Patricia Galina-Tessaro

Evaluación de la población de cerdos asilvestrados (Sus scrofa) y su impacto en la Reserva de la Biosfera Sierra La Laguna, Baja California Sur, México

El cerdo asilvestrado (Sus scrofa) es de las principals especies invasoras con fuertes efectos sobre ecosistemas naturales. Su presencia en la península de Baja California data del siglo XVIII. En este estudio se evalúa la abundancia relativa y distribución en la Reserva de la Biosfera “Sierra La Laguna” (REBISLA); y se presenta un análisis preliminar de su dieta e impacto en suelo y vegetación. Se hicieron entrevistas con rancheros, y se efectuaron 16 recorridos de más de un kilómetro en diferentes tipos de vegetación, tomando registros en 75 puntos. El efecto sobre vegetación y suelo, se evaluó en 40 cuadrantes de 25m2 en sitios con y sin afectación, y se registraron las plantas perennes; se tomaron muestras de semillas y contenido en el suelo en 60 cuadrados de 1m2 con y sin rastros de cerdos. Se analizó el contenido estomacal de ocho cerdos. La presencia del cerdo en la REBISLA es común, con un nivel de afectación moderada. La vegetación más afectada es el bosque de pino-encino. La población de cerdos es muy dinámica y depende de factores climáticos como sequías extremas, y el constante ingreso de cerdos que escapan de rancherías; asimismo presenta una gran movilidad en función de la disponibilidad de alimento y agua, por lo que es necesario continuar con estudios multitemporales y multianuales.

Evaluación de elementos estructurales del hábitat del borrego cimarrón en la Sierra del Mechudo, Baja California Sur, México

La pérdida y fragmentación del hábitat ponen en riesgo de aislamiento y extinción local a especies con poblaciones pequeñas, como la de Ovis canadensis weemsi Goldman, 1937, en la Sierra del Mechudo, Baja California Sur, México. Por tanto, es fundamental evaluar las relaciones entre las especies y su hábitat para diseñar programas de manejo y conservación. El objetivo del estudio fue evaluar la selección de elementos estructurales del hábitat determinantes en el comportamiento del borrego cimarrón para evadir la depredación, Índice de Rugosidad del Terreno (IRT) (terreno de escape) y estructura de la vegetación (visibilidad). Se realizó un análisis de uso-disponibilidad de clases de IRT y se midieron altura y cobertura de la vegetación perenne en tres áreas representativas de la Sierra. Se establecieron cinco clases de terreno, encontrando diferencias significativas entre uso y disponibilidad de las mismas, las sierras medianas con cañadas, sierras altas con cañones y sierras altas con cañones pequeños dentro de cañones grandes fueron seleccionadas. La vegetación perenne es esparcida, con promedios de altura de 1.3 m y cobertura de 21%, lo cual indica una visibilidad adecuada para los borregos. Ante el incremento de actividades humanas en la región, es recomendable evaluar el hábitat estructural a lo largo de la Sierra del Mechudo, relacionando IRT y visibilidad con la estacionalidad y el comportamiento de las diferentes clases de borregos; así como ubicar áreas sensibles o críticas para el manejo y conservación, al menos por arriba de los 300 m de elevación.

Habitat availability for the mule deer (Cervidae) population in a relictual oak-pine forest in Baja California Sur, Mexico

We estimated the mule deer Odocoileus hemionus peninsulae (Lydekker 1898) population in six locations of an oak-pine forest in the Sierra de La Laguna in the Cape Region of Baja California Sur, Mexico, during 7 consecutive years (1987 to 1993). The most important habitat variables for deer (plant biomass, cover, and water) were measured over five wet and dry seasons at the same locations. The population estimation (based on pellet-group counts) resulted in an average density of 19 ± 5 deer/km2. The deer habitat in the area is typified by different association proportions of Black Oak Quercus devia-Pinyon Pine Pinus lagunae-Oak Quercus tuberculata-Madrone Arbutus peninsularis. There is a marked seasonality in the vegetation. In general, the habitat transects revealed ample cover and plant biomass, shrubs being the dominant growth form and that most frequently consumed by the deer. The deer population is less than the habitat’s carrying capacity in the wet and dry seasons. None of the habitat variables measured are a limiting factor, though deer were found to prefer sites with greater amounts of cover and biomass of shrubs. All sites surveyed contain available water and are in rugged terrain. KEY WORDS: mule deer, Odocoileus hemionus peninsulae, Sierra de La Laguna, Baja California Sur, Mexico, habitat, pellet group counts, population density, carrying capacity.

African clawed frog (Xenopus laevis) in Baja California: a confirmed population and possible ongoing invasion in Mexican watersheds

Abstract The African clawed frog (Xenopus laevis) is an invasive amphibian in at least 15 countries. In Mexico, only occasional records have documented it in the state of Baja California. In May 2013, we discovered a population at Puente el Morro in Rosarito. In a 1-h session of trapping, we captured 106 individuals (adults and juveniles) at a small pond. We did not see eggs, tadpoles, or reproductive activity, but lengths of frogs indicate that some have reached sexual maturity. This discovery indicates the need for conservation plans and action against X. laevis dispersion, especially in Mediterranean zone climates.

Lizard assemblages in the Vizcaino Biosphere Reserve, Mexico

Lizard assemblages were surveyed in eight selected habitats in the Vizcaino Biosphere Reserve in Baja California Sur, Mexico. We compared the species composition and relative abundance among habitats, considering habitat characteristics, such as vegetation type, vegetation ground coverage, and soil types. Thirteen lizard species were recorded. The most abundant species in almost all habitats was Uta stansburiana, accounting for 59% of all observations. Cnemidophorus tigris was the second most abundant species, accounting for 12% of all observations. The richest habitat was the rocky lower elevations of the Sierra de San Francisco (nine species). However, the habitat with the highest diversity value was Scammons dunes. Implications of our findings for lizard conservation in this biosphere reserve are discussed.

Distribution and conservation of lizards in the Vizcaíno Biosphere Reserve, Baja California Sur, México

Lizard distribution is described for the Vizcaino Biosphere Reserve in the northern extreme of Baja California Sur, in central Baja California. The 20 species found include 74% of all the Baja California Sur lizards, excluding insular endemics. Five species are widely distributed throughout the Reserve. Four species are restricted to sandy soils (coarse and dunes) and open spaces. Seven species are restricted to rocky areas in the Sierras. Two species are included in the CITES list and 11 in the Official Mexican Norm (NOM 059-94) in some conservation category. This Reserve contains livestock (cows and goats), whose increasing numbers and grazing areas are often unrestricted. This disturbance is a potential threat for some species, especially those with restricted distributions in the eastern sierras where there are large numbers of goats.

Field metabolism of lizards from lower altitude regions of Baja California Sur (Mexico)

Water flux rate and field metabolic rate of three free-ranging sympatric species of lizards (Uta stansburiana, Urosaurus nigricaudus and Cnemidophorus hyperythrus) were measured in the Cape Region, near La Paz (Baja California Sur, Mexico) using labelled water ( 3 H 2 O and H 2 18 O). During the rainy season, the three species consumed the same prey. Caterpillars of Lepidoptera (7.1 ml H 2 O/g DM) were the most important in volume and mass. The lizards showed high water flux rates, which did not differ from those of non-desert species, but were 2 to 7 times higher than during the dry season. During the dry season the low rates of water flux were basically due to low metabolic rates. The water flux rate of C. hyperythrus in September was two to four times higher than rates in two other populations in the southern part of the Cape region, but the field metabolic rate was similar. Adult size in the El Comitan population (BM = 6.3 g) was larger than that in two Cabo San Lucas populations (BM = 4.4 and 3.9 g). These data suggest flexibility of responses of species and populations to environmental variation.