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ECOLOGÍA - MEXICO |
Ecosystem trophic structure and energy flux in the Northern Gulf of California, México Using the Ecopath with Ecosim software, a trophic structure model of the Northern Gulf of California was constructed to represent the main biomass flows in the system. It was based mostly on bibliographic data and provides a snapshot of how the ecosystem operates. The model consisted of 29 functional groups. The total system throughput was 6633 tonnes/km<sup>2</sup> per year, from which 51.7% are for internal consumption, 20.0% are for respiration, 16.0% becomes detritus, and 12.2% are removed through commercial fishing. Main results show that most groups were impacted more by predation and competition than by fishing pressure, and that there are some characteristics that indicate that use of the ecosystem is balanced. Ecological Modelling, Vol. 174, No.4, p331, 15p.
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The reproductive cycle and cycle in fat body mass are described for male and female Sceloporus pyrocephalus taken from the Municipio de Tejupilco, state of Mexico, Mexico. Males reached sexual maturity at 50.0 mm snout-vent length (SVL), females reached sexual maturity at 47.0 mm SVL. Testis of males began to increase in size in early April, maximum testis mass occurred during May through October, and testis mass decreased abruptly in November and December. Maximum testicular growth was associated with increased temperature, photoperiod, and precipitation. This is an oviparous species. Enlarged vitellogenic follicles first appeared during early May in females. Females contained oviductal eggs from May to September. Vitellogenesis, follicular growth, and egg production were associated with increasing photoperiod and precipitation but not with temperature. From a sample of 21 females with oviductal eggs, 13 (61.9%) had two clutches, and eight (38.1%) had a single clutch. Mean clutch size was not correlated with female SVL.. Journal of Herpetology, Vol.38, No. 2, p. 225. |
In this study we analyze the population dynamics of the migratory and nectarivorous Leptonycteris nivalis (Mexican long-nosed bat) in relation to food abundance and environmental factors (temperature and humidity). A 2-year study was conducted in the Mexican state of Nuevo Leon. Bat densities and the number of blooming Agave were estimated by month at El Infierno cave and surrounding areas. Temperature and humidity were recorded at 4.5-h intervals inside and outside the bat roost. Bat density was estimated visually, and the number of blooming Agave was counted in 70 fixed plots along 3 road transects within a 50-km radius of the cave. Examination of data indicates that abundance of L. nivalis at El Infierno cave is correlated with the frequency of blooming Agave and ambient temperature. However, cave temperature, humidity, and external humidity were not correlated with bat numbers. These findings suggest that conservation of this federally protected bat will require maintenance of relatively large areas of wild Agave. Journal of Mammalogy, Vol.85, No. 3, p. 453, 7 p. |
Background and Aims Genetic structure and variability were examined in the only three extant populations of the narrow-endemic tree Antirhea aromatica (Rubiaceae, Guettardeae), an endangered species of the tropical forest of eastern Mexico. Patterns of genetic diversity within and among populations for adult plants and seedlings were obtained......The results indicated that the populations evaluated have high genetic variability, compared with other endemic and geographically narrowly distributed plant species, in areas with high levels of environmental heterogeneity (e.g. tropical forests). The conservation implications of the results are discussed, and in this regard it is proposed that A. aromatica should be considered as an indicator species with economic potential. It is suggested that sustainable management practices should be implemented and that the areas where the species is distributed should be declared a natural reserve to ensure the species conservation. Annals of Botany, Vol.93, No. 5, p. 521. |
We tested whether differences in composition and nutrients of diet explained higher density of Peromyscus aztecm in mature cloud forest and higher density of Reithrodontomys fulvescens in disturbed cloud forest. P. aztecus ate dicot leaves, stems, fruit, and seeds in mature cloud forest and dicot leaves, stems, and seeds, and monocot seeds and insects during the dry-hot season in disturbed cloud forest. R. fulvescens ate dicot leaves, stems, fruit, and seeds in mature cloud forest but monocots and insects during the hot season, dicot leaves, stems, and seeds were eaten in disturbed cloud forest. The diet of P. aztecus contained more protein and soluble carbohydrates in disturbed cloud forest where rodent density was lower, the diet of R. fulvescens contained more protein, lipid, soluble carbohydrate, Na, Mg, and P in mature cloud forest where density was lower. Nutrient differences resulted from R. fulvescens eating more monocots and dicot fruit, P. aztecus eating more monocot seeds and less dicot fruit, and both species eating more insects. Differences in composition or nutrient content of diet did not explain between-habitat differences in demography because nutrients in diet were higher in habitat of lower rodent abundance, suggesting other factors must be considered. Journal of Mammalogy, Vol.85, No. 2, p 196, 10 p. |
Captive male Neotomodon alstoni exhibit paternal care. We tested whether presence of the male in the nest during the postpartum and weaning periods affect maternal care and promoted survival and growth of the offspring. For captive N. alstoni pairs (n = 10) both parents were maintained in the nest until weaning of the young, and in another 10 pairs the male was removed shortly after birth of young. The presence of the male had a negative impact on the time spent by females in huddling with nursing young. In the presence of the male, females groomed and sniffed young less frequently than did females rearing young in the absence of the male. Survival of offspring (84%) and their growth (20.6 ±, 4.7 g) was significantly higher when both parents reared their young. Males provide additional care of young, allowing a higher quality of care by the female during rearing. Journal of Mammalogy , Vol.85, No. 2, p 268, 5 p. |
Intensive cropping systems based on mechanical movement of soil have induced land degradation in most agricultural areas due to soil erosion and soil fertility losses. Thus, farmers have been increasing fertilization rates to maintain an economically competitive crop yield. This practice has resulted in water quality degradation and lake eutrophication in many agricultural watersheds. Research was conducted in the Patzcuaro watershed in central Mexico to develop appropriate technology that prevents nonpoint source pollution from fertilizers. Organic matter (OM) and nitrogen (N) losses in runoff and nitrate (NO^sub 3^-N) percolation in Andisols with corn under conventional till (CT) and no-till (NT) treatments using variable percentages of crop residue as soil cover were investigated for steep-slope agriculture. USLE type runoff plots were used to collect water runoff, while suction tubes with porous caps at 30, 60, and 90 cm depth were used to sample soil water solutes for NO^sub 3^-N analyses. Results indicated a significant reduction of N and OM losses in runoff as residue cover increased in the NT treatments. Inorganic N in runoff was 25 kg/ha for NT without residue cover (NT-0) and 6 kg/ha for the NT with 100 percent residue cover (NT-100). Organic matter losses in runoff were 157 and 24 kg/ha for the NT-0 and NT-100 treatments, respectively. Nitrate-N percolation was evident in CT and NT with 100 percent residue cover (NT-100). However, NT-100 had higher NO^sub 3^-N concentration at the root zone, suggesting the possibility of reducing fertilization rates with the use of NT treatments. Journal of the American Water Resources Association, Vol.40, No. 2, p 401, 8 p. |
Black-tailed and white-sided jackrabbits (Lepus californicus and L. callotis) occur sympatrically throughout much of the Chihuahuan Desert, black-tailed jackrabbits are widely distributed, whereas white-sided jackrabbits are endemic to the Mexican Plateau. I measured abundance, distribution and habitat associations of each species in western Chihuahua, Mexico, during the winters of 1998 and 1999. No difference was observed in mean density, however, black-tailed jackrabbits were more abundant in semi-desert grasslands, whereas white-sided jackrabbits were most abundant in high elevation, plains grasslands. The occurrence of the two species was negatively correlated, a result of different habitat preferences or competition. Black-tailed jackrabbits were solitary, whereas white-sided jackrabbits were usually observed in pairs (74 and 58% of the time for 1998 and 1999, respectively). Dry conditions and heavier grazing pressure present in 1999 accentuated differences in characteristics of sites used and not used by jackrabbit species. The presence of black-tailed jackrabbits was positively associated with vegetation density in 1998 and positively associated with shrub density in 1999. White-sided jackrabbit presence was positively associated blue grama grasslands in 1999. Remaining open patches of desert grassland are important for the persistence of white-sided jackrabbit populations. The American Midland Naturalist, Vol.151, No. 2, p 414, 6 p. |
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