which triggered the onset of activity bouts. The mean distance that the wild boars travelled during activity bouts was 7.2 km and the estimated mean activity range was 104.4 ha. The mean effort when roaming the activity range was 110.9 m/ha. A substantial variance was typical for all activity variables. For activity distance, 72% of the variation was explained by adding wind speed, season, minimum temperature and snow cover to our model. Significant effects of minimum temperature, snow cover and an interaction between activity time and minimum temperature explained 42% of the variation in activity range. The variation in relative air humidity explained 41% of the time active during an activity bout.