Canopy gaps in a second growth forest in East Tennessee were studied to document succession, sapling species partitioning in individual gaps and possible sapling adaptations for gap colonization. Ten gaps (64 to 309 m², mean = 186 m²) and four closed canopy plots (200 m² each) were surveyed. All trees were identified and located, extension growth of the leader stem of saplings (n = 933) was measured and diameter at breast height (dbh) of trees > 3 m tall (n = 504) was measured. Sapling composition in gaps was dominated by Fagus grandifolia Ehrh., Acer rubrum L. and A. saccharum Marsh., indicating that several species in the current canopy, dominated by Quercus spp, Pinus spp, Liriodendron tulipifera L. and F. grandifolia Ehrh., will eventually be replaced. There was little evidence of within gap partitioning either between the north and south portions of gaps or between their centers and edges, perhaps due to a history of instability in disturbance regimes. All three dominant sapling species showed significantly greater extension growth in gaps than in closed forest. Acer rubrum grew significantly less in gaps than A. saccharum. Under closed canopy this result was reversed, suggesting that while A. saccharum may be better adapted to using gaps, A. rubrum may grow better beneath the canopy.

Rates of deforestation and reforestation were measured using Landsat Multispectral Scanner data for a 100-km by 100-km section of the Upper Coastal Plain of South Carolina and Georgia. Landsat data from 1974, 1979, 1984, 1988 and 1991 were (1) classified as pine forest, hardwood forest and nonforested areas and (2) compared across years to indicate forest cutting and regeneration. In 1974 hardwood forests occurred on 268,335 ha, or 27% of the area, and these forests were largely uncut in subsequent years. In 1974 pines occurred on 202,613 ha, or 20% of the area, but cutting rates of approximately 6600 ha y⁻¹ reduced the area of this initial pine forest to 110,146 ha in 1988 and 82,795 ha in 1991. The rate of pine cutting on privately owned land was 4.0% y⁻¹, which is greater than that observed for most tropical forests. Pine reforestation rates were 3200 ha y⁻¹ and were too small to maintain the area in pine. The total pine area in 1988, including remnants of the 1974 forest and reforestation since 1974, was 155,559 ha, or 77% of that in 1974. The rapid rate of loss of pine habitat indicated by the Landsat data was not apparent in the United States Forest Service (USFS) surveys for the same region and time. This discrepancy is due to methodological differences between USFS procedures, which measure forests as product resources, and the Landsat data, which measure forests as habitat area.

We investigated temporal and spatial patterns of woody plant establishment in the first 7 y of succession in southwest Michigan old fields. From the 2nd to the 7th y following agricultural abandonment we conducted annual demographic surveys of woody plants and mapped all stems in six 10 × 20 m permanent grids to measure temporal and spatial patterns of woody stem emergence, mortality, density and species richness. Woody plant succession was characterized by increases in the emergence, density and richness of woody species over time and a shift from early dominance by wind-dispersed species to later dominance by bird-dispersed species. The increase in abundance of bird-dispersed stems reflects both clonal reproduction by the dominant bird-dispersed species, Rhus typhina, and establishment from seed by a variety of other bird-dispersed species. Wind and bird-dispersed species differed in spatial pattern within the grids. Wind-dispersed species were distributed at random and bird-dispersed species were aggregated. Aggregation of bird-dispersed species was due to clonal stem production by R. typhina and the concentration of stems of other bird-dispersed species beneath the canopy of Rhus clones. The results highlight the importance of dispersal mode in controlling both the rate of woody plant succession and the development of spatial structure in plant communities.

Managing and understanding the ecology of endemic plants depends upon understanding the habitat limitations of these highly restricted species. Using transplant experiments we quantified the demographic performance of an endangered annual plant of coastal California, Chorizanthe pungens var.hartwegiana (the Ben Lomond spineflower), in habitats with established populations and in nearby habitats where the plant is never or rarely found. Habitats used for transplants occur on the sandhills soil outcrops to which this species is endemic, including open pine forest, manzanita-dominated chaparral and open erosive sand habitat. We monitored effects of transplant habitat, site from which the transplants originated and intraspecific density on the mortality, final biomass and reproductive effort of individual spineflowers. Habitat largely influenced biomass and reproductive effort and had little effect on mortality. Although spineflowers are currently absent from both pine and chaparral habitats, transplants grew and reproduced best under pines, and worst under chaparral, with intermediate performance in the open areas to which spineflowers are currently restricted. While the habitat needs of spineflowers impose severe restrictions on their population size, management could enhance establishment in pine-dominated areas adjacent to current populations. Patterns of spineflower performance suggest that endemic plants may be excluded from potential habitats by a multiplicity of factors, complicating management for the viability of such species.

We examined the roles of floral scent and color in attracting bumblebees (Bombus spp.) to snapdragon flowers (Antirrhinum, Sonnet cultivar). Corolla color differences covaried with differences in floral scent emissions in two inbred lines of snapdragon. White-flowered plants emitted methyl cinnamate, a scent compound not produced by yellow flowered plants, but lacked methyl benzoate, one of the major floral volatiles of the yellow-flowered line. Qualitative scent differences between the two lines were eliminated by applying the complementary scent compounds to filter paper wicks placed within the corollas. Laboratory analyses were performed using gas chromatography-mass spectrometry to verify appropriate modification of floral scents by this method. Two randomized arrays of control and scent-augmented flowers were visited by freely-foraging bumblebees in subalpine meadows in Colorado. Overall, yellow-flowered plants received more pollinator visits and had more flowers foraged per plant visit than did white-flowered plants. The addition of sweet-smelling methyl benzoate or spicy methyl cinnamate neither stimulated nor deterred bumblebee visits to either flower color.

Soil seed bank dynamics, greenhouse seed germination and field seedling survival were compared in the weakly-clonal shrub Rhus aromatica Ait. and the strongly clonal shrub R. glabra L. (Anacardiaceae). Although both species had persistent soil seed banks, their sizes and dynamics differed greatly. The high seed density (5668 ± 1267 m⁻² to 8739 ± 3303 m⁻²) in R. glabra was depleted by ca. 5% annually and replenished with 1102 ± 316 to 1828 ± 486 seeds m⁻², whereas the low seed density (9 ± 5 to 138 ± 68 m⁻²) in R. aromatica was depleted by ca. 50% annually and replenished with 37 ± 7 to 69 ± 18 seeds m⁻². Seeds of both species germinated within established populations. However, recruitment from seedlings was successful in R. aromatica but not in R. glabra, which depended exclusively on root suckering for aboveground population increase. This difference in local recruitment modes between the two species was correlated with differences in soil seed bank dynamics and other life history traits, such as fecundity, seed weight, seed dormancy, seed dispersal, seedling establishment and growth form. The results of this study have important implications about life history evolution in that they suggest that various traits related to increasing sexual reproduction in time and space evolved in concert with clonal reproduction in clonal woody species.

Previous studies of insect-plant interactions have produced the contradictory Plant Stress Hypothesis (that stressed plants are more suitable hosts for phytophages) and Plant Vigor Hypothesis (that vigorous plants are more suitable hosts for phytophages). However, experimental studies of phytophage responses to host stress have involved only one, or a few, related phytophagous species, not whole communities of organisms associated with a particular plant species. We evaluated responses of various arthropods associated with creosotebush Larrea tridentata to manipulated water availability and plant stress in southern New Mexico during 1990–1991. Of 44 arthropod groups (taxa or functional groups) evaluated in our study only two taxa (including a lepidopteran folivore) showed significant negative response to water availability, thereby supporting the Plant Stress Hypothesis. Ten taxa (including eight phytophages) responded positively to water availability, supporting the Plant Vigor Hypothesis. One phytophage showed a nonlinear response, supporting neither hypothesis. Detrended Correspondence Analysis significantly distinguished the arthropod community on water-deprived shrubs from the communities on watered shrubs. The variation in responses among phytophagous insects on creosotebush indicated that the effect of plant water stress likely reflects the choice of phytophage, and perhaps the host plant, being studied. Therefore, neither the Plant Stress Hypothesis nor the Plant Vigor Hypothesis can explain responses of all phytophages on a particular plant species.

A series of field studies was stimulated by the unexpected finding of a band of junipers (Juniperus virginiana) bearing heavy infestations of bagworms, the band running south-southwest to north-northeast through a woodlot (near Norman, OK) of otherwise lightly infested trees. Fidelity to wind direction was confirmed, and numbers of bagworms ballooning from 3.05 m to 36.58 m was measured, with Tanglefoot® traps mounted on metal fence posts. Ballooning numbers were satisfactorily described with a negative exponential model incorporating both gravitational and trap losses. No significant difference was found between ballooning distances achieved by larvae with and without early-stage bags. A study of infestation levels on ornamental junipers planted around houses on the north and south sides of east-west streets revealed both a strong front- vs. backyard difference, and a weaker but statistically significant side-of-street effect. Patterns reflecting short-range dispersal were found in a linear windbreak planting of northern white cedar (Thuja occidentalis), and in a 12 × 44 = 528-tree lattice of planted junipers (near Urbana, Illinois). A “bonfire” effect showing heaviest infestations in mid-lattice, and reduced infestations on the periphery (especially on the windward edge) was postulated and confirmed. Studies of the effect of increased “target” size of larger trees, and of the incidence of apparent bird and small mammal predation, are also reported.

We measured grasshopper densities on 66 shortgrass, mixed grass, tallgrass and hayfield plots on Boulder, Colorado, open space in 1995–1996. Grasshoppers as a group, and most species individually, were more abundant on relatively sparse short and mixed grass plots than on lusher hayfields and tallgrass plots—a result consistent with the hypothesis that most species require warm and sunny open ground for survival and reproduction. Bandwinged grasshoppers (Oedipodinae) were particularly associated with open ground in shortgrass vegetation, whereas spur-throated grasshoppers (Melanoplinae) were most abundant in mixed grass plots with a high percentage of forb vs. graminoid cover. Slant-faced grasshoppers (Gomphocerinae) were the most uniformly distributed among habitats, but were generally associated with plots including relatively high proportions of grass vs. forb cover. While 20 of the 25 most common grasshopper species on Boulder open space occurred in all four grassland types, each habitat was dominated by a distinctive set of species. However, numerically dominant grasshoppers on short, mixed and tallgrass plots only loosely resembled groups of dominant species in the same habitats elsewhere on the Great Plains. While most Great Plains grasshoppers are widely distributed, they are apparently numerically responsive to combinations of environmental conditions expressed at local scales. Common species of grasshoppers on Boulder open space in 1995–1996 were the same as those collected in the region in the 1950s. Our results suggest these protected grasslands, although invaded by alien vegetation and fragmented by suburbanization, are still effectively conserving this particular insect group.

In 1955–1965, the streams and rivers of the upper Susquehanna River basin in New York were surveyed for unionid mussels. We resurveyed unionid populations at the same sites in 1996–1997 to determine whether populations had declined and whether declines could be correlated with inputs of sediments and nutrients from agriculture, which have been thought to be major threats to imperiled unionid populations in North America. Despite widespread evidence of high nutrient and sediment loading from agriculture and other human activities in the upper Susquehanna basin since at least 1965, we found little change in unionid populations between the two time periods. The range of Alasmidonta varicosa contracted while that of Lampsilis cariosa expanded. Overall species richness and the ranges of the other nine species were unchanged. Six species in the basin were formerly listed as Category 2 species or are now considered “Species at Risk” by the United States Fish and Wildlife Service. Of these, Alasmidonta undulata, A. marginata, Strophitus undulatus and L. cariosa are still abundant and widespread in the basin, Lasmigona subviridis is scattered and rarely abundant (but apparently stable) and A. varicosa is rare and declining, perhaps because of hybridization with A. marginata. We caution that improperly designed surveys may erroneously suggest that stable populations are declining.

Zebra mussels, Dreissena polymorpha, increase macroinvertebrate abundance on hard substrata in lakes and large rivers because they enhance surface area, substratum heterogeneity and the accumulation of benthic organic matter (BOM). We tested the hypothesis that zebra mussel colonization of hard substrata in a lake-outlet stream would similarly increase macroinvertebrate abundance. Zebra mussels were attached to artificial rocks (0.05 m²) in a crossed factorial design with two states of mussels (live or dead) and three densities [low (200·m⁻²), medium (500·m⁻²) or high (1000·m⁻²)] plus a noncrossed control (no attached mussels). Rocks were placed in an erosional zone of a lake-outlet stream in southwestern Michigan that contained low densities of zebra mussels. After 28 d total macroinvertebrate abundance was significantly higher on rocks with high densities of zebra mussels, but live or dead treatment had no effect on macroinvertebrate abundance. Family richness differed significantly among density treatments (high = medium > low = control), but Simpson's diversity index did not differ among treatments. We conclude that changes in macroinvertebrate community structure probably were related to the increased substrate complexity provided by zebra mussels.

The crayfishes Orconectes peruncus and O. quadruncus are endemic to the upper St. Francis River drainage in southeastern Missouri, and were classified as threatened in a recent analysis of the conservation status of crayfishes in the United States and Canada. Their distributions are not documented and little is known about their ecologies. In addition, recent collections suggested that the introduced crayfish O. hylas may be displacing O. quadruncus from its type locality, Stouts Creek (Madison and Iron counties). The purpose of our study was to assess and compare the distributions and selected aspects of the life histories and habitat associations of these crayfishes. Sampling at 57 sites on 30 streams in the upper St. Francis River drainage from October 1996 through March 1998 showed that O. peruncus was more widespread and more abundant than O. quadruncus. The two species were sympatric in only three streams. Patterns of reproductive events in the species' annual life cycles were similar, although O. peruncus showed signs of mating activity a month earlier than O. quadruncus. The crayfishes showed similar habitat associations. Orconectes quadruncus has been largely displaced from Stouts Creek by the introduced O. hylas. Orconectes hylas also potentially threatens O. peruncus in Big Creek, warranting further study.

Rafinesque's big-eared bat (Corynorhinus rafinesquii) is a species of concern throughout much of its range, with limited information available on the life history of this rare bat. We tracked patterns of population size, measured roost temperatures and used radiotelemetry to locate foraging areas of C. rafinesquii inhabiting a sandstone cave, which these bats used as both a hibernaculum and a maternity site. Counts of hibernating C. rafinesquii ranged from 14–49, with summer colony size reaching a maximum of 118 bats. Bats roosted in different rooms of the cave in winter and summer. Temperatures in a room used in winter were consistently cooler and less stable than temperatures in the room used as the maternity site. Size of foraging areas ranged from 61.6–225.3 ha, and distance of foraging areas from the roost varied from 0.12–1.22 km. We detected no bat >2.5 km from the roost of capture. Bats foraged along ridgelines supporting upland oak-hickory forest.

Predation on endangered species by nonnative red foxes (Vulpes vulpes) and the resulting controversy over red fox control efforts in California prompted our investigation of the introduction and range expansion of the red fox in California. Since the late-1800s, nonnative red foxes have been introduced into California by escaping from fur farms and fox hunters, through intentional releases by pet owners and fur-farm owners and translocations of previously introduced foxes. From 1990–1993 we conducted telephone interviews of wildlife professionals to obtain observations of nonnative red foxes outside the historical range of the native Sierra Nevada red fox (V. v. necator). Nonnative red foxes now occur throughout lowland areas of California including the Sacramento and San Joaquin valleys, San Francisco Bay-Delta area, the southern California Coast Range and Coastal Plain and most major urban areas. Their range expansion over the last 100 y was the result of population growth from numerous points of introduction and exhibited by the exponential growth typical of invading species. Fox predation on endangered species and opposition to red fox management have been the two largest management issues associated with this range expansion.

Wallows are circular soil depressions created by repeated bison (Bison bison L.) dust-bathing. Despite more than a century of bison absence from the Great Plains and lack of evidence on wallow persistence, many studies have classified grassland soil depressions as ‘relict’ wallows. We studied bison wallowing on a tallgrass prairie site in Oklahoma where bison were reestablished in late 1993. Bison use of existing soil depressions fitting descriptions for relict wallows located before reintroduction and bison formation of new active wallows were documented from 1993–1995. Bison avoided existing depressions, instead forming active wallows in different locations. Bulk density and soluble salt, sodium and clay content of soils in existing depressions were significantly higher than soils in active wallows or nearby reference sites. These depressions occurred primarily on shale-derived soils rich in silt and clay, whereas active wallows were formed mostly on sandy loam soils overlying sandstone. The spatial distribution and soil conditions of these depressions suggested pedogenic, rather than animal disturbance, origins. Soil sampling beneath the depressions revealed a dense clay lens located above a natric (high exchangeable sodium content) horizon, both of which were absent from soils in nearby reference sites. Natric soil horizons, known as claypans, are formed by pedologic processes common to soils derived from marine shales. Thus, these soil depressions, and possibly other ‘relict’ bison wallows, are not persistent soil disturbances resulting from bison wallowing, but small patches of landscape and soil heterogeneity resulting from variation in underlying geological materials.

Genetic variation was assessed with protein electrophoresis for seven populations of the leopard darter, Percina pantherina, a species restricted to five rivers in the Little River System of southwestern Arkansas and southeastern Oklahoma. Analysis of genetic diversity indicated that only 10% of the total gene diversity (H_T = 0.03) reflects differences among populations; 7.3% was attributable to differences among populations in different rivers and 2.7% to differences among samples within rivers. Average heterozygosity was fairly low (0.020–0.031), but there was a relatively high level of allele diversity with two or more alleles detected at 21 of the 31 gene loci examined. Most polymorphism was due to alleles occurring at low frequencies (≤0.05) in restricted geographic areas. An allele frequency, maximum parsimony analysis revealed three primary clades: (1) populations in Little and Glover rivers, (2) populations from the Mountain Fork River drainage and (3) populations in Robinson Fork and Cossatot rivers. This pattern of geographic variation should be considered in future management of the species.

I monitored 382 red-winged blackbird (Agelaius phoeniceus) nests in natural (wetlands and tallgrass prairie) and human-disturbed (hayfields, roadside ditches) habitats in the vicinity of Boulder, Colorado during 1996 and 1997. I counted blackbirds in a total of 6216 ha and quantified habitat composition to determine both within-habitat population density and regional habitat availability. Population density mirrored habitat-specific productivity of red-winged blackbirds in habitats that had predictable sources of water (wetlands, roadside ditches). However, population density and habitat-specific productivity were decoupled in habitats that were unpredictable in the amount of water present during territory establishment (tallgrass prairie and hayfields, which were flood irrigated). Regional habitat productivity was estimated using data on habitat-specific productivity, habitat-specific population density and regional habitat availability. Red-winged blackbirds breeding in wetlands in the absence of yellow-headed blackbirds (Xanthocephalus xanthocephalus) contributed the most young to the regional population, whereas birds breeding in human-disturbed habitats (hayfields and roadside ditches) contributed relatively few young to the regional population. Due to the scarcity of high quality patches in the landscape (e.g., tallgrass prairie), the highest quality habitats did not always contribute the most young to the regional population.

Although the American badger (Taxidea taxus) is common in grasslands and preys on a wide diversity of foods including birds, little is known about badger diet in areas where nesting ducks are common. Small mammals, primarily Muridae and Geomyidae, were the most common food items in the diet of badgers collected from west-central Minnesota and southeastern North Dakota during April–July 1987 through 1990, based on analysis of gastrointestinal tracts of 47 adult (≥1-y-old) and 5 juvenile (<6-mo-old) badgers. Remains of mammals occurred in 98% of samples from adult badgers. Small quantities of insects were found in 40% of adult samples. Bird remains were in 32% of adult samples, most birds identified as Anatidae; ducks or ducklings occurred in 27% and duck eggs in 60% of those samples. Remains of reptiles, amphibians and mollusks were present, but were less common than other foods. Insects and bird eggs were more common during spring (April–May) than summer (June–July). Birds were more frequent in diets of adults than juvenile badgers.

We used data from lesser prairie-chickens captured on leks to test the hypothesis that age structure of attending birds is reflected in lek age (i.e., years of continuous attendance). As leks become older the age structure of attending birds becomes dominated by adults. Average lek size (number of attending males) was not affected by lek age. Establishment of satellite leks (leks ≤ 2 y of consecutive use) during spring was approximately 1 mo later than other leks and corresponded to a decrease in the number of males attending other leks. Interpretation of data collected from birds attending lesser prairie-chicken leks should include consideration of the lek age.

We document the capture of a red tree vole (Arborimus longicaudus) at a new location and higher elevation than previously recorded for the species. This finding shows that the red tree vole occurs outside the current survey and management areas designated for its protection in Oregon federal forests.

We tested the hypotheses that fecundity in four taxa of Sorex declines with age and that older individuals enter a postreproductive state. As the teeth erode in shrews the dentary shortens and masticatory muscles increase in mass, thereby maintaining bite force. To be adaptive these changes must be subject to natural selection which, in turn, requires that older shrews be reproductively active. Number of embryos was not related significantly to age based on tooth wear in any taxon. Females with the most heavily worn teeth were pregnant or lactating and were among those producing the largest litters. The former suggests that they were capable of producing offspring essentially to the end of their natural lifespans. Thus, continued fecundity in older females provides a mechanism by which the bite-force trait is adaptive.