Species–area relationships across four trophic levels – decreasing island size truncates food chains

That larger areas will typically host more diverse ecological assemblages than small ones has been regarded as one of the few fundamental ‘laws’ in ecology. Yet, area may affect not only species diversity, but also the trophic structure of the local ecological assemblage. In this context, recent theory on trophic island biogeography offers two clear‐cut predictions: that the slope of the species–area relationship should increase with trophic rank, and that food chain length (i.e. the number of trophic levels) should increase with area. These predictions have rarely been verified in terrestrial systems. To offer a stringent test of key theory, we focused on local food chains consisting of trophic specialists: plants, lepidopteran herbivores, and their primary and secondary parasitoids. For each of these four trophic levels, we surveyed species richness across a set of 20 off‐shore continental islands spanning a hundred‐fold range in size. We then tested three specific hypotheses: that species richness is affected by island size, that the slope of the species–area curve is related to trophic rank, and that such differences in slope translate into variation in food chain length with island size. Consistent with these predictions, estimates of the species–area slope steepened from plants through herbivores and primary parasitoids to secondary parasitoids. As a result of the elevated sensitivity of top consumers to island size, food chain length decreased from large to small islands. Since island size did not detectably affect the ratio between generalists and specialists among either herbivores (polyphages vs oligophages) or parasitoids (idiobionts vs koinobionts), the patterns observed seemed more reflective of changes in the overall number of nodes and levels in local food webs than of changes in their linking structure. Overall, our results support the trophic‐level hypothesis of island biogeography. Per extension, they suggest that landscape modification may imperil food web integrity and vital biotic interactions.     

Perch,Perca fluviatilis L., in Small Lakes: Relations between Population Characteristics and Lake Acidity

Perch population characteristics of small lakes were examined with a special reference to lakes which have acidified recently due to atmospheric deposition of air pollutants. The population density and biomass of perch were higher in an acid (pH 4.5) clear water lake with low aluminium concentration than in recently acidified (pH 4.3–4.7) clear water lakes with higher aluminium levels. The structure of perch population in an acid (pH 4.4) humic lake was similar to recently acidified clear water lakes. The population density and the biomass of perch were significantly higher in 6 lakes with pH>5.0 than in 6 lakes of pH<5.0 whereas the mean age and length at a given age were higher in the more acid lakes.     

Lipopolysaccharides of three classes of supersensitive mutants of Salmonella typhimurium

Abstract Cresyl violet acetate was found to be an appropriate redox-indicator dye in anaerobic culture media with low redox potentials. Low redox potentials ( E '_h−250 to −300 mV) in media were obtained by addition of dithiothreitol (DTT). DTT and cresyl violet acetate in media did not influence the total number of anaerobes cultured from human feces.