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Ascertaining the functions bird song requires information about when and where a song or, for males with multisong repertoires, songs are used. Because the need for and type of communication with mates and conspecifics changes with breeding stage and social context, detailed observations may reveal differential use of song or of different song types. Our objective was to examine the use, and determine the possible functions, of the two song types (primary and sustained) in the repertoire of male grasshopper sparrows (Ammodramus savannarum) by observing males throughout the breeding season and in different behavioral contexts in Madison County, Kentucky. For primary songs, rates varied among breeding stages and were highest before pairing, suggesting that primary song plays a role in mate attraction. However, male Grasshopper Sparrows continued to use primary songs after pairing, and likely functions include territory defense. The use of sustained songs also varied among breeding stages, with none uttered before pairing and rates highest during nest building and incubation. Male grasshopper sparrows also uttered more sustained songs when being observed (with one of us in their territories) then when not (neighboring males). These results suggest that sustained songs may serve to alert females to the presence of potential predators while simultaneously distracting such predators. Songs with such functions appear to be uncommon and have been reported in few other species.
We examined response of small mammals to woody invasion of tallgrass prairie in northeastern Kansas by sampling sites that ranged from 0 to 100% in woody cover (i.e., frequently burned prairie to unburned closed-canopy gallery forest; woody coverage mapped from satellite imagery). Abundance and biomass of small mammals initially increased with increasing woody vegetation, but then decreased to their lowest level at 100% woody cover. Richness was greatest (an average of seven species) where woody cover was ≤17% and decreased to one species where woody cover was 100%. Abundance of white-footed mice (Peromyscus leucopus) increased as woody cover increased from 0 to 62% cover, but decreased in forested sites (100% cover). Abundance of western harvest mice (Reithrodontomys megalotis) decreased as woody cover increased; they were not recorded in forested sites. Deer mice (P. maniculatus) were present in sites with no to low levels of woody vegetation, but were absent in sites with moderate to high levels of woody cover. The 11 species captured were recorded in sites that had little woody vegetation (≤17% cover), whereas only seven species were captured at sites where considerable woody vegetation (≥28% cover) occurred. Even white-footed mice and eastern woodrats, which are considered woodland forms, decreased in abundance or were absent from forested sites. Overall, the results demonstrate that even relatively small amounts of woody vegetation in prairie landscapes can alter abundance, biomass and species richness and composition of small mammal communities.
We compared the physiological rates and biochemical composition of dreissenid mussels (Dreissena polymorpha) from a riverine population that were attached to unionid mussels (Amblema plicata) or to rocks. Specimens were collected from Lake Pepin, Mississippi River, Wisconsin and Minnesota. Unionid-attached specimens had greater oxygen uptake and ammonia excretion rates than did rock-attached specimens. However, unionid-attached specimens also had lower carbohydrate and lipid contents. Our results indicate that there are physiological costs of attaching to unionids, at least under some circumstances. Interspecific competition for a limited food resource may negatively impact not only the unionids, but the attached dreissenids as well. This conclusion challenges the assumption that dreissenids benefit from attaching to unionid mussels.
Vegetation composition is often dictated by grazing intensity in semiarid savannas; recovery following drought may depend on pre drought species composition. Nests of the red harvester ant, Pogonomyrmex barbatus, affect the dynamics, composition and recovery of post drought communities due to their larger size, greater seed production and higher perennial grass richness. We hypothesized that vegetation at ant nests would survive drought and recover faster than vegetation in the surrounding grasslands, but that individual and population recovery would depend on plant species composition, which, in turn, would be influenced by grazing intensity. We assessed nest influence on density, cover, number of inflorescences and dynamics of grass and forb species. Disk margins (area encircling the ant nest) were compared with grassland locations in unreplicated heavy, light and ungrazed treatments before, immediately after and one year after a severe drought. Significantly greater aerial and basal cover of grasses was found on disk margins compared to grasslands in each treatment. Grass cover and number of inflorescences increased faster on disk margins compared to grasslands. Fastest grass growth was seen on margins in the ungrazed treatment. There was greater diversity in ungrazed treatments of grazing intolerant mid-grasses compared to the grazed treatments, suggesting that mid-grasses may persist belowground, leading to faster productivity in the ungrazed treatment. Grass densities were generally higher and increased faster in grasslands resulting in smaller grasses compared to the large, more robust grasses on disk margins. Forbs showed significantly lower abundance and cover on margins compared to grasslands. These observations suggest that red harvester ant nests may serve as drought refugia for grass survival and a seed source for recovering grass populations after drought in semiarid savannas.
Knowing the phenologies of species in a region helps guide management and conservation activities in breeding ponds and surrounding terrestrial habitats. We examined the phenology of pond-breeding amphibians in central Missouri oak-hickory forests. Two ponds were monitored for 4 y from 2000–2003 and five other ponds were monitored for 1 y during 2004 using drift fences with pitfall traps. We found 15 species of pond-breeding amphibians, nine of which we captured in sufficient abundance to evaluate breeding phenology. Among the nine species, breeding migrations occur from Feb. to Nov., while subsequent metamorph emigration occurred primarily from May to Oct.. Our ponds were nearly permanent, resulting in salamander-dominated communities in these oak-hickory forests. Pond-use was partitioned by species that differed in their timing of reproduction and post-metamorphic emergence. For example, breeding in the fall gives larval ringed salamanders a potential size advantage over the spring-breeding spotted salamander larvae. However, the fall breeding strategy requires ponds with long hydroperiods that hold water continuously from Aug. through May. Green frogs and central newts also required long hydroperiods for their larval stage (>160 d). American toads, however, are adapted to exploit ponds with shorter, less predictable hydroperiods as they only required ponds to hold water for as little as 60 d. Management for multiple species of pond-breeding amphibians in a landscape benefits from the inclusion of wetlands with a variety of hydroperiods.
The role of animals in seed dispersal is widely acknowledged and turtles have been reported to act as vectors. All reports of turtles dispersing seeds to date have been via endozoochrony. The first evidence of turtles being epizoochronic dispersers of seeds via their carapacial algal mat is reported here. Chelodina longicollis is widespread and abundant throughout most of the eastern fringe of mainland Australia and throughout the largest inland river system, the Murray Darling Basin. They are the most terrestrially mobile of the Australian freshwater turtles and they are the most indiscriminate in habitat choice, inhabiting the entire range of water bodies from rivers to small ephemeral wetlands. Our results showed that turtles with even moderate carapacial algae can act as vectors in the dispersal of seeds associated with wetlands. However, as C. longicollis is unlikely to be unique among the freshwater turtles in this regard, we conclude that epizoochory is likely to occur in other turtle species.
Conservation of isolated wetlands is critical for maintaining regional biodiversity within the southeastern U.S. However, relatively little is known about the ecological communities of these wetland systems, particularly within the karst wetlands of the southeastern Coastal Plain. In southwestern Georgia seasonal isolated wetlands include marshes, cypress savannas and cypress/gum swamps, which have fundamental differences in vegetation and soils, hydrology, water chemistry and invertebrate abundance and diversity. We examined the relationship between wetland type and the distribution of amphibians in 28 relatively undisturbed, seasonally flooded isolated wetlands in southwestern Georgia, USA. We sampled wetlands for amphibians in the winter, spring and summer using aquatic traps, dipnetting, PVC pipe refugia and automated frog call recording devices (frogloggers). Mean amphibian species richness among study wetlands was 12.7 ± 0.5 species (range 7–18). Both species richness and composition varied among wetland types, with different wetland types supporting different amphibian assemblages. Our results highlight the importance of wetland diversity in promoting regional amphibian diversity.
Although behavioral variability has been well documented in the threespine stickleback Gasterosteus aculeatus, very little is known about the extent of variability in the other members of the Gasterosteidae. We investigated the courtship and spawning repertoires of four allopatric populations of brook stickleback Culaea inconstans from Algonquin Park, central Ontario, Tooley Creek, southern Ontario, Two Mile Creek, New York and Sutherland Creek, Nebraska. The results indicated that the male courtship repertoire is quite conservative, with behavioral differences appearing primarily in the frequency and duration of headdown and broadside threat displays performed during courtship and the frequency and duration of male quivering bouts once females enter the nest. In addition to documenting male behavioral variability, data are presented showing that female C. inconstans spend a substantially longer duration of time in the nest than other gasterosteids, and that the length of time a female spends in the nest may be influenced by male behavior performed during egg deposition.
One hundred and twenty five sites from 91 rivers and streams in Indiana were evaluated from 1990–2005 to determine grass pickerel Esox americanus vermiculatus habitat use. Macro-habitat analysis was conducted using the Qualitative Habitat Evaluation Index (QHEI) and had no significant relationship with grass pickerel catch. However, the individual components that made up the QHEI metric of “pool/glide and riffle/run quality” were significant and showed that grass pickerel avoided riffle habitats. At selected (n = 9) stream sites, microhabitat analysis indicated grass pickerel were always associated with either aquatic macrophytes or logs/woody debris. Although the Index of Biotic Integrity has been used to infer overall stream health and community fish quality, this index was minimally related to grass pickerel catch. The results of this study suggested that grass pickerel preferred habitat types in Indiana streams of aquatic macrophytes, logs/woody debris and slow moving water.
We report the expansion of the invasive container mosquito, Aedes albopictus, into pitchers of the carnivorous pitcher plant, Sarracenia purpurea, in southeastern Virginia. The community of aquatic Dipteran larvae commonly associated within S. purpurea pitchers was not present at our research site, creating an unoccupied rearing habitat. We monitored mosquito presence and development within pitchers through two growing seasons. Oviposition traps placed near pitchers confirmed the abundance of gravid A. albopictus in the study area. Females oviposited in both newly opened and in senescing pitchers and larvae matured to adulthood in S. purpurea. Successful development of an exotic mosquito species within unoccupied pitchers of S. purpurea reinforces the hypothesis that invasive species may invade natural communities and occupy vacant niches.
Invasive plants can exert their effects on native plants through both above- and belowground mechanisms. In a fully factorial field study, we examined the effects of activated carbon addition and removal of aboveground biomass (i.e., cutting) on the survival, growth and reproduction of transplanted Impatiens capensis seedlings in habitats dominated by either Lonicera maackii (honeysuckle) or Alliaria petiolata (garlic mustard). Activated carbon can adsorb organic molecules, including potential allelochemicals. Cutting of A. petiolata increased survival and fruit production of I. capensis, while cutting of L. maackii increased survival and tended to increase fruit production. Carbon application tended to increase survival of I. capensis in A. petiolata-dominated plots, but had no effect in L. maackii-dominated plots. The effects of carbon application on growth and fruit production of I. capensis depended upon the cutting treatment in A. petiolata – dominated plots. In plots where A. petiolata was not cut, carbon application increased height and fruit production. In plots where A. petiolata was cut, carbon application decreased height and tended to decrease fruit production. Impatiens capensis tended to survive longer when in competition with A. petiolata than with L. maackii. While carbon application may benefit native plant growth in the presence of A. petiolata, the addition of activated carbon after removal of aboveground biomass, a source of both allelochemicals and light competition, may have little benefit as an understory plant restoration tool.
Understanding the importance of variable local population abundance and the limited potential for dispersal and genetic exchange is crucial for the conservation of many species with limited geographic distribution and specialized habitat requirements. Because of rareity, it is often difficult to study the relative importance of variation in recruitment and survival and their net effect on population growth. We designed a survey of natural populations of endangered Iowa Pleistocene snails (Discus macclintocki) using the robust mark-recapture design to estimate population size and vital rates. A dense population remained stationary throughout the 6-y study whereas vital rates fluctuated substantially in two much smaller populations. In the smaller populations rates of growth varied from sharply increasing to sharply decreasing among years, and changes in estimated recruitment were the primary vital rate influencing these fluctuations. Snails were highly sedentary and sampling at random locations showed that the populations were highly subdivided within a site. Fluctuations in demographic rates and patchy distribution may provide the basis for substantially different rates of genetic change within and among sites. Although in the short-term, fluctuations in recruitment of these snails may influence local dynamics most substantially, long-term threats of habitat loss or climatic change will likely affect survival of adults and persistence of the populations.
Interest in the relationships between soil microbial communities and ecosystem functions is growing with increasing recognition of the key roles microorganisms play in a variety of ecosystems. With a wealth of microbial methods now available, selecting the most appropriate method can be daunting, especially to those new to the field of microbial ecology. In this review, we highlight those methods currently used and most applicable to ecological studies, including assays to study various aspects of the carbon and nitrogen cycles (e.g., pool dilution, acetylene reduction, enzyme analyses, among others), methods to assess microbial community composition (e.g., phospholipid fatty acid analysis (PLFA), denaturing gradient gel electrophoresis (DGGE), terminal restriction fragment length polymorphism analysis (TRFLP), quantitative polymerase chain reaction (qPCR)) and methods to directly link community structure to function (e.g., stable isotope probing (SIP)). In our discussion of these methods, we describe the information each method provides, as well as some of their strengths and weaknesses. Using a case study, we illustrate how these methods can be applied to investigate relationships between microbial communities and the processes they perform in wetland ecosystems. We end our discussion with a series of questions to consider prior to designing experiments, in the hope that these questions will help guide ecologists in selecting the most appropriate method(s) for their research.
As significant nocturnal insectivores, bats are an integral part of many ecosystems. Determining bat species composition in an area is a critical first step in managing for this important resource. Little information exists concerning the bat species composition of Maryland's Coastal Plain, which is located on the northern periphery of the geographic ranges of five bat species occurring in the southeastern United States. We conducted mist net surveys for bats at Assateague Island National Seashore, a barrier island on Maryland's coast, in summer 2005 and summer and autumn 2006. In 2005 we captured 133 bats representing three species, including two big brown bats (Eptesicus fuscus), 129 eastern red bats (Lasiurus borealis) and two purported Seminole bats (L. seminolus). In 2006 we captured 60 eastern red bats in summer and autumn combined. We used Anabat II bat detectors to conduct long-term acoustic monitoring on the island year round and documented three additional bat species, including silver-haired bats (Lasionycteris noctivagans), hoary bats (L. cinereus) and eastern pipistrelles (Pipistrellus subflavus). We documented silver-haired bats during spring and autumn, probably as they were migrating through the area. We used Anabat II bat detectors to conduct short-term monitoring of bat activity at five habitat types during summer 2005 and 2006 and found that total bat activity and eastern red bat activity were similar among forested areas, freshwater pools and bayside marshes. In shrublands, total bat activity and eastern red bat activity was higher than at beach areas, lower than in forested areas and similar at freshwater pools and bayside marshes. The loblolly pine (Pinus taeda) – dominated forests at ASIS provide roosting and foraging habitat mostly for eastern red bats, but also for other migratory bat species.
Multiple captures (34 double, 6 triple) in standard Sherman live traps accounted for 6.3% of 1355 captures of Peromyscus leucopus (white-footed mice) in forested habitat in southern Illinois, from Oct. 2004 through Oct. 2005. There was a significant positive relationship between both the number and the proportion of multiple captures and estimated monthly population size. Multiple captures were all intraspecific and occurred significantly more often from Nov. through Mar. when animals were not reproductively active, but this was confounded by seasonal changes in abundance. Age/gender distribution of animals in double captures did not differ from that expected from random pairing. We suggest that sociality and synchronous entry of two white-footed mice into traps were the primary determinants of double captures; sensitivity of traps may have been the primary factor in triple captures.
Thirty-nine female white-tailed deer (Odocoileus virginianus) were migrators from three study areas in central and northern Illinois, 1980–1993. Migrants averaged 21.5%, 9.4% and 14.6% of marked females known alive each year on the east-central, west-central and northern study areas, respectively. Females migrated to a summer range between late Feb. and early Jul. and to the winter range between late Sep. and early Jan. Spring migration distances averaged between 7.3 and 15.9 km from the winter range. Female fawns of migrating mothers were more likely to disperse or migrate than were fawns of sedentary mothers. Migrating females survived as long as sedentary females and significantly better than females that dispersed, but fawn recruitment was lower for migrating females compared with sedentary females. Winter severity did not affect return behavior from a summer range. Hunter harassment on the summer range initiated migration back to the winter range in 59% of 22 monitored migrations for 14 radio marked females. Prevailing winds from the winter or summer range appeared to help locate these ranges for 10 of 19 spring migrations for 16 females and three of seven fall migrations for four females. Migration behavior allows females to more fully utilize the fragmented landscapes of the agricultural Midwest. Migration behavior among females appears to result from resource competition among females including parturition sites where female densities are high and available habitats are scarce.
Successful coexistence of sympatric canid species often relies on the subdominant species' ability to reduce competition through the differential selection of niche space. Information regarding the process of niche selection and its effect on the structure of canid communities in the Great Basin Desert is unavailable. From Dec. 1999 to Aug. 2001, we quantified the spatial, dietary and temporal resource overlap of kit foxes (Vulpes macrotis) and coyotes (Canis latrans) on the U.S. Army Dugway Proving Ground, Utah. Kit foxes and coyotes demonstrated substantial levels of spatial, temporal and dietary overlap. However, where the two species had overlapping home ranges, space use within the home range differed between the two species, with kit foxes using vegetative and landscape ruggedness characteristics not regularly used by coyotes. Although there was little evidence of seasonal change in either canid's use of habitat, in some areas kit foxes made nightly movements to more productive habitats with moderate ruggedness. Regardless of spatial partitioning, incidents of interference competition were high; 56% of known kit fox deaths were attributed to coyotes. In our study, high levels of temporal and dietary overlap, kit fox movement from extreme to moderate topography during foraging and selection for abundant cover demonstrated competitive pressures exerted on the kit fox population by the sympatric coyote population.
We conducted a study of nest site selection by the eastern woodrat (Neotoma floridana) in the South Carolina coastal plain. We identified 40 active nests in three macrohabitats: a bottomland hardwood–upland pine ecotone, a southern mixed hardwood forest and a disturbed maritime forest. We further conducted an analysis of 21 microhabitat variables at 27 active nests, identified through live-trapping and release. Previous studies suggest that stick houses are preferred nest sites throughout N. floridana's range, and that dwarf palmetto (Sabal minor) may be an important indicator of woodrat habitat in North Carolina. Eastern woodrats inhabited windthrown rootmasses in 77.5% of nests at our study sites. S. minor and stick houses were completely absent from two of the three habitats. Multivariate analysis revealed that nest sites differed from paired non-nest sites by containing higher coarse woody debris and rootmass volume, and lower basal area. We recommend that N. floridana population surveys routinely include microsites previously assumed to be non-preferred alternatives. Windthrown rootmasses are forest floor resources important to N. floridana, and potentially other animals, providing complex structure distinct from coarse woody debris.
Much of the tallgrass prairie remaining in North America occurs in hilly regions, such as the Flint Hills of Kansas and Oklahoma. Despite the conservation importance of these areas for grassland birds, little is known about how topographic variation in habitat affects the nesting ecology of these species. We examined topographic patterns of nest distribution, daily nest survival and nest-site selection for three species: Dickcissel (Spiza americana), Grasshopper Sparrow (Ammodramus savannarum) and Eastern Meadowlark (Sturnella magna). Dickcissels shifted from nesting more in lowlands to uplands as the season progressed. Grasshopper Sparrows and Eastern Meadowlarks generally nested in midland habitats, but seasonal differences were still evident in the relative proportions of nests found in lowlands vs. uplands. Topography did not affect nest survival of Dickcissels or Grasshopper Sparrows and had only a marginal effect on nest survival for Eastern Meadowlarks. Nest survival for Dickcissels and Grasshopper Sparrows was highly dependent on nest-site vegetation, however. Dickcissels and Eastern Meadowlarks both experienced greater daily nest survival with increasing vertical vegetation structure at nest sites, whereas daily nest survival for Grasshopper Sparrows increased with increasing cover of litter and grass. Although topography may not affect nest survival directly, it may have indirect effects mediated through nest-site vegetation because of selective nest placement. For example, Dickcissels and Eastern Meadowlarks selected sites with greater vertical vegetation structure than generally available, even in upland sites where vegetation structure was reduced. Conservation planning for grassland birds may thus need to consider how topographic variation affects habitat quality within hilly regions where much of the remaining tallgrass prairie occurs.
Identifying optimal fire regimes for a given species requires monitoring its responses to different fire regimes. This study examined the effects of fire during the lightning season and clipping in different seasons on the induction of flowering in a fire-adapted species, Pityopsis graminifolia, in two different fire-dependent ecosystems (oak forest edges in north Mississippi and longleaf pine savannas in south Mississippi). The two ecosystems differed in the frequency of lightning (higher in south Mississippi) and the timing of peak drought conditions during the lightning season (earlier in south Mississippi). Flowering was induced by prescribed fires during the lightning season in both regions. Flowering was greater in unburned controls in north Mississippi than in south Mississippi. These differences persisted in a common grass-dominated environment in the greenhouse, suggesting a genetically-based bet-hedging strategy with respect to fire-induced flowering in north Mississippi. Flowering of both varieties responded better to clipping during peak drought periods during the lightning season than to clipping treatments at other times of the year, but the causes of such seasonal differences (be they genetic or environmental) remain unresolved at this time and require further investigation.
Black bear (Ursus americanus) reproduction is critically linked to female nutrition. In highly productive females, litters include up to six cubs. Little is known about the yearly reproductive success of individual females that produce abnormally large litters. Further, survival of offspring born among so many siblings is poorly known. We report on a female bear in highly agricultural habitat that produced two successive litters of quintuplets in alternate years during a period of maternal net growth from Feb. 2005 through Mar. 2007.
During winter in northern North America, white-tailed deer (Odocoileus virginianus) have been reported to consume non-woody browse items such as dried leaves (of woody plants), lichens, and evergreen herbaceous plants. We report use of five species of senescent (dead) herbaceous perennial plants in winter by a high density white-tailed deer herd in south-central Minnesota during a winter of average snow depths and below average temperatures. While low in digestible energy, senescent herbaceous material may present deer with a forage item higher in digestible protein than larger diameter woody twigs during periods of nutritional stress.
Published reports of survival and cause-specific mortality for pronghorn (Antilocapra americana) indicate that mortality differs regionally and seasonally with sex, age and density of pronghorn. Cold winters with deep crusted snow is a primary source of mortality on adult pronghorn, however, predation also can be an important source of adult mortality. We report a visual observation of bobcat (Felis rufus) predation on an adult female pronghorn in northwestern South Dakota.