Riparian vegetation along the middle Snake River, Idaho: zonation, geographical trends, and historical changes

A baseline study was conducted on an 83-km free-flowing reach of the Snake River between Swan Falls Dam and the Idaho-Oregon border. The research had 2 components: (1) field characterization and inventory of existing riparian flora, vegetation, and environment (soils, topography, streamflow), and (2) determination and mapping, using a geographic information system, of historic changes in riparian vegetation based on a time series (1938-39, 1957, 1969, 1987) of aerial photographs. The flora was diverse, with 185 species of vascular plants identified, 63 of which were exotics. Vegetation was structured vertically along the riverbank gradient into lifeform-defined habitat types: emergent, riparian shrub-forb, tree, transitional grass-shrub, and upland. Riverbank seepage, probably of agricultural origin, blurred zonation patterns on some sites and added species to the overall flora. Upstream-downstream differences existed in the physical characteristics and vegetation of river subreaches. Coverage of riparian woodland, island riparian and total riparian vegetation, and area of islands increased since the 1930s, with the greatest changes in the 1969-1987 interval. Possible contributing facts were (1) significant declines in annual minimum flows since the 1950s, (2) decreases in peak flows following the completion of Swan Falls Dam and some upstream dams since the 1920s, (3) introduction and spread of exotic tree species ( Elaeagnus angustifolia and Tamarix spp.) and (4) possible effects of intensive agriculture on river sediment load and soil nutrients. The introduction and proliferation of purple loosestrife ( Lythrum salicaria ) could have considerable future effects on vegetation-channel dynamics in the middle Snake River.     

Characteristics of natal and non-natal kit fox dens in the northern Chihuahuan Desert

We studied kit fox den characteristics of the northern McGregor Range of Fort Bliss Military Reservation, New Mexico, during 1994 to 1995. Twenty radio-collared kit foxes used 132 different dens, including 16 natal dens. Kit fox dens were located primarily in creosote-dominated habitat found in relatively flat, well-drained terrain. Natal dens were virtually indistinguishable from non-natal dens; however, natal den entrances were taller than non-natal den entrances. Entrances found at all dens were oriented more frequently toward the northwest and southwest. Kit foxes used more dens during the breeding (January-February) and pup-rearing season (May-July) than during gestation.     

Ecological comparison of sympatric populations of sand lizards ( Cophosaurus texanus and Callisaurus draconoides )

Sympatric populations of Cophosaurus texanus and Callisaurus draconoides were periodically sampled from March 1973 through April 1974 at Burro Creek, Mohave County, Arizona. Callisaurus were also sampled at Rock Valley, Nye County, Nevada. Sex ratios were skewed in favor of males in the adult Cophosaurus but were equal in both adult populations of Callisaurus. Both species became sexually mature as yearlings. Mean clutch sizes were 3.55 (±0.83) for Cophosaurus, and 4.25 (±1.08) and 5.07 (±1.33) for Callisaurus at Burro Creek and Rock Valley respectively. Evidence of multiple clutches was exhibited by both species. Egg weight/body weight ratios for both species and clutch weight/body weight ratios for Cophosaurus were notably smaller than previously reported. At Burro Creek both species were highly insectivorus, with orthopterans comprising the largest food group of each. Niche overlap for food was high at the ordinal level, but at the familial level it is apparent that Callisaurus probably fed in the more xeric areas of the riparian habitat. No differences were found in the temperature responses of these two lizards. However, minor temporal separations and substantial spatial partitioning were observed. Callisaurus preferred sandy open areas, while Cophosaurus preferred the presence of some rocks and boulders.     

Trapping methods for rangeland insects in burned and unburned sites: a comparison

Different insect trapping methods were compared weekly on recently burned and nearby unburned rangeland in the Great Basin of western Utah. Flight traps (or wing traps) collected the most specimens (total = 4,916 at burned site, 4,384 at unburned site) but represented the fewest species (no more than 11 spp./wk at either site); this method was not recommended because of difficulty in removing specimens from adhesive. Water traps amassed the next largest number of specimens (￣x ± SE/wk = 150.9 ± 75.3 at burned site, 158.0 ± 66.4 at unburned site) and the most species (￣x ± SE/wk = 21.6 ± 6.4 at burned site, 35. 1 ± 4.5 at unburned site). The weekly collections from pitfall traps between the sites were significantly different (P < .05) in number of specimens (￣x ± SE/wk = 8.1 ± 1.5 at burned site, 19.7 ± 4.8 at unburned site) and species (￣x ± SE/wk = 4.7 ± 0.6 at burned site, 9.5 ± 2.0 at unburned site). Malaise traps were the most convenient. Black Malaise traps collected more specimens (￣x ± SE/wk = 99.8 ± 19.4 at burned site, 90.6 ± 16.4 at unburned site) and species (￣x ± SE/wk = 22.9 ± 3.9 at burned site, 19.4 ± 6.5 at unburned site) than white malaise traps (specimens: ￣x ± SE/wk = 72.1 ± 22.4 at burned site, 87.1 ± 31.2 at unburned site; species: ￣x ± SE/ wk = 19.7 ± 6.6 at burned site, 16.4 ± 5.4 at unburned site), although this difference was not significant.     

Atomic structure holography using thermal neutrons.

The idea of atomic-resolution holography has its roots in the X-ray work of Bragg and in Gabor's electron interference microscope. Gabor's lensless microscope was not realized in his time, but over the past twelve years there has been a steady increase in the number of reports on atomic-resolution holography. All of this work involves the use of electrons or hard X-rays to produce the hologram. Neutrons are often unique among scattering probes in their interaction with materials: for example, the relative visibility of hydrogen and its isotopes is a great advantage in the study of polymers and biologically relevant materials. Recent work proposed that atomic-resolution holography could be achieved with thermal neutrons. Here we use monochromatic thermal neutrons, adopting the inside-source concept of Sz?ke, to image planes of oxygen atoms located above and below a single hydrogen atom in the oxide mineral simpsonite.     

Reproductive pair correlations and the clustering of organisms.

Clustering of organisms can be a consequence of social behaviour, or of the response of individuals to chemical and physical cues. Environmental variability can also cause clustering: for example, marine turbulence transports plankton and produces chlorophyll concentration patterns in the upper ocean. Even in a homogeneous environment, nonlinear interactions between species can result in spontaneous pattern formation. Here we show that a population of independent, random-walking organisms ('brownian bugs'), reproducing by binary division and dying at constant rates, spontaneously aggregates. Using an individual-based model, we show that clusters form out of spatially homogeneous initial conditions without environmental variability, predator-prey interactions, kinesis or taxis. The clustering mechanism is reproductively driven-birth must always be adjacent to a living organism. This clustering can overwhelm diffusion and create non-poissonian correlations between pairs (parent and offspring) or organisms, leading to the emergence of patterns.