The Feral Pig in a Low Impacted Ecosystem: Analysis of Diet Composition and Its Utility
Introduction
Feral pigs (Sus scrofa) are an exotic, invasive, and successful species in several ecosystems around the world (Thomson and Challies, 1988; Taylor and Hellgren, 1997; Campbell and Long, 2009). Their success is attributed to their generalist and opportunistic foraging habits, commonly feeding on plants, vertebrates, and invertebrates (Wood and Roark, 1980; Taylor and Hellgren, 1997). Their foraging behavior causes multiple undesirable changes in ecosystems, such as: depletion of the original biodiversity by increasing the number and biomass of exotic plants (Cushman et al., 2004), and reduction of plant cover and the density and biomass of native invertebrates (Howe et al., 1981). Therefore, feral pigs are a target for control or eradication where they have invaded (Campbell and Long, 2009).
The Sierra La Laguna Biosphere Reserve (the Reserve), Baja California Peninsula, Mexico, encompasses an isolated mountain range that supports mesic plant communities in stable states (León-de la Luz and Domínguez-Cadena, 2010), which host feral pigs. Since feral pig populations have been largely described as a pernicious agent in several ecosystems that they have invaded elsewhere in the world (Wood and Roark, 1980; Taylor and Hellgren, 1997; Campbell and Long, 2009), the Reserve managers have concerns about their effect on the plant communities and are also interested in the implementation of effective, low-cost, ethical, and socially acceptable management strategies for its control.
Knowledge about the composition of the feral pig diet could assist to assess the impact on the area and develop strategies for their management within the Reserve. Diet composition and quality are valuable indicators of the potential reproductive success and animal activity distribution on the communities (Singer et al., 1981; Baber and Coblentz, 1987; Bieber and Ruf, 2005; Santos et al., 2006). Although the composition of feral pig diets has been examined in different sites, such as in a forest in New Zealand (Thompson and Challies, 1998), and a forest, marsh, scrubland, and chaparral in the USA (Wood and Roark, 1980; Baber and Coblentz, 1987; Taylor and Hellgren, 1997), there is little information in the Reserve. Similarly, limited information is available about the nutritional composition of diet in feral pigs (Santa Catalina Island, USA; Baber and Coblentz, 1987) and even in wild pigs (Chile; Skewes et al., 2007). Therefore, the objectives of this research were: (a) to identify the components of the seasonal diet selected by feral pigs in different plant communities; (b) to determine the nutritional composition of the selected diet; (c) to estimate the amounts of food resources that feral pigs consume, and (d) to use the diet composition to make recommendations for feral pig control.
Section snippets
Study area
The Reserve occupies an area of 112,437 ha and is located between 23°42’N and 23°20’N, and between 109°46’W and 110°11’W. Topographically, it is a rough mountainous ecosystem composed by three plant communities along the altitudinal gradient: a) tropical deciduous forest between 400 and 1100 m asl; b) oak woodland between 1000 and 1500 m asl; and c) oak-pine woodland between 1500 and 2200 m asl (Fig. 1). Some other plant associations present are the riparian vegetation that follows the drainage
Diet composition
Plant matter prevailed in the stomach contents. The fruits and seeds category was the most consumed, followed by the categories leaves and stems, and underground plant matter. Meanwhile, the intake of the categories woody matter and litter, vertebrates, invertebrates, and minerals were low, ≤3.7% each one (Table 1).
Season, plant community, and their interaction had effects on the presence of the categories fruits and seeds, leaves and stems, and vertebrates in the stomach contents (Table 1).
Diet composition
Feral pigs are classified as generalist consumers (Baber and Coblentz, 1987; Taylor and Hellgren, 1997), which also describes their feeding habits in the Reserve. Feral pigs ate at least 59 identifiable items during a year and 17 to 32 items from different plant communities and seasons, and individually ate 7 items from different origin (plant, vertebrates, and invertebrates). These feral pigs can be also classified as stenophagous since 1 to 4 items with both a high frequency of occurrence
Implications
The biomass production of the main diet components and the food required to meet the energy maintenance costs of feral pigs can be used to estimate the carrying capacity of the Reserve. For instance, the oak Q. devia is a dominant species in 3514 ha of the woodlands and produces 38.6 ton acorns yr−1 (≈ 11 kg DM acorns ha−1 yr−1) during years with low production (2009–2011; Arnaud et al., 2014). Therefore, the area dominated by Q. devia could meet the requirements of metabolizable energy for
Declaration of Competing Interest
None.
Acknowledgements
Our sincere thanks go to the Centro de Investigaciones Biológicas del Noroeste SC and the Facultad de Medicina Veterinaria y Zootecnia of Universidad Nacional Autónoma de México for sample processing. Special thanks go to Abelino Cota-Castro, Carlos Palacios-Cardiel, Franco Cota-Castro, Miguel Domínguez-León, Reymundo Domínguez-Cadena, Joaquín Rivera-Rosas, and Catarino Rosas-Espinosa for their collaboration in this work. Thank you to the reviewers for their help to improve this manuscript.
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