Ecology of Wild Boar, Sus Scrofa, in the Monte Desert Reserve (Mab) of Ñacuñan, Argentina

REPORT ECOLOGY OF WILD BOAR, SUS SCROFA, IN THE TEMPERATE MONTE DESERT RESERVE (MAB) OF ÑACUÑAN, ARGENTINA

Fernanda Cuevas, Agustina Novillo, Mariana Dacar, Benjamín Bender, Claudia Campos and Ricardo A. Ojeda

Grupo de Investigaciones de la Biodiversidad (GiB), IADIZA, CONICET, CRICYT CC 507, 5500 Mendoza, Argentina; Partner #53.

Introduction

Temperate aridlands of Argentina are undergoing rapid habitat conversion as a consequence of several activities (i.e. grazing, logging, agriculture, etc). These arid ecosystems contain many endemic species and have played an important role in the evolution of the South American biota. However, a large number of protected areas have been impacted by biological invasions, threatening their diversity, performance and structure of ecosystems (MacDonald et al., 1989; Vázquez, 2002). Ebenhart, (1988) found 788 mammalian introduction events all over the world. He recorded 15 mammal species for the Neotropics. In Argentina we recorded 17 alien mammals established as feral populations (Novillo and Ojeda, on alien mammals of Argentina, in prep.). One of them, the wild boar, Sus scrofa, is the largest invasive mammal species whose geographic range occupies many Neotropical ecoregions. The success of this species could be associated to its wide tolerance to different climatic conditions, omnivorous diet and high reproductive rate. A small population of wild boars invaded the Monte desert (MaB) Reserve of Ñacuñan (13,000 ha), Mendoza, Argentina, in the early eighties ’80s, from the matrix of cattle grazing ranches that surround the protected area. Alien mammals negatively affect populations of native vertebrates through competition or predation Despite being the largest “ecosystem engineer”, through soil rooting and nest building activities, among others, there are no studies addressing its role in the Monte desert biome and its impact on the native biodiversity .

Objectives

As part of the EU-funded research project ALARM to develop and test methods and protocols for the assessment of large-scale environmental risks (Settele et al., 2005) our research focuses on the ecology and assessment of changes produced by invasive mammals in the temperate aridlands of Argentina. In this report we summarize an assessment of habitat use, food habits, and impact of the wild boar, Sus scrofa in the MaB Reserve of Ñacuñan, Argentina. 2

Materials and Methods

Study area: the Man and Biosphere Reserve of Ñacuñan (340 02' S, 670 58' W) is located in Mendoza Province, Argentina. The area belongs to the Monte Desert phytogeographic province (Morello, 1958). The landscape is heterogeneous and characterized by a mosaic of vegetation partches of different complexity and heterogeneity known as “algarrobal” or mesquite forest (Prosopis flexuosa), “jarillal” or creosotebush shrubland (Larrea ) and sand dunes or “medanal”.

The temperate Monte desert eco-region and the MaB Reserve of Ñacuñan

The climate is semiarid and strongly seasonal, characterized by hot, humid summers and dry, cold winters. Average annual precipitation is 326 mm. Mean temperatures are lower than 10°C in winter and above 20°C in summer (Ojeda et al, 1998).

Vegetation analysis: Ten 0.60 x 0.60 m. squares randomly distributed in rooted and non rooted sites were established. At each squares, we measured vegetation composition and coverage. Vegetation structure was recorded by the point quadrat method. 30 m transects divided into 60 sample points were established at each one of the 15 study units (in rooted and non rooted sites). This method consisted in erecting a 2 m.“stiff wire”, marked at intervals 0.25 m high and then counting the leaves it touched (MacArthur and MacArthur, 1961). The basic records for each sampling point were the number of contacts of each plant species on the wire, and the height at which contact occurred. This basic data allowed determination of plant cover as well as the proportion of foliage in the vertical and 3 horizontal layers. We calculated Shannon diversity index for each transects along rooted and non rooted sites.

Food habits: 41 samples of scats were collected during the dry seasons of 2004 and 2005. They were analyzed (10 grams each) using the microhistological method of Baumgartner and Martin (1939), modified by Dacar and Giannoni (2001). Presence of a food item was recorded, and its relative frequency of occurrence was determined (Holechek & Gross, 1982). Spatial distribution: occurrence of wild boar was determined through transects (walking and by horse). Presence of rooting activity, scats and tracks were recorded. We performed a 10 m x 10 m grid covering the total reserve area. Each rooted site larger than 2 m perimeter was georeferenced. Rooted sites away from each other from 10 m were considered different units.

Results

Plant cover

We recorded 45 species of plants. Of the total of species (percentage of cover) we found two species significantly different between rooted and non rooted sites. During the dry season (October 2005), Lycium sp (p= 0.02) was the most abundant species in non rooted sites. During the wet season (March 2006), Pitraea cuneato-ovata was more abundant in rooted sites (p= 0.038).

Plant diversity

We found no significant differences in plant diversity between sites in both seasons (Humid season: Mann Witney test for independent samples, n=14; t= 0,22; p= 0,83; dry season: Mann Witney test for independent samples, n=13; t= -0,44; p= 0,66).

Vegetation structure

On the dry season the horizontal layers didn’t show differences between rooted and non rooted sites, however we could observe changes in the vertical layers (up to 50 cm. of high). At the700 wet season we found differences in the horizontal layer (herbs), but we didn’t found differences in the vertical layers of vegetation. 600 Vertical structure of vegetation during dry season 2005 500

s Rooted t

e 400 f h

o Non rooted c

º u N o

0 0-50 50-100 100-150 >150 Height (cm) 4

Food habits: The diet of the wild boar, Sus scrofa, includes 36 species of plants (95%) and 5% of arthropods and animal tissue. Of the total of plant items, seventy five percent consisted mainly of leaves (Sphaeralcea miniata) and rhizomes (Pitraea cuneato-ovata).

Food categories consumed by Sus scrofa during dry season 60

Distribution

265 soil rooting records (Fig 4) were obtained during dry season (October and November 2004). 85% were recent rooted areas, and 15% were old (more than a month).

2 0 2 4 6 0 2 Rooted K Tracks, roads m 5 The rooting areas cover a surface of 75, 85 ha, approximately a 0, 62% of the reserve total surface.

Discussion

Our first results on the ecology of the wild boar, Sus scrofa, in the Monte desert show:

- Soil rooting activity was associated with open areas such as roads and trails. Less than 30 % of rooting sites were recorded within the plant community.

- Significant differences in plant cover were found between rooted and non rooted sites.

- Pitraea cuneato-ovata, constitutes an important item in the diet, and shows positive association with rooted soils.

- Vertical structure of vegetation showed differences in the first 0.50 m in the dry season, however we detected no differences in plant diversity. We observed changes in the horizontal structure (herbaceous vegetation ) during the wet season.

- The wild boar feed mainly on vegetal matter (leaves and rhizomes) during the dry season.

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