Determinants of clinal variation in life history of dusky salamanders (Desmognathus ocoee): prey abundance and ecological limits on foraging time restrict opportunities for larval growth

Abstract

Recent models argue that thermal environments are the major cause of ectotherm life-history clines. However, elevational clines in body size in the mountain dusky salamander Desmognathus ocoee (family Plethodontidae) shift from positive at hatching, to negative at metamorphosis to positive again as adults, and so are not consistent with this explanation. The clinal shift from hatching to metamorphosis was investigated by examining the clinal and seasonal feeding patterns of larval salamanders at high and low elevation sites in rockface and woodland habitats. Repeated cohort sampling was also used to examine clinal and seasonal patterns in body size and to estimate average growth rates. Larval growth in both rockface and woodland habitats was tightly correlated with feeding activity. Although temperature was found to vary between high and low elevation sites, the greatest growth occurred in a cold woodland habitat with a high elevation, and the lowest growth occurred in an adjacent rockface habitat. Because this difference in growth cannot be attributed to thermal differences, we conclude that local food resource levels are the predominant source of local differences in growth. These findings, clinal patterns of variation in other predatory salamanders, and experimental analyses in which both food and temperature are orthogonally manipulated, indicate that general models that single out temperature as the principle cause of ectotherm life-history clines should be viewed with caution.

Physiological constraints on organismal response to global warming: mechanistic insights from clinally varying populations and implications for assessing endangerment

“…We supposed that life-history clines (Bernardo 1994;Bernardo & Reagan-Wallin 2002;Bernardo & Agosta 2003) might reflect, in part, evolutionary adaptations of physiological tolerances of the populations (Garland & Adolph 1991;Feder et al 2000). Instead, we found a highly conserved metabolic response to a range of field temperatures (5-15 8C; figure 1) across both species from all sites ( figure 2a; table 1).…”

“…These populations experience dramatically different thermal and prey resource environments, and exhibit substantial phenotypic variation in most life-history traits (Bernardo 1994;Bernardo & Reagan-Wallin 2002;Bernardo & Agosta 2003). We studied resting metabolic rates as a function of temperatures experienced in the natural populations (figure 1).…”

Stream Salamanders Accurately Assess Size-Dependent Predation Threats

“…are suction feeders until metamorphosis and likely to be inefficient foragers if they spend significant time out of water (Deban and Marks 2002). Limited foraging success by D. fuscus could also reduce larval growth rate and body size, and lower survival (Gilliam and Fraser 1987;Skelly 1992;Bernardo and Agosta 2003).…”

Variación morfométrica y geográfica entre poblaciones de <em>Hypsiboas cordobae</em> (Anura: Hylidae) en Argentina

“…Especies distribuidas en un amplio rango geográfi-co a menudo presentan clinas térmicas en correlación con el tamaño corporal, en donde los adultos de la mayoría de las especies presentan mayor tamaño en ambientes más fríos (Bernardo & Agosta 2003;Angilletta et al 2004). En este sentido, la regla de Bergmann establece que los individuos de las especies que habitan ambientes con clima relativamente fríos tienden a ser más grandes que aquellos que habitan ambientes más cálidos (Angilletta et al 2004;de Queiroz & Ashton 2004).…”