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Nest predation is considered a primary factor affecting the life-history characteristics and particularly dispersal of many avian species. We tested the hypothesis that nest predation would increase dispersal probability, dispersal distance and the frequency of renesting. We removed eggs from burrowing owl (Athene cunicularia) nests to simulate nest predation in southeastern California. Owls responded to egg removal with increased dispersal probability, nesting attempts and egg production. We found that nest predation tended to increase dispersal probability (50% depredated nests vs. 14% control nests), which occurred fairly soon after nest predation (0–25 d). Dispersal distance was highly variable among owls (range: 148–13,012 m). Following experimental nest predation, burrowing owls increased the number of nesting attempts and thus the total number of eggs produced in a season, regardless of dispersal. Clutch size, however, decreased as the number of breeding attempts increased. Despite large initial clutch size, burrowing owls in the Imperial Valley may have adapted to nest predation by both dispersal and the ability to renest frequently.
While seasonal ponds in the scrub landscape of the Lake Wales Ridge in south-central Florida are favorable for establishment of small south Florida slash pines (Pinus elliottii var. densa), few seasonal ponds have mature trees. We hypothesize that disturbances (fire and/or flooding) periodically exclude trees from seasonal ponds. We studied the demography of slash pines in relation to water level and fire for a decade from 1992–2001 in four seasonal ponds, two with long and two with short hydroperiods. Seasonal ponds were favorable for pine growth (0.1–0.6 m increase in height annually, growth from grass-stage to one meter in about 7 y) and annual survival (survival generally over 80% in years without fires). Most recruitment (appearance of seedlings in a “grass stage”) occurred in drier ponds. Flooding episodes occurred in most years and lasted 3–11 mo. Mortality increased with flooding intensity (summed flooding depth) in 3 of 9 y and was concentrated in pines <1 m tall. Growth rates were unaffected by flooding. A low-intensity prescribed fire created 72% mortality, while a large intense wildfire caused nearly 100% mortality. Although South Florida slash pine can survive short-term flooding and moderately intense fire, both flooding and fire can exclude trees from many seasonal ponds. Fire was a stronger force during our study. Seasonal ponds in south-central Florida are usually treeless not because conditions are generally unfavorable for growth and establishment of south Florida slash pines, but because episodic flooding and fire cause massive mortality of seedling and sapling pines.
Recent changes in termite management technologies have stimulated a need for better understanding of basic termite ecology. Studies estimating the number of individuals in foraging populations and foraging territory sizes of subterranean termite colonies have been conducted in many areas of the United States. However, colonies of Reticulitermes occurring in the central Great Plains have not been well characterized. Results of studies conducted with three colonies of R. flavipes (Kollar) on an Oklahoma native tallgrass prairie are provided herein. Foraging population numbers, foraging areas, maximum linear foraging distances and soldier caste ratios were determined. Estimated foraging areas for individual colonies ranged from 9.0 to 92.3 m2. Colonies contained 10,357 to 183,495 foragers. Soldiers comprised 2.69 to 4.46% of the foraging populations. We conclude that rather than the result of a few large populations, the widespread termite pressure in this native habitat is likely the result of many small colonies foraging in close proximity.
We conducted a statistical evaluation of the pattern characteristics used to distinguish juvenile and adult copper-bellied (Nerodia erythrogaster neglecta) and yellow-bellied (Nerodia erythrogaster flavigaster) watersnakes. A total of 405 preserved museum specimens (juvenile = 242; adult = 163) was grouped as either neglecta, flavigaster or intermediate based on previous evaluations of the geographical variations of pattern seen in these taxa. Depending on the nature of the character, its state was either scored across its phenotypic range or measured using digital image analysis techniques. The juvenile neglecta and flavigaster phenotypes are consistent with their historical descriptions and the intermediate phenotype is nearly identical to neglecta. The amount and intensity of the dorsal pigment invasion of the ventral scales was the most informative adult charter. Digital image analyses of these characters are consistent with their historical descriptions for the neglecta and flavigaster phenotypes. For the intermediate phenotype, the amount of invading pigment was consistent with the neglecta phenotype, whereas the intensity was consistent with the flavigaster phenotype. The results of this research may provide a more objective means of identifying populations of the Federally threatened N. e. neglecta.
Currently, no flow regulations exist for the protection of riverine fishes in Missouri. Prerequisites for establishing flow guidelines are understanding what habitats are used by fishes at different times of the year and how much of that habitat will be available to each species under different discharge scenarios. We quantified microhabitat associations and selection for juvenile channel catfish Ictalurus punctatus, flathead catfish Pylodictis olivaris and stonecat Noturus flavus in a flow-regulated prairie river during summer (diurnal and nocturnal periods) and autumn (diurnal period) and then presented two-dimensional hydraulic modeling results from a previous study to determine how diel and seasonal microhabitat shifts might impact the availability of selected habitats at different flows. All ictalurid species exhibited seasonal and diel shifts in microhabitat selection. Selected habitat available would generally be maximized for each species between 10 m3/s and 30 m3/s which is greater than the current median discharge. Stonecats are most susceptible to dewatering during the diurnal summer period; however, the availability of selected habitat becomes flow limited (<10 m3/s) for all species during summer nocturnal and autumn periods because of changes in microhabitat selection during these periods. Channel catfish could be substantially impacted by extremely low flows during the summer nocturnal and autumn periods with no selected habitat available below 1 m3/s. Quantifying the amount of selected habitat that may be available under different discharge scenarios will aid managers in determining appropriate minimum flows for maintaining habitats for these species under a flow regime that continues to be partitioned to different stakeholder groups.
The relationship between ecosystem processes and species richness is an active area of research and speculation. Both theoretical and experimental studies have been conducted in numerous ecosystems. One finding of these studies is that the shape of the relationship between productivity and species richness varies considerably among ecosystems and at different spatial scales, though little is known about the relative importance of physical and biological mechanisms causing this variation. Moreover, despite widespread concern about changes in species' global distributions, it remains unclear if and how such large-scale changes may affect this relationship. We present a new conceptual model of how invasive species might modulate relationships between primary production and species richness. We tested this model using long-term data on relationships between aboveground net primary production and species richness in six North American terrestrial ecosystems. We show that primary production and abundance of non-native species are both significant predictors of species richness, though we fail to detect effects of invasion extent on the shapes of the relationship between species richness and primary production.
This study was designed to test hypotheses regarding vigilance (a state of alertness that allows an animal to detect the presence of predators or other threats) in white-tailed deer (Odocoileus virginianus). Based on findings on other species, we predicted that: (1) increasing group size would result in decreased individual vigilance; (2) juveniles would be less vigilant than adults; and (3) males would be less vigilant than females. Deer were observed from a tower in northeastern Kansas from May through Jul. 2001 at dawn and dusk. In accordance with other species, individual vigilance was negatively correlated with group size and juveniles spent less time vigilant than adults. However, there was no apparent difference in vigilance levels between the sexes in adults. We conclude that deer exploit loose aggregations to maximize foraging time by decreasing individual vigilance (without increasing risk) and that the trade off between vigilance and foraging intensity changes with maturation.
We monitored four male and seven female red deer (Cervus elaphus) from Mar. 2001 to Mar. 2003 in Białowieża National Park (BNP), Poland, to determine their home ranges in one of the best preserved old-growth forests in lowland Europe, and with large (>15 kg) carnivores present. Mean home-range size of adult males (36.0 km2) was significantly larger than adult females (8.4 km2). Seasonal home-range sizes differed significantly among seasons for both males and females, with the largest home ranges being in autumn for males (23.0 km2), and winter for females (7.1 km2). Inter-sexual differences in home ranges appeared to be influenced by differences in reproductive strategies and physiological needs. Both sexes exhibited strong range fidelity, although home ranges in different years overlapped more for individual males (93–100%) than females (71–90%). Home ranges of red deer in BNP were substantially larger than that reported in previous studies throughout Europe, suggesting that in old-growth forests with large carnivores present (i.e., the historical situation for most of Europe), red deer need large areas to meet their seasonal and annual requirements.
To assess the effects of deer browsing on understory composition, we examined hardwood forests with documented differences in browse intensity within two regions of the Hiawatha National Forest in Michigan's Upper Peninsula. A deciduous twig damage assessment confirmed that two sites within the southern region experienced high white-tailed deer (Odocoileus virginianus) browse intensity (44–49% of twigs browsed) and two sites within the northern region incurred low browse intensity (0.5% and 0.6% of twigs browsed). We used within-site sample means and site-level rarefaction curves to compare understory species richness in these two forests. The forest experiencing low browse intensity had higher woody species richness on a per plot basis than the heavily browsed forest, but the converse was observed for herbaceous species richness. Site-level evaluation with rarefaction curves confirmed the plot-scale results for herbaceous species, but different patterns in woody species richness emerged due to differences in the distributions of species across the four sites. When graphed as a function of cumulative number of plots, we again found that a low browse site had the highest woody plant species richness, but a high browse site had the highest richness values when richness was graphed as a function of cumulative number of stems sampled. This study demonstrates that although species richness is a useful tool for describing ecosystems, results for the same sites can differ based on how species are grouped and on the scale of analysis.
Determining causes of mortality and estimating survival rates can provide insight into the status of species for which population trends are not well understood. From Apr. 2002–May 2004 we radio-marked and monitored 39 (13 adult males; 6 subadult males; 8 adult females; 12 subadult females) river otters (Lontra canadensis) in the upper Mississippi River watershed to document causes of mortality, and to evaluate the effects of season, age and sex on survival of river otters in southeastern Minnesota. Further, we assessed the relative importance of demographic parameters to population growth using a projection matrix, which incorporated reproductive data with our observed survival estimates. Human induced mortalities, including accidental captures by fur-harvesters targeting other species (n = 6) and vehicle collisions (n = 1), accounted for the majority of deaths while natural mortality was low (n = 1). Annual survival of females was 0.680 (SE = 0.099) and was 0.946 (SE = 0.052) for adult males. Elasticity of adult female survival was 3.1 times higher than subadult survival, 2.7 times higher than juvenile survival and 2.7 times higher than the sum of elasticity for subadult and adult female reproduction. River otters and other furbearers need to be monitored to assess population status, and management should be responsive to ensure persistence of populations experiencing intentional and/or accidental harvest.
The aim of this study was to investigate the use of hedgerows by small mammals in four agricultural landscapes in Prince Edward Island, Canada. The Island has one of the highest percentages of land (about 48%) devoted to crop production and pasture in all of Canada. Therefore, identifying the landscape elements that can mitigate the effects of habitat fragmentation resulting from agricultural practices is essential to preserve the biodiversity of Prince Edward Island. We quantified species richness, abundance and diversity of small mammals in 13 hedgerows and 13 attached forest patches. Although all the species detected in forest patches were also found in hedgerows, significant differences in species diversity and abundance suggest that not all species benefit equally from hedgerows. The abundance of small mammals other than the eastern chipmunk (Tamias striatus) increased in hedgerows longer than about 225–250 m, but was independent of hedgerow's length in hedgerows smaller than 225–250 m. Predators (Mustela erminea) were captured in hedgerows, but not in forest patches. Relationships between small mammal variables and hedgerow features (microhabitat, macrohabitat and landscape) suggested that most small mammal species would benefit from hedgerows having high shrub diversity, ground cover with vines and leaf litter, and few non-vegetated gaps. Removal of hedgerows, especially large ones, may affect long-term survival of some small mammal species inhabiting agricultural landscapes of Prince Edward Island.
In June 1978 the partial skeleton of an American mastodon, Mammut americanum, was salvaged from a drainage ditch in Fulton County, north-central Indiana. The remains were recovered mostly from ca. 170–260 cm below the current land surface in marl overlain by peat and peaty marl. The stratigraphy of the site indicates that the remains were deposited in a small, open-water pond that subsequently filled. The skeleton, which is 41–48% complete, is that of a mature female, ca. 30–34 y old at death based on dental eruption and wear. Postcranial bone measurements indicate that this individual was relatively large for a female. Radiocarbon dating of wood from under the pelvis of the mastodon provided a maximum date of 12,575 ± 260 14C y BP [15,550–13,850 cal y BP] for the animal, which is up to 2575 14C y before the species is believed to have become extinct. Pollen samples from the site corroborate the interpretation that the regional climate was cooler and more humid than at present and supported a mixed spruce-deciduous parkland assemblage. The relatively small size of the molars of this and other mastodons from Indiana supports the hypothesis that late-glacial mastodons—just prior to their extinction—were smaller in size relative to earlier, full-glacial conspecifics. The relationship between molar size and body size is not clear, however, and there may be geographical factors as well as a temporal influence to size variation in these animals.
Although published studies indicate the contrary, there is concern among many sport anglers that migrating red-breasted mergansers (Mergus serrator) and other waterbirds pose a competitive threat to sport fish species such as walleye (Sander vitreus) in Lake Erie. We quantified the diet of autumn-migrant mergansers and walleye during 1998–2000 in Sandusky Bay and adjacent waters of western Lake Erie. We hypothesized that the diets of both predators would be similar in species composition, but because of different foraging ecologies their diets would differ markedly in size of prey consumed. In addition to predator samples, we used trawl data from the same general area as an index of prey availability. We found that mergansers fed almost exclusively on fish (nine species). Gizzard shad (Dorosoma cepedianum), emerald shiner (Notropis atherinoides) and round goby (Neogobius melanostomus) were consumed in the greatest numbers, most frequently and comprised the greatest biomass. Walleye fed exclusively on fish: gizzard shad, alewife (Alosa psuedoharengus) and emerald shiner were consumed in the greatest numbers, most frequently and comprised the greatest biomass. Diet overlap between mergansers and walleye was 67% by weight and 66% by species frequency. Mean total lengths of gizzard shad, emerald shiner and round goby found in walleye stomachs exceeded those captured in trawls by 47%, on average. Mean total lengths of gizzard shad, emerald shiner and round goby were greater in walleye stomachs than in merganser stomachs. Mean total lengths of emerald shiner and round goby were less in merganser stomachs than in trawls. Our results suggest that although the diets of walleye and mergansers overlapped considerably, mergansers generally consumed smaller fish than walleye. Given the abundance and diversity of prey species available, and the transient nature of mergansers on Lake Erie during migration, we conclude that competition for food between these species is minimal.
We surveyed 30 roadsides in North Dakota's Prairie Pothole Region for birds and active nests between May and July 2001–2002. Each roadside transect was 1608 m and had ≥200 linear meters of standing cattail (Typha spp.). We recorded 45 bird species; four species of Icteridae dominated the avifauna. Red-winged blackbirds (Agelaius phoeniceus) were both the most abundant species and most abundant nester, averaging 53 birds/10 ha (se = 7.7) and 30 nests/10 ha (se = 9.7). Among non-icterid species, song sparrow (Melospiza melodia) and common yellowthroat (Geothlypis trichas) ranked first and second consecutively in 2001 and 2002. Canonical correspondence analyses of species compositions indicated that species abundance was related to two roadside variables, length and water depth of cattail stands. Cattails added habitat diversity and acceptable conditions for wetland-dwelling avian species not typically found in rural roadsides outside of the Prairie Pothole Region. We documented use of roadsides by three species of grassland birds of national or regional conservation concern. Roadsides in North Dakota, although dominated mostly by generalist bird species with edge tolerance, may have some management potential for area-dependent grassland birds.
Studies comparing historical data with modern surveys can provide important insights into avian population trends. In 1993–1995 I repeated a breeding bird survey completed by G. W. Salt in 1952 and 1954 in Grand Teton National Park, Wyoming. The composition of breeding birds on all transects were comparable during the four decades, with most species showing no discernable difference in relative abundance (60.7%; n = 54), although 45.6% (n = 41) showed strong annual variation in the 1990s. Long-distance migrants represented the greatest number of species present (52.8%; n = 47) and the largest proportion showing a decline (25.5%; n = 12). Resident species had the largest proportion showing an increase (31.8%; n = 7). One resident species (Clark's nutcracker, Nucifraga columbiana) and one short distance migrant (red-naped sapsucker, Sphyrapicus nuchalis) showed a declining trend. American bitterns (Botaurus lentiginosus) may have disappeared from the sites surveyed in this study. Willow flycatcher (Empidonax traillii) abundance, while highly variable in the 1990s, also showed a significant decline. Close to half of the species occurring in spruce-fir forest declined (42.2%; n = 11), while species occurring in lodgepole pine (Pinus contorta) forest increased (35.3%; n = 12). Large national parks, such as Grand Teton National Park, could act as avian refugium, fundamental in preserving species that are experiencing declines in surrounding areas or on wintering grounds. The value of relatively undisturbed landscapes, such as national parks, to protect and conserve species numbers and diversity is increasingly vital, as the landscape and habitat in the surrounding areas continue to change.
The extent and type of vegetation within watersheds are critical factors influencing stream water chemistry, specifically nitrogen and phosphorus concentrations. As stream productivity can be limited by nutrient supply, nutrient subsidies from red alder, a nitrogen fixing species prevalent in the Pacific Northwest of North America and other temperate climates, may influence the degree of nutrient limitation in streams. Our study was designed to determine the extent that algae are nutrient limited in three red alder and three coniferous forested second and third-order streams on the Olympic Peninsula, Washington, U.S.A. Nutrient diffusing substrates were used in each stream to test whether nitrogen and phosphorus additions at three concentrations (0.05 M, 0.1 M and 0.5 M) increased chlorophyll a concentrations compared to non-nutrient infused substrates. With the addition of nitrogen or phosphorus, three of six streams (two conifer and one alder stream) had significantly higher chlorophyll a concentrations relative to controls. Within each stream, we saw no difference in chlorophyll a concentrations between nutrient type (nitrogen or phosphorus) or concentration (0.05 M, 0.10 M or 0.50 M). Treatments increased chlorophyll a concentrations in alder streams to twice that of conifer streams. We speculate that other factors, such as algae community composition, contributed to differing algae production in alder and conifer streams in response to nutrient supplements.
The effect of shoot damage on plant performance depends partly on a plant's ability to recover by growth compensation. Plant populations in tallgrass prairie likely experience, or historically experienced, high risks of damage and therefore might be expected to have evolved significant compensation ability. We investigated shoot damage and subsequent growth compensation in Iowa populations of the annuals Linum rigidum and L. sulcatum. To estimate damage rate and responses to damage under natural conditions, we collected two data sets. The first consisted of over 200 herbarium specimens collected over a 113-y period and the second consisted of field data for four populations in the same growing season. A companion experiment investigated damage responses under controlled greenhouse conditions and identified possible mechanisms of compensation. The study species frequently experience apical meristem removal in nature. Per-individual damage-rate estimates ranged from 33–54% in L. rigidum and from 12–24% in L. sulcatum. Both species compensate substantially in mature height, branch number and biomass under field conditions. Compensation in the greenhouse tended to be incomplete, perhaps because the greenhouse experiment may have failed to simulate natural conditions and ended before maximum sizes had been reached. The major mechanism of compensation appears to be rapid activation of axillary meristems, without contributions from altered root-shoot partitioning. Shoot damage and subsequent growth compensation appear to be significant features of individual and population biology in these annual forbs.
Although rare in Wisconsin, seven examples of the cedar glade community type were included John T. Curtis's study of the vegetation conducted in the 1950s. Comparison of the contemporary vegetation to historical records revealed major successional changes. Juniperus virginiana (L.) remains the dominant woody plant, though it has since formed closed canopies. Canopy closure led to the replacement of understory savanna and prairie plants by shade-tolerant species, and the stands have become more similar to one another in composition. Many of the taxa that dominated the 2004 understory were present in the 1950s, though at lower abundances. The number of exotic taxa and the abundance of exotic individuals increased, although species native to Wisconsin still accounted for ∼90% of plants present in the understory.
Coarse woody debris is an important structural component of both terrestrial and aquatic ecosystems. We investigated coarse woody debris size-structure, decay class composition and distribution within the interface between second growth mixed conifer-hardwood forests and perennial streams in a catchment of the Lake Superior watershed on the Keweenaw Peninsula, Michigan. Down dead wood accumulation was nonlinearly distributed along transects perpendicular to streams and reached a peak between 30 and 50 m away from the wetted stream channels. Variability in the abundance of standing snags displayed a significant increase with distance. The coarse wood accumulations we observed were consistent with levels reported for upland, second-growth forests and were low compared to old-growth forest remnants in the region. Large (>40 cm diam) down dead wood will probably be the slowest pool to recover from logging and land clearing activities that occurred in the watershed prior to the turn of the 19th Century. Nevertheless, the large woody debris, especially highly-decayed wood, at the sites we examined was relict white pine (Pinus strobus) stumps, a persistent legacy of those same historic anthropogenic disturbances. Unlike dead wood, we detected no similar spatial distributions of living woody biomass. The small diameter of the existing standing wood suggests there will be a lag in the recruitment of new large dead wood into this ecosystem.
Forests of the Western Highland Rim were heavily influenced by the iron industry during the 19th and 20th centuries. The production of iron required large amounts of charcoal. Timber was cut, burned in hearths to produce charcoal and then the charcoal was transported to local furnaces and forges. The goal of our study was to document the lasting effects of charcoal production on soil characteristics, species composition and stand structure for a forest on the Western Highland Rim in Tennessee. Fires used in hearths to produce charcoal were intense, spatially concentrated events that modified soil characteristics differently than typical surface fires. We hypothesized there would still be a footprint of the charcoal making process evidenced by systematic differences in forest composition and structural attributes that could be related to soil properties. Results show there were significant differences in some soil traits between charcoal hearths and surrounding sites. However, differing soil conditions have not significantly influenced forest development. Although tree density differed between hearths and adjacent areas, there were no systematic differences in tree species richness, diversity (H′), evenness (J) or basal area between charcoal hearth and non-hearth sites. Results of this study indicate the historic land use has minimal influence on modern forest communities in our Tennessee study site.
Tallgrass prairie species often require a period of cold stratification to break seed dormancy, but not all species germinate when this occurs. Fire, which has historically played an important role in defining the prairie landscape, may also play some role in breaking dormancy by producing a variety of biologically active smoke substances. The role of smoke as a germination cue was investigated in this study, during which the ex situ germination of 37 prairie species was measured in response to aerosol smoke treatment. Overall, one third of the species responded positively, while others were either inhibited or exhibited no response at all. Smoke may therefore play a more significant role in maintaining the composition and structure of tallgrass prairie communities than was previously realized.