ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats... more ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats to amphibians. Fragmentation is particularly harmful because many amphibians migrate between aquatic and terrestrial habitats, and even narrow bands of unsuitable habitat can act as barriers to movement. Additionally, amphibians are slow-moving and prone to road mortality, and many species are unable to travel long distances to leave unsuitable areas. We addressed several questions, including: 1) Does the number of roads or volume of traffic more strongly affect amphibian populations?, 2) Are roads detrimental to amphibian populations when they separate wetlands from uplands (i.e., habitat split)?, and 3) Are amphibians more sensitive to landscape composition or configuration? This project was integrated into undergraduate biology curricula; students from nine U.S. colleges summarized North American Amphibian Monitoring Program (NAAMP) data in the Eastern and Central U.S. and used GIS to extract and compile landscape data for 1620 survey locations across 14 states. We built generalized linear models to test hypotheses concerning the influence of landscape variables on amphibian species richness and site occupancy by individual species. Results/Conclusions We found that models incorporating local traffic volume, development, and wetland area were the best predictors of amphibian species richness and site occupancy by individual species. For overall species richness in 10 of 11 species examined, traffic volume in the vicinity of a survey site was more closely associated with site occupancy than was road length. We found little evidence for distinct effects of habitat split by roads or development, and in general, landscape composition variables were more useful than landscape configuration variables for predicting amphibian occupancy. Our results suggest that roads, and particularly traffic, exert strong negative effects on calling amphibians across the Eastern and Central U.S., affecting even species considered disturbance-tolerant. Our project demonstrates that networks of undergraduate students can be enlisted to analyze large ecological data sets and can provide students with a meaningful research experience in large-scale ecology. We plan to continue our investigation by addressing the importance of landscape connectivity to amphibian populations using this collaborative course-based research model.
Landscape structure is important for shaping the abundance and distribution of amphibians, but pr... more Landscape structure is important for shaping the abundance and distribution of amphibians, but prior studies of landscape effects have been species or ecosystem-specific. Using a large-scale, citizen science-generated database, we examined the effects of habitat composition, road disturbance, and habitat split (i.e. the isolation of wetland from forest by intervening land use) on the distribution and richness of frogs and toads in the eastern and central United States. Undergraduates from nine biology and environmental science courses collated occupancy data and characterized landscape structure at 1617 sampling locations from the North American Amphibian Monitoring Program. Our analysis revealed that anuran species richness and individual species distributions were consistently constrained by both road density and traffic volume. In contrast, developed land around wetlands had small, or even positive effects on anuran species richness and distributions after controlling for road effects. Effects of upland habitat composition varied among species, and habitat split had only weak effects on species richness or individual species distributions. Mechanisms underlying road effects on amphibians involve direct mortality, behavioral barriers to movement, and reduction in the quality of roadside habitats. Our results suggest that the negative effects of roads on amphibians occur across broad geographic regions, affecting even common species, and they underscore the importance of developing effective strategies to mitigate the impacts of roads on amphibian populations.
ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats... more ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats to amphibians. Fragmentation is particularly harmful because many amphibians migrate between aquatic and terrestrial habitats, and even narrow bands of unsuitable habitat can act as barriers to movement. Additionally, amphibians are slow-moving and prone to road mortality, and many species are unable to travel long distances to leave unsuitable areas. We addressed several questions, including: 1) Does the number of roads or volume of traffic more strongly affect amphibian populations?, 2) Are roads detrimental to amphibian populations when they separate wetlands from uplands (i.e., habitat split)?, and 3) Are amphibians more sensitive to landscape composition or configuration? This project was integrated into undergraduate biology curricula; students from nine U.S. colleges summarized North American Amphibian Monitoring Program (NAAMP) data in the Eastern and Central U.S. and used GIS to extract and compile landscape data for 1620 survey locations across 14 states. We built generalized linear models to test hypotheses concerning the influence of landscape variables on amphibian species richness and site occupancy by individual species. Results/Conclusions We found that models incorporating local traffic volume, development, and wetland area were the best predictors of amphibian species richness and site occupancy by individual species. For overall species richness in 10 of 11 species examined, traffic volume in the vicinity of a survey site was more closely associated with site occupancy than was road length. We found little evidence for distinct effects of habitat split by roads or development, and in general, landscape composition variables were more useful than landscape configuration variables for predicting amphibian occupancy. Our results suggest that roads, and particularly traffic, exert strong negative effects on calling amphibians across the Eastern and Central U.S., affecting even species considered disturbance-tolerant. Our project demonstrates that networks of undergraduate students can be enlisted to analyze large ecological data sets and can provide students with a meaningful research experience in large-scale ecology. We plan to continue our investigation by addressing the importance of landscape connectivity to amphibian populations using this collaborative course-based research model.
Landscape structure is important for shaping the abundance and distribution of amphibians, but pr... more Landscape structure is important for shaping the abundance and distribution of amphibians, but prior studies of landscape effects have been species or ecosystem-specific. Using a large-scale, citizen science-generated database, we examined the effects of habitat composition, road disturbance, and habitat split (i.e. the isolation of wetland from forest by intervening land use) on the distribution and richness of frogs and toads in the eastern and central United States. Undergraduates from nine biology and environmental science courses collated occupancy data and characterized landscape structure at 1617 sampling locations from the North American Amphibian Monitoring Program. Our analysis revealed that anuran species richness and individual species distributions were consistently constrained by both road density and traffic volume. In contrast, developed land around wetlands had small, or even positive effects on anuran species richness and distributions after controlling for road effects. Effects of upland habitat composition varied among species, and habitat split had only weak effects on species richness or individual species distributions. Mechanisms underlying road effects on amphibians involve direct mortality, behavioral barriers to movement, and reduction in the quality of roadside habitats. Our results suggest that the negative effects of roads on amphibians occur across broad geographic regions, affecting even common species, and they underscore the importance of developing effective strategies to mitigate the impacts of roads on amphibian populations.
There is growing appreciation for the idea that plant – soil interactions (e.g. allelopathy and p... more There is growing appreciation for the idea that plant – soil interactions (e.g. allelopathy and plant – microbe feedbacks) may explain the success of some non-native plants. Where this is the case, native plant restoration may require management tools that change plant – soil interactions. Activated carbon (AC) is one such potential tool. Previous research has shown the potential for high concentrations of AC to restore native plant growth to areas dominated by non-natives on a small scale (1 m × 1 m plots). Here we (i) test the efficacy of different AC concentrations at a larger scale (15 m × 15 m plots), (ii) measure microbial responses to AC treatment and (iii) use a greenhouse experiment to identify the primary mechanism, allelopathy versus microbial changes, through which AC impacts native and non-native plant growth. Three years after large-scale applications, AC treatments decreased non-native plant cover and increased the ratio of native to non-native species cover, particularly at concentrations .400 g m 22. Activated carbon similarly decreased non-native plant growth in the greenhouse. This effect, however, was only observed in live soils, suggesting that AC effects were microbially mediated and not caused by direct allelopathy. Bacterial community analysis of field soils indicated that AC increased the relative abundance of an unidentified bacterium and an Actinomycetales and decreased the relative abundance of a Flavobacterium, suggesting that these organisms may play a role in AC effects on plant growth. Results support the idea that manipulations of plant–microbe interactions may provide novel and effective ways of directing plant growth and community development (e.g. native plant restoration).
E xisting data may offer the best insight into many important questions in ecology and conservati... more E xisting data may offer the best insight into many important questions in ecology and conservation biology, but there are various challenges to using existing data effectively. First, although the use of large data repositories is increasing, many ecological data sets are never made publicly available. In addition, ecological data sets are rarely uniform, and reformatting data sets from different sources, sites, and time periods in a consistent manner can be tedious. These difficulties may be particularly pronounced when data sets involve ecological questions over large spatial or temporal scales. In the present study, we organized networks of students in undergraduate courses to address these challenges and to investigate the geographic patterns of nonnative and invasive plants in sites in the US National Wildlife Refuge System. The students collected and compiled the data for refuges in their own region. From the data that the stu dents compiled, we asked (a) how nonnative and invasive plant species richness is related to native species richness; (b) how the pool of nonnative species from the surrounding area (i.e., colonization pressure) contributes to nonnative and invasive species richness in the refuges; (c) how refuge characteristics such as habitat diversity, refuge area, and elevational range contribute to species richness patterns for native, nonnative, and invasive plants; (d) whether inva sion patterns differ between mainland and island refuges; and (e) whether invasion patterns vary among US Fish and Wildlife Service (USFWS) regions. Below, we outline the scientific background for this project, as well as the specific rationale for each of the questions examined.
Here we test an experimental approach that produces estimates of the location, timing and extent ... more Here we test an experimental approach that produces estimates of the location, timing and extent of water uptake by individual plant species in the field. A tracer injection experiment was used to estimate the proportion of active roots across soil depths. These proportions were multiplied by species-specific estimates of evapotranspiration. This approach was repeated in early-and late-season conditions in adjacent native-and non-native-dominated shrub-steppe plant communities. Resulting estimates of water uptake by depth were compared to soil water content. Both communities contained a dominant plant that relied on shallow (i.e., 0e10) soil water, a subdominant that relied on deep-(i.e., 90 þ cm) soil water and a second subdominant that used late-season pulses of shallow water. Combining tracer uptake with evapotranspiration estimates indicated that non-natives removed nearly twice the amount of water early in the season as natives, especially from shallow depths. This was consistent with measures of soil moisture. However, modeled estimates of root water uptake were not always consistent with measurements of soil moisture. Despite the intensive sampling conducted in this study, future use of this approach will require more complete tracer sampling of the plant species present and improved estimation of evapotranspiration in sparse, diverse plant canopies.
Trophic cascades are important drivers of plant and animal abundances in aquatic and aboveground ... more Trophic cascades are important drivers of plant and animal abundances in aquatic and aboveground systems, but in soils trophic cascades have been thought to be of limited importance due to omnivory and other factors. Here we use a meta-analysis of 215 studies with 1526 experiments that measured plant growth responses to additions or removals of soil organisms to test how different soil trophic levels affect plant growth. Consistent with the trophic cascade hypothesis, we found that herbivores and plant pathogens (henceforth pests) decreased plant growth and that predators of pests increased plant growth. The magnitude of this trophic cascade was similar to that reported for aboveground systems. In contrast, we did not find evidence for trophic cascades in decomposer-and symbiont-based (henceforth mutualist) food chains. In these food chains, mutualists increased plant growth and predators of mutualists also increased plant growth, presumably by increasing nutrient cycling rates. Therefore, mutualists, predators of mutualists and predators of pests all increased plant growth. Further, experiments that added multiple organisms from different trophic levels also increased plant growth. As a result, across the dataset, soil organisms increased plant growth 29% and non-pest soil organisms increased plant growth 46%. Omnivory has traditionally been thought to confound soil trophic dynamics, but here we suggest that omnivory allows for a simplified perspective of soil food webs – one in which most soil organisms increase plant growth by preying on pests or increasing nutrient cycling rates. An implication of this perspective is that processes that decrease soil organism abundance (e.g. soil tillage) are likely to decrease aboveground productivity.
Non-native species introductions have the ability to affect both ecological and social systems, t... more Non-native species introductions have the ability to affect both ecological and social systems, thus to address those outcomes both ecological and social influences on an invasion need to be understood. We use a social–ecological systems approach to investigate connections between human and ecological factors that affect efforts to control the non-native coqui frog (Eleutherodactylus coqui) on the island of Hawaii. The coqui frog is recognized as a 'pest' and 'injurious wildlife' by the Hawaii Department of Agriculture. Because the coqui occurs on many small private properties across the island, it is necessary to enlist private citizens in control efforts. Control efforts can include direct chemical control of the coqui as well as landscape manipulations that reduce habitat quality for the frog. On 85 private properties in 12 communities across the island, we measured the relationship between coqui abundance, residents' attitudes toward the coqui, their reported participation in control activities, and environmental variables that affect habitat quality for the frog. Residents' attitudes correlated with coqui frog abundance, but in an unexpected direction: People with more frogs on their property and those who owned that property tended to have less negative attitudes toward the coqui. In addition, negative attitudes toward the coqui were not significantly related to participation in control activities. Coqui abundance was related to a habitat variable, canopy cover, which can be manipulated by residents to reduce habitat quality and discourage coqui occupancy. Tolerance for this non-native species is likely to hinder attempts to engage residents in control efforts as the species' range on the island continues to expand. If this pattern of habit-uation is manifested with other non-native species considered to have potentially negative effects on the ecological or social environment, it would be important to recognize as early as possible because managers may be most effective at engaging citizens in control efforts before habituation becomes widespread.
We describe a new treefrog species of Dendropsophus collected on rocky outcrops in the Brazilian ... more We describe a new treefrog species of Dendropsophus collected on rocky outcrops in the Brazilian Atlantic Forest. Ecologically, the new species can be distinguished from all known congeners by having a larval phase associated with rainwater accumulated in bromeliad phytotelms instead of temporary or lentic water bodies. Phylogenetic analysis based on molecular data confirms that the new species is a member of Dendropsophus; our analysis does not assign it to any recognized species group in the genus. Morphologically, based on comparison with the 96 known congeners, the new species is diagnosed by its small size, framed dorsal color pattern, and short webbing between toes IV-V. The advertisement call is composed of a moderate-pitched two-note call (~5 kHz). The territorial call contains more notes and pulses than the advertisement call. Field observations suggest that this new bro-meligenous species uses a variety of bromeliad species to breed in, and may be both territorial and exhibit male parental care.
Little is known about ecosystem-level responses to multiple, climatic disturbance events. In the ... more Little is known about ecosystem-level responses to multiple, climatic disturbance events. In the subtropical forests of Puerto Rico, the major natural disturbances are hurricanes and droughts. We tested the ecosystem-level effects of these disturbances in sites with different land use histories. From 1989 to 1992, data were collected to determine the effects of Hurricane Hugo and two droughts on litterfall inputs, fine-root biomass, and decomposition rates in three topographic locations (stream, riparian, upslope) within two watersheds. From 1994 to 1998, we added a third watershed and an experiment in which coarse-wood levels were manipulated to simulate hurricane inputs. Data were collected on tree and palm growth rates, litterfall inputs, fine-root biomass, and decomposition rates. From 1994 to 1998, four hurricanes and three droughts were recorded.
ABSTRACT Background/Question/Methods Eleutherodactylus coqui is a small tropical terrestrial frog... more ABSTRACT Background/Question/Methods Eleutherodactylus coqui is a small tropical terrestrial frog that is native to Puerto Rico and was first seen on the Hawaiian Islands in the late 1980s. Millions of dollars have been spent in recent years in an attempt to control E. coqui, but eradication is deemed no longer possible on the Island of Hawaii. Based on preliminary research suggesting a positive relationship between prey, structure, and E. coqui density in Hawaii, we hypthesized that the success of E. coqui (measured by its density) is positively related to resource availability in the form of structure and prey because structure provides the male with more calling sites, and thus more opportunity to mate with females, and prey provides E. coqui with the necessary energy to reproduce, grow, and increase in density. We designed and conducted a large-scale experiment in the Nanawale Forest Reserve in the southeast region of the Island of Hawaii for 6 months to test this relationship. Results/Conclusions E. coqui density was reduced in the 100% leaf litter removal and 100% structure removal treatment plots. E. coqui were observed at lower heights off the forest floor in the 100% structure removal plots than the control plots. Higher quantity of flying and leaf litter invertebrates were found in the 100% structure removal treatment, suggesting a reduction in predation pressure on these invertebrates due to a reduction in coqui frogs. Our results provide a better understanding of the role that specific resources play for the density of an invasive frog in Hawaii. Efforts to efficiently control E. coqui should focus on structure removal and leaf litter removal in areas with large populations of E. coqui.
The Puerto Rican frog (Eleutherodactylus coqui) is an invasive pest in Hawaii. Citric acid is app... more The Puerto Rican frog (Eleutherodactylus coqui) is an invasive pest in Hawaii. Citric acid is approved for controlling these frogs, but has been limited to terrain accessible by foot or vehicle. We determined the effectiveness of helicopter applications of 16% citric acid and repeated 11% citric acid treatments for eradicating and/or reducing densities of E. coqui by monitoring populations before and after treatment using mark-recapture. We also evaluated the effects of the marking technique, toe-clipping, and weather changes on population parameter estimates. We found that a 16% citric acid treatment appears to have reduced adult E. coqui density 3-fold in a plot, T1, completely covered with citric acid, but did not reduce adult density in a plot, T2, where 6% of the plot was unintentionally not treated. Preadults were reduced 3-to 5-fold in treated plots. The apparent reduction in adults in T1 lasted at least 5 months. Repeated treatments of 11% citric acid were studied in T2 and likely reduced adults 440-fold while preadults were reduced 9-fold. E. coqui that had fewer toe-clips had greater recapture probability and survival estimates, while weather had no effect on parameter estimates. In summary, we found that 16% and 11% citric acid treatments can reduce E. coqui density, treatment effects can last 5 months for adults, and repeated treatments appear more effective for reducing density than single applications.
Cladina subtenuis is the most commonly found ' reindeer lichen ' in the southeastern United State... more Cladina subtenuis is the most commonly found ' reindeer lichen ' in the southeastern United States. In the present study C. subtenuis was examined for polymorphism in the small subunit (SSU) ribosomal DNA (rDNA) within and among small clumps of podetia, here referred to as mats, from five geographical locations. Polymorphism in the SSU rDNA was not detected among podetia within mats, but polymorphism was detected among mats from a single location. Therefore, mats of C. subtenuis may represent a single genetic individual, although genetically distinct mats may occur in close proximity. Their proximity could encourage sexual reproduction between genetically distinct individuals, which would maintain variation in these populations. The SSU rDNA types represented three different lengths and restriction-site patterns, reflecting the presence of sequence insertions of at least 200 nucleotides in the SSU rDNA coding region. The insertions, differing in position, number and sequence, are group I introns similar to those previously reported in the Cladonia chlorophaea complex. The intron variation among the SSU rDNA types indicates that molecular evolution has occurred within this species, perhaps since its divergence from related taxa and dispersal across the southeastern United States.
ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats... more ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats to amphibians. Fragmentation is particularly harmful because many amphibians migrate between aquatic and terrestrial habitats, and even narrow bands of unsuitable habitat can act as barriers to movement. Additionally, amphibians are slow-moving and prone to road mortality, and many species are unable to travel long distances to leave unsuitable areas. We addressed several questions, including: 1) Does the number of roads or volume of traffic more strongly affect amphibian populations?, 2) Are roads detrimental to amphibian populations when they separate wetlands from uplands (i.e., habitat split)?, and 3) Are amphibians more sensitive to landscape composition or configuration? This project was integrated into undergraduate biology curricula; students from nine U.S. colleges summarized North American Amphibian Monitoring Program (NAAMP) data in the Eastern and Central U.S. and used GIS to extract and compile landscape data for 1620 survey locations across 14 states. We built generalized linear models to test hypotheses concerning the influence of landscape variables on amphibian species richness and site occupancy by individual species. Results/Conclusions We found that models incorporating local traffic volume, development, and wetland area were the best predictors of amphibian species richness and site occupancy by individual species. For overall species richness in 10 of 11 species examined, traffic volume in the vicinity of a survey site was more closely associated with site occupancy than was road length. We found little evidence for distinct effects of habitat split by roads or development, and in general, landscape composition variables were more useful than landscape configuration variables for predicting amphibian occupancy. Our results suggest that roads, and particularly traffic, exert strong negative effects on calling amphibians across the Eastern and Central U.S., affecting even species considered disturbance-tolerant. Our project demonstrates that networks of undergraduate students can be enlisted to analyze large ecological data sets and can provide students with a meaningful research experience in large-scale ecology. We plan to continue our investigation by addressing the importance of landscape connectivity to amphibian populations using this collaborative course-based research model.
Landscape structure is important for shaping the abundance and distribution of amphibians, but pr... more Landscape structure is important for shaping the abundance and distribution of amphibians, but prior studies of landscape effects have been species or ecosystem-specific. Using a large-scale, citizen science-generated database, we examined the effects of habitat composition, road disturbance, and habitat split (i.e. the isolation of wetland from forest by intervening land use) on the distribution and richness of frogs and toads in the eastern and central United States. Undergraduates from nine biology and environmental science courses collated occupancy data and characterized landscape structure at 1617 sampling locations from the North American Amphibian Monitoring Program. Our analysis revealed that anuran species richness and individual species distributions were consistently constrained by both road density and traffic volume. In contrast, developed land around wetlands had small, or even positive effects on anuran species richness and distributions after controlling for road effects. Effects of upland habitat composition varied among species, and habitat split had only weak effects on species richness or individual species distributions. Mechanisms underlying road effects on amphibians involve direct mortality, behavioral barriers to movement, and reduction in the quality of roadside habitats. Our results suggest that the negative effects of roads on amphibians occur across broad geographic regions, affecting even common species, and they underscore the importance of developing effective strategies to mitigate the impacts of roads on amphibian populations.
ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats... more ABSTRACT Background/Question/Methods Habitat loss and fragmentation represent significant threats to amphibians. Fragmentation is particularly harmful because many amphibians migrate between aquatic and terrestrial habitats, and even narrow bands of unsuitable habitat can act as barriers to movement. Additionally, amphibians are slow-moving and prone to road mortality, and many species are unable to travel long distances to leave unsuitable areas. We addressed several questions, including: 1) Does the number of roads or volume of traffic more strongly affect amphibian populations?, 2) Are roads detrimental to amphibian populations when they separate wetlands from uplands (i.e., habitat split)?, and 3) Are amphibians more sensitive to landscape composition or configuration? This project was integrated into undergraduate biology curricula; students from nine U.S. colleges summarized North American Amphibian Monitoring Program (NAAMP) data in the Eastern and Central U.S. and used GIS to extract and compile landscape data for 1620 survey locations across 14 states. We built generalized linear models to test hypotheses concerning the influence of landscape variables on amphibian species richness and site occupancy by individual species. Results/Conclusions We found that models incorporating local traffic volume, development, and wetland area were the best predictors of amphibian species richness and site occupancy by individual species. For overall species richness in 10 of 11 species examined, traffic volume in the vicinity of a survey site was more closely associated with site occupancy than was road length. We found little evidence for distinct effects of habitat split by roads or development, and in general, landscape composition variables were more useful than landscape configuration variables for predicting amphibian occupancy. Our results suggest that roads, and particularly traffic, exert strong negative effects on calling amphibians across the Eastern and Central U.S., affecting even species considered disturbance-tolerant. Our project demonstrates that networks of undergraduate students can be enlisted to analyze large ecological data sets and can provide students with a meaningful research experience in large-scale ecology. We plan to continue our investigation by addressing the importance of landscape connectivity to amphibian populations using this collaborative course-based research model.
Landscape structure is important for shaping the abundance and distribution of amphibians, but pr... more Landscape structure is important for shaping the abundance and distribution of amphibians, but prior studies of landscape effects have been species or ecosystem-specific. Using a large-scale, citizen science-generated database, we examined the effects of habitat composition, road disturbance, and habitat split (i.e. the isolation of wetland from forest by intervening land use) on the distribution and richness of frogs and toads in the eastern and central United States. Undergraduates from nine biology and environmental science courses collated occupancy data and characterized landscape structure at 1617 sampling locations from the North American Amphibian Monitoring Program. Our analysis revealed that anuran species richness and individual species distributions were consistently constrained by both road density and traffic volume. In contrast, developed land around wetlands had small, or even positive effects on anuran species richness and distributions after controlling for road effects. Effects of upland habitat composition varied among species, and habitat split had only weak effects on species richness or individual species distributions. Mechanisms underlying road effects on amphibians involve direct mortality, behavioral barriers to movement, and reduction in the quality of roadside habitats. Our results suggest that the negative effects of roads on amphibians occur across broad geographic regions, affecting even common species, and they underscore the importance of developing effective strategies to mitigate the impacts of roads on amphibian populations.
There is growing appreciation for the idea that plant – soil interactions (e.g. allelopathy and p... more There is growing appreciation for the idea that plant – soil interactions (e.g. allelopathy and plant – microbe feedbacks) may explain the success of some non-native plants. Where this is the case, native plant restoration may require management tools that change plant – soil interactions. Activated carbon (AC) is one such potential tool. Previous research has shown the potential for high concentrations of AC to restore native plant growth to areas dominated by non-natives on a small scale (1 m × 1 m plots). Here we (i) test the efficacy of different AC concentrations at a larger scale (15 m × 15 m plots), (ii) measure microbial responses to AC treatment and (iii) use a greenhouse experiment to identify the primary mechanism, allelopathy versus microbial changes, through which AC impacts native and non-native plant growth. Three years after large-scale applications, AC treatments decreased non-native plant cover and increased the ratio of native to non-native species cover, particularly at concentrations .400 g m 22. Activated carbon similarly decreased non-native plant growth in the greenhouse. This effect, however, was only observed in live soils, suggesting that AC effects were microbially mediated and not caused by direct allelopathy. Bacterial community analysis of field soils indicated that AC increased the relative abundance of an unidentified bacterium and an Actinomycetales and decreased the relative abundance of a Flavobacterium, suggesting that these organisms may play a role in AC effects on plant growth. Results support the idea that manipulations of plant–microbe interactions may provide novel and effective ways of directing plant growth and community development (e.g. native plant restoration).
E xisting data may offer the best insight into many important questions in ecology and conservati... more E xisting data may offer the best insight into many important questions in ecology and conservation biology, but there are various challenges to using existing data effectively. First, although the use of large data repositories is increasing, many ecological data sets are never made publicly available. In addition, ecological data sets are rarely uniform, and reformatting data sets from different sources, sites, and time periods in a consistent manner can be tedious. These difficulties may be particularly pronounced when data sets involve ecological questions over large spatial or temporal scales. In the present study, we organized networks of students in undergraduate courses to address these challenges and to investigate the geographic patterns of nonnative and invasive plants in sites in the US National Wildlife Refuge System. The students collected and compiled the data for refuges in their own region. From the data that the stu dents compiled, we asked (a) how nonnative and invasive plant species richness is related to native species richness; (b) how the pool of nonnative species from the surrounding area (i.e., colonization pressure) contributes to nonnative and invasive species richness in the refuges; (c) how refuge characteristics such as habitat diversity, refuge area, and elevational range contribute to species richness patterns for native, nonnative, and invasive plants; (d) whether inva sion patterns differ between mainland and island refuges; and (e) whether invasion patterns vary among US Fish and Wildlife Service (USFWS) regions. Below, we outline the scientific background for this project, as well as the specific rationale for each of the questions examined.
Here we test an experimental approach that produces estimates of the location, timing and extent ... more Here we test an experimental approach that produces estimates of the location, timing and extent of water uptake by individual plant species in the field. A tracer injection experiment was used to estimate the proportion of active roots across soil depths. These proportions were multiplied by species-specific estimates of evapotranspiration. This approach was repeated in early-and late-season conditions in adjacent native-and non-native-dominated shrub-steppe plant communities. Resulting estimates of water uptake by depth were compared to soil water content. Both communities contained a dominant plant that relied on shallow (i.e., 0e10) soil water, a subdominant that relied on deep-(i.e., 90 þ cm) soil water and a second subdominant that used late-season pulses of shallow water. Combining tracer uptake with evapotranspiration estimates indicated that non-natives removed nearly twice the amount of water early in the season as natives, especially from shallow depths. This was consistent with measures of soil moisture. However, modeled estimates of root water uptake were not always consistent with measurements of soil moisture. Despite the intensive sampling conducted in this study, future use of this approach will require more complete tracer sampling of the plant species present and improved estimation of evapotranspiration in sparse, diverse plant canopies.
Trophic cascades are important drivers of plant and animal abundances in aquatic and aboveground ... more Trophic cascades are important drivers of plant and animal abundances in aquatic and aboveground systems, but in soils trophic cascades have been thought to be of limited importance due to omnivory and other factors. Here we use a meta-analysis of 215 studies with 1526 experiments that measured plant growth responses to additions or removals of soil organisms to test how different soil trophic levels affect plant growth. Consistent with the trophic cascade hypothesis, we found that herbivores and plant pathogens (henceforth pests) decreased plant growth and that predators of pests increased plant growth. The magnitude of this trophic cascade was similar to that reported for aboveground systems. In contrast, we did not find evidence for trophic cascades in decomposer-and symbiont-based (henceforth mutualist) food chains. In these food chains, mutualists increased plant growth and predators of mutualists also increased plant growth, presumably by increasing nutrient cycling rates. Therefore, mutualists, predators of mutualists and predators of pests all increased plant growth. Further, experiments that added multiple organisms from different trophic levels also increased plant growth. As a result, across the dataset, soil organisms increased plant growth 29% and non-pest soil organisms increased plant growth 46%. Omnivory has traditionally been thought to confound soil trophic dynamics, but here we suggest that omnivory allows for a simplified perspective of soil food webs – one in which most soil organisms increase plant growth by preying on pests or increasing nutrient cycling rates. An implication of this perspective is that processes that decrease soil organism abundance (e.g. soil tillage) are likely to decrease aboveground productivity.
Non-native species introductions have the ability to affect both ecological and social systems, t... more Non-native species introductions have the ability to affect both ecological and social systems, thus to address those outcomes both ecological and social influences on an invasion need to be understood. We use a social–ecological systems approach to investigate connections between human and ecological factors that affect efforts to control the non-native coqui frog (Eleutherodactylus coqui) on the island of Hawaii. The coqui frog is recognized as a 'pest' and 'injurious wildlife' by the Hawaii Department of Agriculture. Because the coqui occurs on many small private properties across the island, it is necessary to enlist private citizens in control efforts. Control efforts can include direct chemical control of the coqui as well as landscape manipulations that reduce habitat quality for the frog. On 85 private properties in 12 communities across the island, we measured the relationship between coqui abundance, residents' attitudes toward the coqui, their reported participation in control activities, and environmental variables that affect habitat quality for the frog. Residents' attitudes correlated with coqui frog abundance, but in an unexpected direction: People with more frogs on their property and those who owned that property tended to have less negative attitudes toward the coqui. In addition, negative attitudes toward the coqui were not significantly related to participation in control activities. Coqui abundance was related to a habitat variable, canopy cover, which can be manipulated by residents to reduce habitat quality and discourage coqui occupancy. Tolerance for this non-native species is likely to hinder attempts to engage residents in control efforts as the species' range on the island continues to expand. If this pattern of habit-uation is manifested with other non-native species considered to have potentially negative effects on the ecological or social environment, it would be important to recognize as early as possible because managers may be most effective at engaging citizens in control efforts before habituation becomes widespread.
We describe a new treefrog species of Dendropsophus collected on rocky outcrops in the Brazilian ... more We describe a new treefrog species of Dendropsophus collected on rocky outcrops in the Brazilian Atlantic Forest. Ecologically, the new species can be distinguished from all known congeners by having a larval phase associated with rainwater accumulated in bromeliad phytotelms instead of temporary or lentic water bodies. Phylogenetic analysis based on molecular data confirms that the new species is a member of Dendropsophus; our analysis does not assign it to any recognized species group in the genus. Morphologically, based on comparison with the 96 known congeners, the new species is diagnosed by its small size, framed dorsal color pattern, and short webbing between toes IV-V. The advertisement call is composed of a moderate-pitched two-note call (~5 kHz). The territorial call contains more notes and pulses than the advertisement call. Field observations suggest that this new bro-meligenous species uses a variety of bromeliad species to breed in, and may be both territorial and exhibit male parental care.
Little is known about ecosystem-level responses to multiple, climatic disturbance events. In the ... more Little is known about ecosystem-level responses to multiple, climatic disturbance events. In the subtropical forests of Puerto Rico, the major natural disturbances are hurricanes and droughts. We tested the ecosystem-level effects of these disturbances in sites with different land use histories. From 1989 to 1992, data were collected to determine the effects of Hurricane Hugo and two droughts on litterfall inputs, fine-root biomass, and decomposition rates in three topographic locations (stream, riparian, upslope) within two watersheds. From 1994 to 1998, we added a third watershed and an experiment in which coarse-wood levels were manipulated to simulate hurricane inputs. Data were collected on tree and palm growth rates, litterfall inputs, fine-root biomass, and decomposition rates. From 1994 to 1998, four hurricanes and three droughts were recorded.
ABSTRACT Background/Question/Methods Eleutherodactylus coqui is a small tropical terrestrial frog... more ABSTRACT Background/Question/Methods Eleutherodactylus coqui is a small tropical terrestrial frog that is native to Puerto Rico and was first seen on the Hawaiian Islands in the late 1980s. Millions of dollars have been spent in recent years in an attempt to control E. coqui, but eradication is deemed no longer possible on the Island of Hawaii. Based on preliminary research suggesting a positive relationship between prey, structure, and E. coqui density in Hawaii, we hypthesized that the success of E. coqui (measured by its density) is positively related to resource availability in the form of structure and prey because structure provides the male with more calling sites, and thus more opportunity to mate with females, and prey provides E. coqui with the necessary energy to reproduce, grow, and increase in density. We designed and conducted a large-scale experiment in the Nanawale Forest Reserve in the southeast region of the Island of Hawaii for 6 months to test this relationship. Results/Conclusions E. coqui density was reduced in the 100% leaf litter removal and 100% structure removal treatment plots. E. coqui were observed at lower heights off the forest floor in the 100% structure removal plots than the control plots. Higher quantity of flying and leaf litter invertebrates were found in the 100% structure removal treatment, suggesting a reduction in predation pressure on these invertebrates due to a reduction in coqui frogs. Our results provide a better understanding of the role that specific resources play for the density of an invasive frog in Hawaii. Efforts to efficiently control E. coqui should focus on structure removal and leaf litter removal in areas with large populations of E. coqui.
The Puerto Rican frog (Eleutherodactylus coqui) is an invasive pest in Hawaii. Citric acid is app... more The Puerto Rican frog (Eleutherodactylus coqui) is an invasive pest in Hawaii. Citric acid is approved for controlling these frogs, but has been limited to terrain accessible by foot or vehicle. We determined the effectiveness of helicopter applications of 16% citric acid and repeated 11% citric acid treatments for eradicating and/or reducing densities of E. coqui by monitoring populations before and after treatment using mark-recapture. We also evaluated the effects of the marking technique, toe-clipping, and weather changes on population parameter estimates. We found that a 16% citric acid treatment appears to have reduced adult E. coqui density 3-fold in a plot, T1, completely covered with citric acid, but did not reduce adult density in a plot, T2, where 6% of the plot was unintentionally not treated. Preadults were reduced 3-to 5-fold in treated plots. The apparent reduction in adults in T1 lasted at least 5 months. Repeated treatments of 11% citric acid were studied in T2 and likely reduced adults 440-fold while preadults were reduced 9-fold. E. coqui that had fewer toe-clips had greater recapture probability and survival estimates, while weather had no effect on parameter estimates. In summary, we found that 16% and 11% citric acid treatments can reduce E. coqui density, treatment effects can last 5 months for adults, and repeated treatments appear more effective for reducing density than single applications.
Cladina subtenuis is the most commonly found ' reindeer lichen ' in the southeastern United State... more Cladina subtenuis is the most commonly found ' reindeer lichen ' in the southeastern United States. In the present study C. subtenuis was examined for polymorphism in the small subunit (SSU) ribosomal DNA (rDNA) within and among small clumps of podetia, here referred to as mats, from five geographical locations. Polymorphism in the SSU rDNA was not detected among podetia within mats, but polymorphism was detected among mats from a single location. Therefore, mats of C. subtenuis may represent a single genetic individual, although genetically distinct mats may occur in close proximity. Their proximity could encourage sexual reproduction between genetically distinct individuals, which would maintain variation in these populations. The SSU rDNA types represented three different lengths and restriction-site patterns, reflecting the presence of sequence insertions of at least 200 nucleotides in the SSU rDNA coding region. The insertions, differing in position, number and sequence, are group I introns similar to those previously reported in the Cladonia chlorophaea complex. The intron variation among the SSU rDNA types indicates that molecular evolution has occurred within this species, perhaps since its divergence from related taxa and dispersal across the southeastern United States.
Aim Non-native reptiles are often detrimental to native communities and ecosystems and can be ext... more Aim Non-native reptiles are often detrimental to native communities and ecosystems and can be extremely difficult to manage once established. Thus, there is considerable interest in predicting the likelihood of establishment of nonnative reptiles. We assessed three hypotheses describing possible factors contributing to the successful establishment of introduced reptiles in an effort to better identify potential invaders.
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