Correlation of environmental variables with patterns of distribution and abundance of common and rare freshwater macroinvertebrates

This study explores the environmental factors underlying variation in abundance of common and rare freshwater taxa. Hybrid multidimensional scaling is used to model variation in distribution and abundance of freshwater microinvertebrate taxa over 17 sample sites in the upper catchment of the LaTrobe River, Victoria, Australia. Initial analysis of 40 common taxa revealed high correlations of the ordination space with physico-chemical variables related to temperature, stream order, particle size and water chemistry. Analysis of all 269 taxa, or alternatively of the 229 rarer taxa alone, resulted in ordination spaces that showed high correlations for additional physico-chemical variables, particularly relating to water chemistry. Monte Carlo significance tests supported this finding in demonstrating that the analysis of all taxa produced a greater number of significant correlations between the ordination space and physico-chemical variables.

The additional important environmental correlates revealed by the analysis of the rare taxa suggested that there might be differences in the set of environmental variables that are related to patterns of distribution and abundance of rare versus common taxa. A Monte Carlo test was carried out to test the null hypothesis that the failure to recover some environmental correlates in the analysis of common taxa simply resulted from the small (40) number of taxa involved. Results of the test generally showed that rareness versus commonness could not be implicated in the greater recovery of these water chemistry variables in the analysis of the rare taxa.

The recovery of additional environmental correlates with the inclusion of rare taxa has implications for conservation studies at the community level. Ordination can be used for survey extension where complete information on distribution and abundance of taxa is unavailable. The ability of ordination methods to summarise distribution and abundance of rare taxa, and incorporate their additional information on environmental variation, suggests that representativeness of the ordination space is a useful criterion for reserve selection.     

Physico-mechanical properties and yield of silage corn as affected by soil compaction and tillage methods

Experimental investigations were conducted over three years to test the hypothesis that soil compaction affects the physical and mechanical properties of corn ears and corn cobs. Field experiments were made on sub-drained clay and sandy loam soils at Macdonald College Farm in Quebec Province of Canada. The mechanical properties of corn ears and corn cobs were determined from quasi-static force-deformation analysis performed with a universal Instron testing machine.

The results showed that soil compaction treatments did not significantly influence corn cob elastic modulus and strength in simple bending nor in radial compression. Cob moisture content did not significantly change as a result of the application of various traffic treatments. However, corn cob diameter and pith diameter were both significantly affected by soil compaction.

Corn ear moisture content and bending strength were not significantly affected by soil compaction. However, corn ear yield in all three years was found to be dependent on the amount of soil compaction applied.

Also studied were the effects of various tillage methods in ameliorating the deleterious effects of soil compaction on crop yield and crop quality. It is concluded that a judicious choice of tillage machinery system can minimize the reductions in ear yield due to soil compaction.     

Habitat correlates of distribution and local population decline of the endemic Sardinian newt Euproctus platycephalus

Habitat-based statistical models relating patterns of presence and absence of species to habitat variables could be useful to resolve conservation-related problems and highlight the causes of population declines. In this paper, we apply such a modelling approach to an endemic amphibian, the Sardinian mountain newt Euproctus platycephalus, considered by IUCN a critically endangered species. Sardinian newts inhabit freshwater habitat in streams, small lakes and pools on the island of Sardinia (Italy). Reported declines of newt populations are not yet supported by quantitative data, however, they are perceived or suspected across the species' historical range. This study represents a first attempt trying to statistically relate habitat characteristics to Sardinian newt occurrence and persistence. Linear regression analysis revealed that newts are more likely to be found in sites with colder water temperature, less riparian vegetation and, marginally, absence of fish. The implications of the results for the conservation of the species are discussed, and suggestions for the short-term management of newt inhabited sites suggested.     

Apparent Rapid Loss of Endocrine Disruptors from Wetlands Used to Store Either Tertiary Treated Sewage Effluent or Stormwater Runoff

The disruption of endocrine systems due to environmental contaminants potentially impacts on the developmental, behavioural, regulatory and reproductive systems of animals. A major source of exposure of animals (terrestrial and aquatic) to endocrine-disrupting compounds is through contact with contaminated surface waters contaminated with sewage effluent and/or stormwater discharge. We studied the response to endocrine-disrupting compounds of Gambusia holbrooki mosquito fish resident of wetlands that were used for the storage of either treated sewage effluent or stormwater runoff. We found that fish from wetlands that received polluted waters directly from the source (treated sewage effluent or stormwater runoff) demonstrated a morphological response consistent with endocrine disruption. In contrast, fish in the second in the series of wetlands that housed treated sewage effluent did not show evidence of such response. However, those from the second in the series of stormwater receiving wetlands did display a morphological response, although it could be considered milder than was observed in fish from the first in this effluent stream. Fish were also smaller in the wetland that received sewage effluent directly from the sewage treatment plant than elsewhere. Although the differences were not statistically significant, the average size of fish in the first in the series of stormwater wetlands were also small and second only to those in the first sewage effluent wetland.