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Pathogens are embedded in multi-trophic food webs, which often include co-occurring cryptic species within the same pathogen complex. Nonetheless, we still lack an understanding of what dimensions of the ecological niche might allow these cryptic species to coexist. We explored the role of climate, host characteristics (tree autumn phenology) and attack by the fungal hyperparasite Ampelomyces (a group of fungi attacking plant pathogens) in defining the niches of three powdery mildew species (Erysiphe alphitoides, E. hypophylla and E. quercicola) within a cryptic pathogen complex on the pedunculate oak Quercus robur at the continental (Europe), national (Sweden and France) and landscape scales (a 5 km(2) island in southwestern Finland). Previous studies have shown that climate separated the niches of three powdery mildew species (E. alphitoides, E. hypophylla and E. quercicola) in Europe and two species (E. alphitoides and E. quercicola) in France. In our study, we did not detect a significant relationship between temperature or precipitation and the distribution of E. alphitoides and E. hypophylla present in Sweden, while at the landscape scale, temperature, but not relative humidity, negatively affected disease incidence of E. alphitoides in an exceptionally warm year. Tree variation in autumn phenology did not influence disease incidence of powdery mildew species, and hyperparasite presence did not differ among powdery mildew species at the continental, national and landscape scale. Climate did not affect the distribution of the hyperparasite at the continental scale and at the national scale in Sweden. However, climate affected the hyperparasite distribution in France, with a negative relationship between non-growing season temperature and presence of the hyperparasite. Overall, our findings, in combination with earlier evidence, suggest that climatic factors are more important than species interactions in defining the niches of cryptic species within a pathogen complex on oak.

Effects of group size (local conspecific density) on individual performance can be substantial, yet it is unclear how these translate to larger-scale and longer-term outcomes. Effects of group size can be mediated by both top-down and bottom-up interactions, can change in type or direction across the life cycle, and can depend on the spatial scale at which group size is assessed. Only by determining how these different processes combine can we make predictions about how selection operates on group size or link hierarchical patterns of density dependence with population dynamics. We manipulated the density of a leaf beetle, Leptinotarsa juncta, at three nested spatial scales (patch, plant within a patch, and leaf within plant) to investigate how conspecific density affects predator-mediated survival and resource-mediated growth during different life stages and across multiple spatial scales. We then used data from field predation experiments to assess how L. juncta densities at hierarchical scales affect different aspects of predation. Finally, we incorporated predator- and resource-mediated effects of density in a model to explore how changes in group size due to density-dependent predation might affect mass at pupation for survivors. The effects of L. juncta density on predation risk differed among scales. Per capita predation risk of both eggs and late instars was lowest at high patch-scale densities, but increased with plant-scale density. The final mass of late instars declined with increasing plant-scale larval density, potentially because of truncated development of high-density larvae. Predation incidence (i.e., group attack rate) increased with larval density at all spatial scales. A high coefficient of variation (i.e., greater aggregation) of L. juncta density was associated with lower predation incidence at some scales. Our model suggested that predator- and resource-mediated effects of density interact: lower survival at high larval density is mitigated by high final mass of larvae in the resulting smaller groups. Our results emphasize the importance of spatial scale and demonstrate that effects of top-down and bottom-up interactions are not necessarily independent. To understand how group size influences fitness, predator- and resource-mediated effects of density should be measured in their demographic and spatial context, and not in isolation.

O_LIClimate change is affecting both the abiotic environment and the seasonal timing of life history events, with potentially major consequences for plant performance and plant-associated food webs. Despite this, we lack insights into how effects of plant phenology on plant performance and food webs depend on environmental conditions, and to what extent effects of phenology and the environment on plant performance are direct vs. mediated by changes in the plant-associated community. C_LIO_LIWe conducted a multifactorial field experiment to test for the effect of spring phenology and shade on Quercus robur seedling traits and performance, as well as attacks by specialist plant pathogens, insects and small mammals. C_LIO_LISpring phenology strongly affected seedling performance whereas shade only affected leaf thickness and chlorophyll. Likewise, spring phenology strongly affected herbivore and pathogen attack, whereas shade and its interaction with spring phenology only explained a minor part of the variation. Small mammals preferentially attacked later phenology seedlings, which strongly affected plant survival, while insect herbivores and pathogens did not mediate the effect of spring phenology and shade on plant performance. C_LIO_LISynthesis: This study highlights that the effect of spring phenology outweighs the effect of environmental context on plant performance and plant attack during the growing season. Interestingly, small mammal herbivores, and not diseases and insect herbivores, may play a key role in mediating the effect of spring phenology on plant performance. Together, these findings advance our understanding of the consequences of climate-induced changes in spring phenology and the abiotic environment on plant performance within a community context. C_LI

Summary 1.Disturbances are widespread in nature and can have substantial population-level consequences. Most empirical studies on the effects of disturbance track population recovery within habitat patches, but have an incomplete representation of the recolonization process. Additionally, recent metapopulation models represent post-disturbance colonization with a recovery state or time-lag for disturbed (“focal”) patches, thus assuming that recolonization rates are uniform. 2.However, the availability of colonists in neighboring “source” patches can vary, especially in frequently-disturbed landscapes such as fire-managed forests that have a mosaic of patches that differ in successional state and undergo frequent local extinctions. To determine how time since disturbance in both focal and neighboring source patches might affect metapopulations, we studied the effects of time since fire (TSF) on abundances of a specialist palmetto beetle within and between fire management units in Apalachicola National Forest, Florida. 3.We measured beetle abundances at three distances from the shared edge of paired units, with units ranging from 0-64 months since fire and the difference in time since burning for a focal-source pair ranging from 3-58 months. 4.Soon after fire, beetle abundances within management units were highest near the unit edge, but this pattern changed with increasing TSF. Between paired units, the more recently-disturbed (“focal”) unit's beetle abundance was positively related to source unit abundance, but the shape of this relationship differed based on focal unit TSF and the units’ difference in time since burning. 5.Results suggest that both focal and source habitat history can influence recolonization of recently-disturbed patches and that these effects may persist over years. Thus, when predicting metapopulation dynamics, variation in habitat characteristics should be considered not only for patches receiving colonists, but for patches supplying colonists as well. This article is protected by copyright. All rights reserved.