| 1. |
- Lange, Katharina, et al.
(författare)
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Light, nutrients and grazing interact to determine stream diatom community composition and functional group structure
- 2011
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 56:2, s. 264-278
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Tidskriftsartikel (refereegranskat)abstract
- P>1. Benthic algal communities are shaped by the availability of nutrients and light and by herbivore consumption. Many studies have examined how one of these factors affects algal communities, but studies simultaneously addressing all three are rare. 2. We investigated the effects of nutrients, light and a herbivore (the snail Potamopyrgus antipodarum) on benthic stream algae in a fully factorial experiment in 128 circular streamside channels. Four nutrient levels (none added to highly enriched), four snail grazing pressures (no snails to 777 individuals m-2) and two light levels (ambient and 65% reduced) were applied. Colonising algae were dominated by diatoms (Bacillariophyta), which were determined to species using acid-cleaned samples and assigned to functional groups according to their physiognomic growth form. 3. Diatom community structure changed considerably in response to our manipulations. Light had the strongest influence (as indicated by manova effect size), whereas nutrients had an intermediate effect and grazing was fairly weak. Relative abundances of six common diatom taxa decreased under reduced light, whereas five others became more prevalent. Eight taxa benefitted from nutrient enrichment, while three became rarer. Grazing affected the relative density of only one common taxon, which increased at higher grazing pressure. 4. Diatom functional groups also responded strongly. 'Low profile' taxa dominated at low resource levels (nutrients and especially light), whereas 'high profile' and 'motile' taxa became markedly more prevalent at higher resource levels. 5. Two-way interactions between experimental factors were quite common. For example, Planothidium lanceolatum and Rossithidium petersenii responded more strongly to nutrient enrichment at reduced than at ambient light, whereas Cocconeis placentula responded more strongly at ambient light. For diatom functional groups, the benefit of nutrient enrichment for 'motile' diatoms was greater at ambient than at reduced light. 6. Our results imply that multifactor experiments are required to determine the main forces driving the composition of benthic algal communities. Further, our findings highlight the considerable potential of using functional algal groups as indicators of changing environmental conditions to complement the traditional taxonomic approach.
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| 2. |
- Liess, Antonia, et al.
(författare)
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Landuse intensity in stream catchments affects the benthic food web : consequences for nutrient supply, periphyton C:nutrient ratios, and invertebrate richness and abundance
- 2012
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Ingår i: Freshwater Science. - : University of Chicago Press. - 2161-9549 .- 2161-9565. ; 31:3, s. 813-824
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic nutrient enrichment increases the supply ratio of N and P to aquatic ecosystems and can affect the identity of the limiting nutrient. Here we focus on how stream communities change along gradients of N and P supply and stream catchment landuse intensity. We used a survey approach in 41 southern New Zealand tributaries to investigate how much changes in water N and P concentrations are reflected in periphyton C:nutrient ratios (C:N or C:P) and how much food quality (high food quality corresponds to low periphyton C:nutrient) is reflected in the abundance and taxonomic richness of benthic invertebrate primary and secondary consumers. We measured streamwater nutrient state, periphyton nutrient ratios, biomass (as chlorophyll a in mu g/cm(2)), algal taxon richness, and macroinvertebrate abundance, taxonomic composition, and richness. We also estimated stream habitat and catchment characteristics, such as current velocity, shading, substrate, geology, and landuse intensity. We calculated the Akaike information criterion (AIC) for each possible multiple linear regression model to select the best predictive models for each response variable. C:nutrient ratios were more strongly negatively related to water-column N than P availability. Neither N nor P availability covaried with periphyton biomass. Lower periphyton C:N partly explained higher grazer, but not predator, abundance. Increased % runoff from pasture and periphyton N:P co-occurred with a decrease in invertebrate taxon richness. For example, a 4x increase in periphyton N:P was related to the loss of similar to 1/2 of invertebrate species, but with high uncertainty (R-2 = 0.13). We conclude landuse intensity affects these southern New Zealand streams, and these effects are mediated by agricultural N runoff into streams (among other factors). Further shifts toward high-intensity farming within stream catchments may lead to losses of benthic species at all trophic levels.
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| 3. |
- Liess, Antonia, et al.
(författare)
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Light, nutrients and grazing interact to determine diatom species richness via changes to productivity, nutrient state and grazer activity
- 2009
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Ingår i: Journal of Ecology. - : Wiley. - 0022-0477 .- 1365-2745. ; 97:2, s. 326-336
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Tidskriftsartikel (refereegranskat)abstract
- 1. Productivity and grazing pressure interact in determining autotroph diversity, because high productivity increases the capability of a plant community to compensate for grazing losses. However, further factors may play a role in shaping diversity, including primary producer nutrient stoichiometry and grazer activity. 2. Our study focuses on the interactions between light, nutrients and grazing in determining species richness and evenness of stream diatoms. By measuring primary producer productivity and nutrient content as well as grazer activity, we attempt to disentangle the different pathways by which the three factors affect diatom species richness and evenness. 3. We hypothesized that high light intensities and nutrient addition would increase species richness by increasing primary productivity and that higher levels of light and nutrients would compensate for negative grazer effects on species richness of primary producers. We also hypothesized that high light intensities would decrease the nutrient content of primary producers, especially when nutrients are limiting, whereas nutrient addition would increase primary producer nutrient content. Last, in addition to changing primary producer nutrient content, light and nutrients would also change grazer activity, thus modifying the interactions between light, nutrients and grazing. 4. We used periphyton and gastropod grazers in an experiment with circular stream channels with four nutrient, two light and four grazing levels to determine individual and combined effects on benthic diatom richness and evenness. After 3 weeks, we determined algal biomass, periphyton nutrient content, diatom species richness and evenness as well as grazer activity. 5. Our results showed that light and nutrients increased species richness and primary producer productivity and nutrient content. Grazing decreased species richness but only at low light levels, possibly because high light levels reduced grazer activity. Evenness was not affected by any single factor alone, but was influenced by nutrient-light and grazing-light interactions. 6. Synthesis. Light, nutrients and grazing interacted in determining primary producer species richness. Their effects were mainly mediated through changes in productivity but primary producer nutrient content and grazer activity also played important roles.
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| 4. |
- Oliveros, Carl H., et al.
(författare)
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Earth history and the passerine superradiation
- 2019
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:16, s. 7916-7925
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Tidskriftsartikel (refereegranskat)abstract
- Avian diversification has been influenced by global climate change, plate tectonic movements, and mass extinction events. However, the impact of these factors on the diversification of the hyper-diverse perching birds (passerines) is unclear because family level relationships are unresolved and the timing of splitting events among lineages is uncertain. We analyzed DNA data from 4,060 nuclear loci and 137 passerine families using concatenation and coalescent approaches to infer a comprehensive phylogenetic hypothesis that clarifies relationships among all passerine families. Then, we calibrated this phylogeny using 13 fossils to examine the effects of different events in Earth history on the timing and rate of passerine diversification. Our analyses reconcile passerine diversification with the fossil and geological records; suggest that passerines originated on the Australian landmass ∼47 Ma; and show that subsequent dispersal and diversification of passerines was affected by a number of climatological and geological events, such as Oligocene glaciation and inundation of the New Zealand landmass. Although passerine diversification rates fluctuated throughout the Cenozoic, we find no link between the rate of passerine diversification and Cenozoic global temperature, and our analyses show that the increases in passerine diversification rate we observe are disconnected from the colonization of new continents. Taken together, these results suggest more complex mechanisms than temperature change or ecological opportunity have controlled macroscale patterns of passerine speciation.
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| 5. |
- Piggott, Jeremy J., et al.
(författare)
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Climate warming and agricultural stressors interact to determine stream periphyton community composition
- 2015
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Ingår i: Global Change Biology. - : John Wiley & Sons. - 1354-1013 .- 1365-2486. ; 21:1, s. 206-222
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Tidskriftsartikel (refereegranskat)abstract
- Lack of knowledge about how the various drivers of global climate change will interact with multiple stressors already affecting ecosystems is the basis for great uncertainty in projections of future biological change. Despite concerns about the impacts of changes in land use, eutrophication and climate warming in running waters, the interactive effects of these stressors on stream periphyton are largely unknown. We manipulated nutrients (simulating agricultural runoff), deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6 °C above ambient) simultaneously in 128 streamside mesocosms. Our aim was to determine the individual and combined effects of the three stressors on the algal and bacterial constituents of the periphyton. All three stressors had pervasive individual effects, but in combination frequently produced synergisms at the population level and antagonisms at the community level. Depending on sediment and nutrient conditions, the effect of raised temperature frequently produced contrasting response patterns, with stronger or opposing effects when one or both stressors were augmented. Thus, warming tended to interact negatively with nutrients or sediment by weakening or reversing positive temperature effects or strengthening negative ones. Five classes of algal growth morphology were all affected in complex ways by raised temperature, suggesting that these measures may prove unreliable in biomonitoring programs in a warming climate. The evenness and diversity of the most abundant bacterial taxa increased with temperature at ambient but not with enriched nutrient levels, indicating that warming coupled with nutrient limitation may lead to a more evenly distributed bacterial community as temperatures rise. Freshwater management decisions that seek to avoid or mitigate the negative effects of agricultural land use on stream periphyton should be informed by knowledge of the interactive effects of multiple stressors in a warming climate.
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| 6. |
- Riede, James O., et al.
(författare)
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Stepping in Elton's footprints: a general scaling model for body masses and trophic levels across ecosystems
- 2011
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Ingår i: Ecology Letters. - : Wiley-Blackwell. - 1461-023X .- 1461-0248. ; 14:2, s. 169-178
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Despite growing awareness of the significance of body-size and predator–prey body-mass ratios for the stability of ecological networks,our understanding of their distribution within ecosystems is incomplete. Here, we study the relationships between predator and prey size,body-mass ratios and predator trophic levels using body-mass estimates of 1313 predators (invertebrates, ectotherm and endothermvertebrates) from 35 food-webs (marine, stream, lake and terrestrial). Across all ecosystem and predator types, except for streams (whichappear to have a different size structure in their predator–prey interactions), we find that (1) geometric mean prey mass increases withpredator mass with a power-law exponent greater than unity and (2) predator size increases with trophic level. Consistent with ourtheoretical derivations, we show that the quantitative nature of these relationships implies systematic decreases in predator–prey bodymassratios with the trophic level of the predator. Thus, predators are, on an average, more similar in size to their prey at the top of foodwebsthan that closer to the base. These findings contradict the traditional Eltonian paradigm and have implications for our understandingof body-mass constraints on food-web topology, community dynamics and stability.
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| 7. |
- Smith, N. G., et al.
(författare)
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Global photosynthetic capacity is optimized to the environment
- 2019
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 22:3, s. 506-517
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Tidskriftsartikel (refereegranskat)abstract
- Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (V-cmax), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co-optimization of carboxylation and water costs for photosynthesis, suggests that optimal V-cmax can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field-measured V-cmax dataset for C-3 plants. Soil fertility indices explained substantially less variation (32%). These results indicate that environmentally regulated biophysical constraints and light availability are the first-order drivers of global photosynthetic capacity. Through acclimation and adaptation, plants efficiently utilize resources at the leaf level, thus maximizing potential resource use for growth and reproduction. Our theory offers a robust strategy for dynamically predicting photosynthetic capacity in ESMs.
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