Plant population and community ecologist. Interests in grasslands and forests, invasive species, restoration, phylogenetics. Just so long as I don't have to get my feet wet.
Locally dominant and highly productive species affect diversity through competitive interactions ... more Locally dominant and highly productive species affect diversity through competitive interactions with subordinate species. The relationship between diversity and productivity is commonly unimodal and referred to as the 'humped-back model' (HBM). The effect of local adaptation in dominant species on occurrence of the HBM is unknown, particularly among the different aspects of diversity. A reciprocal transplant experiment established across a precipitation gradient in the U.S. Great Plains was used to investigate the effect of variation among ecotypes of the dominant prairie grasses Andropogon gerardii (big bluestem) and Sorghastrum nutans (Indian grass) on expression of the HBM. The information from taxonomic, phylogenetic, and functional diversity metrics on diversity-productivity relationships was compared. The HBM was most common for taxonomic diversity (57% of tests), and when locally sourced (compared with distantly sourced) ecotypes were established in the transplant experiment, reflecting a home-site advantage (local adaptation), especially at the extreme ends of the precipitation gradient. Phylogenetic and functional trait diversity exhibited a less frequent humped-back relationship with productivity (26% and 13%, respectively). The HBM has value in providing insights into diversity-productivity relationships in grasslands restored with different ecotypes of a foundation species but is contingent on local environmental conditions and the ecotype of the dominant grass. Keywords Andropogon gerardii • ecotypic variation • grasslands • humped-back model • Sorghastrum nutans •
In 2009, a derecho occurred in southern Illinois affecting large areas of the regional forest sys... more In 2009, a derecho occurred in southern Illinois affecting large areas of the regional forest systems. Previous research reported multi-strata species compositional shifts post-derecho at LaRue Pine Hills/Otter Pond Research Natural Area (LPH/OP RNA). Here, we expand these observations to include phylogenetic and spatial relationships, including elevation as a covariate. Surveys were conducted before and after the derecho. Univariate and multivariate analyses documented diversity and compositional shifts. Spatial analyses identified distinct spatial patterns in taxonomic (TSR) and phylogenetic (PSR) species richness, and metrics of phylogenetic clustering and overdispersion (net relatedness index and nearest taxon index; NRI and NTI, respectively), in seedling, sapling, and tree communities. Decreases in tree TSR and PSR and sapling PSR, and increases in sapling NTI occurred post-derecho. Seedling diversity-elevational relationships exhibited a humped-backed relationship in all case...
Pollinator declines have been documented globally, but little information is available about nati... more Pollinator declines have been documented globally, but little information is available about native bee ecology in Midwestern U.S. agriculture. This project seeks to optimize pollinator support and weed suppression in a 3-yr crop rotation with a fallow growing season. During fallow, one of five cover crop treatments (T1: crimson, red, and ladino clover and Bob oats [Fabales: Fabaceae - Trifolium incarnatum L., Trifolium pratense L., Trifolium repens L., and Cyperales: Poaceae - Avena sativa]; T2: crimson clover and oats; T3: red clover and oats; T4: ladino clover and oats; T5: no cover crop; T6/control: winter wheat [Cyperales: Poaceae - Triticum aestivum] L.) was seeded in one-half of 25 agricultural fields, whereas wheat was left unharvested in the other half as a comparison. Treatments that provide season-long floral resources support the greatest bee diversity and abundance (T1), and treatments with red clover support declining (Hymenoptera: Apidae) Bombus species (T1 and T3). L...
Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across... more Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across the Great Plains (USA) and are widely used in restorations. We ask: Do dominant species' ecotypes influence community diversity and structure evenly across a longitudinal aridity gradient? We established reciprocal common gardens at four sites across the gradient. Ecotypes of the two dominant species were seeded along with a prairie seed mix according to a randomized complete block design. Species composition was measured after 3 and 10 years. We used linear mixed models to analyze the effect of the ecotype and year on community diversity. NMDS and PERMANOVA were applied to examine the contribution of ecotype to community structure. Results showed that ecotype significantly affected species richness and shaped taxonomic, phylogenetic, and functional diversity. Accordingly, restorations should consider ecotypic variation as a critical biological filter to community assembly in grassl...
Background Few studies have incorporated the evolutionary insights provided by analysis of phylog... more Background Few studies have incorporated the evolutionary insights provided by analysis of phylogenetic structure along with community composition to assess the effects of exotic invasion on freshwater wetlands. Here, we assess the taxonomic and phylogenetic relationships among acid seep springs to investigate the potential homogenization or resistance of communities due to invasion of an exotic grass. Results Multivariate community analyses indicated differences in community and phylogenetic composition and dispersion among acid seep springs, associated with gradients in soil moisture, canopy cover, and phylogenetic diversity. By contrast, univariate analyses showed differences in taxonomic diversity but not phylogenetic diversity among acid seep springs. Conclusions Despite exotic invasion, individual acid seep springs remained taxonomically and phylogenetically distinct from each other. Taxonomic and phylogenetic diversity metrics revealed different aspects of composition, reinfo...
AimsThe productivity–plant diversity relationship is a central subject in ecology under debate fo... more AimsThe productivity–plant diversity relationship is a central subject in ecology under debate for decades. Anthropogenic disturbances have been demonstrated to affect productivity and plant diversity. However, the impact of disturbances on the productivity–diversity relationship is poorly understood.LocationAn old‐field located at the Touch of Nature Environmental Center in Jackson County, Illinois, USA.MethodsA manipulative experiment with fertilizer (unfertilized, fertilized annually, fertilized every five years) and mowing (unmowed, mowed in spring only, mowed in spring and fall) in a successional old‐field began in 1996 to examine disturbance effects on above‐ground net primary productivity (ANPP)–plant diversity relationships. Taxonomic (species richness, T0) and phylogenetic (net relatedness index, NRI) diversity were selected as potential plant diversity metrics.ResultsA unimodal relationship of ANPP with T0 and a negative relationship between ANPP and NRI were found across ...
Amaranthus palmeri S. Watson (Palmer amaranth) is a fast-growing, dioecious, highly competitive a... more Amaranthus palmeri S. Watson (Palmer amaranth) is a fast-growing, dioecious, highly competitive agricultural weed species, which is spreading across the US Midwest. Population sex ratios are an important consideration in the management of A. palmeri populations as this species has become resistant to several herbicide sites of action, and there is need to minimize seed production by female plants. Environmental conditions, particularly stressors, may influence sex ratios, and herbicides act as major stressors and evolutionary filters in agricultural fields. Amaranthus spp. have shown a tendency for rapid evolution of herbicide resistance, with the frequency of protoporphyrinogen oxidase (PPO)-inhibitor resistance increasing across the Midwestern US. A greenhouse experiment was conducted to investigate the effect of two PPO-inhibiting herbicide treatments of either lactofen or fomesafen on four different Illinois populations (Cahokia, Collinsville, Rend Lake, and Massac). Plants rais...
Intraspecific competition is an important plant interaction that has been studied extensively abo... more Intraspecific competition is an important plant interaction that has been studied extensively aboveground, but less so belowground, due to the difficulties in accessing the root system experimentally. Recent in vivo and in situ automatic imaging advances help understand root system architecture. In this study, a portable imaging platform and a scalable transplant technique were applied to test intraspecific competition in Arabidopsis thaliana. A single green fluorescent protein labeled plant was placed in the center of a grid of different planting densities of neighboring unlabeled plants or empty spaces, into which different treatments were made to the media. The root system of the central plant showed changes in the vertical distribution with increasing neighbor density, becoming more positively kurtotic, and developing an increasing negative skew with time. Horizontal root distribution was initially asymmetric, but became more evenly circular with time, and mean direction was not...
Sudden death syndrome (SDS) caused by Fusarium virguliforme is a widespread and economically impo... more Sudden death syndrome (SDS) caused by Fusarium virguliforme is a widespread and economically important disease of soybean. SDS is typically distributed unevenly in patches across soybean fields. While certain spots in fields are highly conducive to the development of severe SDS, other areas appear to be naturally healthy or suppressive to the disease. The role of soil microbial communities and soil physical and chemical properties in SDS development was investigated in 45 soybean fields in Illinois, Iowa, and Minnesota. Soil samples were collected from symptomatic patches in fields and from adjacent areas where SDS foliar symptoms did not develop. Multiple edaphic factors were measured, and markers specific to bacteria, fungi, archaea, oomycete, and nematodes, coupled with Illumina MiSeq sequencing, were used to identify key taxa likely associated with SDS development. A total of 14,200,000 reads were mapped against the National Center for Biotechnology Information nucleotide databa...
Agricultural environments allow study of evolutionary change in plants. An example of evolution w... more Agricultural environments allow study of evolutionary change in plants. An example of evolution within agroecological systems is the selection for resistance to the herbicide glyphosate within the weed, Conyza canadensis. Changes in survivorship and reproduction associated with the development of glyphosate resistance (GR) may impact fitness and influence the frequency of occurrence of the GR trait. We hypothesized that site characteristics and history would affect the occurrence of GR C. canadensis in field margins. We surveyed GR occurrence in field margins and asked whether there were correlations between GR occurrence and location, crop rotation, GR crop trait rotation, crop type, use of tillage, and the diversity of herbicides used. In a field experiment, we hypothesized that there would be no difference in fitness between GR and glyphosate-susceptible (GS) plants. We asked whether there were differences in survivorship, phenology, reproduction, and herbivory between 2 GR and 2...
It is important to use the most appropriate plant cultivar in restoration or biofuel trials espec... more It is important to use the most appropriate plant cultivar in restoration or biofuel trials especially when plantings are likely to be invaded by undesirable species. In this study, the competitive response of two lowland and three upland cultivars of the dominant C 4 grass Panicum virgatum to three invasive species (Bromus inermis, Schedonorus phoenix, and Poa pratensis) was tested using a simple pair-wise greenhouse experiment. Response variables (height, number of leaves, tiller density, and biomass of P. virgatum) and resources (soil moisture and light intensity) were measured over a seven-month period. Performance of the different P. virgatum cultivars were differentially reduced by the three invasive species, especially the performance of the Kanlow (lowland) and Blackwell (upland) cultivars. Low soil moisture reduced the performance of P. virgatum in the presence of only one invasive (Bromus inermis) irrespective of cultivar source. Root, shoot, and total biomass depended on cultivar and did not show an interaction with invasive species identity. The results of this greenhouse study suggest that the P. virgatum cultivars differentially responded to the invasive species and that the cultivar used should be considered carefully in planning prairie restorations or biofuel trials in the context of likely invasive species.
Many grasslands, and in particular the tallgrass prairies of North America, are generally thought... more Many grasslands, and in particular the tallgrass prairies of North America, are generally thought to be maintained by periodic fire. Semantic disagreement among researchers, however, threatens to hamper discussion of fire as an ecological force in grassland ecosystems. Some authors emphasize that fires are disturbances (or perturbations) since these fires disrupt or alter ecosystem states, trends, and dynamics (e.g., accumulating nitrogen is volatilized, plant and animal communities change in composition). Other researchers point out that, because these fire-induced disruptions and alterations can maintain the status quo of the ecosystem (e. g., prevent it from becoming woodland), it is the lack of fire rather than fire itself that should be considered a disturbance. We argue that, since both points of view are useful, there is little to be gained by labeling loosely either fire or the lack thereof as a "disturbance" in grassland ecosystems.
It has been suggested that exotic species will colonize within forests more frequently by the con... more It has been suggested that exotic species will colonize within forests more frequently by the continual introduction of seeds through horse dung deposited along trails. Whether or not these exotic species have the ability to spread into and establish in the forest interior has been disputed. To address this, horse dung and soil samples were collected from trails during Autumn 1994 and Summer 1995 from three areas in southern Illinois, USA open to recreational horse travel. In addition, deer dung samples were collected from each of the study areas. Vegetation data were collected from each of the trail systems as well as from a trail along which horse travel was prohibited. The density of vascular plants in 0.25 m 2 quadrats placed at varying distances from the trail center to 5 m into the forest interior were recorded. Finally, dung samples were placed in situ along horse trails at one site to examine seedling germination in natural conditions. While 23 exotic species germinated from samples of horse dung placed out in a greenhouse, only one of these exotic species was also found in trail plots (Kummerowia striata). Similarly, while there were empirically more exotic species found along the trails allowing horse travel than there were on the trail lacking horse travel, the relative importance of those species was negligible along both trails. These results suggest that the emigration of exotic species via horse dung does not pose an immediate threat to the plant communities adjacent to trails in these forest systems. Nevertheless, the large number of exotic species in horse dung reflects the constant threat to any system from these species. Care must be taken, when allowing horseback use in areas, to anticipate invasion by exotic species from horse dung
Random amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity and g... more Random amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity and genetic distinctiveness of Andropogon gerardii from remnant Arkansas prairies. Six oligonucleotide primers, which generated 37 RAPD bands, were used to analyse 30–32 plants from six Grand Prairie populations, Baker Prairie (Arkansas Ozarks), two Illinois prairies and two cultivars. Genetic diversity of the Arkansas remnants ranged from 82.7 to 99.3%, with 89% of the total genetic variation within and 11% among populations. The partitioning of genetic variation was consistent with that reported for other outcrossing perennial grasses, using the more conservative allozyme markers. Principal component analysis indicated a northern and southern association within Arkansas’ Grand Prairie. Although there was no genetic structuring at the landscape level, the Illinois prairies and cultivars were different from all Arkansas prairies tested. There was significant within‐population structuring in f...
The germinable soil seed bank is described from a coastal barrier island off the northwest coast ... more The germinable soil seed bank is described from a coastal barrier island off the northwest coast of Florida, USA. Soil samples collected from seven vegetation types, recently deposited dredge spoil and unvegetated areas in autumn 1990 and spring 1991 were placed out in greenhouse trays. 110 taxa germinated from the samples with the largest number (41) being C 3 perennial dicots. The largest number of taxa germinated from dry (57) and wet (54) swales, the fewest (one species: Heterotheca subaxillaris) from strand. Similarity of seed bank densities to above-ground species cover was low (Jaccard's Index = 0.36), not different between vegetation types, but higher in the autumn than in the following spring. Compositional gradients in the seed bank and above-ground vegetation determined using DCA ordination were highly correlated and related to distance from mean high water, and plot elevation. At the landscape scale, the seed bank provided an equally clear delineation of vegetation types to that based upon the above-ground vegetation. The seed bank of low disturbance, late-succession vegetation types (wooded dunes, swales, marshes) was well developed (high species richness, emergent density, and percentage annual species) with the exception that the large-seeded woody species (i.e. Quercus spp.) were absent from the wooded dune seed bank. By contrast, a poorly developed and transient seed bank occurred in more frequently disturbed (extensive sand movement, salt spray), early successional dredge spoil, unvegetated areas and strand. These contrasts support a general pattern of increasing seed bank development and a persistent rather than transient seed bank with decreasing disturbance frequency, increasing time since disturbance and successional maturity.
Many ecological studies use Two-Term Local Quadrat Variance Analysis (TTLQV) and its derivatives ... more Many ecological studies use Two-Term Local Quadrat Variance Analysis (TTLQV) and its derivatives for spatial pattern analysis. Currently, rules for determining variance peak significance are arbitrary. Variance peaks found at block size 1 and at > 50 % of the transect length are the only peaks whose use is explicitly prohibited. Although the use of variance peaks found at block sizes > 10 % of the transect length have also been warned against, many researchers interpret them regardless. We show in this paper that variance peaks derived from TTLQV are subject to additional 'rules of thumb'. Through the use of randomization and permutation analyses on real and simulated data of species abundance in contiguous plots along a single transect, we show that variance peaks found at block sizes 1, 2 and 3 occur frequently by chance and thus likely do not indicate biologically meaningful patterns. The use of multiple replicate transects decreases the probability of Type II error.
Since its introduction into North America in the late 19th century, Celastrus orbiculatus (Thumb.... more Since its introduction into North America in the late 19th century, Celastrus orbiculatus (Thumb.) has become a serious ecological threat to native ecosystems. Development of a method to accurately map the occurrence of invasive plants, including C. orbiculatus, would greatly assist in their assessment and control. Using an innovative map regression model, we predicted 85% of presence and absence of C. orbiculatus within our study area. We identify environmental characteristics associated with C. orbiculatus and demonstrate the use of this information to predict occurrence of C. orbicul-atus across a broad area in Southern Illinois, USA. Presence and absence information were obtained at sample points within discrete areas of C. orbiculatus occurrence. Forest cover, elevation, slope gradient and aspect, soil pH and texture, distance to nearest road, and potential annual direct incident radiation were recorded for invaded and adjacent non-invaded areas. Presence of oak, elevation, slope gradient, soil pH, soil texture, and distance to road were significant factors associated with the presence or absence of C. orbiculatus. Probability of occurrence of C. orbiculatus was highest on gently sloping interfluves with successional forest canopy not dominated by oak, and less acidic, mesic soil. A logistic regression model was developed and extrapolated over a raster GIS data layer using map algebra to predict current invasion throughout the study area. The model correctly predicted at least 85% occurrence of C. orbiculatus. When combined with logistic regression, map algebra is a potentially powerful tool for evaluating the spatial distribution of invasive plants provided sound statistical principles are applied in extrapolating validated regression models.
Competition is a major density-dependent factor structuring plant populations and communities in ... more Competition is a major density-dependent factor structuring plant populations and communities in both natural and agricultural systems. Seedlings of the model plant species Arabidopsis thaliana cv. Columbia, and the Columbia-derived stomatal mutants sdd1 and tmm1, were grown under controlled conditions at increasing densities of 1, 10, 20, and 50 plants per pot. We demonstrate significant effects of time (days after planting), density, genotype, density and genotype, and the three-way interaction with time upon several fitness components (plant height, silique number, leaf biomass and flowering stalk biomass) in Columbia and these mutants.
Locally dominant and highly productive species affect diversity through competitive interactions ... more Locally dominant and highly productive species affect diversity through competitive interactions with subordinate species. The relationship between diversity and productivity is commonly unimodal and referred to as the 'humped-back model' (HBM). The effect of local adaptation in dominant species on occurrence of the HBM is unknown, particularly among the different aspects of diversity. A reciprocal transplant experiment established across a precipitation gradient in the U.S. Great Plains was used to investigate the effect of variation among ecotypes of the dominant prairie grasses Andropogon gerardii (big bluestem) and Sorghastrum nutans (Indian grass) on expression of the HBM. The information from taxonomic, phylogenetic, and functional diversity metrics on diversity-productivity relationships was compared. The HBM was most common for taxonomic diversity (57% of tests), and when locally sourced (compared with distantly sourced) ecotypes were established in the transplant experiment, reflecting a home-site advantage (local adaptation), especially at the extreme ends of the precipitation gradient. Phylogenetic and functional trait diversity exhibited a less frequent humped-back relationship with productivity (26% and 13%, respectively). The HBM has value in providing insights into diversity-productivity relationships in grasslands restored with different ecotypes of a foundation species but is contingent on local environmental conditions and the ecotype of the dominant grass. Keywords Andropogon gerardii • ecotypic variation • grasslands • humped-back model • Sorghastrum nutans •
In 2009, a derecho occurred in southern Illinois affecting large areas of the regional forest sys... more In 2009, a derecho occurred in southern Illinois affecting large areas of the regional forest systems. Previous research reported multi-strata species compositional shifts post-derecho at LaRue Pine Hills/Otter Pond Research Natural Area (LPH/OP RNA). Here, we expand these observations to include phylogenetic and spatial relationships, including elevation as a covariate. Surveys were conducted before and after the derecho. Univariate and multivariate analyses documented diversity and compositional shifts. Spatial analyses identified distinct spatial patterns in taxonomic (TSR) and phylogenetic (PSR) species richness, and metrics of phylogenetic clustering and overdispersion (net relatedness index and nearest taxon index; NRI and NTI, respectively), in seedling, sapling, and tree communities. Decreases in tree TSR and PSR and sapling PSR, and increases in sapling NTI occurred post-derecho. Seedling diversity-elevational relationships exhibited a humped-backed relationship in all case...
Pollinator declines have been documented globally, but little information is available about nati... more Pollinator declines have been documented globally, but little information is available about native bee ecology in Midwestern U.S. agriculture. This project seeks to optimize pollinator support and weed suppression in a 3-yr crop rotation with a fallow growing season. During fallow, one of five cover crop treatments (T1: crimson, red, and ladino clover and Bob oats [Fabales: Fabaceae - Trifolium incarnatum L., Trifolium pratense L., Trifolium repens L., and Cyperales: Poaceae - Avena sativa]; T2: crimson clover and oats; T3: red clover and oats; T4: ladino clover and oats; T5: no cover crop; T6/control: winter wheat [Cyperales: Poaceae - Triticum aestivum] L.) was seeded in one-half of 25 agricultural fields, whereas wheat was left unharvested in the other half as a comparison. Treatments that provide season-long floral resources support the greatest bee diversity and abundance (T1), and treatments with red clover support declining (Hymenoptera: Apidae) Bombus species (T1 and T3). L...
Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across... more Two dominant species, Andropogon gerardii and Sorghastrum nutans, have a wide distribution across the Great Plains (USA) and are widely used in restorations. We ask: Do dominant species' ecotypes influence community diversity and structure evenly across a longitudinal aridity gradient? We established reciprocal common gardens at four sites across the gradient. Ecotypes of the two dominant species were seeded along with a prairie seed mix according to a randomized complete block design. Species composition was measured after 3 and 10 years. We used linear mixed models to analyze the effect of the ecotype and year on community diversity. NMDS and PERMANOVA were applied to examine the contribution of ecotype to community structure. Results showed that ecotype significantly affected species richness and shaped taxonomic, phylogenetic, and functional diversity. Accordingly, restorations should consider ecotypic variation as a critical biological filter to community assembly in grassl...
Background Few studies have incorporated the evolutionary insights provided by analysis of phylog... more Background Few studies have incorporated the evolutionary insights provided by analysis of phylogenetic structure along with community composition to assess the effects of exotic invasion on freshwater wetlands. Here, we assess the taxonomic and phylogenetic relationships among acid seep springs to investigate the potential homogenization or resistance of communities due to invasion of an exotic grass. Results Multivariate community analyses indicated differences in community and phylogenetic composition and dispersion among acid seep springs, associated with gradients in soil moisture, canopy cover, and phylogenetic diversity. By contrast, univariate analyses showed differences in taxonomic diversity but not phylogenetic diversity among acid seep springs. Conclusions Despite exotic invasion, individual acid seep springs remained taxonomically and phylogenetically distinct from each other. Taxonomic and phylogenetic diversity metrics revealed different aspects of composition, reinfo...
AimsThe productivity–plant diversity relationship is a central subject in ecology under debate fo... more AimsThe productivity–plant diversity relationship is a central subject in ecology under debate for decades. Anthropogenic disturbances have been demonstrated to affect productivity and plant diversity. However, the impact of disturbances on the productivity–diversity relationship is poorly understood.LocationAn old‐field located at the Touch of Nature Environmental Center in Jackson County, Illinois, USA.MethodsA manipulative experiment with fertilizer (unfertilized, fertilized annually, fertilized every five years) and mowing (unmowed, mowed in spring only, mowed in spring and fall) in a successional old‐field began in 1996 to examine disturbance effects on above‐ground net primary productivity (ANPP)–plant diversity relationships. Taxonomic (species richness, T0) and phylogenetic (net relatedness index, NRI) diversity were selected as potential plant diversity metrics.ResultsA unimodal relationship of ANPP with T0 and a negative relationship between ANPP and NRI were found across ...
Amaranthus palmeri S. Watson (Palmer amaranth) is a fast-growing, dioecious, highly competitive a... more Amaranthus palmeri S. Watson (Palmer amaranth) is a fast-growing, dioecious, highly competitive agricultural weed species, which is spreading across the US Midwest. Population sex ratios are an important consideration in the management of A. palmeri populations as this species has become resistant to several herbicide sites of action, and there is need to minimize seed production by female plants. Environmental conditions, particularly stressors, may influence sex ratios, and herbicides act as major stressors and evolutionary filters in agricultural fields. Amaranthus spp. have shown a tendency for rapid evolution of herbicide resistance, with the frequency of protoporphyrinogen oxidase (PPO)-inhibitor resistance increasing across the Midwestern US. A greenhouse experiment was conducted to investigate the effect of two PPO-inhibiting herbicide treatments of either lactofen or fomesafen on four different Illinois populations (Cahokia, Collinsville, Rend Lake, and Massac). Plants rais...
Intraspecific competition is an important plant interaction that has been studied extensively abo... more Intraspecific competition is an important plant interaction that has been studied extensively aboveground, but less so belowground, due to the difficulties in accessing the root system experimentally. Recent in vivo and in situ automatic imaging advances help understand root system architecture. In this study, a portable imaging platform and a scalable transplant technique were applied to test intraspecific competition in Arabidopsis thaliana. A single green fluorescent protein labeled plant was placed in the center of a grid of different planting densities of neighboring unlabeled plants or empty spaces, into which different treatments were made to the media. The root system of the central plant showed changes in the vertical distribution with increasing neighbor density, becoming more positively kurtotic, and developing an increasing negative skew with time. Horizontal root distribution was initially asymmetric, but became more evenly circular with time, and mean direction was not...
Sudden death syndrome (SDS) caused by Fusarium virguliforme is a widespread and economically impo... more Sudden death syndrome (SDS) caused by Fusarium virguliforme is a widespread and economically important disease of soybean. SDS is typically distributed unevenly in patches across soybean fields. While certain spots in fields are highly conducive to the development of severe SDS, other areas appear to be naturally healthy or suppressive to the disease. The role of soil microbial communities and soil physical and chemical properties in SDS development was investigated in 45 soybean fields in Illinois, Iowa, and Minnesota. Soil samples were collected from symptomatic patches in fields and from adjacent areas where SDS foliar symptoms did not develop. Multiple edaphic factors were measured, and markers specific to bacteria, fungi, archaea, oomycete, and nematodes, coupled with Illumina MiSeq sequencing, were used to identify key taxa likely associated with SDS development. A total of 14,200,000 reads were mapped against the National Center for Biotechnology Information nucleotide databa...
Agricultural environments allow study of evolutionary change in plants. An example of evolution w... more Agricultural environments allow study of evolutionary change in plants. An example of evolution within agroecological systems is the selection for resistance to the herbicide glyphosate within the weed, Conyza canadensis. Changes in survivorship and reproduction associated with the development of glyphosate resistance (GR) may impact fitness and influence the frequency of occurrence of the GR trait. We hypothesized that site characteristics and history would affect the occurrence of GR C. canadensis in field margins. We surveyed GR occurrence in field margins and asked whether there were correlations between GR occurrence and location, crop rotation, GR crop trait rotation, crop type, use of tillage, and the diversity of herbicides used. In a field experiment, we hypothesized that there would be no difference in fitness between GR and glyphosate-susceptible (GS) plants. We asked whether there were differences in survivorship, phenology, reproduction, and herbivory between 2 GR and 2...
It is important to use the most appropriate plant cultivar in restoration or biofuel trials espec... more It is important to use the most appropriate plant cultivar in restoration or biofuel trials especially when plantings are likely to be invaded by undesirable species. In this study, the competitive response of two lowland and three upland cultivars of the dominant C 4 grass Panicum virgatum to three invasive species (Bromus inermis, Schedonorus phoenix, and Poa pratensis) was tested using a simple pair-wise greenhouse experiment. Response variables (height, number of leaves, tiller density, and biomass of P. virgatum) and resources (soil moisture and light intensity) were measured over a seven-month period. Performance of the different P. virgatum cultivars were differentially reduced by the three invasive species, especially the performance of the Kanlow (lowland) and Blackwell (upland) cultivars. Low soil moisture reduced the performance of P. virgatum in the presence of only one invasive (Bromus inermis) irrespective of cultivar source. Root, shoot, and total biomass depended on cultivar and did not show an interaction with invasive species identity. The results of this greenhouse study suggest that the P. virgatum cultivars differentially responded to the invasive species and that the cultivar used should be considered carefully in planning prairie restorations or biofuel trials in the context of likely invasive species.
Many grasslands, and in particular the tallgrass prairies of North America, are generally thought... more Many grasslands, and in particular the tallgrass prairies of North America, are generally thought to be maintained by periodic fire. Semantic disagreement among researchers, however, threatens to hamper discussion of fire as an ecological force in grassland ecosystems. Some authors emphasize that fires are disturbances (or perturbations) since these fires disrupt or alter ecosystem states, trends, and dynamics (e.g., accumulating nitrogen is volatilized, plant and animal communities change in composition). Other researchers point out that, because these fire-induced disruptions and alterations can maintain the status quo of the ecosystem (e. g., prevent it from becoming woodland), it is the lack of fire rather than fire itself that should be considered a disturbance. We argue that, since both points of view are useful, there is little to be gained by labeling loosely either fire or the lack thereof as a "disturbance" in grassland ecosystems.
It has been suggested that exotic species will colonize within forests more frequently by the con... more It has been suggested that exotic species will colonize within forests more frequently by the continual introduction of seeds through horse dung deposited along trails. Whether or not these exotic species have the ability to spread into and establish in the forest interior has been disputed. To address this, horse dung and soil samples were collected from trails during Autumn 1994 and Summer 1995 from three areas in southern Illinois, USA open to recreational horse travel. In addition, deer dung samples were collected from each of the study areas. Vegetation data were collected from each of the trail systems as well as from a trail along which horse travel was prohibited. The density of vascular plants in 0.25 m 2 quadrats placed at varying distances from the trail center to 5 m into the forest interior were recorded. Finally, dung samples were placed in situ along horse trails at one site to examine seedling germination in natural conditions. While 23 exotic species germinated from samples of horse dung placed out in a greenhouse, only one of these exotic species was also found in trail plots (Kummerowia striata). Similarly, while there were empirically more exotic species found along the trails allowing horse travel than there were on the trail lacking horse travel, the relative importance of those species was negligible along both trails. These results suggest that the emigration of exotic species via horse dung does not pose an immediate threat to the plant communities adjacent to trails in these forest systems. Nevertheless, the large number of exotic species in horse dung reflects the constant threat to any system from these species. Care must be taken, when allowing horseback use in areas, to anticipate invasion by exotic species from horse dung
Random amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity and g... more Random amplified polymorphic DNA (RAPD) analysis was used to characterize genetic diversity and genetic distinctiveness of Andropogon gerardii from remnant Arkansas prairies. Six oligonucleotide primers, which generated 37 RAPD bands, were used to analyse 30–32 plants from six Grand Prairie populations, Baker Prairie (Arkansas Ozarks), two Illinois prairies and two cultivars. Genetic diversity of the Arkansas remnants ranged from 82.7 to 99.3%, with 89% of the total genetic variation within and 11% among populations. The partitioning of genetic variation was consistent with that reported for other outcrossing perennial grasses, using the more conservative allozyme markers. Principal component analysis indicated a northern and southern association within Arkansas’ Grand Prairie. Although there was no genetic structuring at the landscape level, the Illinois prairies and cultivars were different from all Arkansas prairies tested. There was significant within‐population structuring in f...
The germinable soil seed bank is described from a coastal barrier island off the northwest coast ... more The germinable soil seed bank is described from a coastal barrier island off the northwest coast of Florida, USA. Soil samples collected from seven vegetation types, recently deposited dredge spoil and unvegetated areas in autumn 1990 and spring 1991 were placed out in greenhouse trays. 110 taxa germinated from the samples with the largest number (41) being C 3 perennial dicots. The largest number of taxa germinated from dry (57) and wet (54) swales, the fewest (one species: Heterotheca subaxillaris) from strand. Similarity of seed bank densities to above-ground species cover was low (Jaccard's Index = 0.36), not different between vegetation types, but higher in the autumn than in the following spring. Compositional gradients in the seed bank and above-ground vegetation determined using DCA ordination were highly correlated and related to distance from mean high water, and plot elevation. At the landscape scale, the seed bank provided an equally clear delineation of vegetation types to that based upon the above-ground vegetation. The seed bank of low disturbance, late-succession vegetation types (wooded dunes, swales, marshes) was well developed (high species richness, emergent density, and percentage annual species) with the exception that the large-seeded woody species (i.e. Quercus spp.) were absent from the wooded dune seed bank. By contrast, a poorly developed and transient seed bank occurred in more frequently disturbed (extensive sand movement, salt spray), early successional dredge spoil, unvegetated areas and strand. These contrasts support a general pattern of increasing seed bank development and a persistent rather than transient seed bank with decreasing disturbance frequency, increasing time since disturbance and successional maturity.
Many ecological studies use Two-Term Local Quadrat Variance Analysis (TTLQV) and its derivatives ... more Many ecological studies use Two-Term Local Quadrat Variance Analysis (TTLQV) and its derivatives for spatial pattern analysis. Currently, rules for determining variance peak significance are arbitrary. Variance peaks found at block size 1 and at > 50 % of the transect length are the only peaks whose use is explicitly prohibited. Although the use of variance peaks found at block sizes > 10 % of the transect length have also been warned against, many researchers interpret them regardless. We show in this paper that variance peaks derived from TTLQV are subject to additional 'rules of thumb'. Through the use of randomization and permutation analyses on real and simulated data of species abundance in contiguous plots along a single transect, we show that variance peaks found at block sizes 1, 2 and 3 occur frequently by chance and thus likely do not indicate biologically meaningful patterns. The use of multiple replicate transects decreases the probability of Type II error.
Since its introduction into North America in the late 19th century, Celastrus orbiculatus (Thumb.... more Since its introduction into North America in the late 19th century, Celastrus orbiculatus (Thumb.) has become a serious ecological threat to native ecosystems. Development of a method to accurately map the occurrence of invasive plants, including C. orbiculatus, would greatly assist in their assessment and control. Using an innovative map regression model, we predicted 85% of presence and absence of C. orbiculatus within our study area. We identify environmental characteristics associated with C. orbiculatus and demonstrate the use of this information to predict occurrence of C. orbicul-atus across a broad area in Southern Illinois, USA. Presence and absence information were obtained at sample points within discrete areas of C. orbiculatus occurrence. Forest cover, elevation, slope gradient and aspect, soil pH and texture, distance to nearest road, and potential annual direct incident radiation were recorded for invaded and adjacent non-invaded areas. Presence of oak, elevation, slope gradient, soil pH, soil texture, and distance to road were significant factors associated with the presence or absence of C. orbiculatus. Probability of occurrence of C. orbiculatus was highest on gently sloping interfluves with successional forest canopy not dominated by oak, and less acidic, mesic soil. A logistic regression model was developed and extrapolated over a raster GIS data layer using map algebra to predict current invasion throughout the study area. The model correctly predicted at least 85% occurrence of C. orbiculatus. When combined with logistic regression, map algebra is a potentially powerful tool for evaluating the spatial distribution of invasive plants provided sound statistical principles are applied in extrapolating validated regression models.
Competition is a major density-dependent factor structuring plant populations and communities in ... more Competition is a major density-dependent factor structuring plant populations and communities in both natural and agricultural systems. Seedlings of the model plant species Arabidopsis thaliana cv. Columbia, and the Columbia-derived stomatal mutants sdd1 and tmm1, were grown under controlled conditions at increasing densities of 1, 10, 20, and 50 plants per pot. We demonstrate significant effects of time (days after planting), density, genotype, density and genotype, and the three-way interaction with time upon several fitness components (plant height, silique number, leaf biomass and flowering stalk biomass) in Columbia and these mutants.
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Papers by David Gibson