| 1. |
- Bastviken, David, 1971-, et al.
(författare)
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Methane as a source of carbon and energy for lake pelagic food webs
- 2003
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 84:4, s. 969-981
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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.
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| 2. |
- Ehrlén, Johan, et al.
(författare)
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Dispersal limitation and patch occupancy in forest herbs
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81, s. 1667-1674
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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.
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| 3. |
- Sjöberg, Kjell, et al.
(författare)
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Response of Mallard ducklings to variation in habitat quality : an experiment of food limitation
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. - 0012-9658 ; 81:2, s. 329-335
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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.
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| 4. |
- Andersson, Per Gösta, 1964-
(författare)
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Alternative confidence intervals for the total of a skewed biological population
- 2004
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 85:11, s. 3166-3171
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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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| 5. |
- Brodin, Tomas, et al.
(författare)
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Conflicting selection pressures on the growth/predation risk trade-off in a damselfly
- 2004
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 85:11, s. 2927-2932
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Tidskriftsartikel (refereegranskat)abstract
- Activity is an important behavioral trait that in most animals mediates a trade-off between obtaining food for growth and avoiding predation. Active individuals usually experience a higher encounter rate with food items and predators and, as a consequence, grow faster and suffer higher predation pressure than less active individuals. We investigated how predator-induced mortality and growth of the damselfly Coenagrion hastulatum depend on activity at the level of the genotype. Larvae from six different C. hastulatum families were reared in two different predator treatments: predator present or absent. Families differed in activity, and active families grew to a significantly larger size than less-active families. Within families there was a plastic response to predators. Larvae reared without predators were more active and grew larger than larvae reared with a nonlethal predator. In the presence of a lethal predator the active families experienced higher mortality than the less active families. The results illustrate that the growth/predation-risk trade-off was mediated by activity and clearly show a cost of antipredator behavior. They also suggest that variation in activity level might be genetically regulated and could explain why C. hastulatum are abundant in aquatic systems both with and without potential predators.
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| 6. |
- de Kroon, Hans, et al.
(författare)
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Elasticities : a review of methods and model limitations
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:3, s. 607-618
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Tidskriftsartikel (refereegranskat)abstract
- Elasticity is a perturbation measure in matrix projection models that quantifiesthe proportional change in population growth rate as a function of a proportionalchange in a demographic transition (growth, survival, reproduction, etc.). Elasticities thusindicate the relative "importance" of life cycle transitions for population growth and maintenance.In this paper, we discuss the applications of elasticity analysis, and its extension,loop analysis, in life history studies and conservation. Elasticity can be interpreted as therelative contribution of a demographic parameter to population growth rate. Loop analysisreveals the underlying pathway structure of the life cycle graph. The different kinds ofresults of the two analyses in studies of life histories are emphasized. Because elasticitiesquantify the relative importance of life cycle transitions to population growth rate, it isgenerally inferred that management should focus on the transitions with the largest elasticities.Such predictions based on elasticities seem robust, but we do identify three situationswhere problems may arise. The mathematical properties and biological constraints thatunderlie these pitfalls are explained. Examples illustrate the additional information thatneeds to be taken into account for a sensible use of elasticities in population management.We conclude by indicating topics that are in need of research.
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| 7. |
- Ehrlén, Johan
(författare)
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The dynamics of plant populations : does the history of individuals matter?
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:6, s. 1675-1684
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Tidskriftsartikel (refereegranskat)abstract
- Historical events have been used to explain a wide range of phenomenaincluding geographical distributions of species, community diversity, and population structure.At the level of individuals, historical effects in which past conditions influence futureperformance are particularly likely to occur in long-lived organisms that store resourcesbetween seasons and that form organs months or years before their elaboration. Such carryovermechanisms have been documented in several perennial plant species, but the implicationsfor population processes are poorly known. In this study, I examine how the historyof individuals influences their future performance, population dynamics, and life cycle,structure in the long-lived herb Lathyrus vernus. Overall effects of plant history on populationdynamics, in terms of growth rate, reproductive values, stable stage distribution,and elasticities, are examined by comparing an ordinary first-order matrix model with asecond-order matrix model. In the latter, not only the present state of individuals, but alsotheir past state is allowed to influence future fate.The results demonstrate that the history of individuals is sometimes important in modelsof population dynamics. Plant size change over a one-year period was negatively correlatedamong time intervals. Addition of the previous year's stage in population models shiftedthe growth rate from positive (X = 1.010) to negative (X = 0.986) and increased theproportion of small established individuals in the stable stage distribution. If historicaleffects are due to a capacity to buffer environmental variation and regain size or state, asin L. vernus, then recruitment contributes less and stasis more to population growth thansuggested by ahistorical models. The presence of historical effects at the level of individuals,in any form, may have important consequences for population development and should beincluded in any interpretation of the life-cycle structure.
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| 8. |
- Granberg, G, et al.
(författare)
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Effects of temperature, and nitrogen and sulfur deposition, on methane emission from a boreal mire
- 2001
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 82:7, s. 1982-1998
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the effects of increased air temperature in combination with increased deposition of N and/or S on methane emission. we have raised in situ the temperature and rates of deposition of N and S in a poor fen lawn area of a boreal mixed mire. The experiment was laid out in a factorial design, where the mean daily air temperature 0.3 In above the vegetation surface was increased (by 3.6 degreesC) using greenhouse enclosures. A significant increase in the cover of sedges was observed in the N-supplemented plots after the third year of treatment. All three experimental factors had significant effects on the methane emission. The effects of temperature and N deposition strongly interacted with the sedge cover, which was the single variable explaining most variation in methane emission. Raised temperature affected the emission positively when the sedge cover was high but showed no effect when the sedge cover was low. Nitrogen addition affected methane emission negatively when the sedge cover was high and had a zero or slightly positive effect at low sedge cover. These positive temperature and negative N interaction effects with sedge cover were likely due to changed biomass allocation patterns in the plants. The S additions had negative effects on methane emissions at ambient temperature but no effect at raised temperature. This interaction effect was possibly a result of different retention of S, since the total S concentration was higher in the S addition treatments at normal but not at raised temperature. The results stress the fact that a given variable may affect biogeochemical processes in different directions or to differing degrees depending on other variables. both experimental and natural. Most importantly, the effects of added nitrogen, but also of increased temperature. were critically dependent on the density of sedges.
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| 9. |
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| 10. |
- Hambäck, PA, et al.
(författare)
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Associational resistance: insect damage to purple loosestrife reduced in thickets of sweet gale
- 2000
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Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 81:7, s. 1784-1794
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Tidskriftsartikel (refereegranskat)abstract
- Associational resistance occurs when herbivore damage to a focal plant is reduced by the presence of other plant species. Neighboring plants can reduce herbivore damage (1) by their effects on the predator community, (2) by reducing the ability of herbivores to find their host plants, and (3) by reducing the time herbivores remain on their host plants. We examined how the presence of the aromatic low shrub Myrica gale and of predatory lady beetles affected herbivore damage and reproductive output in a population of the perennial herb Lythrum salicaria in northern Sweden. An observational study showed that L. salicaria growing in Myrica thickets were less damaged by herbivores, had a lower abundance of the monophagous, leaf-feeding, chrysomelid beetle Galerucella calmariensis, and had higher flower and seed production than L. salicaria outside Myrica thickets. To test whether these differences could be explained by (a) differences in some aspect of plant quality, or (b) differences in predator abundance, we placed potted L. salicaria within and outside Myrica thickets. To determine whether differences in the abundance of G. calmariensis were primarily the result of different rates of colonization or emigration, we marked adult beetles and placed them on a second set of potted plants in the two micro-habitats. The results show that differences in herbivore abundance, plant damage, and reproductive output between potted L. salicaria placed within and outside Myrica thickets were in the same direction and of the same magnitude as those observed for naturally occurring plants, indicating that the observed patterns were not an effect of differences in the chemical composition of the host plant. Moreover, we found no support for the hypothesis that a higher abundance of insect predators could explain the lower abundance of G. calmariensis on L. salicaria in Myrica thickets. On the contrary, lady beetles (Coccinella quinqempunctata and Coccinella septempunctata) were observed on a greater proportion of the plants placed outside the Myrica thickets. The monitoring of marked beetles indicated that differences in the abundance of G. calmariensis were the result of a markedly higher colonization rate and a somewhat lower emigration rate from L. salicaria outside Myrica thickets. Outside the Myrica thickets, the survival of G. calmariensis and the magnitude of herbivore damage were lower, and fruit and seed output were higher on plants with observations of lady beetles than on plants without lady beetles. The results indicate that the abundance of the specialist herbivore G. calmariensis, and the herbivore damage and reproductive output of its host plant, L. salicaria, are affected both by the presence of the nonhost Myrica and by predation from lady beetles. We suggest that the most likely mechanism causing decreased feeding on L. salicaria growing in Myrica thickets is that Myrica affects the ability of G. calmariensis to find its host, either through visual or olfactory interference.
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