Influence of Habitat Diversity - Essay Example

Traditionally, the term macro invertebrate refers to aquatic invertebrates (stream dwelling organisms without vertebrae that can be seen with the naked eye). Most macro invertebrates are aquatic insects or aquatic stages of insects (e.g. larvae Ephimeroptera and Trichoptera), crustaceans (e.g. amphipods), mollusks (e.g. aquatic snails) and worms (e.g platyhelmenthes). They usually inhabit a wetland or river channel. Since macro invertebrates have varying degrees of resistance to pollution and other changes in environmental conditions, they serve as "bio indicators" for various factors involving steam health. They are a key component of the food chain and their abundance and diversity have been used to assess the ecosystem health and bio diversity in a given habitat. A very recent study by Leroy et al iexamined the relative importance of litter quality and stream characteristics in determining decomposition rate and macro invertebrate assemblage living on autumn shed leaves. The decomposition rates of five riparian tree species (Populus fermonti, Alnus oblongifolnia, Platanus wrightii, Faxinus velutina, Quercus gambelli) were compared across three south -western streams in the Verde River catchments (Arizona, U.S.A). Also to test whether plant species diversity affects rate, the decomposition of three and five species mixtures was compared to that of a single species. The results showed that decomposition rate was affected by both litter quality and stream although litter quality accounted for most of the variation. The relative importance of litter quantity was shown to decrease from 97% in the first week to 45% by the eighth week. It was also found that the rate of decomposition increased relatively when all the species included were highly labile. The most significant outcome of this study was the difference in invertebrate assemblage, which seemed to be more pronounced across streams than across leaf litter species within a stream. There was also a significant difference between the invertebrate assemblage colonizing leaf mixtures compared to that colonizing pure species litter, indicating non -additive properties of litter diversity on stream invertebrates. The conclusion of the study was that leaf litter diversity has the capacity to affect in -stream decomposition rates and stream invertebrates but these effects depend on both litter quality and stream characteristics. A research conducted in Griffith University, Australiaii studied the basic principles and ecological consequences of altered flow regimens for aquatic bio- diversity. The article stated that the flow regimen is considered to be the primary factor governing river and flood plain wetland ecosystems. Four key principles highlighted the important mechanisms that link hydrology and aquatic bio diversity and the impacts of alteration in the flow regimes: 1. Flow plays a major role in determining the physical habitat in streams, which influences the biotic composition. 2. The evolution of aquatic species has a direct response to the natural flow regimes. 3. The viability of populations of many riverine species requires maintenance of natural patterns of longitudinal and lateral connectivity. 4. The alteration in flow regimes facilitates the invasion and success of exotic and introduced species in riverine systems. Wide ranges of taxonomic groups are impacted by altered flow regimes including riverine plants, invertebrates and fish. A study by Douglas et al iii related macro invertebrate community structure to physical, chemical and biological gradients in flow through constructed wetlands receiving secondarily treated domestic wastewater and lower nutrient river water in Ohio, U.S.A. Benthic colonization plates and emergence traps were used to collect macro invertebrates which were then analyzed with diversity, biotic and combination indices and related to seventeen parameters of water quality, substrate characteristics and primary productivity in both wetland systems. 36 and 39 macro invertebrate taxa were collected from wastewater and river wetland respectively. Communities closer to wastewater wetland had significantly lower (mean S.E). Simpson diversity (0.50 0.13) and Invertebrate Community Index (ICI) scores (2.60 0.80) than those of other sampling location. Closer to the river wetland, diversity scores were (0.84 0.01) and ICI scores were (4.80 0.70). Average dissolved oxygen and specific conductivity wee found to be best environmental predictors of invertebrate community metrics. These variables along with chemical oxygen demand and nitrate nitrogen described nearly 90%of the ICI variation in four-predictor regression model. Multiple correspondence analyses showed sampling locations loosely grouped by average diel dissolved oxygen, which described 65.4% of variation in gradient data and specific conductivity. The study demonstrated that analyses of macro invertebrate in a wetland are valuable means of assessing its ecological status. They can be used as an important supplement for traditional chemical analysis and improving water quality. On similar lines, an article by Nijboeriv also demonstrates the use of macro invertebrate communities to assess the ecological quality or conservation value of freshwater. The article states that a classification of species distribution is needed to target a species for nature conservation and to compare rarity and commonness between regions. The macro invertebrate taxa are defined in six classes: very rare, rare, uncommon, common, very common and abundant. The boundaries for these classes were established using the number of occurrence of taxa. A study done by Oleiveira et alv combined logistic models with multivariate methods for rapid biological assessment of rivers using macro invertebrates as an attempt for defining a simpler method for classifying the relative degree of disturbance in sites in biotic systems by comparing their faunistic compositions with reference sites. The study was done in two stages on two ecotypes with different levels of contamination. In the first stage reference sites were defined using previous Geographic Information Systems. Later, biological quality was assessed using multivariate techniques and non-linear estimation models. This method was found to be sensitive to organic pollution, easy to interpret, namely the species tolerance and thus could be used as a good framework to establish regional ranking based on the ecological impact of river sites. Another study by Effenberger vi investigated the effects of local disturbance history and habitat parameters (abiotic and biotic) on the Benthic invertebrates during several floods in two streams. Metal link scour chains were used to quantify bed movement patterns. Quantitative invertebrate samples were taken before and after each flood from replicate bed patches that underwent sediment scour, fill or remained stable. It was found that invertebrate density patterns varied between floods, sampling dates and streams. Stable patches acted as a refugium for many species and had the highest invertebrate density. Disturbance history and water depth were the most influential habitat parameters. Read More