Given the predicted expansion of cities throughout the world, understanding the effect of urbanization on bee fauna is a major issue for the conservation of bees. The aim of this study was to understand how urbanization affects wild bee assemblages along a gradient of impervious surfaces and to determine the influence of landscape composition and floral resource availability on these assemblages. We chose 12 sites with a proportion of impervious surfaces (soil covered by parking, roads, and buildings) ranging from 0.06% to 64.31% within a 500 m radius. We collected using pan trapping and estimated the landscape composition of the sites within a 500 m radius and the species richness of plant assemblages within a 200 m radius. We collected 1104 bees from 74 species. The proportion of impervious surfaces at the landscape scale had a negative effect on wild bee abundance and species richness, whereas local flower composition had no effect. Ground‐nesting bees were particularly sensitive to the urbanization gradient. This study provides new evidences of the impact of urbanization on bee assemblages and the proportion of impervious surfaces at the landscape scale emerged as a key factor that drives those assemblages.
As an extension of the classic life history theory, the recently highlighted pace-of-life syndrome hypothesis predicts the coevolution of behavioral, physiological and life-history traits. For instance, bolder and shyer individuals do not only differ in personality profiles, but also in neuro-endocrinology and breeding patterns. While theory predicts that bolder (i.e., proactive), more aggressive individuals should colonize more rapidly urbanized habitats than shyer (i.e., reactive), less aggressive individuals, it is also predicted that across generations, adaptive selection processes could favor shyer individuals that are more sensitive to novel environmental cues. Here we compared two personality traits (handling aggression, exploration score in a novel environment), one physiological trait related to stress response (breath rate) and four breeding traits (lay date, clutch size, hatching success and fledging success) in a rural and an urban study population of Mediterranean great tits Parus major. Mixed models revealed strong phenotypic divergence between forest and city in most traits explored, in particular in personality, whereby urban great tits were more reactive to stress and faster explorers compared to rural birds (yet not more aggressive). Urban birds also laid smaller broods earlier in spring compared to their rural conspecifics, and city broods resulted in lower hatching success yet interestingly fledging success was similar. Nest-box centered measures of anthropogenic (artificial light, pedestrians, and cars) perturbation and resource abundance allowed us to go beyond the classical forest/city comparison by exploring the phenotypic variation across an urbanization gradient. This revealed that high urbanization in nest-box surroundings was associated overall with earlier breeding and smaller clutches, but also with faster breath rate, although these trends showed strong annual variation. Ongoing rapid urbanization and non-random gene flow between rural and urban great tits could both contribute to the high prevalence of bold breeders in the city. Our study suggests the existence of urban and rural great tit ecotypes with different pace-of-life, but also a finer-scale divergence along the degree of urbanization within the city. Future studies are required to determine whether this phenotypic variation at different spatiotemporal scales is adaptive and whether it has a genetic basis or results from phenotypic plasticity.
Detailed studies of the mechanisms driving life history effects of food availability are of prime importance to understand the evolution of phenotypic plasticity and the capacity of organisms to produce better adapted phenotypes. Food availability may influence life history trajectories through three nonexclusive mechanisms: (i) immediate and long‐lasting effects on individual quality, and indirect delayed effects on (ii) intracohort and (iii) intercohort interactions. Using the common lizard (Zootoca vivipara), we tested whether a food deprivation during the two‐first months of life influence life history (growth, survival, reproduction) and performance traits (immunocompetence, locomotor performances) until adulthood. We investigated the underlying mechanisms and their possible interactions by manipulating jointly food availability in a birth cohort and in cohorts of older conspecifics. Food deprivation had direct immediate negative effects on growth but positive long‐lasting effects on immunocompetence. Food deprivation had also indirect delayed effects on growth, body size, early survival and reproduction mediated by an interaction between its direct effects on individual quality and its delayed effects on the intensity of intercohort social interactions combined with density dependence on body size. These results demonstrate that interactions between direct and socially mediated effects of past environments influence life history evolution in size‐structured and stage‐structured populations.
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