Landscape contrast: a solution to hidden assumptions in the metacommunity concept?

The metacommunity concept provides a spatial perspective on community dynamics, and the landscape provides the physical template for a metacommunity. Several aspects of landscape heterogeneity, such as landscape diversity and composition, and characteristics of the matrix between habitat patches such as habitat connectivity, and geometry of habitat patches, may moderate metacommunity processes. These aspects of landscape heterogeneity are rarely considered explicitly in the metacommunity discussion, however. We propose landscape contrast (i.e., the average dissimilarity in habitat quality between neighboring patches) as a key dimension of landscape heterogeneity. The concept of landscape contrast unifies discrete and continuous landscape representations (homogeneous, gradient, mosaic and binary) and offers a means to integrate landscape heterogeneity in the metacommunity concept. Landscape contrast as perceived by the organisms affects several fundamental metacommunity processes and may thus constrain which metacommunity models may be observed. In a review of empirical metacommunity studies (n = 123), only 22 % of studies were explicit about their underlying landscape model assumptions, with striking differences among taxonomic groups. The assumed landscape model constrained, but did not determine, metacommunity models. Integration and explicit investigation of landscape contrast effects in metacommunity studies are likely to advance ecological theory and facilitate its application to real-world conservation problems.     

Description of the Infection Status in a Norwegian Cattle Herd Naturally Infected by Mycobacterium avium subsp. paratuberculosis

The Norwegian surveillance and control programme for paratuberculosis revealed 8 seroreactors in a single dairy cattle herd that had no clinical signs of Mycobacterium avium subsp. paratuberculosis (M. a. paratuberculosis) infection. Paratuberculosis had been a clinical problem in goats several years previously in this herd. All 45 cattle were culled and a thorough investigation of the infection status was conducted by the use of interferon-γ (IFN-γ) immunoassay, measurement of antibodies, and pathological and bacteriological examination.In the IFN-γ immunoassay, 9 animals gave positive results, and 13 were weakly positive, while 19 animals were negative. In the serological test,10 animals showed positive reactions, and 5 were doubtful, while 30 animals gave negative reactions. There appeared to be a weak trend toward younger animals having raised IFN-γ and older animals having raised serological tests. Histopathological lesions compatible with paratuberculosis were diagnosed in 4 animals aged between 4 and 9 years. Three of these animals had positive serological reaction and one animal gave also positive results in the IFN-γ immunoassay. Infection was confirmed by isolation of M. a. paratuberculosis from 2 of these 4 animals. One single bacterial isolate examined by restriction fragment length polymorphism (RFLP) had the same profile, B-C1, as a strain that had been isolated from a goat at the same farm several years previously.Despite many animals being positive in one or both of the immunological tests, indicative of a heavily infected herd, none of the animals showed clinical signs and only one cow was shown to be shedding bacteria. A cross-reaction with other mycobacteria might have caused some of the immunoreactions in these animals. It is also possible that the Norwegian red cattle breed is resistant to clinical infection with M. a. paratuberculosis.     

Modeling the Exchanges of Energy, Water, and Carbon Between Continents and the Atmosphere

Atmospheric general circulation models used for climate simulation and weather forecasting require the fluxes of radiation, heat, water vapor, and momentum across the land-atmosphere interface to be specified. These fluxes are calculated by submodels called land surface parameterizations. Over the last 20 years, these parameterizations have evolved from simple, unrealistic schemes into credible representations of the global soil-vegetation-atmosphere transfer system as advances in plant physiological and hydrological research, advances in satellite data interpretation, and the results of large-scale field experiments have been exploited. Some modern schemes incorporate biogeochemical and ecological knowledge and, when coupled with advanced climate and ocean models, will be capable of modeling the biological and physical responses of the Earth system to global change, for example, increasing atmospheric carbon dioxide.     

Late pliocene faunal turnover in the turkana basin, kenya and ethiopia

Analysis of a large sample of well-dated fossil mammals from localities in the Turkana Basin of Kenya and Ethiopia revealed sampling biases that affect patterns of faunal turnover during the late Pliocene. When these biases were accounted for, results indicated that 58 to 77 percent of the mammal species were replaced between 3.0 and 1.8 million years ago (Ma). Overall diversity increased from 3.0 to 2.0 Ma but then declined. No distinct turnover pulse is seen between 2.8 and 2.5 Ma; instead, the most significant period of faunal change began after 2.5 Ma and continued through 1.8 Ma.     

Effect of post‐methanation effluent on soil physical properties under a soybean‐wheat system in a Vertisol

Post‐methanation effluent (PME) generated through bio‐methanation of distillery effluent, a foul‐smelling, dark colored by‐product of distillery industries, is applied to arable land in some areas near the vicinity of the distillery industries as an amendment. The PME contains considerable amount of organic matter and salt besides its high plant‐nutrient content. The present investigation was conducted for three years during 1999–2002 on soybean‐wheat cropping sequence to evaluate the effect of graded levels of post‐methanation effluent (PME) on soil physical properties and crop productivity in a deep Vertisol of central India. Six application doses of PME viz. S_2.5+W₀: 2.5 cm PME applied to soybean and wheat on residual nutrition, S_2.5+W_1.25: 2.5 cm PME to soybean and 1.25 cm to wheat, S_5.0+W₀: 5 cm PME to soybean and wheat on residual nutrition, S_5.0+W_2.5: 5.0 cm PME to soybean and 2.5 cm to wheat, S_10.0+W₀: 10 cm PME to soybean and wheat on residual nutrition, and S_10.0+W_5.0: 10.0 cm PME to soybean and 5.0 cm to wheat, were compared with 100% recommended NPK+FYM ? 4 Mg ha^–1 and control (no fertilizer, manure or PME). The application of PME increased the organic carbon content and electrical conductivity of the soil compared to control and 100% NPK+FYM treatment. The organic C content was maximum in S_10.0+W_5.0 (11.2 g kg^–1) and minimum in control (5.2 g kg^–1). Electrical conductivity increased from 0.47 dS m^–1 in control to 1.58 dS m^–1 in highest dose of PME (S_10.0+W_5.0). The PME treatments have not affected the soil pH. The application of PME showed a significant improvement in the physical properties of the soil. The mean weight diameter (MWD), percent water‐stable aggregation (% WSA), saturated hydraulic conductivity (K_sat), and water retention (WR) at 0.033 MPa suction were significantly (P < 0.05) more while bulk density (BD) and penetration resistance was significantly less in PME‐treated plots than that of control. The MWD showed a linear and positive relationship (r = 0.89**) with the soil organic C. Soybean recorded significantly higher seed yield at all PME treatments than control. Highest average soybean yield (2.39 Mg ha^–1) was recorded in S_10.0+W₀ but yield decreased significantly in S_10.0+W_5.0 (2.08 Mg ha^–1). In wheat, all the PME‐treated plots except S_2.5+W₀ yielded significantly higher than control while the 100% NPK+FYM treatment yielded (3.46 Mg ha^–1) at par with the S_10.0+W_5.0 (4.0 Mg ha^–1) and S_5.0+W_2.5 (3.66 Mg ha^–1). Fresh application of PME to wheat resulted in significant improvement in grain yield over that grown on residual fertility. Thus, application of PME to arable land, as an amendment, could be considered as a viable option for the safe disposal of this industrial waste.     

Determinants of adoption behaviour of the fish farmers of Pabda fish culture (Ompok bimaculatus Bloch, 1794) in Tripura,Northeast India

Aquaculture International - Most of the adoption studies in catfish culture were restricted to feeding habits, growth rate and morphological studies, neglecting the social factors and adoption of...     

Comparison of apparent digestibility coefficient among replicates and different stocking density in red sea bream <Emphasis Type="Italic">Pagrus major</Emphasis>

Two consecutive feeding trials were conducted to know: (i) how the apparent digestibility coefficient (ADC) varies among replicates on different days and during the course of the experiment (Trial 1); and (ii) the effect of stocking density (e.g. 7.17, 5.56, and 3.92 kg fish/t water) on the ADC of nutrients and energy in red sea bream (Trial 2). In both trials, 0.5% Cr₂O₃ was used as an inert marker. In Trial 1, there were no significant differences in ADC within the replicates although the values on different days varied significantly during the second week. The ADC of all parameters in the third and fourth weeks was significantly higher than in the second week (P<0.05). Although statistically insignificant, the lower stocking densities (3.92 and 5.56 kg fish/t water) showed better growth performance and superior ADC of protein, lipid, and energy than the higher stocking density in Trial 2. The results indicated that it may be better to acclimate fish to the diet for at least three weeks to obtain more reliable data by using a single tank for each treatment for digestibility experiments. Results also indicated that growth and digestibility performance can be stimulated by controlling stocking density.     

Identifying scale specific controls of soil water storage in a hummocky landscape using wavelet coherency

High spatio-temporal variability of soil water is contributed from different ecohydrological and soil processes operating in different intensities at different scales. Traditional Pearson correlation analysis only examines linear correlation at the measurement scale. In this study, the correlation between soil water storage and its controlling factors was examined at different scales and locations in a hummocky landscape using wavelet coherency. Time domain reflectometry and neutron probe were used to measure soil water storage up to 1.4 m depth along a transect of 576 m long established in a hummocky landscape at St. Denis National Wildlife Area, Saskatchewan, Canada. In spite of visual similarity of the spatial pattern of soil water storage and elevation, the value of Pearson correlation coefficient was very small. However, wavelet coherency identified strong scale- and location-specific correlations between soil water storage and elevation. The total area of significant correlations as calculated from the total number of significant coherencies at different scales and locations was higher between soil water storage and elevation than between soil water storage and any other factors, which indicated a dominant control from elevation on soil water storage in the hummocky landscape. The largest area of significant correlation was observed at large scales (> 70 m), which can be attributed to the alternating knolls and depressions. The relationship between soil water storage and elevation at different scales was persistent at different times of the year or at different seasons with a slight reduction in the magnitude of correlation. The persistent relationship indicated the dominant control from elevation with slight change in the degree of the control. The scale-location specific correlation provides a complete picture on the controls of soil water storage, which was not possible with traditional correlation analysis.