Nesting habits shape feeding preferences and predatory behavior in an ant genus

We tested if nesting habits influence ant feeding preferences and predatory behavior in the monophyletic genus Pseudomyrmex (Pseudomyrmecinae) which comprises terrestrial and arboreal species, and, among the latter, plant-ants which are obligate inhabitants of myrmecophytes (i.e., plants sheltering so-called plant-ants in hollow structures). A cafeteria experiment revealed that the diet of ground-nesting Pseudomyrmex consists mostly of prey and that of arboreal species consists mostly of sugary substances, whereas the plant-ants discarded all the food we provided. Workers forage solitarily, detecting prey from a distance thanks to their hypertrophied eyes. Approach is followed by antennal contact, seizure, and the manipulation of the prey to sting it under its thorax (next to the ventral nerve cord). Arboreal species were not more efficient at capturing prey than were ground-nesting species. A large worker size favors prey capture. Workers from ground- and arboreal-nesting species show several uncommon behavioral traits, each known in different ant genera from different subfamilies: leaping abilities, the use of surface tension strengths to transport liquids, short-range recruitment followed by conflicts between nestmates, the consumption of the prey’s hemolymph, and the retrieval of entire prey or pieces of prey after having cut it up. Yet, we never noted group ambushing. We also confirmed that Pseudomyrmex plant-ants live in a kind of food autarky as they feed only on rewards produced by their host myrmecophyte, or on honeydew produced by the hemipterans they attend and possibly on the fungi they cultivate.     

Negative relationship between dispersal distance and demography in butterfly metapopulations

Little is known about the connection between demography and dispersal in metapopulations. The meta-analysis of the population time series of five butterfly species indicated that (meta)population dynamics are driven by density-dependent factors. Inter-specific comparison reveals a significant inverse relationship between population growth rate and the magnitude of dispersal distance. As the range of dispersal distances is constrained by the patch system, dispersing individuals moving too far away would (probably) get lost. This generates selective pressures on individuals with a high dispersal propensity, but favors individuals investing more in reproduction and results in a higher (meta)population growth rate. From a conservation perspective, individuals from (meta)populations and species sacrificing dispersal for the sake of reproductive performances are most vulnerable because of their higher sensitivity to stochastic events: the temporal variation of growth rate was much higher in the two metapopulations where dispersal was limited.     

On metapopulation resistance to drift and extinction

The spatial configuration of metapopulations (numbers, sizes, and localization of patches) affects their ability to resist demographic extinction and genetic drift, but sometimes with opposite effects. Small and isolated patches, for instance, contribute marginally to demography but may play a large role in genetics by maintaining a sizeable amount of genetic variance among demes. In source-sink systems, similarly, connectivity may be beneficial in terms of effective size, but detrimental in terms of survival, by lowering the reproductive value of source populations. How to reconcile these opposite effects? Here we propose an analytical framework that integrates fixation time (ability to resist genetic drift) and extinction time (ability to resist demographic extinction) into a single index of resistance, measuring the ability of a metapopulation to maintain its demo-genetic integrity. We then illustrate with numerical examples how conflicting demands may be resolved.     

Impact of global warming on European tidal estuaries: some evidence of northward migration of estuarine fish species

The aim of this study was to determine whether the latitudinal distribution of fish species that use estuaries to complete their entire life cycle has shifted northward as an expected consequence of global warming. The mean latitude of past fish species distributions found in 1970s’ literature was compared with the mean latitude of distributions today based on fish density indices collected in 55 tidal estuaries along the Atlantic European seaboard, from Portugal to Scotland. Among the 15 most common species, 11 displayed a positive difference between current and past mean latitudes suggesting a northward shift of the populations. Using the occurrence of subtropical species in temperate areas as an indicator of water warming, the northernmost range limit of 10 subtropical species was subsequently focused on. Six of them were recorded up to their past northern latitudinal limit. These results reinforced the idea that a number of fish species associated to estuaries have migrated northwards over the last 30 years, possibly due to water warming. These ecological changes can get important managerial implications, i.e. in the assessment of the ecological status in European directives.     

Climate Change Implications on Flood Response of a Mountainous Watershed

The modification of the flood response due to future climate change is presented for the Illecillewaet watershed of British Columbia, Canada. The Canadian Centre for Climate Modeling Analysis General Circulation Model (CGCMa1) was used for the assessment of changes of precipitation and temperature due to climate change. The runoff was simulated using the UBC watershed model and considering, also, changes on the spatial distribution of precipitation with elevation, cloud cover, glaciers, vegetation distribution, vegetation biomass production, and plant physiology. The results show that the future climate would be wetter and warmer than the present climate affecting the type, the magnitude and the temporal distribution of floods as well as the frequency of flood peaks. The above changes in the flood response of the study watershed could be explained by the change of the form of precipitation from snowfall to rainfall, the consequent decrease of the snowpack, and the initiation of the snowmelt earlier in the season, under the altered climate.