Vosteen et al. 2016_R Skript_Fig. 5 less suitable plant 2014

Fig. 5 – less suitable plants I: Trifolium and Pisum race aphids were placed both on Trifolium pratense and Pisum sativum, so that each race was reared on its native host and a less suitable plant. Plants were left for 14 days in the field and number of hoverfly eggs, hoverfly larvae and surviving aphids was recorded several times. A randomized block design was used in this experiments. Each block consisted of all four treatments. Data was analyzed with mixed effects models using blocks as random effects (random intercept) and treatments as fixed effects. P-values for explanatory variables were obtained by sequentially deleting explanatory variables and comparison of the more complex model with the simpler model with a likelihood ratio test (Zuur et al. 2009). Factor level reductions were used to reveal differences between levels of a treatment (Crawley 2013). Number of hoverfly eggs and larvae were analyzed with generalized linear mixed models with either a Poisson error distribution, or a negative binomial error distribution (glmm with the lmer function of the lme4 package (Bates et al. 2014) whichever fitted best the data of a certain experiment. In cases were only a few hoverfly eggs or larvae were present and several plants without hoverfly eggs or larvae occurred, presence / absence data were used and analyzed with Bernoulli glmms.