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Your search keyword '"Gislason, Gisli M."' showing total 2 results
Start Over Author "Gislason, Gisli M." Topic arctic
2 results on '"Gislason, Gisli M."'

1. Temperature effects on fish production across a natural thermal gradient

Author

Demars, Benoit O. L., Friberg, Nikolai, Gudbergsson, Gudni, Hannesdottir, Elisabet R., Jackson, Michelle C., Johansson, Liselotte S., Mc Laughlin, Orla, Olafsson, Jon S., Woodward, Guy, Gislason, Gisli M., O'Gorman, Eoin J., and Olafsson, Olafur P.

Subjects
natural experiment, Arctic, Hengill, freshwater, Salmo trutta fario, PIT tag, mark-recapture, ecosystem services
Abstract

Global warming is widely predicted to reduce the biomass production of top predators, or even result in species loss. Several exceptions to this expectation have been identified, however, and it is vital that we understand the underlying mechanisms if we are to improve our ability to predict future trends. Here, we used a natural warming experiment in Iceland and quantitative theoretical predictions to investigate the success of brown trout as top predators across a stream temperature gradient (4-25 degrees C). Brown trout are at the northern limit of their geographic distribution in this system, with ambient stream temperatures below their optimum for maximal growth, and above it in the warmest streams. A five-month mark-recapture study revealed that population abundance, biomass, growth rate, and production of trout all increased with stream temperature. We identified two mechanisms that contributed to these responses: (1) trout became more selective in their diet as stream temperature increased, feeding higher in the food web and increasing in trophic position; and (2) trophic transfer through the food web was more efficient in the warmer streams. We found little evidence to support a third potential mechanism: that external subsidies would play a more important role in the diet of trout with increasing stream temperature. Resource availability was also amplified through the trophic levels with warming, as predicted by metabolic theory in nutrient-replete systems. These results highlight circumstances in which top predators can thrive in warmer environments and contribute to our knowledge of warming impacts on natural communities and ecosystem functioning.

Published
2016

2. Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier-fed streams.

Author

Castella, Emmanuel, Adalsteinsson, Hákon, Brittain, John E., Gislason, Gisli M., Lehmann, Anthony, Lencioni, Valeria, Lods-Crozet, Brigitte, Maiolini, Bruno, Milner, Alexander M., Olafsson, Jon S., Saltveit, Svein J., and Snook, Deborah L.

Subjects
BENTHOS, AQUATIC invertebrates, RIVERS
Abstract

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier-fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near-pristine reaches were studied on each stream in 1996–97. 2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non-insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa). 3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell-shaped with an optimum at an intermediate level of stability. 4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross-validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated. 5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier-fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier-fed streams under climate or hydrological change scenarios. [ABSTRACT FROM AUTHOR]

Published
2001
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