Climatic and geographic predictors of life history variation in Eastern Massasauga (Sistrurus catenatus): A range-wide synthesis

Abstract

Elucidating how life history traits vary geographically is important to understanding variation in population dynamics. Because many aspects of ectotherm life history are climate-dependent, geographic variation in climate is expected to have a large impact on population dynamics through effects on annual survival, body size, growth rate, age at first reproduction, size–fecundity relationship, and reproductive frequency. The Eastern Massasauga (Sistrurus catenatus) is a small, imperiled North American rattlesnake with a distribution centered on the Great Lakes region, where lake effects strongly influence local conditions. To address Eastern Massasauga life history data gaps, we compiled data from 47 study sites representing 38 counties across the range. We used multimodel inference and general linear models with geographic coordinates and annual climate normals as explanatory variables to clarify patterns of variation in life history traits. We found strong evidence for geographic variation in six of nine life history variables. Adult female snout-vent length and neonate mass increased with increasing mean annual precipitation. Litter size decreased with increasing mean temperature, and the size–fecundity relationship and growth prior to first hibernation both increased with increasing latitude. The proportion of gravid females also increased with increasing latitude, but this relationship may be the result of geographically varying detection bias. Our results provide insights into ectotherm life history variation and fill critical data gaps, which will inform Eastern Massasauga conservation efforts by improving biological realism for models of population viability and climate change.

Sunning themselves in heaps, knots, and snarls: The extraordinary abundance and demography of island watersnakes

“…Consequently, it is unclear whether high survival leads to increased body size, large body size leads to increased survival, or some other mechanism underlies variation in both size and survival. Given that our 14 study sites are separated by less than 20 km, variation in climatic conditions is likely to be small and certainly far less than that seen in range‐wide demonstrations of variation in survival (Jones et al., 2012) or body size (Hileman, King, et al., 2017; Hileman, Powell, et al., 2017). Study sites differ in the extent of human activity and may differ in predator abundance, but how these variables affect mortality awaits further investigation.…”

Geographic variation in body size and its relationship with environmental gradients in the Oriental Garden Lizard,Calotes versicolor

“…Climate change is predicted to have a large impact on the distributions of fauna (Hileman et al., ). Reptiles may be particularly vulnerable due to their thermal constraints and life cycles (Hileman et al., ). Our results suggest that multiple factors might affect geographic variation of body size in C. versicolor .…”

Eastern massasauga demography and extinction risk under prescribed‐fire scenarios

“…Climatic conditions within Cass County are intermediate for the eastern massasauga range based on 30‐year annual climate normals (Hileman et al ). For example, mean annual frost‐free days, temperature, and precipitation were recorded as 175 days, 8.8 °C, and 1,034.8 mm at a weather station within 11.2 km of the study site.…”

“…The prescribed‐fire projection models we constructed incorporated site‐specific parameter estimates from a population that appears to be healthy and where poaching and road mortality are likely negligible. Eastern massasauga population parameters are known to vary geographically (Aldridge et al , Jones et al , Hileman et al ) and road mortality in this species has been documented elsewhere (Choquette and Valliant ) and may even be a primary source of mortality for some populations (Shepard et al , Baker et al ). Thus, caution is warranted in extrapolating the results from this study to other managed eastern massasauga populations.…”

“…With few exceptions (Bailey et al , Jones et al ), demographic estimates for the eastern massasauga are qualitative in nature (Faust et al ) or based on quantitative data from populations near the northern (Middleton and Chu , Jones et al ), southern (Dreslik , Aldridge et al , Dreslik et al ), or eastern (Johnson et al ) range limits for the species. Although these studies yield valuable information, eastern massasaugas at these sites may exhibit climate‐dependent life‐history extremes (Hileman et al ), which highlights the need for equally detailed information from more centrally located populations where the largest number of eastern massasauga populations may still persist (Szymanski et al ). Assessing population viability for centrally located populations using poorly estimated parameters or surrogate estimates from range extremes may result in misleading predictions (Patterson and Murray , Hernández‐Camacho et al ).…”