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Small granivorous mammals may have marked effects on plants through their seed predation. Using live-trapping efforts and tagged sugar maple (Acer saccharum) seeds in 2006 at eight mixed forest sites in the northern Great Lakes region, we asked: (1) Were small mammals seed dispersers or predators at these sites? (2) How did seed predator (i.e., all granivorous small mammals) and sciurid (chipmunks and squirrels only) biomasses affect the proportion of seeds eaten? (3) How did habitat structure affect seed predator biomasses? We found that small mammals, particularly eastern chipmunks (Tamias striatus), were predators of sugar maple seeds as the proportion of seeds eaten and seed predator biomasses were positively related. We also found a larger seed predator biomass and the presence of eastern chipmunks in areas with higher proportions of deciduous trees. Our findings have important implications for forest regeneration, as seed predators may negatively impact restoration efforts.
After defoliation occurs leaf photosynthetic rate (Pn) can increase, decrease or remain unchanged relative to control uninjured leaves depending on the plant species. With common milkweed Asclepias syriaca (Asclepiadaceae) we conducted 27 experiments with insect herbivory or mechanical tissue removal to examine whether A. syriaca leaf Pn reductions were correlated with the occurrence of gross cardenolide induction and/or with reproductive phenology. Using spectrophotometry, positive cardenolide induction was detected in only one study when Pn impairment was detected with gas exchange data from injured A. syriaca leaves, while negative or no cardenolide induction was detected in the other five A. syriaca studies with Pn impairment. The occurrence of Pn impairment after partial leaf defoliation did have a seasonal pattern which correlated with A. syriaca reproductive phenology: little or no Pn impairment occurred on leaves of pre-flowering or maturing seed pod plants, while moderate to severe leaf Pn impairment occurred on leaves of flowering and early seed pod formation plants. Our results fail to support either constitutive cardenolide levels or gross cardenolide induction trade-offs to be reflected in injured leaf Pn impairment; however, our results could be explained by a resource or hormone trade-off between investment into reproduction with maintaining leaf photosynthesis after herbivory. Specifically, we suggest that a physiological ‘cost of reproduction’ is increased susceptibility to Pn impairment after herbivory injury on a leaf. Future studies will need to examine whether resource or hormonal regulation trade-offs cause this proposed physiological trade-off between reproduction and photosynthesis.
Introduced plants may compete for pollination with native species, leading to increased pollinator limitation for one or both species. In this study, I test the hypothesis that the introduced plant Euphorbia esula (Euphorbiaceae, leafy spurge) competes for pollination with the native prairie perennial Sisyrinchium campestre (Iridaceae, blue-eyed grass). A breeding system study revealed that Sisyrinchium is self- incompatible, potentially increasing its vulnerability to competition for pollination. Interspecific competition for pollinator visits occurred, as visit rates were lower for Sisyrinchium near Euphorbia than for Sisyrinchium more than 10 m from Euphorbia. However, supplemental hand pollinations of Sisyrinchium did not increase fruit or seed set either near to or far from Euphorbia, indicating that visits were not limiting. More than one- third of Sisyrinchium stigmas received Euphorbia pollen, but hand-pollination experiments detected no effect of Euphorbia pollen receipt on fruit or seed set, whether Euphorbia pollen was applied immediately or 2 h before application of Sisyrinchium pollen. Overall, this study suggests that Euphorbia does not reduce Sisyrinchium's pollination success despite competing for pollinator visits and being a source of heterospecific pollen on Sisyrinchium stigmas.
Wild pollinators provide important services in both wild and human-dominated ecosystems, yet this group may be threatened by widespread anthropogenic landscape change. We explored the responses of wild bees to exotic floral species and novel habitat in a fragmented, suburban landscape using pollen grain identification. Pollen loads from bee specimens collected in 13 suburban grassland fragments in Denver, Colorado were sampled and compared with a pollen reference collection. Averaged across two seasonal sampling rounds, 45% of the bee-borne pollen grains were identified to the species level. Wild bees in this system were very receptive to using alien plants for pollen foraging; at least 45% of pollen sampled from bee specimens consisted of non-native pollen grains. During peak flowering in early summer, bees obtained at least 32% of their pollen resources from within-fragment sources and at least 7.5% from surrounding suburban residential yards. In midsummer, within-fragment sources represented 58% of pollen sampled while yards dropped to 1.5%. These bees appear to be more accepting of exotic floral species than of exotic habitat types (yards). The advantages and disadvantages of pollen load analysis for movement studies are discussed.
We used radio telemetry to evaluate activity area size, habitat use, diurnal activity, and the influence of weather, environmental temperatures and sex on daily movements in 18 Sternotherus odoratus in southwestern Michigan. Turtles mainly moved within the highly vegetated littoral zone but two individuals used wet meadow areas adjacent to the lake and an adjoining stream. Activity area size, as measured by the 95% fixed kernel method using 40 radio telemetry days per individual, did not vary between the sexes. Mean total daily distance moved (TDDM) over a 12 h time period averaged 27 m and was not influenced by sex or by variation in daily weather conditions. However, seasonal changes in environmental temperatures were positively correlated with mean daily shell temperature (Ts) and TDDM indicating limits on activity on relatively cool days. While turtles were found to move at any time over the course of a day, distances moved during six, 4 h intervals over a 24 h period were greatest during the late morning and late afternoon. Mean Ts was greatest during the afternoon but did not differ between the sexes and mean Ts was similar to prevailing water temperatures indicating that bimodal activity was probably not dictated by diel variation in temperature.
Chub shiner Notropis potteri is unique among Notropis species in dietary habits, but remaining aspects of life history as well as native distribution and current population status are unresolved. Recent work in the lower Brazos River of Texas indicated a significant decline in chub shiner abundance within the native range of the species. Causes for such decline are not fully understood and further life history information is needed. Purpose of this study was to assess life history aspects, conservation status and native distribution of the chub shiner. We collected chub shiner monthly at three sites on the lower Brazos River, Texas from Nov. 2003 through Dec. 2005. Abundance and occurrence of chub shiner throughout our intensive 2 y study was low, precluding comprehensive assessment of reproductive ecology and habitat associations. Chub shiners exhibited three age groups with a maximum life span of 2.5 y. Fish and aquatic insects constituted the largest proportions of diet. Unpublished museum records and zoogeography data suggest that chub shiner is native, rather than introduced, to the Red River Drainage.
Tamarix ramosissima has caused dramatic morphological changes to riparian ecosystems and their bank structures over the last century throughout the southwestern United States. Growing as either small trees or dense stands of shoots, Tamarix species displace or actively outcompete native species of willow (Salix exigua) and cottonwood (Populus deltoides) on the Arkansas River in Colorado. Under normal conditions for colonization by native species, Tamarix seedlings are at a great competitive disadvantage due to slow above ground biomass accumulation. However, damming and the resulting altered disturbance regime may give Tamarix an advantage over native species. Damming on the Arkansas River, Colorado, dramatically reduces the intensity and recurrence interval of downstream flooding. Using two dams in eastern Colorado as proxies for flood control, we assessed physiological, demographic and abiotic factors in order to understand how flooding and damming might influence riparian community dynamics. Our study demonstrates that drought and salinity stress may influence native species recruitment and survival in areas with reduced flooding. Moreover, Tamarix water-use may be quite plastic in drought conditions, suggesting that it conserves water at below dam sites.
In Canada, the jeffersonii subspecies of the North American badger, Taxidea taxus, is found only within the southern portion of the province of British Columbia. The subspecies is considered endangered and small populations are believed to be the result of a loss of grassland habitat along the valley bottoms; despite this, knowledge of the basic ecology of the animal is limited. We used radio-telemetry to document the size, configuration and attributes of home ranges of the animal living in south-central British Columbia. Home range size was particularly large (x¯ = 78.6 km2, n = 9), and individuals were capable of moving greater distances than has been reported outside the province (x¯ = 645 m over 12 h in summer, sd = 985.3). Even though our sample size was small and heavily biased towards males, we found that the animals did not use their home ranges uniformly, and there was considerable variation in the patterns of use between individuals. We therefore argue that an important first step in understanding the basic ecology of these animals is to recognize the high degree of individual variation in landscape use.
We compared roost site characteristics of the Indiana bat (Myotis sodalis) and northern bat (M. septentrionalis), which form maternity colonies in cavities and beneath bark of dead (snags) and living trees in eastern North American forests. We used published data (n = 28 sources; n = 1145 roost trees) from studies completed where the distributions of the two species overlap and evaluated a suite of habitat features that might affect roost selection and interspecific competition between these two congeners. We found no differences between these species in average height of roost aboveground, density of snags in the vicinity of roosts, selection of live trees versus snags or relative elevation. Populations of northern bats were more likely to choose roosts in crevices or cavities (88.9%) than Indiana bats (30.0%; P < 0.1), and roosted in trees that averaged smaller in diameter (30.0 ± 5.4 cm) than trees selected by Indiana bats (41.4 ± 2.4 cm; P < 0.1). Northern bats demonstrated greater variability than Indiana bats in height of roosts aboveground and in stem diameter of roost trees. Existing data indicate northern bats exhibit greater plasticity in choice of summer roosts than Indiana bats, explaining, in part, why northern bats are more widely distributed and more common in forests of eastern North America than are Indiana bats.
We report on FMR of free-living American martens (Martes americana) in autumn and winter in northern Wisconsin. Mean body mass was significantly higher in males (1099 ± 43 [S.E.] g) than females (737 ± 28 g), with no significant difference by season. Daily mass change rates of martens did not differ from zero, and mass change rate and percent of body fat did not differ by gender or season. These data are consistent with our expectation that non-reproductive martens balance their energy budget on a near daily basis, even in winter, and rely little on body energy reserves. Energy expenditure, and hence food requirements, declined 24% from fall (1006 ± 96 kJ/d) to winter (725 ± 96 kJ/d), despite colder temperatures and deep snow. Both males and females were active nearly 50% less in winter (4.8 ± 1.0 h/d) than in autumn (9.1 ± 0.7). It appears that, in addition to lowering core body temperature and seeking thermal cover, martens decreased activity levels from fall to winter to reduce energy expenditures and food requirements.
We evaluated translocation as a restoration technique for southern fox squirrels (Sciurus niger niger) by capturing squirrels from six donor populations in coastal South Carolina and releasing them into unoccupied habitats on St. Phillips (n = 24) and Hall Islands (n = 28), South Carolina, during Jan. 1999–Jan. 2000. We monitored survival, home range size and habitat use during ≤90-d post release, 91–180-d post release and >365-d post release. Annual survival on St. Phillips Island (71%) was similar to reports for other populations in the Southeast, but survival on Hall Island (34%) was lower than reported for those populations. Home range sizes of males and females on St. Phillips Island and females on Hall Island decreased from ≤90-d to 91–180-d post release, and were similar to those of reported populations by >365-d post release. Home range size for males on Hall Island remained large throughout our study. During ≤90-d post release, males and females on St. Phillips Island established home ranges containing a disproportionate amount of tall grass marsh causing that habitat to rank higher than mature pine habitat. Tidal flats were represented less in home ranges than expected. By 91–180-d post release, squirrels on St. Phillips Island used habitats within their home ranges in proportion to availability. On Hall Island, squirrels used habitats within their home ranges randomly except for males at ≤90-d who used food plots more than mature pines and all habitats ranked above fallow fields and young planted pines. Our data suggested translocation is a useful tool in the management of southern fox squirrels.
Home range size, habitat use and survival of coyotes are variable throughout their range. Because coyotes have recently become established in South Carolina, we investigated their spatial distribution, habitat use and mortality on the Savannah River Site (SRS) in western South Carolina, USA. Annual survival for adult coyotes on the SRS was 0.658. Off-site trapping and shooting accounted for 60% of mortality. Home ranges averaged 30.5 km2 and 31.85 km2 by the 95% minimum convex polygon and 95% fixed kernel methods, respectively. We detected no difference in home ranges size between males and females. Intraspecific home range overlap averaged 22.4%, excluding mated pair interactions, with 87.5% of coyotes sharing their home range with one or more individuals. Coyotes selected home ranges containing higher proportions of early successional habitat than was available on the landscape. Core areas likewise contained a greater proportion of early successional habitat than available in the animal's home range.
Northern flying squirrels (Glaucomys sabrinus) of the Black Hills National Forest (BHNF) of South Dakota represent a unique and isolated population, but little is known about the distribution and habitat use of this population. A resource selection function (RSF) habitat model was created for northern flying squirrels (G. sabrinus) throughout BHNF. Using methods from Manly et al. (2002) and Johnson et al. (2006), logistic regression was used to compare habitat variables at used habitat locations (radio-tracking and trapping locations) to a random sample of available habitat locations throughout the study area. Logistic regression coefficient estimates of significant variables were incorporated into a GIS raster layer to produce a map with RSF values for BHNF. The RSF values were transformed to a relative probability of habitat use ranging from 0 to 1. Independent validation data were used to determine model fit based on predictive performance of the RSF. Data used in the model determined that northern flying squirrels in BHNF used habitats with higher precipitation, closer distance to a stream, aspen (Populus tremuloides), northwest aspect, higher basal area of snags and a higher density of live trees and snags than randomly available habitats. The RSF map identifies possible high use areas of habitat by northern flying squirrels throughout BHNF and is useful for management purposes, as well as a baseline for future research and monitoring for an isolated population at the southern edge of their range.
The population of resident giant Canada geese (Branta canadensis maxima) has increased dramatically in eastern South Dakota since reintroduction efforts were initiated in the 1960s. In order to effectively manage this population of Canada geese, it is important to determine their reproductive success. We collected information on goose nesting success and related brood movements using Very High Frequency (VHF) telemetry. We captured Canada geese in seven counties in eastern South Dakota during summers, 2000–2003. The reproductive success of 88 females was monitored during spring 2001–2004. Half of the geese had successful nests, 20.5% were unsuccessful, and 29.5% did not attempt to nest. Apparent and Mayfield nesting success estimates averaged 71% and 63%, respectively. Overall egg success was 62.6% and overall hatching success was 88.8%. Mean total clutch size averaged 5.73 ± 0.17 while the number of goslings leaving the nest averaged 5.02 ± 0.25. Forty-nine percent of marked females nested on or around the shoreline of their previous summers capture wetland. The remaining 51% nested on peripheral wetlands ranging from seasonal wetlands to permanent lakes. Mean distance from the capture wetlands to nest sites across years was 1.5 km ± 0.18. Biologists need to consider long distance movement of giant Canada goose broods when making management decisions.
We report a natural cross-fostering experiment of two House Wren (Troglodytes aedon) eggs and nestlings by Tree Swallows (Tachycineta bicolor). We document an increase in duration of the House Wren incubation period by 1–2 d, which closely corresponds to the mean incubation period of their hosts. We also documented nestling growth rates of both the host Tree Swallows and the alloparented House Wrens. The host parents apparently fed the House Wren nestlings; however, the wrens exhibited slow growth compared with conspecific nestlings in neighboring nests. The wren nestlings eventually died at 6 and 13 d of age. We hypothesize that the lower incubation temperatures, and later, interspecific sibling competition that the House Wren nestlings were exposed to in the Tree Swallow nest may have prolonged the incubation period and slowed the growth rates of the House Wren nestlings.
To learn more about the basic biology of exotic relative to native tree species we conducted a greenhouse experiment comparing the germination and early seedling growth of four early successional tree species found in the southeastern United States: two exotics (Ailanthus altissima and Paulownia tomentosa) and two natives (Liquidambar styraciflua and Platanus occidentalis). Five soil types and three water regimes were used for the experiment. Liquidambar and Platanus, the native species, germinated significantly more quickly and were more sensitive to soil type than were the exotics, Ailanthus and Paulownia. Platanus grew tallest, and along with Paulownia, accumulated the greatest total biomass. Ailanthus alone exhibited a high root/shoot ratio in all soil types. In addition, species differed in their response to soil types for multiple growth traits. The results suggest that native tree species could be used to help retard the establishment of invasive tree species on bare soil.
Changes in the standing crop of Vaccinium corymbosum shrubs were documented over 10 y at six sites throughout eastern North America. Populations in Florida, North Carolina, New Jersey and Nova Scotia showed few significant changes in standing crops over the 10 y of observation. The Ontario population had a significant decrease in standing crop whereas the Maine population increased significantly. Larger shrubs grew proportionately less at the New Jersey site but proportionately more at the Florida site. Seedling recruitment and plant mortality were very low at all sites.
The body size of white-tailed deer (Odocoileus virginianus) increases with latitude and thus exhibits the pattern predicted by Bergmann's rule on the basis of surface to volume ratios and heat loss. This pattern is more simply explained by the distribution of food available per individual animal, which is driven by two factors, the net primary production (NPP) of plants and deer population density. Food availability is often overlooked as a cause of an increase in body size in large terrestrial herbivores in temperate latitudes because of a fundamental misconception about the global distribution of plant productivity. Within a small latitudinal range, white-tailed deer body size as evidenced by modern deer and Holocene paleozoological remains is inversely related to population density and directly related to food availability. Food availability per animal is a product of plant productivity and population density, and is correlated with both local and regional body size variability. These local and regional food-body size patterns are consistent with recent analyses of global NPP datasets which show that ecologically relevant NPP is highest in the north temperate latitudes where white-tailed deer attain their largest body size.
Forest community dynamics in the Illinois Ozark Hills was studied over a 300 y period that included three sequential disturbance regimes. Presettlement forest community patterns were reconstructed using witness tree data taken from the 1806–7 General Land Office survey records. Species, stem diameter and distance from the corner were obtained for a total sample of 958 witness trees on 479 section and quarter-section corners. Data were separated by site type based on 13 aspect and slope positions, but later were combined into six Ecological Land Type Phases (ELTPs) using cluster analysis and percent similarity. At the end of the presettlement and Disturbance Phase 1 (ca. 1810), Quercus and Carya species dominated forest communities (combined Importance Value, IV100 = 68–76) on the Southwest Slope, South Slope, Ridgetop and North Slope ELTPs. The combined IVs for all early successional species ranged from 74–81 while IVs of late successional fire-intolerant mesophytic species ranged from 19–26. Using mortality/damage data on mesophytic stems after prescribed fire and growth data on healthy stems, we estimated that the presettlement forest of mid to upper slopes and ridgetops developed under a fire return cycle of 30–45 y, a range that permitted a modest proportion of mesophytes to attain tree size. Forest communities on the cool moist Low Slope and Terrace ELTPs were dominated by mesophytic species, mostly Fagus grandifolia and Acer saccharum (combined IV100 = 50 and 63, respectively). We believe forest composition at the time of the land survey in 1806–7 primarily reflected the long-term effect of Early American burning during the 1600s and 1700s. The start of the Disturbance Regime 2, distinguished by the severe 1810–11 earthquakes that damaged thousands of hectares of forest, was followed by a period of settlement (ca. 1820–1930) characterized by a high level of fire, grazing and timber cutting. Based on early records, this level of disturbance was judged to be greater than that of presettlement time. The present forest was established in the mid to late 1800s and early 1900s of Regime 2. To provide continuity and reliability, tree, sapling and seedling data on the present forest were collected in all ELTPs from nested quadrats located at randomly selected, but continuously forested section and quarter-section corners from which witness tree data were previously recorded. In the presently mature forest overstory, Quercus and Carya had higher combined importance values on the Southwest Slope, South Slope and Ridgetop ELTPs (combined IV100 = 73–88) than presettlement communities on these ELTPs. On the North Slope ELTP, a sharp decrease in Quercus importance was partially offset by increases in Carya and Liriodendron tulipifera importance. On the Low Slope ELTP, there was an increase in the Quercus, Carya and L. tulipifera component from the presettlement forest to the present forest. The Terrace ELTP community was composed primarily of early successional lowland species in contrast to the forest of presettlement time. Disturbance Regime 3 of the last 75 y (ca. 1930–2005) was marked by near complete protection with the cessation of fire that accompanied the development of national and state forests, wilderness areas and wildlife refuges. This third period served as a reference to demonstrate the effect of absence of disturbance on the Quercus–Carya community. The absence of fire per