Landscape influence on the local distribution of western pond turtles

Abstract

Abstract. Spatial and temporal scales are important for understanding habitat associations because organisms have neither unbounded mobility nor perfect knowledge of their environment, but still must make decisions on where to seek food, shelter, and mates. Semi-aquatic turtles exemplify the need to evaluate potential habitat characteristics at a range of scales, because their ectothermy makes these animals particularly sensitive to local environmental conditions, yet their limited mobility spatially constrains selection of microsites. Microsite choice may also be sensitive to larger geographic context. We explored site occupancy and abundance of western pond turtles (Actinemys [Emys] marmorata) as a function of environmental variables over a range of spatial scales up to that of the entire watershed. We modeled occupancy at ponds and abundance at river sites using data from surveys conducted at 50 ponds and 58 river locations throughout the South Umpqua, Umpqua, and North Umpqua watersheds in western Oregon, USA in 1999-2000. The South Umpqua supported the greatest abundance of western pond turtles in rivers and the highest rates of occupancy in ponds. No turtles were detected in rivers of the North Umpqua, and only low numbers were detected in ponds in that watershed. Increasing amount of potential relative solar radiation was associated with increased probability of pond occupancy, particularly in the North Umpqua watershed. Pond turtle abundance in rivers increased with increasing distance to nearest pond, decreasing area of nearby ponds, and increasing area of nearby wetland habitat of all types, particularly in the Klamath Mountain and Coast Range physiographic provinces, which dominate the South Umpqua and Umpqua watersheds, respectively. Western pond-turtle occupancy and abundance varied with both broadscale and fine-scale habitat features, not solely to the fine-scale features that are most often measured.

High freshwater turtle occupancy of streams within a sustainably managed tropical forest in Borneo

“…We scaled all climatological, environmental, and logging-associated covariates to have a mean of 0 and a standard deviation of 1 prior to modeling. We tested collinearity between covariates using Spearman's rank correlation in the package Hmsic version 4.2-0 (Harrell 2019) and removed all correlated covariates ( | r | > 0.7) from subsequent analysis. Additionally, as our data set consisted of 82 subplots (sampling units), with unique covariate values nested within 8 VES river reach sites, we included a random effect in all models to account for the nested spatial effect among subplots within the same VES river reach.…”

“…Quantifying abundance and occupancy are an effective approach for determining the effects of disturbances, such as logging, on turtles (Horn and Gervais 2018, Čapkun‐Huot et al 2021). However, the detection of turtles is typically imperfect because of observer error (Nichols et al 2000), low population density, cryptic behaviors of individuals, or environmental conditions that influence the likelihood of detection (Gu and Swihart 2004).…”

Pond Occupancy by Western Pond Turtles in the Diablo Range of Santa Clara County, California

“…The presence of bullfrogs did not appear to impact WPT occupancy, a finding supported by Horn & Gervais (2018), who found no predictive relationship between bullfrog presence and pond occupancy by WPT in the North Umpqua watershed of Southwestern Oregon. Bullfrogs are capable of only consuming small sized turtles.…”

“…However, the same study found that proximity to other wetlands was not a significant predictor for the Blanding's turtle (Emydoidea blandingii), due to it being a vagile species. Horn & Gervais (2018) found that WPT abundance in rivers increased as distance to nearest ponds and wetland habitat types increased, suggesting that WPTs are more likely to disperse to ponds when they are closer. Whether there is a significant difference between WPT occurrence in stock ponds and distance to the nearest WPT population is unknown.…”

“…Basking structures positioned away from sunlight may be less useful than ones that are directly facing the sun. In the North Umpqua watershed, Oregon, WPT occupancy in ponds increased with more solar radiation (Horn & Gervais, 2018), but the relationship between solar radiation and basking structure placement has not been investigated. Nevertheless, to determine whether the number of basking structures plays a role in stock pond occupancy, a much larger sample size will be needed for future studies.…”