Appendix 1 B
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Oikos OIK-05265 Stam, J. M, Dicke, M. and Poelman, E.H. 2018. Order of herbivore arrival on wild cabbage populations influences subsequent arthropod community development. - Oikos doi: 10.1111/oik.05265 Appendix 1 B. brassicae and P. xylostella numbers in the community B. brassicae aphids and P. xylostella caterpillars were placed on the plants early in the season, thereby directly manipulating their numbers. To test whether their numbers on those plants indeed were changed, season-wide cumulative B. brassicae numbers (total over all 12 time points in 2012) of B. brassicae aphids per plot for the treatments A, C and None for each of the two plant populations were analysed by ANOVA. The number of B. brassicae aphids did not differ between the herbivory treatments. However, a marginally non-significant effect (ANOVA F2:3.096, P=0.066) of aphid inoculation causing more B. brassicae was recorded on Winspit plants. Because their numbers were directly affected by the experimental manipulation, and thus direct density effects and indirect interaction effects could not be separated, B. brassicae and P. xylostella were left out of further community composition analyses. Interpretation of ordination plots Ordination analyses of community composition in field season 2012 resulted in PRC graphs, that show the first ordination axis against time and the ordination scores of each species as projected on the first ordination axis. A high line in the graph (high PRC score for a treatment at a certain time point), correlates with a larger abundance of species scoring high on the species axis; species with a negative score correlate with lower abundance of this species compared to the average abundance on plants with the treatment set as baseline (ordination score = 0). Ordination analyses of community composition in field season 2013 resulted in RDA biplots, that show on the first two ordination axes the ordination of species (arrows from origin to their ordination on [axis 1, axis 2]), and the ordination of the plant population-early herbivore treatment combinations (WIN A&C, WIN A-C, WIN C-A, KIM A&C, KIM A-C, KIM C-A), which are the centroids of the ordination scores of all plots of the same treatment. RDA graphs can be interpreted using the biplot rule (Šmilauer and Lepš 2014), in which the position of a species in the ordination graph is projected with right angles to the (imaginary) line through the treatment’s position and the origin of the ordination graph. Species thus projected far away from the origin are predicted to have a large abundance on plots with that treatment (if they are on the same side of the origin), or a lower than average abundance (if they are on opposite sides of the origin). Plants with treatments with an ordination position close to each other (low Euclidean distance) are predicated to have similar arthropod community compositions. Herbivore induction * plant population specificity The specificity of community changes to early herbivore arrival on the different plant populations was apparent from the RDA biplot results, but we further elucidated it with pairwise comparisons of the herbivore induction*plant population combinations using case scores on the first three principal component axes of the community composition in 2013. Therefore, unconstrained linear principal component analyses (PCA, ordination of the field plots without prior knowledge on applied treatments) with week number as covariate were performed. Thus obtained ordination scores on each of the first three ordination axes of each field plot were used for ANOVA analyses on ‘treatments’, formulated as the plant population*order of herbivore arrival combinations, and round monitored, and their interaction term. A forward accumulated Wald test (normal distribution) with estimated dispersion parameter was performed, followed by an LSD post hoc test to assess significant differences between all ‘treatment’ pairs (plant population * early herbivore interaction) if the main effect was significant. ANOVA’s over PCA plot scores were performed with GenStat ver. 17 (VSN International Ltd, Hemel Hempstead, UK). These tests between plant population * herbivore order combinations showed that effects of the two factors on the responding community could not be separated, as both pair- wise differences between herbivore sequences (e.g. a significant difference between A&C WIN versus C-A WIN), between plant populations (e.g. A-C KIM versus A-C WIN), and across both herbivore induction and plant population (e.g. A&C WIN versus A-C KIM) were significant (Supplementary Table 4). Also when the responding community was divided into functional groups, herbivores responded very specific to the herbivore induction * plant population interaction: using case scores of the herbivore community ordination, these two factors could similarly not be separated (Supplementary Table 5). This indicates that plant populations differ in their response to early season herbivores and the order of herbivore species arrival, affecting the development of the subsequent herbivore community on those plants. References Šmilauer, P. and Lepš, J. 2014. Multivariate analysis of ecological data using CANOCO 5. - Cambridge Univ. Press. Table A1. Arthropod species found during field monitoring in 2012 and 2013, including their functional group (herbivore / predator / parasitoid). a Species was only encountered during 2013 field season; b Only cocoons of the species were recorded; c Only mummified aphids were recorded. Species Order Family Functional Remark group Phyllotreta undulata Coleoptera Chrysomelidae Herbivore Phyllotreta atra Coleoptera Chrysomelidae Herbivore Coccinella spp. Coleoptera Coccinellidae Predator Meligethes aeneus Coleoptera Nitidulidae Herbivore Ceutorhynchus assimilis Coleoptera Curculionidae Herbivore Cantharis spp. Coleoptera Cantharidae Predator 2013 onlya Amphimallon solstitiale Coleoptera Scarabaeidae Herbivore 2013 only Unknown spp. of tortoise beetle Coleoptera Chrysomelidae Herbivore Pieris rapae Lepidoptera Pieridae Herbivore Pieris brassicae Lepidoptera Pieridae Herbivore Plutella xylostella Lepidoptera Yponomeutidae Herbivore Mamestra brassicae Lepidoptera Noctuidae Herbivore Lacanobia suasa Lepidoptera Noctuidae Herbivore Autographa gamma Lepidoptera Noctuidae Herbivore Evergestis forficalis Lepidoptera Crambidae Herbivore Brevicoryne brassicae Hemiptera Aphididae Herbivore Myzus persicae Hemiptera Aphididae Herbivore Philaenus spp. Hemiptera Aphrophoridae Herbivore 2013 only Orius insidiosus Hemiptera Anthocoridae Predator Lygus spp. Hemiptera Miridae Herbivore Eurydema oleracea Hemiptera Pentatomidae Herbivore Aleyrodes spp. Hemiptera Aleyrodidae Herbivore Several species of Symphyta Hymenoptera - Herbivore (sawfly) larvae Cotesia rubecula Hymenoptera Braconidae Parasitoid Cocoonsb Cotesia glomerata Hymenoptera Braconidae Parasitoid Cocoons Microplitis mediator Hymenoptera Braconidae Parasitoid Cocoons Praon spp. Hymenoptera Braconidae Parasitoid Cocoons Diadegma spp. Hymenoptera Ichneumonidae Parasitoid Cocoons Several species parasitizing Hymenoptera - Parasitoid Mummiesc Brevicoryne brassicae Several species of Syrphidae Diptera Syrphidae Predator Unknown species of gall midge Diptera Cecidomyiidae Predator larvae Unknown species of thrips Thysanoptera - Herbivore Several species of Neuroptera Neuroptera - Predator Several species of Spiders Araneae - Predator Several species of snails and slugs - - Herbivore Class Gastropoda Several (unknown) species of leaf - - Herbivore 2013 only mining insects Table A2. ANOVAs of arthropod abundance and species richness affected by early season herbivore treatment, plant population and their interaction in both years. Numbers in bold indicate significant effects. Treatment Plant population Treatment * Plant population df F p df F p df F p 2012 Total abundance 5 0.432 0.852 1 10.950 0.001 5 2.026 0.083 Herbivore abundance 5 0.403 0.846 1 9.387 0.003 5 1.691 0.146 Carnivore abundance 5 0.696 0.628 1 5.826 0.018 5 2.305 0.052 Total species richness 5 0.432 0.832 1 0.336 0.563 5 2.021 0.084 Herbivore species richness 5 0.741 0.595 1 1.233 0.270 5 2.184 0.063 Carnivore species richness 5 0.703 0.623 1 0.142 0.707 5 1.222 0.306 2013 Total abundance 2 0.486 0.619 1 0.052 0.821 2 0.028 0.973 Herbivore abundance 2 0.461 0.634 1 0.568 0.455 2 0.243 0.786 Carnivore abundance 2 0.471 0.628 1 0.002 0.968 2 0.250 0.780 Total species richness 2 0.517 0.600 1 0.002 0.961 2 0.351 0.706 Herbivore species richness 2 0.582 0.564 1 0.207 0.651 2 0.435 0.650 Carnivore species richness 2 0.170 0.844 1 0.014 0.907 2 0.152 0.860 Table A3. Results of post-hoc principal component analyses (PCA; a redundancy analysis with time component) to explore the treatment differences of single and dual herbivore induction on two B. oleracea plant populations. The post-hoc analyses were performed after finding a significant overall effect of induction treatments on community composition in a PRC analysis. Early season herbivore induction treatments (None, A, C, A&C, A-C, C-A) on two plant populations Kimmeridge (KIM) and Winspit (WIN) were tested in 2012 on different parts of the community with Monte Carlo permutation tests. a Percentages show the % explained variation on the first RDA axis; b df (i,j) show the degrees of freedom of explanatory variables (i) and covariates (j). c F-values are pseudo-F values of Monte Carlo Permutation test. d parasitoids associated with the aphid B. brassicae (Bb) (‘mummies’) were excluded from the community analysis. Part