Abstract
Three congeneric lizards from the southeastern United States (Plestiodon fasciatus, P. inexpectatus, and P. laticeps) exhibit a unique nested distribution. All three skink species inhabit the US Southeast, but two extend northward to central Ohio (P. fasciatus and P. laticeps) and P. fasciatus extends well into Canada. Distinct interspecific differences in microhabitat selection and behavior are associated with the cooler temperatures of the more Northern ranges. We hypothesized that interspecific differences in metabolic temperature sensitivity locally segregates them across their total range. Resting oxygen consumption was measured at 20°, 25° and 30°C. Plestiodon fasciatus, from the coolest habitats, exhibited greatly elevated oxygen consumption compared to the other species at high ecologically-relevant temperatures (0.10, 0.17 and 0.83 ml O2. g-1. h-1 at 20°, 25° and 30°C, respectively). Yet, P. inexpectatus, from the warmest habitats, exhibited sharply decreased oxygen consumption compared to the other species at lower ecologically-relevant temperatures (0.09, 0.27 and 0.42 ml O2. g-1. h-1 at 20°, 25° and 30°C, respectively). Plestiodon laticeps, from both open and closed microhabitats and intermediate latitudinal range, exhibited oxygen consumptions significantly lower than the other two species (0.057, 0.104 and 0.172 ml O2. g-1. h-1 at 20°, 25° and 30°C, respectively). Overall, Plestiodon showed metabolic temperature sensitivities (Q10s) in the range of 2–3 over the middle of each species’ normal temperature range. However, especially P. fasciatus and P. inexpectatus showed highly elevated Q10s (9 to 25) at the extreme ends of their temperature range. While morphologically similar, these skinks are metabolically distinct across the genus’ habitat, likely having contributed to their current distribution.
Highlights
Ecological physiologists have long questioned how species distribution is affected by local environment, phenotype and phylogenesis
P. inexpectatus, from the warmest habitats, exhibited sharply decreased oxygen consumption compared to the other species at lower ecologically-relevant temperatures (0.09, 0.27 and 0.42 ml O2. g-1. h-1 at 20 ̊, 25 ̊ and 30 ̊C, respectively)
In P. laticeps was the relationship between mass and snout-to-vent length (SVL) significant
Summary
Ecological physiologists have long questioned how species distribution is affected by local environment, phenotype and phylogenesis. Adult P. laticeps represent an obvious exception to these generalities because they are considerably larger than adult P. fasciatus and P. inexpectatus, allowing them to exploit different resources [2, 6, 7]. The ecological physiology of these closely related species is still poorly known, but they are of interest because they occur in regional sympatry and may be using the same set of resources. This is an apparent violation of both the competitive exclusion hypothesis and Jordan’s Rule, which states that an organism’s closest relative would be found either in adjacent, dissimilar habitats or separate but similar habitats [8,9,10]. While an important point to consider, this contravention of Jordan’s Rule may be irrelevant if one considers fine scale differences in microhabitat rather than broader habitat generalizations
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