Julia Ersan (Former Employee)
Science and Products
Growth and Capture Mark Recapture Data from Giant Gartersnakes (Thamnophis gigas) in Rice Irrigation Canals 2018 to 2023 (ver. 2.0, July 2025) Growth and Capture Mark Recapture Data from Giant Gartersnakes (Thamnophis gigas) in Rice Irrigation Canals 2018 to 2023 (ver. 2.0, July 2025)
These data support a study modeling the growth, capture, and survival of giant gartersnakes (Thamnophis gigas). We captured giant gartersnakes inhabiting rice irrigation canals in the Sacramento Valley, California, USA from 2018 to 2023. We analyzed capture-mark-recapture data from 19 populations of giant gartersnakes sampled with an integrated growth-survival model. We tested how growth...
Giant Gartersnake (Thamnophis gigas) Prey Preference (2014) Giant Gartersnake (Thamnophis gigas) Prey Preference (2014)
This is an examination of the diet of a threatened snake, giant gartersnake (Thamnophis gigas). Prey preference, prey selection and prey availability (in the laboratory and the field) were measured to understand prey dynamics for better conservation of this snake. In the laboratory, olfactory trials were performed on neonate snakes and tongue-flicks, lounges and attacks were counted and...
A tale of two valleys: Endangered species policy and the fate of the giant gartersnake A tale of two valleys: Endangered species policy and the fate of the giant gartersnake
By the mid-20th Century, giant gartersnakes (Thamnophis gigas) had lost more than 90% of their Central Valley marsh habitat and were extirpated from more than two-thirds of their range. This massive habitat loss led to their inclusion in the inaugural list of rare species under the California Endangered Species Act (CESA). Listing under the CESA provided giant gartersnakes legal...
Authors
Brian J. Halstead, Patricia Valcarcel, Richard Kim, Anna Jordan, Jonathan P. Rose, Shannon Skalos, Gabriel Reyes, Julia Ersan, Michael L. Casazza, Allison Essert, Alexandria M Fulton
Distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento–San Joaquin Delta, California, 2018–2019 Distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento–San Joaquin Delta, California, 2018–2019
SummaryWe examined the occurrence of giant gartersnakes in the Sacramento–San Joaquin Delta, California, in 2018 and 2019. We made eight captures of seven giant gartersnakes (three females, four males) in 2018, and six captures of six giant gartersnakes (four females, two males) in 2019. Detection probabilities were exceedingly low despite using methods that achieve much higher detection...
Authors
Kristen J. Fouts, Richard Kim, Anna C. Jordan, Alexandria M. Fulton, Jonathan P. Rose, Julia S. M. Ersan, Brian J. Halstead
Giant Gartersnakes (Thamnophis gigas) exploit abundant non-native prey while maintaining their appetite for native anurans Giant Gartersnakes (Thamnophis gigas) exploit abundant non-native prey while maintaining their appetite for native anurans
The introductions of nonnative species can cause great change in the trophic dynamics of native species. Giant Gartersnakes, endemic predators in the Central Valley of California, are listed as threatened because of the conversion of their once vast wetland habitat to agriculture. Further contributing to this snake's changing ecology is the introduction of many nonnative prey species...
Authors
Julia Ersan, Brian J. Halstead, Erica L Wildy, Michael L. Casazza, Glenn D. Wylie
Intrinsic prey preference and selection of the giant gartersnake: A threatened predator in a nonnative prey-dominated community Intrinsic prey preference and selection of the giant gartersnake: A threatened predator in a nonnative prey-dominated community
The introduction of exotic species into an environment can introduce great change in the trophic dynamics of native species. This is of even greater concern if the native species is of conservation concern. The giant gartersnake, Thamnophis gigas, an endemic predator of the Central Valley of California and a species of conservation concern at the state and federal levels, has declined as...
Authors
Julia Ersan, Brian J. Halstead, Erica L Wildy, Michael L. Casazza, Glenn D. Wylie
Demographic factors affecting population growth in giant gartersnakes Demographic factors affecting population growth in giant gartersnakes
Demographic models provide insight into which vital rates and life stages contribute most to population growth. Integral projection models (IPMs) offer flexibility in matching model structure to a species’ demography. For many rare species, data are lacking for key vital rates, and uncertainty might dissuade researchers from attempting to build a demographic model. We present work that...
Authors
Jonathan P. Rose, Julia Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Findings from a preliminary investigation of the effects of aquatic habitat (water) availability on giant gartersnake (Thamnophis gigas) demography in the Sacramento Valley, California, 2014–17 Findings from a preliminary investigation of the effects of aquatic habitat (water) availability on giant gartersnake (Thamnophis gigas) demography in the Sacramento Valley, California, 2014–17
The giant gartersnake (Thamnophis gigas) is a semi-aquatic species of snake precinctive to the Central Valley of California. Because the Central Valley has experienced a substantial loss of wetland habitat, giant gartersnake populations are largely found in aquatic habitats associated with rice agriculture. In dry years, less water may be available for rice agriculture, resulting in less...
Authors
Jonathan P. Rose, Julia S. M. Ersan, Gabriel A. Reyes, K. Benjamin Gustafson, Alexandria M. Fulton, Kristen J. Fouts, Raymund F. Wack, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas) Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas)
How reproductive output changes with age or size is a key life-history trait that can affect which demographic rates most influence population growth. Although many studies have investigated the reproductive ecology of gartersnakes, we know little about reproduction in the threatened Giant Gartersnake, Thamnophis gigas. We used X-radiography to determine reproductive status and estimated...
Authors
Jonathan P. Rose, Julia Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Construction and analysis of a giant gartersnake (Thamnophis gigas) population projection model Construction and analysis of a giant gartersnake (Thamnophis gigas) population projection model
The giant gartersnake (Thamnophis gigas) is a state and federally threatened species precinctive to California. The range of the giant gartersnake has contracted in the last century because its wetland habitat has been drained for agriculture and development. As a result of this habitat alteration, giant gartersnakes now largely persist in and near rice agriculture in the Sacramento...
Authors
Jonathan P. Rose, Julia S. M. Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape
Most extant giant gartersnake (Thamnophis gigas) populations persist in an agro-ecosystem dominated by rice, which serves as a surrogate to the expansive marshes lost to flood control projects and development of the Great Central Valley of California. Knowledge of how giant gartersnakes use the rice agricultural landscape, including how they respond to fallowing, idling, or crop...
Authors
Gabriel A. Reyes, Brian J. Halstead, Jonathan P. Rose, Julia S. M. Ersan, Anna C. Jordan, Allison M. Essert, Kristen J. Fouts, Alexandria M. Fulton, K. Benjamin Gustafson, Raymund F. Wack, Glenn D. Wylie, Michael L. Casazza
An evaluation of the efficacy of using environmental DNA (eDNA) to detect giant gartersnakes (Thamnophis gigas) An evaluation of the efficacy of using environmental DNA (eDNA) to detect giant gartersnakes (Thamnophis gigas)
Detecting populations of rare or cryptic species is essential for their conservation. For species like giant gartersnakes (Thamnophis gigas), conventional survey methods can be expensive and inefficient. These sampling difficulties might be overcome by modern techniques that detect deoxyribonucleic acid (DNA) shed by organisms into the environment (eDNA). We evaluated the efficacy of...
Authors
Brian J. Halstead, Dustin A. Wood, Lizabeth Bowen, Shannon C. Waters, Amy G. Vandergast, Julia S. Ersan, Shannon M. Skalos, Michael L. Casazza
Science and Products
Growth and Capture Mark Recapture Data from Giant Gartersnakes (Thamnophis gigas) in Rice Irrigation Canals 2018 to 2023 (ver. 2.0, July 2025) Growth and Capture Mark Recapture Data from Giant Gartersnakes (Thamnophis gigas) in Rice Irrigation Canals 2018 to 2023 (ver. 2.0, July 2025)
These data support a study modeling the growth, capture, and survival of giant gartersnakes (Thamnophis gigas). We captured giant gartersnakes inhabiting rice irrigation canals in the Sacramento Valley, California, USA from 2018 to 2023. We analyzed capture-mark-recapture data from 19 populations of giant gartersnakes sampled with an integrated growth-survival model. We tested how growth...
Giant Gartersnake (Thamnophis gigas) Prey Preference (2014) Giant Gartersnake (Thamnophis gigas) Prey Preference (2014)
This is an examination of the diet of a threatened snake, giant gartersnake (Thamnophis gigas). Prey preference, prey selection and prey availability (in the laboratory and the field) were measured to understand prey dynamics for better conservation of this snake. In the laboratory, olfactory trials were performed on neonate snakes and tongue-flicks, lounges and attacks were counted and...
A tale of two valleys: Endangered species policy and the fate of the giant gartersnake A tale of two valleys: Endangered species policy and the fate of the giant gartersnake
By the mid-20th Century, giant gartersnakes (Thamnophis gigas) had lost more than 90% of their Central Valley marsh habitat and were extirpated from more than two-thirds of their range. This massive habitat loss led to their inclusion in the inaugural list of rare species under the California Endangered Species Act (CESA). Listing under the CESA provided giant gartersnakes legal...
Authors
Brian J. Halstead, Patricia Valcarcel, Richard Kim, Anna Jordan, Jonathan P. Rose, Shannon Skalos, Gabriel Reyes, Julia Ersan, Michael L. Casazza, Allison Essert, Alexandria M Fulton
Distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento–San Joaquin Delta, California, 2018–2019 Distribution of giant gartersnakes (Thamnophis gigas) in the Sacramento–San Joaquin Delta, California, 2018–2019
SummaryWe examined the occurrence of giant gartersnakes in the Sacramento–San Joaquin Delta, California, in 2018 and 2019. We made eight captures of seven giant gartersnakes (three females, four males) in 2018, and six captures of six giant gartersnakes (four females, two males) in 2019. Detection probabilities were exceedingly low despite using methods that achieve much higher detection...
Authors
Kristen J. Fouts, Richard Kim, Anna C. Jordan, Alexandria M. Fulton, Jonathan P. Rose, Julia S. M. Ersan, Brian J. Halstead
Giant Gartersnakes (Thamnophis gigas) exploit abundant non-native prey while maintaining their appetite for native anurans Giant Gartersnakes (Thamnophis gigas) exploit abundant non-native prey while maintaining their appetite for native anurans
The introductions of nonnative species can cause great change in the trophic dynamics of native species. Giant Gartersnakes, endemic predators in the Central Valley of California, are listed as threatened because of the conversion of their once vast wetland habitat to agriculture. Further contributing to this snake's changing ecology is the introduction of many nonnative prey species...
Authors
Julia Ersan, Brian J. Halstead, Erica L Wildy, Michael L. Casazza, Glenn D. Wylie
Intrinsic prey preference and selection of the giant gartersnake: A threatened predator in a nonnative prey-dominated community Intrinsic prey preference and selection of the giant gartersnake: A threatened predator in a nonnative prey-dominated community
The introduction of exotic species into an environment can introduce great change in the trophic dynamics of native species. This is of even greater concern if the native species is of conservation concern. The giant gartersnake, Thamnophis gigas, an endemic predator of the Central Valley of California and a species of conservation concern at the state and federal levels, has declined as...
Authors
Julia Ersan, Brian J. Halstead, Erica L Wildy, Michael L. Casazza, Glenn D. Wylie
Demographic factors affecting population growth in giant gartersnakes Demographic factors affecting population growth in giant gartersnakes
Demographic models provide insight into which vital rates and life stages contribute most to population growth. Integral projection models (IPMs) offer flexibility in matching model structure to a species’ demography. For many rare species, data are lacking for key vital rates, and uncertainty might dissuade researchers from attempting to build a demographic model. We present work that...
Authors
Jonathan P. Rose, Julia Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Findings from a preliminary investigation of the effects of aquatic habitat (water) availability on giant gartersnake (Thamnophis gigas) demography in the Sacramento Valley, California, 2014–17 Findings from a preliminary investigation of the effects of aquatic habitat (water) availability on giant gartersnake (Thamnophis gigas) demography in the Sacramento Valley, California, 2014–17
The giant gartersnake (Thamnophis gigas) is a semi-aquatic species of snake precinctive to the Central Valley of California. Because the Central Valley has experienced a substantial loss of wetland habitat, giant gartersnake populations are largely found in aquatic habitats associated with rice agriculture. In dry years, less water may be available for rice agriculture, resulting in less...
Authors
Jonathan P. Rose, Julia S. M. Ersan, Gabriel A. Reyes, K. Benjamin Gustafson, Alexandria M. Fulton, Kristen J. Fouts, Raymund F. Wack, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas) Reproductive frequency and size-dependence of fecundity in the Giant Gartersnake (Thamnophis gigas)
How reproductive output changes with age or size is a key life-history trait that can affect which demographic rates most influence population growth. Although many studies have investigated the reproductive ecology of gartersnakes, we know little about reproduction in the threatened Giant Gartersnake, Thamnophis gigas. We used X-radiography to determine reproductive status and estimated...
Authors
Jonathan P. Rose, Julia Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Construction and analysis of a giant gartersnake (Thamnophis gigas) population projection model Construction and analysis of a giant gartersnake (Thamnophis gigas) population projection model
The giant gartersnake (Thamnophis gigas) is a state and federally threatened species precinctive to California. The range of the giant gartersnake has contracted in the last century because its wetland habitat has been drained for agriculture and development. As a result of this habitat alteration, giant gartersnakes now largely persist in and near rice agriculture in the Sacramento...
Authors
Jonathan P. Rose, Julia S. M. Ersan, Glenn D. Wylie, Michael L. Casazza, Brian J. Halstead
Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape Behavioral response of giant gartersnakes (Thamnophis gigas) to the relative availability of aquatic habitat on the landscape
Most extant giant gartersnake (Thamnophis gigas) populations persist in an agro-ecosystem dominated by rice, which serves as a surrogate to the expansive marshes lost to flood control projects and development of the Great Central Valley of California. Knowledge of how giant gartersnakes use the rice agricultural landscape, including how they respond to fallowing, idling, or crop...
Authors
Gabriel A. Reyes, Brian J. Halstead, Jonathan P. Rose, Julia S. M. Ersan, Anna C. Jordan, Allison M. Essert, Kristen J. Fouts, Alexandria M. Fulton, K. Benjamin Gustafson, Raymund F. Wack, Glenn D. Wylie, Michael L. Casazza
An evaluation of the efficacy of using environmental DNA (eDNA) to detect giant gartersnakes (Thamnophis gigas) An evaluation of the efficacy of using environmental DNA (eDNA) to detect giant gartersnakes (Thamnophis gigas)
Detecting populations of rare or cryptic species is essential for their conservation. For species like giant gartersnakes (Thamnophis gigas), conventional survey methods can be expensive and inefficient. These sampling difficulties might be overcome by modern techniques that detect deoxyribonucleic acid (DNA) shed by organisms into the environment (eDNA). We evaluated the efficacy of...
Authors
Brian J. Halstead, Dustin A. Wood, Lizabeth Bowen, Shannon C. Waters, Amy G. Vandergast, Julia S. Ersan, Shannon M. Skalos, Michael L. Casazza