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101.
Ernesto G. Verga Gerardo C. Leynaud Julián N. Lescano Laura M. Bellis 《European Journal of Wildlife Research》2012,58(5):823-832
The High Mountains of Córdoba, Argentina have a long evolutionary history of grazing by large herbivores. However, about 400?years ago, European livestock were introduced and gradually replaced native herbivores. Since the 1920s, domestic herbivores have been the only large herbivores present in the area, causing severe soil erosion and a threat to the system diversity. The endemic fauna of the region includes four amphibian species. We evaluated the effect of livestock rearing on amphibian diversity and water bodies in woodlands and grasslands of the High Mountains of Córdoba. The work was conducted on stream stretches and ponds in two contrasting grazing situations: an area with livestock presence and another area where livestock was excluded 14?years ago. The following variables were recorded at each sampling site: amphibian richness and abundance, percentage of emergent, submerged and peripheral vegetation in areas surrounding the water bodies, water pH, and water dissolved O2. No significant differences were detected in amphibian diversity between streams of both grazing situations, whereas a greater diversity (p?<?0.01) was observed in ponds in grazed grasslands. Our results suggest that livestock rearing, qualitatively measured as grazing and 14?years of livestock exclusion, in the study area would not have negative effects on amphibian diversity. This finding might be due to the long evolutionary grazing history of the area, large-scale livestock exclusion exhibiting a novel scenario. The ongoing reintroduction of native grazers may provide the benefits of grazing without the consequent soil erosion and habitat degradation associated with domestic livestock. 相似文献
102.
Emily J. Wundrow Juli Carrillo Christopher A. Gabler Katherine C. Horn Evan Siemann 《PloS one》2012,7(10)
Ecosystems that are heavily invaded by an exotic species often contain abundant populations of other invasive species. This may reflect shared responses to a common factor, but may also reflect positive interactions among these exotic species. Armand Bayou (Pasadena, TX) is one such ecosystem where multiple species of invasive aquatic plants are common. We used this system to investigate whether presence of one exotic species made subsequent invasions by other exotic species more likely, less likely, or if it had no effect. We performed an experiment in which we selectively removed exotic rooted and/or floating aquatic plant species and tracked subsequent colonization and growth of native and invasive species. This allowed us to quantify how presence or absence of one plant functional group influenced the likelihood of successful invasion by members of the other functional group. We found that presence of alligatorweed (rooted plant) decreased establishment of new water hyacinth (free-floating plant) patches but increased growth of hyacinth in established patches, with an overall net positive effect on success of water hyacinth. Water hyacinth presence had no effect on establishment of alligatorweed but decreased growth of existing alligatorweed patches, with an overall net negative effect on success of alligatorweed. Moreover, observational data showed positive correlations between hyacinth and alligatorweed with hyacinth, on average, more abundant. The negative effect of hyacinth on alligatorweed growth implies competition, not strong mutual facilitation (invasional meltdown), is occurring in this system. Removal of hyacinth may increase alligatorweed invasion through release from competition. However, removal of alligatorweed may have more complex effects on hyacinth patch dynamics because there were strong opposing effects on establishment versus growth. The mix of positive and negative interactions between floating and rooted aquatic plants may influence local population dynamics of each group and thus overall invasion pressure in this watershed. 相似文献
103.
104.
Serotonin 1A (5-HT(1A)) receptors are found in high densities in prefrontal cortex. However, their distribution within cortical cell populations is unknown in both humans and primates. We used double in situ hybridization histochemistry to quantify the percentage of glutamatergic and GABAergic neurons expressing 5-HT(1A) receptors in human and monkey prefrontal cortex. Moreover, in the case of the monkey, we also quantified the parvalbumin and calbindin GABAergic subpopulations expressing this receptor. 5-HT(1A) receptor mRNAs were expressed in about 80% of glutamatergic neurons in external layers II and upper III, and in around 50% in layer VI; they were also present in approximately 20% of GABAergic neurons in both species. Although they were found in up to 43% of the calbindin cell subpopulation they were rarely present in parvalbumin cells in monkey prefrontal cortex. The knowledge of the phenotype of the prefrontal cortex (PFC) cells expressing 5-HT(1A) will help understanding serotonin actions in PFC. 相似文献
105.
Alejandro R. Giraudo Silvia D. Matteucci Julián Alonso Justo Herrera Raúl R. Abramson 《Biodiversity and Conservation》2008,17(5):1251-1265
The Atlantic Forest (AF) is one of the five most threatened and megadiverse world hotspots. It is arguably the most devastated
and highly threatened ecosystem on the planet. The vast scope of habitat loss and extreme fragmentation in the AF hotspots
has left intact very few extensive and continuous forested fragments. We compared bird assemblages between small (<100 ha)
and large (>6,000 ha) forest remnants, in one of the largest AF remnants in Argentina. We performed 84 point-counts of birds
in four large fragments (LF) and 67 points in 25 small fragments (SF). We recorded 4,527 bird individuals belonging to 173
species; 2,632 belonging to 153 species in LF and 1,897 in 124 species in SF. Small fragments suffered a significant loss
of bird richness, mainly forest dependent species, but the birds abundance did not decrease, due to an increase in abundance
of forest independent and semi-dependent bird species (edge and non forest species) that benefit from forest fragmentation.
The bird guilds of frugivores, undestory, terrestrial and midstory insectivores, nectarivores and raptors, and the endemic
species of AF were area sensitive, decreasing significantly in richness and abundance in the SF. Terrestrial granivores were
the only guild positively affected by forest fragmentation, containing mainly edge species, which forage in open areas or
borders including crops. Our first observations on fragmentation effects on bird assemblages in the southernmost Argentinean
Atlantic Forests did not validate the hypothesis on pre-adaptation to human disturbances in the bird communities of AF. On
the contrary, we observed that forest dependent, endemic and several sensitive bird guilds were strongly affected by fragmentation,
putting in evidence the vulnerability to the fragmentation process and the necessity to conserve large remnants to avoid reduction
of the high biodiversity of AF birds. 相似文献
106.
Controversies on the origin of life. 总被引:1,自引:0,他引:1
Juli Peretó 《International microbiology》2005,8(1):23-31
Different viewpoints, many with deep philosophical and historical roots, have shaped the scientific study of the origin of life. Some of these argue that primeval life was based on simple anaerobic microorganisms able to use a wide inventory of abiotic organic materials (i.e. a heterotrophic origin), whereas others invoke a more sophisticated organization, one that thrived on simple inorganic molecules (i.e. an autotrophic origin). While many scientists assume that life started as a self-replicative molecule, the first gene, a primitive self-catalytic metabolic network has also been proposed as a starting point. Even the emergence of the cell itself is a contentious issue: did boundaries and compartments appear early or late during life's origin? Starting with a recent definition of life, based on concepts of autonomy and open-ended evolution, it is proposed here that, firstly, organic molecules self-organized in a primordial metabolism located inside protocells. The flow of matter and energy across those early molecular systems allowed the generation of more ordered states, forming the cradle of the first genetic records. Thus, the origin of life was a process initiated within ecologically interconnected autonomous compartments that evolved into cells with hereditary and true Darwinian evolutionary capabilities. In other words, the individual existence of life preceded its historical-collective dimension. 相似文献
107.
Although it has long been held that plant diversity must influence animal diversity, the nature of this relationship remains poorly understood at large spatial scales. We compare the species richness patterns of vascular plants and mammals in north‐eastern Spain using a 100‐km2 grain size to examine patterns of covariation. We found that the total mammal richness pattern, as well as those of herbivores and carnivores considered separately, only weakly corresponded to the pattern of plants. Rather, mammal richness was best described by climatic variables incorporating water inputs, and after adding these variables to multiple regression models, plant and mammal richness were virtually independent. We conclude that the observed association, although weak, is explained by shared responses of both groups to climate, and thus, plant richness has no influence on the richness pattern of Catalan mammals. 相似文献
108.
Pausas Juli G. Bladé Carme Valdecantos Alejandro Seva José P. Fuentes David Alloza José A. Vilagrosa Alberto Bautista Susana Cortina Jordi Vallejo Ramon 《Plant Ecology》2004,171(1-2):209-220
Pines have been extensively used for land restoration in the Mediterranean basin and in other parts of the world, since the late 19th century. The theoretical basis supporting pine utilisation was its stress-tolerant and pioneer features, and their attributed role of facilitating the development of late-successional hardwoods in the long-term. In the present work, the use of pines and hardwoods in forest restoration is discussed in the frame of the current disturbance regime and social demands for Mediterranean forests. Large pine plantations have recently disappeared because of their sensitivity to fire (e.g., Pinus nigra) or because of the short fire-intervals (e.g., Pinus halepensis). Combined pine and oak plantations are proposed for degraded land restoration on the basis of the complementary features of both groups of species. Seeding and containerised seedling plantation, soil amendments and plantation techniques to reduce transplant shock are evaluated for reforestation under water-stressing conditions, on the basis of several experiments performed in eastern Spain. Both P. halepensis and Quercus ilex are tested. 相似文献
109.
110.
The applicability of batch respirometry, as a simple technique for monitoring off-line nitrifying activity and kinetic parameters, was evaluated using two sets of ammonia and nitrite concentrations. The O2 uptake rate (OUR) profiles obtained from the assays were adjusted to a substrate inhibition model. The maximum specific ammonia-oxidizing biomass activity (rSmax) was 0.079 g N-NH4
+ g VSS–1 d–1 with a half saturation coefficient (KS) of 11 mg N-NH4
+ l–1 and an inhibition coefficient (Ki) of 3300 mg N-NH4
+ l–1. Besides, the maximum specific value of nitrite-oxidizing activity was 0.082 g N-NO2
– g VSS–1 d–1 with a KS of 4.1 mg N-NO2
– l–1 and Ki of 1400 mg N-NO2
– l–1. 相似文献