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Geology topics

N.J. Scott

Publications and source records attributed to N.J. Scott.

At least 37 records · Page 2Linked to original sources
USGS1993

Ecologically correlated morphological variation in tadpoles of the leopard frog, Rana chiricahuensis

Interspecific differences in tadpole morphology among leopard frogs of the Rana pipiens complex may represent adaptations to larval habitats. We documented variation in tadpole morphology among populations of R. chiricahuensis and compared intraspecific patterns of variation to those among species. Traits that exhibit similar patterns of variation in intraspecific and interspecific comparisons may represent adaptations to different larval habitats. Tadpoles of R. chiricahuensis found in streams have more contrasting melanic patterns on the tail, thicker dorsal fins, and somewhat larger tail muscles than those from ponds. Unexpected differences between tadpoles from two stream habitats might represent nonadaptive morphological variation. Alternatively, such differences may represent different morphological responses to similar selection pressures, to subtly different aquatic habitats (different selective regimes), or different developmental responses to different environmental cues. Parallels in variation for some morphological traits within and among tadpoles of leopard frog species support, but do not demonstrate, the contention that those morphological differences represent adaptations to larval habitats.

Journal of Herpetology↗
USGS1989

Distribution, habitat, and future of Harter's water snake, Nerodia harteri, in Texas

Detailed studies of the distribution and habitat use of the endemic Texas snake Nerodia harteri were conducted from 1979 to 1987. The Brazos water snake N. h. harteri is restricted to the upper Brazos River drainage; it is found in about 303 km of stream plus two reservoirs, Possum Kingdom Lake and Lake Granbury. The Concho water snake, N. h. paucimaculata occupies 396 stream-km in the Concho-Colorado River drainage, and about 25 km of lake. As such, Harter's water snake has one of the smallest ranges of any North American snake species. Medium to large, flat rocks on an unshaded shore for hiding places and rocky shallows for feeding grounds appear to be important for juveniles. There is an ontogenetic habitat shift in N. harteri that may also be common in many other Nerodia. We found that adult N. harteri are not restricted to rocky riffles in flowing rivers but can inhabitat a much wider range of habitats in pools and lakes. Several sections of both the Brazos and Colorado rivers are uninhabited by N. harteri, apparently because juvenile habitat is lacking or scarce. Riffles are more isolated on the uninhabited stretches, and they may be too far apart to recolonize after catastrophic local population extinctions. Past dam projects have eliminated populations of Nerodia harteri through habitat destruction by inundation and siltation. Fragmentation of populations may also prevent recolonization after local extinctions. A major dam being constructed on the Colorado River near Stacy, McCullough County, will inundate about 18% of the known habitat of Nerodia h. paucimaculata and perhaps degrade another 8% or more. A unique agreement whereby the dam-constructing authority will construct artificial habitats and fund biological studies could ameliorate the negative effects of the dam and reservoir on populations of the Concho water snake.

Journal of Herpetology↗
USGS1988

Habitat requirements of New Mexico’s endangered salamanders

We measured habitat components for two state-listed endangered salamanders in New Mexico in 1986 and 1987. Both species are restricted to mesic environments within high-elevation, mixed coniferous forests. Steep slope and high elevation were the most useful variables for predicting the occurrence of Jemez Mountains salamanders and Sacramento Mountain salamanders, respectively. Although the discriminant models show some predictive value in detecting salamanders based on habitat variables, we believe that the best survey technique is ground-truth surveys in wet weather. A better fit of the discriminant models might be obtained by including variables not measured e.g., fire and logging history, and soil characteristics. We offer interim management guidelines as a result of our analysis.

New Mexico↗