Seedling size and survival for Chrysothamnus nauseosus

Seedling size and survival in relation to summer drought were examined for Chrysothamnus nauseosus growing under field and greenhouse conditions. In the field, summer survival rates were less than 2% annually for the three years monitored. The effect of initial seedling height on subsequent survival was examined in both the field and greenhouse by grouping seedlings into live and dead categories on each census date and comparing initial heights for seedlings in these categories. For a majority of the census dates, the initial height of surviving seedlings was greater than the initial height of those that subsequently died (significant differences ranged from 1 to 8 mm), indicating that seedlings that were taller at the initiation of the drought period had a higher probability of survival. In the greenhouse, taller seedlings had greater shoot and root biomass and rooting depth. Seedlings that are larger (i.e., taller and have greater aboveground biomass) in late spring appear to have a higher probability of surviving summer drought due to greater rooting depth and hence increased access to moisture in deeper soil layers. Seed availability and safe sites for germination were probably not limiting since large numbers of seedlings successfully germinated in a patchy pattern during the study period. Seedling size and probability of survival were not related to either seedling density or the distance to nearest seedling neighbor. Survival through summer drought appears to be the main limitation to seedling recruitment in this population.     

Controls on radial growth of mountain big sagebrush and implications for climate change

Mountain big sagebrush ( Artemisia tridentata Nutt. ssp. vaseyana ) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.     

Avian use of scoria rock outcrops

Avian use of scoria outcrop habitats was compared to use of sagebrush ( Artemisia spp.)/grassland habitats. Outcrop habitats exhibited higher species richness, total population density, density of lark sparrows ( Chondestres grammacus ), and density of rock wrens ( Salpinctes obsoletus ). Western meadowlarks ( Sturnella neglecta ) and vesper sparrows ( Pooecetes gramineus ) were more abundant in sagebrush/grassland habitats than in scoria outcrops. Habitat relationship models indicated that the unique plant community and structural diversity diversity provided by the scoria outcrops were correlated with increased avain use.     

Reproductive ecology of black-tailed prairie dogs in Montana

Reproductive ecology of black-tailed prairie dogs ( Cynomys ludovicianus ) was studied on the Charles M. Russell National Wildlife Refuge in northeastern Montana (1978–1980 and 1985). Breeding took place from early March through early April in most years. Persistent snow cover and below normal temperatures in February and March of 1978 delayed the start of breeding. Litter size averaged 4.4 but varied significantly among years. Average yearly litter size was correlated (r 2 = 0.986) with summer (June-September) precipitation prior to the breeding season. Largest average yearly litter size (5.0) followed record precipitation, while the smallest average yearly litter size (3.8) followed extreme drought. More than half the yearling females failed to breed while 88% of the females two years and older bred. Testes weights were greatest early in the breeding season and regressed rapidly during April.     

Some relationships of black-tailed prairie dogs to livestock grazing

Reproductive ecology of black-tailed prairie dogs ( Cynomys ludovicianus ) was studied on the Charles M. Russell National Wildlife Refuge in northeastern Montana (1978–1980 and 1985). Breeding took place from early March through early April in most years. Persistent snow cover and below normal temperatures in February and March of 1978 delayed the start of breeding. Litter size averaged 4.4 but varied significantly among years. Average yearly litter size was correlated (r 2 = 0.986) with summer (June-September) precipitation prior to the breeding season. Largest average yearly litter size (5.0) followed record precipitation, while the smallest average yearly litter size (3.8) followed extreme drought. More than half the yearling females failed to breed while 88% of the females two years and older bred. Testes weights were greatest early in the breeding season and regressed rapidly during April.     

Winter habitat-use pattern of elk, mule deer, and mosse in southwestern Wyoming

Habitat-use patterns of mule deer, elk, and moose were determined on two winter range near Kemmerer, Wyoming. Mule deer used areas with the least snow depth and dominated by sagebrush. Elk were located more often than expected on wind-swept hills but used sagebrush communities more frequently as snow depths increased. Moose were generally found associated with broad, riparian zones. All three species occasionally used the same area but differed in their use of specific vegetation types and topography.     

Body size, body composition, and behavior of juvenile Belding ground squirrels

Juvenile Belding ground squirrels were studied in the Sierra Nevada. Females were more trappable, had smaller home ranges, and tended to enter hibernation earlier than males. The primary sex ratio was 1:1. Individuals first emerged from the natal burrow at three to four weeks of age and a body weight of 35 g. Body weight and linear dimensions increased thereafter until hibernation began. Maximum prehibernatory weight of 200 to 260 g was attained at about 12 weeks of age. Prehibernatory fattening began at about six weeks of age. Maximum lipid stores attained weighed about 80 percent of the lean, dry body compartment. Seasonal changes occurred in weight of white and brown fat depots, adrenal glands, spleen, heart, kidneys, liver, and testes. Annual variations in snowpack and emergence schedule caused the reproductive period, and thus phenology of juveniles, to vary by as much as three weeks. The last animals to immerge were unusually small, being from late litters. Nonetheless, they may have had lipid stores sufficient for surviving hibernation.     

Timing, distribution, and abundance of kokanees spawning in a Lake Tahoe tributary

We counted kokanee spawners and carcasses every 1-7 days from mid-September through mid-November in 1991 and 1992 in Taylor Creek, a tributary to Lake Tahoe, California-Nevada. Less than 1% of the spawning run entered Taylor Creek before flow from Fallen Leaf Lake was increased on 2 October 1991; in 1992 the peak occurred on 30 September or 1 October after flows increased on 29 September. In both years spawners concentrated in the middle three of five stream reaches below the impassable Fallen Leaf Lake dam. From tab-and-recovery experiments, the average longevity of male spawners in the stream was 3.5 days in 1991 and 2.8 days in 1992, whereas the average female longevity was 2.0 days in 1991 and 2.3 days in 1992. Observed carcasses accounted for less than 10% of spawners counted, suggesting removal by scavengers or high predation on prespawners. An estimated 1928 males and 1309 females spawned in 1991, and 8021 males and 8712 females spawned in 1992. Our estimate of 3237 spawners in 1991 compared favorably to our estimate of 3520 ± 1474 prespawners staging in Lake Tahoe in mid-September. An index of kokanee abundance in Lake Tahoe has historically been based on 1-day surveys every 1 November since 1960; however, estimated total spawner abundance was 19 times higher than the annual index of 158 spawners in 1991, 141 times higher than the index count of 100 spawners in 1992. The index count and mean fork lengths of spawners (278 ± 10 mm [2 SE] for males, and 248 ± 3 mm for females) in 1991 and 1992 were the lowest on record.     

Waterfowl distribution and abundance during spring migration in southern Oregon and northeastern California

We used aerial surveys to study abundance and distribution of waterfowl (ducks, geese, swans, and coots) during spring in southern Oregon and northeastern California (SONEC). Total waterfowl-use days in SONEC during the 119-day, 5 January–3 May, spring period was similar during 2002 (127,977,700) and 2003 (128,076,200) and averaged 1,075,900 birds per day (bpd); these estimates should be adjusted upward 4%–10% to account for areas not surveyed. Waterfowl abundance peaked in mid-March in both years: 2,095,700 in 2002 and 1,681,700 in 2003. Northern Pintail ( Anas acuta ) was the most abundant species in both years, accounting for 25.6% of the 2002 and 24.5% of the 2003 waterfowl-use days. Pintail abundance peaked during the 13 March survey at 689,300 in 2002 and 532,100 in 2003. All other dabbling ducks accounted for 27.6% and 28.6%, diving ducks for 13.5% and 9.2%, geese for 24.6% and 29.3%, swans for 2.8% and 1.9%, and coots for 5.8% and 6.4% of the spring waterfowl-use days in SONEC during 2002 and 2003, respectively. Although use days changed little for total waterfowl (+0.08%) and dabbling ducks (–0.1%), diving duck use was lower (–32%), and goose use days were greater (+19%) in 2003 than in 2002. Distribution was similar in both years, with the most waterfowl use in the Lower (66%) and Upper (14%) Klamath subregions; 2%–6% occurred in each of the other subregions. Although the Lower Klamath subregion received the greatest overall waterfowl use, distribution among subregions varied among species and surveys, and all subregions were important during some part of the spring for 1 or more species. Peak spring abundance in SONEC during 2002 and 2003 averaged 50.3% of the midwinter abundance in California (all survey regions) and southern Oregon (69-3 survey region) for all waterfowl, 46.1% for dabbling ducks, 62.4% for diving ducks, 68.8% for geese, 109.4% for swans, and 43.8% for coots. Each spring, 75% of all waterfowl use in SONEC occurred on federal, state, or Nature Conservancy lands (i.e., protected areas). On protected areas there was a higher percentage of dabbling ducks (80.5%), geese (70.5%), and coots (81.5%) than diving ducks (60.4%) and swans (49%). Waterfowl use of Klamath Basin National Wildlife Refuge (NWR) averaged 42% greater during spring 2002–2003 (568,500 bpd) than during 1998–2001 (Gilmer et al. 2004). Numerous factors likely impacted magnitude and distribution of waterfowl use of SONEC during spring, including weather, waterfowl populations, SONEC habitat, and species ecology. SONEC is a critical spring staging area for waterfowl that winter in the Central Valley of California and other Pacific Flyway regions and should be a major focus area for waterfowl-habitat conservation efforts.     

LX.—Copepoda and Cladocera of the Cuillin Hills of the Isle of Skye

Summary

The life history of the African grasshopper Ornithacris turbida (Walker) was studied under controlled laboratory conditions. No phase variation was observed between isolated and crowded stock in respect of colour, morphometrics, weight of hatchlings or fledglings. All the females reared in isolation Had seven nymphal instars but in the case of the isolated males the majority had six but some had seven nymphal instars. This variation was also observed in the crowded stock for both males and females.

In isolation the mean nymphal life of 15 females was 78·7 ± 3·2 days, the mean for nine males having six instars was 59·9 ± 3·2 days and for five males having seven instars the mean nymphal life was 74·6 ± 3·8 days. Overall the nymphal life for the insects reared in crowds was slightly shorter, but no attempt was made to separate the insects having six or seven instars.

The stripes in the compound eye correlated with the number of nymphal instars. Colour changes in the compound eye coincided with overall body colour changes and maturation.

The mean maturation period of females reared in isolation was 101 days, varying from 72 to 158 days. The mean maturation period of the crowded females, estimated by the collection of the first egg-pod, was 73 days with a range of 62 to 84 days; when estimated by the collection of egg-pods averaging one per female it varied with the cage from 91 to 114 days. This suggests that maturation in the crowded females was quicker.

The isolated females lived longer than ones reared in crowded conditions, and laid more egg-pods. There was, however, no difference in the number of eggs per pod or their hatchability between crowded and isolated stock. In both cases 76% of the total number of eggs hatched. Hence overall the isolated females had a greater fecundity than those reared in crowds.

The average weight of a single hopper from isolated parents was 15·5 mg and that from crowded parents was 14·0 mg.     

Temporal changes in burrow structure of the thalassinidean ghost shrimps Trypaea australiensis and Biffarius arenosus

The thalassinidean ghost shrimps Trypaea australiensis and Biffarius arenosus are dominant burrowing macroinvertebrates of soft‐sediment habitats in Western Port, Victoria, Australia. Burrow structure has been described for both species but little is known about how the burrows change over time. This study used resin casting to investigate temporal variation by making burrow casts each month over a 12‐month period. It was found that the overall burrow morphology of both T. australiensis and B. arenosus was consistent over time, but in the warmer months (summer and spring), both species constructed burrows that were deeper and of greater volume than burrows constructed in winter and autumn. Possible reasons for this variation are discussed.     

Influence of soil water availability on competition among leafy spurge ( Euphorbia Esula ) and grasses

Some perturbations differentially influence invasive plant and grass production. For example, growth regulator herbicides and biological control agents can dramatically reduce leafy spurge production while having little or no influence on grass production, and overgrazing can reduce grass production while not substantially influencing leafy spurge production because cattle typically ingest little or no leafy spurge. To predict how grass production will respond to a perturbation that influences only leafy spurge and to predict how leafy spurge production will respond to a perturbation that affects only grasses, competitive relationships must be understood. Seeding mixtures of leafy spurge and 2 grasses were planted in experiments and grown for 127 days to determine whether different water application regimes influenced competition among these 3 species. Competition became less intense as the number of water applications increased. If this finding holds true under field conditions, then it indicates that competition is less intense in years and locations with numerous precipitation events. Competitive interactions (i.e., competition coefficients) were less variable when water was applied more frequently, but the ability of models to account for variation in plant weight (i.e., r 2 ) was not influenced by the frequency of water application. This suggests that models will predict invasive plant and grass biomass with equal accuracy in years with few or many precipitation events. Competitive effects were similar regardless of grass species, which suggests that grasses might be considered collectively in predicting response to perturbations in the field.     

The influence of fallen tree timing on spruce beetle brood production

This study compared brood production of the spruce beetle ( Dendroctonus rufipennis Kirby [Coleoptera: Curculionidae, Scolytinae]) in downed host material felled during summer and spring seasons on the Wasatch Plateau in south central Utah. Thirty-three matched pairs of Engelmann spruce ( Picea engelmannii Parry ex Engelm.) trees were selected for study in spring 1996. One tree of each pair was cut during August 1996 (summer-felled), and the other tree was cut in early April 1997 (spring-felled), so that trees would be colonized by spruce beetles of the same flight period. Brood adults were collected and counted from bark samples, which were removed from the top, bottom, and sides of all sample trees in October 1998. The number of emergent adults produced in June 1999 was determined from exit holes counted in bark samples removed from these same locations. Mixed-model procedures were used to compare differences in the mean number of adults produced in summer-felled versus spring-felled trees in each year. The results indicated that significantly fewer spruce beetles were produced in summer-felled trees than in spring-felled trees. More brood adults were also present in, or emerged from, unexposed bole aspects (bottom, north, and east) of sample trees than exposed aspects (top, south, and west). These findings suggest that disturbances providing spruce beetles with an abundance of fresh host material in the spring result in the greatest potential for spruce beetle production, particularly beneath unexposed bark aspects. Examples of such disturbances include snow avalanches, blowdown, and snow and ice damage.     

Intraspecific larval aggression in two species of Hyperini (Coleoptera: Curculionidae)

Two unusual types of behaviour (wandering and intraspecific aggressive behaviour) have been observed when rearing larvae of two species of the tribe Hyperini. Wandering of Hypera postica in search for food was observed in L1, L2 and L3 larvae, as well as in young L4 larvae. L1 larvae also disperse in response to crowding. Wandering of L2 to young L4 instars was a response to food shortage. Wandering of late L4 larva (‘prepupa’) occurs because of searching for a place to spin the cocoon and pupate. Encounters between the larvae may result in agonistic behaviour, and some larvae may die as a consequence of fighting. This aggression increases with food limitation. Agonistic intraspecific behaviour has not been described to date in weevil’s larvae and it probably may not occur under natural conditions when there is a plenty of food and larval densities are decreased by pathogens or parasitoids.     

Further details concerning the Darwin–Wallace presentation to the Linnean Society in 1858, including its submission on 1 July,not 30 June

Evidence from the Linnean Society’s ledger of papers received in 1858 points to 1 July as the date of submission of the Darwin–Wallace papers for the famous meeting of the same evening. It has been widely assumed, and repeatedly stated, that the submission was on 30 June. but this article shows that this seems to be a wrong assumption. Acceptance of this later submission date also provides an explanation of the ‘oddities’ in the letter of transmittal. In turn, this reading implies further details about the separate roles of Hooker and Lyell in the crucial 13 days before the meeting.     

Hatching phenology,life history and population dynamics of the Oriental clam shrimp Eulimnadia indocylindrova Durga Prasad and Simhachalam with notes on phenology patterns in the Spinicaudata

We studied the natural history, hatching phenology and egg bank composition of the Oriental spinicaudatan clam shrimp Eulimnadia indocylindrova Durga Prasad and Simhachalam using both field studies and ex situ sediment rehydration. Field observations revealed that hatching began very early (1–2 days) after inundation, and continued for about 5 days. Mature adults could be observed by 10 days, and they survived up to 16 days. The population showed a largely hermaphrodite-biased sex ratio (male:hermaphrodite 1:3) observed over three years, with a decrease in number of males throughout the hydroperiod. Both amphigenic and monogenic hermaphrodites were observed. The total lifetime fecundity recorded was about 300 eggs laid in multiple clutches. The egg bank composition showed a high proportion of intact eggs, indicative of predictable hydrations and low sediment adversity. Hatching began on the first day post-inundation for all successive cyclical hydration treatments, with peak hatching on days 2 and 3. Hatching rate was highest (57% of total hatching in successive cycles) for the first hydration, decreasing subsequently for the further hydrations. Hatching duration decreased with successive hydrations and was the longest (around 7 days) for the first hydration. Maximum hatching (93%) occurred in the first 10 days for the continuous hydration treatment. Overall, the total emergence of nauplii in successive hydrations was larger than that observed for the continuous hydration treatment, indicative of a risk-spreading strategy across hydroperiods. Early and concentrated naupliar emergence, along with decreased hatching durations for successive cycles, was observed for all the hydrations. A survey of literature revealed a general lack of data on hatching phenology of clam shrimps, particularly from tropical and sub-tropical regions. Based on the available data, it appears that hatching patterns, particularly high, early hatching fractions, are commonly observed in Spinicaudata species, and do not seem to differ much across biogeographical regions.     

Demographic characteristics of American marten populations in Jackson Hole, Wyoming

Some American marten population characteristics (numbers, density, body weights, sex and age ratios, natality, mortality-survivorship, immigration-emigration, home ranges) were studied at four sites in the southern part of the Greater Yellowstone Ecosystem, Teton County, Wyoming, in 1975-1979. Ninety-eight different martens were examined. Males (n = 25) weighed 1,111 g (± 110 SD, range 875-1,235), whereas females (n = 17) averaged 743 g (± 83 SD, range 600-900). Live-trapping showed sex ratios of 1.5M:1.0F, whereas carcasses showed 3.0M:1.0F. Of 27males that were aged, 12 (44%) were less than 1 year old and 2 were 9-10 years old. Of 10 females, 6 were less than 1 year old and 1 was 12-13 years old. The mean length of time a male was present on the major study area was 144 days (± 266 SD, range 1-1,364), and for females it was 145 days (± 45 SD, range 1-560). Home ranges for six males averaged 3.2 km 2 (± 20 SD, range 0.7-5.8) on the main study area. Some management implications are given.     

Foliage biomass and cover relationships between tree- and shrub-dominated communities in pinyon-juniper woodlands

Woodlands dominated by singleleaf pinyon ( Pinus monophylla Torr.and Frem.) and Utah ( Juniperus osteosperma [Torr.] Little) cover extensive areas in the Great Basin and Southwest. Both species are aggressive and can nearly eliminate the previous shrub-dominated community. Successional pathways from shrub-dominated communities before tree establishment to the tree-dominated communities that follow are known only for a few specific sites. How site growing conditions affect successional patterns needs further study. We compared the relationship of foliage biomass and percentage of cover between paired shrub-dominated and tree-dominated plots over several sites. Sites studied are from different elevation and topographic conditions on one mountain range. Foliage biomass in shrub-dominated plots had about a three-to-one variation over the range of site conditions sampled. Tree-dominated plots varied by about two-to-one. Cover in shrub-dominated plots had a four-to-one variation; cover in the tree-dominated plots varied by about two-to-one. Total foliage biomass in both tree- and shrub-dominated plots correlated best with the site index of height at 200 years of age. Variation in percentage of cover in both tree and shrub-dominated plots correlated best with elevation. Foliage biomass variation in shrub-dominated plots was proportional to the variation in the paired tree-dominated plots. A similar proportional relationship was present for percentage of cover between paired tree- and shrub-dominated plots. Foliage biomass was more sensitive to topographic differences than to cover. Variation in plant species sampled in the shrub-dominated plots correlated with total foliage biomass of the same plots. Species sampled also correlated with pinyon height at 200 years of age and total foliage biomass in the paired tree-dominated plots.     

Soil loosening processes following the abandonment of two arid western Nevada townsites

Soil compaction was measured at four sites within two abandoned mining camps in the western Great Basin Desert, Nevada. Bulk density and macroporosity values were generated from soil samples collected in areas of different land use intensities in camps that had been abandoned for approximately 70 years. Results show that significant differences remain in bulk density values between abandoned roads and undisturbed areas in both towns, and that the areas around foundation peripheries are still significantly more compacted in one town. There were no significant differences between land use groups as measured by macroporosity. Estimated soil recovery, based on a linear model using bulk density values, suggests that approximately 100 to 130 years are necessary for complete loosening to occur for abandoned roads, and that 100 or fewer years are necessary for complete amelioration of the foundation periphery areas. The wetter townsite, with more freeze-thaw days, finer-grained soils, and greater plant cover, had shorter recovery estimates. These finding suggest that the results of human-use impacts in arid areas may still be apparent long after disturbances cease.     

Effects of suspended sediment on leaf processing by Hesperophylax occidentalis (Trichoptera: Limnephilidae) and Pteronarcys californica (Plecoptera: Pteronarcidae)

The effects of suspended sediments on stream invertebrate detrital processing were investigated under replicated conditions in light and temperature-controlled chambers in the laboratory. The leaf-shredding insects Pteronarcys californica and Hesperophylax occidentalis were studied. Mean daily ingestion rates were lower among insects subjected to suspended sediments (1.5 and 3.0 g/l) than insects held in suspended sediment-free environments for seven of the eight trials. In five of the eight trials, mean ingestion rates were suppressed by ≥41% when compared to insects held in suspended sediment-free environments. Feeding inhibition was typically greater at the end of the feeding trials (14 days) than at the beginning (0–4 days). The effects of suspended sediments on ingestion were apparently related to the feeding status of the insects at the time of a trial. Insects in an active feeding mode were less influenced by suspended sediment than those in an inactive feeding mode. We conclude that, depending on the season and the duration of impact, suspended sediment can suppress processing of coarse particulate organic matter and thus adversely influence important nutrient and energy pathways in low-order streams.