Pogonomyrmex ewyheei nest site density and size on a minimally impacted site in central Oregon

Little is known about the basic characteristics of the western harvester ant ( Pogonomyrmex owyheei ) in the absence of anthropogenic disturbances. We examined the role of P. owyheei as an agent of disturbance in an area of semiarid vegetation in central Oregon known as the Horse Ridge Research Natural Area (HRRNA) that has been largely free of livestock grazing and other significant anthropogenic influences for over 23 yr. We determined density and size characteristics of nest sites and estimate total area cleared by P. owyheei activities on HRRNA. From random sampling of twenty-five 0.04-ha plots we found a mean nest density/standard error of 1.6(± 0.16) nests/0.04 ha. Mean area cleared per nest site was 4.8 m 2 , which results in an estimated barren area of 46,080 m 2 on the 240-ha HRRNA. Comparing our findings to others on P. owyheei and P. occidentalis , we found nest density and mean cleared area to be in the middle range of reported observations under a variety of land-use influences. The literature suggests that moderate disturbance may increase nest site density, but little relationship exists between disturbance history and mean size of nest sites.     

Composition and abundance of periphyton and aquatic insects in Sierra Nevada, California, stream

The species composition of periphyton and benthic insect communities and abundances of common taxa (&;gt;0.1&;#37; of individuals) were examined during snow-free months in Convict Creek, a permanent snowmelt- and spring-fed stream in the Sierra Nevada of California. The communities were highly diverse. The most abundant taxa in the periphyton were diatoms ( Achnanthes minutissima, Cocconeis placentula lineata, Cymbella microcephala, C. sinuata, Fragilaria construens, F. crotonensis , Navicula spp., Synedra acus , and S. rumpens ), except in late spring and summer when several seasonal blue-green algae ( Chamaesiphon incrustans, Lyngbya spp. and Oscillatoria spp.) are at their maximum densities. Most common periphyton taxa vary systematically in abundance with season, but relative abundances of taxa also appear to be influenced by streambed scouring and by concentrations of ambient nutrients. Data on population densities and length frequencies of larval and nymphal stages of common benthic insects and occurrences of pupal and adult stages were examined to determine life history patterns. Taxa hatching in winter and spring and abundant as immatures in late spring include ephemeropterans ( Epeorus longimanus, Drunella flavilinea , and Caudatella heterocaudata ), plecopterans ( Calineuria californica, Doroneuria baumanni, and Pteronarcys princeps ) and dipterans ( Cryptolabis sp.). Common taxa hatching in late spring or summer are the plecopteran Malenka ( californica? ) and the trichopterans Arctopsyche grandis and Rhyacophila acropedes . Several bivoltine and multivoltine ephemeropterans ( Baetis devinctus and B. tricaudatus ) and dipterans ( Simulium spp. and Chironomidae) have summer cohorts. Taxa hatching in late summer or autumn and most abundant in autumn include ephemeropterans ( Baetis spp., Ephemerella infrequens, Epeorus dulciana, Ironodes lepidus , and Paraleptophlebia pallipes ), trichopterans ( Hydropsyche oslari, Lepidostoma spp., Glossosoma califica, Micrasema sp., Brachycentrus americanus, Neophylax sp., and Rhyacophila vaccua ) and dipterans ( Antocha monticola, Pericoma sp., and Chironomidae). Major recurring events that may influence life history patterns and structure of the benthic insect community are (1) near-freezing, nighttime winter water temperatures and occasional anchor ice, (2) a prolonged period of high discharge in late spring and early summer (3) a brief summer, and (4) a prolonged period of moderate stream discharge in autumn when the substratum is stable and food is abundant.     

Influence of fine sediment on macroinvertebrate colonization of surface and hyporheic stream substrates

Colonization of macroinvertebrates was assessed in a stream impacted by inputs of fine sediments. Colonization was examined at the stream surface and within the hyporheos with Whitlock-Vibert (W-V) boxes. Hyporheic areas accumulated much greater amounts of all size categories of sediment. No significant difference was observed in the amounts of organic matter accumulated at either depth. Only 150-μm sediment had significant effects on macroinvertebrate total numbers and number of taxa. Total numbers of invertebrates at 30 cm were only 20% of those at the surface. Canonical Correspondence of Analysis indicated that the strongest influence on macroinvertebrates colonizing W-V boxes at the surface was stream size and secondarily fine sediments. Within the hyporheos, abundance of fine sediment was the dominant influence on macroinvertebrate assemblages. Impacts of sedimentation on hyporheic environments can have significant and persistent impacts on streams.     

Population structure and ecological effects of the crayfish Pacifastacus leniusculus in Castle Lake, California

The recent appearance of the ""California crayfish,"" Pacifastacus leniusculus , in Castle Lake, California, and interest in its potential impacts on the lake ecosystem provided motivation for a study of the population structure and habitat use of this species and its effects on aquatic macrophytes. Mark-recapture studies indicated that the total number of adult (3 + yr or older) crayfish in the lake was ca 10,100 individuals, yielding an estimate of lakewide crayfish density in preferred crayfish habitats of 0.13 adults m -2 . Using mean body mass of individuals, we estimated that ambient biomass density was 5.9 g m -2 . Length-weight relationships determined for captured individuals were sex dependent, with males having greater body mass for a given carapace length. Length-frequency and weight-frequency diagrams indicated that P. leniusculus reaches larger sizes in Castle Lake than do populations of P. leniusculus in ultraoligotrophic Lake Tahoe. Population-wide, males were significantly larger in both carapace length and body mass than females. We also examined sex dependence of interhabitat differences in crayfish body size by comparing animals trapped in rocky areas with those from areas with macrophytes and soft sediments. No significant differences in overall body size were found between habitats, but a significant habitat-sex interaction term occurred because the sex-dependent size differences were more pronounced in sediment than in rocky areas. Exclosure and enclosure experiments indicated that crayfish had large but differential impacts on Castle Lake macrophyte species, as the abundance of two of the dominant species ( Chara sp., Potamogeton richardsonii ) declined in the presence of crayfish and, in one case, increased in exclosures. These effects occurred via both consumptive and nonconsumptive mechanisms. These studies indicate that and expanding population of P. leniusculus in Castle Lake may be producing sizable impacts on the littoral zone habitat.     

Ecological investigation of a suspected spawning site of Colorado squawfish on the Yampa River, Utah

On 5 July 1981, 13 adult Colorado squawfish were found in spawning condition at river mile 16.5 in the Yampa River, a major tributary to the Green River. An investigation was undertaken to quantitatively describe this section of the river to gain insights on the spawning requirements of this endangered species. The substrate at the suspected spawning site was cobble with large interstitial spaces devoid of organics, silts, or clays. It appeared that larvae of several fish species utilized these cobble areas and the associated voids. Diurnal sampling indicated that larval drift occurred between 0100 and 0125 hours. Substrate size also appeared to be a dominant factor in fish distribution. Feeding intensities of these fish corresponded to macroinvertebrate drift.         

Substrate color matching in the grasshopper, Circotettix rabula (Orthoptera: Acrididae)

Mechanisms important in maintaining substrate color matching in the grasshopper, Circotettix rabula, were studied near Aspen, Colorado, during the summers of 1968 – 70. Studies concentrated on populations on gray shale and red sandstone substrates. In both areas, collections revealed appreciable numbers of mismatched phenotypes among all age groups. The possibility of developmental homochromy was examined by observation of nymphs held in rearing boxes on matching and contrasting soil colors. The behavioral selection of matching substrate colors was tested by preference experiments. While not negating the possibility of these mechanisms, results suggested that they were of minor importance. Predation experiments, using Sceloporus lizards, demonstrated significant levels of selective predation on mismatched nymphs on both red and gray substrates. Experiments with bird and mammal predators, using adult grasshoppers, gave similar results. Release - recapture experiments with marked adults in areas of red and gray substrates showed markedly higher disappearance rates for mismatched animals. These results are interpreted to indicate that selective predation on mismatched animals is a major factor in maintaining substrate color matching in this species.     

Regional assessment of wadable streams in Idaho, USA

There has been a resurgence in applying bioassessment techniques for evaluating and monitoring the biological integrity of stream ecosystms. In all cases biological metrics have been refined to account for regional variation in aquatic habitats and fauna. This study evaluated environmental and macroinvertebrate properties for wadable streams in 3 major ecoregions of Idaho: Northern Basin and Range, Snake River Plain, and Northern Rocky Mountain. These 3 ecoregions constitute > 80% of the land area in Idaho. Reference streams were delineated from test streams in each ecoregion using standard habitat assessment protocols. (Plafkin et al. 1989). Multiple discriminant analysis effectively determined habitat (quantified measures) and macroinvertebrate differences between reference and test streams within ecoregions, although the results suggested that quantifiable habitat measures (e.g., water chemistry and nutrients) and biotic measures based on taxonomic groups (e.g., % Elmidae) improved the discriminatory power of evaluation procedures. Our results support the contention of a multi-metric approach for assessing differences among streams within an ecoregion. Lastly, individual metrics differed in their importance for evaluating stream condition among ecoregions, further emphasizing the importance of regionally stratifying metric selection or scoring procedures.     

Changes in the littoral macroinvertebrate assemblages of Oak Mere from 1980 to 1998

Data on the macroinvertebrate assemblages of Oak Mere, England are presented for the period 1980 to 1998. There was a marked fall in species richness and numbers of individuals associated with a fall in surface level. Correlations between surface level, areas of vegetation and aspects of the macroinvertebrate assemblages are demonstrated.     

Aquatic macroinvertebrate assemblages associated with root masses of water hyacinths,Eichhornia crassipes (Mart.) Solms-Laubach, 1883 (Commelinales: Pontederiaceae) in Taabo Lake,Ivory Coast

We examined aquatic macroinvertebrates associated with Eichhornia crassipes roots at five sampling sites in Taabo Lake. An average density of 1644 individuals (ind.)/m² was recorded. In total, 68 macroinvertebrate taxa belonging to 34 families and 14 orders were identified. Among these, Insecta was predominant (77.94%). The highest densities were recorded at Taabo cité during both rainy and dry seasons. Taxon diversity differences were not observed among all stations according to a Kruskal–Wallis test. High densities of predators were recorded. Next most prevalent in the trophic structure were detritivores. Indicator taxa analysis, using the Indval method, showed that stations upstream of the lake were characterized by eight taxa, while 11 appeared as indicators of the station near the dyke. Predators and herbivores dominated within those indicators. Sites near bays were distinguished by 18 indicator taxa with a predominance of predators and detritivores. Conductivity, NH₄ ⁺, temperature, PO₄ ^3?, turbidity and dissolved oxygen were parameters that strongly influenced the macroinvertebrate community.     

Female life‐history characteristics of the Mosor rock lizard,Dinarolacerta mosorensis (Kolombatović, 1886) from Montenegro (Squamata: Lacertidae)

Analysis of the female life history of the poorly studied endemic Balkan lizard species Dinarolacerta mosorensis was conducted on three population samples from Montenegro. One clutch is produced annually. Females mature at body sizes of 56–57 mm snout–vent length (SVL), attained at age 3–4 years. SVL increases with age. The average clutch size ranged from 4.3 to 5.2 eggs, and was significantly positively correlated with maternal SVL in two population samples. There were no trade‐offs between egg size/offspring size and clutch size, nor between variation in egg size/offspring size and maternal SVL. The incubation period averaged 26.5 days, while hatching success in captivity was 72%. Significant positive correlations were found between the hatchling mass and egg mass and size, and also between the hatchling total length and egg width and volume. There was a significant negative relationship between the hatchling mass and incubation duration.     

Effects of livestock grazing exlosure on aquatic macroinvertebrates in a montane stream, New Mexico

Aquatic macroinvertebrate populations inhabiting reaches of a stream within areas excluded from livestock grazing for a decade were markedly different from those in grazed areas when density, biomass, biotic condition indices, and mean chi square indices of the two populations were compared. Increased densities and biomasses of more tolerant forms of macroinvertebrates were observed in grazed reaches. Because pretreatment data were not available, differences in macroinvertebrate populations and relative tolerances of taxa in grazed and ungrazed areas could be as easily attributed to linear changes in stream habitat as to removal of domestic livestock. Results of this study have implications for the design of future research on the effects of livestock grazing on stream environments and biota: (1) baseline/pretreatment information is prerequisite, and (2) the study should take a watershed (ecosystem) approach.     

Douglas-fir beetle ( Dendroctonus pseudotsugae Hopkins, Coleoptera: Scolytidae) brood production on Douglas-fir defoliated by western spruce budworm ( Choristoneura occidentalis Freeman, Lepidoptera: Tortricidae) in Logan Canyon, Utah

Douglas-fir beetle brood production was studied on Douglas-fir ( Pseudotsuga menziesii [Mirb. ] Franco)trees defoliated by the western spruce budworm between 1983 and 1985. Tallies were made of the number of attacks, total length and number of egg galleries, number of eggs deposited, number of larval tunnels, number of pupal chambers, and number of emerging beetles (per female and per unit area). Data analysis showed no significant differences among the three years studied. The number of emerging beetles per female parent was 0.59, and emergence per 90 cm 2 was 2.32 beetles. Egg, larval, and pupal survivals were 47.5%, 30.0%, and 15.5%, respectively.     

Size, structure, and habitat characteristics of populations of Braya humilis var. humilis (Brassicaceae): an alpine disjunct from Colorado

Size, structure, and habitat characteristics were studied in three populations of Braya humilis var. humilis (C. A. Meyer) Robins, in Gray & Wats. (Brassicaceae), a small, herbaceous perennial of the alpine tundra in central Colorado. There was a significant association between numbers of reproductive, juvenile, and seedling individuals and population location. Plant size within reproductive, juvenile, and seedling size classes varied significantly among three populations. Plots containing Braya had significantly lower total plant cover, a different set of dominant plant species, more rock, bare ground, and less litter than plots without Braya . Braya appears to be restricted to calcareous substrates that experience a moderate level of disturbance, such as solifluction lobes and abandoned roads. Populations are small despite the existence of much potential habitat. Population studies are necessary for active conservation management of Braya .     

Ecological impacts of Pogonomyrmex on woody vegetation of a Larrea-Ambrosia shrubland

Discovery of distinct mid-elevational bands of blackbrush ( Coleogyne ramosissima Torr.) shrublands on desert mountain slopes in the Mojave Desert caused an investigation of the relationships between environmental factors and Coleogyne distribution. Environmental factors were quantitatively examined to determine which were significant predictors of Coleogyne density at upper-elevational limits (ecotones) in the Spring Mountains of southern Nevada. Path analysis revealed significant, direct causal effects of air temperature, soil moisture, soil depth, and percent litter cover on the distribution of Coleogyne . Specifically, air temperature was a significant positive predictor, while soil moisture, soil depth, and percent litter cover were significant negative predictors of Coleogyne density, with the effects of other environmental variables parceled out. Path analysis also indicated that indirect effects of soil pH, bulk density, compaction, percent pore space, organic matter, soil temperature, salinity, cryptogam, and percent bare soil and rock cover on Coleogyne density were substantially more potent than their direct casual effects. Environmental attributes associated with elevational changes correlate with and may determine the density of Coleogyne shrubs at upper ecotones in southern Nevada.     

Comparative demography of the high-altitude lizard, Sceloporus grammicus (Phrynosomatidae), on the Iztaccihuatl Volcano, Puebla, México

Population density, reproduction, and survivorship were compared between 2 populations of Sceloporus grammicus occurring at different altitudes (3700 m and 4400 m) on the eastern slopes of Iztaccihuatl Volcano, Puebla, México. Lizards in both populations matured at the same age (14-15 mon) and size (39-42 mm SLV). Population density was slightly greater at high altitude (131-163 per ha) than at low altitude (52-83 per ha). Survivorship and R o were higher at the low-altitude areas, but in general there were no significant demographic variations between altitudes that have been reported in lizard population at higher latitudes. Studies of lower-elevation populations might reveal some differences because previous studies indicated that litter size increases at lower altitudes, although they do not differ between our 3700 m and 4400 m populations.     

Environmental attributes correlating with density of blackbrush ( Coleogyne ramosissima ) shurbs in the Spring Mountains of southern Nevada

Discovery of distinct mid-elevational bands of blackbrush ( Coleogyne ramosissima Torr.) shrublands on desert mountain slopes in the Mojave Desert caused an investigation of the relationships between environmental factors and Coleogyne distribution. Environmental factors were quantitatively examined to determine which were significant predictors of Coleogyne density at upper-elevational limits (ecotones) in the Spring Mountains of southern Nevada. Path analysis revealed significant, direct causal effects of air temperature, soil moisture, soil depth, and percent litter cover on the distribution of Coleogyne . Specifically, air temperature was a significant positive predictor, while soil moisture, soil depth, and percent litter cover were significant negative predictors of Coleogyne density, with the effects of other environmental variables parceled out. Path analysis also indicated that indirect effects of soil pH, bulk density, compaction, percent pore space, organic matter, soil temperature, salinity, cryptogam, and percent bare soil and rock cover on Coleogyne density were substantially more potent than their direct casual effects. Environmental attributes associated with elevational changes correlate with and may determine the density of Coleogyne shrubs at upper ecotones in southern Nevada.     

Intertidal distribution,symbiotic association and reproduction of Pinnotheres bidentatus (Brachyura: Pinnotheridae) from Taiwan

The intertidal distribution of the free-swimming stage of the pea crab Pinnotheres bidentatus Sakai, 1939 was examined on the Kaomei coastal flat of western central Taiwan. Most pea crabs were collected from tidal waters close to the shoreline regardless of the collecting treatments utilized. Results suggest that the pea crab population remains inshore during ebb tides. Many hard and post-hard stages of P. bidentatus were discovered, including ovigerous females. The host was found to be Laternula marilina (Valenciennes, 1860) (Mollusca: Bivalvia: Laternulidae). The infestation percentage of the bivalve was high (average 74.6%). However, this may be due to collections of the bivalve population in the present study being skewed towards large sizes. This biased size structure of the host population may be also responsible for lack of positive size correlation between number and size of male and female symbiotic crabs and the host. Multiple infestations of P. bidentatus appear to be uncommon for L. marilina. Single infestations might be a model for bivalves in tropical regions where the sea is relatively oligotrophic and food competition may be enhanced with multiple infestations. In comparison to other members of the genus Pinnotheres or related species (e.g. P. pisum (Linnaeus, 1767) and Zaops ostreum (Say, 1817)), the body size of sexually mature female P. bidentatus is relatively small, even though it produces similar size eggs (approximately 300 microns). The general rule for size correlation between fecundity and female size in brachyuran crabs holds for P. bidentatus.     

Size, age, and density relationships to curlleaf mahogany ( Cercocarpus ledifolus ) populations in western and central Nevada: competitive implications

Size-density-age relationships in curlleaf mountain mahogany communities were studied in 25 study plots, each 30 x 30 m, in western and central Nevada. The influence of total vegetation cover (site potential) and relative mahogany cover (mahogany dominance) on the observed size-density-age relationships was investigated. A positive linear relationship was found between mean mahogany height and mean mahogany age. A positive nonlinear relationship was found between mean mahogany crown volume and mean mahogany age. Negative nonlinear relationships were found between mean mahogany density and mean mahogany age, and mean mahogany density and mean mahogany crown volume. Strong negative relationships were found between the mean combined density of established seedlings, juvenile, and immature mahogany and mean mahogany age and mean mahogany crown volume. Including total cover in the regression relationships between size, age, and density never increased the r 2 value by more than .05. The addition of relative mahogany cover improved the r 2 value for the relationship between mean mahogany density and mean mahogany crown volume by .28. The strong size-density and age-density relationships found indicate that intraspecific competition is probably occurring in the communities sampled, and that established seedlings, juvenile, and immature plants are the first individuals affected. Direct tests are needed to confirm these relationships.     

Seasonal trends and colonization patterns of macroinvertebrate assemblages in two streams with contrasting flow regimes

Patterns of colonization by macroinvertebrates were examined in two streams that differ in flow regime: a snowmelt system and a mesic groundwater system. Experiments were conducted during spring runoff, summer baseflow, and winter baseflow using artificial substrata. Colonization patterns reflected seasonal changes in benthic macroinvertebrate assemblages and life histories in each stream. The density and biomass of benthic organisms were approximately 3X greater in winter than in either spring or summer for both streams. Similarly, colonization was greater in winter than in spring or summer for both streams. In spring, colonization patterns were different between streams, with colonization being imperceptible in the snowmelt stream. Macroinvertebrate abundance fluctuated during the summer colonization experiment at both sites, resulting from a complex interplay among population emergence, recruitment, and/or movement. Assemblages in the snowmelt system primarily comprised mobile or ruderal taxa, such as Beatis tricaudatus and Chironomidae, whereas relatively sessile taxa, such as Glossoma nigrior , were predominant in the mesic groundwater system. Seasonal patterns of colonization differed among stream types primarily because of the profound interplay of flow regime and temperature on benthic community structure and organism life history.     

Disentangling prey-handling efficiency of larval newts through multivariate prey trait analysis

Multivariate prey trait analysis is a functional approach to understand predator–prey relationships. In the present study, six prey macroinvertebrate ecological traits were used to identify several key factors in the handling efficiency of seven predatory larval newt species. The results revealed a remarkable similarity in the feeding behaviour among species, suggesting a foraging behaviour convergence among species in the prey-handling efficiency of larval newts. Nevertheless, larvae of some newt species showed clear preferences for particular categories of ecological trait; for example, Lissotriton vulgaris tended to feed on macroinvertebrate taxa with random trajectory, and Calotriton asper fed on macroinvertebrate taxa with high agility. In contrast, Mesotriton alpestris showed a clear ability to feed on prey with movable accessories (cases/tubes) and patterned concealment. This study shows how multivariate approaches can complement traditional diet analyses, and the method has wide applicability across life-stages and species.