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The Karner blue butterfly, Lycaeides melissa samuelis, is an endangered species residing in savanna and barrens habitats in the Midwest and Northeast United States. To improve our understanding of nectar plant selection patterns by the Karner blue, we examined nectar plant choices made by 146 butterflies. Within observation areas of 2-m radius butterflies usually chose the nectar species with the greatest total number of flowers or flowering heads. This suggests that the Karner blue is opportunistic in selecting nectar plants. However, certain nectar species, including Arabis lyrata, Coreopsis lanceolata, Melilotus alba and Rubus flagellaris, were selected in a significant majority of cases when other nectar species were available nearby. At least in the case of R. flagellaris, this preference was not directly related to the species' local flower abundance. In a significant majority of cases (77.5%) adult Karner blues selected nectar plant species with yellow or white flowers over species with other-colored flowers. Comparison of nectar plant selections at Indiana Dunes National Lakeshore to selections from Michigan and Wisconsin suggests that the Karner blue most frequently chooses a suite of nectar plant species that includes A. lyrata, C. lanceolata,Euphorbia corollata, M. alba, Monarda punctata, Potentilla simplex, Rubus spp., Solidago speciosa and, perhaps, Asclepias tuberosa and Helianthus divaricatus. This suite includes plant species that readily flower in the sun and others that readily flower in the shade, an important consideration since Karner blues often move across the sun-shade interface.
This study examined the adaptive significance of ovipositing near conspecifics by pairs of the dragonfly Sympetrum vicinum. Studies were conducted at two artificial ponds in New York using a series of 1 m2 plots along their shorelines. Although the majority of pairs oviposited alone, pairs also tolerated the presence of others only 5–10 cm away, and sometimes 2–7 pairs oviposited together within a single plot. Habitat selection (preference for certain plots over others) partially accounted for such behavior. However, where adjoining plots were homogeneous (i.e., used equally for oviposition), newly arriving pairs were more likely to begin dipping in a plot in which one or more pairs were already present, thus also suggesting mutual attraction among pairs. Oviposition efficiency (measured as no. abdominal dips/s) was apparently not compromised by ovipositing near conspecifics. Harassment from unpaired males had little effect on oviposition since unpaired males were uncommon and rarely approached pairs. However, lone pairs were attacked relatively more frequently by frogs than were pairs present simultaneously in the same plot. Although none of the 112 predation attempts I recorded were successful, frog attacks forced pairs to change sites, thereby lengthening the time required for oviposition. The absence of frogs or frog attacks at a site provided favorable conditions for pairs to accumulate at a site; thus the presence of conspecifics may have signaled a safe area for oviposition.
Drosophila subobscura and D. azteca are closely related species that have coexisted on the west coast of North America since that area was colonized by D. subobscura in the late 1970s. We have studied competition between the two species by the serial transfer technique at different initial proportions (20%, 50%, 80% and 100%) and at two densities (20 and 100 individuals). The cultures were maintained at 18 C. In the mixed cultures D. subobscura outcompeted D. azteca at both densities and all initial proportions. Survivorship was similar for both species, although the productivity of D. azteca was reduced, especially in the mixed cultures. The productivity of D. subobscura in the mixed cultures was a function only of the initial number of individuals of this species, and was completely unaffected by the number of D. azteca in the populations. Carrying capacity was attained by both species when the number of founder individuals was twenty; however, the number of descendants was much lower for D. azteca than for D. subobscura. In the pure cultures an important effect of season was detected in the replicates: the productivity of D. subobscura was much higher in spring than in autumn, while the reverse was observed in D. azteca. This effect was not detected in the mixed populations. Thus, lower carrying capacity, lower fecundity, longer mean eclosion rate, delayed oviposition or a combination of all of them could explain the low success of D. azteca in the mixed cultures.
Several studies have reported that some grassland birds are area sensitive; they exhibit a nonrandom avoidance of small fields. The methods used to test for area sensitivity, however, differed among studies. Some investigators sampled fields with sampling effort proportional to field size, whereas others used equal sampling effort in all fields. We created a simulation model with the same number of fields and field sizes as those examined in earlier studies to determine if birds that select habitat randomly would display area sensitivity if fields were sampled in proportion to their size. The three species that we modeled to settle randomly, upland sandpiper (Bartramia longicauda), Henslow's sparrow (Ammodramus henslowii) and eastern meadowlark (Sturnella magna), had positive relationships between occurrence and field size when a complete census or proportional sampling was used, and therefore, would have been considered area sensitive by the methods used by some previous authors. When equal-effort sampling was used, these species showed no relationship between occurrence and field size. Future studies on area sensitivity that use proportional sampling should compare results to a null model. Otherwise, conclusions made about area sensitivity may be erroneous because the response is a sampling artifact.
Negative effects on native plant populations are often attributed to invasions by exotic plants, but experimental evidence is lacking to support many of these claims. Lonicera maackii, an exotic shrub with long leaf phenology, has become naturalized throughout the eastern United States. This study investigated the effects of L. maackii on demography of Galium aparine, Impatiens pallida and Pilea pumila, native annual herbs in differing phenological categories. These interactions were examined in two Ohio forest stands. One stand has a history of logging, burning and grazing and a higher L. maackii density, whereas the other stand has little anthropogenic disturbance and a lower L. maackii density. Three types of experimental plots were established: L. maackii removal, L. maackii present and, at the less disturbed stand, L. maackii absent. Seedlings of the annuals were transplanted and monitored for 1 y for survival to reproductive age and fecundity.
In the more disturbed stand, survival of Galium aparine and Impatiens pallida and fecundity of all three species were significantly greater in the removal treatment than where Lonicera maackii was present. In the less disturbed stand there was no treatment effect on survival, but fecundity of all annuals was greater in the removal treatment than where L. maackii was present. Also, fecundity of I. pallida and Pilea pumila was greater where L. maackii was absent than where it was present. At both sites fitness (estimated as the product of survival and fecundity) was highest for each species in the removal treatment and lowest where L. maackii was present.
These results demonstrate direct effects of the invasive shrub Lonicera maackii on populations of annuals. They suggest that other annuals, particularly those that are shade-intolerant or photosynthesize only in the early spring, will decline in the presence of shrubs with early leaf expansion.
The three-dimensional characteristics of canopy structure and light environment of clones of a common tallgrass prairie species, Andropogon gerardii (big bluestem), were analyzed in native and reconstructed prairies near Ames, Iowa to determine if clones are limited in size by the effects of self-shading. Clones tended to be nearly circular, with a mean circumference of 158 cm and a mean cross-sectional area of 2060 cm2; clone height was consistently near 60 cm in early summer. Irradiance at a given height in the canopy, calculated as a fraction of radiation above the canopy, decreased rapidly during May and June as plants completed most of their seasonal growth, but was relatively constant in July and August. A vertical gradient in light dominated the spatial variation in light within clones. Horizontally through a clone, light levels were higher around the southern (sun-side) periphery. Spatial variation in light, in terms of the range of values found, was least at the bottom and upper parts of the canopy and greatest in the middle of the canopy. Leaf mass/area and total leaf area per increment of canopy height were highest at 30 cm below the top of the canopy and were lower at 15 cm and 45 cm below the top of the canopy. Mean leaf area index of clones was 6.58. Diameter of clones had a weak effect, if any, on the light environment within a clone. Only clones with diameters of <20–30 cm are likely to have substantially less self-shading than larger clones. Competition with other plants or limitation by other morphological constraints, rather than limitation by self-shading, may control the upper size limit of clones.
Mead's milkweed, Asclepias meadii, is a rare long-lived perennial of North American tallgrass prairies. Stems of this clonal species are spatially aggregated and, therefore, observing survivorship and flowering of “patches” of stems best approximates the fate of genetic individuals. Population size is likely to be underestimated because more than one genotype can sometimes occur in a patch. The number of patches detected at a site in Kansas has greatly increased over the last 11 y since marking locations of individual patches allowed detection of nonflowering stems in subsequent years. The A. meadii population at our site (managed by biennial dormant-season burning) often had more flowering ramets and produced more mature follicles in years with burning. High rainfall in the preceding year, in conjunction with burning, was associated with the highest follicle production. The difficulties in detection of plants at the site mean that counts of numbers of patches over an 11-y period cannot be used to assess whether the population is increasing, decreasing or remaining constant. Several factors indicate a positive outlook for the population: management (burning) enhances fruit production, patch survivorship is high and a likelihood that more patches exist than are counted. However, the low fruit production in most years at the site is a concern for the long-term viability of the population.
Livestock effects on plant communities through overgrazing (desertification) should affect the structure and functioning of semarid rangeland communities. We measured plant, granivorous ant and rodent communities and rates of seed removal by rodents and ants in grazed (by livestock) and ungrazed desert grasslands as well as mesquite and creosotebush shrublands to test hypotheses on the effects of grazing and desertification on ecosystem structure and functioning. In desert grasslands grazing reduced the cover of perennial grasses, particularly the dominant Bouteloua eriopoda, but the cover of forbs and shrubs did not differ between treatments. One species of perennial grass, Dasyochloa pulchellum, increased in grazed grasslands compared with grassland exclosures. Detrended correspondence analysis showed that grazing caused desert grasslands to shift in community structure towards the shrublands. There were more seed harvesting ant and rodent species in the creosotebush shrublands than in the grasslands and mesquite shrublands. Grazing had no effect on the diversity of ants or rodents within grasslands, and detrended correspondence analysis revealed no clear trends in granivorous ant community structure in the grazed and ungrazed grasslands or the mesquite and creosotebush shrublands. Ants removed more seeds than did rodents in the grassland sites but rodents removed more seeds than did ants in the creosotebush sites and seed removal rates by rodents and ants were the same in the mesquite sites. Our data support the hypothesis that livestock grazing leads to a shift from grassland to shrubland in the Chihuahuan Desert, with associated changes in the structure and functioning of faunal communities. Because grasslands support few species and low densities of rodents, seed harvesting ants are the most important granivores in these desert grasslands. On a larger scale, we therefore hypothesize that the observed dominance of rodents as seed harvesters in the Chihuahuan desert is a function of the desertification of desert grasslands to shrublands by livestock, and that associated feedback effects may complicate the regeneration of degraded communities.
Alien annual grasses in the genera Bromus and Schismus are widespread and abundant in the Mojave Desert, and negative correlations between these aliens and native annual plants suggest that competition may occur between them. Effects of competition were evaluated by thinning alien annual grass seedlings and measuring the responses of native annual plants at three sites in the central, southcentral and southwestern Mojave Desert during 2 y of contrasting plant productivity. Effects of Bromus and Schismus were evaluated separately in the microhabitat where each was most abundant, beneath the north side of creosote bushes (Larrea tridentata) for Bromus and in the open interspace between shrubs for Schismus. Thinning of Bromus and Schismus significantly increased density and biomass of native annuals at all three sites, only during a year of high annual plant productivity and species richness. Effects of thinning were greatest for Amsinckia tesselata and for a group of relatively uncommon native annuals. Thinning also significantly increased the density and biomass of the alien forb, Erodium cicutarium. These results show that alien annual grasses can compete with native annual plants and an alien forb in the Mojave Desert and that effects can vary among years.
We compared browsing on twigs of small and large antelope bitterbrush (Purshia tridentata) shrubs among ten sites in the south Okanagan valley, British Columbia. We tested whether there were any age preferences by browsers and determined whether these preferences changed between seasons and mode of browsing. Two different types of browsing were observed: leaf stripping which occurred in the summer and twig clipping which occurred predominantly in the winter. We calculated age and size relationships showing that shoot volume and especially stem diameter were good predictors of shrub age. Among the ten sites, clipping removed 0.02 to 15.7% of a shrub's total twig length and stripping removed leaves from 0 to 5.2% of total twig length. Observations suggested that California bighorn sheep (Ovis canadensis california) stripped antelope bitterbrush leaves in late summer, mule deer (Odocoileus hemionus hemionus) clipped twigs in the winter and cattle clipped twigs in the summer. Browsers preferred to clip twigs on smaller and hence younger antelope bitterbrush shrubs. In contrast, larger and older shrubs were preferred for leaf stripping. Since twig clipping was more prevalent than leaf stripping in antelope bitterbrush, overall preference for younger shrubs may lead to difficulties in seedling establishment in regions where it is heavily used as winter forage.
Sarracenia purpurea L. is a carnivorous pitcher plant that attracts insect prey by producing nectar. We compared amount of sugar in different samples of nectar collected during the day and night and from bagged and nonbagged pitchers. Sugar content was measured in nectar samples from 87 pitchers at 3 h intervals over a 24 h period through the use of a wick-sampling technique and a colorimetric assay. We monitored environmental conditions at the time of nectar collection and correlated them with the amount of sugar/wick. We also measured ten pitcher characteristics and examined their relationship to variations in 24 h sugar amount. Sugar amount was higher at night for both bagged and nonbagged pitchers. During the day nonbagged pitchers had lower sugar amounts than bagged pitchers, perhaps due to removal of nectar by insects. A similar, but less pronounced, difference was observed at night. Relative humidity, air and ground temperature and time of day had little effect on sugar amount. Our data suggest that nectar may crystallize during the day and dissolve when dew forms at night.
The conservation status of the eastern spotted skunk (Spilogale putorius) was assessed in the Appalachian Mountains of Tennessee from November 1995 through June 1997. Population status and seasonal abundance were examined using live-trapping on an 8 × 8 grid in Monroe County. Relative abundance was assessed at selected sites in Blount, Greene, Monroe, Unicoi and Washington counties employing additional live-trapping methods. In 5723 trap-nights only four S. putorius were captured (trap-success rate = 0.07%). The most common mammals captured were the opossum (Didelphis virginiana) and the raccoon (Procyon lotor). All eastern spotted skunks were captured in rhododendron (Rhododendron spp.) thickets near streams. A program to monitor the status of the species in the Appalachians is recommended as a management measure.
I investigated spatial relationships and mating in a population of individually marked nine-banded armadillos, Dasypus novemcinctus, in a riparian habitat in south Texas. Adults had larger home ranges than younger individuals. Home ranges of adult females overlapped extensively with those of other adult females and breeding and nonbreeding males. Breeding males had almost exclusive home ranges from one another, but overlapped considerably with adult females and nonbreeding males. Observations of paired males and females indicated a well-defined breeding season, from June through November, with 83% of pairings occurring from June through August, confirming morphological data reported previously. The mating system was polygynous because most breeding males paired with more than one female during the breeding season, although most females paired with just one male. Polygyny and competition among males for mates was further suggested by sexual dimorphism in body mass and by the observation that just a few older males monopolized pairings.
Relocation of nest sites is common among mice of the genus Peromyscus. We documented the occupation of artificial nest boxes by litters of white-footed mice (P. leucopus) at different stages of development to determine if nest relocation by lactating females is related to the developmental stage of the offspring. Three stages of development (neonates, age 0–5 d; nestlings, age 6–14 d; and juveniles, age 15–27 d) were recognized. Although the nest boxes were monitored at approximately weekly intervals, 72% of 134 litters were observed during only one of the stages of development, indicating that movement of young during lactation was common. Comparison of observed use of the boxes at different stages of development of young to expected use indicated that use of boxes was not random. Boxes were used relatively infrequently by dams with neonates and nestlings and most frequently by dams and juveniles. We believe that the suitability of a nest site to a lactating female depends on the age of her litter and that the size of the nest cavity may be an important factor in nest selection.
Wallowing is a common behavior of American bison (Bos bison). Past explanations and current hypotheses suggested for wallowing behavior include grooming behavior associated with shedding, male-male interaction (typically rutting behavior), social behavior for group cohesion, play behavior, relief from skin irritation due to biting insects, reduction of ectoparasite (tick and lice) load and thermoregulation. We monitored circannual and circadian patterns of wallowing frequency by American bison during 1996–1997 in the tallgrass prairie region of eastern Kansas. Wallowing activity increased from April to late June or July (during 1996 and 1997, respectively), decreased during midsummer, peaked again in September, decreased from September to October and then remained low from November to March. Diurnally, wallowing was low in early morning, increased to a peak in early afternoon and then decreased during mid afternoon and evening. Within the herd adult males wallowed more frequently than adult females and both adult males and females wallowed more frequently than yearlings. We observed behaviors that were consistent with all of the hypotheses previously suggested to explain wallowing behavior by bison. Based on our observations we suggest that the alternate explanations for wallowing behavior are not mutually exclusive. However, only the relief from biting insects hypotheses was consistent with both the circannual and circadian patterns of frequency of wallowing by American bison.
We used retreats made from white polyvinyl chloride (PVC) pipes to capture hylids and determined how pipe design and placement influenced the frequency with which hylids used pipes as retreats. Pipes were hung vertically in trees on three sites in north-central Florida. Pipes were checked twice weekly for 10 mo during which 788 individuals of four species (Hyla squirella, H. cinerea, H. femoralis and H. gratiosa) were captured, with 2658 recaptures. Retreats on hardwoods were used significantly more than retreats on pines, and retreats hung at 2 m and 4 m aboveground were used significantly more than retreats at 0 m. Long and T shaped retreats (both 60 cm long) were used significantly more than short (30 cm) retreats. Retreats capped on the bottom with water inside and 3.81 cm in diameter were used more frequently than retreats of the same diameter that were either capped on the top or not capped and retreats 1.75 cm in diameter with no cap.
The Topeka shiner (Notropis topeka) is imperiled by extensive changes in stream hydrology. Responses of shiners to changes or variation in stream hydraulics, however, have not been quantified, hampering conservation efforts. We quantified swimming endurance and behavior for Topeka shiners in a laboratory swim tunnel. Sustained swimming (>200 min) was observed at water velocities of 30–40 cm/s. Prolonged and burst swimming (approximately 10 min to less than 0.1 min) was observed at water velocities of 40–75 cm/s and endurance was negatively correlated with water velocity. Larger individuals (4.4–5.5 cm standard length) exhibited greater sustained swimming ability than smaller individuals (3.0–4.2 cm standard length). Oral grasping of wire mesh within the swim tunnel was frequently employed at moderate water velocities (35–50 cm/s); this behavior may limit downstream displacement of shiners during freshets. Topeka shiners are capable of swimming speeds faster than water velocities which they typically inhabit. Fishways and culverts, therefore, may be employed to facilitate dispersal and recolonization. Swimming endurance data are used to determine optimal size and water velocities for such structures.
Spawning behaviors were filmed and observed in the nest-building minnows, the bluehead chub, Nocomis leptocephalus, and river chub, N. micropogon. Analysis of videotapes exposed previously unreported behaviors (e.g., female retroflexure) and a precise sequence of male-female interactions that coordinated a successful spawn. Reproductive behaviors were classified into six sequential categories (interim, approach, alignment, run, clasp, dissociation) to facilitate interspecific comparisons. The most conspicuous differences between species involved the intensity of the female's retroflexure and the male's spawning clasp (strong in N. leptocephalus vs. weak in N. micropogon) and reproductive behaviors of subordinate males. In N. leptocephalus, subordinate males spawned concurrently and independently of the resident male over a communal nest, whereas in N. micropogon a subordinate acted like a satellite male and stole spawns from the nest-building male. In addition, heterogeneric spawning clasps involving a male and female N. leptocephalus and a male central stoneroller, Campostoma anomalum, are newly described.
We used seed traps (n = 119) to quantify seed dispersal of the Chinese tallow tree (Sapium sebiferum (L.) Roxb.) by birds in South Carolina during the October 1995 to April 1996 fruiting season. We tested if crop size, habitat type (spoil area vs. forest) and tree distribution (isolated vs. clustered) affected the dispersal efficiency and number of seeds dispersed from tallow trees. Traps captured 55,275 seeds and 107,993 functional locules; birds removed 48.8% of the available seeds. After scaling for canopy area of sample units (1570 m2; n = 32), birds removed an estimated 675,000 ± 56,000 of 1,681,000 ± 113,000 seeds, about 40% of the total seed crop. There was a trend for forest units to have greater dispersal efficiency than spoil area units but isolated and clustered trees were similar. Crop size was not a significant predictor of dispersal efficiency in either habitat but was an excellent predictor of the number of seeds dispersed in both habitats. The most productive unit was the only one to have a persistent seed crop. These findings show that birds in coastal South Carolina use the tallow tree heavily as a food resource and are not generally saturated by present levels of tallow tree seed availability. Fourteen bird species consumed a total of 476 tallow tree seeds. The mean number of seeds probed, dropped, swallowed and taken away in a beak were significantly different among bird species, as was the mean number of individuals per observation. Species differed in the estimated numbers of seeds consumed per visit and total seed consumption for the entire fruiting season. Important seed consumers included the northern flicker, American robin, boat-tailed grackle, gray catbird and the northern mockingbird. Red-winged blackbirds and boat-tailed grackles were species that dropped many seeds. Heavy use and effective seed dispersal by different birds have contributed to the invasion success of the Chinese tallow tree in coastal South Carolina.
We collected and identified 1852 prey items from 89 boluses delivered to 62 nestling tree swallows (Tachycineta bicolor) at 14 nests in an upland old field in western Michigan. We found that 90.8% of nestling diets was insects from the Orders Diptera, Homoptera, Hymenoptera and Coleoptera. We also found clam and snail shells in boluses. Over the most common brood sizes of 4–6 nestlings, brood size was inversely proportional to the number of items per bolus delivered to nestlings although mean dry and mean organic weight of boluses did not differ. Bolus composition was not influenced by weather conditions. Nestling diets at our study site were similar in the proportions of many prey items, such as Diptera and Homoptera, to tree swallow nestling diets in other habitats but contained fewer aquatic forms such as Odonata and Ephemeroptera.
We measured habitat characteristics at 34 arboreal nest sites of golden mice (Ochrotomys nuttalli) and 34 paired random sites from May–Sept. 1997. Microhabitat was significantly different between the two types of sites. Arboreal nest sites differed from random sites in 5 of the 12 habitat characteristics measured including: more climbing vines and woody vegetation, greater horizontal vegetative cover as measured by a density board at a distance of both 3 m and 6 m from the nest and closer to understory trees. The presence of thick vegetation at arboreal nest sites may provide increased protection from predators, increased substrate for attachment of nests, protection from inclement weather and thermoregulatory advantages. Management strategies that increase the density of understory vegetation in areas where golden mice occur will enhance populations by improving nesting habitat and increasing recruitment and survival.