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  • Bastviken, David, 1971-, et al. (författare)
  • Methane as a source of carbon and energy for lake pelagic food webs
  • 2003
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 84:4, s. 969-981
  • Tidskriftsartikel (refereegranskat)abstract
    • Water-column methane oxidation can represent a substantial carbon transformation pathway in lakes, and circumstantial evidence indicates that methane may be a potentially important source of carbon for pelagic food webs. We estimated methanotrophic bacterial production (MBP), methanotrophic bacterial growth efficiency (MBGE), heterotrophic bacterial production (HBP), primary production (PP), and the relative contribution of methanotrophic bacteria to overall bacterial biomass in three very different lakes during summer and winter. In addition, we measured stable carbon isotope ratios in particulate organic matter (POM), surface sediments, zooplankton, and methane. MBP corresponded to 0.3-7% of the organic C production by primary producers, and 0.5-17% of HBP during summer. During winter, MBP was 3-120% of HBP. MBP generally dominated the heterotrophic bacterial production at greater depths. Methanotrophic biomass was 3-11% of total bacterial biomass on a depth-integrated basis. Zooplankton were generally more depleted in 13C than POM. If phytoplankton d13C signatures were -35 to -30ë, such as the POM signals, observed zooplankton signatures could be explained by a fraction of 5-15% methanotrophic bacteria in their diet. The results indicate that methanotrophic bacteria can provide a significant food source for zooplankton, and that methane oxidation represents a potentially important benthic-pelagic carbon and energy link in many lakes, particularly during winter.
  • Brose, Ulrich, et al. (författare)
  • Consumer-resource body-size relationships in natural food webs
  • 2006
  • Ingår i: Ecology. - : Ecological Society of America esa. - 0012-9658 .- 1939-9170. ; 87:10, s. 2411-2417
  • Tidskriftsartikel (refereegranskat)abstract
    • It has been suggested that differences in body size between consumer and resource species may have important implications for interaction strengths, population dynamics, and eventually food web structure, function, and evolution. Still, the general distribution of consumer-'resource body-size ratios in real ecosystems, and whether they vary systematically among habitats or broad taxonomic groups, is poorly understood. Using a unique global database on consumer and resource body sizes, we show that the mean body-size ratios of aquatic herbivorous and detritivorous consumers are several orders of magnitude larger than those of carnivorous predators. Carnivorous predator-prey body-size ratios vary across different habitats and predator and prey types (invertebrates, ectotherm, and endotherm vertebrates). Predator-prey body-size ratios are on average significantly higher (1) in freshwater habitats than in marine or terrestrial habitats, (2) for vertebrate than for invertebrate predators, and (3) for invertebrate than for ectotherm vertebrate prey. If recent studies that relate body-size ratios to interaction strengths are general, our results suggest that mean consumer-resource interaction strengths may vary systematically across different habitat categories and consumer types.
  • Ehrlén, Johan, et al. (författare)
  • Dispersal limitation and patch occupancy in forest herbs
  • 2000
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81, s. 1667-1674
  • Tidskriftsartikel (refereegranskat)abstract
    • The distribution of species depends on the availability of suitable habitats, the capacity to disperse to these habitats, and the capacity of populations to persist after establishment. Dispersal limitation implies that not all suitable habitat patches will be occupied by a species. However, the extent to which dispersal limits local distribution is poorly known. In this study, we transplanted seeds, bulbils, and juvenile plants to examine patterns of dispersal limitation and patch occupancy in seven temperate-forest herbs. Recruitment was recorded during four years in 48 patches. The investigated species varied considerably in their natural abundance in the patches. Patterns of seedling emergence and establishment among patches were not related to any of nine investigated abiotic factors. In contrast, the availability of seeds or bulbils was found to limit recruitment in six of the investigated species. Establishment was also successful in many patches where the species did not occur naturally. Estimated patch occupancy in the investigated species ranged from 17.2% to 94.6%. Seed size was positively correlated with the probability of successful establishment of seeds and negatively correlated with patch occupancy. The results suggest that dispersal limitation is an important structuring factor in temperate-forest herb communities. The distribution of species can be perceived as the result of processes operating both among and within patches. Seed size is a key trait in these processes.
  • Romaní, Anna Maria, et al. (författare)
  • Interactions of bacteria and fungi on decomposing litter : Differential extracellular enzyme activities
  • 2006
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 87:10, s. 2559-2569
  • Tidskriftsartikel (refereegranskat)abstract
    • Fungi and bacteria are key agents in plant litter decomposition in freshwater ecosystems. However, the specific roles of these two groups and their interactions during the decomposition process are unclear. We compared the growth and patterns of degradative enzymes expressed by communities of bacteria and fungi grown separately and in coexistence on Phragmites leaves. The two groups displayed both synergistic and antagonistic interactions. Bacteria grew better together with fungi than alone. In addition, there was a negative effect of bacteria on fungi, which appeared to be caused by suppression of fungal growth and biomass accrual rather than specifically affecting enzyme activity. Fungi growing alone had a high capacity for the decomposition of plant polymers such as lignin, cellulose, and hemicellulose. In contrast, enzyme activities were in general low when bacteria grew alone, and the activity of key enzymes in the degradation of lignin and cellulose (phenol oxidase and cellobiohydrolase) was undetectable in the bacteria-only treatment. Still, biomass-specific activities of most enzymes were higher in bacteria than in fungi. The low total activity and growth of bacteria in the absence of fungi in spite of apparent high enzymatic efficiency during the degradation of many substrates suggest that fungi provide the bacteria with resources that the bacteria were not able to acquire on their own, most probably intermediate decomposition products released by fungi that could be used by bacteria.
  • Sjöberg, Kjell, et al. (författare)
  • Response of Mallard ducklings to variation in habitat quality : an experiment of food limitation
  • 2000
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. - 0012-9658 ; 81:2, s. 329-335
  • Tidskriftsartikel (refereegranskat)abstract
    • Occurrence of Mallard (Anas platyrhynchos) pairs and broods was studied on 86 boreal lakes in two areas in south Finland during 1988-1997 (35 lakes) and 1989-1996 (51 lakes), and field experiments were conducted to determine whether food limitation is an important factor regulating population densities. In general, pairs and broods used and avoided the same lakes, but in both study areas, the proportion of lakes that were unoccupied every year was higher for broods (71% and 69%) than for pairs (26% and 31%). We hypothesized that lakes without breeding Mallards, and especially broods, were too poor to raise young in, and we tested that in field experiments on 22 lakes in boreal Sweden. Based on concentration of total phosphorus in the water, these lakes were divided into two groups: 11 "poor" lakes and 11 "rich" lakes. Mallard ducklings imprinted on humans were used to address brood-stage food limitation by studying mass change. Thirty-one individually marked ducklings were divided into three experimental groups: 12 ducklings were used in poor lakes, 12 ducklings in rich lakes, and 7 ducklings were used as controls receiving no experimental treatment in the field. Each group was studied in 11 daytime trials on 11 different lakes, except the control group which was kept in a pen with free access to food. Ducklings of all groups spent nights together as a big 31-individual group in the same pen and with free access to food. Ducklings foraging on poor lakes gained significantly less body mass than those feeding on rich lakes. At night, when ducklings of both groups had equal and free access to food, ducklings that had been feeding in a poor lake that day gained more mass than those that had been feeding in a rich lake. Overall, similar to 95% of daily mass gain was accounted for by daytime gain in the control group, the corresponding percentage was 35% in the rich-lake experimental group and 11% in the poor-lake experimental group. Thus, we have observational, as well as experimental, evidence to conclude that many boreal lakes are inferior breeding habitat for Mallards, especially during the brood stage. Our results suggest (1) that it is important to recognize at what stage of the yearly reproductive cycle food limitation may occur, (2) that brood stage may be more important than nesting stage for possible population limitation and regulation in breeding Mallards, and (3) that the reason why so many lakes in the boreal region lack breeding Mallards may be food limitation.
  • Beisner, Beatrix E., et al. (författare)
  • The role of environmental and spatial processes in structuring lake communities from bacteria to fish
  • 2006
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 87:12, s. 2985-2991
  • Tidskriftsartikel (refereegranskat)abstract
    • We assessed the relative roles of local environmental conditions and dispersal on community structure in a landscape of lakes for the major trophic groups. We use taxonomic presence–absence and abundance data for bacteria, phytoplankton, zooplankton, and fish from 18 lakes in southern Quebec, Canada. The question of interest was whether communities composed of organisms with more limited dispersal abilities, because of size and life history (zooplankton and fish) would show a different effect of lake distribution than communities composed of good dispersers (bacteria and phytoplankton). We examine the variation in structure attributable to local environmental (i.e., lake chemical and physical variables) vs. dispersal predictors (i.e., overland and watercourse distances between lakes) using variation partitioning techniques. Overall, we show that less motile species (crustacean zooplankton and fish) are better predicted by spatial factors than by local environmental ones. Furthermore, we show that for zooplankton abundances, both overland and watercourse dispersal pathways are equally strong, though they may select for different components of the community, while for fish, only watercourses are relevant dispersal pathways. These results suggest that crustacean zooplankton and fish are more constrained by dispersal and therefore more likely to operate as a metacommunity than are bacteria and phytoplankton within this studied landscape.
  • Alatalo, Rauno V., et al. (författare)
  • Exploitation competition influences the use of foraging sites by tits : Experimental evidence
  • 1987
  • Ingår i: Ecology. - : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 68:2, s. 284-290
  • Tidskriftsartikel (refereegranskat)abstract
    • In coniferous forests of central Sweden, tits (Paridae) and the Goldcrest, Regulus regulus, exploit nonrenewable resources in their group territories during winter. The smaller and socially subordinate species, the Goldcrest and the Coal Tit, Parus ater, forage on the outermost tree parts, while the larger and dominant Willow Tit, Parus montanus, and Crested Tit, Parus cristatus, forage on the inner tree parts. We removed Coal Tits and Goldcrests in three flocks in early winter to see if their absence would cause changes in the foraging patterns of the two dominant species. In late winter, Crested Tits foraged farther outward on branches of spruce in experimental flocks than they did in the control flocks. In spruce, Willow Tits foraged nearer the trunk than Crested Tits, and they did not respond to the experiment. In pine, Willow Tits, however, did move from branches to twigs in the absence of Coal Tits and Goldcrests. The experiment indicates that exploitation competition directly based on food depletion, without any interference, may influence the use of foraging sites by tits in coniferous forests.
  • Andersson, Martin, et al. (författare)
  • The spatial structure of bacterial communities is influenced by historical environmental conditions
  • 2014
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 95:5, s. 1134-1140
  • Tidskriftsartikel (refereegranskat)abstract
    • The spatial structure of ecological communities, including that of bacteria, is often influenced by species sorting by contemporary environmental conditions. Moreover, historical processes, i.e., ecological and evolutionary events that have occurred at some point in the past, such as dispersal limitation, drift, priority effects, or selection by past environmental conditions, can be important, but are generally investigated much less. Here, we conducted a field study using 16 rock pools, where we specifically compared the importance of past vs. contemporary environmental conditions for bacterial community structure by correlating present differences in bacterial community composition among pools to environmental conditions measured on the same day, as well as to those measured 2, 4, 6, and 8 d earlier. The results prove that selection by past environmental conditions exists, since we were able to show that bacterial communities are, to a greater extent, an imprint of past compared to contemporary environmental conditions. We suggest that this is the result of a combination of different mechanisms, including priority effects that cause rapid adaptation to new environmental conditions of taxa that have been initially selected by past environmental conditions, and slower rates of turnover in community composition compared to environmental conditions.
  • Andersson, Per Gösta, 1964- (författare)
  • Alternative confidence intervals for the total of a skewed biological population
  • 2004
  • Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 85:11, s. 3166-3171
  • Tidskriftsartikel (refereegranskat)abstract
    • In a 1999 Ecology article, T. G. Gregoire and O. Schabenberger addressed the problem of obtaining truly symmetric confidence intervals for the total of a positively skewed biological population under simple random sampling. Their simulation study revealed that the skewness induced a substantial positive correlation between the estimator of the total and the estimator of its variance. This caused the standard nominally symmetric t-based intervals, based on approximate normality of the estimator of the total, to be highly unbalanced, i.e., intervals much more often missed from below than from above. To better cope with this situation I suggest an alternative confidence interval procedure that takes into account and adjusts for the induced correlation. A simulation study based on one of the populations used by Gregoire and Schabenberger shows that the resulting adjusted intervals have more balanced noncoverage probabilities and often higher coverage probability than the standard intervals in cases of substantial correlation. I also provide an example of an unequal probability design using auxiliary information, where there is much less need for an adjustment.
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