We performed hand-pollinations to assess the compatibility of crosses within and between long-styled (pin) and short-styled (thrum) morphs of Houstonia serpyllifolia and H. longifolia. For both species, percentage fruit-set and seed-set per capsule were significantly higher following intermorph (legitimate) than intramorph (illegitimate) crosses, as expected for distylous species. Fruit-set was significantly higher for intramorph crosses than for unpollinated controls, but seed-set did not differ significantly between the two treatments. Fruit-set in intramorph crosses was 10% to 28% of that in intermorph crosses. In the case of H. serpyllifolia, we suspect that intramorph fruit-set may have been due to the transfer of some compatible pollen by thrips. Crosses were also made between H. longifolia and H. purpurea, a co-occurring species that also belongs to subgenus Chamisme. Fruit-set and seed-set per fruit in interspecific crosses were not significantly lower than those in intraspecific crosses, but most of the seeds were small or immature and probably inviable. We conclude that H. serpyllifolia and H. longifolia express the heteromorphic genetic incompatibility typical of distylous species.

The sustainability of natural grasslands is in large part dependent upon the successful ingress and propagation of alien plant species. We attempted to characterize the propagation potential of the dominant plant species of a southeastern Montana mixed-grass prairie community including two introduced grasses, Bromus japonicus and B. tectorum. Aboveground standing crops and densities of seeds were estimated on 10 dates between September 1991 and August 1993 and seedling densities were estimated on 21 dates between September 1991 and July 1993. Total aboveground standing crop ranged from about 110 to 340 g m⁻² and was dominated by three grasses: Bouteloua gracilis, a warm-season, perennial; Pascopyrum smithii, a cool-season, perennial; and B. japonicus, a cool-season, annual grass. Seed production was dominated by B. japonicus (∼10,400 seeds m⁻²). Bouteloua gracilis and P. smithii seed production was negligible with maximum densities of about 120 and 25 seeds m⁻², respectively. Density of seedlings was greatest for B. japonicus (∼2100 seedlings m⁻²), Festuca octoflora (∼1100 seedlings m⁻²), and Plantago patagonica (∼350 seedlings m⁻²). Maximum number of B. gracilis seedlings was 25 m⁻². No P. smithii seedlings were observed during the study. Temporal differences in seedling densities were closely tied to late summer-early fall precipitation patterns. Although community-level seed production and seedling establishment processes were dominated by B. japonicus, the overwhelming presence of herbage produced by the two vegetative propagating species, B. gracilis and P. smithii, casts doubt on a trend in ecological succession toward an annual grass-dominated community.

This study investigates how recent foraging gain affects the web-building behavior of the garden spider, Argiope trifasciata, especially stabilimentum-building. Adult female spiders in the field and in cages were randomly assigned to two groups, fed and unfed. Spiders in the fed group received three grasshoppers each day; spiders in the unfed group received no prey. The experiment was terminated after each A. trifasciata had built four consecutive webs; the number of days required by each spider was recorded. During the experiment I recorded silk length, catching area, mesh size and stabilimentum area of each web spun by test spiders. Continuously fed, field and caged spiders decreased silk output and web size, increased mesh size and increased the interval between successive foraging bouts. Unfed, caged spiders increased silk output and web size, maintained mesh size and shortened the interval between successive foraging bouts. Although unfed spiders in the field exhibited the same trend, changes in the web characteristics were not statistically significant. Stabilimentum size of fed caged spiders was greatly enhanced, but that of field spiders was unaffected. The size of stabilimenta built by unfed spiders in both field and cage was unaffected by the treatment. These results indicate that Argiope trifasciata do not alter size of stabilimenta in response to recent foraging gain alone, and factors other than food intake are involved.

Horsenettle (Solanum carolinense: Solanaceae) plants possess the ability to bear both hermaphroditic and male flowers on the same plant, a breeding system referred to as andromonoecy. As part of an ongoing investigation into the evolution and maintenance of andromonoecy in horsenettle we conducted a field investigation that addressed the following questions:

We conducted pollen additions on 25 plants in each of two populations, and monitored 25 open pollinated control plants at each site. Mean percentage fruit set and seed set per fruit was significantly greater in the pollen addition treatment than in the control, which indicates that both populations were pollen limited. The percentage of flowers on a plant that were male was significantly greater in the pollen addition treatment than in the control, which suggests that pollen addition affects sex expression in horsenettle. Percentage fruit set did not correlate with total flower number or percentage of male flowers, which indicates that a larger floral display does not affect pollinator behavior in ways that influence female reproductive success. The results document the existence of pollen limitation in the two horsenettle populations studied and suggest that future studies should determine if male flower production influences male fitness or vegetative reproduction.

The distribution and diversity of macroinvertebrates in relation to bison crossings was studied for four seasons in a headwater reach of a tallgrass prairie stream. Species richness was significantly higher above crossings only during the fall. Summer samples revealed significantly higher EPT (richness within only Ephemeroptera, Plecoptera and Trichoptera) index values above crossings than at crossings. On average, over 10% more fine sediment (<0.2 mm) occurred at the crossings than above or below crossings. Densities of two taxa (Hydropsyche spp. and Elmidae) were significantly higher above or below crossings, whereas three taxa (Bezzia/Palpomyia spp., Culicoides sp., and Naididae/Tubificidae) were significantly higher at crossings for at least one season. Overall, this study suggests that impact of bison on benthic communities of headwater streams was spatially limited. Although bison may have less impact upon stream communities than previous studies of cattle impacts have shown, differences in climate and stocking rate could be important factors.

We used discriminant analysis to examine morphological variation within the Plethodon vandykei species group. Significant differentiation was found among the nine samples used in the study. Canonical discriminant analysis and UPGMA clustering of Mahalanobis' distances among samples revealed morphological divergence of P. vandykei and P. idahoensis. The greatest intraspecific differentiation was found between coastal and Cascade Mountains populations of P. vandykei. Morphological variation within the P. vandykei species group is consistent with protein variation revealed by previous studies. Our results support the long contested taxonomic validity of P. vandykei and P. idahoensis, and indicate that detailed morphometric analyses can be useful in evolutionary studies of Plethodon.

Quadrula metanevra were collected monthly from Pickwick Dam tailwater (Tennessee River mile 201.3), Tennessee, between July 1988 and June 1990. A total of 227 specimens were examined. The population consisted primarily of dioecious individuals (98%) and had an unequal sex ratio (1.5 female: 1 male). Histological examinations showed that typical spermatogenesis began in autumn (September), increased in spring (March–April), and continued until midsummer (July). Atypical spermatogenesis predominated during July and August, and may have increased the number of sperm produced in autumn and winter. Oogenesis followed a pattern similar to that of typical spermatogenesis, with smallest average oocyte size observed in August. Gamete release occurred between late winter-early spring (March) and midsummer (July). Brooding females were found between late March and July.

The intensity of nest predation in small woodlots was compared across three regions in Ohio: (1) suburban Cuyahoga County, (2) semirural Lorain County and (3) rural Huron County. Artificial nests, each holding three Japanese quail eggs, were placed in seven Cuyahoga Co. woodlots, four Lorain Co. woodlots and four Huron Co. woodlots during July and August 1991. Half of the nests were placed on the ground, half were placed in the lower branches of trees. Eggs were removed from 257of 354 nests. Ground nests suffered significantly more predation than tree nests, indicating that mammals were the primary predators. No significant difference in egg removal was found among the three regions, and no significant dependence was found between woodlot size and rate of nest predation. The lack of a suburban/rural difference and the insignificance of the woodlot size/predation relationship do not corroborate previously published studies that used methodologies similar to ours. The deviant nature of our results may reflect the more extensive cropland in our rural study region that provides food resources to sustain large populations of mammalian nest predators.

Caterpillars of the eastern North American moth Pyrrharctia isabella (Lepidoptera: Arctiidae) overwinter under plant debris where they are exposed to subfreezing temperatures. We measured supercooling points (scps), susceptibility to ice formation in body fluids at temperatures above the SCP following contact with external ice (inoculative freezing), freeze tolerance, cryoprotectant accumulation and metabolism of P. isabella caterpillars. They were collected between September 1996 and January 1997 and tested either immediately after collection (field acclimatization) or following 5 C acclimation in the laboratory. Hibernaculum temperatures were previously recorded between late November 1995 and late March 1996. In a dry laboratory environment, caterpillars had scps ranging between −5 to −10 C throughout the study. Moreover, caterpillars survived prolonged (7 days) supercooling at −5 C for 7 days and determinations of their scps, which caused brief internal freezing. We induced inoculative freezing of caterpillars by cooling them to −5 C on frozen substrate. Low postfreeze survival (14%) occurred during September 1996 following a 3-day freeze at −5 C but all caterpillars tolerated a 7-day freeze at −5 C in November (100%). Cold acclimation and seasonal conditioning increased hemolymph osmolality and glycerol content by 2× and 6–12×, respectively. Caterpillars showed partial compensation in O₂ consumption upon acclimation to 5 C vs. 25 C. Hibernaculum temperatures ranged from −7.5 C to 14.6 C during the winter of 1995–1996. Temperatures rarely dropped below the scp of caterpillars but the hibernaculum cooled below the melting point of their hemolymph (−1.6 C) for up to 2–4 days. Nevertheless, thaws were common and temperatures changed more than 5 C/day on 22 days. The present study demonstrates that the cold hardiness of Pyrrharctia isabella caterpillars allows them to endure subfreezing conditions beneath leaf litter in western Pennsylvania and that the metabolic capacities of these caterpillars allow them to exploit their environment during the late autumn and early winter.

Bipalium adventitium Hyman, an exotic terrestrial planarian invading North America, is an aggressive predator on earthworms. The spread and ecological impact of this flatworm will be determined in part by the its interactions with potential predators and prey. In laboratory trials, we tested the ability of B. adventitium to prey upon earthworms of different species and sizes. We also tested the predatory responses of six salamander species and two snake species to the flatworms. Bipalium adventitium attacked and ate members of all earthworm species offered and attacked earthworms over 100 times their mass. However, flatworm predatory success was related to the relative size of the prey. The largest prey eaten in our study was 12.1 times the mass of the flatworm that killed it. When attacking, B. adventitium often used a previously undescribed behavior of capping the anterior end of the earthworm, causing subdued escape behavior. None of the amphibians and reptiles tested as predators treated B. adventitium as a regular prey item. Only a few salamanders (2%) struck and ate a flatworm, with most salamanders and all snakes showing little interest in the planarian. Salamanders that consumed flatworms showed no apparent long-term ill effects.

Larval food-limitation may be an important factor influencing growth of lepidopteran populations. We tested effects of food-limitation on larval growth of Vanessa cardui Linnaeus (Lepidoptera: Nymphalidae), the painted lady butterfly. Vanessa cardui is a major pest of corn and soybeans in Iowa, making it a species of special interest. Larvae of V. cardui were reared on a commercial diet apportioned to two food-limited and one control (ad libitum) treatment, and treatments were tested in three trials with varied temperature and onset of food limitation. Trial I was conducted at 18 C and food limitation started on day 12; Trials II and III were conducted at 22 C and food limitation started on days 7 and 12, respectively. Larvae were analyzed for potential differences in both larval and adult weight and time to pupation and emergence. In Trial I, there were more days to pupation and a prolonged adult emergence in the food-limited treatments. Control larvae developed and achieved maximal weights faster than food-limited larvae. Adult weights were also significantly higher in the control. Higher temperature in Trials II and III accelerated larval development. Early onset of food limitation at this higher temperature (Trial II) exacerbated differences among treatments, whereas later onset food limitation dampened these differences.

In the nonglaciated Allegheny Plateau of northwestern Pennsylvania ground-layer plant communities of headwater riparian forests are among the most species-rich of the region. We examined the influence of inundation potential (geomorphic surfaces with high, moderate or low probability of seasonal inundation) and forest overstory (stems ≥2.5 cm dbh) characteristics (percent overstory cover, overstory basal area, overstory stem density and basal area of eastern hemlock, Tsuga canadensis) on species richness, biomass and cover of the summer ground-layer (all vascular plants ≤1 m tall) at six riparian sites. The study design used inundation as a class variable with sites or portions of sites within each class as replicates (n = 4 for each inundation class). Mean total species richness (7.3 ± 1.3 se species/0.25 m²) and biomass (51.0 ± 12.4 se gm dry weight/0.25 m²), forb species richness (4.3 ± 0.8 se species/0.25 m²) and biomass (9.3 ± 4.5 se gm dry weight/0.25 m²) and graminoid species richness (2.4 ± 0.3 se species/0.25 m²) and biomass (40.3 ± 8.7 se gm dry weight/0.25 m²) were significantly greater for geomorphic surfaces of high inundation potential than for those of moderate and low inundation potential. Overstory cover, overstory stem density and basal area of T. canadensis were not correlated with ground-layer species richness, biomass and cover within inundation classes. Wetland species (obligate facultative wetland species), chiefly forbs and graminoids, occurred most often on geomorphic surfaces of high inundation potential (66.7% of total species for which wetland indicator status has been determined); upland species (facultative facultative upland upland species), mainly tree seedlings, occurred principally on geomorphic surfaces of moderate and low inundation potential (81.5% and 74.3% respectively, of total species for which wetland indicator status has been determined). Differences in species composition, richness, biomass and cover suggest that the ground-layer of Allegheny Plateau riparian forests is composed of a series of wetland and upland species guilds that replace each other along the stream to mesic forest gradient.

We documented the occurrence of 12 bird species within Prairie Ridge State Natural Area, Jasper County, Illinois, a matrix of nine grassland tracts (range 7–120 ha, totaling 489 ha), from 1994 to 1997 and analyzed the presence of these species relative to the area of the nine grassland tracts. Grassland tract area was correlated with the occurrence of greater prairie-chickens (Tympanuchus cupido) (P = 0.016), upland sandpipers (Bartramia longicauda) (P = 0.012), savannah sparrows (Passerculus sandwichensis) (P = 0.009) and Henslow's sparrows (Ammodramus henslowii) (P = 0.005). Minimum area requirements varied from 12 ha for grasshopper sparrows (Ammodramus savannarum), 55 ha for northern harriers (Circus cyaneus), 65 ha for greater prairie-chickens and upland sandpipers, to 75 ha for Henlsow's and savannah sparrows. Therefore, grasslands larger than 60 ha may be required to attract nine breeding grassland bird species. Each grassland tract was divided into 2- to 6-ha management units (mode = 2.8 ha). Our results suggest the area of grassland tracts influences the perception of habitat suitability by area-sensitive species more than size or configuration of management units within tracts.

Enneacanthus gloriosus occurs in coastal plain drainages from New York to Florida and W to Mississippi, but little is known about its life history. Enneacanthus gloriosus is smaller and shorter-lived in Mississippi than in eastern populations. The spawning season of E. gloriosus ranges from April to September and gonadosomatic index values were highest between April and August, peaking in May with an additional but lower peak in August. Ripe eggs are also found during every month of the spawning season. These data indicate E. gloriosus is a multiple batch spawner. The sex ratio did not differ from 1:1, the diameter of mature ova averaged 0.68 mm, and the number of ripe ova per female averaged 117.2. Enneacanthus gloriosus at the periphery of its western distribution in Mississippi exhibit substantial variation in a number of life-history patterns including size, age, length at maturity and spawning season compared to populations ranging from New Jersey to Florida.

The incidence of infection and reproductive success of Phoradendron californicum (desert mistletoe) on its host, Acacia gregii (catclaw), was quantitatively investigated in two localities of the Las Vegas Valley, Nevada, from March through November 1997. Similar patterns were detected between the two study sites. The abundance of Phoradendron was significantly positively correlated with age of Acacia trees, and more positively correlated with size. Phoradendron-infested trees were significantly older and larger, and had significantly lower diurnal and seasonal water potentials than adjacent uninfested trees. Phoradendron-infested trees were significantly more water-stressed than uninfested trees of similar age and size. Infested Acacia trees occurring on an extensive terrace surface were significantly more water-stressed than Acacia occurring along an intermittent wash during the dry summer season. Phoradendron canopy cover and fruit production were significantly larger on Acacia trees occurring along the wash than on the terrace. High levels of Phoradendron infestation greatly increased host-plant water stress, and low host-plant water potentials significantly reduced the canopy cover and fruit production of Phoradendron. However, characteristics of Phoradendron fruits were not significantly different between the two geomorphic surfaces. A combination of age, size and water status of Acacia trees largely influences the infection and reproductive success of Phoradendron in the Las Vegas Valley of southern Nevada.

Fragmentation of habitat has been found to create dispersal barriers for some species. Less well understood is the possibility that physical barriers to dispersal between habitat patches might be reinforced or modified by behavioral barriers. We assessed whether there are differences in aggressive behavior between Peromyscus leucopus from large continuous tracts of woods and habitat islands (i.e., isolated woodlots). Data from studies of mainland and true island habitats suggest that mice are less aggressive on islands. If decreased aggressiveness also characterizes mice in habitat islands, populations may be more permeable to immigrants than their physical isolation suggests. To determine if this pattern is evident in habitat islands, we paired adult males from the two habitats (continuous woods and isolated woodlot) in a neutral arena and measured frequencies of aggressive behaviors. Males from both habitats were equally aggressive. We suggest that physical isolation of habitat islands is not ameliorated by decreased aggression to immigrants as it seems to be in the mainland/island complex.

Zizia aurea (L.) Koch (Apiaceae) planted in a tallgrass restoration near Viola, Wisconsin, declined in numbers in randomly assigned plots left unburned or burned in May (41 to 9 and 63 to 30 individuals, respectively), but tripled in numbers in plots burned in August (72 to 209). Fire intensity varied widely, with a nine-fold range in May (86-782 kW/m) and a 49-fold range in August (58-2831 kW/m). In the August burn treatment, Z. aurea was most common in plots experiencing intense fires that cleared most or all ground litter. These same plots harbored 95% of the Z. aurea that flowered in 1996. A separate mowing experiment removed grass canopies to 10 cm, while leaving litter intact. Zizia aurea numbers did not change in plots mowed in May (76 to 77 individuals), but doubled in plots mowed in August (66 to 121). Zizia aurea is strongly favored by fire that simulates the timing of summer lightning fires thought to be common throughout grasslands and savannas of central North America before European settlement.

Various growth parameters and the requirements for flowering of Senna (=Cassia) marilandica, an herbaceous polycarpic perennial native to the eastern United States, and Senna (=Cassia) obtusifolia, a pantropical-warm temperate annual weed, were compared in greenhouse and growth chamber studies. Relative growth rate (RGR) of seedlings-juveniles of S. marilandica and S. obtusifolia did not differ. However, after growth (from seeds) in the greenhouse from 28 May 1991 to 18 September 1991: (1) dry mass of S. obtusifolia plants was nearly twice that of S. marilandica plants; (2) root/shoot ratio of S. marilandica plants was more than four times that of S. obtusifolia plants; and (3) reproductive effort (dry mass of fruits/dry mass of whole plant) of S. obtusifolia plants was 27%, whereas plants of S. marilandica did not flower. Compared to the control, shoots of cold-treated S. marilandica plants emerged earlier, and a higher percentage of them flowered. Senna marilandica was confirmed to be an obligate long-day plant, and S. obtusifolia was shown to be a facultative short-day plant. Results of this study and of others clearly show that S. obtusifolia is a more strictly r (sensu MacArthur and Wilson) or R (sensu Grime) species than is S. marilandica.

Eastern hemlock (Tsuga canadensis) was a major component of mesic forests in the Upper Great Lakes region, but presently persists in only a few locations. Many of these stands experience poor regeneration due to herbivory by white-tailed deer (Odocoileus virginianus), suggesting that hemlock will become progressively less common in these stands. We tested the hypothesis that balsam fir (Abies balsamea) facilitates establishment of eastern hemlock at 11 sites in northern Wisconsin. Hemlock saplings are three times as dense and twice as tall when growing within patches of balsam fir compared to growing outside such patches. Hemlock saplings growing outside balsam fir patches are also four times as likely to exhibit deer browsing damage as those growing inside. These results suggest that patches of balsam fir create a physical or visual barrier to deer and thus provide a refuge for hemlock saplings from white-tailed deer browsing. Because balsam fir saplings are much more abundant than hemlock in northern Wisconsin forests and establish on a wider range of sites, foresters could use patches of balsam fir to facilitate local hemlock establishment and so promote restoration of this important forest type.

We studied the diet and prey selection of Desmognathus brimleyorum in southeastern Oklahoma relative to salamander size class and availability of prey. We found significant differences in prey consumed by large and small size classes. Also, by comparison with invertebrate samples taken in one salamander habitat, prey selected by D. brimleyorum was significantly disproportionate to its availability. Dipterans were taken more commonly than encountered in the habitat, and isopods taken less commonly.

The Great Lakes region has come to be occupied by at least two species of Dreissena, the zebra mussel, D. polymorpha and the quagga mussel, D. bugensis. The species are distinguished on the basis of shell morphology and electrophoretic patterns. Comparisons of the posterior mantle regions reveals differences between the two species in the extent of sensory papillae above the exhalant siphon and the point of union of the middle mantle fold.

Genetic polymorphisms were investigated in fishers (Martes pennanti) using horizontal starch gel electrophoresis of allozymes. During the 1996–1997 fisher trapping season muscle and liver samples were collected from animals in New Hampshire, New York, Wisconsin, and West Virginia, whereas blood samples were collected from New Hampshire and New York animals only. A total of 30 gene loci were resolved from muscle, liver and blood samples. For the entire pooled sample, the mean multilocus heterozygosity (direct count) was 0.047 and the percentages of loci polymorphic (0.95 criterion and 0.99 criterion) were 20.8 and 45.8, respectively.