Wade Worthen - Academia.edu (original) (raw)

Papers by Wade Worthen

Insects

The community structure of lotic odonates (Insecta: Odonata) changes downstream, but it is diffic... more The community structure of lotic odonates (Insecta: Odonata) changes downstream, but it is difficult to untangle natural and anthropogenic causes. We surveyed larvae and adults at 15 sites along the Reedy River in Greenville Co., SC, USA, from sites in forested suburban landscapes through the urban core of the city of Greenville. We used principal component analyses and Akaike information criteria models to describe the relationships between larval and adult community descriptors (abundance, richness, and diversity) and habitat characteristics at several spatial scales, including water chemistry, sediment and detritus, aquatic and streamside vegetation, and the percent cover of landforms in the surrounding landscape. At all scales, larval abundance, richness, and diversity correlated with the amount of detritus. At a small scale, adult indices correlated with the amount of sunlight and streamside vegetation. Zygopteran community composition was nested at a large scale; richness and ...

An examination of Charles Darwin\u27s On the Origin of Species -- and how, 150 years after public... more An examination of Charles Darwin\u27s On the Origin of Species -- and how, 150 years after publication, his ideas have been applied and adapted in a host of different areas

International Journal of Odonatology, 2020

Dragonflies (Insecta: Odonata) use both aquatic and terrestrial ecosystems, and the abundance and... more Dragonflies (Insecta: Odonata) use both aquatic and terrestrial ecosystems, and the abundance and diversity of odonates should be good indicators of habitat integrity. To determine which environmental variables affect odonates, we sampled adult dragonflies three times at 12 sites in Pickens and Greenville Counties, SC, USA, in different habitats, at different spatial scales, across a landscape gradient from intact forest to urban locations. At each site, we established two 2 m × 20 m plots along the shoreline of each aquatic habitat. We sampled dragonflies in ten 2 m × 2 m subplots/plot, described the vegetation and substrate in these subplots and adjacent aquatic subplots, and measured the percent cover of different landforms within 500 m of each plot center. Using nested ANOVA and Akaike information criteria models, habitat type and correlating environmental variables (substrate type and bank vegetation) were the best predictors of community structure at all spatial scales. Streams and rivers had fewer individuals and species than lakes, and had a nested subset of species found in lake communities. Landscape elements were also important, with indices declining as barren land and grasslands increased. At the largest scale, anthropogenic changes to the landscape had mixed effects. Small habitats isolated in urban areas had a significantly depauperate, nested subset of species found in communities inhabiting larger natural areas. However, odonate abundance and diversity was highest at human-made lakes and ponds, suggesting that these anthropogenic features help maintain odonate communities.

International Journal of Odonatology, 2018

In a previous study conducted during the dry season at La Selva Biological Station, Costa Rica, m... more In a previous study conducted during the dry season at La Selva Biological Station, Costa Rica, mean perch height of libellulid dragonfly species (Odonata: Libellulidae) correlated with male body size, and interactions between species suggested a size-dependent competitive hierarchy. Here, I report on a wetseason study that examined whether seasonal changes in community composition affect these patterns. Males were captured, photographed, and marked, perch heights among individuals and species on natural and artificial perches (25, 50, and 100 cm) were compared, and the frequencies of aggressive interactions between species were analyzed. I also examined the responses of Micrathyria atra and Micrathyria mengeri males to decoys of these species placed in their territory at different heights (50 or 100 cm). Although the wet season community differed from the dry season community (Jaccard dissimilarity = 0.778), there was still a significant correlation between species perch height and body size, on both natural and artificial perches. Interspecific interactions supported the size-dependent competitive hierarchy hypothesis: smaller species that perched low avoided attacks by larger species. These patterns were confirmed in the decoy experiment. The larger M. atra, which perches at ∼ 100 cm, attacked decoys at 100 cm almost exclusively, and attacked decoys of the smaller M. mengeri more than conspecifics. In contrast, M. mengeri (which perches at 50 cm) only attacked decoys placed at 50 cm. Although community membership changed, the correlation between body size and perch height was maintained by a size-dependent competitive hierarchy in both dry and rainy seasons.

Southeastern Naturalist, 2002

Odonate larvae were collected at 127 sites in the Enoree River and nine of its tributaries in the... more Odonate larvae were collected at 127 sites in the Enoree River and nine of its tributaries in the summers of 1999 and 2000. Mean odonate abundance, species richness, and Simpson's diversity were compared across tributaries and the main channel of the Enoree River with one-way ANOVA. These indices were significantly lower in Brushy Creek, Rocky Creek, and the Upper Enoree than in the other streams (Tukey multiple comparison test, p < 0.05). These three streams also differed from the others in species composition (MANOVA p < 0.0001), as measured by changes in the relative abundances of the five most abundant species: Progomphus obscurus, Boyeria vinosa, Macromia illinoiensis, Cordulegaster maculata, and Ophiogomphus mainensis. For example, O. mainensis was nearly absent from Brushy, Rocky, and the Upper Enoree, but was a significant component of the assemblages in other streams. Cordulegaster maculata was rare in Rocky Creek but dominated the Upper Enoree where other species were less abundant. Brushy, Rocky, and the Upper Enoree are areas of either rapid residential development or known industrial contamination. The different structure of odonate assemblages in these streams may reflect the impact of these local anthropogenic effects.

Psyche: A Journal of Entomology, 2016

In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive... more In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive hierarchy creates a positive relationship between male body size and perch height. We tested for this pattern among three similar-sized species:Celithemis elisa,C. fasciata, andC. ornata.Males were caught and photographed from May to July 2015 at Ashmore Heritage Preserve, Greenville County, SC, USA, and perch heights and perch distance to open water were measured. Five indices of body size were measured with ImageJ software: abdomen length, forewing length, hindwing length, area of forewing, and area of hindwing.Celithemis fasciatawas significantly larger than the other two species for all five anatomical characters and used perches that were significantly taller and closer to open water than the other species, though these differences changed over the summer. Aggressive interactions between and within species were tallied and compared to expected distributions based on mean relative a...

Journal of insect science (Online), 2016

Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encap... more Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encapsulation, in which the mite's stylestome is clogged and the mite starves. In summer 2014, we counted the engorged and resisted mites on 2,729 adult odonates sampled by aerial net at 11 water bodies in Greenville Co. and Pickens Co., SC, and tested the hypothesis that the frequency and intensity of resistance correlates with parasite prevalence (the percentage of parasitized hosts). Resistance prevalence (the percentage of parasitized hosts that resisted at least one mite) varied significantly among host species, exceeding 60% for Argia fumipennis(Burmeister) and Celithemis fasciata Kirby but less than 20% for other species. However, neither resistance prevalence nor mean resistance intensity (mean percentage of resisted mites on resisting hosts) correlated with parasite prevalence. We described potential effects of parasitism on host development ofA. fumipennis and Pachydiplax longip...

Journal of insect science (Online), 2015

Dragonfly larvae were sampled in Little Creek, Greenville, SC. The distributions of five common s... more Dragonfly larvae were sampled in Little Creek, Greenville, SC. The distributions of five common species were described relative to sediment type, body size, and the presence of other larvae. In total, 337 quadrats (1 m by 0.5 m) were sampled by kick seine. For each quadrat, the substrate was classified as sand, sand-cobble mix, cobble, coarse, or rock, and water depth and distance from bank were measured. Larvae were identified to species, and the lengths of the body, head, and metafemur were measured. Species were distributed differently across sediment types: sanddragons, Progomphus obscurus (Rambur) (Odonata: Gomphidae), were common in sand; twin-spotted spiketails, Cordulegaster maculata Selys (Odonata: Cordulegastridae), preferred a sand-cobble mix; Maine snaketails, Ophiogomphus mainensis Packard (Odonata: Gomphidae), preferred cobble and coarse sediments; fawn darners, Boyeria vinosa (Say) (Odonata: Aeshnidae), preferred coarse sediments; and Eastern least clubtails, Stylogom...

International Journal of Odonatology, 2001

International Journal of Odonatology, 2006

Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA... more Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA. We collected individuals at five ponds throughout summer 2005, weighed them in the field, and calculated wing loading (N•m-2) and wing aspect ratios from digital photographs. We measured the perch-height preferences of these species in 'low perch' (10, 20, 30, and 40 cm) and 'high perch' (20, 40, 60 and 80 cm) experiments. Flywheel anemometers recorded wind speeds at each perch height. Species differed significantly in mean body mass, spanning nearly an order of magnitude from Perithemis tenera (67 mg) to Libellula vibrans (633 mg). There were also significant differences in wing morphology that correlated with mean mass; larger species had greater wing loadings and greater wing aspect ratios that smaller species. Species also differed significantly in their perch-height preferences in both experiments, in a manner correlating with body mass and hindwing aspect ratios. Erythemis simplicicollis and P. tenera preferred short perches, Celithemis fasciata, Pachydiplax longipennis and Plathemis lydia used perches of intermediate height, and Libellula auripennis, L. cyanea, L. incesta, L. luctuosa, and L. vibrans preferred the tallest perches. Because mean wind speed and maximum wind speed also increased with perch height, larger species may prefer taller perches to experience greater wind speed and generate more compensatory lift to offset their larger wing loadings. However, it is also possible that correlations between body mass and perch height are the result of large species competitively restricting smaller species to lower perches.

The American Biology Teacher, 2010

Several common dragonfly species perch at different heights. Using dowels as perches and simple c... more Several common dragonfly species perch at different heights. Using dowels as perches and simple chi-square tests, this pattern of resource partitioning can be described quickly and easily. Additional experiments can examine the effect of interspecific competition on perch selection, and the relationships between perching height, body size, and wing aerodynamics.

Journal of Freshwater Ecology, 2001

International Journal for Parasitology, 1998

Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight speci... more Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight species of marine fishes were analysed to examine whether nestedness is related to sample size, abundance, species richness, and prevalence of infection, and whether the use of z-scores or Monte Carlo simulations yields different results. No significant differences in the number of nested assemblages were found with the two methods, and neither sample size nor abundance, but prevalence of infection of ectoparasites was correlated with nestedness. Species richness was significantly correlated with nestedness only when fish species with fewer than three parasite species were not excluded. Differential colonisation probabilities are the most likely cause of nestedness.

International Journal of Odonatology, 2003

Communities have a nested-subset structure if the species found in species-poor assemblages are a... more Communities have a nested-subset structure if the species found in species-poor assemblages are also found in progressively more species-rich assemblages. This nested-subset structure can be caused by differential colonization rates among species, differential extinction rates among species, or nested niche space. In this study, the assemblages of larval odonates in the Enoree River of South Carolina (USA) and nine of its tributaries were found to have statistically significant nested-subset structure. In addition, the degree of nestedness in these ten streams correlated with several chemical and physical variables. Nestedness was correlated with pH, turbidity, and concentrations of silica, bicarbonate, and calcium; suggesting that differential extinction in response to environmental stress may play a role in structuring these assemblages. However, nestedness also correlated with a crude measure of habitat homogeneity. Drainages with a heterogeneous mix of substrate types (cobbles and sand) maintained different sets of species from site to site, and had the lowest nestedness scores. Drainages with exclusively sandy substrates were dominated by burrowing species at all sites, and showed the strongest nested-subset patterns. As such, nested-subset structure in these assemblages is related to both chemical and physical parameters.

International Journal of Odonatology, 2007

For eleven species of sympatric libellulids, male mean mass was positively correlated with wing a... more For eleven species of sympatric libellulids, male mean mass was positively correlated with wing aspect ratio, wing loading, and mean perch height. We tested the hypotheses that perch height selection was governed by interspecific competition or biomechanical responses to increased wind speed at higher perches. Although larger odonates might prefer higher perches to offset their increased wing loading, species' mean perch height did not correlate with changes in mean or maximum wind speeds. Rather, perch height selection is best explained by competitive interactions. Mean mass (log 10 transformed) of these species are distributed in a significantly non-random manner, consistent with community-wide character displacement. Also, observations of aggressive interactions and the response to decoys of three abundant species revealed a competitive hierarchy based on body size. Libellula luctuosa, the largest species, avoided stations with conspecific decoys but was attracted to stations with the decoys of two smaller species. L. incesta avoided stations with larger L. luctuosa decoys, but was attracted to stations with smaller Pachydiplax longipennis decoys. P. longipennis avoided stations with conspecific and L. incesta decoys. L. luctuosa was also more successful in displacing perchers (82.4%) than L. incesta (68.9%) and P. longipennis (46.6%). In pair-wise contrasts, the larger species was always more successful at displacing the smaller species. Finally, P. longipennis was attacked at significantly higher rates when it perched on high perches than when it perched at lower perches. We conclude that interspecific competition causes niche partitioning of perch height in this community.

In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive... more In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive hierarchy creates a positive relationship between male body size and perch height. We tested for this pattern among three similar-sized species: Celithemis elisa, C. fasciata, and C. ornata. Males were caught and photographed from May to July 2015 at Ashmore Heritage Preserve, Greenville County, SC, USA, and perch heights and perch distance to open water were measured. Five indices of body size were measured with ImageJ software: abdomen length, forewing length, hindwing length, area of forewing, and area of hindwing. Celithemis fasciata was significantly larger than the other two species for all five anatomical characters and used perches that were significantly taller and closer to open water than the other species, though these differences changed over the summer. Aggressive interactions between and within species were tallied and compared to expected distributions based on mean relative abundances derived from hourly abundance counts. Patterns of interspecific aggression were also consistent with a size-dependent hierarchy: the large C. fasciata was attacked less frequently, and the small C. ornata more frequently, than predicted by their relative abundances. We conclude that even small differences in body size may contribute to niche partitioning in perch selection.

Insects

The community structure of lotic odonates (Insecta: Odonata) changes downstream, but it is diffic... more The community structure of lotic odonates (Insecta: Odonata) changes downstream, but it is difficult to untangle natural and anthropogenic causes. We surveyed larvae and adults at 15 sites along the Reedy River in Greenville Co., SC, USA, from sites in forested suburban landscapes through the urban core of the city of Greenville. We used principal component analyses and Akaike information criteria models to describe the relationships between larval and adult community descriptors (abundance, richness, and diversity) and habitat characteristics at several spatial scales, including water chemistry, sediment and detritus, aquatic and streamside vegetation, and the percent cover of landforms in the surrounding landscape. At all scales, larval abundance, richness, and diversity correlated with the amount of detritus. At a small scale, adult indices correlated with the amount of sunlight and streamside vegetation. Zygopteran community composition was nested at a large scale; richness and ...

An examination of Charles Darwin\u27s On the Origin of Species -- and how, 150 years after public... more An examination of Charles Darwin\u27s On the Origin of Species -- and how, 150 years after publication, his ideas have been applied and adapted in a host of different areas

International Journal of Odonatology, 2020

Dragonflies (Insecta: Odonata) use both aquatic and terrestrial ecosystems, and the abundance and... more Dragonflies (Insecta: Odonata) use both aquatic and terrestrial ecosystems, and the abundance and diversity of odonates should be good indicators of habitat integrity. To determine which environmental variables affect odonates, we sampled adult dragonflies three times at 12 sites in Pickens and Greenville Counties, SC, USA, in different habitats, at different spatial scales, across a landscape gradient from intact forest to urban locations. At each site, we established two 2 m × 20 m plots along the shoreline of each aquatic habitat. We sampled dragonflies in ten 2 m × 2 m subplots/plot, described the vegetation and substrate in these subplots and adjacent aquatic subplots, and measured the percent cover of different landforms within 500 m of each plot center. Using nested ANOVA and Akaike information criteria models, habitat type and correlating environmental variables (substrate type and bank vegetation) were the best predictors of community structure at all spatial scales. Streams and rivers had fewer individuals and species than lakes, and had a nested subset of species found in lake communities. Landscape elements were also important, with indices declining as barren land and grasslands increased. At the largest scale, anthropogenic changes to the landscape had mixed effects. Small habitats isolated in urban areas had a significantly depauperate, nested subset of species found in communities inhabiting larger natural areas. However, odonate abundance and diversity was highest at human-made lakes and ponds, suggesting that these anthropogenic features help maintain odonate communities.

International Journal of Odonatology, 2018

In a previous study conducted during the dry season at La Selva Biological Station, Costa Rica, m... more In a previous study conducted during the dry season at La Selva Biological Station, Costa Rica, mean perch height of libellulid dragonfly species (Odonata: Libellulidae) correlated with male body size, and interactions between species suggested a size-dependent competitive hierarchy. Here, I report on a wetseason study that examined whether seasonal changes in community composition affect these patterns. Males were captured, photographed, and marked, perch heights among individuals and species on natural and artificial perches (25, 50, and 100 cm) were compared, and the frequencies of aggressive interactions between species were analyzed. I also examined the responses of Micrathyria atra and Micrathyria mengeri males to decoys of these species placed in their territory at different heights (50 or 100 cm). Although the wet season community differed from the dry season community (Jaccard dissimilarity = 0.778), there was still a significant correlation between species perch height and body size, on both natural and artificial perches. Interspecific interactions supported the size-dependent competitive hierarchy hypothesis: smaller species that perched low avoided attacks by larger species. These patterns were confirmed in the decoy experiment. The larger M. atra, which perches at ∼ 100 cm, attacked decoys at 100 cm almost exclusively, and attacked decoys of the smaller M. mengeri more than conspecifics. In contrast, M. mengeri (which perches at 50 cm) only attacked decoys placed at 50 cm. Although community membership changed, the correlation between body size and perch height was maintained by a size-dependent competitive hierarchy in both dry and rainy seasons.

Southeastern Naturalist, 2002

Odonate larvae were collected at 127 sites in the Enoree River and nine of its tributaries in the... more Odonate larvae were collected at 127 sites in the Enoree River and nine of its tributaries in the summers of 1999 and 2000. Mean odonate abundance, species richness, and Simpson's diversity were compared across tributaries and the main channel of the Enoree River with one-way ANOVA. These indices were significantly lower in Brushy Creek, Rocky Creek, and the Upper Enoree than in the other streams (Tukey multiple comparison test, p < 0.05). These three streams also differed from the others in species composition (MANOVA p < 0.0001), as measured by changes in the relative abundances of the five most abundant species: Progomphus obscurus, Boyeria vinosa, Macromia illinoiensis, Cordulegaster maculata, and Ophiogomphus mainensis. For example, O. mainensis was nearly absent from Brushy, Rocky, and the Upper Enoree, but was a significant component of the assemblages in other streams. Cordulegaster maculata was rare in Rocky Creek but dominated the Upper Enoree where other species were less abundant. Brushy, Rocky, and the Upper Enoree are areas of either rapid residential development or known industrial contamination. The different structure of odonate assemblages in these streams may reflect the impact of these local anthropogenic effects.

Psyche: A Journal of Entomology, 2016

In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive... more In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive hierarchy creates a positive relationship between male body size and perch height. We tested for this pattern among three similar-sized species:Celithemis elisa,C. fasciata, andC. ornata.Males were caught and photographed from May to July 2015 at Ashmore Heritage Preserve, Greenville County, SC, USA, and perch heights and perch distance to open water were measured. Five indices of body size were measured with ImageJ software: abdomen length, forewing length, hindwing length, area of forewing, and area of hindwing.Celithemis fasciatawas significantly larger than the other two species for all five anatomical characters and used perches that were significantly taller and closer to open water than the other species, though these differences changed over the summer. Aggressive interactions between and within species were tallied and compared to expected distributions based on mean relative a...

Journal of insect science (Online), 2016

Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encap... more Some adult odonates resist parasitism by larval water mites (Arrenurus spp.) with melanotic encapsulation, in which the mite's stylestome is clogged and the mite starves. In summer 2014, we counted the engorged and resisted mites on 2,729 adult odonates sampled by aerial net at 11 water bodies in Greenville Co. and Pickens Co., SC, and tested the hypothesis that the frequency and intensity of resistance correlates with parasite prevalence (the percentage of parasitized hosts). Resistance prevalence (the percentage of parasitized hosts that resisted at least one mite) varied significantly among host species, exceeding 60% for Argia fumipennis(Burmeister) and Celithemis fasciata Kirby but less than 20% for other species. However, neither resistance prevalence nor mean resistance intensity (mean percentage of resisted mites on resisting hosts) correlated with parasite prevalence. We described potential effects of parasitism on host development ofA. fumipennis and Pachydiplax longip...

Journal of insect science (Online), 2015

Dragonfly larvae were sampled in Little Creek, Greenville, SC. The distributions of five common s... more Dragonfly larvae were sampled in Little Creek, Greenville, SC. The distributions of five common species were described relative to sediment type, body size, and the presence of other larvae. In total, 337 quadrats (1 m by 0.5 m) were sampled by kick seine. For each quadrat, the substrate was classified as sand, sand-cobble mix, cobble, coarse, or rock, and water depth and distance from bank were measured. Larvae were identified to species, and the lengths of the body, head, and metafemur were measured. Species were distributed differently across sediment types: sanddragons, Progomphus obscurus (Rambur) (Odonata: Gomphidae), were common in sand; twin-spotted spiketails, Cordulegaster maculata Selys (Odonata: Cordulegastridae), preferred a sand-cobble mix; Maine snaketails, Ophiogomphus mainensis Packard (Odonata: Gomphidae), preferred cobble and coarse sediments; fawn darners, Boyeria vinosa (Say) (Odonata: Aeshnidae), preferred coarse sediments; and Eastern least clubtails, Stylogom...

International Journal of Odonatology, 2001

International Journal of Odonatology, 2006

Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA... more Ten common libellulid species perch along the shoreline of lakes and ponds in South Carolina, USA. We collected individuals at five ponds throughout summer 2005, weighed them in the field, and calculated wing loading (N•m-2) and wing aspect ratios from digital photographs. We measured the perch-height preferences of these species in 'low perch' (10, 20, 30, and 40 cm) and 'high perch' (20, 40, 60 and 80 cm) experiments. Flywheel anemometers recorded wind speeds at each perch height. Species differed significantly in mean body mass, spanning nearly an order of magnitude from Perithemis tenera (67 mg) to Libellula vibrans (633 mg). There were also significant differences in wing morphology that correlated with mean mass; larger species had greater wing loadings and greater wing aspect ratios that smaller species. Species also differed significantly in their perch-height preferences in both experiments, in a manner correlating with body mass and hindwing aspect ratios. Erythemis simplicicollis and P. tenera preferred short perches, Celithemis fasciata, Pachydiplax longipennis and Plathemis lydia used perches of intermediate height, and Libellula auripennis, L. cyanea, L. incesta, L. luctuosa, and L. vibrans preferred the tallest perches. Because mean wind speed and maximum wind speed also increased with perch height, larger species may prefer taller perches to experience greater wind speed and generate more compensatory lift to offset their larger wing loadings. However, it is also possible that correlations between body mass and perch height are the result of large species competitively restricting smaller species to lower perches.

The American Biology Teacher, 2010

Several common dragonfly species perch at different heights. Using dowels as perches and simple c... more Several common dragonfly species perch at different heights. Using dowels as perches and simple chi-square tests, this pattern of resource partitioning can be described quickly and easily. Additional experiments can examine the effect of interspecific competition on perch selection, and the relationships between perching height, body size, and wing aerodynamics.

Journal of Freshwater Ecology, 2001

International Journal for Parasitology, 1998

Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight speci... more Assemblages of metazoan ectoparasites of 79 species and gastrointestinal helminths of eight species of marine fishes were analysed to examine whether nestedness is related to sample size, abundance, species richness, and prevalence of infection, and whether the use of z-scores or Monte Carlo simulations yields different results. No significant differences in the number of nested assemblages were found with the two methods, and neither sample size nor abundance, but prevalence of infection of ectoparasites was correlated with nestedness. Species richness was significantly correlated with nestedness only when fish species with fewer than three parasite species were not excluded. Differential colonisation probabilities are the most likely cause of nestedness.

International Journal of Odonatology, 2003

Communities have a nested-subset structure if the species found in species-poor assemblages are a... more Communities have a nested-subset structure if the species found in species-poor assemblages are also found in progressively more species-rich assemblages. This nested-subset structure can be caused by differential colonization rates among species, differential extinction rates among species, or nested niche space. In this study, the assemblages of larval odonates in the Enoree River of South Carolina (USA) and nine of its tributaries were found to have statistically significant nested-subset structure. In addition, the degree of nestedness in these ten streams correlated with several chemical and physical variables. Nestedness was correlated with pH, turbidity, and concentrations of silica, bicarbonate, and calcium; suggesting that differential extinction in response to environmental stress may play a role in structuring these assemblages. However, nestedness also correlated with a crude measure of habitat homogeneity. Drainages with a heterogeneous mix of substrate types (cobbles and sand) maintained different sets of species from site to site, and had the lowest nestedness scores. Drainages with exclusively sandy substrates were dominated by burrowing species at all sites, and showed the strongest nested-subset patterns. As such, nested-subset structure in these assemblages is related to both chemical and physical parameters.

International Journal of Odonatology, 2007

For eleven species of sympatric libellulids, male mean mass was positively correlated with wing a... more For eleven species of sympatric libellulids, male mean mass was positively correlated with wing aspect ratio, wing loading, and mean perch height. We tested the hypotheses that perch height selection was governed by interspecific competition or biomechanical responses to increased wind speed at higher perches. Although larger odonates might prefer higher perches to offset their increased wing loading, species' mean perch height did not correlate with changes in mean or maximum wind speeds. Rather, perch height selection is best explained by competitive interactions. Mean mass (log 10 transformed) of these species are distributed in a significantly non-random manner, consistent with community-wide character displacement. Also, observations of aggressive interactions and the response to decoys of three abundant species revealed a competitive hierarchy based on body size. Libellula luctuosa, the largest species, avoided stations with conspecific decoys but was attracted to stations with the decoys of two smaller species. L. incesta avoided stations with larger L. luctuosa decoys, but was attracted to stations with smaller Pachydiplax longipennis decoys. P. longipennis avoided stations with conspecific and L. incesta decoys. L. luctuosa was also more successful in displacing perchers (82.4%) than L. incesta (68.9%) and P. longipennis (46.6%). In pair-wise contrasts, the larger species was always more successful at displacing the smaller species. Finally, P. longipennis was attacked at significantly higher rates when it perched on high perches than when it perched at lower perches. We conclude that interspecific competition causes niche partitioning of perch height in this community.

In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive... more In many communities of perching dragonflies (Odonata: Libellulidae), a size-dependent competitive hierarchy creates a positive relationship between male body size and perch height. We tested for this pattern among three similar-sized species: Celithemis elisa, C. fasciata, and C. ornata. Males were caught and photographed from May to July 2015 at Ashmore Heritage Preserve, Greenville County, SC, USA, and perch heights and perch distance to open water were measured. Five indices of body size were measured with ImageJ software: abdomen length, forewing length, hindwing length, area of forewing, and area of hindwing. Celithemis fasciata was significantly larger than the other two species for all five anatomical characters and used perches that were significantly taller and closer to open water than the other species, though these differences changed over the summer. Aggressive interactions between and within species were tallied and compared to expected distributions based on mean relative abundances derived from hourly abundance counts. Patterns of interspecific aggression were also consistent with a size-dependent hierarchy: the large C. fasciata was attacked less frequently, and the small C. ornata more frequently, than predicted by their relative abundances. We conclude that even small differences in body size may contribute to niche partitioning in perch selection.