The information about ecological topics of mosquitoes at the southernmost tip of South America is fragmentary and scarce. The present study evaluates lentic freshwater habitat located in the surroundings of main roads of the Argentine sector of Tierra del Fuego as larval habitat of Ochlerotatus albifasciatus, also analyzes the relationships between their presence and several environmental variables: water turbidity, percentage of gramineans, percentage of macrophytes, presence of crustaceous cyanobacteria, and filamentous chlorophyceans. Mosquito inmatures were collected with dip nets. A generalized linear model (GLM) with negative binomial error distribution was used to determine the effects of different variables of the water bodies on abundance of Oc. albifasciatus in the larval habitats. Collections were made in 45 lentic freshwater bodies. Preimaginal stages were found in 17.70% of the studied habitats. Oc. albifasciatus was the only culicid registered. The GLM explained 93.17% of the variability, and showed a negative relationship between the abundances of Oc. albifasciatus and water turbidity, and a positive relationship with percentage of gramineans. The gramineans would improve food supply, because the plants are providing suitable substrate for different types of microbiota, a layer of leaves would protect eggs from extreme temperatures, and could help the larvae to hide from potential predators. The negative association between abundance of this species with water turbidity could be related to the presence of vegetation that favors retaining the substrate, reducing water turbidity.
1. Loss or deterioration of wetlands, which represent highly valuable environments, is a worldwide phenomenon. Sustainable management of wetlands, however, requires detailed understanding of the factors controlling their communities. The present study report the taxonomic composition and richness of invertebrate assemblages in different wetland types in Tierra del Fuego.2. Aquatic invertebrates from 79 freshwater wetlands in Tierra del Fuego were inventoried in January 2001 and 2002 (austral summer). All wetlands were classified into six categories: roadside pools, floodplain pools, flooded quarries, peatland ponds, beaver ponds and large ponds. The wetland type effect on the taxonomic richness was analysed by one-way ANOVA. To identify wetland types with similar invertebrate communities, cluster analysis has been performed using occurrence frequency of each taxa in each wetland type and the Jaccard similarity index.3. A total of 35 taxa were identified, including 21 microcrustaceans, 12 insects, 1 gastropod and 1 cnidarian. Copepods and cladocerans were among the most frequent taxa (occurrence frequency >40%) in most wetland types. No significant differences in taxonomic richness were found among wetlands types (P = 0.076). The cladogram based on invertebrate taxonomic composition resulting from similarity in taxonomic composition among wetland types showed three distinct clusters; one included flooded quarries, peatland ponds, beaver ponds and floodplain pools, the second one the large ponds and the third one roadside pools. 4. Our results suggest that the wetland types studied have different conservation values, like the clusters obtained in the cladogram show. Artificial wetlands, such as the roadside pools, could play an important role in maintaining connectivity between isolated fragments of pristine, natural wetlands.
Settlement is one of the critical points in the development of organisms with complex life cycles. Some marine invertebrates respond to specific cues such as substratum and conspecifics, and the larvae of species presenting gregarious settlement are characterized by a preference for settlement in patches with conspecifics over those without. An evaluation was made in the field of the effect of conspecifics density on the settlement of Petrolisthes laevigatus during two settlement seasons. The size-distribution and density were maintained constant throughout the first settlement season, while in the second year they were adjusted to match those presented in three previously identified periods during the season. The settlement rate of P. laevigatus was higher in the presence than the absence of conspecifics. There was evidence of saturation in the settlement of the higher densities, mainly at the beginning of the settlement season, when approximately 80% of the settlement occurred. We propose that gregarious settlement is an important factor in determining the distribution and abundance of P. laevigatus at different spatial scales, both within and among coastal areas, and could restrict the colonization of new areas and the recovery of populations reduced by disturbances.
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