RESUMEN
Non-native earthworms found in Eastern Canada substantially affect soil properties and plant diversity, but less is known about their impacts on higher faunal species. We investigated the effects of non-native earthworms on populations of Plethodon cinereus, a common woodland salamander. We hypothesized that earthworms could adversely affect P. cinereus by consuming the forest floor, thereby decreasing soil moisture and the abundance of native preys. Conversely, earthworms could positively affect P. cinereus by providing refuge in their abandoned burrows and by being a novel prey. We installed 25 coverboards in 38 mature sugar maple (Acer saccharum) forests, 24 of which were earthworm-free. Over the next two years, we monitored earthworm and salamander populations using hot mustard extractions and visible implant elastomers, respectively. At a subset of four sites, two with and two without earthworms, we determined salamander diets in the spring (May-June), summer (July-August) and fall (September-October) seasons, using gastric lavage techniques. Forest floor depth decreased, whereas population density, body size and total prey volume of P. cinereus increased, with earthworm abundance. Earthworms, which are soft-bodied and nutritious prey, composed most of the salamander diet at sites with earthworms, volumetrically accounting for > 50% of total prey volume. Despite this, we found fewer prey items in the stomach of salamanders at earthworm-invaded sites, indicating that salamanders are getting a higher caloric intake per feeding while expending less energy. We conclude that non-native earthworms have a net beneficial effect on P. cinereus populations in Eastern Canada, mainly by improving diet quality. Supplementary Information: The online version contains supplementary material available at 10.1007/s10530-023-03168-3.
RESUMEN
1. Phenotypic plasticity, the response of individual phenotypes to their environment, can allow organisms to cope with spatio-temporal variation in environmental conditions. Recent studies have shown that variation exists among individuals in their capacity to adjust their traits to environmental changes and that this individual plasticity can be under strong selection. Yet, little is known on the extent and ultimate causes of variation between populations and individuals in plasticity patterns. 2. In passerines, timing of breeding is a key life-history trait strongly related to fitness and is known to vary with the environment, but few studies have investigated the within-species variation in individual plasticity. 3. Here, we studied between- and within-population variation in breeding time, phenotypic plasticity and selection patterns for this trait in four Mediterranean populations of blue tits (Cyanistes caeruleus) breeding in habitats varying in structure and quality. 4. Although there was no significant warming over the course of the study, we found evidence for earlier onset of breeding in warmer years in all populations, with reduced plasticity in the less predictable environment. In two of four populations, there was significant inter-individual variation in plasticity for laying date. Interestingly, selection for earlier laying date was significant only in populations where there was no inter-individual differences in plasticity. 5. Our results show that generalization of plasticity patterns among populations of the same species might be challenging even at a small spatial scale and that the amount of within-individual variation in phenotypic plasticity may be linked to selective pressures acting on these phenotypic traits.
Asunto(s)
Passeriformes/genética , Passeriformes/fisiología , Animales , Tamaño de la Nidada , Demografía , Femenino , Masculino , Modelos Biológicos , Oviposición , Selección Genética , Factores de Tiempo , Árboles/clasificaciónRESUMEN
The regulation of reproductive schedules is an important determinant of avian breeding success. In heterogeneous environments, the optimal breeding period may fluctuate temporally across habitats, often on a spatial scale much shorter than the average dispersal range of individuals. The synchronisation of reproductive events with the most favourable period at a given site therefore involves the integration of a suite of fine-scale environmental signals which contain information about future breeding conditions. In this study, we monitored clutch initiation date of blue tits (Cyanistes caeruleus) breeding in a wide range of environmental conditions (altitude, temperature regimes, habitat type) in Corsica (France) to understand the role of spring temperature and leafing phenology on the precise fine-tuning of egg laying on a local scale. Timing of breeding in blue tits was strongly correlated with phenology of the dominant vegetation (r(2) = 0.87). In contrast, spring temperature was not as robust a predictor of the timing of breeding, because a large part of the residual variation in egg-laying date was accounted by differences (ca. 2 weeks) in the development of the vegetation between habitat types (evergreen vs. deciduous oak forests). Female blue tits therefore appear to use the environmental variable (vegetation phenology) that is most closely linked to the future production of insect prey in order to accurately time laying over the entire spatio-temporal breeding landscape.