Effects of urbanization on the population structure of freshwater turtles across the United States

Abstract

Landscape-scale alterations that accompany urbanization may negatively affect the population structure of wildlife species such as freshwater turtles. Changes to nesting sites and higher mortality rates due to vehicular collisions and increased predator populations may particularly affect immature turtles and mature female turtles. We hypothesized that the proportions of adult female and immature turtles in a population will negatively correlate with landscape urbanization. As a collaborative effort of the Ecological Research as Education Network (EREN), we sampled freshwater turtle populations in 11 states across the central and eastern United States. Contrary to expectations, we found a significant positive relationship between proportions of mature female painted turtles (Chrysemys picta) and urbanization. We did not detect a relationship between urbanization and proportions of immature turtles. Urbanization may alter the thermal environment of nesting sites such that more females are produced as urbanization increases. Our approach of creating a collaborative network of scientists and students at undergraduate institutions proved valuable in terms of testing our hypothesis over a large spatial scale while also allowing students to gain hands-on experience in conservation science.

Reexamining effects of urbanization on population structure of freshwater turtles: response to Bowne et al. 2018

“…This phenomenon is thought to have increased over time with expanding road networks (Gibbs & Steen 2005) and is likely sufficient to impact population sizes (Gibbs & Shriver 2002). However, Bowne et al (2018) conclude that adult painted turtle (Chrysemys picta) sex ratios are not affected by roads and that urbanization produces female-biased populations.…”

“…Sex ratios (proportion female) of painted turtles (a) by U.S. states (MA, Massachusetts; MD, Maryland; MI, Michigan; MN, Minnesota; NC, North Carolina; NJ, New Jersey; NY, New York; OH, Ohio; PA, Pennsylvania; WI, Wisconsin) and latitude (black curve, binomial fit; dashed and dotted line, hypothetical 50:50 sex ratio) and (b) in 22 study ponds in Bowne et al. () arrayed from the highest proportions of males to highest proportions of females detected (point sizes, proportional to adult sample sizes; below the dashed black line, sex ratios significantly male biased; gray dashed and dotted line, equal sex ratios at parity).…”

“…However, Bowne et al. () conclude that adult painted turtle ( Chrysemys picta ) sex ratios are not affected by roads and that urbanization produces female‐biased populations.…”

“…Although money for conservation is limited, much has been used to mitigate the impacts of roads and urbanization on turtles. However, Bowne et al.’s () results could be used to suggest that resources may be better allocated elsewhere. Therefore, we felt it necessary to better understand why this study's conclusions differed from our expectations.…”

A broader approach to understanding urbanization effects on freshwater turtles: reply to Lambert and Steen 2019

“…We thank Lambert and Steen () for the attention they have given to our paper (Bowne et al. ) and welcome productive discussions of how human activities affect turtle populations. Scientists who study the conservation biology of turtles do so from a commitment to scientific integrity and preservation of these species.…”