| 1. |
- 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.
|
|
| 2. |
|
|
| 3. |
- 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.
|
|
| 4. |
- Jonsson, Per R., 1957, et al.
(författare)
-
Interactions between wave action and grazing control the distribution of intertidal macroalgae
- 2006
-
Ingår i: Ecology. - 0012-9658 .- 1939-9170. ; 87:5, s. 1169-1178
-
Tidskriftsartikel (refereegranskat)abstract
- Canopy-forming macroalgae are key species on temperate rocky shores. However, there is a lack of understanding of how the relative balance of physical and biological factors controls the establishment and persistence of intertidal macroalgae. Here we present an integrated study of the relative importance of wave-induced forces and grazing for the recruitment and Survival of the canopy-forming intertidal macroalgae Fucus vesiculosus and F. spiralis. A set of overtopped breakwaters provided a nearly unconfounded gradient in wave exposure between seaward and landward sides. A biomechanical analysis was performed based on empirical measurements of maximum drag forces in breaking waves, a model of long-term maximum wave height, and the breaking stress of Fucus spp. The estimated maximum flow speed (7-8 m/s) on the seaward side of the breakwaters was predicted to completely dislodge or prune Fucus spp. larger than similar to 10 cm, while dislodgment was highly unlikely on the landward side for all sizes. Experimental transplantation of Fucus spp. supported the biomechanical analysis but also suggested that mechanical abrasion may further limit survival in wave-exposed locations. Experimental removal of the limpet Patella vulgata, which was the principal grazer at this site, resulted in recruitment of Fucus spp. on the seaward side. We present a model of limpet grazing that indicates that limpet densities > 5-20 individuals/m(2) provide a proximate mechanism preventing establishment of Fucus spp., whereas wave action > 2 m/s reduces persistence through dislodgment and battering. In a conceptual model we further propose that recruitment and survival of juvenile Fucus spp. are controlled indirectly by wave exposure through higher limpet densities at exposed locations. This model predicts that climate change, and in particular an increased frequency of storm events in the northeast Atlantic, will restrict fucoids to more sheltered locations.
|
|
| 5. |
- Carpenter, Stephen R., et al.
(författare)
-
Ecosystem subsidies : Terrestrial support of aquatic food webs from C-13 addition to contrasting lakes
- 2005
-
Ingår i: Ecology. - : John Wiley & Sons. - 0012-9658 .- 1939-9170. ; 86:10, s. 2737-2750
-
Tidskriftsartikel (refereegranskat)abstract
- Whole-lake additions of dissolved inorganic C-13 were used to measure allochthony (the terrestrial contribution of organic carbon to aquatic consumers) in two unproductive lakes (Paul and Peter Lakes in 2001), a nutrient-enriched lake (Peter Lake in 2002), and a dystrophic lake (Tuesday Lake in 2002). Three kinds of dynamic models were used to estimate allochthony: a process-rich, dual-isotope flow model based on mass balances of two carbon isotopes in 12 carbon pools; simple univariate time-series models driven by observed time courses of delta(13)CO(2); and multivariate autoregression models that combined information from time series of delta(13)C in several interacting carbon pools. All three models gave similar estimates of allochthony. In the three experiments without nutrient enrichment, flows of terrestrial carbon to dissolved and particulate organic carbon, zooplankton, Chaoborus, and fishes were substantial. For example, terrestrial sources accounted for more than half the carbon flow to juvenile and adult largemouth bass, pumpkinseed sunfish, golden shiners, brook sticklebacks, and fathead minnows in the unenriched experiments. Allochthony was highest in the dystrophic lake and lowest in the nutrient-enriched lake. Nutrient enrichment of Peter Lake decreased allochthony of zooplankton from 0.34-0.48 to 0-0.12, and of fishes from 0.51-0.80 to 0.25-0.55. These experiments show that lake ecosystem carbon cycles, including carbon flows to consumers, are heavily subsidized by organic carbon from the surrounding landscape.
|
|
| 6. |
- Angeler, David
(författare)
-
Statistical performance and information content of time lag analysis and redundancy analysis in time series modeling
- 2009
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 90, s. 3245-3257
-
Tidskriftsartikel (refereegranskat)abstract
- Time lag analysis (TLA) is a distance-based approach used to study temporal dynamics of ecological communities by measuring community dissimilarity over increasing time lags. Despite its increased use in recent years, its performance in comparison with other more direct methods (i.e., canonical ordination) has not been evaluated. This study fills this gap using extensive simulations and real data sets from experimental temporary ponds (true zooplankton communities) and landscape studies (landscape categories as pseudo-communities) that differ in community structure and anthropogenic stress history. Modeling time with a principal coordinate of neighborhood matrices (PCNM) approach, the canonical ordination technique (redundancy analysis; RDA) consistently outperformed the other statistical tests (i.e., TLAs, Mantel test, and RDA based on linear time trends) using all real data. In addition, the RDA-PCNM revealed different patterns of temporal change, and the strength of each individual time pattern, in terms of adjusted variance explained, could be evaluated. It also identified species contributions to these patterns of temporal change. This additional information is not provided by distance-based methods. The simulation study revealed better Type I error properties of the canonical ordination techniques compared with the distance-based approaches when no deterministic component of change was imposed on the communities. The simulation also revealed that strong emphasis on uniform deterministic change and low variability at other temporal scales is needed to result in decreased statistical power of the RDA-PCNM approach relative to the other methods. Based on the statistical performance of and information content provided by RDA-PCNM models, this technique serves ecologists as a powerful tool for modeling temporal change of ecological (pseudo-) communities.
|
|
| 7. |
- Araújo, M.S., et al.
(författare)
-
Network analysis reveals contrasting effects of intraspecific competition on individual versus population diets
- 2008
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 89:7, s. 1981-1993
-
Tidskriftsartikel (refereegranskat)abstract
- Optimal foraging theory predicts that individuals should become more opportunistic when intraspecific competition is high and preferred resources are scarce. This density-dependent diet shift should result in increased diet breadth for individuals as they add previously unused prey to their repertoire. As a result, the niche breadth of the population as a whole should increase. In a recent study, R. Svanback and D. I. Bolnick confirmed that intraspecific competition led to increased population diet breadth in threespine stickleback (Gasterosteus aculeatus). However, individual diet breadth did not expand as resource levels declined. Here, we present a new method based on complex network theory that moves beyond a simple measure of diet breadth, and we use the method to reexamine the stickleback experiment. This method reveals that the population as a whole added new types of prey as stickleback density was increased. However, whereas foraging theory predicts that niche expansion is achieved by individuals accepting new prey in addition to previously preferred prey, we found that a subset of individuals ceased to use their previously preferred prey, even though other members of their population continued to specialize on the original prey types. As a result, populations were subdivided into groups of ecologically similar individuals, with diet variation among groups reflecting phenotype-dependent changes in foraging behavior as prey density declined. These results are consistent with foraging theory if we assume that quantitative trait variation among consumers affects prey preferences, and if cognitive constraints prevent individuals from continuing to use their formerly preferred prey while adding new prey.
|
|
| 8. |
- Ask, Jenny, 1976-, et al.
(författare)
-
Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes
- 2009
-
Ingår i: Ecology. - Washington, DC, USA : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 90:7, s. 1923-1932
-
Tidskriftsartikel (refereegranskat)abstract
- This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.
|
|
| 9. |
- 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.
|
|
| 10. |
- Bergvall, Ulrika Alm, et al.
(författare)
-
Plant secondary compounds and the frequency of food types affect food choice by mammalian herbivores
- 2005
-
Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 86:9, s. 2450-2460
-
Tidskriftsartikel (refereegranskat)abstract
- We have investigated food choice in individual fallow deer (Dama dama) encountering different relative frequencies of food types in the form of bowls containing pellets with either high or low concentrations of hydrolyzable tannin. We performed two similar experiments, one with large and one with small differences in tannic acid concentration. With small differences in tannic acid concentration, the ratio of the consumption per low- and high-tannin bowl was independent of frequency of occurrence, but with large differences in tannic acid concentration, we found frequency-dependent food choice. The deer ate proportionally less from high-tannin bowls if these occurred at low relative frequency. Variation between frequency treatments in the average order of encounter of bowl types might have produced this effect, because we found that the deer left a high-tannin bowl more quickly if they had switched to it from a low-tannin bowl. We argue that the perceived contrast between the tastes of different food types can play a role for food choice by mammalian herbivores.
|
|
