| 1. |
- Diehl, Eva, et al.
(författare)
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Effects of predator specialization, host plant and climate on biological control of aphids by natural enemies: a meta-analysis
- 2013
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Ingår i: Journal of Applied Ecology. - : Wiley. - 1365-2664 .- 0021-8901. ; 50:1, s. 262-270
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Forskningsöversikt (refereegranskat)abstract
- Aphids are among the most severe invertebrate pests of crops and cause high economic losses. The control of aphids by natural enemies is an essential ecosystem service with high relevance to management strategies applied in agricultural plant production and horticulture. However, the current knowledge on the effectiveness of specialist and generalist predators in aphid control with respect to host plants and climatic conditions has not yet been summarized in a meta-analytical approach. We collected 60 studies providing 168 independent cases of predator exclusion experiments to analyse how predator and host plant group and climatic conditions affect aphid control by natural enemies. Effects of natural enemies on aphid populations were strongest in assemblages that included specialist predators, either alone or with generalist predators. Generalists alone also reduced aphid numbers significantly, but not to the same extent as specialists. Effects of natural enemies were weaker on aphid populations feeding on legumes compared with aphids on grasses or herbs. The percentage reduction of aphids feeding on grasses, herbs or legumes was higher in treatments with assemblages or specialists alone compared with generalists with the largest difference on grasses. According to all field studies from the temperate zone, effects of natural enemies on aphid populations were strongest in areas with high precipitation seasonality. A relationship between predator effects and temperature seasonality was only found for the USA. Synthesis and applications. Specialist predators alone or assemblages of specialists and generalists had the strongest effect on aphid populations, especially when either feeding on grasses and herbs or when exposed to extreme weather events. The control of aphids by natural enemies is most promising in grass and herb crops, whereas it is less suited for controlling aphids in legume crops. Facing climate change, the effect of extreme weather events on aphid control by natural enemies will have further implications for developing management strategies for aphid control in the future.
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| 2. |
- Sereda, Elvira, et al.
(författare)
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Addition of crop residues affects a detritus-based food chain depending on litter type and farming system
- 2015
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Ingår i: Basic and Applied Ecology. - : Elsevier BV. - 1618-0089 .- 1439-1791. ; 16:8, s. 746-754
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Tidskriftsartikel (refereegranskat)abstract
- The addition of crop residues is a common farming practice to increase the organic carbon content of agricultural soils with particular importance in organically managed crops. Residues can be added either from the crop plant itself or from other plants and the type of litter may differentially affect decomposer populations. Effects of litter addition may cascade up to affect generalist predators via trophic cascades or modifications of structural microhabitat properties with unknown consequences for the role of these predators in below- and aboveground food webs. Wheat and maize litter were added to organically and conventionally managed wheat fields and effects on generalist predator and Collembola numbers, litter decomposition and carbon utilization as estimated by stable isotope analysis were studied, Significantly more predators were sampled in plots with maize litter compared to plots with wheal litter and under organic farming. Collembola numbers were not significantly affected by litter type or farming system.. Litter mass loss was highest in plots that received wheat litter under organic management and was negatively related to predator, but not Collemhola numbers. :Individuals of Lepidocyrtus spp. (Collembola) incorporated high percentages of maize-borne carbon compared to predator species. Two linyphiid spider species were more closely linked to the maize-consuming prey in organically managed fields and one carabid species showed this pattern in conventionally managed fields. High litter decomposition levels and generalist predator numbers were only observed in wheat litter plots in organically managed fields. The addition of crop residues from the growing crop under organic management may therefore be a promising farming practice to simultaneously promote decomposition services and numbers of natural enemies. Future studies need to address this practice and potential effects on the litter decomposer predator food chain across sites that cover a range of different soil types and climatic conditions.
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| 3. |
- Sereda, Elvira, et al.
(författare)
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Assessing spider diversity on the forest floor: expert knowledge beats systematic design
- 2014
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Ingår i: Journal of Arachnology. - 1937-2396. ; 42:1, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- The design of sampling schemes affects the results of biodiversity inventories. As an approach for quantifying the implications of such effects, we compared data on spider communities sampled in a beech-dominated forest floor habitat by 1) a regular grid of pitfall traps (systematic design) and 2) an expert-based distribution of traps (stratified design). We tested whether the two designs would lead to similar conclusions about the diversity and composition of ground-dwelling spider communities. Estimates of species richness, rarefied species richness and activity density calculated per trap were significantly higher in the stratified than in the systematic design. The community composition based on the presence or absence of sampled species or based on log-transformed activity densities differed significantly. Most of the dissimilarity between the community estimates of the two designs was attributable to three species, with Pardosa saltans Topfer-Hofmann 2000 being more common in traps of the stratified design and Tenuiphantes zimmermanni (Bertkau 1890) and Walckenaeria cuspidata Blackwall 1833 being more frequently observed in traps of the systematic design. Our study suggests that a stratified sampling design is better suited for inventory surveys of spider communities of forest-floor habitats, as trap locations of this design reflect specific habitat needs. It is important to note that inventories are a major field for the application of such designs and that greater care is needed for the application of inferential statistics. For example, the non-randomness that is caused by expert selection of sampling sites may violate fundamental assumptions of simple linear models.
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| 4. |
- Sereda, Elvira, et al.
(författare)
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Spatial distribution of spiders and epedaphic Collembola in an environmentally heterogeneous forest floor habitat
- 2012
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Ingår i: Pedobiologia. - : Elsevier BV. - 1873-1511 .- 0031-4056. ; 55:5, s. 241-245
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Tidskriftsartikel (refereegranskat)abstract
- Describing the biotic and abiotic processes that are responsible for the formation of spatial patterns in predators and their prey is crucial for improving our understanding of food-web interactions. We studied the spatial distribution of four abundant spider species and three common groups of epedaphic Collembola prey in a beech-dominated (Fagus sylvatica) forest floor habitat and related the observed patterns to environmental heterogeneity, overall predator activity (all ground beetles and spiders) and prey availability (all Collembola) at the local scale. Spiders and epedaphic Collembola were sampled over 392 days in a spatially explicit design based on a regular grid of 25 pitfall traps (inter-trap distance 100 m). Environmental heterogeneity was characterized by cover of moss and litter as well as the amount of dead wood at each trap location. We first used the index of dispersion to characterize the spatial distribution of spider species and Collembola and then related the observed patterns to environmental heterogeneity, predator and prey availability while testing for spatial autocorrelation within the same models. All taxa were significantly more aggregated than expected from the assumption of random distribution. The distribution of spider species was positively (Coelotes terrestris) or negatively (Tenuiphantes zimmermanni and Tapinocyba insecta) related to the cover of moss and negatively related to litter cover (C. terrestris) or the local availability of prey (T. insecta). The distribution of Collembola was negatively related to local litter cover (Lepidocyrtus spp.) and positively related to the amount of medium deadwood pieces (all other Entomobryidae). Our study suggests that none of the spider species preferred areas of low overall predator activity density. Moreover, it does not indicate association of spider species to prey-rich areas at the analyzed scale of WO m. It further highlights the importance of environmental heterogeneity, as different habitat properties differentially affected the local activity density of spiders and Collembola and thus considerably contributed to the understanding of distribution patterns. (c) 2012 Elsevier GmbH. All rights reserved.
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