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LATITUDINAL VARIATION IN RATES OF OVERWINTER MORTALITY IN THE LIZARD UTA STANSBURIANA
Author(s) -
Wilson Byron S.,
Cooke David E.
Publication year - 2004
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/03-4075
Subject(s) - transect , latitude , biology , temperate climate , range (aeronautics) , overwintering , ecology , lizard , mortality rate , seasonality , predator , demography , predation , geography , materials science , geodesy , sociology , composite material
The relatively shorter growing seasons, lower temperatures, and severe winter weather associated with higher latitudes have long been assumed to limit the size of populations, and therefore to constrain the geographical ranges of species. In particular, conspicuous instances of catastrophic mortality during periods of severe winter weather suggest that losses to “winterkill” may often determine latitudinal range limits. However, actual comparisons of overwinter mortality among latitudinally separated populations have been exceedingly rare, and no such study has focused on temperate‐zone lizards, one of the groups thought to experience greater overwinter mortality at higher latitudes. Here we examine latitudinal variation in overwinter mortality among seven populations of the side‐blotched lizard ( Uta stansburiana ) along a transect spanning nearly 15° of latitude in the western United States. We used standard mark–recapture techniques to estimate daily mortality rates for the fall through spring (overwinter) period for three consecutive years. Using these data, we directly test the hypothesis that rates of overwinter mortality increase with increasing latitude. Surprisingly, daily mortality rates during the overwinter period appear to be lower— not higher—at higher latitudes. And, in spite of longer winters in the north, even total seasonal losses to winterkill appear, if anything, to be lower at higher latitudes. Mortality rates during the overwinter period were consistently lower than during the activity season, and this pattern was especially pronounced at cold northern sites. These observations indicate that winterkill may not be an important determinant of annual mortality for these populations, and they support the view that predator‐mediated mortality during the activity season is the primary source of population loss. Because Uta are inactive during cold winter weather, and because their primary predators are either similarly inactive (e.g., other lizards and snakes) or may have migrated south (e.g., birds), predator–prey encounter rates are lower during higher latitude winters.