The allocation between egg size and clutch size depends on local nest survival rate in a mean of bet-hedging in a shorebird

Background:The allocation of resources between offspring size and number is a central question of life-history theory.Although several studies have tested the existence of this trade-off,few studies have investigated how environmental variation influences the allocation of resources to offspring size and offspring number.Additionally,the relationship between population dynamics and the offspring size and number allocation is far less understood.Methods:We investigate whether resource allocation between egg size and clutch size is influenced by the ambient temperature and whether it may be related to apparent nest survival rate.We measured 1548 eggs from 541 nests of two closely related shorebird species,the Kentish Plover(Charadrius alexandrinus)and the White-faced Plover(C.dealbatus)in China,in four populations that exhibit contrasting ambient environments.We weighed females,monitored nest survival,and calculated the variance of ambient temperature.Results:Although we found that egg size and clutch size were all different between the four breeding populations,the reproductive investment(i.e.total clutch volume)was similar between populations.We also found that populations with a high survival rate had relatively larger eggs and a smaller clutch than populations with a low nest survival rate.The latter result is in line with a conservative/diversified bet-hedging strategy.Conclusions:Our findings suggest that plovers may increasing fitness by investing fewer,larger or many,small according local nest survival rate to make a similar investment in reproduction,and thereby may have an impact on population demography.

Long-term temporal patterns in flight activities of a migrant diurnal butterfly

Recent studies demonstrated that the Painted Lady(Vanessa cardui),a cosmopolitan diurnal butterfly performs long-range migration between subtropical Africa and north-western Europe,covered by individuals belonging to up to six generations.Here we analyze temporal patterns of complete annual migratory activity of the Painted Lady in Hungary,located in its Central European migratory route,almost completely unstudied before.To do so,we used field occurrence data collected between 2000 and 2019 and estimated temporal patterns in migratory activity by fitting kernel density functions on the daily mean number of individuals and observation frequency.The temporal distributions of kernel density estimates were analyzed as a function of time and key climatic predictors of the study area.We found that(i)the timing of spring arrivals has been advancing;(ii)the relative intensity of the first and last migratory peaks of the Painted Lady significantly increased during the past decades;and(iii)intensity of the last migratory peak is related to the mean temperature of the previous month,inferring that the migration is shifting to earlier dates and their volume of the migration has substantially intensified,evoking mutually nonexclusive,competing hypotheses.Our study indicates the strengthening migration activities of a southerly distributed,long-distance migrant diurnal butterfly,most probably linked to the northward shift of wintering areas induced by warming trends of the southern parts of Europe.However,the complexity of the likely processes leading to changing migratory strategies calls up for further research in both breeding and wintering areas.