| 181. |
- Östman, Örjan, et al.
(författare)
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Meta-analysis reveals top-down processes are as strong as bottom-up effects in North Atlantic coastal food webs
- 2016
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 53:4, s. 1138-1147
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Tidskriftsartikel (refereegranskat)abstract
- Seagrass and seaweed habitats constitute hotspots for diversity and ecosystem services in coastal ecosystems. These habitats are subject to anthropogenic pressures, of which eutrophication is one major stressor. Eutrophication favours fast-growing ephemeral algae over perennial macroalgae and seagrasses, causing habitat degradation. However, changes in top-down control, caused by, for example, overfishing, may also have negative impacts on such habitats by decreasing grazer control of ephemeral algae. Meanwhile, systematic analyses estimating top-down effects of predator manipulations across a wide range of studies are missing, limiting the potential use of top-down control measures in coastal management. Here, we review the literature on experiments that test top-down and bottom-up controls in seagrass Zostera marina and seaweed Fucus spp. food webs in the North Atlantic. Using meta-analysis and meta-regression, we compare effect sizes of consumer and nutrient manipulations on primary producers, grazers and mesopredators. Presence of mesopredators on average doubled the biomass of ephemeral algae through trophic cascades, mainly mediated via negative effects on amphipods and isopods. Of the grazers, gastropods had twice as strong a negative effect on ephemeral algae as amphipods/isopods, but responded weakly to both predators and fertilization. In accordance with theory, top-down effects became stronger with eutrophication. Across studies, top-down effects on ephemeral algae at all trophic levels are on par with eutrophication effects. However, the few studies manipulating piscivorous fish make estimates of their top-down effects uncertain. Synthesis and applications. Consistently strong top-down effects in coastal ecosystems call for an integrated ecosystem perspective. Management should consider measures to improve stocks of predatory fish and reduce mesopredators for restoration and conservation of essential seagrass and seaweed habitats, thereby increasing the long-term viability of ecosystem services from coastal habitats.
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| 182. |
- Östman, Örjan, et al.
(författare)
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Top-down control as important as nutrient enrichment for eutrophication effects in North Atlantic coastal ecosystems
- 2016
-
Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 53:4, s. 1138-1147
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Forskningsöversikt (refereegranskat)abstract
- Seagrass and seaweed habitats constitute hotspots for diversity and ecosystem services in coastal ecosystems. These habitats are subject to anthropogenic pressures, of which eutrophication is one major stressor. Eutrophication favours fast-growing ephemeral algae over perennial macroalgae and seagrasses, causing habitat degradation. However, changes in top-down control, caused by, for example, overfishing, may also have negative impacts on such habitats by decreasing grazer control of ephemeral algae. Meanwhile, systematic analyses estimating top-down effects of predator manipulations across a wide range of studies are missing, limiting the potential use of top-down control measures in coastal management. Here, we review the literature on experiments that test top-down and bottom-up controls in seagrass Zostera marina and seaweed Fucus spp. food webs in the North Atlantic. Using meta-analysis and meta-regression, we compare effect sizes of consumer and nutrient manipulations on primary producers, grazers and mesopredators. Presence of mesopredators on average doubled the biomass of ephemeral algae through trophic cascades, mainly mediated via negative effects on amphipods and isopods. Of the grazers, gastropods had twice as strong a negative effect on ephemeral algae as amphipods/isopods, but responded weakly to both predators and fertilization. In accordance with theory, top-down effects became stronger with eutrophication. Across studies, top-down effects on ephemeral algae at all trophic levels are on par with eutrophication effects. However, the few studies manipulating piscivorous fish make estimates of their top-down effects uncertain.Synthesis and applications. Consistently strong top-down effects in coastal ecosystems call for an integrated ecosystem perspective. Management should consider measures to improve stocks of predatory fish and reduce mesopredators for restoration and conservation of essential seagrass and seaweed habitats, thereby increasing the long-term viability of ecosystem services from coastal habitats.
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| 183. |
- Angeler, David, et al.
(författare)
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Biological responses to liming in boreal lakes: an assessment using plankton, macroinvertebrate and fish communities
- 2010
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 47, s. 478-486
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Tidskriftsartikel (refereegranskat)abstract
- P>1. Biological responses to liming of acidified surface waters are equivocal and limit the overall assessment of food web responses. In this study, we analysed community structure in limed, acidified and circumneutral lakes, based on the analyses of phytoplankton, zooplankton, macroinvertebrates (littoral, sublittoral, profundal) and fish between 2000 and 2004. We also studied associations between functional feeding groups in food webs.2. Most univariate metrics of structure and function revealed similar community attributes among lake types, suggesting that community responses to natural recovery from acidification and liming management converge with those observed in circumneutral lakes. These trends were less clear in the multivariate analyses which showed significant community differences among lake types. For phytoplankton, these patterns were partly mediated by the invasive raphidophycean flagellate Gonyostomum semen.3. The associations between functional feeding groups indicated less connectivity and food web complexity in limed lakes relative to the other lake types. We speculate that repeated lime applications comprise frequent pulse disturbances which offset the establishment of stable trophic relationships in the food webs of limed lakes.4. Synthesis and applications. The limited structural and functional food web similarity among lake types supports the argument that liming constitutes an ecosystem-level disturbance. Managers should be aware of the ecosystem impacts of altered disturbance regimes when designing their management schemes because this can influence the success of restoration programmes. Furthermore, the lack of recovery, mediated in part by species invasions, suggests that impacts derived from global change are likely to lead to novel environmental situations. This calls for adaptive management strategies where managers are challenged to tackle multiple forms of anthropogenic stress simultaneously.
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| 184. |
- Auffret, Alistair G., et al.
(författare)
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Past and present management influences the seed bank and seed rain in a rural landscape mosaic
- 2011
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 48:5, s. 1278-1285
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Tidskriftsartikel (refereegranskat)abstract
- 1. Seed bank and seed rain represent dispersal in time and space. They can be important sources of diversity in the rural landscape, where fragmented habitats are linked by their histories. 2. Seed bank, seed rain and above-ground vegetation were sampled in four habitat types (abandoned semi-natural grassland (ABA), grazed former arable field (FAF), mid-field islet (MFI) and grazed semi-natural grassland (SNG)) in a rural landscape in southern Sweden, to examine whether community patterns can be distinguished at large spatial scales and whether seed bank and seed rain are best explained by current, past or intended future vegetation communities. 3. We counted 54 357 seedlings of 188 species from 1190 seed bank and 797 seed rain samples. Seed bank, seed rain and above-ground vegetation communities differed according to habitat. Several species characteristic of managed grassland vegetation were present in the seed bank, seed rain and vegetation of the other habitats. 4. The seed banks of SNGs and the seed rain of the FAFs were generally better predicted by the surrounding above-ground vegetation than were the other habitat types. The seed rain of the grazed communities was most similar to the vegetation in the FAFs, while the seed banks of the abandoned grasslands most resembled the vegetation in SNGs. 5. Gap availability and seed input could be limiting the colonisation of target species in FAFs, while remnant populations in the seed bank and the presence of grassland specialists in the above-ground vegetation indicate that abandoned grasslands and mid-field islets could be valuable sources of future diversity in the landscape after restoration. 6. Synthesis and applications. SNG communities are able to form seed banks which survive land-use change, but their seed rain does not reflect their above-ground communities. It is important that grassland plants set seed. By connecting existing grasslands with restoration targets, increased disturbance in the target habitats would allow for colonisation via the seed bank or seed rain, while decreased grazing intensity would benefit seed production in the source grasslands. Otherwise, landscape-wide propagule availability might increase with a more varied timing and intensity of management.
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| 185. |
- Axelsson, Petter, et al.
(författare)
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Leaf litter from insect-resistant transgenic trees causes changes in aquatic insect community composition
- 2011
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Ingår i: Journal of Applied Ecology. - Malden : Wiley-Blackwell. - 0021-8901 .- 1365-2664. ; 48:6, s. 1472-1479
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Tidskriftsartikel (refereegranskat)abstract
- 1. Recent research has addressed how transgenic residues fromarable crops may influence adjacent waterways, aquatic consumers and important ecosystem processes such as litter breakdown rates. With future applications of transgenic plants in forestry, such concerns may apply to forest stream ecosystems. Before any large-scale release of genetically modified (GM) trees, it is therefore imperative to evaluate the effects of genetic modifications in trees on such ecosystems. 2. We conducted decomposition experiments under natural stream conditions using leaf litter from greenhouse grown GM trees (Populus tremula x Populus tremuloides) that express Bacillus thuringiensis (Bt) toxins (cry3Aa; targeting coleopteran leaf-feeding beetles) to examine the hypothesis that GM trees would affect litter decomposition rates and/or the aquatic arthropod community that colonizes and feeds on leaf litter in streams. 3. We show that two independent transformations of isogenic Populus trees to express Bt toxins caused similar changes to the composition of aquatic insects colonizing the leaf litter, ultimately manifested in a 25% and 33% increases in average insect abundance. 4. Measurements of 24 phenolic compounds as well as nitrogen (N) and carbon (C) in the litter did not significantly differ among modified and wild-type trees and were thus not sufficient to explain these differences in the insect assemblage. 5. Decomposition rates were comparable among litter treatments suggesting that the normal suite of leaf traits influencing decomposition was similar among litter treatments and that the shredding functions of the community were maintained despite the changes in insect community composition. 6. Synthesis and applications. We report that leaf litter from GM trees affected the composition of aquatic insect communities that colonized litter under natural stream conditions. This suggests that forest management using GM trees may affect adjacent waterways in unanticipated ways, which should be considered in future commercial applications of GM trees. We also argue that studies at different scales (e.g. species, communities and ecosystems) will be needed for a full understanding of the environmental effects of Bt plants.
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| 186. |
- Björklund, Niklas
(författare)
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Climate change and range expansion of an aggressive bark beetle: evidence of higher beetle reproduction in naive host tree populations
- 2010
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 47, s. 1036-1043
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Tidskriftsartikel (refereegranskat)abstract
- 5. Synthesis and applications. The current study demonstrates that the mountain pine beetle has higher reproductive success in areas where its host trees have not experienced frequent beetle epidemics, which includes much of the current outbreak area in north central British Columbia. This increased productivity of mountain pine beetle is likely to have been a key reason for the rapid population buildup that resulted in unprecedented host tree mortality over huge areas in western Canada. The outbreak thus provides an example of how climate change-driven range expansion of native forest insects can have potentially disastrous consequences. Since an increased reproductive success is likely to accelerate the progression of outbreaks, it is particularly critical to manage forests for the maintenance of a mosaic of species and age classes at the landscape level in areas where host tree populations are naive to eruptive herbivores.
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| 187. |
- Breed, Martin F., 1981-, et al.
(författare)
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Clarifying climate change adaptation responses for scattered trees in modified landscapes
- 2011
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 48:3, s. 637-641
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Tidskriftsartikel (refereegranskat)abstract
- 1. Many studies have investigated adaptation to climate change. However, the term ‘adaptation’ has been used ambiguously and sometimes included parts of both classic evolutionary processes and conservation planning measures (i.e. human-mediated adaptation).2. To reduce ambiguity, we define three classes of evolutionary processes involved in adaptation – migrational, novel-variant and plasticity. Migrational adaptation describes the process of redistribution of standing genetic variation among populations. Novel-variant adaptation describes the increase in frequency of beneficial, new genetic variants. Plasticity adaptation refers to adaptive plastic responses of organisms to environmental stressors. Quite separately, human-mediated adaptation aims to maintain these evolutionary processes.3. Whilst the role of scattered trees in migrational adaptation of fauna may have been neglected in the past, their capacity to assist migrational adaptation of trees has been previously documented. However, their role in novel-variant and plasticity adaptation is generally unrecognised, and warrants further attention.4. Synthesis and applications. By defining different aspects of adaptation carefully, we show that scattered trees should not be cleared since they may facilitate gene flow across fragmented landscapes. However, they should be avoided as dominant seed sources since their stock may be of poor quality.
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| 188. |
- Dannewitz, Johan, et al.
(författare)
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Reproductive success of hatchery produced and wild born brown trout Salmo trutta in an experimental stream
- 2004
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 41:2, s. 355-364
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Tidskriftsartikel (refereegranskat)abstract
- 1.Although releases of hatchery-produced salmonids to support conspecific wildpopulations have increased dramatically during recent decades, little information isavailable about the performance in the wild of hatchery fish and their offspring.Important factors determining the success and genetic outcomes of supportive breedingprogrammes include (i) the relative reproductive success of released hatchery fish in thewild, and (ii) the extent to which the propagation affects the variance in reproductivesuccess in the population as a whole.2.We performed two field experiments on brown troutSalmo truttafrom the RiverDalälven in Sweden, where we examined reproductive success in an experimental stream.In experiment 1 we compared reproductive success between trout from a seventhgenerationhatchery stock of native origin and wild-born trout from the river. In experiment2, we compared reproductive success between seventh-generation hatchery troutand hatchery-reared trout derived from wild-born parents. Individual reproductivesuccess, based on the number of offspring assigned using microsatellite markers, wasassessed on three occasions after reproduction: immediately after hatching and after thefirst and second growth seasons.3.In experiment 1 there were no significant differences in reproductive success betweenseventh-generation hatchery trout and wild-born trout. In experiment 2, males from wildbornparents were more successful than males from the seventh-generation hatcherystock, but this difference was not observed among females.4.There was some evidence for a positive association between body size and reproductivesuccess among females but not males. For males, the number of mates was significantlyassociated with reproductive success, but this relationship was not evident among females.5.The variance in reproductive success was pronounced in both experiments, yieldingestimates of the ratio between the genetically effective size and the census size of ourexperimental populations ranging from 0·12 to 0·59.6.Synthesis and applications. Our results suggest that the reproductive success in thewild of hatchery-produced and wild-born trout with a common genetic backgroundmay be rather similar. These findings, in combination with the pronounced variancein reproductive success observed among breeders, indicate that supportive breedingcan be managed to increase not only the census but also the genetically effective sizeof small, endangered salmonid populations. However, to minimize negative effects ofhatchery selection, it is important to give priority to the restoration of natural habitatsand thereby increase the reproductive output from individuals in the wild.
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| 189. |
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| 190. |
- Engström, Johanna, 1981-, et al.
(författare)
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Effects of stream restoration on dispersal of plant propagules
- 2009
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Ingår i: Journal of Applied Ecology. - : Wiley. - 0021-8901 .- 1365-2664. ; 46:2, s. 397-405
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Tidskriftsartikel (refereegranskat)abstract
- 1. Species immigration is vital for the success of restoring degraded ecosystems, but the effectiveness of enhancing dispersal following restoration is seldom evaluated. Running water is an important vector for plant dispersal. Frequency and duration of floods and channel-network complexity are important factors influencing propagule dispersal. In Sweden, these functions have been modified by channelization to facilitate timber floating, thus hampering emigration and immigration of riparian propagules.2. During the last 10–20 years, affected watercourses have been restored by removing barriers and replacing boulders into channels. This is hypothesized to facilitate retention of water-dispersed propagules. We studied the efficiency of propagule retention following restoration by releasing propagule mimics and by placing propagule traps in the riparian zone.3. Retention of propagule mimics was highest in sites restored with boulders and large wood. Retention occurred at both high and low flows but was most efficient during low flows when mimics were trapped by boulders and wood. Waterborne propagules ending up at such sites are unlikely to establish unless they can reach the riparian zone later. At high flows, floating propagules are more likely to reach riparian areas suitable for establishment. According to propagule traps placed at various levels of the riparian zone, deposition of plant propagules and sediments did not increase in restored sites.4. Synthesis and applications. Our study not only demonstrates that restoration of channel complexity through replacement of boulders and wood can enhance retention of plant propagules, but also it highlights the importance of understanding how restoration effects vary with flow. Most streams are restored to function optimally during median or average flows, whereas communities often are controlled by ecological processes acting during extreme flow events. We advocate that stream restoration should be designed for optimal function during those discharges under which the ecological processes in question are most important, which in this case is, during high flow.
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