Greenhouse and field studies were used to assess the effects of a cottonwood leaf beetle (Chrysomela scripta) outbreak on growth and survivorship of Fremont cottonwood (Populus fremontii) along a segment of the Yampa River in northwestern Colorado. Exposure of greenhouse-reared seedlings to either 1 or 3 larvae reduced survivorship and the shoot and root masses of surviving seedlings. In the field sapling survivorship in unmanipulated, naturally established patches of saplings was inversely related to the intensity of beetle damage noted the previous year in both 1998–1999 and 1999–2000. Floodplain saplings treated with the insecticide esfenvalerate during two growing seasons added more height and radial growth than untreated saplings. Field observations in riparian stands along the Yampa River indicated that beetles preferentially oviposited and fed on cottonwood seedlings over saplings and mature trees during late summer. Taken together, the greenhouse and field studies suggest herbivory by C. scripta is a major determinant of Fremont cottonwood distribution and abundance at the Yampa River site. Repeated surveys detected few or no beetles in stands along the neighboring but regulated Green River. We hypothesize that flow regulation, by reducing P. fremontii seedling abundance, precludes C. scripta from reaching outbreak status along the Green River.

For pairwise coevolution to occur between a plant and one of its insect herbivores, the effects on plant fitness of that herbivore must be independent of other herbivore species. Here we present an experiment designed to test whether the effects of herbivory by Trirhabda beetle larvae and Philaenus spittlebugs are additive or whether the presence of one herbivore alters the impact of the other. We found that beetles and spittlebugs feeding together on tall goldenrod (Solidago altissima) reduce the mass of the apical bud and the foliage more than would be expected from either insect feeding alone. Reductions in stem, lateral shoot and root mass were also greater than expected, but these differences were not statistically significant. A multivariate analysis to examine effects on all components of the plant revealed greater reductions in plant biomass when beetles and spittlebugs fed together than when either fed alone. This suggests that the effects of herbivory by these two insects are not independent and that neither is likely to develop a simple pairwise coevolutionary relationship with the tall goldenrod. However, because damage to goldenrods is increased when the beetles and spittlebugs feed together, these insects may select more for increased plant resistance to herbivory when feeding together than feeding separately.

Selective herbivory by animals can have significant effects on the succession of a plant community. Damage resulting from major insect outbreaks has been shown to alter species dominance and competitive balance of woody plants in temperate North America. In this study we examine the effects over three seasons of a visually striking herbivory event: periodical cicada (Magicicada cassini) oviposition into an early successional tree community in the prairie-forest ecotone in eastern Kansas. Oviposition damage during cicada emergence in 1998 was large in overall magnitude, highly variable in space and varied by host tree species. From 1998–2000 we monitored four measures of tree growth on individuals of each tree species on the study site, and infructescence production on the dominant species (rough leaved dogwood, Cornus drummondii). Cicada damage in 1998 was regressed against each measure of tree performance in following years. Only a few statistically significant results were found. Overall, we concluded that the widespread oviposition damage from periodical cicadas did not have any important effects on successional dynamics of the host plants, suggesting that the trees appeared to compensate sufficiently for physiological damage during the emergence. We suggest that documenting the absence of substantial impacts from episodes of herbivory is useful in gauging the general significance of herbivory in succession.

I hypothesized that the naturally elevated Ni concentration of Melanotrichus boydi (718–789 μg g⁻¹) might protect this insect species against pathogen attack. I contrasted survival of M. boydi against survival of the low-Ni mirid Lygus hesperus when treated with three entomopathogenic biocontrol agents. Biocontrol agents used were the fungus, Beauveria bassiana, and infective juveniles of two nematode species (Steinernema carpocapse and Heterorhabditis bacteriophora). Biocontrol agents suspended in water were sprayed onto insects placed in petri plates in the laboratory. Control treatments consisted of spraying water onto comparable replicates. Separate experiments examined effects of biocontrol agents on nymphs and adults of each species. I monitored insect survival for 4 d after treatment and used survival analysis to contrast survival of individuals receiving control and biocontrol treatments for each species. Biocontrol agents significantly reduced the survival of L. hesperus in all but two trials and reduced the survival of M. boydi in all experimental trials. Both insect species were susceptible to these pathogens and I rejected the hypothesis that elevated body Ni concentration protects M. boydi from pathogen attack.

Average length of time between fires is thought to limit shrub height of some Florida scrubs which has been found to exceed 3 m within 30 to 40 y, a height at which these scrubs no longer support the Florida scrub jay (Aphelocoma coerulescens) and possibly other rare species endemic to this vegetation type. We hypothesize, however, that stem lifespan, rather than the average fire return interval, limits the height attained by Quercus inopina, a dominant shrub oak endemic to scrubs on the Lake Wales Ridge in south-central Florida. To determine stem longevity and height growth, the perimeters of 56 stem clusters at nodes on the rhizomes of Q. inopina were outlined with wire flags in four scrub stands at Archbold Biological Station in south-central Florida and all stems in each cluster tagged. Height growth and survival of 448 stems were followed for 9–10 y, along with that of any new stem sprouts appearing within the perimeters of the marked clusters during this time. Between 80 and 90% of the initially tagged oak stems died within 10 y. New stem sprouts replaced these stems such that the total number of stems at the marked clusters either remained roughly the same or increased slightly. Median life span of stems was approximately 4 y, with maximum age estimated at 9 y. Rapid turnover limits the median height attained by stems of Q. inopina to <2 m, precluding the scrubs it dominates from reaching the 3–4 m height unfavorable to the Florida scrub jay, at least in the same 30–40 y time period as do scrubs dominated by its close relative Q. myrtifolia.

Forest edges are known to affect plant community composition and habitat use by animals. However, the direct influence of edges in determining patterns of tree regeneration is poorly understood. Survival of and herbivore damage to Quercus rubra seedlings were experimentally determined for seedlings planted across a forest—old-field edge gradient. Seedling survival was lowest inside the forest (1%), intermediate at the edge (25%) and highest within the old-field portion of the gradient (49%). Deer herbivory decreased with increasing distance into the old field. Seedling survival increased under Rosa multiflora and decreased in plots with mammalian herbivory. Seedling height was significantly affected by distance from the edge but was unaffected by mammalian herbivory. Based on our results, herbivore effects on Quercus rubra growth and survivorship appear secondary to influences of distance from the forest edge.

As interest in invasive species management increases, new information with respect to invasive species abundance and distribution in invaded habitats is imperative. One essential type of information is demographic data. When invasive plants colonize a new habitat, their numbers may be low at first, but the population may undergo rapid expansion. We were interested in the effect of intraspecific density on the population dynamics and life history attributes of Alliaria petiolata a Eurasian biennial herb that has become an invasive pest in portions of North America. Thirty plots were established in a mesic second-growth deciduous forest in high, medium and low density patches of A. petiolata rosettes. Demographic data were collected for all A. petiolata cohorts present in the plots from 1996–1998. In June 1998 all first year rosette and second year mature individuals were harvested, dried and weighed. Stage-based population projection matrices were constructed in order to compare demography among plots and years, and models were used to predict trends in future population growth. There were significant differences among demographic parameters as a function of density and year. Survival to flowering in 1998 was greatest for plants in low density plots. These plants were also larger and produced more fruits than plants in either medium or high density plots. Initial differences among plots in plant density diminished and by 1998 there was no significant difference among density treatment plots in number of flowering plants or number of seeds produced. Seed bank formation ensures that, even under less favorable circumstances, A. petiolata can remain at a site for a number of years. Lambda values indicated that the number of plants in plots of each density is increasing, with the greatest increase in low density plots (λ = 1.45). As this study shows, due to abundant seed production, patches of low A. petiolata density in a newly colonized mesic forest can grow rapidly and in a few years form a dense stand.

A new source of data on early postsettlement woodlands, witness trees in woodlot subdivision surveys, is described. Subdivision surveys of Thorn Grove, Will County, Illinois (1848–1856), using 92 witness trees, are compared to the presettlement 1834 Public Land Survey (PLS) including the same area. The woodland described in the subdivision surveys was richer in species, lower in density and composed of smaller trees than the woodland described in the PLS. Decreased density and tree size suggest beginning deforestation, but surveyor bias is a possibility.

Temporal changes in the abundance of trees and a common shrub, Cornus drummondii, were quantified for 15 y (1981–1996) in seven tallgrass prairie watersheds in Northeast Kansas. Woody plant responses to different fire frequencies and grazing were assessed with a data set that included >9000 individuals. Although 15 tree species were included in this data set, only four (Juniperus virginiana, Celtis occidentalis, Gleditsia triacanthos and Ulmus americana) were sufficiently abundant for detailed analysis. Over the 15 y study tree density increased by two- to 10-fold, except in watersheds burned annually where woody plants remained almost completely absent throughout the study. Although increased woody plant abundance was expected in watersheds protected from fire, tree and shrub density also increased substantially in watersheds burned only once in 4 y. An intermediate fire frequency (burned every 3–5 y) actually increased the abundance of C. drummondii relative to a low fire frequency (burned only once in 15 y). Moreover, a severe wildfire in 1991, which affected all watersheds, did not markedly reverse this pattern of increase in abundance in most tree species. Four years after the addition of native herbivores (Bos bison) to three of the long-term experimental watersheds (infrequently and annually burned) woody plant abundance increased by four- and 40-fold, respectively, compared to corresponding ungrazed watersheds. Thus, the presence of large ungulate grazers in tallgrass prairie resulted in a significant increase in woody plant abundance. The most parsimonious explanation for this phenomenon is that fire intensity and extent was reduced in grazed grasslands allowing greater success of woody species.

Clone size of plants of Andropogon gerardii from Konza Prairie Biological Station, Manhattan, Kansas was estimated from spatial patterns of genetic variation, using proteins detected by starch gel electrophoresis and DNA content (ploidy) measured by flow cytometry. Unique multi-locus protein banding patterns and differences in ploidy were used to exclude plants as members of the same clone. Individual clones averaged about 2 m in diameter and areas of prairie of 100 m² were calculated to contain an average of 31.8 genetic individuals.

Predation patterns on artificial waterfowl and passerine nests were studied in upland habitats adjacent to freshwater marshes located in urban, agricultural and natural habitats, near Ottawa, Ontario in 1989 and 1990. Nest predation on waterfowl nests did not change during the breeding season in urban and in agricultural habitats but it increased significantly in natural habitats. There were no significant differences over time of year in predation on passerine nests in any of the three types of habitats. Nest camouflage was not a factor in preventing nest destruction. Nest predation was higher on passerine nests than on waterfowl nests in urban and natural habitats but was similar in agricultural habitats. Losses of waterfowl nests were similar among habitats in both years. Passerine nests were more frequently destroyed in natural habitats than in urban and agricultural habitats. Small predators such as the blue jay (Cyanocitta cristata) and red squirrel (Tamiasciurus hudsonicus), more commonly observed in urban and natural habitats compared to agricultural habitats, would most likely explain differences in nest predation among habitats as well as differences between nest types.

Pastures provide substantial habitat for grassland birds of management concern in the Driftless Area of southwestern Wisconsin. The rolling topography in this region is characterized by lowland valleys surrounded by relatively steep and often wooded slopes which are set apart from more expansive treeless uplands. We hypothesized that there would be lower densities of area sensitive grassland passerines in lowland grasslands compared to upland grasslands because of their preference for larger more open grasslands. To test this hypothesis and assess how well pasture area and vegetation structure predicted grassland passerine density compared to upland/lowland status, we conducted point counts of birds in 60 pastures in May–June 1997 and 1998. Upland pastures generally supported greater densities of grassland passerines than lowland pastures. Densities of Savannah sparrow (Passerculus sandwichensis) and bobolink (Dolichonyx oryzivorus) were significantly higher in upland pastures than in lowland pastures. Grasshopper sparrow (Ammodramus savannarum) density was significantly higher on uplands in one of the study years. The density of eastern meadowlark (Sturnella magna), western meadowlark (S. neglecta) and sedge wren (Cistothorus platensis) did not differ significantly between uplands and lowlands. Grassland passerine density was also predicted by pasture size and vegetation structure. Densities of bobolink and grasshopper sparrow were higher in larger pastures. Bobolink and Savannah sparrow occurred on pastures with greater vegetation height-density and less bare ground; bobolink also preferred shallower litter depths. Lowland pastures supported grassland bird species of management concern and should not be neglected. However, we recommend that pasture management for grassland passerines in areas of variable topography favor relatively large upland pastures that will contain higher densities of species of management concern.

Adult female Orconectes illinoiensis, O. indianensis, O. kentuckiensis, O. cf. propinquus and O. virilis were investigated for evidence of form alternation similar to that in conspecific males. Living females were categorized qualitatively as form I or form II. Form I females exhibited one of the following, swollen white glair glands, dependent offspring (embryos to 3^rd instar juveniles) or eggstalks with remnants of eggs attached to pleopods. All other females were classified as form II. Only form I females were observed mating with form I males, therefore the form I condition is considered to be sexually active. Quantitative differences were observable for living and preserved specimens for carapace length to pleonite 2 width ratio (CL/P). Form I females have wider abdomens and a lower CL/P ratio than same-sized form II female conspecifics. Form II females are most prevalent during the summer growing season. Form I females first appear in the fall mating season and are the most abundant female form through the end of the spring spawning season for females of adult dimensions. Six female O. illinoiensis collected in the late growing season as form II of minimum adult dimensions or greater and nine collected in berry (form I) during the spring spawning season were held under natural photoperiod for instar advancement. All six females collected in early fall as form II molted into a form I instar while 8 of 9 collected in spring as form I (in berry) molted into a form II instar. Two females collected as form I molted into a form I instar after a single intervening form II instar while one female proceeded through 2 form II instars.

The reproductive biology of the crayfish Orconectes luteus (Creaser) from the Jacks Fork River, Missouri, was studied. Data on reproduction, fecundity and growth were obtained from monthly or semimonthly collections over 27 mo. Females oviposited in March or April, depending on water temperature, and the young became independent by May or June. Seasonal growth and molting began when water temperatures exceeded about 9 C in spring and ceased when water temperatures dropped below 8 C in fall. About one-third of the male and female crayfish became sexually mature their first year of life. Adult males began molting to the reproductive state (Form I) in September and October and returned to the nonreproductive state (Form II) in April and May when the females were carrying eggs and young. Newly hatched young went through two molts before becoming independent from the female in the third instar. A significant positive relation was found between crayfish size and number of ovarian eggs, pleopodal eggs and size of pleopodal eggs. Significantly greater numbers of ovarian vs. pleopodal eggs were found at both sites.

Seeds of seven fleshy-fruited shrubs used by American black bears (Ursus americanus) were extracted from fresh fruit (controls) and from scats of free-ranging and captive bears (ingestion treatments). Effects of the digestive process on viability, germinability and germination rate were measured against controls. Results were species specific. Filled control seeds of all species were highly viable (>74%). Digestion by bears had no significant effect on initial viability, except for serviceberry (Amelanchier alnifolia) for which viability of seeds passed through captive bears decreased 14%. Percent germination of control seeds summed over five chilling durations at 1 C was significantly different from that of at least one bear ingestion treatment for five of the seven species. For chokecherry (Prunus virginiana), Oregon grape (Mahonia repens) and skunkbush sumac (Rhus trilobata), seeds ingested by wild black bears germinated to a significantly higher percentage than controls, but for snowberry (Symphoricarpos oreophilus) control seeds germinated significantly better. For serviceberry all viable seeds germinated after sufficient chilling, but germination of controls was higher than ingested seeds after shorter chilling durations. When seeds were prewarmed for 5 wk before chilling, percent germination of Oregon grape, skunkbush sumac and snowberry significantly increased. For serviceberry, prewarming lengthened the minimum chilling requirement from 7 to 14 wk. Results from ingestion treatments suggest that the digestive process of black bears may simulate prewarming of seeds. Future work clarifying the role of bears as seed dispersers should involve characterization of: (1) scat deposition sites, (2) activities of seed predators and secondary dispersers at the scats and (3) the relative importance of bears in communities containing other dispersal agents.

We studied the food habits of the Italian wall lizard, Podarcis sicula, that was introduced to Long Island, New York in 1966. We recovered 436 prey items from 96 lizards. There was no significant relationship between the percentage of lizards without prey items and date of capture. On average, females had significantly more prey items per lizard, lower overall prey diversity and lower prey evenness, than did males. This suggests important differences in foraging habits between the sexes. We found remarkably high similarity between prey species diversity for the Long Island and two of four European populations. There was no correlation between prey size and either head width or snout-vent length of the lizards.

Reproductive behavior of the eastern garter snake (Thamnophis sirtalis sirtalis) was evaluated in the field at the Mosquito Hill Nature Center, New London, Wisconsin. In addition, twenty-eight males (24 adult; 4 subadult) were collected during the active season to examine the reproductive physiology. Courtship behavior and mating in this population was similar to previous reports on Thamnophis with the exception of a relatively abbreviated courtship season lasting only 3–5 d. Our study population exhibited a dissociated reproductive pattern in which spermatogenisis was initiated after the breeding season had ended and sperm over wintered in the vas deferens. Upon emergence from low temperature dormancy, the testis mass and seminiferous tubules were regressed with spermatogonia the dominant cell type. Maximum tubule and epithelial development occured in late summer corresponding to peak spermatogenesis and elevated testosterone levels (T). While the tubule diameter and epithelial height of the renal sexual segment (RSS) did not exhibit seasonal fluctuation, sexual granules within the cells of the epithelia did display a seasonal variation that was determined by the absolute number, individual granule density and staining properties. Testosterone levels (T), elevated in the fall before entering winter dormancy, were not significantly different from the levels of animals sampled immediately upon emergence. There was, however, a significant reduction in circulating T in animals sampled following the end of the breeding season. Four small males collected in mid-to-late summer had just initiated spermatogenesis. Examination of the caudal vertebrae by skeletochronology revealed these individuals were in their second active season. In these subadults, development of the testes and RSS development was not as advanced as that of adult males collected at the same time. In addition, the level of circulating T in the subadults was significantly lower than in adults collected at the same time.

The desiccation tolerance of three mycophagous Drosophila species was measured by enclosing sets of 20 sexed flies in Drosophila vials with 2 g of Drierite® calcium sulfate desiccant at 23 C and recording the time until 10 flies were dead (LT₅₀). Female D. putrida were the most desiccation tolerant; they had LT₅₀ periods (X̄ ± 1, sd = 21.55 ± 1.36 h) twice as long as male D. putrida and males and females of D. falleni and D. tripunctata. Although D. putrida had the lowest initial wet mass, it had significantly higher percentage body water and lost a smaller percentage of body water at LT₅₀ than the other species. These differences in desiccation tolerance may explain, in part, why D. putrida is more abundant than the other species in dry habitats or during dry periods.

To determine sexual dimorphism in spotted gar (Lepisosteus oculatus), variation in standard length, mass, snout length, snout width and body depth was compared between sexes using analysis of covariance. Females were significantly longer and had longer snouts when effects of variation in mass, snout width, body depth and age were accounted for. Discriminant function analysis (DFA) discriminated between sexes with 78% accuracy from 159 field collected specimens using standard length and snout length. Using coefficients from the DFA, the sex of 65 museum specimens was predicted to 85% accuracy. Sexually dimorphic standard length is probably related to gonad size differences between males and females. Reasons for snout length dimorphism are not apparent. This study demonstrates the existence of sexual dimorphism in spotted gar.

Naïve laboratory-spawned Etheostoma nigrum (johnny darter) exhibited a fright response (reduced movement) following exposure to the skin extract of wild conspecifics, indicating that the response is at least partially innate. No response was elicited by exposure to extract from lab-reared conspecifics.

Many studies have examined seed removal by rodents without regard to possible biases from inadvertent olfactory cues left by the researcher. I compared removal rates of seeds that had direct contact with human skin (scent treatment) with those that had no direct contact (no-scent treatment). Seeds of two species were alternated at 5 m intervals along a straight transect in a native grassland in northwestern Illinois. Each treatment had 100 seeds, equally divided among two woodland species that are regularly dispersed by birds into grasslands. Seeds were monitored for removal for 30 d. The rate of seed removal was significantly faster for the scent than no-scent treatment. At the end of the study 88% of scented seeds had been removed compared with 55% of the no-scent seeds. Researchers should minimize unintentional olfactory cues during seed removal studies in order to get more accurate estimates of the impact of seed removers.

Effects of mate loss on gray fox behavior are poorly understood. We examined space use and gross movements of mated gray foxes following loss of their respective mates in central Mississippi during 1994–1997. We monitored 9 mated pairs of gray foxes and documented 4 instances of mate loss. Of 2 instances where the remaining pair member was a male, 1 male substantially (by 500%) increased his space use and movements following loss of the female. The other male reduced (by 58%) his space use around the den site where kits were confirmed as being present. Of 2 instances where the remaining pair member was a female, 1 female reduced her space use (by 33%) around a den site before leaving the study area 10 d later. The other female increased her space use (by 42%), but maintained an area that overlapped the spaces maintained formerly by herself and her mate. Our findings suggest that gray fox distribution is potentially affected by loss of mates, but that both genders will maintain areas used previously by the pair. Furthermore, our findings offer evidence that male gray foxes contribute to parental care responsibilities and may maintain dens with postweaned kits following loss of a mate.

We examined fungus consumption (mycophagy) by the southern red-backed vole, Clethrionomys gapperi, at 4 sites within two mixed mesophytic forests in the southern Appalachians in 1996 and 1999. Fecal pellet analysis was used to determine the fungi consumed by 30 voles. Overall mean spore frequency, measured as the proportion of fields of view that contained a spore, was 0.68, whereas mean frequency of plant material was 0.57 and frequency of insect material was less than 0.04. Voles primarily consumed 5 types of fungi, consisting of 4 genera and Glomalean spores, although 29 unidentified spore morphotypes were also observed. Among identified spores, mean frequency of Melanogaster was greatest, followed by Coprinus, Elaphomyces and Glomalean spores. Spores of Hymenogaster were least frequent. The consistent presence of spores in fecal pellets suggests that fungi are an important food item and that C. gapperi may be an important disperser of fungal spores. Compared with previous studies, our research supports the notion that C. gapperi is a fungal generalist and analysis of vole diets may be useful for assessing the availability of fungi for other, more specialized small mammal mycophagists such as the northern flying squirrel, Glaucomys sabrinus.