Key elements such as nitrogen （N） and phosphorus （P） are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, ...Key elements such as nitrogen （N） and phosphorus （P） are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small-scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar-N and -P in tallgrass prairie. Grasshopper densities were 67% greater in N-fertilized plots but detected no effect to grasshopper densities from P-fertilizer. Leaf damage to the dominant grass Andropogon gerardii was 32% greater in N-fertilized plots, but no response to foliar-P was detected. Herbivore damage to a common forb, goldenrod （Solidago missouriensis）, was not strongly linked by fertilizer treatments, although there was increased leaf damage in N-fertilizer treatments when no P was applied （a significant N ~ P interaction）. Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar-N in host plants with little evidence that P-levels contribute to the spatial patterns.展开更多
Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plan...Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plant community structure,has been tested many times in artificial productivity gradients(fertilization studies),but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient,I conducted a cross-site field experi-ment in southwest michigan,USA.A each of six old fields natu-rally varying in productivity,I exposed transplanted seedlings of big bluestem(Andropogon gerardii)to a light addition(tie-back)treat-ment that increased light availability and measured their biomass after one and two growing seasons.Important Findingsseedlings responded positively to the tie-back treatment,but positive responses did not increase across the natural productivity gradient.These results suggest that although light does limit seedling establishment,the strength of light limitation does not depend on variation in productivity in natural systems.Instead,light limitation interacted with a variety of site differences to determine establishment.although the general principle that light limitation increases with productivity is well established,these results indicate that it may not always occur in natural systems.展开更多
Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosys...Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosystem function.We examined patterns of genetic diversity of a dominant grass species,Andropogon gerardii,in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments(burned every 1,2,4 or 20 years)since the 1970s.In addition,we were able to assess the relationships between genetic diversity of A.gerardii,species diversity and productivity across this range of fire frequencies.Important Findings We found no significant relationships between genetic diversity of A.gerardii at the local scale(1 m^(2) plot level)and disturbance frequency(burned 2 to 32 times over a 38-year period).However,at the site level(i.e.across all plots sampled within a site,~100 m^(2))there were differences in genotype richness and composition,as well as genomic dissimilarity among individuals of A.gerardii.Genotype richness was greatest for the site burned at an intermediate(4-year)frequency and lowest for the infrequently(20-year)burned site.In addition,genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites.Genotype composition of A.gerardii was not significantly different between the frequently burned sites(annual vs.2 year)but did differ between frequently burned and infrequently burned sites(1 and 2 year vs.4 and 20 year,etc.).Together,these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies,likely driven by alterations in environmental conditions.Frequent fire promotes the abundance of dominant grass species,reduces plant community diversity and impacts ecosystem processes such as productivity.Our study suggests that genetic diversity within dominant grass species 展开更多
文摘Key elements such as nitrogen （N） and phosphorus （P） are often limiting relative to the nutritional needs of herbivores that feed on them. While N often limits insect herbivores in natural terrestrial ecosystems, the effect of P is poorly studied in the field, even though compelling hypotheses from the ecological stoichiometry literature predict its importance. We evaluated small-scale spatial distributions of, and herbivory by, grasshoppers among neighboring plots that vary in foliar-N and -P in tallgrass prairie. Grasshopper densities were 67% greater in N-fertilized plots but detected no effect to grasshopper densities from P-fertilizer. Leaf damage to the dominant grass Andropogon gerardii was 32% greater in N-fertilized plots, but no response to foliar-P was detected. Herbivore damage to a common forb, goldenrod （Solidago missouriensis）, was not strongly linked by fertilizer treatments, although there was increased leaf damage in N-fertilizer treatments when no P was applied （a significant N ~ P interaction）. Under field conditions at local scales, we conclude that spatially heterogeneous distributions of grasshoppers are primarily affected by foliar-N in host plants with little evidence that P-levels contribute to the spatial patterns.
基金National Science Foundation[0909942]Lauff and Porter awards from the Kellogg Biological Station+2 种基金an A.L.Rogers Endowed Research Scholarship from Michigan State Universitythe NSF Long-Term Ecological Research Program at KBSMSU AgBioResearch.This is KBS contribution 1705.
文摘Aims a key idea in plant community ecology is that the identity of the limiting resource shifts from soil nutrients in low productivity sites to light in high productivity sites.This idea,and its implications for plant community structure,has been tested many times in artificial productivity gradients(fertilization studies),but whether it applies to natural productivity gradients is unclear.Methods To test whether seedling light limitation would increase across a natural productivity gradient,I conducted a cross-site field experi-ment in southwest michigan,USA.A each of six old fields natu-rally varying in productivity,I exposed transplanted seedlings of big bluestem(Andropogon gerardii)to a light addition(tie-back)treat-ment that increased light availability and measured their biomass after one and two growing seasons.Important Findingsseedlings responded positively to the tie-back treatment,but positive responses did not increase across the natural productivity gradient.These results suggest that although light does limit seedling establishment,the strength of light limitation does not depend on variation in productivity in natural systems.Instead,light limitation interacted with a variety of site differences to determine establishment.although the general principle that light limitation increases with productivity is well established,these results indicate that it may not always occur in natural systems.
基金National Science Foundation:Doctoral Dissertation Improvement Grant(NSF-DDIG),(DEB-1011371)Yale Institute for Biospheric Studies-Field Ecology Grant(YIBS)to CCC.
文摘Aims and Methods Diversity-disturbance research has focused on community diversity,but disturbance frequency could impact diversity within species as well,with important consequences for community diversity and ecosystem function.We examined patterns of genetic diversity of a dominant grass species,Andropogon gerardii,in native North American tallgrass prairie sites located in eastern Kansas that have been subjected to a gradient of fire frequency treatments(burned every 1,2,4 or 20 years)since the 1970s.In addition,we were able to assess the relationships between genetic diversity of A.gerardii,species diversity and productivity across this range of fire frequencies.Important Findings We found no significant relationships between genetic diversity of A.gerardii at the local scale(1 m^(2) plot level)and disturbance frequency(burned 2 to 32 times over a 38-year period).However,at the site level(i.e.across all plots sampled within a site,~100 m^(2))there were differences in genotype richness and composition,as well as genomic dissimilarity among individuals of A.gerardii.Genotype richness was greatest for the site burned at an intermediate(4-year)frequency and lowest for the infrequently(20-year)burned site.In addition,genotypes found in the frequently burned sites were more similar from each other than expected by random chance than those found in the infrequently burned sites.Genotype composition of A.gerardii was not significantly different between the frequently burned sites(annual vs.2 year)but did differ between frequently burned and infrequently burned sites(1 and 2 year vs.4 and 20 year,etc.).Together,these results suggest site-level ecological sorting of genotypes in intact prairie across a broad gradient of disturbance frequencies,likely driven by alterations in environmental conditions.Frequent fire promotes the abundance of dominant grass species,reduces plant community diversity and impacts ecosystem processes such as productivity.Our study suggests that genetic diversity within dominant grass species
