2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights fro... more 2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model. Ecosphere 8(4): Abstract. The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost-and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling.
Ecosystem responses to changes in species diversity are often studied individually. However, chan... more Ecosystem responses to changes in species diversity are often studied individually. However, changes in species diversity can simultaneously influence multiple interdependent ecosystem functions. Therefore, an important challenge is to determine when and how changes in species diversity that influence one function will also drive changes in other functions. By providing the underlying structure of species interactions, ecological networks can quantify connections between biodiversity and multiple ecosystem functions. Here, we review parallels in the conceptual development of biodiversity–ecosystem functioning (BEF) and food web theory (FWT) research. Subsequently, we evaluate three common principles that unite these two research areas by explaining the patterns, concentrations, and direction of the flux of nutrients and energy through the species in diverse interaction webs. We give examples of combined BEF–FWT approaches that can be used to identify vulnerable species and habitats and to evaluate links that drive trade-offs between multiple ecosystems functions. These combined approaches reflect promising trends towards better management of biodiversity in landscapes that provide essential ecosystem services supporting human well-being
Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient u... more Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient uptake, plant productivity and by influencing plant diversity. The importance of soil biota for the sustainability of ecosystems is still unresolved. Moreover, it is unclear how multiple ecosystem functions are simultaneously affected by changes in soil biodiversity and community composition. We manipulated soil biodiversity in outdoor lysimeters filled with 230 kg soil and planted with an agricultural crop rotation. In addition to this we manipulated soil biodiversity and soil community composition in microcososm with experimental grassland. Subsequently we tested how changes in soil biodiversity and soil community composition influenced a number of ecosystem functions including nutrient leaching losses, greenhouse gas (N2O) production, plant productivity, nutrient uptake and plant diversity. Results/Conclusions Here we show that soil organisms and soil biodiversity can enhance the susta...
Background/Question/Methods Soil microbes, although for the most part unseen, represent the large... more Background/Question/Methods Soil microbes, although for the most part unseen, represent the largest portion of life on this planet and are crucial for the functioning of terrestrial ecosystems. But, soil community composition is dependent on soil history and may consequently alter the sensitivity of soil communities to biodiversity loss. Increased biodiversity supports ecosystem functioning as different organisms perform dissimilarly when abiotic conditions fluctuate over space and time. However, the ability of diverse soil communities to maintain multiple ecosystem functions in the face of a changing climate is not well known. We focused on understanding the link between soil community composition and diversity as a mechanism for stabilizing multiple ecosystem functions. To do this, soil was collected from three sites with varying soil histories. Within each we created a soil community diversity gradient based on species body size. Multiple ecosystem functions were traced over a on...
ABSTRACT Interactions between plant and soil communities are known to play an integral role in sh... more ABSTRACT Interactions between plant and soil communities are known to play an integral role in shaping ecosystems. Plants influence the composition of soil communities and soil communities in turn influence plant performance. Such a plant–soil feedback may incur selection pressure on plants and the associating soil community. However, the evolutionary consequences of these above-belowground feedback interactions remain largely speculative. Here we assess whether plant–soil feedback effects differ between intraspecific plant populations and between generations within the same plant population. We used two populations of Trifolium pratense and assessed their performance when grown in association with their home versus away soil biota. Both populations were colonized by distinct microbial communities and performed better with their own home soil communities than with the soil community from the other intraspecific population, demonstrating intraspecific positive feedback effects of home soil. In one of the two populations, we found that plant performance and the root associated microbiota community differed between parental and progeny plants when inoculated with their own home soil. Differences in root associated community characteristics could explain more than 80% of the variation in performance among the progeny and parental plants. Our results highlight that intraspecific differences in both plant and associated soil communities shape plant–soil feedback effects, and consequently indicate that plant–soil feedback can influence the direction of selection between intraspecific plant populations.
Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessi... more Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessive number of nodules due to genetic lesions in the HAR1 autoregulatory receptor kinase gene. In order to expand the repertoire of mutants available for the genetic dissection of the root nodule symbiosis (RNS), a screen for suppressors of the L. japonicus har1-1 hypernodulation phenotype was performed. Of 150,000 M2 plants analyzed, 61 stable L. japonicus double-mutant lines were isolated. In the context of the har1-1 mutation, 26 mutant lines were unable to form RNS, whereas the remaining 35 mutant lines carried more subtle symbiotic phenotypes, either forming white ineffective nodules or showing reduced nodulation capacity. When challenged with Glomus intraradices, 18 of the 61 suppressor lines were unable to establish a symbiosis with this arbuscular mycorrhiza fungus. Using a combined approach of genetic mapping, targeting induced local lesions in genomics, and sequencing, all non-nodulating mutant lines were characterized and shown to represent new alleles of at least nine independent symbiotic loci. The class of mutants with reduced nodulation capacity was of particular interest because some of them may specify novel plant functions that regulate nodule development in L. japonicus. To facilitate mapping of the latter class of mutants, an introgression line, in which the har1-1 allele was introduced into a polymorphic background of L. japonicus ecotype MG20, was constructed.
ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well a... more ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well as in mycorrhiza formation are valuable resources for studying the events required for the establishment of functional symbioses. In this study, 11 mutant lines derived from a screen for genetic suppressors of har1-1 hypernodulation were assessed quantitatively for their ability to form arbuscular mycorrhizal (AM) symbiosis. The presence of extraradicalmycelia, appressoria, intraradical hyphae, arbuscules and vesicles were scored. Roots of the har1-1 parental line were heavily colonised by six weeks after inoculation with the AM fungus Glomus intraradices showing the typical Arum-type colonisation pattern. Five mutants lacked internal root colonisation with blocks either at the surface of epidermal cells or at the outer tangential wall of cortical cells. These AM-lines showed some differences in relation to the amount of extraradical hyphae, the number of appressoria, and the degree of abnormal appressorium morphology. Four mutants had internal root colonisation but at a lower level than the parental line. Two mutants showed no difference from the parental line. Results of this study provide additional genetic resources for studying the mechanism of root colonisation by AM fungi.
Current Opinion in Environmental Sustainability, 2012
ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosy... more ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend on plant biodiversity and vice versa. Soil biota govern nutrient cycling and storage, soil organic matter (SOM) formation and turnover. Agriculture manipulates plants, soils and SOM. With intensification, regulation of functions through biodiversity is replaced by regulation through agricultural measures. Fertilizers and agrochemicals exert strong effects on soil biodiversity and functioning. Resulting community shifts feed back on soil functions such as carbon and nutrient cycling and pest control. Therefore, agricultural systems with less inputs may promote self-regulating systems and higher biodiversity.
2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights fro... more 2017. Pitfall trap sampling bias depends on body mass, temperature, and trap number: insights from an individual-based model. Ecosphere 8(4): Abstract. The diversity and community composition of ground arthropods is routinely analyzed by pitfall trap sampling, which is a cost-and time-effective method to gather large numbers of replicates but also known to generate data that are biased by species-specific differences in locomotory activity. Previous studies have looked at factors that influence the sampling bias. These studies, however, were limited to one or few species and did rarely quantify how the species-specific sampling bias shapes community-level diversity metrics. In this study, we systematically quantify the species-specific and community-level sampling bias with an allometric individual-based model that simulates movement and pitfall sampling of 10 generic ground arthropod species differing in body mass. We perform multiple simulation experiments covering different scenarios of pitfall trap number, spatial trap arrangement, temperature, and population density. We show that the sampling bias decreased strongly with increasing body mass, temperature, and pitfall trap number, while population density had no effect and trap arrangement only had little effect. The average movement speed of a species in the field integrates body mass and temperature effects and could be used to derive reliable estimates of absolute species abundance. We demonstrate how unbiased relative species abundance can be derived using correction factors that need only information on species body mass. We find that community-level diversity metrics are sensitive to the particular community structure, namely the relation between body mass and relative abundance across species. Generally, pitfall trap sampling flattens the rank-abundance distribution and leads to overestimations of ground arthropod Shannon diversity. We conclude that the correction of the species-specific pitfall trap sampling bias is necessary for the reliability of conclusions drawn from ground arthropod field studies. We propose bias correction is a manageable task using either body mass to derive unbiased relative abundance or the average speed to derive reliable estimates of absolute abundance from pitfall trap sampling.
Ecosystem responses to changes in species diversity are often studied individually. However, chan... more Ecosystem responses to changes in species diversity are often studied individually. However, changes in species diversity can simultaneously influence multiple interdependent ecosystem functions. Therefore, an important challenge is to determine when and how changes in species diversity that influence one function will also drive changes in other functions. By providing the underlying structure of species interactions, ecological networks can quantify connections between biodiversity and multiple ecosystem functions. Here, we review parallels in the conceptual development of biodiversity–ecosystem functioning (BEF) and food web theory (FWT) research. Subsequently, we evaluate three common principles that unite these two research areas by explaining the patterns, concentrations, and direction of the flux of nutrients and energy through the species in diverse interaction webs. We give examples of combined BEF–FWT approaches that can be used to identify vulnerable species and habitats and to evaluate links that drive trade-offs between multiple ecosystems functions. These combined approaches reflect promising trends towards better management of biodiversity in landscapes that provide essential ecosystem services supporting human well-being
Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient u... more Background/Question/Methods Soil organisms play a key role in ecosystems by regulating nutrient uptake, plant productivity and by influencing plant diversity. The importance of soil biota for the sustainability of ecosystems is still unresolved. Moreover, it is unclear how multiple ecosystem functions are simultaneously affected by changes in soil biodiversity and community composition. We manipulated soil biodiversity in outdoor lysimeters filled with 230 kg soil and planted with an agricultural crop rotation. In addition to this we manipulated soil biodiversity and soil community composition in microcososm with experimental grassland. Subsequently we tested how changes in soil biodiversity and soil community composition influenced a number of ecosystem functions including nutrient leaching losses, greenhouse gas (N2O) production, plant productivity, nutrient uptake and plant diversity. Results/Conclusions Here we show that soil organisms and soil biodiversity can enhance the susta...
Background/Question/Methods Soil microbes, although for the most part unseen, represent the large... more Background/Question/Methods Soil microbes, although for the most part unseen, represent the largest portion of life on this planet and are crucial for the functioning of terrestrial ecosystems. But, soil community composition is dependent on soil history and may consequently alter the sensitivity of soil communities to biodiversity loss. Increased biodiversity supports ecosystem functioning as different organisms perform dissimilarly when abiotic conditions fluctuate over space and time. However, the ability of diverse soil communities to maintain multiple ecosystem functions in the face of a changing climate is not well known. We focused on understanding the link between soil community composition and diversity as a mechanism for stabilizing multiple ecosystem functions. To do this, soil was collected from three sites with varying soil histories. Within each we created a soil community diversity gradient based on species body size. Multiple ecosystem functions were traced over a on...
ABSTRACT Interactions between plant and soil communities are known to play an integral role in sh... more ABSTRACT Interactions between plant and soil communities are known to play an integral role in shaping ecosystems. Plants influence the composition of soil communities and soil communities in turn influence plant performance. Such a plant–soil feedback may incur selection pressure on plants and the associating soil community. However, the evolutionary consequences of these above-belowground feedback interactions remain largely speculative. Here we assess whether plant–soil feedback effects differ between intraspecific plant populations and between generations within the same plant population. We used two populations of Trifolium pratense and assessed their performance when grown in association with their home versus away soil biota. Both populations were colonized by distinct microbial communities and performed better with their own home soil communities than with the soil community from the other intraspecific population, demonstrating intraspecific positive feedback effects of home soil. In one of the two populations, we found that plant performance and the root associated microbiota community differed between parental and progeny plants when inoculated with their own home soil. Differences in root associated community characteristics could explain more than 80% of the variation in performance among the progeny and parental plants. Our results highlight that intraspecific differences in both plant and associated soil communities shape plant–soil feedback effects, and consequently indicate that plant–soil feedback can influence the direction of selection between intraspecific plant populations.
Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessi... more Lotus japonicus har1 mutants respond to inoculation with Mesorhizobium loti by forming an excessive number of nodules due to genetic lesions in the HAR1 autoregulatory receptor kinase gene. In order to expand the repertoire of mutants available for the genetic dissection of the root nodule symbiosis (RNS), a screen for suppressors of the L. japonicus har1-1 hypernodulation phenotype was performed. Of 150,000 M2 plants analyzed, 61 stable L. japonicus double-mutant lines were isolated. In the context of the har1-1 mutation, 26 mutant lines were unable to form RNS, whereas the remaining 35 mutant lines carried more subtle symbiotic phenotypes, either forming white ineffective nodules or showing reduced nodulation capacity. When challenged with Glomus intraradices, 18 of the 61 suppressor lines were unable to establish a symbiosis with this arbuscular mycorrhiza fungus. Using a combined approach of genetic mapping, targeting induced local lesions in genomics, and sequencing, all non-nodulating mutant lines were characterized and shown to represent new alleles of at least nine independent symbiotic loci. The class of mutants with reduced nodulation capacity was of particular interest because some of them may specify novel plant functions that regulate nodule development in L. japonicus. To facilitate mapping of the latter class of mutants, an introgression line, in which the har1-1 allele was introduced into a polymorphic background of L. japonicus ecotype MG20, was constructed.
ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well a... more ABSTRACT Mutant lines of Lotus japonicus (Regel) Larsen that show defects in nodulation as well as in mycorrhiza formation are valuable resources for studying the events required for the establishment of functional symbioses. In this study, 11 mutant lines derived from a screen for genetic suppressors of har1-1 hypernodulation were assessed quantitatively for their ability to form arbuscular mycorrhizal (AM) symbiosis. The presence of extraradicalmycelia, appressoria, intraradical hyphae, arbuscules and vesicles were scored. Roots of the har1-1 parental line were heavily colonised by six weeks after inoculation with the AM fungus Glomus intraradices showing the typical Arum-type colonisation pattern. Five mutants lacked internal root colonisation with blocks either at the surface of epidermal cells or at the outer tangential wall of cortical cells. These AM-lines showed some differences in relation to the amount of extraradical hyphae, the number of appressoria, and the degree of abnormal appressorium morphology. Four mutants had internal root colonisation but at a lower level than the parental line. Two mutants showed no difference from the parental line. Results of this study provide additional genetic resources for studying the mechanism of root colonisation by AM fungi.
Current Opinion in Environmental Sustainability, 2012
ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosy... more ABSTRACT Soil biodiversity vastly exceeds aboveground biodiversity, and is prerequisite for ecosystem stability and services. This review presents recent findings in soil biodiversity research focused on interrelations with agricultural soil management. Richness and community structure of soil biota depend on plant biodiversity and vice versa. Soil biota govern nutrient cycling and storage, soil organic matter (SOM) formation and turnover. Agriculture manipulates plants, soils and SOM. With intensification, regulation of functions through biodiversity is replaced by regulation through agricultural measures. Fertilizers and agrochemicals exert strong effects on soil biodiversity and functioning. Resulting community shifts feed back on soil functions such as carbon and nutrient cycling and pest control. Therefore, agricultural systems with less inputs may promote self-regulating systems and higher biodiversity.
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Papers by Cameron Wagg