Stronger diversity effects with increased environmental stress : a study of multitrophic interactions between oak, powdery mildew and ladybirds

Recent research has suggested that increasing neighbourhood tree species diversity may mitigate the impact of pests or pathogens by supporting the activities of their natural enemies and/or reducing the density of available hosts. In this study, we attempted to assess these mechanisms in a multitrophic study system of young oak (Quercus), oak powdery mildew (PM, caused by Erysiphe spp.) and a mycophagous ladybird (Psyllobora vigintiduo-punctata). We assessed ladybird mycophagy on oak PM in function of different neighbourhood tree species compositions. We also evaluated whether these species interactions were modulated by environmental conditions as suggested by the Stress Gradient Hypothesis. We adopted a complementary approach of a field experiment where we monitored oak saplings subjected to a reduced rainfall gradient in a young planted forest consisting of different tree species mixtures, as well as a lab experiment where we independently evaluated the effect of different watering treatments on PM infections and ladybird mycophagy. In the field experiment, we found effects of neighbourhood tree species richness on ladybird mycophagy becoming more positive as the target trees received less water. This effect was only found as weather conditions grew drier. In the lab experiment, we found a preference of ladybirds to graze on infected leaves from trees that received less water. We discuss potential mechanisms that might explain this preference, such as emissions of volatile leaf chemicals. Our results are in line with the expectations of the Natural Enemies Hypothesis and support the hypothesis that biodiversity effects become stronger with increased environmental stress

Postsecular pacification: Pentecostalism and military urbanism in Rio de Janeiro

In this chapter, we reflect on the installment of Pacifying Police Units (Unidades de Polícia Pacificadora, UPPs) and on Brazilian military interventions in Rio de Janeiro in the years leading up to the Summer Olympics of 2016. We argue that the ‘pacification’ of the city entailed a rapprochement between religious groups and practices on the one hand and military and police actions on the other. Governmental promises to regain sovereign control of ‘wild’ urban territories leaned on Biblical representations of angelic intervention while governmental practices in urban places leaned on Pentecostal actors. The main argument of the chapter is that the continuum between this political theology and this religious governmentality amounts to what we call ‘postsecular pacification’, which we roughly define as the fusion of military interventions on national soil under democracy on the one hand and religious modes of governing urban territories on the other. To make this argument, this chapter by and large engages with two contemporary scholarly discussions: one centered on the militarization of urban life and the other on postsecular urbanism. We argue that insights harvested from these discussions should be united if we want to understand contemporary power and rule in Rio de Janeiro

Mycophagy in function of choice experiment running time.

<p>The different watering treatments are distinguished (DR0, 1 and 2 corresponding to weekly watering of 1, 0.8 and 0.6 L respectively) and ladybird gender (m = male, f = female). Values were determined based on fixed parameter estimates of the full mixed model at average initial PM infected area.</p

Example of a ladybird choice feeding experiment.

<p>Picture taken after 24 hours. The ladybird was removed to take this picture, but evidence of mycophagy can be noted in particular on the two leaf segments on the left. The leaf on the bottom also contains multiple particles of feces.</p

Parameter estimates of the mixed models of the PM and mycophagy scores (%) and total number of ladybirds over 4 measuring moments in function of rainfall reduction (DR) and species richness (SR).

<p>Parameter estimates of the mixed models of the PM and mycophagy scores (%) and total number of ladybirds over 4 measuring moments in function of rainfall reduction (DR) and species richness (SR).</p

Soil moisture content by volume of the lab experiment oak trees.

<p>The different watering treatments (black = 1L, dark grey = 0.8 L and light grey 0.6 L per week) are shown with their 95% confidence intervals.</p

Average PM infected area of the lab experiment oak trees.

<p>The different watering treatments (black = 1L, dark grey = 0.8 L and light grey 0.6 L per week) are shown with their 95% confidence intervals.</p

Example of ladybird grazing marks on oak PM.

<p>Example of ladybird grazing marks on oak PM.</p

PM mycophagy in function of species richness in weeks 3 and 4 of monitoring, when a significant interaction was found.

<p>The mycophagy scores were transformed according to the effect of the PM covariate.</p