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: Supporting information S4: Study of the effects of different colours of bowl traps
Data analysis
The attractiveness for wild bees of different colours of bowl traps were first analysed with standard GLMMs: abundance and species richness of captured wild bees served as response variables, bowl colours (yellow, white or blue) and experimental treatmentsas fixed effects, and sites as a random factor. Secondly, species-specific preferences were investigated using a model-based analysis of multivariate abundance, using the function manyglm() from the package mvabund ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.1111/j.2041-210X.2012.00190.x", "abstract" : "1. The mvabund package for R provides tools for model-based analysis of multivariate abundance data in ecology. 2. This includes methods for visualising data, fitting predictive models, checking model assump- tions, as well as testing hypotheses about the community\u2013environment association. 3. This paper briefly introduces the package and demonstrates its functionality by example.", "author" : [ { "dropping-particle" : "", "family" : "Wang", "given" : "Yi", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Naumann", "given" : "Ulrike", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Wright", "given" : "Stephen T", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Warton", "given" : "David I", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Methods in Ecology and Evolution", "id" : "ITEM-1", "issue" : "3", "issued" : { "date-parts" : [ [ "2012" ] ] }, "page" : "471-474", "title" : "mvabund \u2013 an R package for model-based analysis of multivariate abundance data", "type" : "article-journal", "volume" : "3" }, "uris" : [ "http://www.mendeley.com/documents/?uuid=6b529cfd-e29a-4ca7-abb9-73b0caa75486" ] } ], "mendeley" : { "previouslyFormattedCitation" : "(Wang et al. 2012)" }, "properties" : { "noteIndex" : 0 }, "schema" : "https://github.com/citation-style-language/schema/raw/master/csl-citation.json" }(Wang et al. 2012). Multivariate abundance data analyses were performed only on species that were present in at least eight sampling areas so as to ensure sufficient statistical power and scientifically sound inferences. Data of the two sampling periods (June, July) were first pooled and then analysed separately.
Results
In the pooled analyses, the abundance observed (average SE) in yellow bowl traps was (20.58 4.96) higher than in blue traps (8.42 2.54; GLMM with Poisson; Z = -13.091, P <0.001) and white traps (16.00 4.18; Z =-4.519, P < 0.001); white traps were in turn more efficient than blue traps (Z = 9.050, P < 0.001). In June, yellow traps collected, on average, a higher number (7.64 2.46) than blue traps (2.41 0.77; Z = -9.285, P <0.001) and white traps (3.95 1.10; Z = -6.315, P < 0.001). In July, the abundances recorded in yellow (12.95 3.68) and white (12.06 3.75) traps were not different (Z = -1.103, P = 0.27), but blue traps (6.00 2.01) caught significantly fewer wild bees than the two other colours; Z = -9.365, P < 0.001).
Species-specific preferences were then investigated i n t h e m o r e w i d e s p r e a d s p e c i e s ( p r e s e n t i n e" 8 a r e a s , o u t o f 1 2 ) . T w e l v e w i l d b e e s p e c i e s m e t t h a t c r i t e r i o n , w i t h 8 s h o w i n g s i g n i f i c a n t d i f f e r e n c e s r e g a r d i n g c o l o u r p r e f e r e n c e . Y e l l o w t r a p s c a u g h t m o r e s p e c i m e n s t h a n b l u e t r a p s . W h i t e w a s i n f o u r s p e c i e s as successful as yellow (Bombus sensus stricto group, Halictus tumulorum, Lasioglossum calceatum and Lasioglossum puaxillum); it was even significantly more attractive than the other two colours in the Halictus simplex group (Table S3). Analyses carried out with separate seasonal datasets (June, July) showed the same patterns as with the pooled data; they are therefore not presented here.
Discussion
Overall (June and July pooled), wild bees were mostly attracted by yellow traps, followed by white traps, and finally blue traps. In June, similar preferences were observed as with pooled seasonal samples. However, in July, no significant difference between yellow and white traps could be detected, though both were more efficient than the blue ones. This result shows that attractiveness of bowl traps can vary among species and according to season. It confirms the recommendations of Westphal et al. (2008) of using the three (yellow, blue and white) colours in parallel.
Despite this recommendation several studies have used only one or two colours ADDIN CSL_CITATION { "citationItems" : [ { "id" : "ITEM-1", "itemData" : { "DOI" : "10.1016/j.biocon.2011.03.014", "author" : [ { "dropping-particle" : "", "family" : "Krewenka", "given" : "Kristin M.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Holzschuh", "given" : "Andrea", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Tscharntke", "given" : "Teja", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Dormann", "given" : "Carsten F.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Biological Conservation", "id" : "ITEM-1", "issue" : "6", "issued" : { "date-parts" : [ [ "2011", "6" ] ] }, "note" : " From Duplicate 2 ( Landscape elements as potential barriers and corridors for bees, wasps and parasitoids - Krewenka, Kristin M.; Holzschuh, Andrea; Tscharntke, Teja; Dormann, Carsten F. )\n \nWe installed pan traps to sample bees (i) on the grasslands; (ii) on grassland edges behind adjacent hedges (potential barriers) and without hedges; (iii) on grass strips in 100 m distance to the grassland, which were connected or unconnected to the grassland; and (iv) unconnected (isolated) grass strips in 300 m and 750 m distance to test for corridor and isolation effects on abundance and species richness of foraging wild bees.\nAdditionally we provided trap nests for bees, wasps and their parasitoids on the grasslands and the strips. Species abundance and richness declined with increasing isolation from grasslands for foraging solitary bees, trap-nesting bees, wasps and parasitoids, but not for foraging bumblebees.\nMany studies investigating corridor effects on plants and animals have been conducted in a forest matrix\nwith cleared grassland plots (Damschen et al., 2006; Haddad and Tewksbury, 2005; Tewksbury et al., 2002; Townsend and Levey,\n2005), and these results cannot be readily transferred to the situation in intensively used agricultural landscapes.\nHypothese were :\n(i) Abundance and species richness of wild bees and trap-nesting wasps and their parasitoids decline with increasing isolation from the source habitat.\n(ii) Abundance and species richness of wild bees and trap-nesting wasps are higher on grass strips that are connected to a semi-natural habitat than on unconnected grass strips.\n(iii) Hedges\u00a0 can\u00a0 function\u00a0 as\u00a0 an\u00a0 obstacle\u00a0 and\u00a0 restrict\u00a0 foraging movements of wild bees.\n(iv) Parasitism\u00a0 rates\u00a0 of\u00a0 hosts\u00a0 in\u00a0 the\u00a0 trap\u00a0 nests\u00a0 decline\u00a0 with increasing isolation and are higher in connected than unconnected strips.\nIn total 110 pan trap yellow and blue, UV reflecting for a duration of three weeks, emptied each week\nLMM used and some package for post-hoc comparisons !\n \n ", "page" : "1816-1825", "publisher" : "Elsevier Ltd", "title" : "Landscape elements as potential barriers and corridors for bees, wasps and parasitoids", "type" : "article-journal", "volume" : "144" }, "uris" : [ "http://www.mendeley.com/documents/?uuid=68c4d642-bc59-41cf-bb63-a84c8641592f" ] }, { "id" : "ITEM-2", "itemData" : { "author" : [ { "dropping-particle" : "", "family" : "Tuell", "given" : "Julianna K.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Ascher", "given" : "John S.", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" }, { "dropping-particle" : "", "family" : "Isaacs", "given" : "Rufus", "non-dropping-particle" : "", "parse-names" : false, "suffix" : "" } ], "container-title" : "Conservation Biology and Biodiversity", "id" : "ITEM-2", "issue" : "2", "issued" : { "date-parts" : [ [ "2009" ] ] }, "page" : "275-287", "title" : "Wild Bees (Hymenoptera : Apoidea : Anthophila) of the Michigan Highbush Blueberry Agroecosystem", "type" : "article-journal", "volume" : "102" }, "uris" : [ "http://www.mendeley.com/documents/?uuid=6a34ec2e-ac22-41cf-92de-7bb01c070f45" ] } ], "mendeley" : { "manualFormatting" : "(e.g. Tuell, Ascher, & Isaacs 2009; Krewenka et al. 2011)", "previouslyFormattedCitation" : "(Tuell, Ascher, & Isaacs 2009; Krewenka et al. 2011)" }, "properties" : { "noteIndex" : 0 }, "schema" : "https://github.com/citation-style-language/schema/raw/master/csl-citation.json" }(e.g. Tuell, Ascher, & Isaacs 2009; Krewenka et al. 2011). In our case, white traps were as successful in July as the yellow ones, probably because more flowers with white corolla were blooming at that time of the year (P. Buri, personal observations). Notwithstanding the fact that yellow remains the most attractive colour for measuring general bee abundance, this does not apply to all wild bee species, which calls for systematically using traps of different colorations. Four species were equally attracted by the yellow and white traps, while the Halictus simplex group was even more linked to white traps (Table S3). Regarding blue traps, they seemed quite unattractive in our experiment, although five individuals of four different species were caught only in blue traps (one Bombus sylvestris, one Halictus confusus, two Chelostoma campanularum, and one Eucera longicornis). We recognize that this pattern could emerge randomly, but cannot exclude the possibility that these species would have been missed if no blue traps were set.Table S2. Bowl traps colour attractiveness. Species or species groups included in the multivariate analysis, with indication of the total number of individuals trapped, the number of replicates that harboured the species or species group, bowl trap colour preference with respective P-values. For more details, see Fig. S3 that provides information about bee abundance vs bowl trap colours for each species or species group. Significant differences in bold.
Species or species groupNumber of individualsNumber of replicatesBowl trap colour preferenceP-value (adjusted)Halictus simplex group17710white > blue = yellow0.001Halictus tumulorum11812yellow = white > blue0.001Lasioglossum calceatum14411white > blue0.001Lasioglossum malachurum34610yellow > white > blue0.001Lasioglossum zonulum18112yellow > white > blue0.001Lasioglossum pauxillum9110white > blue0.002Bombus sensus stricto8912yellow > white = blue0.029Halictus scabiosae258yellow = white = blue0.111Bombus lapidarius288yellow = white = blue0.285Lasioglossum leucozonium218yellow = white = blue0.285Bombus hortorum188yellow = white = blue0.859Bombus pascuorum2411yellow = white = blue0.859
Figure S2. Mean (SE) number of wild bees trapped with respect to bowl trap colour. . Significance codes R S T b
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