Reproductive Ecology of Recently Established Wild Pigs in Canada

By Koen, Erin L.; Wal, Eric Vander et al. | The American Midland Naturalist, April 2018 | Go to article overview

Reproductive Ecology of Recently Established Wild Pigs in Canada


Koen, Erin L., Wal, Eric Vander, Kost, Ruth, Brook, Ryan K., The American Midland Naturalist


INTRODUCTION

Invasive species are one of the main drivers of species endangerment and extinction worldwide (Clavero and Garcia-Berthou, 2005; Bellard et al, 2016), impacting native ecosystems and agriculture (Pimentel et al, 2005). Therefore, a major challenge in management and conservation is control and eradication of invasive species (Mack et al., 2000). Models of population growth and spread can help to predict current and future invasions (e.g., Muirhead et al., 2006) and assess the efficacy of potential management strategies (e.g., Bieber and Ruf, 2005; Goldstein et al, 2016). Life history is one important predictor of the invasion success of mammals (Forsyth et al, 2004; Jeschke and Strayer, 2006). As such, modelling population growth and spread depends on empirical estimates of life history traits, such as reproduction and survival.

Wild pigs (Sus scrofa), one of the most invasive and destructive terrestrial mammals in North America and worldwide (Lowe et al, 2000), were introduced to the United States in the 16th century (Mayer and Brisbin, 1991) and have since expanded to over 6 million animals in at least 37 states (Mayer, 2014). Wild pigs represent a large and widespread threat to native plant and animal communities through predation, competition, disease transmission, and habitat destruction (Barrios-Garcia and Ballari, 2012; Bevins et al, 2014) and have contributed to the decline of numerous species at risk (USDA, 2002; Parkes et al, 2010). Populations of introduced wild pigs have recently become established in large parts of Saskatchewan, Alberta, and Manitoba, Canada (Brook and van Beest, 2014), and there have been occasional sightings of wild pigs in most other Canadian provinces. Originally, domesticated European wild boar were imported into western Canada from different parts of Europe in the 1980s and 1990s to diversify agriculture (Brook and van Beest, 2014). Indeed, domesticated wild boar farming remains common: in 2011 there were over 9000 domesticated wild boar on 150 farms across Canada (Michel et al., 2017). Farming for meat production and penned sport shooting operations are the original sources of free-living wild pig populations in Canada (Michel et al, 2017). Wild pigs are extremely fecund in other parts of their native and introduced range (Comer and Mayer, 2009), making established populations notoriously difficult to control and almost impossible to eradicate (Cruz et al, 2005; Barrios-Garcia and Ballad, 2012). For consistency we refer to the population in Canada as "wild pigs" (Keiter et al, 2016), as we do not know whether these nonnative, free-living animals are pure feral European wild boar, feral domestic pigs, or hybrids of wild boar and domestic pigs.

Although there are estimates of reproductive rates and litter sizes for wild pig populations across much of their worldwide distribution, these rates vary (reviewed by Comer and Mayer, 2009). As such, local estimates of these parameters are essential for effective management. It is predicted that range-edge populations have reduced reproductive output (Gaston, 2009), whereas life history theory predicts that expanding populations will have higher reproductive rates (Philips et al., 2010). Interestingly, litter size of European wild boar in Europe tends to increase with latitude (Bywater et al., 2010). Little is known about the reproductive ecology of wild pig populations in Canada, currently at the northern limit of their distribution in North America. Here, we report number of fetuses, fetal sex ratio, parturition dates, and the relationship between reproduction and maternal condition of wild pigs in Saskatchewan, Canada, representing the first reported life history estimates of wild pigs in their Canadian distribution following their initial introductions.

METHODS

Our study area (51.110"N, 103.231"W) was based in the Prairie Ecozone, an agriculturedominated landscape in southeastern Saskatchewan, Canada. The average (SD) temperature over 10 у (2007-2016) in our study area was -13. …

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