Showing papers in "American Midland Naturalist in 1991"

Comparison of Presettlement, Second-growth and Old-growth Forest on Six Site Types in the Illinois Shawnee Hills

Abstract: -Witness tree data from the General Land Office 1806-1807 survey records were used to reconstruct presettlement forest community data and a landscape pattern in the Illinois Shawnee Hills region. Using topographic maps, we categorized section and quarter section corners by physiographic site type: rocky S slope, S slope, ridgetop, high N slope, low N slope and terrace. For each type, species importance values (relative basal area) and community basal area, density and average diameter were determined from witness tree data. These data were compared to plot data of second-growth and old-growth forest communities on analogous sites. Presettlement communities had lowest basal area and highest mean diameter; old-growth had the highest basal area level. Second-growth stands had highest density and lowest mean diameter. Presettlement, second-growth and old-growth forest communities of rocky S slopes, S slopes and ridgetops were compositionally similar (percent similarity = 58-84%). Quercus stellata was the major dominant on xeric rocky S slopes while Q. alba was the most important species on xeric-mesic S slopes and ridgetops. Ridgetops supported a more open presettlement community of large Q. alba and Q. velutina. On these three site types, oldgrowth stands appear to be an acceptable representation of presettlement forest. On mesic high north, low north and terrace sites, presettlement forest communities were more similar to disturbed second-growth (percent similarity = 46-79%) than to old-growth (percent similarity = 22-30%). In presettlement forest, Quercus alba and Q. velutina were the dominants on high and low N slopes; Q. alba, Q. rubra and Liriodendron tulipifera were the most important species on terraces. Acer saccharum was absent or of minor importance. In second-growth forest, Q. alba and Q. alba with Q. rubra were the dominant species of high and low N slopes, respectively. On terraces, A. saccharum dominated but Q. alba, Q. rubra and L. tulipifera also were important. Old-growth forest on high N slopes was dominated by Q. rubra but A. saccharum was the major dominant of low N slope and stream terrace communities. While both presettlement and old-growth communities represent virgin (uncut) forest on mesic sites in the Shawnee Hills, they are relatively dissimilar in composition and structure. This difference exists because our present old-growth forest is an artifact of near total protection while presettlement forest developed under a fire regime.

Water Table and Plant Species Relationships in Sierra Nevada Meadows

Abstract: -Baseline information on water table fluctuation patterns was collected at Sagehen Creek Field Station, near Truckee, California, from June 1987 through November 1989. Relationships between plant community types and water table patterns were examined. Water table patterns were determined from bimonthly measurements of piezometers. Species composition was determined using a 10-point frame placed randomly near each piezometer. Four distinctive water table patterns were identified based on examination of specific water table variables during 2 growing seasons. Five plant community types were identified, designated Deschampsia caespitosa/Carex nebrascensis, Poa pratensis/Potentilla gracilis, Poa pratensis/Carex, Carex angustata/Poa pratensis and Carex angustata. These plant communities were related to specific water table patterns. The D. caespitosa/C. nebrascensis type experienced the greatest annual fluctuation in water table of any of the types. The P. pratensisl Carex plant community type occupied sites with the smallest water table fluctuation. Water table patterns associated with the P. pratensis/Potentilla gracilis community type indicated dry sites, whereas Carex angustata sites had small overall water table fluctuations and were generally wet to moist sites. The complexity of the physical and biological components of meadow ecosystems was demonstrated, suggesting site variation and changes in meadow species may be predicted by monitoring water table pattern.

Distribution of Gopherus polyphemus and Its Vertebrate Symbionts in Three Burrow Categories

Abstract: -We classified burrows of a population of gopher tortoises (Gopherus polyphemus) as active, inactive or abandoned according to the physical characteristics of the entrances. We excavated 1019 burrows (454 active, 449 inactive and 116 abandoned) to determine if either tortoises (males, females and juveniles) or symbionts differentially used these three burrow categories. We captured 400 tortoises in burrows. We classified all burrows immediately prior to excavation. Tortoises were captured significantly more often in active than in either inactive or abandoned burrows. Juveniles were captured significantly more often than adults in inactive burrows only. Numerically, 53% of the symbiont individuals were reptiles, 36% were amphibians and 11% were mammals. The number of reptilian species was greater than that of both amphibians and mammals. Mammalian individuals were significantly under-represented in our sample relative to reptiles and amphibians. When all vertebrate symbionts were combined, we could detect no difference in use of the three burrow categories. Reptiles, however, were found significantly more often in active burrows. When snakes and lizards were analyzed separately, only lizards were found significantly more often in active burrows; snakes were randomly distributed in burrow categories. We present several hypotheses to account for these observed distributions.

Bird Abundance and Species Richness in Grassed Waterways in Iowa Rowcrop Fields

Abstract: -Grassed waterways have been used for decades to prevent soil erosion in agricultural cropland, but their benefits to wildlife had not been evaluated prior to our study. We documented bird species composition and relative abundance during the breeding season in 44 grassed waterways in central Iowa. The waterways were planted predominately to smooth brome (Bromus inermis) and were in cornfields and soybean fields. Forty-eight bird species were observed in waterways, compared with only 14 in the surrounding crop fields. Red-winged blackbirds (Agelaius phoeniceus), dickcissels (Spiza americana), barn swallows (Hirundo rustica), western meadowlarks (Sturnella neglecta), brown-headed cowbirds (Molothrus ater), grasshopper sparrows (Ammodramus savannarum) and song sparrows (Melospiza melodia) were the most abundant bird species in the grassed waterways. Total bird abundance in the grassed waterways averaged 2198 birds observed/census/100 ha compared with 682 in crop fields. Temporal patterns in bird abundance were attributed primarily to aspects of the waterways and surrounding cropland that changed over time, such as vegetation height. Because most (53%) of the bird species were at peak abundance in the waterways during 4-22 July, grassed waterways should not be mowed until the end of August or early

Capture rates and composition of insect prey of the pitcher plant Sarracenia purpurea.

Abstract: -The insect prey of 214 pitchers of Sarracenia purpurea were monitored for 55 days. A total of 504 individual prey with a dry weight of 569.5 mg were recovered. The catch comprised individuals from 49 families and 13 orders, with most individuals from the Diptera. The distribution of the prey among pitchers was highly uneven; over 50% of pitchers caught nothing and about 8% of the pitchers caught 66% of the prey biomass. Experimental manipulations failed to produce an effect of pitcher density on prey capture rates. Indeed, no significant spatial variation in prey capture rates was found. Spiders that spun webs inside pitcher apertures prevented pitcher function on about 10% of trap days and may have imposed an important reduction on pitcher success.

Ant mound influence on vegetation and soils in a semiarid mountain ecosystem

Abstract: -We examined vegetation patterns and soil properties associated with western harvester (Pogonomyrmex occidentalis) mounds in a pinyon-juniper community and a ponderosa pine community near Los Alamos, New Mexico. Plant-clearing habits of the ants exerted a minor influence on total plant cover. Denuded zones (discs) around the mounds in the pinyon-juniper and ponderosa pine sites represented 1.2% and 1.0% of the total surface area and reduced plant cover 0.35% and 0.49%, respectively. Vegetation near the perimeter of the cleared discs had decreased species richness and lowered percent cover compared with adjacent reference areas (sampled 3.0 m from discs). Comparisons of plant species occurrences around the discs revealed that (1) most species, including dominant understory plants, were evenly dispersed in relation to nest discs; (2) two species-one in each site-were significantly associated with areas near discs; and (3) six species-four in the pinyon-juniper site and two in the ponderosa pine site-were significantly associated with reference areas. Analysis of vegetation on abandoned mounds suggested that seed predation by the ants influences patterns of plant species occurrence adjacent to nests. Active mounds in the pinyon-juniper and ponderosa pine sites occurred at densities of 17/ha and 14/ha and had an average mass of 38 kg and 48 kg, respectively. Particle size analysis indicated that the ants construct mounds primarily of gravel and sand fractions. Mound soils at both sites had elevated concentrations of NO3, P and K, increased conductivity and lower water content compared with disc and reference soils. Disc soils in both sites had lower organic matter content but were otherwise similar to reference soils. Activities of P. occidentalis cause localized accumulations of nutrients that are unavailable to plants until mound abandonment. Colony influences on vegetation patterns beyond the denuded discs and lingering effects of abandoned mounds contribute to plant community heterogeneity.

Growth, survivorship and longevity of painted turtles, Chrysemys picta, in a southwestern Michigan marsh

Abstract: -This paper reports results of a mark-recapture study of painted turtles inhabiting a marsh in Kalamazoo County, Michigan, first begun in 1964-1966 and continued intermittently from 1980-1989. The relationship between plastron length (PL) and age (t) was described by von Bertalanffy growth equations for males PL = 111.8(1 0.792e-0?184t) and females PL = 152.2(1 0.852e-01281). Annual survivorship of males and females (26 yr old) was estimated as 0.64-0.83 and 0.29-0.50, respectively. Annual survivorship of juveniles (<6 yr old) was 0.21-0.51. Based on estimated minimum ages of individuals first captured as adults in the 1960s and recaptured in the 1980s, the four oldest males were 31 and the oldest female was 34 yr old. The oldest known-age male and female were 21 yr and 15 yr old, respectively. A comparison of data from the 1960s with that gathered in the 1980s revealed that the growth rates of juveniles and the density of turtles in the marsh have increased, while survival rates have apparently decreased. We speculate that the enhanced growth rates and population density are the result of warmer and drier weather during the 1980s.

The quality of pollination by diurnal and nocturnal insects visiting common milkweed, Asclepias syriaca.

Abstract: -We studied the contributions of diurnal and nocturnal insects to pollination of common milkweed Asclepias syriaca L. (Asclepiadaceae) in Maine. Diurnal insects (mainly bumblebees, Bombus spp.) visited five times as many flowers and removed 10 times as many pollinaria as nocturnal visitors (mainly moths). Stalks exposed to diurnal insects produced 2.5 times as many pods as did those exposed to nocturnal insects. However, hand pollination of flowers at midday and at midnight resulted in similar pod production. Seeds per pod, seed mass, germination time and seedling quality did not differ between diurnal and nocturnal treatments. We conclude that nocturnal visitors performed pollination of higher quality in terms of pods produced per pollinator visit, because a visit from a nocturnal insect was twice as likely to result in the production of a pod than a diurnal visit. However, diurnal flower visitors were more important pollinators as a consequence of the large number of individuals participating.

Reproductive biology and fish hosts of the Tennessee clubshell Pleurobema oviforme (Mollusca: Unionidae) in Virginia

Abstract: -The reproductive cycle and fish hosts of the freshwater mussel Pleurobema oviforme were determined during a 14-mo study (1979-1980) in Big Moccasin Creek, southwestern Virginia. Histological sectioning of mussel gonads collected throughout the year showed that gametogenesis for both sexes began in late spring and continued into early autumn; fertilization began in late March. Glochidial development in the outer gills of females required 3-5 wk. Judged by biweekly samples of stream drift, glochidia were released from mid-April through July. Six species of cyprinids, collected between May and September 1979, were naturally infested with amblemine glochidia. Induced infestations of putative fish hosts in the laboratory confirmed five host species: whitetail shiner (Notropis galacturus), common shiner (N. cornutus), river chub (Nocomis micropogon), stoneroller (Campostoma anomalum) and fantail darter (Etheostoma fiabellare).

Productivity of creosotebush foilage and associated canopy arthropods along a desert roadside.

Abstract: -A sampling study was designed to test the hypothesis that creosotebush (Larrea tridentata) shrubs along a roadside were larger, more vigorous and supported greater populations of foliage arthropods than shrubs growing 20 m away from the road margin. Structural and chemical attributes of shrubs and associated foliage arthropods were measured. Roadside shrubs were larger, had denser foliage, more flowers, higher foliar nitrogen contents and lower foliar resin contents than shrubs growing away from the road. Foliage arthropod densities were significantly higher on roadside shrubs. Sap-feeding herbivores dominated numerically and accounted for most of the differences in arthropod abundances between roadside and nonroadside shrubs. Numbers of foliage arthropods were positively correlated with shrub size, density and foliar nitrogen contents, and negatively correlated with foliar resin contents. These findings, in concordance with other studies, indicate that in arid environments productive, vigorous plants are preferred hosts for herbivorous insects.

Observations on the Ecology, Reproduction and Growth of the Burrowing Crayfish Fallicambarus (Creaserinus) fodiens (Decapoda: Cambaridae) in North-central Ohio

Abstract: -Breeding (Form I) and nonbreeding (Form II) males were present throughout the year. Occupancy of the same burrow by Form I males and females occurred from April to late October. Eggs were extruded, developed eyed embryo stage by mid-October and overwintered in this condition. Hatching occurred in late March to mid-April. Subadults in November were 20 mm-30 mm carapace length (CL). Molting to adult occurred in the following summer or autumn. Maximum age was over 6 yr and maximum size was 49.3 mm CL. Growth per molt was quite variable; adults averaged 1.39 mm CL. Burrow temperature ranged from near 2 C in February to near 22 C in August at a depth of 106 cm. Coinhabiting and burrow-sharing were interand intraspecific, involved members of the same or opposite sex and on occasion involved more than two crayfish.

Shifts in the Effects of Tuft-weaving Midges on Filamentous Algae

Abstract: -During summer low-flow periods massive growths of filamentous green algae (dominated by Cladophora glomerata) in the Eel River of Northern California become infested with chironomid larvae that weave the algae into retreats, or "tufts." Field experiments suggest that these midges (primarily Pseudochironomus richardsoni) have negative early effects, and positive later effects on the biomass of algae they inhabit. During initial colonization and tuft construction by midges, weight loss of Cladophora and associated epiphytes in stream enclosures increased with increasing midge densities. In an in situ incubation experiment, chlorophyll a content and final damp weight of Cladophora and epiphytes were higher with old, feces-filled tufts, or with nitrate fertilizer, and were lower in controls or with new midge tufts. These results suggest that tuft-weaving midges have complex effects on algae they inhabit that change with the ontogeny of midges and the age of the retreats they construct.

Comparisons of Aboveground Arthropods in Burned, Mowed and Untreated Sites in Sandplain Grasslands on Nantucket Island

Abstract: -Arthropod abundance and vegetation composition were studied in four 0.25ha grassland plots on Nantucket Island, Massachusetts. Treatments included burning in April, burning in August and mowing in August, in 1983 and again in 1985. Cover and frequency of plants in 1985 was little changed from pretreatment levels. Arthropods were sampled in July, August and September of 1985. In the April burn plot, numbers of Arachnida were lower and Orthoptera were higher throughout the season than in an untreated reference plot. Other orders showed little consistent change. In the August burn and mow plots, total numbers of arthropods, especially Hymenoptera, Orthoptera, and Lepidoptera, were higher early in the season in 1985 compared to the reference plot. Following treatments in August, most orders declined in abundance compared to the reference plot, with the exception of the Homoptera, which increased.

Foliar Shelters for Mites in the Eastern Deciduous Forest

Abstract: -The leaves of many woody plant species of the eastern deciduous forest product special structures in the vein axils (over 70% of species sampled in E-central Illinois). These structures are called domatia when they are well-developed and discrete, but poorly developed, less discrete structures may have similar functions. Mites (mostly predatory and fungivorous) use these structures for shelter (>50% of domatia showed evidence of mite occupancy in most species examined). Mite populations on the leaves build up gradually and reach their peaks on older leaves. Mite-plant associations of this type are likely to be mutualistic and are far more common and widespread than previously recognized.

Differential escape of insects from carnivorous plant traps.

Abstract: -The escape of some insects from the traps of carnivorous plants depends on the type of trap and the body size of the insect species. Body size thresholds vary: for "sticky traps" of Pinguicula lutea Walt. and Drosera filiformis Raf. tracyi MacFarlane, they are 5 mm and 10 mm, respectively. In contrast, the "pitfall trap" of Sarracenia leucophylla Raf. retains almost all sizes of insects captured. Differential escape may have provided strong selection pressures for the evolution of large carnivorous plant species, which can trap insect prey of a wide range of sizes.

Response of Raptors to Reduction of a Gunnison's Prairie Dog Population by Plague

Abstract: -Raptors were counted at approximately 2-week intervals between March and November 1985-1987 in the Moreno Valley, Colfax Co., New Mexico. During that period, an epizootic of plague (Yersinia pestis) swept through the valley and sequentially killed Gunnison's prairie dogs (Cynomys gunnisoni) n three areas of approximately 25 km2 each. Red-tailed hawk (Buteo jamaicensis) numbers did not change significantly over the study period. Although golden eagles (Aquila chrysaetos) declined in abundance, their numbers did not recover with the recovery of prairie dogs in 1987. Ferruginous hawks (B. regalis) were abundant during autumn migration where prairie dogs were abundant, but their numbers declined significantly with the population decline of prairie dogs. Gunnison's prairie dogs appeared to be an important food resource for ferruginous hawks during their migration through the Moreno Valley.

The effect of caudal lamellae loss on swimming speed of the damselfly Argia moesta (Hagen) (Odonata: Coenagrionidae).

Abstract: -Burst swimming speed in the damselfly Argia moesta is directly proportional to body length, provided that at least one of its three caudal lamellae remain attached to its abdomen. If two of these lamellae are missing, larger individuals swim faster than smaller individuals but statistically slower than individuals that retain two or three lamellae which swim at the same speed. Reduced swimming speed probably subjects larvae to higher risk of predation.

Population Dynamics of Chaetogaster limnaei limnaei (Oligochaeta) as Affected by a Trematode Parasite in Helisoma anceps (Gastropoda)

Abstract: The population dynamics of Chaetogaster limnaei limnaei, a commensal and predatory oligochaete living in the mantle cavity of the pulmonate snail, Helisoma anceps, were studied. The densities of the oligochaete infrapopulations were positively correlated with water temperature, declining in the autumn, reaching their lowest levels in winter and rising in spring and summer to their highest levels. This pattern was also influenced by the annual reproduction and mortality cycle within the snail population. Most importantly, however, in snails shedding cercariae of the hemiurid trematode, Halipegus occidualis, den- sities of the oligochaete were significantly higher than those in uninfected snails. The continually accessible and nonmotile cercariae of this trematode were especially vulnerable to predation by Ch. 1. limnaei which enhanced the rate of asexual reproduction (by budding) of the oligochaete.

Species Interactions in Cave Stream Communities: Experimental Results and Microdistribution Effects

Abstract: -The interspecific interactions of three pairs of cave isopods and amphipods, previously thought to be competitors, were examined by analyzing washouts and losses from laboratory streams and from manipulation experiments in streams of Organ Cave, West Virginia. None of the pairs were in fact competitors. The isopod Caecidotea holsingeri was an amensalist of the amphipod Stygobromus spinatus in the laboratory, but the two did not interact in the field. The amphipod Gammarus minus was a predator on C. holsingeri both in laboratory streams and in the field, and C. holsingeri was a competitor of G. minus, at least in laboratory streams. Stygobromus emarginatus was an amensalist of G. minus in laboratory streams and in the field; but in the field G. minus was a commensalist of S. emarginatus. This combination of commensalism and amensalism produces the dynamics of a predator-prey system. Interactions in both laboratory streams and cave streams were asymmetric and often had characteristics of several kinds of interspecific interactions. Negative interactions dominated in laboratory streams while positive interactions were more common in the field experiments. Negative interactions had an effect on microdistribution only at the level of individual stones in a riffle. Positive interactions may contribute to the positive association of some species at larger scales.

Distribution, Life History and Production of Crayfish in the James River, Virginia

Abstract: -Species composition, distribution, life history and production of crayfish were determined in a 5th-6th-order river in Virginia. Three sites representing distinct geomorphic areas (Ridge and Valley province, Piedmont and Fall Line) were sampled monthly from April 1988 through June 1989. Two species of crayfish, Orconectes virilis and Cambarus bartoni, were collected. Orconectes virilis was only collected from the Ridge and Valley site, whereas C. bartoni was collected from all three sites. Both species had a minimum possible 24-mo lifespan, although few individuals survived past 18 mo. Females extruded eggs in April and by June young were no longer carried by females. Highest growth rates occurred in May and June, during which 68-86% of annual production occurred. The Ridge and Valley site had the greatest abundance of the preferred cobble and boulder substrate. It also had the highest substrate-weighted density (0.4 individuals/M2), biomass (129 mg AFDM/m2) and annual production (155 mg AFDM/m2) of crayfish. Density, biomass and production were much lower at the other two sites, annual substrate-weighted production being only 8-14 mg AFDM/m2. P/B ratios were 0.7-1.1. The predominance of unsuitable habitat, especially a highly embedded substrate, was a primary factor causing the low biomass and production at all three sites.

Foraging phenology of the Formosan subterranean termite (Isoptera: Rhinotermitidae) in Louisiana.

Abstract: -A 2-yr field study was done to measure seasonal changes in feeding rates, number of workers, mass of individual workers and percentage of soldiers of foraging groups from colonies of the Formosan subterranean termite, Coptotermes formosanus Shiraki, living in cypress trees (Taxodium distichum [L.] Rich.) at the Calcasieu River near Lake Charles, Louisiana. There was distinct seasonality with most dependent variables. Feeding rate was highest in summer and varied positively with day length and daily maximum temperature. Number of workers was highest in summer, increased with increasing day length but leveled off at higher values of day length. Mass of individual workers was fairly uniform but tended to be higher in summer; it varied positively with temperature but leveled off at higher temperatures. Percentage of soldiers was highest in early winter and varied inversely with day length and temperature. On average, these colonies ate 7265.2 ? 1653.3 g (range = 4647.1 g to 9969.9 g) of pine (Pinus sp.) wood in baits over 2 yr.

A field study of host size effects on sex ratio of the parasitoid wasp Spalangia cameroni.

Abstract: -I examined aspects of Charnov et al.'s (1981) host-size model for the parasitoid wasp Spalangia cameroni, using collections of fly pupae (hosts) from a poultry house. The model predicts that female parasitoid wasps should emerge from larger hosts than males. This prediction was supported for two collection dates in which only one host species, house flies, was parasitized by S. cameroni. The prediction was not supported either within host species or combining host species for the collection date in which both house flies and stable flies were parasitized. In fact, female S. cameroni emerged from smaller stable fly pupae than did males. The prediction of the host-size model also was not supported on a between-host species basis. Though stable fly pupae are significantly smaller than house fly pupae, the sex ratio (proportion of males) of S. cameroni emerging from stable flies was not significantly greater than from house flies. Contrary to expectations, field data showed no positive relationship between host size and female wasp size either within or between host species. Laboratory experiments indicated that female S. cameroni judge host size relative to the size of other hosts encountered, as predicted based on the significant temporal variation found in the host size distribution in the field.

Species-dependent effects of seed predation and ground cover on seedling emergence of old-field forbs.

Abstract: -Seed predation may limit seedling emergence by reducing seed supply but in old fields suppression of seedling emergence by dense ground cover could override any potential effect of seed predation. Experiments were conducted with sown seeds of three old-field forbs (Medicago lupulina L., Centaurea nigra L., Taraxacum officinale Weber) to test whether seed predation affected seedling emergence in densely vegetated hollows and on less densely vegetated ridges in an abandoned pasture. Some seeds were protected from potential seed predators (i.e., ants, rodents and birds) while other seeds were not protected. Unprotected seeds disappeared faster in hollows than on ridges. Excluding ants or ants plus rodents and birds reduced the rate that seeds disappeared in hollows more than on ridges. Excluding only rodents and birds had little effect on the rate that seeds disappeared. Fewer seedlings emerged in hollows than on ridges when seeds were not protected from predators. Excluding ants plus rodents and birds increased seedling emergence for Centaurea nigra and Taraxacum officinale, especially in hollows. In contrast, seedling emergence of Medicago lupulina did not increase in hollows when seed predators were excluded. Dense ground cover in hollows likely suppressed seedling emergence of Medicago lupulina. Our results indicate that seed predation reduces seedling emergence for some but not all old-field forbs. It is inappropriate to assume that seed predation always reduces seedling emergence.

Pollinium Germination and Putative Ovule Penetration in Self- and Cross-pollinated Common Milkweed Asclepias syriaca

Abstract: -We compared success and speed of pollinium germination and putative ovule penetration in selfand cross-pollinated flowers from three clones of common milkweed (Asclepias syriaca). Even though common milkweed is largely or entirely self-incompatible, success of selfed flowers equalled or exceeded that of crossed ones (87% vs. 74% germination, 78% vs. 63% putative penetration). This result is consistent with the postfertilization incompatibility mechanism proposed for A. syriaca. Clones differed in success, and the recipient clone with the highest combined selfed and crossed success (97% vs. 74% germination for the others, 95% vs. 56% putative penetration for the others) also developed most rapidly (90% vs. 45% germination for the others 1 day after pollination; 90% vs. 13% putative penetration after 1 day). The significant among-clone variation suggests that factors intrinsic to the clones strongly affect rates of fertilization and putative penetration.

Behavioral (Predator-Prey) Interactions of Captive Grasshopper Mice (Onychomys torridus) and Horned Lizards (Phrynosoma cornutum and P. modestum)

Abstract: -In predatory attacks by Onychomys torridus 20% of the 30-min encounters involving Phrynosoma cornutum were fatal, whereas 43% of those with Phrynosoma modestum were fatal. When the trials of juvenile P. cornutum were combined with those of adult P. modestum, which are similar in size, large horned lizards (adult P. cornutum) suffered 0% mortality whereas small lizards (adult P. modestum plus juvenile P. cornutum) experienced significantly higher mortality, 55%. Horned lizard antipredator behaviors involved displays that increase apparent size, aggressive attacks that intimidate, and the absence of flight responses that might elicit Onychomys attack behavior. Lizard mortality was mainly attributable to attacks involving chewing of the cranium around the orbit. Adult Phrynosoma cornutum possess sufficient armament around the eyes and parietal region to successfully defend against such attacks. Also their tough dorsal skin hinders laceration by the mice. In contrast, P. modestum and juvenile P. cornutum were easy prey for 0. torridus.

Effects of pollen-load size on sporophyte competitive ability in two epilobium species.

Abstract: -Competition among pollen-tubes for ovules can lead to increased sporophytic vigor. This phenomenon has been well studied in a few cultivated species, but little is known about whether it occurs in natural populations. I tested for effects of pollen-tube competition on progeny performance in Epilobium septentrionale and E. canum ssp. canum. Three maternal plants of each species received small vs. excessive pollen-loads, using mixtures of pollen from three paternal plants. Progeny from these treatments were grown in competition with wild oats and harvested after nine weeks in the greenhouse. Intense pollen competition led to significantly larger progeny in only one of the six maternal families. In another maternal family, offspring from excessive pollen-loads were actually smaller than those from small pollen-loads. Pollination treatment had inconsistent effects on seed size, which did not appear to influence plant size. This study does not support the hypothesis that pollen competition fosters selection for faster-growing progeny.

Reproductive-behavioral Phylogenetics of Nocomis Species-groups

Abstract: -Descriptions of nest construction and reproductive behaviors of Nocomis species, identified from field observations and laboratory analysis of video tapes, are used to evaluate previous species-group designations (biguttatus, leptocephalus and micropogon) based on morphology. Three behavioral synapomorphies, the three-stage process of nest construction (excavating a concavity, forming a platform and building a mound), pit fanning of spawning troughs and pits with the anal fin of nesting males, and circle swims (reported for the first time) support the monophyly of Nocomis. Nocomis biguttatus and N. leptocephalus form a monophyletic group based on two behavioral synapomorphies (spawning pit excavation and covering eggs after spawning).

Soil respiration of five aspen stands in northern lower Michigan

Abstract: -Soil respiration rates of five successional forest stands dominated by bigtooth aspen (Populus grandidentata Michx.) in northern lower Michigan were measured during the growing seasons of 1981-1983. Forest age ranged from 11-70 yr, and aboveground biomass varied fivefold among sites. There were no significant differences among sites in soil respiration rate in any one year. Mean rates over all sites from June through September were 9.1, 8.6 and 6.1 g m-2 day-' in 1981-1983, respectively. Rates in 1983, which had a dry, warm summer, were significantly lower than rates in 1981 and 1982, which did not differ. Estimated yearly CO2 released ranged from 1700-2250 g/m2. Litterfall on the sites (3-yr mean) ranged from 187-408 g m-2 year-', with leaves contributing 90.1% of the litter. Litter inputs accounted for only 15-30% of the yearly CO2 released from the soil. Similarity of soil respiration rates among sites resulted in no correlation with forest age, aboveground woody biomass, or site fertility.

Direct and indirect effects of generalist predators on a terrestrial arthropod community.

Abstract: -The densities of an assemblage of cursorial spiders and a mantid, Mantis religiosa, were elevated in replicated field enclosures to compare their impact on a terrestrial arthropod community. Mantids reduced overall biomass 88% relative to controls by directly eliminating grasshoppers and crickets, and to a lesser extent by reducing numbers of cursorial spiders. Spiders also eliminated grasshoppers, but indirectly enhanced cricket numbers, a compensatory effect which canceled their effect on total biomass. Numbers of cursorial spiders were lower in enclosures initially containing elevated spider densities than in controls, suggesting that increased predation among these spiders reduced predation on crickets.