Influence of habitat diversity and substratum on the composition of Essay

Influence of habitat diversity and substratum on the composition of macroinvertebrate communities from riverine systems - Essay Example 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 la bile. 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

Econometrics Essay Example | Topics and Well Written Essays - 1500 words

Econometrics - Essay Example Moreover, the scatter plots of income versus consumption and income versus investment are also plotted. The graphs show that the actual plots of all the variables except the government non-wage income show fluctuating trends with alternative peaks and troughs in the period of analysis. The correlograms of all the variables except the government non-wage income become zero from the third order ones. This shows that all the variable except the government non-wage income show fluctuating trends in the period of analysis. Government non-wage income show steady rising trend in the period of analysis. The correlogram of this variable is not gradually declining and remains the same. The scatter plots show that there is a significant positive correlation between income and consumption .Though a positive correlation can be seen income and investment, it is not so significant compared to the previous one. The OLS estimation for consumption shows perfect model fit. The coefficients for wage income and profit income are positive and significant. One percent rise in wage income leads to a significant rise of 19 percent consumption while one percent rise in wage income leads to a significant rise of 79 percent in consumption. The actual and fitted values of Consumption shows perfect fit as shown from the graphs in appendix 2. The 2SLS estimation shows that only wage income is significant in determining consumption .Here the coefficient for wage income has increased to 81.6 percent compared to the OLS estimation. At the same time profit income lost its significance here. The actual and fitted vales show perfect fit in this case also. For the estimation of investment with OLS, current and lagged values of profit income are positive and significant while lagged value of capital stock is significant and negative in determining investment. One percent rise in current and lagged