USGS Science⌕ Search

SEARCH · USGS Science

Results for “Growth”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
USGS2006

Correlated growth and survival of juvenile spectacled eiders: Evidence of habitat limitation?

We studied the growth and survival of Spectacled Eider ( Somateria fischeri ) ducklings to 30 days of age along the lower Kashunuk River on the Yukon-Kuskokwim Delta from 1995 to 2000. We replicated this study at a second site, Kigigak Island, in 1999 and 2000. Age-adjusted estimates of duckling mass and survival at 30 days posthatching were highly variable. Duckling survival was consistently higher on Kigigak Island in 1999 and 2000, averaging 67%, while survival on the Kashunuk River averaged 45% during the same time period. Duckling survival was negatively related to hatching date. At the Kashunuk River site our data supported models that indicated age-adjusted mass varied with habitat type and declined with hatching date. Ducklings from Kashunuk River were heavier in 1999, while ducklings from Kigigak Island were heavier in 2000. However, we found a positive correlation between 30-day duckling survival and age-adjusted mass, suggesting a localized environmental effect on both parameters. We conclude that predation may be the proximate mechanism of mortality, but habitat conditions are likely the ultimate factors influencing duckling survival. Geographic variation in rates of duckling survival and apparent growth suggest that spatial heterogeneity in population vital rates is occurring at multiple levels.

Alaska↗
USGS2012

Age, Growth and Reproduction of the Eastern Mudminnow (Umbra pygmaea) at the Great Swamp National Wildlife Refuge, New Jersey.

Umbra pygmaea DeKay (Eastern Mudminnow) is one of four species of Umbridae in North America. There is little published life-history information on the species within its native range, particularly on age, growth, and reproduction. This study focuses on these aspects of the life history of this fish at the Great Swamp National Wildlife Refuge in Morris County, NJ. A total of 336 fish of seven species was collected from June 1978 through May 1979, with the Eastern Mudminnow comprising 74% of the total. The average annual growth increment in total length for the Eastern Mudminnow was 15.3 2.06 mm, with age-1 fish averaging 40 mm total length and age-5 fish, the oldest collected, averaging 107 mm total length. The length-weight relationship was log10W = -5.291 + 3.182 log10TL mm for males and log10W = -4.999 + 3.032 log10TL mm for females. We observed no statistically significant sexually dimorphic differences in length-weight relationships in this population. The ratio of females to males increased from a low of 0.6 (predominance of male fish) at age-1 to a high of 4.6 (predominance of females) at age-5. Annual mortality for age 2–5 fish ranged from 40–76% with a mean of 59 13%. Age-specific fecundity estimates ranged from 250 eggs/female at age-1 to 2168 eggs/female at age-5. The relationship of number of mature ova to age was best described by the exponential function y = 149.29e0.5287x, where y = age-specific fecundity and x = age in years. Ova ranged from 0.1–0.2 mm in diameter in June and July and averaged 1.41 0.1 mm (range = 1.29–1.62 mm) in early February prior to spawning. Peak spawning occurred in mid-April at temperatures of 9–12 °C, and all females were spent by late April (13–15 °C).

Northeastern Naturalist↗
USGS2007

Did debris-covered glaciers serve as pleistocene refugia for plants? A new hypothesis derived from observations of recent plant growth on glacier surfaces

This study proposes a new hypothesis: Debris-covered glaciers served as Pleistocene biological refugia. This is based on detailed studies of vascular plant growth on six debris-mantled glaciers, literally around the world, as well as many casual observations also across the globe. We find that such glaciers are quite common and are distributed globally. Using Carbon Glacier, Mount Rainier, U.S.A., as a type locality and case study, we show aspects of the floristic and structural diversity as well as spatial patterns of plant growth on the glacier surface. Migration strategies, root characteristics, and origin and dispersal strategies for vascular plant species are documented. Also reported are special microclimatic conditions in these areas allowing for this remarkable plant ecology. We find that alpine taxa can grow considerably below their usual altitudinal niche due to the cooler subsurface soil temperatures found on glacial debris with ice underneath, and that may have significantly altered the spatial distribution of such flora during full glacial conditions. This in turn creates previously undocumented areas from which alpine, and perhaps arctic, plant species reestablished in post-glacial time. This hypothesis is complementary to both the nunatak hypothesis and tabula rasa theory and possibly helps solve the ongoing controversy between them. ?? 2007 Regents of the University of Colorado.

Arctic, Antarctic, and Alpine Research↗
USGS2005

Juvenile frogs compensate for small metamorph size with terrestrial growth: Overcoming the effects of larval density and insecticide exposure

I reared four species of anurans ( Rana sphenocephala [Southern Leopard Frog], Rana blairi [Plains Leopard Frog], Rana clamitans [Green Frog], and Bufo woodhousii [Woodhouse's Toad]) for seven to 12 months in small, outdoor terrestrial enclosures (1 × 2 m) to examine the consequences of larval competition (via density) and contaminant exposure (via the insecticide carbaryl). I added six Rana clamitans , eight R ana sphenocephala , eight Rana blairi , and 10 Bufo woodhousii to terrestrial enclosures shortly after metamorphosis and recaptured them during the following spring. All anurans from low-density ponds were significantly larger than those from high-density ponds, but these size differences did not significantly affect survival to or size at spring emergence. However, R. sphenocephala , R. blairi , and R. clamitans that survived to spring had been larger at metamorphosis on average than those that did not survive; in contrast, B. woodhousii that survived the winter were smaller at metamorphosis on average than those that did not survive. Carbaryl exposure affected mass at metamorphosis of R. clamitans and B. woodhousii that were added to enclosures, but this difference disappeared or did not increase by spring emergence. Overall, exposure to carbaryl during the larval period did not have any apparent effects on survival or growth during the terrestrial phase. In my study, anurans were able to offset small size at metamorphosis with terrestrial growth, although there was a trend of reduced overwinter survival for ranid species that metamorphosed at a smaller size.

Journal of Herpetology↗
USGS2002

Effects of cottonwood leaf beetle Chrysomela scripta (Coleoptera: Chrysomelidae) on survival and growth of Fremont cottonwood ( Populus fremontii ) in northwest Colorado

Greenhouse and field studies were used to assess the effects of a cottonwood leaf beetle ( Chrysomela scripta ) outbreak on growth and survivorship of Fremont cottonwood ( Populus fremontii ) along a segment of the Yampa River in northwestern Colorado. Exposure of greenhouse-reared seedlings to either 1 or 3 larvae reduced survivorship and the shoot and root masses of surviving seedlings. In the field sapling survivorship in unmanipulated, naturally established patches of saplings was inversely related to the intensity of beetle damage noted the previous year in both 1998–1999 and 1999–2000. Floodplain saplings treated with the insecticide esfenvalerate during two growing seasons added more height and radial growth than untreated saplings. Field observations in riparian stands along the Yampa River indicated that beetles preferentially oviposited and fed on cottonwood seedlings over saplings and mature trees during late summer. Taken together, the greenhouse and field studies suggest herbivory by C. scripta is a major determinant of Fremont cottonwood distribution and abundance at the Yampa River site. Repeated surveys detected few or no beetles in stands along the neighboring but regulated Green River. We hypothesize that flow regulation, by reducing P. fremontii seedling abundance, precludes C. scripta from reaching outbreak status along the Green River.

Colorado↗
USGS2010

High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

Washington↗
USGS2003

Effects of pore‐water ammonia on in situ survival and growth of juvenile mussels (;Lampsilis cardium); in the St. Croix Riverway, Wisconsin, USA

We conducted a series of in situ tests to evaluate the effects of pore‐water ammonia on juvenile Lampsilis cardium in the St. Croix River (WI, USA). Threats to this river and its associated unionid fauna have accelerated in recent years because of its proximity to Minneapolis–St. Paul, Minnesota, USA. In 2000, caged juveniles were exposed to sediments and overlying water at 12 sites for 10 d. Survival and growth of juveniles was significantly different between sediment (mean, 47%) and water column (mean, 86%) exposures; however, these effects were unrelated to pore‐water ammonia. During 2001, juveniles were exposed to sediments for 4, 10, and 28 d. Pore‐water ammonia concentrations ranged from 0.3 to 62.0 μg NH 3 ‐N/L in sediments and from 0.5 to 140.8 μg NH 3 ‐N/L within exposure chambers. Survival (mean, 45, 28, and 41% at 4, 10, and 28 d, respectively) and growth (range, 3–45 μm/d) of juveniles were highly variable and generally unrelated to ammonia concentrations. Although laboratory studies have shown unionids to be quite sensitive to ammonia, further research is needed to identify the route(s) of ammonia exposure in unionids and to understand the factors that contribute to the spatial variability of ammonia in rivers.

Minnesota, Wisconsin↗
USGS2004

Petroleum reserves and undiscovered resources in the total petroleum systems of Iraq: Reserve growth and production implications

Iraq is one of the world's most petroleum-rich countries and, in the future, it could become one of the main producers. Iraq's petroleum resources are estimated to be 184 billion barrels, which include oil and natural gas reserves, and undiscovered resources. With its proved (or remaining) reserves of 113 billion barrels of oil (BBO) as of January 2003, Iraq ranks second to Saudi Arabia with 259 BBO in the Middle East. Iraq's proved reserves of 110 trillion cubic feet of gas (TCFG) rank tenth in the world. In addition to known reserves, the combined undiscovered hydrocarbon potential for the three Total Petroleum Systems (Paleozoic, Jurassic, and Cretaceous/Tertiary) in Iraq is estimated to range from 14 to 84 BBO (45 BBO at the mean), and 37 to 227 TCFG (120 TCFG at the mean). Additionally, of the 526 known prospective structures, some 370 remain undrilled. Petroleum migration models and associated geological and geochemical studies were used to constrain the undiscovered resource estimates of Iraq. Based on a criterion of recoverable reserves of between 1 and 5 BBO for a giant field, and more than 5 BBO for a super-giant, Iraq has 6 super-giant and 11 giant fields, accounting for 88% of its recoverable reserves, which include proved reserves and cumulative production. Of the 28 producing fields, 22 have recovery factors that range from 15 to 42% with an overall average of less than 30%. The recovery factor can be increased with water injection, improved and enhanced oil recovery methods (IOR and EOR) in various reservoirs, thus potentially increasing Iraq's reserves by an additional 50 to 70 BBO. Reserve growth is a significant factor that has been observed, to some extent, in nearly all Iraqi oil fields. Historically, producing fields have shown an average growth of 1.6 fold (or 60%) in their recoverable reserves over a 20-year period (1981-2001). With periodic assessments of reservoirs, application of available technology, and an upgrading of facilities, increases in reserves are expected in the future.

GeoArabia↗
USGS2002

Characterization and modeling of illite crystal particles and growth mechanisms in a zoned hydrothermal deposit, Lake City, Colorado

Mean thickness measurements and crystal-thickness distributions (CTDs) of illite particles vary systematically with changes in hydrothermal alteration type, fracture density, and attendant mineralization in a large acid-sulfate/Mo-porphyry hydrothermal system at Red Mountain, near Lake City, Colorado. The hydrothermal illites characterize an extensive zone of quartz-sericite-pyrite alteration beneath two deeply rooted bodies of magmatic-related, quartz-alunite altered rock. Nineteen illites from a 3000 ft vertical drill hole were analyzed by XRD using the PVP-10 intercalation method and the computer program MudMaster (Bertaut-Warren-Averbach technique). Mean crystallite thicknesses, as determined from 001 reflections, range from 5-7 nanometers (nm) at depths from 0-1700 ft, then sharply increase to 10-16 nm at depths between 1800-2100 ft, and decrease again to 4-5 nm below this level. The interval of largest particle thickness correlates strongly with the zone of most intense quartz-sericite-pyrite alteration (QSP) and attendant high-density stockwork fracturing, and with the highest concentrations of Mo within the drill core. CTD shapes for the illite particles fall into two main categories: asymptotic and lognormal. The shapes of the CTDs are dependent on conditions of illite formation. The asymptotic CTDs correspond to a nucleation and growth mechanism, whereas surface-controlled growth was the dominant mechanism for the lognormal CTDs. Lognormal CTDs coincide with major through-going fractures or stockwork zones, whereas asymptotic CTDs are present in wallrock distal to these intense fracture zones. The increase in illite particle size and the associated zone of intense QSP alteration and stockwork veining was related by proximity to the dacitic magma(s), which supplied both reactants and heat to the hydrothermal system. However, no changes in illite polytype, which in other studies reflect temperature transitions, were observed within this interval.

Colorado↗
USGS2020

Vapor-bubble growth in olivine-hosted melt inclusions

Melt inclusions record the depth of magmatic processes, magma degassing paths, and volatile budgets of magmas. Extracting this information is a major challenge. It requires determining melt volatile contents at the time of entrapment when working with melt inclusions that have suffered post-entrapment modifications. Several processes decrease internal melt inclusion pressure, resulting in nucleation and growth of a vapor bubble and, time permitting, diffusion of volatiles (especially CO2) into the vapor bubble. Methods exist that attempt to reconstruct the entrapped CO2 contents, but they are difficult to apply and yield inconsistent results. Here, we explore bubble growth, evaluate CO2 reconstruction approaches, and develop improved experimental and computational approaches. Piston-cylinder experiments were conducted on olivine-hosted melt inclusions from Seguam (Alaska, USA) and Fuego (Guatemala) volcanoes at the following conditions: 500-800 MPa, 1140-1200 °C for Seguam and 1110-1140 °C for Fuego, 4-8 wt% H2O in the KBr brine, and run durations of 10-120 minutes. Heated melt inclusions form well-defined S-CO2 trends that can be described by degassing models. CO2 contents are enriched by a factor of ~2.5, on average, relative to those of the glasses within unheated melt inclusions, whereas S contents of heated and unheated melt inclusion glasses overlap, indicating insignificant amounts of S partition into the vapor bubble. Low closure temperatures enable CO2 diffusion into vapor bubbles during quench upon eruption, while a higher closure temperature for S limits its loss to vapor bubbles. We evaluate the timescales of post-entrapment processes and use the results to develop a new computational model to restore entrapped CO2 contents: MIMiC (Melt Inclusion Modification Corrections). Heated melt inclusion data are used as a benchmark to evaluate of the results from MIMiC and other published methods of CO2 reconstruction. The methods perform variably well. Key advantages to our experimental rehomogenization technique are that it enables accurate measurements of CO2 contents and allows for large quantities of melt inclusions to be rehomogenized efficiently. Our new computational model produces more accurate results than other computational methods, has similar accuracy to the Raman method of CO2 reconstruction in cases where Raman can be applied (i.e., no C-bearing phases in bubble), and can be applied to the vast body of published melt inclusion data. To obtain the most robust data on bubble-bearing melt inclusions, we recommend taking both experimental- and MIMiC-based approaches.

American Mineralogist↗
USGS2011

Anatomy of a metabentonite: Nucleation and growth of illite crystals and their coalescence into mixed-layer illite/smectite

The illite layer content of mixed-layer illite/smectite (I/S) in a 2.5 m thick, zoned, metabentonite bed from Montana decreases regularly from the edges to the center of the bed. Traditional X-ray diffraction (XRD) pattern modeling using Markovian statistics indicated that this zonation results from a mixing in different proportions of smectite-rich R0 I/S and illite-rich R1 I/S, with each phase having a relatively constant illite layer content. However, a new method for modeling XRD patterns of I/S indicates that R0 and R1 I/S in these samples are not separate phases (in the mineralogical sense of the word), but that the samples are composed of illite crystals that have continuous distributions of crystal thicknesses, and of 1 nm thick smectite crystals. The shapes of these distributions indicate that the crystals were formed by simultaneous nucleation and growth. XRD patterns for R0 and R1 I/S arise by interparticle diffraction from a random stacking of the crystals, with swelling interlayers formed at interfaces between crystals from water or glycol that is sorbed on crystal surfaces. It is the thickness distributions of smectite and illite crystals (also termed fundamental particles, or Nadeau particles), rather than XRD patterns for mixed-layer I/S, that are the more reliable indicators of geologic history, because such distributions are composed of well-defined crystals that are not affected by differences in surface sorption and particle arrangements, and because their thickness distribution shapes conform to the predictions of crystal growth theory, which describes their genesis.

Montana↗
USGS2009

Contributions of vital rates to growth of a protected population of American black bears

Analyses of large, long-lived animals suggest that adult survival generally has the potential to contribute more than reproduction to population growth rate (λ), but because survival varies little, high variability in reproduction can have a greater influence. This pattern has been documented for several species of large mammals, but few studies have evaluated such contributions of vital rates to λ for American black bears ( Ursus americanus ). We used variance-based perturbation analyses (life table response experiments, LTRE) and analytical sensitivity and elasticity analyses to examine the actual and potential contributions of variation of vital rates to variation in growth rate (λ) of a population of black bears inhabiting the Pisgah Bear Sanctuary in the southern Appalachian Mountains of North Carolina, using a 22-year dataset. We found that recruitment varied more than other vital rates; LTRE analyses conducted over several time intervals thus indicated that recruitment generally contributed at least as much as juvenile and adult survival to observed variation in λ, even though the latter 2 vital rates had the greater potential to affect λ. Our findings are consistent with predictions from studies on polar bears ( U. maritimus ) and grizzly bears ( U. arctos ), but contrast with the few existing studies on black bears in ways that suggest levels of protection from human-caused mortality might explain whether adult survival or recruitment contribute most to variation in λ for this species. We hypothesize that λ is most strongly influenced by recruitment in protected populations where adult survival is relatively high and constant, whereas adult survival will most influence λ for unprotected populations.

Ursus↗
USGS2005

Bait stations, hard mast, and black bear population growth in Great Smoky Mountains National Park

Bait-station surveys are used by wildlife managers as an index to American black bear ( Ursus americanus ) population abundance, but the relationship is not well established. Hard mast surveys are similarly used to assess annual black bear food availability which may affect mortality and natality rates. We used data collected in Great Smoky Mountains National Park (GSMNP) from 1989 to 2003 to determine whether changes in the bait-station index (ΔBSI) were associated with estimated rates of bear population growth (λ) and whether hard mast production was related to bear visitation to baits. We also evaluated whether hard mast production from previous years was related to λ. Estimates of λ were based on analysis of capture-recapture data with the Pradel temporal symmetry estimator. Using the Akaike's Information Criterion (AIC), our analysis revealed no direct relationship between ΔBSI and λ. A simulation analysis indicated that our data were adequate to detect a relationship had one existed. Model fit was marginally improved when we added total oak mast production of the previous year as an interaction term suggesting that the BSI was confounded with environmental variables. Consequently the utility of the bait-station survey as a population monitoring technique is questionable at the spatial and temporal scales we studied. Mast survey data, however, were valuable covariates of λ. Population growth for a given year was negatively related to oak mast production 4 and 5 years prior. That finding supported our hypothesis that mast failures can trigger reproductive synchrony, which may not be evident from the trapped sample until years later.

North Carolina, Tennessee↗
USGS2006

Growth and sustainability of black bears at White River National Wildlife Refuge, Arkansas

The black bear ( Ursus americanus ) population at White River National Wildlife Refuge is isolated and genetically distinct, but hunting occurs adjacent to refuge boundaries and females with cubs are removed annually for a reintroduction project. We trapped and radiotracked bears to determine level of exploitation and compare methods for estimating population growth and sustainability. We captured 260 bears (113 M:147 F), 414 times, from 1998 through 2003. Survival estimates based on radiotracking and mark–recapture indicated that hunting and translocations were significant sources of loss. Based on mark–recapture data (Pradel estimator), the annual population growth rate (λ) averaged 1.066 (SE = 0.077) when translocation removals occurred and averaged 0.961 (SE = 0.155) when both harvest and translocations occurred. Estimates of λ based on a population simulation model (program RISKMAN) averaged 1.061 (SD = 0.104) and 1.100 (SD = 0.111) when no removals occurred, 1.003 (SD = 0.097) and 1.046 (SD = 0.102) when translocations occurred, and 0.973 (SD = 0.096) and 1.006 (SD = 0.099) when both harvest and translocations occurred, depending on the survival rate estimates we used. The probability of population decline by >25% over a 10-year period ranged from 13.8 to 68.8%, given our estimated removal rates. We conclude that hunting and translocation losses are at or exceed the maximum the population is capable of sustaining. Although extinction risks of this important bear population are low over the near term, it should continue to be closely monitored by state and federal agencies. The mark–recapture method we used to estimate λ proved to be a reliable alternative to more costly population modeling methods.

Arkansas↗
USGS1970

Growth, age at metamorphosis, and sex ratio of northern brook lamprey in a tributary of southern Lake Superior

Growth was studied of five year classes of the northern brook lamprey, Ichthyomyzon fossor, collected from the Sturgeon River during intervals between treatment of the stream with a lampricide. Growth varied considerably among year classes. Larvae of the 1963 year class were slightly longer at age II and 30% longer at age III than the III-group larvae of the 1960 year class. About 6% of 558 III-group lampreys of the 1963 year class had metamorphosed by 17 August 1966. Although the sex ratio of larvae was about 1:1, 97% of the metamorphosed lampreys were males. The distribution of pigmentation on the caudal fin and upper lip in ammocoetes less than 40 mm long permitted accurate and rapid separation of northern brook lampreys from the sea lamprey, Petromyzon marinus.

Copeia↗
USGS2003

Growth and secondary production of aquatic insects along a gradient of Zn contamination in Rocky Mountain streams

Secondary production estimates from several Rocky Mountain streams were used to test hypotheses about the effects of chronic metal contamination on insect populations and ecosystem processes. Quantitative samples of chemistry, habitat, and benthic insects were collected monthly during the ice-free period (May–November) from five 2 nd - to 3 rd -order streams that varied primarily in Zn contamination. Secondary production was estimated for the 19 dominant taxa using increment-summation, size-frequency, and P/B methods. Uncertainty was estimated by bootstrapping estimates of mean abundance, biomass, and cohort production intervals. Secondary production of metal-sensitive Heptageniidae ( Rhithrogena robusta , Cinygmula spp., and Epeorus longimanus ) was lower in lightly to moderately contaminated streams than in reference streams. Experiments were done to determine whether herbivore growth was influenced by food quality in contaminated streams. Growth estimates from field and microcosm experiments revealed that low mayfly production in contaminated streams was caused mostly by reduced population abundances. Production of predatory stoneflies was also lower in contaminated streams than reference streams. Estimates of the trophic basis of production revealed that, although the relative contribution to community production from various food sources was similar among streams, total production attributable to algae and animal prey declined in contaminated streams. Much of the reduction in herbivory in contaminated streams was the result of lower production of heptageniids, especially R. robusta . Assemblage and taxon-specific estimates of secondary production were sensitive to variation in metal contamination and indicated that relatively low metal concentrations may have ecosystem-wide consequences for energy flow.

Journal of the North American Benthological Societ↗
USGS1993

Chick growth in the California Gull: Relationships with hatching asynchrony and parental age

Chick mass and growth during a six-day period were investigated among California Gulls ( Larus californicus ) in 1979 and 1980. In broods of two, levels of hatching asynchrony between siblings ranging from 0 - 4 days were observed. Hatching asynchrony resulted in initial mass differences between siblings that persisted and accelerated with time. Fledging success was unrelated to hatching asynchrony but was related to large offspring mass and increased with parental age. Parental age was unrelated to hatching asynchrony but heavily influenced the brood's gain in mass. Six days after the second egg hatched, chick mass was highest at those levels of hatching asynchrony where mean age of parent was highest. Mass differences between siblings at day six were related to fledging success only to the extent that rapid growth among siblings of older parents usually resulted in large differences in mass. Implications of results to investigations of Lack's brood reduction hypothesis are discussed.

Wyoming↗
USGS1983

Late Holocene ice wedges near Fairbanks, Alaska, USA: Environmental setting and history of growth

Test trenches excavated into muskeg near Fairbanks in 1969 exposed a polygonal network of active ice wedges. The wedges occur in peat that has accumulated since about 3500 yr BP and have grown episodically as the permafrost table fluctuated in response to fires, other local site conditions and perhaps regional climatic changes. Radiocarbon dates suggest one or two episodes of ice-wedge growth between about 3500 and 2000 yr BP as woody peat accumulated at the site. Subsequent wedge truncation evidently followed a fire that charred the peat. Younger peat exhibits facies changes between sedge-rich components that filled troughs over the ice wedges and woody bryophytic deposits that formed beyond the troughs. A final episode of wedge development took place within the past few hundred years. Pollen data from the site indicate that boreal forest was present throughout the past 6000 yr, but that it underwent a gradual transition from a predominantly deciduous to a spruce-dominated assemblage. This change may reflect either local site conditions or a more general climatic shift to cooler, moister summers in late Holocene time. The history of ice-wedge growth shows that wedges can form and grow to more than 1 m apparent width under mean annual temperatures that probably are close to those of the Fairbanks area today (-3.5°C) and under vegetation cover similar to that of the interior Alaskan boreal forest. The commonly held belief that ice wedges develop only below mean annual air temperatures of -6 to -8°C in the zone of continuous permafrost is invalid.

Alaska↗