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Between 1993 and 1995 we sampled ground-layer vegetation on 150 plots in Facus-Acer saccharum/Arisaema Mesic Slope and Quercus alba-Acer saccharum/Parthenocissus Dry-Mesic Slope forests to determine how the understory of these forests responded to forest management. Four different stand types, clear-cuts (2–12 ha), group-selection openings (0.1–1.6 ha), single-tree selection openings (0.005–0.013 ha) and uncut 80–100 y-old reference stands were sampled. There was little relationship between the percent cover of most ecological species groups and opening age or size on either mesic or dry-mesic slopes. While clear-cuts and group-selection openings had significantly greater cover of several ecological species groups (used to classify mesic and dry-mesic slopes) than reference stands, single-tree selection openings did not differ significantly from reference stands in the cover of any ecological species group. Pearson correlation analysis indicated that more ground-layer species were significantly correlated with opening size than opening age, suggesting that the size of the initial opening has more influence on species composition than opening age. Overall, forest management has not constituted a severe enough disturbance to shift ground-layer species composition away from that associated with the sampled ecological landtype phases (mesic and dry-mesic slopes). Aspect was the dominant factor determining species distribution in Canonical Correspondence Analysis ordinations of ground-layer vegetation in both openings and reference stands.
Twelve belt transects were used to sample woody vegetation in a 110-y-old regrowth forest on a natural levee ridge bordering Bayou Sauvage, Orleans Parish, Louisiana. Elevation was measured along each transect and species flood tolerances, based upon measured elevational ranges, were assessed. Codominant native hardwoods included Celtis laevigata, Quercus virginiana and Salix nigra; palmetto (Sabal minor) was the principal understory species. An invasive exotic species, Sapium sebiferum, was found throughout the study site (2485 adults >2 m tall per ha), and showed high flood tolerance. Among saplings (0.3–2 m tall), S. sebiferum abundance (3916 per ha) far exceeded that of all native species combined. The forest showed complex species zonation along an elevational gradient of 163.5 cm across a forest-marsh ecotone. Correspondence analysis delimited at least three plant communities, two dominated by single woody plant species and a third with 15 species. These communities were: (1) a Salix nigra community characteristic of bayou margins, (2) a ridge-forest community of 15 hardwood species with overlapping flood tolerances and (3) a Daubentonia drummondii community giving way to freshwater marsh. The analysis tentatively resolved species associations within the ridge-forest community into “low-” and “high-ridge” subcommunities though insufficient data existed for their formal recognition. Elevational distributions of individual species compared reasonably well with published regional assessments of their flood tolerances and value as wetland indicators.
Although much is known about variation in both seed bank composition and disturbance effects in temperate deciduous forests, understanding of how these components interact to determine the importance of seed banks to regeneration is limited. To examine the interactive influences of seed bank composition and postdisturbance environment on seed bank recruitment, a seed bank transplant experiment was conducted in a disturbed temperate zone deciduous forest in eastern Pennsylvania. On average, 75% of the seed bank remained ungerminated. This was mainly the result of failed germination by alien species. The postdisturbance environment differed in its influence or the two dominant species, Rubus allegheniensis and Phytolacca americana. Whereas R. allegheniensis recruitment did not differ between postdisturbance environments, significantly more P. americana seedlings emerged under more open conditions. Different proportions of P. americana seeds germinated from the two seed bank sources. These results show that a large portion of the seed bank remains ungerminated under natural disturbances, and the age and history of the component seeds may influence the regenerative function of seed banks in natural ecosystems.
The release of anthers held under tension which catapult pollen onto the stigma near the end of floral life has been proposed as a mechanism for autonomous self-fertilization in normally outcrossing Kalmia latifolia. We examined the importance of this delayed autonomous self-pollination to fruit production and the efficiency of the pollen deposition mechanism under field conditions. By comparing intact open-pollinated flowers with emasculated flowers we found that autonomous self-pollination did not increase fruit production. To evaluate the efficiency of the catapult mechanism of selfing, we compared the relative fruit production of flowers that were hand-pollinated with self-pollen with those that self-pollinated spontaneously. Fruit set was higher in hand-selfed flowers than in the autonomously-selfed flowers, indicating that the natural mechanism of selfing is inefficient. Through the observation of flowers protected from pollinators we determined the natural pattern of floral phenology and anther release. The effect of timing of autonomous selfing on fruit production was assessed by manipulating the time of anther release. The timing of selfing is not related to fruit production and varies widely among flowers. Although autonomous selfing did not contribute to fruit production under natural conditions, it can assure reproduction in the absence of pollinators.
The effect of intraspecific competition and nutrient supply on the endangered northeastern bulrush, Scirpus ancistrochaetus, was examined in a full-factorial greenhouse experiment. Seedlings were exposed to 4 densities (1, 5, 10 or 25 plants/pot) and 3 nutrient concentrations (3, 25 or 50% of full strength) for 9 wk. Height, mass and survival generally decreased with increasing density. Root to shoot ratio (R : S) increased with density, indicating that competition primarily involved belowground resources. Nutrient concentration significantly affected average plant height, total mass and R : S but did not affect survival. Plant height and total mass generally increased with increasing nutrient concentration, whereas R : S decreased. In general, the negative effect of intraspecific competition on plant height and total mass was greatest at the highest nutrient concentration, confirming that the intensity of intraspecific competition increases with resource supply in this species. Neither density nor nutrient concentration affected the population distribution of plant sizes in densities over 1 plant/pot, suggesting that size hierarchies, and therefore asymmetric competition, are not important during seedling growth in this species. Information gained from this study can be used towards understanding seedling establishment in the field and, in turn, towards effective management and reintroduction of this endangered species.
Tallgrass prairie sites subjected to 10 y of annual burning, mowing, nitrogen (N) fertilization or phosphorus (P) fertilization and untreated reference sites were studied to examine effects of these management practices on arbuscular mycorrhizal (AM) symbiosis. Spring burning of native prairie field plots significantly reduced AM fungal species diversity, while increasing spore abundance. This increase in total spore number was due to a general increase in most of the 17 fungal species present. In general, the management treatments had larger effects on the richness component of diversity than on the evenness of AM species abundances. Burning and mowing had no significant effects on AM fungal colonization of roots or extraradical mycorrhizal hyphae (EMH) development. However, nitrogen fertilization significantly increased root colonization and EMH development, and P amendment decreased EMH development. There was no significant effect of fertilizer amendment on AM spore abundance, fungal species diversity or richness, but N and P fertilization decreased fungal species evenness. Effects of management practices on AM fungi may be mediated through changes in soil resources or microclimate or through changes in their host plants. These effects on AM symbiosis and community structure are important because AM fungi strongly influence the growth, demography, competitive relationships, relative abundances and diversity of plants in grassland communities.
The effect of ingestion by coyotes (Canis latrans) and raccoons (Procyon lotor) on seed germination was investigated for four tree species in Illinois. The germination rate of persimmon (Diospyros virginiana) seeds ingested by raccoons was significantly higher than the rate for uningested seeds. Both were significantly higher than the rate for coyote-ingested seeds. Among coyote-ingested seeds, germination rates of persimmon were significantly higher when seeds were protected by undigested fruit pulp or intact seed sheaths thus reducing the exposure of seeds to gastrointestinal enzymes. American plum (Prunusamericana) seeds ingested by coyotes had a significantly lower germination rate compared to uningested seeds, whereas germination of pawpaw (Asimina triloba) seeds was similar between coyote-ingested and uningested seeds. Germination was significantly lower for hackberry (Celtis occidentalis) seeds ingested by raccoons compared to uningested seeds. Ingestion improved germination only for persimmon seeds consumed by raccoons, but tree species may realize other benefits from dispersal by coyotes and raccoons (e.g., decreased parental competition).
Food storage in animals allows foragers to reap when food is plentiful and costs are low and eat when food is scarce and costs are high, thus shifting resources from periods of low value or high availability to periods of high value or low availability. To a caching animal, a food item has two components: its present value for immediate consumption and its future value if stored. We explored some properties of caching in the context of a food's future value using free-living fox squirrels (Sciurus niger) and manipulations of cacheability of supplemental food. We assessed squirrel behavior using giving-up densities (GUDS) of noncacheable food in artificial food patches. Squirrels had higher GUDs in assessment trays when given noncacheable supplemental food than when food was not augmented; when given supplemental food in a highly storable form, squirrels had intermediate GUDs. Thus, future value of food affects the foraging behavior of squirrels through the balancing of present and future needs.
We investigated the annual pattern of elk (Cervus elaphus) social group sizes and associations in Michigan's nonmigratory herd. Group observations were used to determine social group sizes and patterns throughout the year. Social group associations of individual elk were determined from 31 cow and 20 bull elk equipped with radio-collars. Bull and cow elk differed in their probabilities of belonging to single sex or mixed groups in 6 of 7 biological periods. Bull-only groups were small (mean = 1.3–2.7) and constant in size annually, while cow-calf (mean = 1.6–9.6) and mixed (mean = 5.2–35.1) groups were larger and varied in size throughout the year. Annual grouping patterns in Michigan were similar to grouping patterns observed for western North American elk herds. In contrast to other sedentary herds in stabilized habitats, elk in Michigan showed little annual (mean coefficients of association = 0.16) or seasonal (mean coefficients of association = 0.07–0.32) cohesion in social group membership, likely a result of seasonal limitations on the availability of food resources and/or hunting harassment.
In the Canadian prairies maternal dens of striped skunks (Mephitis mephitis) are often located under a building in a farmstead. However, not all farmsteads or buildings are used by skunks, suggesting that striped skunks have specific preferences. To test this hypothesis, we measured a variety of parameters of farmsteads and buildings present in an area where striped skunks were intensively radio-tracked from 1993–1995. Farmsteads that were used by skunks as maternal dens or resting sites did not differ from unused farmsteads by number of buildings, degree of use by humans, distance to water or habitat availability within a 1-km radius. However, buildings that were used for dens could be differentiated from buildings not used for dens by the presence of a closed space underneath them. The presence of a closed space underneath a building floor is important for striped skunks, possibly because of low construction and maintenance costs of dens, thermoregulatory advantages and reduced predation risk. Abandoned buildings suitable for skunks may be managed by removal, or by more effective exclusion or trapping of resident skunks.
We document the use of goldenrod (Solidago spp.) gall insects by eastern gray squirrels (Sciurus carolinensis) as a winter food resource. We also examined the foraging patterns of gray squirrels on these gall insects by presenting goldenrod gall feeders at ten sites around Hamilton, New York, during the winters of 1996–1997 and 1997–1998. We predicted that squirrels would attack larger-than-average galls among those presented because larger galls are more likely to contain the larger fly larvae (Eurosta solidaginis), rather than the smaller parasitoid (Eurytoma gigantea) or nothing at all. Squirrels attacked galls at least once at 6 of the 10 sites where gall feeders were maintained. Galls at feeders were attacked from 11 February to 17 April, and the number of separate attacks on galls at a particular site ranged from 1 to 17. We detected no evidence that squirrels preferentially attacked galls of a particular size class (small, medium, large). There was no indication that squirrels attacked increasingly larger-than-average galls over the duration of the study, which would be expected if squirrels were learning by positive reinforcement. Our results suggest either (1) that squirrels are unable to discriminate among food rewards in galls of different sizes or (2) that all gall insects, regardless of size, provide an important dietary supplement for squirrels during the winter.
In the mid 1930s, A.G. Huntsman hypothesized that in the Miramichi River, New Brunswick, predation by kingfishers and American mergansers upon Atlantic salmon (Salmo salar) parr became especially severe in years of low July–August rainfall, these years being reflected 3 y later by reduced commercial catches. Huntsman attempted to demonstrate this predation effect with visual comparisons of aligned graphs of July–August rainfall for the city of Chatham, N.B., and commercial landings of 2½-sea-y salmon in Northhumberland County at the mouth of the Miramichi River. With detrended fishery data, and rainfall data augmented by additional weather stations, we confirmed that Huntsman's 3 y alignment provides the strongest and most significant correlation available in these data. We found that Huntsman's 2-mo correlation is strengthened by inclusion of September rainfall, and is strongest as a 5-mo May-to-September correlation. In the discussion, we distinguish between Huntsman's 3-y correlation and the bird-predation mechanism he proposed to account for it. Investigation of alternative pathways, such as the effect of rainfall upon growth rates of parr, is urged. We found slightly weaker, but statistically significant, correlations for September–October rainfall of −5 y, June–July and September–October rainfall of −1 y, July rainfall of −6 y and March–April and November rainfall of −2 y. The possibility that each of these unanticipated correlations may be biologically real is discussed.
The reproductive biology, glochidial morphology and recruitment of the federally endangered shinyrayed pocketbook, Lampsilis subangulata, were studied from May 1995 to July 1996 in the Flint River system, Georgia. Gravid female L. subangulata were found nine months of the year. On 19 May 1995, a L. subangulata was discovered releasing a superconglutinate, the first record confirming that this species used this specialized reproductive strategy. Superconglutinate release occurred from late May to mid-July in water temperatures ranging from 20.0 to 23.5 C. Laboratory experiments indicated that two fish species served as primary hosts, the spotted bass (Micropterus punctulatus) and largemouth bass (M. salmoides). Secondary host fish included the eastern mosquitofish (Gambusia holbrooki), guppy (Poecilia reticulata) and bluegill (Lepomis macrochirus). The glochidial morphology of L. subangulata was similar to other lampsiline species. Using quantitative survey methods, no evidence of recent juvenile recruitment was found in the largest known extant L. subangulata population.
Von Bertalanffy growth-curve parameters were calculated from plastral annuli of specimens of Graptemys ouachitensis and G. pseudogeographica kohnii captured in western Kentucky, and museum specimens of G. ernsti from Alabama and G. caglei (males only) from Texas. Males had estimated values of k (intrinsic rate of growth toward asymptotic plastron length, PLA) ranging from 0.264 to 0.498. Values of k for females of three species (range 0.110–0.182) were significantly less than the corresponding values for males, whereas PLA values for females (range 175.3–220.2 mm) greatly exceeded PLA values of males (range 91.5–114.5 mm). There was a significant negative correlation of PLA with k within 13 emydid turtle populations for which von Bertalanffy parameter estimates were available, with a slope similar to those reported for fish taxa; however, this relationship was not evident for either male values or female values when data were analyzed by phylogenetically independent contrasts. Use of the Richards model, a parent growth curve to the von Bertalanffy model, improved model fit for only one of seven data sets, whereas use of sine-wave versions of the von Bertalanffy and Richards models improved model fit for only two of seven data sets.
Thirty-four anuran species in Comoé National Park, Ivory Coast (West Africa), were checked for infestation by larvae of the intradermal chigger mite, Endotrombicula pillersi (Acarina: Trombiculidae) for 5 y (1991–1995). Endotrombicula pillersi is a species-specific parasite of Phrynobatrachus francisci (Anura: Ranidae) at this site. Up to 84% of these frogs had irregular red excrescences on their ventral side, the typical symptom of chigger mite infestation. None of the other 33 sympatric anuran species was infested, with the exception of 1 individual of Bufo maculatus (Anura: Bufonidae). Local populations of P. francisci had a similar prevalence of mites in successive years, with nearby populations showing considerable differences between 1 and 227 larval mites/host. The encapsulated larval mites were densely clumped on the ventral side of the legs and near the cloacal opening of frogs. High intensities of up to 100 parasites/host caused pathological effects. Such as necrosis or rectal prolapsus. We found no change in number and position of larval mites, nor any pathological effects, in frogs with low intensities of infestation that were kept in terraria up to 3 y. Histological examinations demonstrated that the lining of capsules surrounding embedded mites consisted of connective tissue of the host dermis. Both the gnathosoma and extremities of the larval mites were embedded in the tissue of capsules.
We examined the influence of plant genotype and early-season water deficits on oviposition preference and several measures of offspring performance in the goldenrod ball gallmaker (Eurosta solidaginis). Replicates of eight genotypes of goldenrod (Solidago altissima; Asteraceae), subjected to one of two watering regimes, were exposed to mass-released E. solidaginis. Oviposition preference was significantly affected by plant genotype and early-season water deficits, but not by their interaction; generally fewer plants in the low-water regime than the control treatment were ovipunctured in the first 24 h. In contrast, the number of ovipunctured plants forming galls was significantly affected by plant genotype and the interaction between plant genotype and early-season water deficits. Only plant genotype significantly affected the mass of adult offspring, which was highly correlated with potential fecundity in females. In the genotypes examined, oviposition preference was not affected by the interaction between plant genotype and early-season water deficits, but gall formation was. These results demonstrate the importance that the interaction between plant genotype and early-season water deficits can have on gall formation in E. solidaginis, and suggest that ovipositing females may be selecting hosts based on a subset of the traits that influence offspring performance.
We measured habitat characteristics in colony sites and at nest sites of endangered least terns (Sterna antillarum athalassos) on an expansive alkaline flat at Salt Plains National Wildlife Refuge, Oklahoma, in 1992 and 1993. Least terns nested in 12 colony sites on the alkaline flat during 1992 and 1993. Number of nests per colony site ranged from 5–25 and density of nests ranged from 0.1–0.75 nests/ha. Density of least terns in colony sites ranged from 0–2.1 terns/ha and was not correlated with soil color (P = 0.66) or soil texture (P = 0.12). Only a small percentage of ground cover was provided by vegetation (0.0–1.2%), driftwood (0.0–0.4%) and debris (0.0–1.1%) in colony sites. Least terns selected nest sites with coarser soil (loamy sand to sandy loam) than that of random points (P ≤ 0.0003). The coarser soils were lighter in color (P = 0.0001). Least tern nests were closer to driftwood or debris than random points (P = 0.0001). Internest distances in active colony sites ranged from 21.4 to >100 m. Nearest-neighbor analyses indicated that nests were distributed randomly in 58% and uniformly in 42% of active colony sites. Nests were distributed uniformly in small active colony sites and randomly in large active colony sites. No differences in densities of nests were noted relative to size of colony sites. Increasing availability of coarse light-colored soils in areas of ≥20 ha on alkaline flats may enhance recovery of least terns by improving nesting habitat and recruitment.
Research on ducklings and goslings has demonstrated that young birds hatched in moderate to high saline environments without access to fresh drinking water grow and develop slower, and have increased mortality rates. Most direct saline-induced mortality happens before day 6 of life, after which time the nasal salt glands become functional. At Fish Springs National Wildlife Refuge in western Utah, the water available to Canada goose (Branta canadensis) goslings ranged from brackish to highly saline (3100–25,000 µS/cm) throughout the summer and differed spatially across the impoundments; no fresh water was available. We followed collar-marked, radio-marked and unmarked broods from hatching to day 15 to determine early survival of all goslings hatched in 1997. Nineteen broods hatched between 25 April and 25 May. We analyzed the relationship between specific conductivity of water and gosling mortality in 1997. The levels of salinity found at the refuge within 15 d after hatching were independent of mortality. During dry years salinity levels increase earlier in the Spring and may limit gosling productivity.
Sternotherus odoratus (Latreille) is reported from a Holocene peat deposit in northern Indiana. In addition to turtle bones, sediment included subfossils of aquatic plants (Najas flexilis, Ceratophyllum demersum, Brasenia schreberi, Nymphaea odorata, Drepanocladus aduncus, Calliergon stramineum, Meesia triquetra), a gastropod (Gyraulus parvus) and fish (Centrarchidae). Vascular plant fragments from the sediment immediately surrounding the bones yielded a radiocarbon (14C) date of 3680 ± 80 y BP.
The influence of predation risk on microhabitat selection in male adult deer mice (Peromyscus maniculatus) was examined using an enclosure experiment. The relative amount of time spent by the deer mice on coniferous leaf litter, hardwood leaf litter and logs was measured. Mice preferred dry coniferous litter over dry hardwood litter, but had no preference when both litter types were wet. Deer mice traveled more along logs placed on hardwood litter than on coniferous litter. Nocturnal mammalian and avian predators of deer mice often use sound to locate their prey, and mice rustling in hardwood leaf litter should be more easily detected. Therefore, deer mice restrict their movements to routes that reduce the risk of auditory detection by predators.
Loggerhead shrikes were observed using barbed wire to anchor and tear nest-lining materials in Indiana. This is a previously unreported function of impaling by shrikes and may explain the impaling of certain inedible objects.