Darren Johnson is a Statistician at the USGS Wetland and Aquatic Research Center.
Darren provides statistical advice and consultation in areas applying to the development of research plans, sampling designs, the selection of statistical analyses, assistance with statistical analyses, conducting analyses for scientists, review of plans, reports, and publications for statistical procedures.
Education and Certifications
University of Louisiana at Lafayette
Doctor of Philosophy
08/1995The Ohio State University
Masters of Applied Statistics
06/1989The Ohio State University
Bachelor of Science
06/1988
Science and Products
Effects of shading on the rare plant species, Physostegia correllii (Lamiaceae)
The original distribution of the study species Physostegia correllii included freshwater floodplains of large rivers in the southcentral U.S. (Colorado, Rio Grande, Mississippi). Experiments to determine the effects of shading on P. correllii were conducted using short-term shade cloth treatments (full sunlight vs. 30% shading for 2-3 weeks). Mean height and cover responses of individuals were det
Establishing a standard ploidy assessment method using grass carp from Ohio, 2015-2016
In 2015-2016, the Ohio Division of Wildlife's undercover law enforcement purchased 1,200 grass carp (Ctenopharyngodon idella). Fish heads and eyeballs were sent overnight to U.S. Geological Survey Wetland and Aquatic Research Center for ploidy analysis. Field and laboratory standard operating procedures were established and followed. Fish lengths, fish weights, and eyeball weights were obtained fr
Filter Total Items: 26
Local weather and endogenous factors affect the initiation of migration in short- and medium-distance songbird migrants
Migratory birds employ a variety of mechanisms to ensure appropriate timing of migration based on integration of endogenous and exogenous information. The cues to fatten and depart from the non-breeding area are often linked to exogenous cues such as temperature or precipitation and the endogenous program. Shorter distance migrants should rely heavily on environmental information when initiating m
Effects of shading on the rare plant species, Physostegia correllii (Lamiaceae) and Trillium texanum (Melanthiaceae)
Rare plant species that are constrained by shading may be threatened by a lack of natural disturbance that removes overhanging vegetation. The original distribution of the study species Physostegia correllii (Lundell) Shinners included freshwater floodplains of large rivers in the southcentral U.S. (Colorado, Rio Grande, and Mississippi rivers). A second species, Trillium texanum Buckley was found
Surface elevation change dynamics in coastal marshes along the northwestern Gulf of Mexico: Anticipating effects of rising sea-level and intensifying hurricanes
Accelerated sea-level rise and intensifying hurricanes highlight the need to better understand surface elevation change in coastal wetlands. We used the surface elevation table-marker horizon approach to measure surface elevation change in 14 coastal marshes along the northwestern Gulf of Mexico, within five National Wildlife Refuges in Texas (USA). During the 2014–2019 study period, the mean rate
Juvenile African clawed frogs (Xenopus laevis) express growth, metamorphosis, mortality, gene expression, and metabolic changes when exposed to thiamethoxam and clothianidin
Neonicotinoids (NEO) represent the main class of insecticides currently in use, with thiamethoxam (THX) and clothianidin (CLO) primarily applied agriculturally. With few comprehensive studies having been performed with non-target amphibians, the aim was to investigate potential biomarker responses along an adverse outcome pathway of NEO exposure, whereby data were collected on multiple biological
The Louisiana Amphibian Monitoring Program from 1997 to 2017: Results, analyses, and lessons learned
To determine trends in either frog distribution or abundance in the State of Louisiana, we reviewed and analyzed frog call data from the Louisiana Amphibian Monitoring Program (LAMP). The data were collected between 1997 and 2017 using North American Amphibian Monitoring Program protocols. Louisiana was divided into three survey regions for administration and analysis: the Florida Parishes, and 2
Establishment of baseline cytology metrics in nestling American kestrels (Falco sparverius): Immunomodulatory effects of the flame retardant isopropylated triarylphosphate isomers
Avian populations must mount effective immune responses upon exposure to environmental stressors such as avian influenza and xenobiotics. Although multiple immune assays have been tested and applied to various avian species, antibody-mediated immune responses in non-model avian species are not commonly reported due to the lack of commercially available species-specific antibodies. The objectives o
Home ranges and movements of two diamondback terrapins (Malaclemys terrapin macrospilota) in northwest Florida
The diamondback terrapin (Malaclemys terrapin) is a small estuarine turtle distributed along the Atlantic and Gulf Coasts of the USA that is threatened by drowning in crab pots, road mortality, exploitation in the pet trade, and habitat loss. Little is known about the movement patterns and home ranges of these turtles, particularly along the U.S. Gulf of Mexico coast. Satellite tags were deployed
Movements of marine and estuarine turtles during Hurricane Michael
Natural disturbances are an important driver of population dynamics. Because it is difficult to observe wildlife during these events, our understanding of the strategies that species use to survive these disturbances is limited. On October 10, 2018, Hurricane Michael made landfall on Florida’s northwest coast. Using satellite and acoustic telemetry, we documented movements of 6 individual turtles:
Variation in species composition, size and fitness of two multi-species sea turtle assemblages using different neritic habitats
The neritic environment is rich in resources and as such plays a crucial role as foraging habitat for multi-species marine assemblages, including sea turtles. However, this habitat also experiences a wide array of anthropogenic threats. To prioritize conservation funds, targeting areas that support multi-species assemblages is ideal. This is particularly important in the Gulf of Mexico where resto
Growth rates for immature Kemp’s ridley sea turtles from a foraging area in the northern Gulf of Mexico
Examining vital rates helps clarify how environmental characteristics, biological resources and human activities affect population growth. Carapace lengths were gathered for 241 Kemp’s ridley Lepidochelys kempii sea turtles that were marked and recaptured (n = 23) between 2011 and 2019 at a foraging location in northwest Florida, USA. There was a strong correlation between length, width and weight
The incubation environment of nests deposited by a genetically distinct group of loggerhead sea turtles in Northwest Florida
The warming climate presents a challenge to conservation of all threatened and endangered species but particularly to those that exhibit temperature-dependent sex determination such as sea turtles. Changes in temperature may result in changes in the sex ratio of the population which can directly affect reproductive rate, abundance and population dynamics. The NW Atlantic loggerhead turtle populati
The potential resiliency of a created tidal marsh to sea-level rise
The purpose of this study was to determine the elevation dynamics of a created tidal marsh on the North Carolina coast. Deep rod surface elevation tables (RSET) and feldspar marker horizons (MH) were installed in plots to measure net surface elevation changes and to quantify contributing processes. Twelve total plots were placed on four elevation gradient transects (three transects within the crea
Non-USGS Publications**
K. Krishnamoorthy, Darren J. Johnson (1997) Combining Independent Information in a Multivariate Calibration Problem. Journal of Multivariate Analysis 61(2):171-186[3]
Darren J. Johnson & K. Krishnamoorthy (1996) Combining Independent Studies in a Calibration Problem. Journal of the American Statistical Association, Volume 91, 1707-1715[23]
Darren J. Johnson & K. Krishnamoorthy (1996) Combining Independent Studies in a Calibration Problem. Journal of the American Statistical Association, Volume 91, 1707-1715[23]
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.
Science and Products
- Data
Effects of shading on the rare plant species, Physostegia correllii (Lamiaceae)
The original distribution of the study species Physostegia correllii included freshwater floodplains of large rivers in the southcentral U.S. (Colorado, Rio Grande, Mississippi). Experiments to determine the effects of shading on P. correllii were conducted using short-term shade cloth treatments (full sunlight vs. 30% shading for 2-3 weeks). Mean height and cover responses of individuals were detEstablishing a standard ploidy assessment method using grass carp from Ohio, 2015-2016
In 2015-2016, the Ohio Division of Wildlife's undercover law enforcement purchased 1,200 grass carp (Ctenopharyngodon idella). Fish heads and eyeballs were sent overnight to U.S. Geological Survey Wetland and Aquatic Research Center for ploidy analysis. Field and laboratory standard operating procedures were established and followed. Fish lengths, fish weights, and eyeball weights were obtained fr - Publications
Filter Total Items: 26
Local weather and endogenous factors affect the initiation of migration in short- and medium-distance songbird migrants
Migratory birds employ a variety of mechanisms to ensure appropriate timing of migration based on integration of endogenous and exogenous information. The cues to fatten and depart from the non-breeding area are often linked to exogenous cues such as temperature or precipitation and the endogenous program. Shorter distance migrants should rely heavily on environmental information when initiating mEffects of shading on the rare plant species, Physostegia correllii (Lamiaceae) and Trillium texanum (Melanthiaceae)
Rare plant species that are constrained by shading may be threatened by a lack of natural disturbance that removes overhanging vegetation. The original distribution of the study species Physostegia correllii (Lundell) Shinners included freshwater floodplains of large rivers in the southcentral U.S. (Colorado, Rio Grande, and Mississippi rivers). A second species, Trillium texanum Buckley was foundSurface elevation change dynamics in coastal marshes along the northwestern Gulf of Mexico: Anticipating effects of rising sea-level and intensifying hurricanes
Accelerated sea-level rise and intensifying hurricanes highlight the need to better understand surface elevation change in coastal wetlands. We used the surface elevation table-marker horizon approach to measure surface elevation change in 14 coastal marshes along the northwestern Gulf of Mexico, within five National Wildlife Refuges in Texas (USA). During the 2014–2019 study period, the mean rateJuvenile African clawed frogs (Xenopus laevis) express growth, metamorphosis, mortality, gene expression, and metabolic changes when exposed to thiamethoxam and clothianidin
Neonicotinoids (NEO) represent the main class of insecticides currently in use, with thiamethoxam (THX) and clothianidin (CLO) primarily applied agriculturally. With few comprehensive studies having been performed with non-target amphibians, the aim was to investigate potential biomarker responses along an adverse outcome pathway of NEO exposure, whereby data were collected on multiple biologicalThe Louisiana Amphibian Monitoring Program from 1997 to 2017: Results, analyses, and lessons learned
To determine trends in either frog distribution or abundance in the State of Louisiana, we reviewed and analyzed frog call data from the Louisiana Amphibian Monitoring Program (LAMP). The data were collected between 1997 and 2017 using North American Amphibian Monitoring Program protocols. Louisiana was divided into three survey regions for administration and analysis: the Florida Parishes, and 2Establishment of baseline cytology metrics in nestling American kestrels (Falco sparverius): Immunomodulatory effects of the flame retardant isopropylated triarylphosphate isomers
Avian populations must mount effective immune responses upon exposure to environmental stressors such as avian influenza and xenobiotics. Although multiple immune assays have been tested and applied to various avian species, antibody-mediated immune responses in non-model avian species are not commonly reported due to the lack of commercially available species-specific antibodies. The objectives oHome ranges and movements of two diamondback terrapins (Malaclemys terrapin macrospilota) in northwest Florida
The diamondback terrapin (Malaclemys terrapin) is a small estuarine turtle distributed along the Atlantic and Gulf Coasts of the USA that is threatened by drowning in crab pots, road mortality, exploitation in the pet trade, and habitat loss. Little is known about the movement patterns and home ranges of these turtles, particularly along the U.S. Gulf of Mexico coast. Satellite tags were deployedMovements of marine and estuarine turtles during Hurricane Michael
Natural disturbances are an important driver of population dynamics. Because it is difficult to observe wildlife during these events, our understanding of the strategies that species use to survive these disturbances is limited. On October 10, 2018, Hurricane Michael made landfall on Florida’s northwest coast. Using satellite and acoustic telemetry, we documented movements of 6 individual turtles:Variation in species composition, size and fitness of two multi-species sea turtle assemblages using different neritic habitats
The neritic environment is rich in resources and as such plays a crucial role as foraging habitat for multi-species marine assemblages, including sea turtles. However, this habitat also experiences a wide array of anthropogenic threats. To prioritize conservation funds, targeting areas that support multi-species assemblages is ideal. This is particularly important in the Gulf of Mexico where restoGrowth rates for immature Kemp’s ridley sea turtles from a foraging area in the northern Gulf of Mexico
Examining vital rates helps clarify how environmental characteristics, biological resources and human activities affect population growth. Carapace lengths were gathered for 241 Kemp’s ridley Lepidochelys kempii sea turtles that were marked and recaptured (n = 23) between 2011 and 2019 at a foraging location in northwest Florida, USA. There was a strong correlation between length, width and weightThe incubation environment of nests deposited by a genetically distinct group of loggerhead sea turtles in Northwest Florida
The warming climate presents a challenge to conservation of all threatened and endangered species but particularly to those that exhibit temperature-dependent sex determination such as sea turtles. Changes in temperature may result in changes in the sex ratio of the population which can directly affect reproductive rate, abundance and population dynamics. The NW Atlantic loggerhead turtle populatiThe potential resiliency of a created tidal marsh to sea-level rise
The purpose of this study was to determine the elevation dynamics of a created tidal marsh on the North Carolina coast. Deep rod surface elevation tables (RSET) and feldspar marker horizons (MH) were installed in plots to measure net surface elevation changes and to quantify contributing processes. Twelve total plots were placed on four elevation gradient transects (three transects within the creaNon-USGS Publications**
K. Krishnamoorthy, Darren J. Johnson (1997) Combining Independent Information in a Multivariate Calibration Problem. Journal of Multivariate Analysis 61(2):171-186[3]
Darren J. Johnson & K. Krishnamoorthy (1996) Combining Independent Studies in a Calibration Problem. Journal of the American Statistical Association, Volume 91, 1707-1715[23]
**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.