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.
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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
horizontal layers. We calculated Shannon diversity index for each transects along rooted
and non rooted sites.
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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 the wet season we found differences in the horizontal layer (herbs), but we didn’t
found differences in the vertical layers of vegetation.
Vertical structure of vegetation during dry season 2005
700
600
Nº of t
touches
500
Rooted
400
Non rooted
300
200
100
0
0-50
50-100
100-150
Height (cm)
>150
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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
50
40
%
30
20
10
Animal tissue
Steams
Gra sses
Art hropods
Seeds
Fru its
Rhizomes
Leaves
0
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
Rooted
0
2
K
m
The rooting areas cover a surface of 75, 85 ha, approximately a 0, 62% of the reserve total
Tracks, roads
surface.
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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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