Valiela
Ivan
Valiela
Ivan
No Thumbnail Available
Search Results
Now showing
1 - 4 of 4
-
ArticleThe relative ineffectiveness of bibliographic search engines(American Institute of Biological Sciences, 2005-08) Valiela, Ivan ; Martinetto, PaulinaThe increasing number of scientific publications has made bibliographic search engines essential tools in all disciplines. These software-based devices, however, are far from perfect. Comparisons of software-based bibliographic search engines with complete lists of three authors' publications showed that reference citations were not generally available before 1970, and that the effectiveness of recovery was improving but was quite variable, yielding on average 36 percent of the publications. There was marked year-to-year inconsistency in the recovery of titles. The inconsistency could not be explained by differences in indexing due to journal reputation: there was no evident relationship between search effectiveness and journal impact factor, but the percentage of recovered citations was higher for indexed journals. Search engines are widely used in bibliographic searches performed for evaluating researchers, awarding promotions, or assessing journal performance. Given the ineffectiveness of search engines, their use in making such important personal and institutional decisions needs careful consideration.
-
ArticleImpact of burrowing crabs on C and N sources, control, and transformations in sediments andfood webs of SW Atlantic estuaries(Inter-Research, 2005-06-02) Botto, Florencia ; Valiela, Ivan ; Iribarne, Oscar ; Martinetto, Paulina ; Alberti, JuanThe intertidal burrowing crab Chasmagnathus granulatus is the dominant species in soft bare sediments and vegetated intertidal areas along the SW Atlantic estuaries (southern Brazil, 28°S, to northern Patagonia, 42°S). C. granulatus creates burrows that can reach densities of 60 burrows m–2, and its burrowing activities increase water and organic matter content of sediments. To evaluate the long-term effect of burrows on the origin and transformation of accumulated organic matter within sediments, we compared C and N stable isotope signatures of sediments, plants, and consumers within areas with and without crabs. 15N signatures of sediments and primary producers were enriched by 3 to 7‰ in areas with crabs. The enrichment was present in 4 different Argentine estuarine environments (Mar Chiquita coastal lagoon, 37°46’S, 57°19’W, Bahia Blanca, 38°50’S, 62°07’W, San Blas, 40°33’S, 62°14’W, San Antonio, 40°48’S, 64°52’W). Enrichment owing to crab activity appeared to overwhelm possible different N loads, anthropogenic influence, and other properties. Crab activity thus uncoupled the nitrogen dynamics in sediments from external controls. Enrichment of the heavier isotope of N could be the result of an increase in denitrification rates in areas with burrows. Crabs therefore forced faster transformation of available to unavailable nitrogen, making less inorganic nitrogen available to deeper waters. Food webs in areas with and without crabs were similar in shape, but less mobile benthic organisms (nematodes, fiddler crabs and the polychaete Laeonereis acuta) showed enriched N isotopic signatures. The benthic food web seemed separate from that of suspension feeders or water column consumers. Benthic microalgae were an important source for infauna, and marsh plants were particularly important for burrowing crabs.
-
ArticleChanges in bird abundance in eastern North America : urban sprawl and global footprint?(American Institute of Biological Sciences, 2007-04) Valiela, Ivan ; Martinetto, PaulinaThe abundance of birds recorded in the North American Breeding Bird Survey decreased by up to 18 percent between 1966 and 2005. The abundance of US and Canadian resident species decreased by 30 percent, and that of migrants within the United States and Canada decreased by 19 percent. By contrast, Neotropical migrants increased by up to 20 percent. Land-cover changes in northern latitudes therefore seem more consequential for bird populations than those occurring in Neotropical habitats. Lower abundances were most marked for resident breeding birds that used open, edge, and wetland habitats, the environments most affected by human disturbances—particularly urban sprawl—in northern latitudes. The abundance of resident and migrant forest-dwelling birds increased (although trends varied from species to species), with the increases seeming to follow the 20th-century expansion of forest area in northern latitudes, rather than the loss of Neotropical forests. The geographic footprint of changes in bird abundance linked to habitat changes in North America may thus be extending southward, with negative effects on birds that use open habitats and positive effects on forest birds.
-
ArticleCoupling of estuarine benthic and pelagic food webs to land-derived nitrogen sources in Waquoit Bay, Massachusetts, USA(Inter-Research, 2006-01-24) Martinetto, Paulina ; Teichberg, Mirta ; Valiela, IvanThe fact that land-derived sources of nutrients promote eutrophication in the receiving coastal waters implies coupling between land and marine environments. Increasing nitrogen inputs in the estuaries are followed by major shifts in biota composition and abundances. In the present paper we used N and C isotopic ratios to analyze the coupling of benthic and pelagic components of food webs to estuaries receiving different N loads from their watersheds. We found that primary producers, benthic taxa, and fishes were coupled to the watersheds and estuaries where they were collected. In contrast, zooplankton was uncoupled. Primary consumers and predators feeding on benthic prey within the estuaries were also coupled to the watershed and estuaries, but predators feeding on zooplankton were not. We hypothesized that short water residence time in these estuaries uncoupled plankton from terrestrial influence. Stable isotopic measurements of N in producers, consumers, POM, and sediment in different estuaries of Waquoit Bay, Massachusetts, USA, demonstrate a consistent link between land-use on contributing watersheds and the isotopic ratio in all the benthic components and food webs. The remarkably consistent link suggests that the benthos was tightly coupled to land-derived inputs, and that these components, particularly macrophytes, could be good indicators for monitoring increases in land-derived N inputs. Our results showed that stable isotopes of N and C have the potential for use in basic research and applied monitoring, but need to be applied considering the features of estuaries that might couple or uncouple organisms regarding dependency on land, such as hydrodynamic exchanges.