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14 juin 2017

Cascading effects of herbivore protective symbionts on hyperparasitoids [Ecological Entomology]

Keywords : aphid, hyperparasitoid, parasitoid, symbiont, symbiosis, trophic cascade

1. Microbial symbionts can play an important role in defending their insect hosts against natural enemies. However, researchers have little idea how the presence of such protective symbionts impacts food web interactions and species diversity.
2. This study investigated the effects of a protective symbiont (Hamiltonella defensa) in pea aphids (Acyrthosiphon pisum) on hyperparasitoids, which are a trophic level above the natural enemy target of the symbiont (primary parasitoids).(...)

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13 juin 2017

Genetic divergence of early song discrimination between two young songbird species [Nature Ecology & Evolution]

Keywords : animal behaviour, behavioural genetics, evolutionary biology, sexual selection, speciation

Juvenile songbirds express species-specific song discrimination from an early age, which focuses learning onto the songs of their parental species. However, it remains unknown whether this early song discrimination is influenced by early social experience or maternal effects or whether it is instead largely genetically determined. We manipulated early social experience by swapping young embryos between the nests of two co-occurring songbird species—pied and collared flycatchers. We show that nestlings are more active in response to playbacks of conspecific songs, even when raised by adults from the other species, thus enabling us to reject social experience as the main determinant of early song discrimination. We then crossed the two species in captivity and showed that the song responses of hybrid nestlings do not depend on social experience or maternal species, implying genetic divergence of early song discrimination. Our results provide conclusive evidence that early song discrimination has a largely genetic component, which can stabilize reproductive isolation by reducing song learning across closely related species.

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13 juin 2017

The future distribution of river fish : The complex interplay of climate and land use changes, species dispersal and movement barriers [Global Change Biology]

Keywords : barriers, climate change, edge populations, habitat shift, land use change, river Elbe, species distribution modeling, species range shift

The future distribution of river fishes will be jointly affected by climate and land use changes forcing species to move in space. However, little is known whether fish species will be able to keep pace with predicted climate and land use-driven habitat shifts, in particular in fragmented river networks. In this study, we coupled species distribution models (stepwise boosted regression trees) of 17 fish species with species-specific models of their dispersal (fish dispersal model FIDIMO) in the European River Elbe catchment. We quantified (i) the extent and direction (up- vs. downstream) of predicted habitat shifts under coupled “moderate” and “severe” climate and land use change scenarios for 2050, and (ii) the dispersal abilities of fishes to track predicted habitat shifts while explicitly considering movement barriers (e.g., weirs, dams). (...)

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13 juin 2017

Global hotspots and correlates of alien species richness across taxonomic groups [Nature Ecology & Evolution]

Keywords : biogeography, invasive species, macroecology

Human-mediated transport beyond biogeographic barriers has led to the introduction and establishment of alien species in new regions worldwide. However, we lack a global picture of established alien species richness for multiple taxonomic groups. Here, we assess global patterns and potential drivers of established alien species richness across eight taxonomic groups (amphibians, ants, birds, freshwater fishes, mammals, vascular plants, reptiles and spiders) for 186 islands and 423 mainland regions.(...)

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13 juin 2017

The relationship between species richness and ecosystem variability is shaped by the mechanism of coexistence [Ecology Letters]

Keywords : coexistence, consumer-resource dynamics, diversity-stability hypothesis, pulsed differential equation, relative nonlinearity, storage effect

Theory relating species richness to ecosystem variability typically ignores the potential for environmental variability to promote species coexistence. Failure to account for fluctuation-dependent coexistence may explain deviations from the expected negative diversity–ecosystem variability relationship, and limits our ability to predict the consequences of increases in environmental variability. We use a consumer-resource model to explore how coexistence via the temporal storage effect and relative nonlinearity affects ecosystem variability. We show that a positive, rather than negative, diversity–ecosystem variability relationship is possible when ecosystem function is sampled across a natural gradient in environmental variability and diversity. We also show how fluctuation-dependent coexistence can buffer ecosystem functioning against increasing environmental variability by promoting species richness and portfolio effects. Our work provides a general explanation for variation in observed diversity–ecosystem variability relationships and highlights the importance of conserving regional species pools to help buffer ecosystems against predicted increases in environmental variability.

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