RESUMEN
Aquatic systems have been degraded by environmental changes aimed at increasing the productivity of farmland and ranches. These changes affect aquatic assemblages at both local and regional scales. The hypothesis of this study is that in-stream environmental conditions are more important determinants of species richness and composition of Gerromorpha assemblage, given that they are affected directly by changes that occur within the stream, rather than by landscape conditions. To test our hypothesis, we collected at 20 sites of agricultural and forested regions in the Brazilian Cerrado. We relate predictors of the landscape and sites, of the streams with the assemblages of Heteroptera. While landscape metrics play an important role in the formation of stream conditions, local and physico-chemical variables had a significant influence on the structure of the Gerromorpha assemblages in the study area. This indicates that these organisms are more dependent on the processes that occur within the stream than those that occur outside the area of the gallery forest, considering the spatial scale of this study.
Asunto(s)
Heterópteros/crecimiento & desarrollo , Ríos , Agricultura , Animales , Brasil , Bosques , Pradera , Dinámica PoblacionalRESUMEN
Determining thresholds of species loss in response to gradients of human impact is becoming an increasingly important component of stream conservation and management. We analyzed the thresholds of change in populations and communities of the infraorder Nepomorpha along a gradient of environmental integrity in streams of the Brazilian savannah, based on samples from 20 sites. We used the Threshold Indicator Taxa Analysis (TITAN) to identify the location and magnitude of changes associated with the environmental quality and the frequency and abundance of the different taxa. We also used TITAN to calculate the positive and negative thresholds of the community and species along the habitat integrity gradient. Nepomorphan species were generally associated with sites of higher environmental quality, which presented larger populations and greater species richness. Only a few nepomorphan species groups were associated with impacted streams. Thresholds were evident in some aquatic nepomorphan populations, but not for the community as a whole. This indicates that species have idiosyncratic responses to the environmental gradient, but in general nepomorphans appear to be a good indicator of healthy environments or less impacted streams in the Brazilian savannah.
Asunto(s)
Conservación de los Recursos Naturales , Monitoreo del Ambiente , Heterópteros/clasificación , Ríos , Animales , Brasil , Ecosistema , Dinámica PoblacionalRESUMEN
This study investigated the effects of environmental variation on assemblages of dragonfly larvae (Odonata). We hypothesize that there is a significant correlation between species richness, species composition, and abundance of Odonata individuals, and habitat integrity and abiotic variables. To test this hypothesis, we sampled odonate larvae at 12 streams in the Suiá-Miçú River basin in Mato Grosso, Brazil, during three different periods of the year. Local physical and chemical variables (temperature, pH, turbidity, electrical conductivity (EC), dissolved oxygen (DO), total dissolved solids (TDS), and oxidation reduction potential (ORP)) were measured at each site using a multi-parameter probe, and integrity was assessed using the Habitat Integrity Index (HII). The variation in richness, abundance, and composition of Odonata species was related to the environmental variables analyzed, primarily by the abiotic factors pH, electrical conductivity, dissolved oxygen, total dissolved solids, and oxidation reduction potential. Our hypothesis was corroborated for the suborder Anisoptera, which showed a significant relationship with these variables, whereas Zygoptera was only related to pH. Our results show the importance of physical and chemical conditions in ecological studies using Odonata larvae as tools for the management and conservation of freshwater ecosystems.
Asunto(s)
Distribución Animal , Ecosistema , Odonata , Ríos , Animales , Brasil , Conservación de los Recursos Naturales , LarvaRESUMEN
Odonata have been widely used as indicators for the biomonitoring of terrestrial and aquatic habitats due to their sensitivity to environmental impacts. We aimed to determine whether the larval or adult phases of these insects were the best predictors of variation in habitat parameters and the loss of environmental integrity. Specimens were collected during three seasons (dry, rainy, and ebb) from 12 points in the Suiá-missu River basin, at the headwaters of the Xingu River in Mato Grosso, Brazil. The Protest analysis indicated a high degree of congruence between the assemblages of larvae and adults in streams with varying degrees of habitat integrity (R = 0.832, p < 0.001, m 2 = 0.307). When the congruence with environmental factors was analyzed, a significant association was found only for the larval phase (R = 0.318, p = 0.03, m 2 = 0.888). When the suborders were analyzed separately, congruence was confirmed for anisopteran adults (R = 0.338, p = 0.031, m 2 = 0.885) and larvae (R = 0.417, p = 0.003, m 2 = 0.826) and for the zygopteran adults (R = 0.345, p = 0.027, m 2 = 0.881) and larvae (R = 0.405, p = 0.011, m 2 = 0.836). These results indicate that both larvae and adults respond systematically to environmental impacts. We suggest that either life phase can be used for biomonitoring, given their effectiveness for the interpretation of disturbance in terrestrial and aquatic habitats. These findings further reinforce the effectiveness of this insect order for the detection of modifications to the environment, showing that they are good indicators of environmental conditions.
Asunto(s)
Monitoreo del Ambiente , Odonata/crecimiento & desarrollo , Animales , Ecosistema , Ambiente , Larva/crecimiento & desarrollo , Larva/fisiología , Odonata/fisiología , Densidad de PoblaciónRESUMEN
Patterns of species' abundance and occurrence over time and space allow division of species into (i) common species, which are abundant, but have a low diversity, and (ii) rare species, which are far more diverse and less abundant. Understanding the relationships among these two species groups and how they are affected by environmental conditions is a major challenge for ecologists, especially considering the distinction between local environmental factors and regional factors and variations in abundance over the course of the year. In this study, we focused on the long-term relationship between the abundance of rare and common ephemeropterans and abiotic factors on local and regional scales. Our hypotheses are that common species will be affected primarily by regional environmental variables (i), whereas rare species will be influenced more by temporal variation (ii). Together, both local and regional abiotic variables, plus temporal variation, best explained the abundance of the common species, whereas temporal variation was the best predictor of rare species. Considering the theoretical aspects and the empirical evidence, we discuss the results based on the plasticity of the common species and the life cycle of the rare ones. We believe that our findings reinforce the need for the deconstruction of communities for a deeper understanding of their relationships with abiotic variables and, in particular, the specific aspects of these relationships in the context of the different guilds of the community.
Asunto(s)
Biodiversidad , Ephemeroptera , Animales , Brasil , Densidad de PoblaciónRESUMEN
We demonstrate that the distribution of the functional feeding groups of aquatic insects is related to hierarchical patch dynamics. Patches are sites with unique environmental and functional characteristics that are discontinuously distributed in time and space within a lotic system. This distribution predicts that the occurrence of species will be based predominantly on their environmental requirements. We sampled three streams within the same drainage basin in the Brazilian Cerrado savanna, focusing on waterfalls and associated habitats (upstream, downstream), representing different functional zones. We collected 2,636 specimens representing six functional feeding groups (FFGs): brushers, collector-gatherers, collector-filterers, shredders, predators, and scrapers. The frequency of occurrence of these groups varied significantly among environments. This variation appeared to be related to the distinct characteristics of the different habitat patches, which led us to infer that the hierarchical patch dynamics model can best explain the distribution of functional feeding groups in minor lotic environments, such as waterfalls.
Asunto(s)
Distribución Animal , Organismos Acuáticos , Biodiversidad , Insectos , Animales , Brasil , Ecosistema , PraderaRESUMEN
Effects of riparian vegetation removal on body size and wing fluctuating asymmetry (FA) of Argia tinctipennis Selys (Odonata: Coenagrionidae) were studied in the River Suiá-Miçú basin, which is part of the Xingu basin in Brazilian Amazonia. A total of 70 specimens (n = 33 from preserved and n = 37 from degraded areas) was measured. Five wing measures of each wing (totalizing ten measured characters) were taken. Preserved and degraded points presented non-overlapped variations of a Habitat Integrity Index, supporting the environmental differentiation between these two categories. FA increases in degraded areas approximately four times for the width between the nodus and proximal portion of the pterostigma of forewings (FW), two times for the width of the wing in the region of nodus of FW, and approximately 1.7 times for the number of postnodal cells of FW. The increase is almost five times for the width between the nodus and the proximal portion of the pterostigma of hind wings (HW), three times for the number of postnodal cells of HW, and approximately 1.6 times the width between quadrangle and nodus of HW. Individuals of preserved sites were nearly 3.3% larger than for degraded sites, based on mean hind wing length. Our results supports that the development of A. tinctipennis in degraded areas is affected by riparian vegetation removal and may reflect in wing FA variations. Consequently, these FA measures may be a useful tool for bioassessment using Odonata insects as a model.