Although food supplementation is well known to increase population density,there is still debate on the causative effects of food supplementation on reproduction,survival,and immigration.Large manipulative experiments...Although food supplementation is well known to increase population density,there is still debate on the causative effects of food supplementation on reproduction,survival,and immigration.Large manipulative experiments,which exclude any confounding effects of dispersal and predation,are essential for clarifying the debate.In this study,we investigated the effects of food supplementation on Brandt's vole population dynamics and plant community in eight large enclosures(0.48 ha each) from2010 to 2014.Food supplementation showed significant positive effects on population density due to increases in recruitment;however,it showed a complex effect on survival of voles:positive in non-breeding seasons,but negative in breeding seasons.In addition,food supplementation increased the quality of plants(as reflected by increased crude protein content),but decreased the quantity of less preferred plants in experimental enclosures.Thus,food seems to have direct positive effects on small rodents through improvement of food supply and indirect negative effects through food-induced density-dependent effects,and may have long-term effects on rodents through altering plant community composition and abundance.展开更多
Climatic warming affects plant growth and physiology,yet how warming alters chemistry in invasive plants and indirectly affects herbivorous insects remains largely unknown.Here,we explored warming-induced changes in l...Climatic warming affects plant growth and physiology,yet how warming alters chemistry in invasive plants and indirectly affects herbivorous insects remains largely unknown.Here,we explored warming-induced changes in leaf chemistry of the invasive plant Alternanthera philoxeroides and its native congener Alternanthera sessilis,and further examined how these changes affected the performance of the herbivores,Cassida piperata and Spodoptera litura.We conducted a simulated warming experiment to address its effects on 13 leaf chemical traits of A.philoxeroides and A.sessilis.We measured growth and development time of two herbivores reared on plants from warming or ambient controls.Warming significantly affected leaf chemistry composition for both the invasive and native Alternanthera.Warming decreased nitrogen concentration in A.philoxeroides and increased total flavonoid and total phenol concentration in A.sessilis.The effects of warming on nutrients(i.e.fructose,sucrose,total soluble sugar and starch)varied with individual chemicals and plant species.Weight of C.piperata pupal and S.litura larval reared on warming-treated A.sessilis significantly decreased compared with non-warmed control,and a similar pattern was observed for weight of S.litura larval feeding on warming-treated A.philoxeroides.In addition,warming-treated A.sessilis significantly prolonged larval development time of S.litura.These results indicate that warming can directly affect the leaf chemistry in both invasive plant and its native congener,but these effects vary by species.Such differences in warming-induced changes in plant chemistry could indirectly affect herbivorous insects associated with the invasive and native plants.展开更多
Motivated by an analysis of causal mechanism from economic stress to entrepreneurial withdrawals through depressed affect,we develop a two-layer generalized varying coefficient mediation model.This model captures the ...Motivated by an analysis of causal mechanism from economic stress to entrepreneurial withdrawals through depressed affect,we develop a two-layer generalized varying coefficient mediation model.This model captures the bridging effects of mediators that may vary with another variable,by treating them as smooth functions of this variable.It also allows various response types by introducing the generalized varying coefficient model in the first layer.The varying direct and indirect effects are estimated through spline expansion.The theoretical properties of the estimated direct and indirect coefficient functions including estimation biases,asymptotic distributions and so forth,are explored.Simulation studies validate the finite-sample performance of the proposed estimation method.A real data analysis based on the proposed model discovers some interesting behavioral economic phenomenon,that self-efficacy influences the deleterious impact of economic stress,both directly and indirectly through depressed affect,on business owners’withdrawal intentions.展开更多
基金supported by National Basic Research Program of China(2007CB109102)
文摘Although food supplementation is well known to increase population density,there is still debate on the causative effects of food supplementation on reproduction,survival,and immigration.Large manipulative experiments,which exclude any confounding effects of dispersal and predation,are essential for clarifying the debate.In this study,we investigated the effects of food supplementation on Brandt's vole population dynamics and plant community in eight large enclosures(0.48 ha each) from2010 to 2014.Food supplementation showed significant positive effects on population density due to increases in recruitment;however,it showed a complex effect on survival of voles:positive in non-breeding seasons,but negative in breeding seasons.In addition,food supplementation increased the quality of plants(as reflected by increased crude protein content),but decreased the quantity of less preferred plants in experimental enclosures.Thus,food seems to have direct positive effects on small rodents through improvement of food supply and indirect negative effects through food-induced density-dependent effects,and may have long-term effects on rodents through altering plant community composition and abundance.
基金supported by the National Key Research and Development Program(2017YFC1200104).
文摘Climatic warming affects plant growth and physiology,yet how warming alters chemistry in invasive plants and indirectly affects herbivorous insects remains largely unknown.Here,we explored warming-induced changes in leaf chemistry of the invasive plant Alternanthera philoxeroides and its native congener Alternanthera sessilis,and further examined how these changes affected the performance of the herbivores,Cassida piperata and Spodoptera litura.We conducted a simulated warming experiment to address its effects on 13 leaf chemical traits of A.philoxeroides and A.sessilis.We measured growth and development time of two herbivores reared on plants from warming or ambient controls.Warming significantly affected leaf chemistry composition for both the invasive and native Alternanthera.Warming decreased nitrogen concentration in A.philoxeroides and increased total flavonoid and total phenol concentration in A.sessilis.The effects of warming on nutrients(i.e.fructose,sucrose,total soluble sugar and starch)varied with individual chemicals and plant species.Weight of C.piperata pupal and S.litura larval reared on warming-treated A.sessilis significantly decreased compared with non-warmed control,and a similar pattern was observed for weight of S.litura larval feeding on warming-treated A.philoxeroides.In addition,warming-treated A.sessilis significantly prolonged larval development time of S.litura.These results indicate that warming can directly affect the leaf chemistry in both invasive plant and its native congener,but these effects vary by species.Such differences in warming-induced changes in plant chemistry could indirectly affect herbivorous insects associated with the invasive and native plants.
基金Liu’s research was supported by NNSFC 12271456,71988101the Ministry of Education Research in the Humanities and Social Sciences 22YJA910002.
文摘Motivated by an analysis of causal mechanism from economic stress to entrepreneurial withdrawals through depressed affect,we develop a two-layer generalized varying coefficient mediation model.This model captures the bridging effects of mediators that may vary with another variable,by treating them as smooth functions of this variable.It also allows various response types by introducing the generalized varying coefficient model in the first layer.The varying direct and indirect effects are estimated through spline expansion.The theoretical properties of the estimated direct and indirect coefficient functions including estimation biases,asymptotic distributions and so forth,are explored.Simulation studies validate the finite-sample performance of the proposed estimation method.A real data analysis based on the proposed model discovers some interesting behavioral economic phenomenon,that self-efficacy influences the deleterious impact of economic stress,both directly and indirectly through depressed affect,on business owners’withdrawal intentions.
