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Large effects of white-tailed deer (Odocoileus virginianus) upon individual plants, plant populations and communities have been documented in a number of studies. However, well-supported experimental measures of the magnitude and geographical extent of these effects are still surprisingly scarce. Deer-caused changes in stem morphology and reductions in plant growth rates are well-documented in some parts of the North America. Furthermore, deer have been shown to affect the composition of several plant communities in the north-central and northeastern United States. There are some documented cases of deer-caused reductions in plant survival; most of these are tree seedlings and saplings. However, many studies have detected no effects on plant survival or fecundity, or have found that negative effects occur only in a fraction of years, seasons, sites or deer densities. Little is known about population-level or ecosystem-level impacts. Many regions and plant communities with large deer populations have not been studied. Whereas deer density is clearly important in determining spatial and temporal variation in the presence and magnitude of deer effects, other factors that may modify the effects of deer density are poorly understood.
We compared the activity patterns of coyotes (Canis latrans) in a suburban/agricultural area to those in an adjacent undeveloped area in northwest Wyoming from August 1998 to August 1999. Activity patterns were recorded using variable-pulse radio-collars. Correlation of recorded activity and observed activity indicated differences in the sensitivity of the collars. The mean percent of active signals for coyotes in the suburban/agricultural area was significantly lower during diurnal periods and significantly higher during nocturnal periods than the mean percent of active signals in those periods for coyotes in the undeveloped area. No differences between the two areas were observed during crepuscular times. Environmental stimuli, such as human activity, increased the amplitude of the circadian rhythms of coyotes. This increase in amplitude is a result of increased nocturnal activity and decreased diurnal activity.
We examined allozymic variation at 42 loci in a translocated population of the endangered Delmarva fox squirrel, Sciurus niger cinereus, as well as the naturally occurring (source) population from which individuals were obtained to establish it. The translocated population was founded more than 20 y ago by a total of 30 animals introduced directly from the source population and by descendants from a previous translocation from the same source population. Genetic variation, as measured by mean heterozygosity, did not differ significantly between the source and translocated populations. The mean number of alleles per locus was significantly lower in the translocated population relative to the source population. Genetic variation in both S. n. cinereus populations is within the range of values found in other populations of S. niger. Nevertheless, we suggest that the Chincoteague population and other translocated populations of S. n. cinereus be examined periodically (using larger samples sizes, if possible) for losses of genetic variation. Also, additional methods (e.g., analysis of mitochondrial and/or nuclear DNA) should be used to document genetic variation within and among translocated and naturally occurring populations of S. n. cinereus.
Many aspects of spatial organization in solitary carnivores remain unknown due to prohibitively low sample sizes and reliance on only annual home range and overlap data. We estimated size, overlap and fidelity of annual and seasonal home ranges and core areas of 52 (22 male, 30 female) adult bobcats (Lynx rufus) in southern Illinois during 1995–1999 and quantified temporal spacing. We report an unusual pattern of spatial organization for bobcats such that, although male and female annual home-range sizes were similar to other regional populations, we found relatively high levels of intrasexual home-range overlap for males and females. Although intrasexual home-range overlap was extensive, core areas were nearly exclusive, implying that core areas confer benefits to bobcats by reducing competition for resources and may represent areas of more aggressive territoriality within the home range. Only 4 of 52 (8%) bobcats shifted annual home ranges, indicating stable spatial organization in the absence of harvest. Home-range size did not differ between seasons and seasonal home-range shifts were minor, suggesting it was either advantageous to be familiar with the same area year-round for maximum exploitation of resources, or that territorial behavior prevented seasonal shifts.
Burrow systems constructed by house mice (Mus musculus domesticus) in four large outdoor enclosures were excavated. Burrows ranged from 10–835 cm in length, contained 1–7 entrance holes and had 1–8 distinct tunnel segments and 0–5 cavities. Longer burrows had more segments, more entrances and at least one cavity. Only a few nest cavities and burrow segments contained stored food, probably because we excavated burrows in summer when food was abundant. We also recorded a novel behavior we termed ‘burrow cleaning’. During March and April we found many burrows with enlarged holes and considerable debris and/or grass deposited at burrow entrances. We propose that this burrow-cleaning behavior is designed to remove winter accumulations of older decayed material that may contain parasites. Female house mice occupy burrow systems that are longer, contain more entrances and more branches and have more cavities than burrow systems occupied by males. Possible functions of the various burrow systems include sites for nesting females and their litters, locations for communal nests during winter months and places where male mice can live in the summer months.
Space use patterns of female voles may or may not be related to quality and quantity of food available. We examined the relationship between food quality and home range size in female prairie voles (Microtus ochrogaster) by radiotracking voles on grids of tall fescue (Festuca arundinacea). Four grids were infected with a fungal endophyte (Neotyphodium coenophialum) while three grids of uninfected fescue served as references. This endophyte is known to lower food quality for mammalian herbivores, affecting growth rates and reproductive success. We predicted that home range sizes would be larger on endophyte-infected grids if range size is affected by access to food resources. Conversely, if space use is unrelated to food availability, changes in food quality should not change the home range size of female voles. We found no difference in home range size of voles on endophyte-infected and uninfected grids. Our results indicate that patterns of space use in female meadow voles may be driven by factors other than food.
Frequencies of size classes of deer-mice (Peromyscus maniculatus) femora and humeri from a sample of what are believed to be barn-owl (Tyto alba) pellets collected from Columbia County, southeastern Washington, indicate that most prey were of intermediate age. Behaviors of individuals in this age class indicate that they are more susceptible to predation than older (adult) and younger individuals because intermediate-age individuals are likely to have been in unfamiliar territory during dispersal and establishment of new individual home ranges. Frequencies of size classes of montane-vole (Microtus montanus) femora and humeri in the pellet sample indicate more adults than other age classes were taken as prey. Most individual deer-mice and montane-vole prey were adult or near-adult size when captured.
To document year-to-year reuse of roost trees by forest-dwelling bats we monitored trees in southern British Columbia that we first identified as maternity roosts of California bats (Myotis californicus) in 1995. Initially we identified roost trees by tracking radio-tagged individuals. Then we revisited each tree in subsequent years up to 2000. At the start of the study the bats roosted under loose bark or in cavities in dead trees. Seven of eight trees were still standing in 2000, although all had lost bark since 1995, particularly ponderosa pines (Pinus ponderosa). In 1995, after radio-tagged bats had moved and the tags had fallen off, trees either were occupied by colonies of 5 to 52 M. californicus or they were unoccupied. In contrast, roost counts in subsequent years indicated that colonies rarely used the same trees and most observations were of one or two bats. Thus, while bats continued to use most of the trees over the 5 y period, the numbers of individuals declined and much of the use may have been by males or non-reproductive females. Although our study is preliminary, the results suggest that the suitability of roosts of tree-dwelling bats declines relatively rapidly compared to the loss of the snags themselves. More intensive studies are required given the current focus on preserving roosting habitat for forest-dwelling bats.
From 1996–1998 I estimated the density of prairie skinks (Eumeces septentrionalis) in old fields and evaluated the influence of habitat characteristics on density. I estimated prairie skink density from a trapping grid using a mark-recapture method in seven old fields. For each field I estimated arthropod density, percent plant cover and recorded field age and if the field had been burned in the last 5 y. Arthropod density was highly variable among years and fields. Percent plant cover did not explain this variation, as it varied little among fields and years. Prairie skink density ranged from 58–206 adults per ha among fields and was significantly correlated with field age, arthropod abundance and burn treatment. Because of the small number of replicated sampling units, however, I was unable to determine the independent effects of each factor. Prairie skink density increased with successional age but the mechanisms responsible for this pattern remain unclear.
Bird abundance in cornfield edges in Iowa was documented from mid-April through early August 1992. During this period the barren, sparsely vegetated fields are transformed into fields with dense plant cover; the availability of food resources (corn and arthropods) also changes. Temporal patterns of bird abundance in cornfield edges differed greatly among species—some were present in cornfield edges throughout most, if not all, of the study period (e.g., American robin and eastern kingbird), whereas others restricted their use to brief periods. Some were more abundant early in the season (e.g., killdeer and horned lark); others were more abundant later (e.g., black-capped chickadee and indigo bunting). Much of the seasonal change in bird abundance in cornfield edges was attributed to the habitat affinities of the various species and to seasonal shifts in available food resources. Birds that feed on the ground or in low herbaceous vegetation became less abundant later in the season, whereas species that characteristically feed in shrubs or the lower canopy of trees became more numerous. The availability of waste corn on the soil surface, the phenology of the developing crop and the life history stages of major corn insect pests all contribute to the temporal dynamics of bird abundance in cornfields. Also, seasonal patterns of bird abundance in cornfields influence avian risk of exposure to agricultural pesticides. Effective management and conservation of avian communities associated with cornfields require understanding temporal patterns of bird abundance and their implications.
We investigated the association of grassland birds with field- and landscape-level habitat variables in south-central Wisconsin during 1985–1987. Landscape-level variables were measured and digitized at 200, 400 and 800 m from the perimeter of 38 200 m × 100 m strip transects. A mixture of field and landscape variables was associated with the density of savannah sparrow (Passerculus sandwichensis) and grasshopper sparrow (Ammodramus savannarum). Only landscape variables were associated with the density of bobolink (Dolichonyx oryzivorus), eastern meadowlark (Sturnella magna) and all birds that were grassland species of management concern. Field size was not an important predictor of bird density. Cover-type diversity of the surrounding area was commonly selected in the models for three species and all birds that were grassland species of management concern. Higher bird densities in the transects were associated with landscapes where the cover types were less diverse. Landscapes with low cover type diversity were dominated by grassland, pasture and hay. Field habitat, mean patch size of cover types and distance to woody vegetation were the next most common predictors of avian density. The density of some grassland birds increased as nonlinear woody features such as woodlots and shrub carrs decreased in patch size, decreased in total amount in the landscape and increased in distance from a transect. However, density of other species was positively associated with linear woody features such as the total amount and nearness of hedgerows. The composition of the surrounding landscape, at least out to 800 m, is important in grassland bird management.
The spatial genetic structure of Polygonum thunbergii was investigated by DNA fingerprinting, using an oligonucleotide probe (GACA)4 and restriction enzyme Dra I. The genetic similarity of DNA fingerprints among 15 plants collected over a distance of 230 m continuously decreased with increasing distance. This significant negative correlation between similarity of DNA fingerprint and distance means that there is a spatial genetic structure within the population of P. thunbergii because similarity of DNA fingerprint and genetic relatedness are strongly correlated. The genetic structure would be caused by the strictly limited seed dispersal in this species, which has cleistogamous and chasmogamous flowers with no specialized seed dispersal mechanism.
Many cypress-gum wetlands in the southeast United States are isolated from rivers and streams and are seasonally inundated by rainfall. Organic matter processing in these wetlands is caused primarily by biotic components (i.e., microbes and invertebrates), which are influenced by timing and duration of seasonal inundation, and low dissolved oxygen levels. Using litter bags, we examined breakdown of cypress (Taxodium spp.) and gum (Nyssa sylvatica var. biflora) leaves in three wetlands with different hydroperiods: (1) flooded exposed (FE; 5 mo flooded/6 mo litter exposed), (2) multiple flooded exposed (MFE; 6 mo flooded/exposed/flooded/exposed) and (3) permanently flooded (PF; 11 mo flooded). Breakdown was fastest in the MFE wetland suggesting cycles of wetting and drying accelerated decomposition by promoting microbial activity through aeration. Even though ergosterol content, an indicator of fungal biomass on the litter, was similar among wetlands, we hypothesized that within the MFE wetland microbial activity was promoted by exposed conditions, but during subsequent flooding microbial biomass was kept at a low level by invertebrate consumers. Macroinvertebrate density and biomass were comparable between litter types, but were highest in the PF wetland, followed by MFE, then FE wetlands. Chironomids, oligochaetes, Caecidotea and Crangonyx were the dominant taxa indicating litter inputs are vital in maintaining the aquatic foodweb in this system. Cypress litter (k = −1.61 y−1) had faster breakdown rates than gum litter (k = −1.02 y−1), most likely because of plant morphology and greater surface area available to microbial decomposers. Ergosterol (mg g−1 AFDM leaf material) levels were higher on cypress (34.5) than gum (22.5) litter. In both litter types initial C:N and N:P ratios were >20, and C:P ratios were >500, indicating a possible P or N/P co-limitation in cypress-gum wetlands. Elemental gains or losses in litter were influenced predominantly by litter type and to a lesser extent by hydrologic regime. Gum leaves accumulated P, N, Ca and K and lost Mg, whereas cypress leaves had initial declines of these elements, followed by some accumulations in P and K. Temporal patterns of P showed that the drier sites (FE and MFE) immobilized more P than the wetter site (PF), suggesting that exposed conditions promoted microbial activity. In addition, N and P accumulations on gum leaves were highest in the summer at the time when wetlands would normally dry, indicating a seasonal period when moisture and temperature conditions are optimal for microbial growth. Net flux rates to the 1 y-old component of litter indicated that the FE wetland is accumulating more organic matter (172 g m−2 y−1) than the other wetlands (65 and 72 g m−2 y−1), which we attributed to higher cypress litter production. We concluded that hydrologic regime influences breakdown rates and element accumulations, but that net productivity is more important in determining litter accumulation rates.
We examined the effects of garlic mustard (Alliaria petiolata) leachates on germination of arbuscular mycorrhizal (AM) fungal spores, colonization of plant roots by AM fungi and germination and root growth of monocot and dicot plants under laboratory conditions. In the field we examined the effect of garlic mustard on AM inoculum potential (MIP). Water leachates of garlic mustard prevented germination of spores of the AM fungus Gigaspora rosea, inhibited the formation of AM associations with tomato (Lycopesicum esculentum) and significantly reduced germination of tomato seeds. Garlic mustard leachates also reduced root length of tomato and sorghum (Sorghum bicolor) seedlings. Under field conditions we found a significant negative correlation between the density of garlic mustard and the mycorrhizal inoculum potential of the soil in which the plants grew. These results suggest that garlic mustard may reduce the competitive abilities of native plants by interfering with the formation of mycorrhizal associations and root growth.
A number of animals escape predation by sacrificing a body part. Spiders commonly lose legs in encounters with predators or conspecifics. We investigated the frequency of leg loss and its affect on locomotion and prey capture activities of the wolf spider, Pardosa milvina (Araneae; Lycosidae). In addition, we determined if Pardosa were easier to subdue by the larger wolf spider predator, Hogna helluo (Araneae; Lycosidae), once they had experienced leg loss. A field census demonstrated that Pardosa autotomized members of all pairs of legs with equal frequency but overall leg loss was high and increased significantly late in the season. Laboratory experiments revealed that leg loss had no effect on locomotory behavior or prey capture. However, injured spiders tended to take smaller prey. The ability of Hogna, to attack and subdue 7 or 8-legged Pardosa was not different, although 8-legged Pardosa tended to lose multiple legs as they were killed whereas 7-legged Pardosa only lost one. These data suggest that the costs of autotomizing one leg are marginal for Pardosa females and, thus, support the “spare leg hypothesis” that has been proposed for other arachnids.
We investigated sexual dimorphism in feeding behavior and morphological characteristics associated with prey capture in the wolf spider, Rabidosa rabida (Araneae, Lycosidae). Female R. rabida attack and consume more prey than do males. In addition to behavioral differences between males and females, morphological features such as chelicerae size and venom gland size are also larger in females. These morphological differences are significant even after accounting for their positive correlation with body size. These data suggest that differences between the sexes in the relationship between fitness and foraging result in a dichotomy between male and female foraging behavior and differences in morphology associated with prey capture.
Top-down control by predaceous insects has rarely been demonstrated in terrestrial communities, but invasive species may be particularly suited to exert such control. The red imported fire ant, Solenopsis invicta, has strong interactions with spiders, other ants and phytophageous insects, and we predicted that it would exert top-down control, cascading to plants in early successional plant communities. In forest gaps in South Carolina, we measured levels of folivory, growth and fecundity for five common herbaceous plant species in plots where ants were present vs. excluded (ant exclusion study) and in plots with varying abundance of fire ants and sympatric ants (ant substitution study). For all plant species in the ant exclusion study, folivory was greater when fire ant abundance was low (P < 0.01). Light levels, spider abundance and herbivore abundance were also related to folivory for some plant species in both studies (P < 0.01). Mean folivory over the growing season was low for all plant species (mean amount of leaf tissue removed for the most-chewed species was 11%). Variation in plant growth and fecundity were not well explained or consistent for any plant species in either study (partial R2 ≤ 0.10 for eight significant variables related to aboveground vegetative biomass and three significant variables related to reproductive biomass). Our results indicated that fire ants are important in determining the level of folivory on early successional plants; however, their top-down influence was not enough to cascade and impact plant growth or fecundity.
The recent discovery of herbivores that feed on Ni-hyperaccumulating plants and contain elevated Ni concentrations in their bodies suggests that Ni may be transferred to their predators. We tested this hypothesis using the high-Ni herbivore Melanotrichus boydi and four predator species: the spiders Pholcus phalangioides and Misumena vatia, the mantid Stagmomantis californica and the lacewing Chrysoperla carnea. Survival of each predator species was compared when individuals were fed either M. boydi or low-Ni prey. No significant survival difference between diets was observed for P. phalangioides or S. californica, although individuals fed M. boydi contained significantly elevated Ni concentrations (470 μg Ni g−1 for P. phalangioides and 460 μg Ni g−1 for S. californica). No significant difference in survival to adulthood was observed for C. carnea: adult production was 45% for high-Ni and 55% for low-Ni diets. In contrast, survival of M. vatia was significantly decreased when fed high-Ni prey: only 32% of those fed M. boydi survived after 20 d, in contrast to 89% of those fed low-Ni prey. Misumena vatia collected from Ni-hyperaccumulating Streptanthus polygaloides plants in the wild contained some Ni (a maximum of 110 μg Ni g−1), but significantly less than the 420 μg Ni g−1 measured in those fed M. boydi. This indicated that M. vatia, which is native to S. polygaloides sites, consumes some M. boydi under natural conditions. We concluded that: (1) Ni can be transferred from a high-Ni herbivore to its predators; (2) predators varied in their sensitivity to the Ni contained in M. boydi, and; (3) Ni can poison predators which specialize upon high-Ni herbivores and thus may act as an elemental herbivore defense.
The current literature treats the plains killifish as a single species (Fundulus zebrinus). However, a recent range-wide survey of genetic variation detected two distinct groups. The presence of the two groups suggests that the plains killifish may actually represent two species (F. zebrinus and F. kansae), as has been proposed in prior taxonomic treatments. Previous molecular studies within the genus Fundulus have relied upon the mitochondrial cytochrome b gene. I generated a set of cytochrome b sequences in order to compare the phylogenetic support for the putative species F. zebrinus and F. kansae with that found in other accepted sister species of Fundulus. Both neighbor-joining and maximum parsimony analyses recovered two clades of plains killifish that were strongly supported by a variety of measures including branch lengths, decay indices and bootstrap proportions. The strength of support for the putative F. kansae and F. zebrinus clades was comparable to, or better than, similar measures for six other sister species pairs of Fundulus. While the molecular data supported the recognition of two species of plains killifish, the groups recognized were not in agreement with the range descriptions previously proposed for the two species.
We studied the food habits of the coyote (Canis latrans) in a tropical deciduous forest along the Mexican Pacific coast during 1996 and 1997. Small mammals, chiefly the Jaliscan cotton rat (Sigmodon mascotensis), were the main prey items during the dry season. Cultivated fruits, like mango and papaya, were the most important food for coyotes during the wet season. Given the importance in our study area of human related food items like the Jaliscan cotton rat, mango and papaya, we expect the expansion of coyote populations due to deforestation of the tropical deciduous forest.
Small mammal responses to flooding in the lower Missouri River floodplain are poorly understood. Our study examined the survival of marked populations of small mammals in mature and regenerating forest seral stages in response to a brief flood. Peromyscus spp. were the most abundant species captured before (94% of individuals captured) and after (98%) the flood and survival in inundated mature forest sites did not significantly differ from unflooded reference sites. However, the lowest number (n = 14) and percentage (29%) of Peromyscus spp. recaptures occurred in a young regenerating forest site. Elliot's short-tailed shrews (Blarina hylophaga), which are less adapted for arboreal habitats, declined in abundance after the flood.