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A.P. Clevenger and T.A. Langton, WTI
STATEWIDE ASSESSMENT OF ROAD RELATED RISKS TO REPTILE AND AMPHIBIAN SPECIES C. Brehme & R. Fisher, USGS In collaboration with A.P. Clevenger and T.A. Langton, WTI
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Comparative Risk Assessment
Objective: provide Caltrans and other agencies guidance to prioritize road mitigation efforts for amphibian and reptile species in California Which species are at highest risk from negative road impacts? Barrier and Depletion Effects
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California Species Snakes Lizards Salamanders Frogs & Toads Chelonids
Snakes Lizards Salamanders Frogs & Toads Chelonids Glossy Snake Striped Whipsnake Coast (Blainville's) Horned Lizard Desert Spiny Lizard Santa Cruz Black Salamander Southern California Slender Salamander California Red-legged Frog Pond Turtle (Northwestern & Southwestern) California Glossy Snake Spotted Leaf-nosed Snake Pygmy Short-horned Lizard Common Sagebrush Lizard Desert Slender Salamander Lesser Slender Salamander Oregon Spotted Frog Mohave Desert Tortoise Baja California Ratsnake Gopher Snake San Diego Banded Gecko Granite Night Lizard Garden Slender Salamander Black-bellied Slender Salamander Northern Red-legged Frog Sonora Mud Turtle Northern Rubber Boa Western Blind snake Orange-throated Whiptail Wiggins' Night Lizard California Tiger Salamander Channel Islands Slender Salamander Cascades Frog Southern Rubber Boa Long-nosed Snake Western Whiptail Western Skink Northwestern Salamander Kings River Slender Salamander Foothill Yellow-legged Frog Western Shovel-nosed Snake Western Patch-nosed Snake Coachella Fringe-toed Lizard Desert Night Lizard Long-toed Salamander Relictual Slender Salamander Sierra Nevada Yellow-legged Frog Racer Coast Patch-nosed Snake Western Banded Gecko Great Basin Collared Lizard Santa Cruz Long-toed Salamander Kern Plateau Slender Salamander California Chorus frog Forest Sharp-tailed Snake Western Groundsnake Desert Iguana Baja California Brush Lizard Southern Long-toed Salamander Kern Canyon Slender Salamander Lowland Leopard Frog Common Sharp-tailed Snake Southwesterm Black-headed Snake Panamint Alligator Lizard Ornate Tree Lizard Clouded Salamander Tehachapi Slender Salamander Coastal Tailed Frog Western Diamond-backed Rattlesnake California Black-headed Snake Mohave Fringe-toed Lizard Long-tailed Brush Lizard Black Salamander California Giant Salamander Southern Mountain Yellow-legged Frog Sidewinder Aquatic Gartersnake Peninsula Leaf-toed Gecko Mearns' Rock Lizard Arboreal Salamander Pacific Giant Salamander Pacific Chorus Frog Speckled Rattlesnake Sierra Gartersnake Colorado Desert Fringe-toed Lizard Wandering Salamander Ensatina Black Toad Western Rattlesnake Western Terrestrial Gartersnake Common Chuckwalla Slender Salamanders Yellow-blotched Ensatina Yosemite Toad Red Diamond Rattlesnake Giant Gartersnake Northern Alligator Lizard Greenhorn Mountains Slender Salamander Large-blotched Ensatina Sonoran Desert Toad Mojave Rattlesnake Two-striped Gartersnake Zebra-tailed Lizard California Slender Salamander Limestone Salamander Arroyo Toad Panamint Rattlesnake Checkered Gartersnake Common Side-blotched Lizard Fairview Slender Salamander Mount Lyell Salamander Western Spadefoot Ring-necked Snake Northwestern Gartersnake Granite Spiny Lizard Inyo Mountains Slender Salamander Scott Bar Salamander Great Plains Toad Regal Ring-necked Snake Common Gartersnake Island Night Lizard Hell Hollow Slender Salamander Dunn's Salamander Woodhouse's Toad Desert Nightsnake California red-sided Gartersnake Sierra Night Lizard San Gabriel Mountains Slender Salamander Del Norte Salamander Couch's Spadefoot Coast Nightsnake San Fransisco Gartersnake Sandstone Night Lizard Gabilan Mountains Slender Salamander Siskiyou Mountains Salamander Western Toad California Kingsnake Sonoran Lyresnake Western Fence Lizard Gregarious Slender Salamander Southern Torrent Salamander Great Basin Spadefoot California Mountain Kingsnake California Lyresnake Southern Alligator Lizard San Simeon Slender Salamander Rough-skinned Newt Red-spotted Toad Rosy Boa Baja California Coachwhip California Legless Lizard Sequoia Slender Salamander Red-bellied Newt Coachwhip Striped Racer Baja California Collared Lizard Santa Lucia Mountains Slender Salamander Sierra Newt San Joaquin Coachwhip Alameda Striped Racer Gilbert's Skink Coast Range Newt
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How can we determine which species are at highest risk?
Lots of species Few with road related studies Most species no information or anecdotal Avoid only focusing on only listed or iconic species What to do?
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Comparative Risk Assessment
Objective ranking based upon Species life history & space use Informed by road ecology literature
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Comparative Risk Assessment
Objective ranking based upon Species life history & space use Informed by road ecology literature
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Comparative Risk Assessment
Objective ranking based upon Species life history Informed by road ecology literature Meta-analysis (Rytwinski and Fahrig 2012) Relationship between life history characteristics and negative responses to roads Reptiles: Few studies Amphibians: High reproductive rates associated with lower population level effects Mammals: Strong relationship between body size, greater mobility, lower reproductive rates, and negative road effects.
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Stepwise Approach Individual Road Risk Population Level Risk
Species Level Risk 1-100 1-400 1-1200
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Individual Road Risk Probability of Encountering Road
Risk of Vehicular Collision Individual Road Risk 1-100
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Aq/Terr Individual Road Risk Movement Distance
Probability of Encountering Road Risk of Vehicular Collision Individual Road Risk Movement Distance Movement Frequency 1-100
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Linear Movement Distances: Diameter of home-range Migratory distances
Aq/Terr Probability of Encountering Road Risk of Vehicular Collision Individual Road Risk Movement Distance Movement Frequency 1-100 Linear Movement Distances: Diameter of home-range Migratory distances Not extreme environments Largest population movement distances used 95% Population buffer Distance upper tolerance interval Mean *SD Exclude rare dispersal events Terrestrial & Aquatic
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Aq/Terr Individual Road Risk
Probability of Encountering Road Risk of Vehicular Collision Individual Road Risk Movement Distance Movement Frequency Probability of moving onto road/ attempt crossing Crossing Speed Habitat Preference Road as attractant? Aq/Terr 1-100
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Individual Road Risk Population Level Risk
Probability of Encountering Road Risk of Vehicular Collision Individual Road Risk Population Level Risk Movement Distance Movement Frequency Probability of moving onto road/ attempt crossing Crossing Speed Habitat Preference Road as attractant? Fecundity Proportion of population at risk Territorial vs. non- Territorial vs. Migratory Aq/Terr 1-100 1-400
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Individual Road Risk Population Level Risk Species Level Risk
Probability of Encountering Road Risk of Vehicular Collision Individual Road Risk Population Level Risk Species Level Risk Movement Distance Movement Frequency Probability of moving onto road/ attempt crossing Crossing Speed Habitat Preference Road as attractant? Fecundity Proportion of population at risk Territorial vs. non- Territorial vs. Migratory Conservation Status USFWS, CDFW, ARSSC Priority Levels Range Size Aq/Terr 1-100 1-400 1-1200
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Risk Categories Semi-aquatic species with 2 scores (max used)
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Proportion by Group “High” & “Very High” Risk
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Proportion by Group “High” & “Very High” Risk
Gibbs an Shriver 2002, Andrews et al. 2015, Jackson et al. 2015
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Chelonids Photos by Chris Brown, CaliforniaHerps.com
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Snakes _______________________________________
Photos by Gary Nafis, Randy Rice, William Flaxington
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Frogs & Toads _______________________________________
Photos by Chris Brown, Jamie Bettaso, Donald Gudehus
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Salamanders & Newts _______________________________________
Photos by Chris Brown, wildherps.com
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Lizards ________________________________________
Photos by Chris Brown, James Cross, Jason Jones
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Initial Validation of Results
Special Status Species Caltrans PI Road Risk Level No. species in road risk level No. species with roads listed as threat % of Total No. Spp in road risk level Very High 26 14 54% 11 High 9 3 33% 5 Medium 8 1 13% 2 Low 0% Very Low
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Initial Validation of Results
Special Status Species Caltrans PI Road Risk Level No. species in road risk level No. species with roads listed as threat % of Total No. Spp in road risk level Very High 26 14 54% 11 High 9 3 33% 5 Medium 8 1 13% 2 Low 0% Very Low
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First Step First step in highlighting species that may be at high risk from roads transecting their habitat. CA-wide: circumstances for particular populations may elevate or reduce the risk. Reassess risk at local population level Incorporate behavioral models to specific road types Age structured & spatially explicit PVA Compare & predict outcomes mitigation alternatives
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Conclusions First objective comparative road risk assessment across multiple species Results consistent with road ecology literature. Identified known high risk listed species non-listed potential high risk species Applicable to other regions and taxa Highlight species that deserve consideration for aquatic or terrestrial road mitigation to reduce mortality and to maintain population connectivity
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Thank you!
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5 year Project- Caltrans
Primary Goals: provide Caltrans with Best Management Practices for the construction of wildlife crossings for amphibians and reptiles in California by 2020. BMPs would include specifications for size, materials, spacing, barrier walls, light and moisture requirements Photos: K. Gunsson, M. Trocme
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Components of Project Species Road Risk Assessment
Salamanders, Frogs, Toads, Turtles, Tortoises, Lizards, Snakes Literature Review by group GAP Analysis Field Studies Best Management Practices 2020
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Information Provided for each Species
Road Risk Scores Terrestrial & Aquatic Species and Population Levels 95% population distance -> “buffer distance” Confidence level (low to high) Surrogate Species (if used) Maps crosswalked with CEHC
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Barriers →Habitat Fragmentation
Road Impacts Barriers →Habitat Fragmentation reduced effective population size reduced ability to find mates and resources decreased abundance genetic structuring more prone to extirpation Road Mortality → Fragmentation Population Sink All of the above + Reduced survivorship Decline attributed to habitat loss, human modifications to the water flow regime (i.e. loss of natural cycles and scouring events), and the introduction of non-native predators.
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