In a field experiment, I examined the effect of wood hardness, condition, texture and substrate type on colonization of stream invertebrates and resulting community structure. Bundles of wood differing in hardness (firm and soft), condition (conditioned and unconditioned), and texture (rough and smooth) were placed in a Michigan stream and colonized for 30, 61 and 91 days. In addition, plexiglass rods were used as an inert analog of wood. Taxa richness was significantly greater on (1) rough-conditioned wood vs. rough-unconditioned wood and (2) smooth wood vs. smooth plexiglass. Larval Chironomidae were numerically dominant on all substrates and their density was affected by the interaction between wood condition and time, as well as wood condition and wood hardness. Densities of four of the six most abundant taxa were significantly greater on rough-soft wood than rough-firm wood. Densities of two taxa were significantly greater on rough-conditioned wood than rough-unconditioned wood. Wood texture was unimportant, as no taxon was found in significantly greater densities on rough-unconditioned-firm wood than smooth-unconditioned-firm wood. Finally, total invertebrate densities, as well as densities of three taxa, were significantly greater on smooth wood than on smooth plexiglass, indicating that inorganic substrates are less suitable as sites of attachment and/or food source than similar wood substrates. The fact that wood presents various hardness states to potential colonizers appears to be an important determinant of invertebrate community structure on wood substrates. Likewise, previous stream conditioning of wood and substrate type both are important in determining numbers of invertebrate taxa and individuals that colonize wood substrates in streams.

Sampling conducted by personnel of two separate laboratories of the U.S. Environmental Protection Agency showed a single amphipod species, Crangonyx pseudogracilis, present in the Ohio River before the early 1970s. Subsequent sampling by personnel of both laboratories, along with invertebrate collections made by the West Virginia Department of Natural Resources and the first author of this paper showed that this species disappeared from the river in approximately 1973. Another amphipod species, Gammarus nr. fasciatus, invaded the Ohio River in 1973. Gammarus nr. fasciatus spread rapidly throughout the Ohio River, and is now one of its most common macroinvertebrate species. Although the evidence is circumstantial, it seems likely that the elimination of C. pseudogracilis from the Ohio River was caused by the damming of the river, especially the use of high-lift dams, completed from 1936 through the present. Experimental evidence indicates that the existing amphipod, G. nr. fasciatus, has a proclivity for slow-water conditions, which have been favored by the installation of the high-lift dams.

We studied the effect of an engineered flow disturbance on macroinvertebrates in an intermittent N Texas stream. To augment a drinking water supply, water is being diverted through the natural stream channel. Quantitative sampling of sediments and woody debris was conducted immediately before water diversion, immediately after and periodically during recovery, for three diversion events over a 2-yr period. Reduction in total density of macroinvertebrates was dependent on type of substrate, averaging 76% in sediments as compared with 66% on woody debris. Recovery was rapid for most taxa, which often reached predisturbance density in less than 1 mo. For the entire macroinvertebrate assemblage in 1992 and chironomids only in 1991, resilience was greater on woody debris than on sediments. Compared with sand, the common inorganic substrate in this stream, woody debris was more stable, due in part to its retention by debris dams. It appears that woody debris is an important refuge and source of recolonizers to this sandy prairie stream after flow disturbances.

Pteronarcys stoneflies, which are traditionally considered shredders in eastern North America, inhabit second- through seventh-order streams in the Little Tennessee River (LTR) drainage basin. Because very little coarse allochthonous particulate organic matter occurs in the relatively large (sixth- and seventh-order) LTR, we analyzed the gut contents of five individuals from each of five sites and two dates (August and December) (n = 50) along a fourth- through seventh-order stretch of this stream continuum. Pteronarcids consumed significantly different percentages of some food items between sampling dates. Pteronarcys progressively consumed significantly more diatoms (from <1% of gut contents at stream order 4 to 46% at stream order 7) and significantly less detrital material (from >90% of gut contents at stream order 4 to ca. 50% at stream order 7) from fourth- to seventh-order sites, and the amount of Pteronarcys production attributable to each of these food items shifted significantly along the stream continuum. This diet shift raised the obvious question: Does the shift reflect changing Pteronarcys species composition or is only one species present throughout the continuum? We conducted an allozyme electrophoretic analysis on 62 pteronarcids from the LTR drainage basin using five diagnostic gene loci for eastern USA Pteronarcys species. We determined that three apparent species occur along this continuum. Pteronarcys species A inhabits the upstream sites (fourth- through sixth-order), Pteronarcys species C the downstream sites (sixth- and seventh-order), and Pteronarcys species B the mid-reach site where A and C co-occur (sixth-order). Based on their diet and distribution, Pteronarcys sp. A and P. sp. C exhibit different patterns of food consumption along the continuum, with the former consuming mainly detritus and the latter consuming detritus and diatoms.

This study suggests that heterotrophic components of prairie ecosystems can be used with autotrophic components to assess the degree to which a restored prairie approaches the biotic complexity of a native prairie. Springtails (Collembola) were collected from prairie vegetation and litter samples from 13 prairie sites (seven native and six restored) located in southwestern Michigan and northeastern Illinois. The diversity and abundance of these insects and the plant and litter biomass were compared. There were 27 different taxa of springtails in the 225 samples collected. Native prairies had the greatest species richness with 26 species. The oldest restored prairie had 17 species. Three common species were Hypogastrura boletivora, Isotoma viridis, and Lepidocyrtus pallidus. Neanura muscorum, Xenylla grisea, and Pseuduosinella rolfsi were rare. Tomocerus flavescens was found primarily in native prairies with only one occurrence in the oldest restored prairie in this study. Native prairies and restored prairies of 17 and 24 yr did not differ significantly in numbers of springtails.

Differences in springtail numbers did occur, however, between restored prairies of <6 yr and native prairies, and between younger (<6 yr) and older (17 and 26 yr) restored prairies. An analysis of plant and litter biomass indicated significant differences among the prairie sites sampled. These results suggest that all components of the prairie ecosystem are useful for making restoration management decisions.

This study documents variation in the number of florets per flower head and the number of flower heads per flowering shoot for individuals of Solidago macrophylla, a perennial composite, on an elevational gradient in the White Mountains of New Hampshire, and asks if variation in floret distribution vs. plant insect attack predicts variation in reproductive success. Fifteen populations were censused over 2–3 yr to document the number of florets per head, the number of heads per shoot, aphid infestation and seedling emergence per flowering shoot. Additionally, levels of seed predation by tephritid flies were measured during the final year.

Flowering shoots in populations at higher elevations produced significantly more florets per head and fewer flowering heads than flowering shoots in populations at lower elevations. Overall, populations at lower elevations produced more florets than populations at higher elevations. However, this difference in reproductive potential did not result in differential reproduction in either 1993 or 1994. Populations at higher elevations had fewer plants with aphids than populations at lower elevations. In 1993 neither aphid infestation levels nor floral life history traits predicted the mean number of emerging seedlings per shoot in the greenhouse. In 1994 the percent of flowering shoots per population with aphids was a significant negative predictor of the mean number of emerging seedlings per shoot in the greenhouse, whereas the number of seed predators per head per shoot was a significant positive predictor of the number of emerging seedlings. Floral life history traits did not predict reproduction in 1994. Finally, patterns of seedling emergence over the environmental gradient resulted in a greater opportunity for selection in lower vs. higher elevation populations.

Overwinter weight loss of Indiana bats (Myotis sodalis) was assessed during the 1989–1990 and 1990–1991 winters at three hibernacula (high, low, and no human visitation) in southern Indiana. We weighed 4264 M. sodalis captured during the autumn swarming and spring emergence periods. Mean spring weights were less than mean autumn weights for males and females in both years. Overwinter weight loss, expressed as a percentage of mean autumn weight, ranged from 15% to 33% and was least at the cave that received no human visitation in three of four sex-year combinations. The magnitude of overwinter weight loss differed among caves in three of four tests, but the effect of cave on weight loss was inconsistent between sexes in both years and between years within sex. Percent weight loss was less at the hibernaculum with low visitation (x̄ = 5.5 visits/winter) than at the hibernaculum with high visitation (x̄ = 378 visits/winter) in two of four sex-year combinations. Increases of populations in both disturbed hibernacula suggest M. sodalis is affected by limiting factors other than, or in addition to, human visitation in winter.

During autumn 1991, we sampled small mammals in six grass-dominated habitats including upland ungrazed native prairie, upland improved pastures, upland mowed native prairie, upland roadside fencerows, lowland ungrazed native prairie and lowland ungrazed native prairie with forbs and shrubs in southeastern Oklahoma. Eleven species of small mammals were represented in 405 captures. Species diversity (H′) was high in upland (1.57) and lowland (1.47) ungrazed prairie and least for upland fencerows (0.86). Evenness (J′) exhibited a similar pattern and was high in upland (0.88) and lowland (0.82) ungrazed prairie and least for lowland ungrazed prairie with forbs and shrubs (0.53). Community overlap (R_o) varied from 1.00 (upland improved pastures and upland roadside fencerows) to 0.57 (upland improved pastures and upland ungrazed prairie). Abundance of small mammals was greatest in fencerows, largely due to the prevalence of hispid cotton rats (Sigmodon hispidus). Different land-use practices elicited both positive and negative species-specific responses. Current human activity in some locations may produce habitat mosaics that result in an overall greater abundance and diversity of small mammals.

Mammalian herbivores in boreal areas selectively browse on mature-stage growth rather than on juvenile-stage growth of conspecific plants during winter. Such stage-dependent selection often is mediated by levels of secondary metabolites that decline as plants mature. Little is known regarding the extent to which this pattern is repeated for temperate-zone plants browsed by different mammalian species. We conducted field experiments in a temperate forest with free-ranging white-tailed deer (Odocoileus virginianus) to test whether selection of coniferous browse was influenced by a plant's maturational stage. Trials conducted during February 1990 in western Connecticut demonstrated that deer browsed a significantly greater percentage of eastern red cedar (Juniperus virginiana) collected from reproductively mature plants (mean = 72%) than from juvenile plants (mean = 16%). Trials with eastern hemlock (Tsuga canadensis) produced similar results: deer browsed a significantly greater percentage of shoots from mature trees (mean = 70%) than shoots from juvenile plants (mean = 21%). Chemical analyses revealed that crude protein levels were significantly (P < 0.05) greater in mature-stage eastern hemlock (8.2%) than in juvenile-stage growth (7.3%), but no differences existed between crude protein levels of the red cedar growth stages. Protein-precipitating phenolics were present at low levels but were 1.5 times more concentrated in mature-stage growth of eastern hemlock than in juvenile-stage growth (P < 0.05). Comparison of our results with previous research indicates that white-tailed deer exhibit stage-dependent selection of temperate plants similar to the patterns demonstrated by other species of mammals browsing on plants in boreal forests.

Predatory behaviors of bobcats (Lynx rufus) that preyed on 39 radio-instrumented white-tailed deer (Odocoileus virginanus) in the Everglades during a 3-yr study, 1 April 1989–31 March 1992, are described and compared with those of other felids. Bobcats killed 33 fawns and six adults by administering ≥one bite to the neck and throat region. The maximum prey:predator weight ratio was 8:1. Twelve (31%) of 39 kills were dragged 2–10 m to concealment cover before being eaten. Twelve (71%) of 17 carcasses that were not dragged from the kill site exhibited a characteristic death form in that the head on each was twisted backwards (throat dorsal) and positioned diagonally under the shoulder. Feeding was initiated on large muscle masses, predominantly on the hindquarters. Bobcats eviscerated 29 (83%) of 35 carcasses, severed ≥ one fore- or hind-limbs from 18 (55%) of 33 kills, and plucked hair from 13 (33%) of 39 carcasses. Bobcats partially or completely covered 17 (52%) of 33 carcasses with plant litter. Thus, bobcats preying on deer in the Everglades displayed notable differences in eviscerating, feeding, and covering behaviors.

The use of fish communities to evaluate stream habitat typically requires that the community at a target site be compared with concurrently or recently sampled reference communities at nearby sites. For this approach to be effective, spatial and temporal variation in the reference communities of a region must both be known. This study relates 307 recent (1976–1994) fish survey records in the Schuylkill River drainage, southeastern Pennsylvania, to four concurrent measures of water chemistry (pH, conductivity, alkalinity, hardness), two measurements of stream size (stream order, stream width) and three variables describing site position within the drainage network (elevation, link number and C-link number defined herein). Based on canonical correspondence analysis, stream size and position within the watershed influenced fish species composition more strongly than did water chemistry. Species richness, dominated by the families Cyprinidae (minnows) and Centrarchidae (sunfishes), increased from a median of four species in 1st-order streams to 21 species in 5th-order streams. Secondly, recent frequencies of occurrence are compared to frequencies inferred from historical collections using log-linear analysis. Nine species have increased in frequency, while the frequencies of eight species have declined. Eighteen species, or about ⅓ of the recent community, have been introduced. All but three of these introduced species were absent from collections before 1931, and many are now widespread. Several previously common species associated with clear, vegetated streams are now uncommon or rare (e.g., Esox americanus americanus, Notropis bifrenatus); one species, N. chalybaeus, was not found in the recent dataset. Substantial historical changes in the fish community thus accompany the influences of stream habitat and location in determining species composition at sites within the drainage.

The influence of specific types of habitat structure on fish assemblage structure, diversity and abundance in large rivers is largely unknown. This study determined whether fish assemblages differed among various artificial and natural habitats within the main channel border (shallow, nearshore areas) of the upper Mississippi River, and assessed whether different types of artificial structure influenced fish assemblage structure over long (>0.2 km) sections of shoreline habitat. Daytime electrofishing during August and October 1994 captured 31 different fish taxa from main channel border habitats in Pool 6 of the upper Mississippi River. Nine species of fish preferred specific types of nearshore habitat. Fish abundance and diversity measures differed little among habitat types, but significantly larger fish were present at locations with structure (wing dikes, woody snags) than at sites without (bare shore). Cluster analysis indicated that different fish assemblages occupied different habitat types. Riprapped shorelines had fish assemblages different from those in river sections containing only instream artificial rocky structures. Aggregations of various habitat types, especially artificial rocky structures, are important in determining fish assemblage structure within large river sections.

We compared the abundance and species composition of birds in Conservation Reserve Program (CRP) fields with the same aspects in row-crop fields during the winter (January and February) over several years (1992–1995) for six midwestern states (Indiana, Iowa, Kansas, Michigan, Missouri and Nebraska). Field techniques were standardized in all states. CRP fields consisted of either permanent introduced grasses and legumes (CP1) or permanent native grasses (CP2), and the plant species seeded in CRP fields differed within and among states. Vegetation characteristics of CRP fields varied considerably from state to state, but vertical density and total canopy cover (primarily grasses) were particularly high in Nebraska. Mean annual total bird abundance ranged from 0.1 to 5.1 birds per km of transect in CRP fields and from 0.1 to 24.2 in row-crop fields. The total number of bird species recorded in CRP fields in the six states ranged from 6 to 32; the range for row-crop fields was 8 to 18. The most abundant species in CRP fields differed among states but included the ring-necked pheasant, American tree sparrow, northern bobwhite, dark-eyed junco and American goldfinch. The most abundant species in row-crop fields included the horned lark, American tree sparrow, European starling, mourning dove, lapland longspur, meadowlarks and Canada goose. Some of the most abundant bird species wintering on CRP fields have been undergoing long-term population declines, thus this program has the potential to mitigate population losses.

We collected data for flight speeds of foraging common nighthawks (Chordeiles minor) flying under natural conditions using a Doppler radar and compared them with data collected by timing flights over a known distance for the same species. We also compared our Doppler radar measures of flight speed with the values of minimum power speed (V_mp) and maximum range speed (V_mr) predicted from aerodynamic models. Our measurements showed that under natural conditions, nighthawks flew at 6.5 ± 1.1 m-s⁻¹, significantly faster than the 5.3 ± 1.2 m-s⁻¹ derived by timing flights over measured distances. Doppler measurements indicate that on average, nighthawks flew significantly faster than the predicted V_mp, but slower than the predicted V_mr although there was considerable variation. Our results confirm that the method of measuring flight speeds can be important and suggest that the mechanics of hunting insects and not energetics, may be most important in determining the flight speed used by foraging common nighthawks.

Nine sites in the Neosho River (Kansas) were surveyed for unionid mussels during summer 1994 to compare the effectiveness of quadrat sampling vs. timed snorkel searches for evaluating relative abundance, species richness and diversity, size distribution and evidence of recruitment. At each site, timed snorkel searches were conducted in a 100-m stretch, 10-m wide, of wadable habitat. Mussels were returned to their original location following identification and sizing. Next, 40 1 m² quadrats were sampled from the same stretch. Finally, 15 qualitative substrate samples (approximately 1 m²) were sieved in an attempt to detect recruitment. A total of 786 mussels were caught during 12 h, 11 min of snorkel searches compared to 896 mussels from 360 1-m² quadrats. Quadrula metanevra was the most abundant species collected by either qualitative or quantitative methods. Differences in assessments of species diversity and relative abundance between methods were not significant; however, timed searches revealed significantly fewer species, and were less effective in detecting cryptic species than were quadrat samples. Little evidence of recent recruitment was detected in any of the methods. Quantitative methods are recommended for assessments of density, biomass, size demographics and local scale phenomena, whereas qualitative searches are more efficient when targeting large species or examining broad distributional patterns. However, some form of substrate sieving is necessary to detect small mussels.

In 1957, the exotic balsam woolly adelgid (Adelges piceae Ratz.) was discovered in the southern Appalachians. It quickly spread throughout the spruce-fir forests, decimating adult Fraser fir (Abies fraseri (Pursh) Poir.) populations. In 1990 and 1991, a system of temporary and permanent plots was established on five mountains in the Great Smoky Mountains. Almost seventy percent of total standing fir basal area in the study area was dead. Mt. Collins, which experienced the major wave of fir mortality about 4 yr before sampling, had the greatest percentage (91%) of dead fir basal area of the five mountains. Despite catastrophic mortality, fir dominated (11–16 m²/ha) live stand basal area on the tops of the three higher elevation mountains, whereas red spruce (Picea rubens Sarg.) and deciduous taxa dominated the two lower mountains. Live fir density over the short term was positively associated with time since the major wave of mortality. Patterns of fir mortality, treefall rates and recruitment determined the proportion of dead fir stems in the overstory. These three factors in turn were dependent on time since major mortality. A logistic regression model predicted that the proportion of standing dead fir would increase until 5—8 yr after an episode of major mortality and decrease thereafter as dead trees fall and young fir reach the overstory.

It has been hypothesized that Juniperus virginiana facilitates tree seedling establishment in secondary succession. To test this hypothesis, we sampled four old fields in southwestern Ohio and monitored experimentally planted seeds and seedlings of Acer saccharum and Fraxinus americana for two years. Seeds and seedlings were placed into herbivore exclosures placed 0.3 and 3.0 m from J. virginiana trees in an old field in Ohio. We found a significant positive spatial association between Juniperus virginiana and tree seedling densities in all four old fields. Soil temperature, soil moisture, evaporative demand and light level in the 0.3 m treatment were significantly reduced, whereas litter depth was increased. Germination of A. saccharum, but not F. americana, was reduced in the 0.3 m treatment, whereas seedling survival was unaffected in either species. Growth of F. americana seedlings was reduced by proximity to J. virginiana but A. saccharum growth was not affected. Stomatal conductance was reduced in the 0.3 m treatment for F. americana but unaffected in A. saccharum. Although there was a positive spatial association between J. virginiana and tree seedlings in the old fields sampled, experimental seedlings did not exhibit an early demographic response that indicated facilitation.

It has been assumed that secondary dispersal of winged pine seeds across the ground occurs, but the process has been little studied. We monitored the fates of 287 inedible pine seeds that differed in size (lodgepole pine, Pinus contorta, mean fresh seed mass with wing 9 ± 2 mg; ponderosa pine, P. ponderosa, 62 ± 11 mg; and Jeffrey pine, P. jeffreyi, 185 ± 23 mg) to determine the effects of wind and gravity on secondary dispersal across the ground. Animals largely ignored the seeds. Most seeds moved <1 m during the 37-day observation period. Only seven seeds were known to have moved >1 m. Nineteen seeds disappeared, but rodents and birds probably took many of these. Seeds placed on mineral soil moved significantly farther than those placed on pine needle litter, and, on needle litter, large seeds moved significantly farther than small seeds. Except during an initial windy period, most seeds moved <5 cm/day. Most seeds became immobile after about 8 days because they became entrapped in plant litter. By the end of the study, only two lodgepole pine seeds had become completely buried in soil. Wind and gravity appear to be relatively ineffective at moving pine seeds long distances across the ground surface. For large pine seeds (e.g., those of ponderosa and Jeffrey pine), rodents and birds serve as an alternative means of secondary dispersal by scatter hoarding seeds in soil, whereas small pine seeds (e.g., those of lodgepole pine) are more likely to be overlooked by foragers as they are gradually buried in plant litter and soil.

Petrophytum cinerascens (Piper) Rydb. (Rosaceae) is a highly restricted endemic found on steep rocky outcrops and sandy soils along the Columbia River in eastern Washington. Our goal was to examine the plant's ability for photosynthetic acclimation to increased growth temperature. Plants collected from the field were subjected to three sets of day/night growth temperatures and to two different watering regimes. Leaf gas exchange was measured at step-intervals of leaf temperature. Data were fitted to individual temperature response curves, and the optimum temperature for assimilation (T_opt), the high temperature compensation point (T_high) and assimilation rate at the optimum temperature for assimilation (A_opt) were calculated from the regressions. We analyzed the data using a 3 × 2 split plot experimental design with growth temperature as the main effect and watering treatment as the split plot factor. A_opt for plants grown at 30/16 and 34/20 C was significantly greater than that for plants grown at 38/24 C, but the main effects of growth temperature on T_opt and T_high were not significant. The relative decrease in A_opt from the lowest growth temperature to the highest was almost 60% for well-watered plants and over 20% for plants with periodic drought treatments. The lack of change in T_opt and T_high, coupled with the decrease in A_opt with increased growth temperature, suggests that P. cinerascens is not able to acclimate to increased global temperature and therefore may serve as a sensitive indicator species of global warming.

The Asian shrub Lonicera maackii (Rupr.) Herder has been widely used as an ornamental in the eastern United States. First planted in Oxford, Ohio, around 1960, it has since spread into forest patches in the surrounding agricultural landscape. Despite its abundance, and its bird-dispersed fruits, the spread of Lonicera maackii has been unequal in different directions, with local distribution limits much farther N than W of Oxford. Our objective was to determine whether the distribution limits of L. maackii in these two directions were correlated with differences in landscape structure: percentage of forest land and degree of forest connectivity. Aerial surveys were used to determine the current distribution of L. maackii in forest patches in a belt transecting N and W from Oxford. The N transect, which had more extensive spread of L. maackii, had greater forest cover and connectivity. In both transects, L. maackii reached its distribution limit when forest cover dropped to <5% and forest connectivity was 0%. Large expanses of agricultural land apparently act as a barrier to the dispersal of this naturalized shrub.

An example is cited from a published study of forceps (cerci) asymmetry and copulatory success in earwigs (Forficula auricularia). Its authors scored eight pairs of male earwigs—one with symmetric and one with asymmetric forceps—according to which male first succeeded in mating with a female earwig enclosed with them in a petri dish. Their categories “symmetric males successful” (seven observed among the eight pairs) and “asymmetric males unsuccessful” (the seven pairmates of the successful males) were thereby locked together like the observations “seven Heads up” and “seven Tails down” in tosses of eight coins. The authors assumed, however, that their eight petri dishes were providing two independent observations per dish. They analyzed this assumed total of 16 observations by the Fisher exact test of a 2 × 2 table, obtaining an apparent two-sided probability of 0.01. In fact, the study provided only eight independent observations, correctly testable by a binomial exact test of the 7:1 ratio. By this appropriate analysis, observed counts of 7 to 1 fail to achieve conventional significance (0.05) at a two-sided probability of 0.07.

Timing of parturition has been proposed as a factor allowing coexistence of sympatric shrews. We examined the timing of parturition for three species of sympatric long-tailed shrews (Sorex) in the southern Appalachians. We found a marked similarity in patterns of parturition among these species, with significant correlations between S. fumeus and both S. cinereus (r = 0.86, P = 0.0004) and S. hoyi (r = 0.72, P = 0.0080). However, parturition dates for S. cinereus and S. hoyi were not significantly correlated (r = 0.43, P = 0.1588), with the average parturition date significantly earlier for S. hoyi. We suggest that patterns of breeding among Sorex spp. in the southern Appalachians are highly similar, although early breeding may help S. hoyi avoid competition with S. cinereus.