Showing papers in "American Midland Naturalist in 1993"
TL;DR: Estimation of insect biomass is extremely important to studies of ecosystem processes because of the great abundance of insects, their ecological and taxonomic diversity (Stork, 1988) and their importance as a vertebrate food resource (Rotenberry, 1980).
Abstract: -Length-weight regression models were generated for 10 orders and 35 families of adult and larval insects using a power model. Additional models were generated that incorporated width as an independent variable, to account for varying body morphology within insect taxa. Inclusion of width improved the generalized insect model and models at the order level, but was of less value in improving family level models. The predictive value of all models was high; estimates were generally within ?2 mg of the actual values. The parameter values for our models were similar to those produced by other researchers. INTRODUCTION Estimation of insect biomass is extremely important to studies of ecosystem processes because of the great abundance of insects, their ecological and taxonomic diversity (Stork, 1988) and their importance as a vertebrate food resource (Rotenberry, 1980). Traditionally, biomass values were derived by weighing several individuals within a taxa, calculating a mean biomass, and multiplying by the number of individuals collected. This procedure was tedious, time-consuming, and expensive (Rogers et al., 1977). Additionally, accurate measurement of biomass requires access to precision electronic balances, particularly for small specimens. Such accuracy may not be possible in field studies. The use of length-weight regression equations has been suggested as an alternative method for determining insect biomass. In addition to a general formula for all insects (Rogers et al., 1976), equations have been generated for specific orders and families of insects (Beaver and Baldwin, 1975; Rogers et al., 1977; Schoener, 1980; Jarosik, 1989). Other methods for estimating insect biomass include wing length indices (Miller, 1977), liquid displacement (Ciborowski, 1983) and optical measurement (Smiley and Wisdom, 1982). While use of length-weight formulae may simplify biomass estimation, Schoener (1980) cautions against lumping of insects of widely different body proportions into the same formula. Because longer insects tend to be more narrow, they tend to reduce the slope of the length-weight regression line, particularly at the upper end (Schoener, 1980). To reduce the effect of body shape on the formulae, the use of taxa-specific equations was suggested (Rogers et al., 1976; Sage, 1982; Schoener, 1980). In this paper we expand on the length-weight formulae of Rogers et al. (1976 and 1977) and Schoener (1980). In addition, we develop new models that include width, for use with taxa with differing body proportions. Actual vs. estimated biomass values are compared to evaluate the predictive value of these models. METHODS Adult and larval insects were collected with light traps, malaise traps, and foliage clipped from forested areas in eastern West Virginia between 1988 and 1991. All specimens were stored in a freezer until measured. The methods we employed were chosen to be representative of other studies of lengthPresent address: Department of Biology, Memphis State University, Memphis, Tennessee 38152 2 Present address: Exxon Biomedical Sciences Inc., Mettlers Rd., CN-2350, East Millstone, New Jersey 08875 234 This content downloaded from 157.55.39.203 on Sun, 11 Jun 2017 18:34:48 UTC All use subject to http://about.jstor.org/terms 1993 SAMPLE ET AL.: ESTIMATING INSECT BIOMASS 235 weight relations. Lengths and widths were measured to the nearest 0.01 mm with a dendrochronometer (Model 3, Fred C. Hanson Co., Mission Viejo, Calif. 92690) equipped with a 1-2.5 x zoom stereoscope. This device is designed for digital measurement of tree ring widths in age determination and was chosen over calipers and ocular micrometers for its accuracy and precision. Specimens were pinned to cardboard sheets, placed on the dendrochronometer platform, advanced beneath the stereoscope, and length or width values were recorded from the dendrochronometer display. Body length was measured from the frons to the tip of the abdomen. Antennae, ovipositors and wings extending beyond these points were not included in the total length measurement. Width was measured at the mesothorax for all insects, including larvae. All insects were dried in a 70 C drying oven for 48 h, allowed to cool, then weighed to the nearest 0.1 mg on an electronic balance (Model SWA-200-DR, Sargent-Welch Inc.). Specimens damaged at any state of the study (storage, measurement or drying) were excluded from analyses. We used the power model (Rogers et al., 1977) to describe the length-weight relationship of adult and larval insects. This model is: y = a(X)b Where: y = weight x = length or length*width Data were transformed to natural logarithms to linearize for regression analyses. The transformed model is: ln(y) = ln(a) + b ln(x). Regression coefficients and Pearson's correlation coefficients were calculated using PROC REG (SAS Institute Inc., 1988). Regression models were calculated at the class, order and family level for those taxa in which sample size was n 10. Predictive value of selected models was evaluated by comparing the esimtated to actual biomass for a sample of specimens that had been excluded from the data set from which the models had been generated. Matched-pair t-tests (Dowdy and Wearden, 1983) were used to determine if the difference between the calculated and actual biomass values was significantly different from 0. Because the chance of committing a Type I error increases as the number of tests increases, the alpha level (P < 0.05) was adjusted for the number of taxa-specific t-tests performed using the Bonferonni adjustment (Rice, 1989). To verify that the validation data originated from the same population as the model data, regression analyses identical to those performed on the model data were performed on the validation data. The slopes obtained from the validation data were compared to those from the model data using Z-tests (Dowdy and Wearden, 1983). Nonsignificant differences between slopes were assumed to indicate that model and validation data originated from the same population. Additional validation was performed by comparing the slope (power) parameters from our data to those of Rogers et al. (1976 and 1977) and Schoener (1980). Only models with length as the independent variable were evaluated. Z-tests (Dowdy and Wearden, 1983) were performed to determine if the slopes differed significantly. RESULTS AND DISCUSSION Data were collected for 1673 adult insects, representing 13 orders and 99 families. In total, 84 models were generated for adult insects (Table 1). Larval models were calculated This content downloaded from 157.55.39.203 on Sun, 11 Jun 2017 18:34:48 UTC All use subject to http://about.jstor.org/terms 236 THE AMERICAN MIDLAND NATURALIST 129(2) 00 'C ~~~~ C'C \ 'CO TTT'C LO C' C' "tLo~ ", C' 0 LO n LO rL(n 'C n 00 ( C' C'C\''CC'0C' 'C' C' C' nC'Cr-C C' C' C' C' C'CON0C' C'O mC' C' C'00 rn T~~r L O Lrn T-'"t\C00 cn TLO LOn c ( C'CLOCr00 C' c100 c1 c00 VO
223Â citations
TL;DR: The influence of fire regime on grazing patterns of North American bison (Bison bison) was studied on the Konza Prairie in northeastern Kansas as discussed by the authors, where bison grazing was spatially and temporally nonrandom and was influenced by fire regime and local plant community composition.
Abstract: -Fire and native large herbivore grazing were two important influences on the structure and function of North American grasslands. In 1988 and 1989 the influence of fire regime on grazing patterns of North American bison (Bison bison) was studied on the Konza Prairie in northeastern Kansas. Bison grazing was spatially and temporally nonrandom and was influenced by fire regime and local plant community composition. During the growing season, bison were observed up to 3 x more frequently than expected on watersheds burned in the spring. Summer grazing was concentrated in large watershed areas (79-119 ha) dominated by warm-season, perennial, C4 grasses. During the autumn and winter, bison grazed both burned and unburned watersheds more uniformly but grazed most intensively in areas with large stands of cool-season, C3 grasses. On a smaller spatial scale (5-10 m2), bison selected patches during the growing season with low forb cover dominated by the perennial C4 grass, Andropogon gerardii. Grazed patches were larger on frequently burned than on infrequently burned watersheds. The importance of fire history in determining patterns of bison grazing over the landscape indicates that interactions between bison grazing and fire regime may be important to the composition and spatial heterogeneity of tallgrass prairie vegetation.
219Â citations
TL;DR: Ordination indicates that evergreen herbaceous species and sprawling or vining understory species may be more tolerant of L. tatarica, suggesting that its effects on the community may be related to seasonal competition for light.
Abstract: -A shrubby, exotic honeysuckle, Lonicera tatarica L., has aggressively invaded woodlands throughout the northeastern United States. This paper explores its effects on herbaceous species and tree regeneration in three stands in southwestern Vermont and one in northwestern Massachusetts. In mesic stands with relatively rich soil, total herbaceous cover, herb species richness and density of tree seedlings were substantially depressed when L. tatarica cover exceeded ca. 30%, a relationship not observed at a dry poor site. Ordination indicates that evergreen herbaceous species and sprawling or vining understory species may be more tolerant of L. tatarica, suggesting that its effects on the community may be related to seasonal competition for light.
185Â citations
TL;DR: It is suggested that the higher tannin levels may render the apical portion of the seeds less palatable, and thereby increase the probability of embryo survival after attack by seed consumers.
Abstract: -A common assumption in studies of seed predation is that seeds survive attack and are dispersed only 'when animals fail to find seeds, drop undamaged seeds or fail to recover seeds after they are cached. This study, however, suggests that many acorn consumers consistently eat only a portion of the cotyledon of several species of acorns and thereby permit embryo survival. Several vertebrates [gray squirrels (Sciurus carolinensis), common grackles (Quiscalus quiscula) and blue jays (Cyanocita cristata)] were observed to consume only 30-60% of the cotyledon from the basal portion (cap end) of willow oak (Quercus phellos) acorns. Gray squirrels exhibited a similar preference for the basal end of acorns of several other species of red oaks (Q. rubra, Q. laevis, Q. nigra, Q. palustris and Q. coccinea) from a wide geographic region. In addition, acorn weevil larvae (Curculio sp.) were observed significantly (>35%) more often in the basal portion than in the apical end of Q. alba acorns. Chemical analyses of acorns from two tree species revealed that the concentration of protein-precipitable phenolics (primarily tannins) was 12.5% (Q. phellos) and 84.2% (Q. laevis) higher in the apical portion of the seeds where the embryo is located. Moreover, germination experiments revealed equal or greater germination frequencies for partially consumed acorns than for intact acorns. We suggest that the higher tannin levels may render the apical portion less palatable, and thereby increase the probability of embryo survival after attack by seed consumers.
150Â citations
TL;DR: Stream insects are an important food resource for insectivorous birds in riparian habitats of the tallgrass prairie, although insect emergence is likely insufficient to support observed insectivore densities.
Abstract: The relationship between emergence production of aquatic insects from Kings Creek, a taligrass prairie stream, and densities of insectivorous birds (flycatcher and gleaner guilds) was examined using concurrent measurements of insect emergence and bird densities at six sites on 31 dates during May to July from 1987 to 1990. Daily insect emergence averaged 10.6 g/100-reach in the gallery forest habitat and 2.5 g/reach in the prairie/shrub habitat. Principal taxa included Chironomidae (> 50% of emergence biomass), Ephemeroptera and Plecoptera. Common flycatchers were the eastern wood-pewee (Contopus virens) and great crested flycatcher (Myiarchus crinitus) in the gallery forest, and eastern kingbird (Tyrannus tyrannus) in the prairie/shrub habitat. Common gleaners were black- capped chickadee (Parus atricapillus) in the gallery forest and common yellowthroat (Geoth- lypis trichas) in the prairie/shrub. Flycatcher densities were highly correlated with total emergence in both habitats, but gleaner densities were correlated with emergence only in the gallery forest habitat. Both emergence and insectivore densities varied directly with the stream hydrograph, even over short, postflood recovery periods. Direct observations of feeding behavior showed that insectivores preyed upon a variety of aquatic and nonaquatic prey. Thus stream insects are an important food resource for insectivorous birds in riparian habitats of the tallgrass prairie, although insect emergence is likely insufficient to support observed insectivore densities.
147Â citations
TL;DR: Chela size differences, coupled with differential body size, likely contributes, via differential predatory susceptibility and reproductive success, to the replacement of 0.
Abstract: -In northern Wisconsin lakes, the crayfish Orconectes rusticus is replacing 0. propinquus, a previous invader, and 0. virilis, a native crayfish. Because chela size dictates success in aggressive encounters, predatory defense and reproduction, interspecific size differences could lend insight to this ongoing replacement. To quantify chela size differences among these three species, we measured chela lengths and widths of Form II (FII, nonreproductive) males, Form I (Fl, reproductive) males and females. For Fl and FII males, both 0. rusticus and 0. propinquus had larger chelae than similar-sized 0. virilis. Females differed only slightly in chela size. Females had smaller chelae than their male conspecifics. Chela size differences, coupled with differential body size, likely contributes, via differential predatory susceptibility and reproductive success, to the replacement of 0. propinquus and 0. virilis by 0. rusticus. INTRODUCTION The crayfishes, Orconectes rusticus, 0. propinquus and 0. virilis occur within littoral zones of N temperate lakes, often in sympatry (Crocker and Barr, 1968; Berrill, 1978; Capelli and Capelli, 1980; Corey, 1988). In northern Wisconsin lakes, 0. virilis is endemic; both 0. propinquus and 0. rusticus are exotics (Capelli, 1982). First to invade these lakes, 0. propinquus appears to displace 0. virilis, whereas 0. rusticus, the most recent invader, displaces both 0. virilis and 0. propinquus (Capelli, 1982; Lodge et al., 1986). Mechanisms explaining this replacement remain elusive, though predation, competition and reproductive interference all have been implicated (Capelli and Capelli, 1980; Capelli, 1982; Capelli and Munjal, 1982; Lodge et al., 1986). Herein, we quantify interspecific morphological differences that potentially could contribute to this replacement. Orconectes rusticus, 0. propinquus, and 0. virilis share similar gross external morphological characteristics (Capelli and Capelli, 1980; Hobb and Jass, 1988). However, chela size differs among these crayfishes. Chelae comprise a substantial portion of crayfish dry weight (Stein, 1976) and though energetically costly to grow, large chelae benefit crayfish in a variety of ways. Crayfish with large chelae are less susceptible to fish predation (Stein, 1976) and able to dominate similar-sized crayfish having small chelae (Bovbjerg, 1956; Stein, 1976; Snedden, 1990; Garvey, 1992). Furthermore, males with large chelae are better able to secure and hold females during copulation than similar-sized males with small chelae (Stein, 1976; Snedden, 1990). Though chela size is important, 0. rusticus and 0. virilis grow larger than 0. propinquus (Corey, 1988; Olsen et al., 1991). Because large crayfish are less susceptible to predation and able to dominate small crayfish (Stein and Magnuson, 1976; Stein, 1977), chela plus body size differences likely combine to influence interspecific interactions among these crayfishes. By quantifying chela length and width for these crayfishes, we can assess chela size differences. We then can evaluate the effect of chela size coupled with body size differences on the replacement of 0. virilis and 0. propinquus by 0. rusticus.
128Â citations
TL;DR: Results indicate that in coarse alluvial sands of low fertility, 47% of germinating P. deltoides seeds were able to survive in association with a drawdown rate of 2.9 cm/d and a final water table depth of 80 cm.
Abstract: -Establishment, growth and survival of seedlings of Populus deltoides subsp. monilifera (plains cottonwood) were examined in an experimental facility simulating five rates of declining alluvial groundwater. The treatments were permanent saturation, drawdown rates of 0.4, 0.7, 2.9 cm/d and immediate drainage. The experiment was conducted outdoors in planters near Fort Collins, Colorado. Seedling survival was highest under the two slowest drawdown rates and declined significantly with faster drawdown rates. The highest growth rate was associated with the drawdown rate of 0.4 cm/d, in which mean shoot height was 2.4 cm and mean root length was 39 cm 98 days after planting. Growth of shoots and roots was reduced both by saturated conditions and by the more rapid drawdown rates of 0.7 and 2.9 cm/d. No establishment was observed in the immediate drawdown treatment. Whereas maximum biomass accumulation is associated with the most gradual drawdown or saturated conditions, seedlings establishing naturally under such conditions are also most likely to be removed by ice or subsequent flooding. Seedlings establishing in higher topographic positions, in contrast, are subject to increased mortality and reduced shoot growth, resulting from reduced soil moisture. Rapid root extension following establishment allows P. deltoides seedlings to grow across a wide range of groundwater drawdown rates, and thus a variety of positions across a gradient of riparian soil moisture. Our results indicate that in coarse alluvial sands of low fertility, 47% of germinating P. deltoides seeds were able to survive in association with a drawdown rate of 2.9 cm/d and a final water table depth of 80 cm.
113Â citations
TL;DR: A statewide study of Panax quinquefolium L. (American ginseng), a herb commonly collected for commercial sale, was conducted on 33 protected and unprotected forested sites in the northern, central and southern sections of Illinois, indicating that plant age could be accurately determined by counting bud scale scars on the rhizome.
Abstract: -A statewide study of Panax quinquefolium L. (American ginseng), a herb commonly collected for commercial sale, was conducted on 33 protected and unprotected forested sites in the northern, central and southern sections of Illinois. Within these sites, data on the tree, sapling, seedling, shrub and herbaceous strata, and on soil texture and nutrients were collected from a 0.05-ha circular plot in each site. Additional recorded site data included aspect, slope position, steepness and exposure, and disturbance from grazing or timber harvesting. Populations of Panax quinquefolium were found in stands dominated by Acer saccharum, Quercus alba or Q. rubra and with a variety of other herbaceous species common to cool, moist site conditions; 84% of the sites were located on NW-, Nand NE-facing slopes and 80% were in midto low-slope positions. Phenological events began in early May and progressed from S-N; plants were dormant by mid-October. Seeds from individuals growing on several sites within each region were planted at the time of leaf senescence. Seedlings did not appear until the 2nd spring; 66% of the seeds produced seedlings. An anatomical and morphological study of 30 whole field-collected plants indicated that plant age could be accurately determined by counting bud scale scars on the rhizome. These data were used to develop a multiple regression model to predict rhizome age from stem height and number of leaflets. For 30 field-collected and 65 forest-cultivated roots, average weight increased linearly up to age 20, the age of the oldest roots. Population age structure and fruit production on protected sites were compared with that of sites where roots had been removed by collectors. We found fewer plants of all ages on unprotected sites. Fruit production was lower on unprotected sites because fewer 5to 11yr-old plants limit fruit production and rate of population recovery after harvesting.
84Â citations
TL;DR: A heuristic model is presented that considers pollen dispersal of anemophilous monoecious plants as a function of plant geometry and predicts that plants that approximate a more spherical form should increase in female floral allocation with increasing size.
Abstract: -Size-related patterns of floral sex allocation were examined in 14 anemophilous and eight entomophilous monoecious plants. Among the anemophilous species, eight increased male floral allocation and six increased female floral allocation with increased plant size. An increase in female floral allocation with increased plant size occurred in all eight entomophilous monoecious species examined. Pollination vector has a significant effect on size-related floral sex ratio patterns. We present a heuristic model that considers pollen dispersal of anemophilous monoecious plants as a function of plant geometry. The surface area to volume ratio of plants approximating geometric extremes (cylindrical or spherical forms) should affect pollen dispersal and floral sex ratio due to aerodynamic effects on the whole plant. Plants approximating cylinders should increase male floral allocation with increasing height. Plants that approximate a more spherical form should increase in female floral allocation with increasing size. All entomophilous plants conformed to a resource limitation model; however, anemophilous plants increased in either male or female floral allocation with increased size. Results for 13 anemophilous species support the predictions of our geometric model. One species does not approximate an extreme geometry and does not appear to conform to the geometrical model's predictions.
78Â citations
TL;DR: A reproductively active colony of the Indiana bat is discovered only 15 km S of the northern edge of the species' range in Michigan, and all roost trees were green ash, the first report of Indiana bat maternity colonies using green ash.
Abstract: -We discovered a reproductively active colony of the Indiana bat (Myotis sodalis) only 15 km S of the northern edge of the species' range in Michigan. Eight different roost trees were located, and all were green ash (Fraxinus pennsylvanica). This is the first report of Indiana bat maternity colonies using green ash. Unlike maternity colonies in more southern states, all roost trees in Michigan were exposed to direct sunlight throughout the day. Bats were still present as late as 10 September, well after the beginning of the swarming (mating) season at southern hibernacula. Population size at the main roost tree varied from 4-45. These bats roosted underneath the loose bark of dead trees, and we hypothesized that intertree movement was a response to the ephemeral nature of such roosting sites.
76Â citations
TL;DR: To study tree/nontree interactions, soil characteristics, aboveground biomass and plant composition were compared in areas under and adjacent to canopies of open grown bur oaks and northern pin oak x black oak hybrids in two savannas and two pastures in S-central Wisconsin.
Abstract: To study tree/nontree interactions, soil characteristics, aboveground biomass and plant composition were compared in areas under and adjacent to canopies of open grown bur oaks (Quercus macrocarpa) and northern pin oak x black oak hybrids (Q. ellipsoidalis x velutina) in two savannas and two pastures in S-central Wisconsin. One savanna and one pasture were paired on loam soils, the other sites were on sandy soils. In general, soil moisture was higher below tree canopies than outside canopies during a drying trend and was similar between areas after a period of rain. Soil organic matter and potassium (K) decreased with increasing distance from tree boles on all sites, while phosphorus (P) showed a similar trend only on the pastures. Pastures had greater soil organic matter and P than savannas of similar soil texture, while the loam soil sites had higher soil pH, organic matter, K, Ca and Mg than sandy sites of similar disturbance history. Areas below canopies received 67% of the ambient rainfall and 27-48% of the ambient photosynthetically active radiation and had 2.3-5.2 C lower soil temperatures compared to areas outside the canopies. Although soil moisture, nutrient and organic matter levels seemed more favorable for plant growth under the canopies, aboveground biomass was lower below canopies compared to open areas at the two savannas, while biomass was equal between canopy and open areas on the one pasture that was measured. This indicates that other factors, such as light, were more important in determining plant biomass. For all sites, plant composition under tree canopies differed from that outside the canopies. Savanna plant species were predominantly perennial and native while pasture species were mostly perennial and exotic. Grazing, fire and previous introductions of prairie species may have been major factors in determining the prevalent species (>5% cover) for a given site. Poa spp. were more prevalent below canopies compared to open areas on all sites, despite their different disturbance histories.
TL;DR: Rates of litter decomposition and metabolic rates of microbes were studied for 3 yr in four forest types at the E. N. Huyck Preserve on the Helderberg Plateau in eastern New York State to determine if differences were a function of differences in litter type or the decomposer community.
Abstract: -Rates of litter decomposition and metabolic rates of microbes were studied for 3 yr in four forest types at the E. N. Huyck Preserve on the Helderberg Plateau in eastern New York State. The four forests were floristically distinct, being dominated by beech (Fagus grandifolia), red pine (Pinus resinosa), hemlock (Tsuga canadensis) and mixedhardwood (Acer saccharum and Quercus alba), respectively. Decomposition rates ranged from 0.12 g/yr/g for hemlock to 0.42 g/yr/g for mixed hardwood. To determine if these differences were a function of differences in litter type or the decomposer community, we performed a mixed litter bag experiment, in which each type of litter was placed in each forest type. Rate of decomposition was primarily a function of litter type although decomposer community and decomposer community/litter type interactions were also important. Metabolic rate of decomposers, as measured by their ability to convert C-14-glucose to C-14-CO2, corresponded to the rate at which they decomposed litter. Relative importance of bacteria and fungi to total metabolism also varied among forest types, with bacterial contribution ranging from a high of 42% in mixed hardwood to a low of 8% in hemlock.
TL;DR: Although the prairie in its undisturbed state seems to resist invasion of these two exotic species, Daucus is able to escape disturbed microhabitats more extensively than is Melilotus.
Abstract: -Invasion by exotic plant species is a serious threat to the integrity of natural communities. The distribution of an exotic species depends upon environmental conditions, the structure of the native community, patterns of disturbance and ecological features of the species itself. This study identifies (1) associations between two exotic and seven native species in a tallgrass prairie in southeastern Wisconsin and (2) factors underlying the distribution of these species, with special regard to the effects of human disturbance. The distribution of two exotic species, Melilotus alba (white sweetclover) and Daucus carota (Queen Anne's lace), and seven native species, Potentilla arguta (prairie cinquefoil), Pedicularis canadensis (Canada lousewort), Dodecatheon meadia (Mead's shooting star), Equisetum laevigatum (scouring rush), Pycnanthemum virginianum (Virginia mountain mint), Phlox glaberrima (smooth phlox) and Solidago graminifolia (bushy goldenrod), were studied in 100, 4 m2 quadrats on five transects. Plant densities and soil characteristics were recorded for each quadrat and analyzed using nonparametric comparison of means and Spearman correlation analysis. Densities of the two exotic species were positively correlated with each other and negatively correlated with those of five of the seven natives. Most species exhibited a clear segregation between disturbed and undisturbed transects; Melilotus and Daucus dominated the disturbed transects, and native species dominated the undisturbed transects. Edaphic conditions appear to be the most important factor driving this habitat segregation between exotics and natives. Our finding is instructive for prairie restoration, because it suggests that in some cases, soil restoration may be desirable even if it results in additional mechanical disturbance. Although the prairie in its undisturbed state seems to resist invasion of these two exotic species, Daucus is able to escape disturbed microhabitats more extensively than is Melilotus.
TL;DR: Quantitative and qualitative sampling methods were used to study community characteristics, density, recruitment rates and population demography of abundant species of freshwater mussels, at Ohio River Miles 444.2-445.6, indicating generally sustained recruitment with some annual variation.
Abstract: -Quantitative and qualitative sampling methods were used to study community characteristics, density, recruitment rates and population demography of abundant species of freshwater mussels (Family: Unionidae), at Ohio River Miles 444.2-445.6 in July 1989 and September 1990. Mean unionid densities (?SD) based on 100, 0.25-sq m total substratum samples at four sites ranged from 4.4 ? 6.8 to 52.4 ? 13.9 individuals/ sq m. Mean densities of Corbicula fluminea ranged from 66.8 ? 67.7 to 1352.8 ? 96.1 individuals/sq m. Shannon-Weaver species diversity log23026 (2.32 to 2.50) and evenness (0.76 to 0.90) at these sites indicated an equitable distribution of species within the community. Individuals of two abundant species, Quadrula pustulosa pustulosa and Pleurobema cordatum, were represented by most size classes, indicating generally sustained recruitment with some annual variation. Both sampling methods provided similar estimates of community composition, species richness, diversity and evenness. A comparison of these results with those from a previous survey at this bed indicates no major changes in biotic conditions between 1984 and 1989-1990.
TL;DR: The observed changes in juvenile growth rates and age at maturity of male C. picta are in accord with recent field and laboratory studies of emydid turtles, and support predictions of life history theory, and may serve as working hypotheses that can be tested with data from other long-term projects.
Abstract: -Growth rates of juveniles and age at maturity of males were examined in a population of painted turtles, Chrysemys picta, inhabiting a marsh in southwestern Michigan (approximately 42024'N, 85024'W) to compare temporal variation in these two important life history traits within a decade. Elongation of the third right foreclaw was used as an indicator of incipient sexual maturity of males. Males in the late 1980s reached maturity at least a year earlier than did those in the early 1980s. Analysis of climatological data revealed that growing seasons in the late 1980s were typically warmer and longer than in the early years of the decade. The observed changes in juvenile growth rates and age at maturity of male C. picta are in accord with recent field and laboratory studies of emydid turtles. They also support predictions of life history theory, and may serve as working hypotheses that can be tested with data from other long-term projects. If substantiated, these patterns may indicate how some freshwater turtle populations in temperate latitudes might respond to predicted global warming trends.
TL;DR: A relationship was demonstrated between pitcher morphology, prey capture and frequency of resource parasitism among pitchers of the carnivorous plant Sarracenia purpurea.
Abstract: -TO infer the functional significance of morphological variation among pitchers of the carnivorous plant Sarracenia purpurea, I measured 8 traits on 87 pitchers and recorded prey captures and frequency of occlusion by spider webs for 47 days. A principal component analysis summarized 78% of the variance in the morphological traits on three component axes, which expressed variation in pitcher size, in pigmentation and available nectar and in pitcher height, respectively. Regression analysis found that the biomass of prey captured was significantly dependent only on the component of variation in pitcher size. However, the number of prey caught was significantly dependent on the component of variation in pitcher size and the component of variation in pigmentation and available nectar. The frequency of inhabitation by spiders was significantly dependent on the components of pitcher size and height. Thus, a relationship was demonstrated between pitcher morphology, prey capture and frequency of resource parasitism.
TL;DR: The influence of glochidial incubation on the ventilation rate, valve activity and oxygen consumption of the unionid mussel Pyganodon cataracta was investigated using bivalves collected during brooding and prebrooding periods.
Abstract: -The influence of glochidial incubation on the ventilation rate, valve activity and oxygen consumption (N02) of the unionid mussel Pyganodon cataracta was investigated using bivalves collected during brooding and prebrooding periods. Pumping rates of mussels ranged between 1.7 and 2.5 liters h-1 but were not significantly influenced by season or the presence of developing larvae in the lateral gills of females. The valve activity of adults held under constant conditions varied seasonally, but there was no apparent difference in the amount of time that the valves of gravid females were open and presumably engaged in suspension feeding and aerobic metabolism compared to males collected at the same time. Oxygen uptake by all mussels decreased under declining oxygen tensions suggesting that P. cataracta is an oxyconformer from 100% to 40% air saturation. Oxygen consumption of females was significantly lower than that of males during brooding periods, but did not differ between sexes during nongravid periods. Aerobic respiration was proportionally larger in isolated lateral demibranchs of gravid females than in males, and estimates of the contribution of developing larvae to the 0o2 of adults approached 10%. Under hypoxia, the presence of larvae in the gills of females had no effect on the dependence of N02 on oxygen tension for intact adults or their excised outer ctenidia.
TL;DR: Overall use generally reflected availability of dens, but den use varied across seasons and among raccoons of different age and sex, and females consistently used tree cavities more frequently than males.
Abstract: -Fifteen raccoons were fitted with radio-transmitters and monitored from March 1987 to May 1988; 1091 locations were classified according to occurrence within three available den types: tree cavities, rock outcroppings and ground burrows. Overall use generally reflected availability of dens, but den use varied across seasons and among raccoons of different age and sex. Rock dens were used most often during winter, especially when temperatures fell below freezing; adult males showed the most frequent and consistent use of rock dens. Ground burrows were consistently used more often by juveniles, especially males, as compared to adults. Use of ground burrows by the raccoon population was greatest during autumn. Females consistently used tree cavities more frequently than males; the greatest disparity occurred during summer and was associated with parturition and rearing of young.
TL;DR: It is concluded that this invertebrate predator can learn to delay attacks on distasteful prey and that pattern in aposematic coloration may influence aversion learning by mantids.
Abstract: -We experimentally tested visual cues used by the mantid (Tenodera ardifolia) in learning aversion to noxious prey. For 2 wk, we repeatedly presented mantids with milkweed bugs (Oncopeltusfasicatus) that were fed cardenolide-containing seeds of the milkweed, Asclepias syriaca. Milkweed bugs were painted with one of four color patterns: solid black, solid orange, half black and half orange, and alternately striped with orange and black. A fifth treatment included naturally colored (orange and black mottling), unpainted bugs. As mantids gained experience with unpalatable prey, they became significantly more hesitant to strike and struck less frequently. Furthermore, our data suggest mantids presented prey with broken patterns hesitate to strike longer than those presented prey with solid patterns. We conclude that this invertebrate predator can learn to delay attacks on distasteful prey and that pattern in aposematic coloration may influence aversion learning by mantids. INTRODUCTION There is accumulating evidence for the ability of insects, and invertebrates in general, to learn. Flies have been shown to exhibit a wide array of learning phenomena. For example, induced responsiveness to a second water stimulus when preceded by sucrose stimulation was demonstrated in the blowfly Phormia regina (Dethier et al., 1965) and classical conditioning of the proboscis extension reflex was shown with the same species (Nelson, 1971). Vargo and Hirsch (1982) demonstrated induced responsiveness similar to that described by Dethier et al. (1965) but with Drosophila melanogaster. Classical conditioning with regard to the proboscis extension reflex has also been shown for D. melanogaster (Holliday and Hirsch, 1986). Bees also possess a considerable ability to learn; classical conditioning of proboscis extension was demonstrated in Apis mellifera (Bitterman et al., 1983); A. mellifera also exhibited aversion conditioning to odor (Abramson, 1986) and shock (Abramson and Bitterman, 1986). Bees were shown to associate color with odor of food (Couvillon et al., 1991) while Smith et al. (1991) demonstrated proboscis extension conditioning with both aversive and appetitive stimuli. In addition, seed-harvester ants are able to learn a suite of behaviors that enhances foraging efficiency (Johnson, 1991), while cockroaches exhibit probability-learning and habit-reversal (Longo, 1964). Past studies of learning in mantids have dealt with physiological aspects of learning Present address: Department of Biology, University of South Florida, Tampa, Florida 33620
TL;DR: Autumn and spring burning of Festuca grassland reduced peak, green, graminoid biomass production in the 1st and 2nd yr after fire; autumn burning had the most negative effect.
Abstract: -Grassland communities dominated by Festuca scabrella or by Stipa curtiseta and Agropyron dasystachyum were burned experimentally in spring or autumn. Forb, shrub and graminoid biomasses were greater in the unburned Festuca community than in the StipaAgropyron type. Spring and autumn burning delayed early season growth of graminoids in both grassland types in the 1st growing season after fire. Peak green biomass was reached later in the season in burned plots relative to reference areas. Plant growth in the spring of the 2nd yr after fire was more rapid in burned plots and peak biomass was reached earlier than in the reference plots. Autumn burning reduced forb biomass significantly early in the growing season during 1 of 3 yr that this parameter was measured. No effect of burning on shrub biomass was detected. Autumn and spring burning of Festuca grassland reduced peak, green, graminoid biomass production in the 1st and 2nd yr after fire; autumn burning had the most negative effect. Reductions in graminoid biomass after burning Stipa-Agropyron stands were smaller than in the Festuca community. Nitrogen concentrations in F. scabrella shoots regrown after fire were higher than those from the reference areas. Soil water content during the growing season, and snow trapping were reduced by burning. Peak green biomass and total graminoid biomass in Festuca grassland recovered to the level of the reference plots 2-3 yr after burning. Recovery was slower in the Stipa-Agropyron community.
TL;DR: Although males in the field population are on average significantly heavier than females, males in precopula are not proportionately heavier than the females they carry, indicating that precopulatory mate guarding takes place in a nonsize assortative manner.
Abstract: -The mating system of the freshwater amphipod Hyalella azteca consists of precopulatory mate guarding, in which males compete for the possession of females by guarding them before copulation. Although males in the field population are on average significantly heavier than females, males in precopula are not proportionately heavier than the females they carry, indicating that precopulatory mate guarding takes place in a nonsize assortative manner. In the laboratory, the guarding pattern and pairing success are dependent upon the operational sex ratio (OSR). When the OSR is female-biased, males are more successful at obtaining females due to the active male mate choice, but when OSR is malebiased, females are less frequently taken into precopula because of intensified male-male interference. At female/male OSR values of 1:2 or 2:1, males demonstrate a preference for large prospective mates. However, at the OSR values of 1:3 or 3:1, pairs are randomly formed with no size-dependent responses. This flexibility of guarding behavior is explained by time and energy investment tactics in mate selection by both sexes.
TL;DR: Early egg-laying and subsequent growth of hatchlings resulted in a significant size advantage for larvae from paedomorphic parents at the time that terrestrial-morph eggs hatched, suggesting that, under certain environmental conditions, facultative paedomomorphosis is advantageous.
Abstract: Facultative paedomorphosis in salamanders is a plastic trait that may represent an adaptation to fluctuating environmental conditions. The author compared the timing of reproduction in paedomorphic and terrestrial-morph Ambystoma talpoideum at the same pond. Paedomorphic adults laid eggs approximately 6 wk earlier than terrestrial morphs. Early egg-laying and subsequent growth of hatchlings resulted in a significant size advantage for larvae from paedomorphic parents at the time that terrestrial-morph eggs hatched. These observations suggest that, under certain environmental conditions, facultative paedomorphosis is advantageous. 36 refs.
TL;DR: Greenfall is viewed as a high-quality substrate supplying nitrogen to decomposer organisms and is thus a potential mechanism by which herbivorous insects speed nutrient cycling.
Abstract: -Herbivorous insects are responsible for a portion of foliar litterfall in forest ecosystems. There is little information on the nutrient content of this litterfall despite speculation that herbivores regulate nutrient cycles. We quantified herbivore-caused "greenfall" (green leaves falling as a direct result of herbivore feeding activity) in four Appalachian watersheds and analyzed samples for total nitrogen. Concentrations of nitrogen in greenfall fluctuated significantly from May through September and were always higher than concentrations of nitrogen in autumn senesced leaves. Annual inputs of greenfall nitrogen ranged from 0.08-0.18 g-m-2 yr-' and resulted in 3.2% to 6.5% of total nitrogen transferred to the forest floor in autumn foliar litterfall. Greenfall is viewed as a high-quality substrate supplying nitrogen to decomposer organisms and is thus a potential mechanism by which herbivorous insects speed nutrient cycling.
TL;DR: Results suggest that changes in the taxonomic composition of stream macroinvertebrate communities due to disturbance may have significant effects on ecosystem processes for at least 2 yr after termination of disturbance.
Abstract: -Two headwater streams draining catchments 53 and 54 (C53 and C54, respectively) at the Coweeta Hydrologic Laboratory in western North Carolina were treated with insecticide in 1980 (C53) and 1986-1988 (C54). During recovery periods in both streams, Lepidostoma spp. were abundant, early colonizers. Densities of Lepidostoma in litterbags and benthic samples collected from recovering streams were substantially higher than in untreated streams (pretreatment and reference streams). During treatment years, leaf-litter processing rates were severely reduced relative to pretreatment and reference streams. In contrast, litter processing rates in C53 and C54 during recovery were faster than those in untreated streams (pretreatment and reference). Rhododendron is one of the most refractory leaves commonly found in Coweeta streams; however, percent increase of rhododendron processing rates from treatment periods to recovery was greater than that of more labile red maple. Laboratory feeding experiments were performed in order to examine and quantify use of rhododendron and red maple litter by Lepidostoma larvae. In the laboratory, Lepidostoma consumed significantly more rhododendron (1.062 mg AFDM/mg AFDM body wt/day) than red maple (0.479 mg AFDM/mg AFDM body wt/day) (P = 0.001). Results suggest that changes in the taxonomic composition of stream macroinvertebrate communities due to disturbance may have significant effects on ecosystem processes for at least 2 yr after termination of disturbance. Lepidostoma colonize rapidly following disturbance, enhancing the restoration of vital ecosystem processes such as litter decomposition in Coweeta streams.
TL;DR: Radial growth of upper canopy trees continued to decline throughout the drought period, whereas understory trees remained nearly constant following an initial decline, suggesting differential growth response may result from modification of microclimate caused by the vertical structural complexity of a deciduous forest.
Abstract: -Annual ring growth was measured in trees subjected to 8 successive yr of drought and a severe, late-spring frost in eastern Kentucky. Trees in all vertical strata were significantly (P < 0.05) influenced by the microclimatic changes. Trees in dominant and codominant crown-classes exhibited significantly greater reduction of radial growth in both drought (23%) and frost (15%) years than suppressed stems (3% and 3%, respectively). Radial growth of upper canopy trees continued to decline throughout the drought period, whereas understory trees remained nearly constant following an initial decline. This differential growth response may result from modification of microclimate caused by the vertical structural complexity of a deciduous forest.
TL;DR: In this paper, the authors examined the effect of differential survival of seedlings on the distribution of native grasses along topographic gradients in the Nebraska Sandhills and found that seedling survival was greatest in the rototilled and irrigated treatment on the lowland site.
Abstract: -This study examines the effect of differential survival of seedlings on the distribution of native grasses along topographic gradients in the Nebraska Sandhills. In 1981, seeds of three ridge species (Andropogon hallii, Sorghastrum nutans, Panicum virgatum) were planted into rototilled, irrigated, rototilled and irrigated, or untreated soils on three sites: one ridge site (ridge) and two valley sites (valley and lowland). The three sites represented a gradient of topography and soil moisture-holding capacity. For all species, seedling survival was greatest (86%) in the rototilled and irrigated treatment on the lowland site. No seedlings survived in untreated plots along the gradient. In 1982 and 1983, seeds of a ridge species (Andropogon hallii) and a valley species (Bouteloua gracilis) were planted in replicated ridge and valley plots. Seeds were planted into either untreated plots, or plots where plants received weekly clipping treatments around seedlings. Although clipping significantly increased survival of both species in both sites, it had a significantly greater effect in valley sites. In untreated plots, seedling survival was greatest (20%) in ridge sites in a year of average precipitation (1982) and in valley sites (49%) in a year that was exceptionally wet (1983). In 1983, soil moisture explained 98% of the variation in the survival of A. hallii seedlings and 82% in B. gracilis seedlings. Competition from existing vegetation severely limited the probability of seedling establishment. The distribution pattern of ridge species likely results from differential survival of juveniles and adults along the gradient, rather than the ability of seedlings to have higher establishment success on ridge sites. Significant establishment of the valley species (Bouteloua gracilis) occurred only during an exceptionally wet year when the pattern of survival of seedlings reflected the distribution pattern of adult plants. Establishment of prairie grass seedlings appears to depend on the availability of soil moisture, which may only be adequate in relatively large disturbance areas (> 1 m2), or in years of higher than normal precipitation.
TL;DR: The reproductive ecology of this species near its extreme northern limit in Wood Buffalo National Park is examined, indicating that there is no single suite of life history traits that characterizes northern T. sirtalis.
Abstract: -The common garter snake, Thamnophis sirtalis, ranges farther N than any other North American reptile. We examined the reproductive ecology of this species near its extreme northern limit in Wood Buffalo National Park (WBNP, 59?49'N, 112?W, Northwest Territories, Canada). Our data suggest that individual females in this population rarely gave birth in 2 successive yr. Parturition normally occurred away from the den, in summer habitat, with the females subsequently migrating back to the hibernaculum. These life cycle features were similar to those reported for another northern population in Manitoba (50?30'N, 97?53'W) and may be a consequence of the climate and the distance between summer and winter habitat. However, there were important differences in the reproductive characteristics of WBNP and Manitoba populations. Most strikingly, female snakes at WBNP matured at larger body sizes (?570 mm SVL) than Manitoba snakes (?527 mm SVL). Also, mean litter size for WBNP females was smaller than for Manitoba females (12.5 vs. 18.8 offspring/litter, respectively), but WBNP neonates were considerably larger than Manitoba neonates (191 vs. 154 mm SVL, respectively). Whether these differences between cold-climate populations of T. sirtalis are genetic or environmental in origin remains to be determined. Regardless, these two populations differ substantially in demography, indicating that there is no single suite of life history traits that characterizes northern T.
TL;DR: In this paper, a multivariate analysis of 31 scute and shell measurements of North American tortoises is presented, which is not concordant with a phenogram based on genetic data, although relationships among three major populations of G. agassizii are the same.
Abstract: -Significant differences exist in adult carapace lengths among the four species of North American tortoises (Gopherus spp.). However, after measures of whole shell and scute dimensions are adjusted for these size differences, shape is more similar between the largest species, G. favomarginatus, and the smallest species, G. berlandieri, than with either of the intermediate-sized species, G. polyphemus and G. agassizii. Recent data based on an analysis of mitochondrial DNA of North American tortoises provide a phylogeny of the four extant species. A phenogram based on a multivariate analysis of 31 scute and shell measurements of North American tortoises is not concordant with a phenogram based on genetic data, although relationships among three major populations of G. agassizii are the same. Morphometric data are also not concordant with a matrix based on measures of precipitation and temperature, but are significantly correlated with a matrix based on growth variables (R2 = 0.74, P = 0.029). Other environmental parameters may affect shape of shells.