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Cattle grazing has been shown to alter various features of desert communities that may impact microhabitats required by various species of desert rodents, with unknown implications for desert rodent communities. We conducted a series of studies at heavily and lightly grazed sites to investigate effects of cattle grazing on desert rodent relative abundances, home range sizes and microhabitat use in salt desert shrub communities of the western Great Basin Desert. Monitoring of rodent populations with repeated live trapping showed that different levels of grazing were associated with differences in relative abundances of some species of rodents. Specifically, Dipodomys merriami was significantly more abundant in heavily grazed areas, and Perognathus longimembris was significantly more abundant in lightly grazed areas. Our studies showed that cattle, by preferentially feeding on certain plants, can create conditions that are more suitable for some species of rodents, while reducing important microhabitat for other species.
We quantified the combustion characteristics of bison fecal pats following three prescribed grassland fires conducted during three different seasons on an Oklahoma tallgrass prairie. We compared heat per unit area, rate of energy consumption and duration of combustion of the burning fecal pats with fireline intensity, reaction intensity and heat per unit area of the fires. Environmental conditions at the time of burning determined the intensity of the fire in the grassland fuels. However, we found no correlation between grassland fire behavior and fecal pat combustion characteristics, suggesting that grassland fuels and fecal pats respond differently to several environmental factors. The heat released per unit area of fecal pat was extreme in each fire. The results suggest the flux of heat created by combusting bison fecal pats may potentially alter patterns of soil resources. If so, this should contribute to species richness and spatial heterogeneity in tallgrass prairie in a manner similar to other small-scale disturbances.
We estimated growth rates and sex and age-specific seasonal weight fluctuations for raccoons (Procyon lotor) in San Patricio Co., Texas. During 1990–1992 we recorded 248 weights for 167 raccoons. Growth rate parameters for raccoons <2-years-old differed (P < 0.05) between males and females. Females reached adult size as yearlings, while males did not reach adult size until they approached 2 yr of age. Mean weights of adult raccoons differed between sexes (P < 0.0001) and among months (P < 0.0001). Raccoons in a subtropical climate experienced seasonal fluctuations in body weight; however, these seasonal patterns differed in their timing and magnitude from those of raccoons in temperate climates.
Although chronically low soil fertility is widely recognized as an important selection pressure on carnivorous plants, the effects of other potentially important selection pressures, such as natural disturbances, have largely been ignored. In this study, I examined the effects of fire and removal of live plants and litter on seedling establishment of Drosera capillaris (pink sundew), a small insectivorous plant common to wet, nutrient-poor pine savannas of the southeastern United States. I also examined the effects of soil disturbances associated with crayfish burrows on mortality. Fires occurring during the winter of 1996/1997 increased the density, growth and establishment of seedlings during the growing season of 1997. In addition to fires, local removal of established plants and their associated litter greatly increased seedling density and growth within savannas. The proportion of rosettes that flowered at sites not burned recently (>1 year before) was nearly twice that at sites burned more recently (<1 year before; 0.183 vs. 0.107, respectively). Between May and August of 1997, mortality of sundews at recently-burned sites resulted in nearly equivalent densities at all sites by August 1997. Most of this mortality was caused by burial by shifting sediment associated with erosion of crayfish chimneys, rather than by competition from resprouting vegetation. Smaller rosettes were disproportionately buried by sediment and killed. These results suggest that frequent burial of sundews, with its disproportionate effects on juvenile mortality, selects for rapid growth and establishment. I hypothesize that fire and carnivory permit rapid growth of juveniles and facilitate establishment of sundews in nutrient-poor wet savannas.
The invasive shrub Lonicera maackii (Rupr.) Herder (Amur honeysuckle) dominates the understory of many deciduous forests in southwestern Ohio and other areas. Extensive sampling of an isolated population of L. maackii was used to elucidate its colonization of a forest woodlot and subsequent growth and development. The current population age structure indicated that colonization likely occurred by a series of small dispersal events. The population remained small for about ten years and then increased dramatically, presumably due to the seed reproduction of the early colonizers. Young prereproductive shrubs are characterized by rapid height growth and high stem recruitment. After shrubs become reproductive at age 5–8, height growth continues but basal stem recruitment is reduced and radial growth increases shrub basal area. Allocation of primary production apparently shifts from stem recruitment and height growth in young shrubs to a balance of height growth, radial expansion and reproduction in older shrubs.
Woody plant species in grassland ecosystems can be subjected to damage from fire and multiple herbivore species, but interactions between fire and herbivory can modify their separate impacts on woody plant life histories. We studied how galling (by Periploca ceanothiella, Lepidoptera: Cosmopterigidae), deer browsing (Odocoilius virginianus) and fire affected the growth and reproduction of the woody shrub Ceanothus herbaceous (Rhamnaceae) on a burned and an unburned site at Konza Prairie Research Natural Area in eastern Kansas. Fire was the major influence on C. herbaceous growth, causing plants to produce long unbranched vegetative ramets from protected belowground meristems, while unburned plants were heavily branched and bore shorter shoots and numerous inflorescences. Unburned plants experienced higher gall frequencies, more galls on their longest shoots, but similar deer browsing compared to burned plants. Ramets with herbivore damage had more branches and inflorescences than undamaged ramets, especially where both herbivores were present. Ceanothus herbaceous' flexible life history responses suggest tolerance of multiple forms of damage.
Flower color change, floral rewards, and the size of a floral display in relation to pollinator attraction were studied in Aster vimineus. The center disk florets of A. vimineus are either all yellow or all red in a given flower. We determined that this variation in disk color was due to localized color change from yellow to red. Yellow florets contained more pollen and a greater percentage of viable pollen than red florets. All pollinator types consistently preferred flowers with yellow disks over those with red disks. The addition of nectar did not influence pollinator visitation rates, unless the pollinators were choosing only among flowers with red disks. Retention of the flowers with red disks allowed for greater floral display which increased pollinator visitation rates.
The heterogenous structure of eastern deciduous forest canopies creates an understory light continuum ranging from deep shade to extended periods of direct solar irradiance below large canopy gaps. We designed an experiment to explore how shagbark hickory (Carya ovata (Mill.) K. Koch; Juglandaceae) seedlings respond to changes in both the total amount of available light and the durations of experimental sun patches. Seedlings were grown in a common garden under shadehouses where they experienced one of two light levels (high vs. low light), one of two sun patch durations (short vs. long duration) and 100% light (control). Over the growing season, seedlings responded morphologically to the amount of available light by changes in mean stem height, weight, basal diameter, specific leaf mass, chlorophyll content, taproot length, primary and secondary root weight and root ash weight. Chlorophyll content and stem height were negatively related to the amount of available light whereas the other morphological characters were positively related to increased amounts of light. Changes in the duration of experimental sun patches significantly affected stem biomass, basal diameter, secondary root dry weight and root ash weight independent of total light amount. Though the effects of sun patch duration were not as pronounced as those found for amount of light, our results demonstrate the importance of including periods of direct light in experimental designs involving responses of seedlings to varying light regimes. The ecological responses of many hardwoods, especially those of midshade tolerance, to the middle portion of the gap-understory continuum remain poorly studied.
Fire and soil moisture gradients are thought to influence oak community structure in longleaf pine (Pinus palustris Mill.) woodlands. To explore these influences, we measured oak density and species composition within a longleaf pine-wiregrass (Aristida stricta Michaux) dominated landscape subjected to frequent cool-season fires for 70 yr. At 64 locations within the Joseph W. Jones Ecological Research Center in southern Georgia, oak trees, saplings and regeneration (seedlings plus sprouts) were counted in nested plots, and 20 additional measurements were taken to assess physical and chemical properties of soils, disturbance, density of other vegetation and topography. Principal components analysis of soil data revealed a soil moisture and soil chemistry gradient. Trees and saplings were sparse (mean of 37 and 81 per ha) and most common in dry and dry-mesic sites, while regeneration was abundant (mean of 110,100 stems per ha) and well-distributed across the soil moisture gradient. Fifty percent or more (depending on vegetation stratum analyzed) of cumulative species-environment relation was accounted for in the first two axes of a canonical correspondence analysis with axes representing gradients in soil moisture and several chemical and physical properties including mineralizable N, extractable Ca and Mg and soil texture. Three oak species were concentrated in the dry end of the soil moisture gradient, four in the moist end and one was common across much of the gradient. Species distributions probably reflect physiological tolerances of soil moisture extremes plus variation in fire regime caused by differences in soil moisture. Forest fragmentation and prescribed cool season burning may have increased oak densities in this landscape. If so, then this legacy of past management should be considered if managers wish to change fire regimes to better mimic natural disturbance patterns.
How vegetation develops from a source of potential species remains poorly understood. I explored whether colonizing species assemble randomly, or if local deterministic factors alter species establishment to create consistent vegetation patterns. Early primary successional vegetation in 111 small self-contained depressions (potholes) on Mount St. Helens was sampled. Mean richness was 8.8 species and mean cover was 2.6%. Mean percent similarity (PS) between potholes was 46%. A nearby grid of 100 contiguous 100 m2 quadrats on a level barren plain was sampled for comparison. Barren quadrats had mean richness of 12.2 species, mean cover of 1.4% and mean PS of 63%. Pothole vegetation was much more variable than that of the barrens. Canonical correspondence analysis revealed a slight relationship between environmental factors and pothole vegetation. Species composition, cover and species rank orders were predicted extremely well by a stochastic model based on observed frequencies and random accumulation of species. These findings suggest that early colonization of isolated sites is stochastic, and that dispersal affects species composition more strongly than environmental factors or competitive interactions. Which species succeed at any particular site is poorly predictable, but once established, a local population can persist. As a result, there is often a poor correlation between species composition and environmental factors in mature vegetation.
We surveyed the nonvolant mammals in 10 forest fragments embedded in a matrix of row crop agriculture in east-central Illinois to assess the impact of forest fragmentation on mammalian diversity and distributions. A total of 19 species were recorded during our study, including 16 native species that occur naturally in forest habitat. We found a significant species-area relationship and a significantly nested subset structure. In particular, gray squirrels, chipmunks and flying squirrels were only encountered in the larger, more continuous sites suggesting a negative effect of habitat fragmentation. Seven species were ubiquitous and we believe that several others occur periodically at all study sites, indicating that most mammalian species currently present have not had their distributions altered by changes in the intervening habitat. Though an analogy to oceanic islands may apply for some species, we believe that most mammals treat forest remnants as habitat patches rather than islands, and that mechanisms such as habitat selection, constraints due to home range size and differential dispersal ability best explain the observed distributions of mammals.
We report characteristics of a previously unknown population of Ambystoma tigrinum mavortium (barred tiger salamander) from eastern South Dakota, a location that extends the formerly known range of this subspecies about 150 km north. This population contains paedotypic animals and a small percentage of cannibal morphs. At least one cannibal morph was paedotypic. The vomerine tooth hypertrophy characteristic of cannibal morphs described here differs from the cannibal morph A. t. tigrinum from nearby (about 160 km) northwestern Iowa; in particular the pair of caudolateral tooth ridges has smaller teeth in individuals from the A. t. mavortium population. The study wetland is located near the convergence of four recognized (pending revision) tiger salamander subspecies (A. t. diaboli and A. t. melanosticum in addition to A. t. mavortium and A. t. tigrinum), making it an excellent region to examine subspecific morphological features in light of shared ecological factors. We suggest creating a formal nomenclatural distinction between cannibal morph larval phenotypes and cannibal morph paedotypic phenotypes.
Reproduction of Megalonaias nervosa (Rafinesque, 1820) has not been documented for over 20 y in much of the Cumberland River, where water temperatures have decreased and flow regimes have been greatly altered by hypolimnetic discharges from impoundments. Studies in other streams have implicated low temperatures or changes in discharge patterns as causative factors inhibiting reproduction. Megalonaias nervosa were collected from the Cumberland River, translocated to the Tennessee River, and held in an embayment of Kentucky Lake. After the first and second y, samples of M. nervosa were taken from the Cumberland River, an existing population in Kentucky Lake, and the translocated group. Histological examination indicated that translocated mussels had a high incidence of hermaphroditism, and like mussels originating in Kentucky Lake, had undergone an otherwise normal reproductive development. Individuals functioning successfully as females from the translocated group had mature glochidia in their marsupia. Females from the Kentucky Lake sample also had mature glochidia present. In contrast, there was no indication of reproductive activity in gonads or marsupia of individuals collected from the Cumberland River. Our results indicate that a return to a more natural temperature regime in the Cumberland River would reinstate a normal reproductive cycle. We suspect that the altered temperature regime is also disrupting the gametogenic cycle of all mussels, including at least six federally listed endangered species occurring in the Cumberland River. These relic populations will disappear unless they are translocated or the thermal regime returned to normal.
Suitable host fishes were identified for two species of freshwater mussels (Unionidae) from the Coosa River drainage, Mobile Basin: Lampsilis altilis, the fine-lined pocketbook and Villosa vibex, the southern rainbow. Suitable hosts are defined as fishes that produce juvenile mussels from glochidial infestations in the laboratory. Larvae of both L. altilis and V. vibex transformed successfully on four species of sunfishes (Centrarchidae): Lepomis cyanellus, Micropterus coosae, M. punctulatus and M. salmoides. For both mussel species transformation success on L. cyanellus was highly variable and generally lower than on Micropterus spp. Gravid female L. altilis and V. vibex display highly modified mantle margin lures in the early spring. In addition to displaying mantle lures, L. altilis produce superconglutinates, similar to those recently described for three other species of Lampsilis in the southeastern U.S.
Beaver ponds are a widely distributed and abundant wetland resource in the southeastern United States, but their value as avian habitat is poorly documented. We sampled bird populations at six South Carolina Piedmont beaver ponds from April 1993 through June 1994 to examine seasonal community composition and discern microhabitat variables that are associated with bird group abundance and richness. The resident/short-distance migrant group and the neotropical migrant group were most abundant in the spring seasons and waterbirds were least abundant. In fall and winter the resident/short-distance migrant group was most abundant at all ponds with the exception of one pond in winter, which had very high use by waterfowl. Seasons were generally most important in predicting bird species richness and abundance of the resident/short-distance migrant group. Vegetation interspersion, patch evenness, plant richness and total area were most important in explaining abundance of waterfowl, waterbirds, neotropical migrants and woodpeckers, respectively.
Retention of riparian buffers is a common management practice used to protect streams from the effects of upslope forest harvest. We compared bird use of riparian buffers along main stem rivers, tributary streams, and reference riparian zones having intact, upslope forests. Community composition differed considerably between buffers and references, and also between main stems and tributaries. Density of the more common species (those detected >20 times) was significantly higher along main stems than along tributaries. Four species (bay-breasted warbler, black-throated green warbler, blue jay, Cape May warbler) were more abundant along main stems than along tributaries; no species was more abundant along tributaries. The overall density of less common species was significantly higher in buffer strips than in reference sites, but four of the more common species (bay-breasted, blackburnian, black-throated green, and Cape May warblers) were more abundant in reference sites than in buffer strips. We did not detect differences in species diversity or richness among the different site types, but edge-species were significantly more common in buffer strips than in reference sites. Interior-species, in contrast, were significantly more common in reference sites.
Between 4 January and 15 May 1988, we captured 16 female and 10 male ring-necked pheasants (Phasianus colchicus) in north-central Maryland at the southern edge of their North American range and fitted them with radiotransmitters. We monitored their movements on an agricultural landscape encompassing 2002 ha from the day of capture until death, transmitter failure or 15 December 1988. Eight of 16 females and seven of 10 males survived to the nesting season. Predation accounted for 61% of the mortality of adult pheasants. Seven males and 12 females, each with ≥30 fixes per analytical time period (winter, nesting, postnesting or maximum), were used in analysis of home and core ranges, seasonal movements and habitat selection and use. Home range sizes did not differ significantly between sexes or among seasons. Pheasants had significantly larger core ranges during the nesting season than during winter or postnesting seasons. Pheasants selected home ranges with a higher proportion of shrublands and wetlands than expected from availability within the study area. A comparison of habitat use within core ranges to that available within home ranges in winter showed that forests were significantly less used than wetlands, croplands, shrublands and developed lands. There were no significant differences in proportional habitat use of home versus core ranges during the nesting season. Based on our study, conservation measures should include (1) enhancing preferred nesting cover by compensating landowners for delaying or not mowing hay fields or leaving crop fields fallow and (2) providing suitable dispersed male territory cover (i.e., shrubs or woody cover at crop borders) around existing patches of winter cover (i.e., wetlands and shrublands) and in close proximity to nesting cover.
Differential survivorship within or between stages is an important component of most explanations of turtle reproductive patterns. We tested the null hypothesis that a sample of adult female Trachemys scripta found killed by predators was a random sample of adult females found nesting at a site in W-central Illinois by comparing plastron lengths of the two samples. Mean plastron length of 19 dead female T. scripta was significantly smaller than mean plastron length of 79 females found alive. Apparently smaller females were at greater risk of mortality than were larger ones. Cubic spline analysis indicated that mortality was strongly concentrated among the smallest and perhaps youngest nesting females and was distinctly nonlinear. This finding was consistent with the suggestion that the minimum threshold of maturation size was influenced by the size at which the probability of predation decreases.
Six hundred sixty-three Uta stansburiana from the San Gabriel Mountains, Los Angeles County, California collected at monthly intervals from February 1974 to January 1975 were examined for helminths. One species of cestode, Oochoristica macallisteri, two species of nematodes, Physaloptera retusa (larvae) and Spauligodon giganticus and one species of an oligacanthorhynchid acanthocephalan (cystacanths) were found. Spauligodon giganticus had the highest prevalence (23%) and greatest mean abundance (1.0 ± 3.7 sd). It was present in 11 of the 12 mo studied. This is the first report of an oligacanthorhynchid acanthocephalan for U. stansburiana. Infection prevalences and mean intensities appear to be determined by a lizard's position within the habitat and its behavior patterns.
We document the occurrence of freshwater mussels living on bedrock, a substrate generally considered to be unsuitable. We found 54 individuals of six species in this habitat. Our observations support the hypothesis that substrate stability is an important component of mussel habitat.
Over 75% of the seedlings of the endemic sandplain grassland perennial, northern blazing star (Liatris scariosa var novae-angliae), die within their first growing season. During a study of the reproductive ecology of this rare plant, we found 17 seedlings whose leaves had become completely desiccated and brown and were classified as dead. Upon subsequent inspection, we discovered that these seedlings had developed a new shoot with green leaves. We have called this rejuvenation “the Lazarus effect.” These seedlings became dormant by late June, which coincided with extended periods of drought, and were senescent for periods of 4–10 wk. Rejuvenation of leaf-senescent seedlings occurred in late July and August, coincident with periods of increased precipitation. Survivorship of “Lazarus” seedlings to their second summer (9 of 17, 53%) was similar to survivorship of “normal” seedlings (≈58%) which did not senesce. Thus, becoming senescent did not have undue costs to survivorship.