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Geology topics

N.J. Scott

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

At least 19 recordsLinked to original sources
USGS2002

Avian species richness in different-aged stands of riparian forest along the middle Rio Grande, New Mexico

Riparian forests are important for maintaining vertebrate species richness in the southwestern United States, but they have become restricted in distribution due to both historical and current management practices. In order to counteract continued loss of this habitat, several mitigation programs were developed in the middle Rio Grande Valley of New Mexico. Three areas ranging from 50 to 140 ha were revegetated with native trees using pole planting and cattle exclosures, and changes in vegetation structure were quantified after 2, 3, and 5 years of growth. As expected, the older site contained the most heterogeneous mix of plant species and the greatest structural diversity. We compared year-round avian use of the revegetated sites with a mature cottonwood forest site of approximately 30 years of age. As the revegetated sites matured and salient habitat features changed, the population dynamics of individual avian species and patterns of guild structure varied. The older revegetated sites showed a greater similarity to the mature cottonwood site, suggesting that reclamation efforts established quality riparian habitats for birds in as little as 5 years. The revegetated sites appeared especially important for Neotropical-migrant birds. We suggest that a mosaic of riparian woodlands containing mixtures of native tree and shrub species of different size classes is necessary to maintain avian species richness in the middle Rio Grande drainage, and probably throughout the southwestern United States.

New Mexico↗
USGS2002

Terrestrial habitat use by pacific pond turtles in a Mediterranean climate

The Pacific pond turtle (Clemmys marmorata) is a widespread aquatic turtle in the Pacific states, yet relatively little is known about its ecology. We radio-tracked 34 individuals during an 8 year period in 4 small coastal creeks in central California to determine their use of terrestrial upland habitats. Most of our turtles left the drying arroyos during late summer and returned after winter floods. Turtles spent an average of 111 days at these land refuges, which were located in woodland and coastal sage scrub habitats an average of 50 m from arroyos. Most gravid females left the creeks during June to oviposit in sunny upland habitats with low vegetation structure, such as grazed pastures. Nest sites were an average of 28 m from creeks. Terrestrial basking sites averaged 4.5 m from streams, but were only used for a few days. We believe the use of terrestrial upland sites was related to the Mediterranean climate and the resulting unique hydrodynamics of the small coastal arroyos (dry in summer and flooding in winter).

Southwestern Naturalist↗
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↗