The role of weather and density dependence on population dynamics of Alpine-dwelling red deer

The dynamics of red deer Cervus elaphus populations has been investigated across different environmental conditions,with the notable exception of the European Alps.Although the population dynamics of mountain-dwelling ungulates is typically influenced by the interaction between winter severity and density,the increase of temperatures and the reduction of snowpack occurring on the Alps since the 1980s may be expected to alter this pattern,especially in populations dwelling at medium-low elevations.Taking advantage of a 29-year time series of spring count data,we explored the role of weather stochasticity and density dependence on growth rate and vital rates(mortality and weaning success),and the density-dependent variation in body mass in a red deer population of the Italian Alps.The interaction between increasing values of density and snow depth exerted negative and positive effects on growth and mortality rates,respectively,while weaning success was negatively affected by increasing values of density,female-biased sex ratio and snow depth.Body mass of males and females of different age classes declined as population size increased.Our data support the role of winter severity and density dependence as key components of red deer population dynamics,and provide insight into the species’ecology on the European Alps.Despite the recent decline of snowpack on the Alpine Region,the negative impacts of winter severity and population abundance on growth rrate(possibly mediated by the density-dependent decline in body mass)confirms the importance of overwinter mortality in affecting the population dynamics of Alpine-dwelling red deer.

Demographic mechanisms of disturbance and plant diversity promoting the establishment of invasive Lupinus polyphyllus

Aims Community characteristics,such as disturbances and interspecific competition that affect the availability of microsites and resources,contribute to the success or failure of the establishment of exotic plant species.In particular,these two community characteristics may have adverse effects on plant emergence and survival,which are particularly important for population establishment and there-fore it may be necessary to consider both these vital rates simul-taneously when assessing demographic mechanisms.Here,we investigated the impacts of disturbance and interspecific compe-tition on the establishment of a perennial invasive herb,Lupinus polyphyllus Lindl.Methods Over the course of 2 years,we conducted an experiment in 10 populations of this species in Finland in which we manipulated the levels of soil disturbance.We recorded community charac-teristics(i.e.the number of vascular plant species,vegetation height,and the proportions of bare ground,litter and moss),and observed the emergence and survival of L.polyphyllus individuals in study plots.Important Findings A mild disturbance(breaking the soil surface mechanically)slightly increased seedling emergence but did not affect plant survival.Instead,an intense disturbance(vegetation and litter removal)had no effect on seedling emergence,although it significantly increased the proportion of bare ground and,consequently,seedling survival.Survival was not affected by the height of the surrounding vegetation,but both seedling emergence and plant survival increased with an increasing number of plant species in the study plots.These find-ings demonstrate that single disturbance events may considerably promote the establishment of invasive herbs,although the overall effect and demographic mechanisms behind the increased establish-ment are likely to vary depending on disturbance type.Moreover,our results suggest that species diversity per se may not be a crucial mechanism for locally preventing the establishment of exotic plants.