Suburbs: dangers or drought refugia for freshwater turtle populations?

Abstract

Urbanization is one of the most rapidly expanding forms of habitat alteration worldwide. Wildlife differs in their responses to urbanization depending upon species and site‐specific factors. We used capture‐mark‐recapture to examine the abundance, population demographics, growth, and movements of the eastern long‐necked turtle (Chelodina longicollis) in Australia over 1 year in a suburban environment and an adjacent nature reserve during drought. Contrary to expectations, sex ratios, injury incidence, and frequency of juvenile size classes did not differ between turtles in the suburbs and the nature reserve. Moreover, turtles in the suburbs were nearly 3 times more abundant, grew 5 times faster, and had populations comprised of more adults in the larger size classes than nature reserve populations. These findings, together with net movements from the nature reserves into the suburbs, suggest that suburban water bodies were the higher quality habitat, effectively buffering turtles from temporal fluctuations in environmental conditions during drought. However, reserve managers and urban planners need to recognize that suburban water bodies have the potential to attract turtles from nearby reserves during drought, and that even low levels of persistent mortality during these travels across reserve boundaries may have consequences for populations of long‐lived vertebrates. © 2011 The Wildlife Society.

Reptile bycatch in a pest-exclusion fence established for wildlife reintroductions

“…2), suggesting turtles were attempting to access habitats and resources within the reserve. Previous research in this system revealed that, before the fence was built, drought conditions forced many turtles to move from the nature reserve into the larger suburban ponds for refuge (Rees, Roe, & Georges 2009;Roe, Rees, & Georges 2011), opposite the predominant direction we observed in our study. During drought, water levels in the nature reserve ponds tend to fluctuate more and experienced greater drying than the suburban ponds (Rees, Roe, & Georges 2009).…”

“…We used recapture probabilities derived from previous studies using similar trapping protocols in the same study system (Roe, Rees, & Georges 2011). We then calculated population density (number/ha) in the five surveyed ponds and extrapolated density estimates to all ponds within the fenced area to obtain a within-reserve population size estimate.…”

“…In each pond, we set four traps baited with sardines and liver once per month (5 consecutive days of trapping per month) from January 2012 to March 2013. More details on trapping methods are discussed by Roe, Rees, and Georges (2011). Turtles in the ponds were marked and measured in the same way as along the fence.…”

Ecological spillover dynamics of organisms from urban to natural landscapes

“…We found five studies that examined source-sink dynamics as related to urban spillover. Roe, Rees and Georges (2011) found that urban water sources act as drought refugia for the eastern long-necked turtle (Chelodina longicallis) in Australia, though accessing these desirable urban sites requires individuals from wildland populations to traverse a dangerous urbanized matrix, leading to high mortality and therefore a negative spillover effect on wildland populations. Kauffman, Pollock and Walton (2004) found that coastal populations of peregrine falcons (Falco peregrinus anatum) in southern California preferentially disperse to urban areas, which may act as a pseudo-sink given that the urban areas are used as sources for relocation efforts.…”

The effects of drought and fire in the extirpation of an abundant semi-aquatic turtle from a lacustrine environment in the southwestern USA

“…Examination of aerial photos during the drought revealed only two small ponds in the vicinity and it is unlikely that they could support a large number of turtles emigrating away from Elizabeth Lake across a landscape fragmented by roads and low-density housing. Others have demonstrated that turtles will use suburban water bodies during droughts that affect more ephemeral natural wetlands (Roe et al, 2011). However we were unable to sample ponds near Elizabeth Lake.…”