Comparative thermal ecology of two lizards

Summary In a habitat judged to be energetically costly for thermoregulation, mean body temperatures (MBT's) ofAnolis sagrei are significantly higher than those ofA. distichus. As indexed by the slope of the regression of body temperatures (T_b) on substrate temperature (T_s),A. sagrei is more dependent upon environmental temperatures thanA. distichus.In a habitat judged to be less costly for thermoregulation and where interspecific competition for perch sites may be less, MBT's ofA. sagrei are significantly higher, proportionally more lizards occupy sunny perches, and the slope of the regression of T_b on T_s is significantly less, than for conspecifics in the costly habitat.As indexed by length-specific fat body weights, well-nourished lizards in the costly habitat have T_b's which are independent of environmental temperature; T_b's of poorly-nourished lizards are highly dependent upon environmental temperature. This relationship does not hold for lizards in the low-cost habitat.These results corroborate the hypothesis that energetic costs are important in controlling the extent to which lizards thermoregulate. In high-cost habitats lizards thermoregulate less precisely than in low-cost habitats. Lizards that exploit the habitat as if it were highly productive thermoregulate more precisely than lizards that exploit the environment as if it were of low productivity.     

Perpetuation of the Lyme disease spirochete Borrelia lusitaniae by lizards

To determine whether the Lyme disease spirochete Borrelia lusitaniae is associated with lizards, we compared the prevalence and genospecies of spirochetes present in rodent- and lizard-associated ticks at a site where this spirochete frequently infects questing ticks. Whereas questing nymphal Ixodes ricinus ticks were infected mainly by Borrelia afzelii, one-half of the infected adult ticks harbored B. lusitaniae at our study site. Lyme disease spirochetes were more prevalent in sand lizards (Lacerta agilis) and common wall lizards (Podarcis muralis) than in small rodents. Although subadult ticks feeding on rodents acquired mainly B. afzelii, subadult ticks feeding on lizards became infected by B. lusitaniae. Genetic analysis confirmed that the spirochetes isolated from ticks feeding on lizards are members of the B. lusitaniae genospecies and resemble type strain PotiB2. At our central European study site, lizards, which were previously considered zooprophylactic for the agent of Lyme disease, appear to perpetuate B. lusitaniae.     

Impact of the experimental removal of lizards on Lyme disease risk

The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (Ixodes pacificus--the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi. Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. Following experimental removal of lizards, we documented incomplete host switching by larval ticks (5.19%) from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae failed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in nymphal tick infection prevalence. The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk through the maintenance of higher vector density and therefore, higher density of infected vectors.     

A Brugia species infecting rabbits in the northeastern United States

Brugia sp. microfilariae were observed in more than 60% of wild rabbits collected on Nantucket Island, Massachusetts. The microfilariae measured 294-344 microns in length and had the characteristic subterminal and terminal nuclei observed in other Brugia microfilariae. The microfilaria is similar to those described for Brugia leporis in rabbits in Louisiana. This may be the Brugia species responsible for 21 documented cases of human infection in the northeastern United States.     

New records for two mosquito predators [Turbellaria: Mesostoma] in the northeastern United States

The accumulated data indicate that mesostomid flatworms are efficient predators of mosquito larvae. This paper presents the 1st published records for 3Mesostoma Ehrenberg, including 2 predators of mosquitoes.Mesostoma californicum Hyman,Mesostoma vernale Hyman, andMesostoma sp. cf.lingua Abildgaard were discovered in a temporary pool in Massachusetts.M. californicum andM. sp. cf.lingua were found to be efficient predators on mosquitoe larvae.

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Résumé Les observations accumulées indiquent que les larves des Plathelminthes mesostomides sont des prédateurs efficaces des larves de moustiques. Cette note présente les premières mentions de 3Mesostoma Ehrenberg incluant 2 prédateurs de moustiques.Mesostoma californicum Hyman,Mesostoma vernale Hyman, etMesostoma sp. cf.lingua Abildgaard furent découverts dans une mare temporaire du Massachusetts.M. californicum etM. sp. cf.lingua ont été reconnus comme des prédateurs efficaces des larves de moustiques.

     

Avian community structure along elevational gradients in the northeastern United States

Summary Breeding birds were censused along four elevational gradients in the Adirondack Mountains, New York, and the Green Mountains, Vermont. The bird communities of the four gradients were basically similar in species composition, richness and amplitude patterns. Three measures of species diversity decreased with increasing elevation. Low-elevation communities contained higher proportions of rare species and the relative abundances conformed to the broken-stick distribution. At higher elevations the communities showed greater dominance and the dominance-diversity curves approached geometric series. The species characteristic of high-elevation communities had the broadest altitudinal distributions.The upper and lower distributional limits of most species were independent of one another except at ecotones where marked changes in vegetation structure occurred. On each mountain, slightly more than half of the species limits coincided with ecotones. This is a significantly greater proportion than has been found in similar studies of tropical forest bird communities. In further contrast to tropical communities, we found no convincing cases of altitudinal competitive exclusion between species. Interspecific competition in the past seems to have been translated primarily into differences in habitat selection by temperate forest birds.Many of the differences between temperate forest breeding bird communities and tropical ones can be understood in terms of the migratory nature of most of the temperate species and the lower species richness in temperature forests.     

The Holdridge life zones of the conterminous United States in relation to ecosystem mapping

Aim Our main goals were to develop a map of the life zones for the conterminous United States, based on the Holdridge Life Zone system, as a tool for ecosystem mapping, and to compare the map of Holdridge life zones with other global vegetation classification and mapping efforts. Location The area of interest is the forty-eight contiguous states of the United States. Methods We wrote a PERL program for determining life zones from climatic data and linked it to the image processing workbench (IPW). The inputs were annual precipitation (Pann), biotemperature (T_bio), sea-level biotemperature (T₀bio), and the frost line. The spatial resolution chosen for this study (2.5 arc-minute for classification, 4-km for mapping) was driven by the availability of current state-of-the-art, accurate and reliable precipitation data. We used the Precipitation-elevation Regressions on Independent Slopes Model, or PRISM, output for the contiguous United States downloaded from the Internet. The accepted standard data for air temperature surfaces were obtained from the Vegetation/Ecosystem Modelling and Analysis Project (VEMAP). This data set along with station data obtained from the National Climatic Data Center for the US, were used to develop all temperature surfaces at the same resolution as the Pann. Results The US contains thirty-eight life zones (34% of the world's life zones and 85% of the temperate ones) including one boreal, twelve cool temperate, twenty warm temperate, four subtropical, and one tropical. Seventy-four percent of the US falls in the ‘basal belt’, 18% is montane, 8% is subalpine, 1% is alpine, and < 0.1% is nival. The US ranges from superarid to superhumid, and the humid province is the largest (45% of the US). The most extensive life zone is the warm temperate moist forest, which covers 23% of the country. We compared the Holdridge life zone map with output from the BIOME model, Bailey's ecoregions, Küchler potential vegetation, and land cover, all aggregated to four cover classes. Despite differences in the goals and methods for all these classification systems, there was a very good to excellent agreement among them for forests but poor for grasslands, shrublands, and nonvegetated lands. Main conclusions We consider the life zone approach to have many strengths for ecosystem mapping because it is based on climatic driving factors of ecosystem processes and recognizes ecophysiological responses of plants; it is hierarchical and allows for the use of other mapping criteria at the association and successional levels of analysis; it can be expanded or contracted without losing functional continuity among levels of ecological complexity; it is a relatively simple system based on few empirical data; and it uses objective mapping criteria.     

Sandstone rockhouses of the eastern United States,with particular reference to the ecology and evolution of the endemic plant taxa

Rockhouses are semicircular recesses extending far back under cliff overhangs that are large enough to provide shelter for humans. The largest sandstone rockhouses in the eastern United States are at the heads of gorges, and they are in stream valleys cut during the Pleistocene; most are formed in Mississippian and Pennsylvanian-age rocks. Compared to the surrounding environment, the interior of rockhouses is shaded, is warmer during winter and cooler during summer, and has lower evaporation rates and higher humidities. Water enters rockhouses primarily by groundwater seepage and by dripping from the ceiling. Soil consists mostly of sand with low pH, but high levels of some nutrients are associated with saltpeter earth and with ecofactual and artifactual remains left by human occupants during prehistoric time. Most plant taxa in sandstone rockhouses in eastern United States are native C₃ phanerophytes or hemicryptophytes, and similarities in species composition among rockhouses are low. Eleven plant taxa belonging to eight families of flowering plants and ferns are endemic or nearly endemic to sandstone rockhouses in eastern United States. Three endemics are restricted to the gorges of a single river, and only one taxon ranges far north of the Wisconsinan Glacial Boundary. The endemic ferns are Tertiary relicts derived from tropical taxa. The majority of endemic flowering plants are derived from temperate taxa that grow in habitats in the vicinity of rockhouses; their relative age ranges from Late Tertiary to the Recent. All the endemic taxa are perennial; two ferns occur as independent gametophytes. The endemic taxa of rockhouses are threatened primarily by disturbances associated with recreation.     

Assessment of soil calcium status in red spruce forests in the northeastern United States

Long-term changes in concentrations of available Ca in soils of redspruce forests have been documented, but remaining questions aboutthe magnitude and regional extent of these changes have precluded anassessment of the current and future status of soil Ca. To addressthis problem, soil samples were collected in 1992—93from 12 sites in New York, Vermont, New Hampshire, and Maine toprovide additional data necessary to synthesize all availableresearch results on soil Ca in red spruce forests. Sites werechosen to encompass the range of environmental conditionsexperienced by red spruce. Concentrations of exchangeableCa ranged from 2.13 to 21.6 cmol_ckg^–1 in the Oa horizon, and from 0.11 to 0.68cmol_c kg^–1 in the upper 10 cm of theB horizon. These measurements expanded the range of exchangeable Ca reported in the literature for both horizons in northeastern redspruce forests. Exchangeable Ca was the largest Ca fraction in theforest floor at most sites (92% ofacid-extractableCa), but mineral Ca was the largest fraction at the three sites that also had the highest mineral-matter concentrations. Theprimary factor causing variability in Ca concentrations among siteswas the mineralogy of parent material, but exchangeable concentrationsin the B horizon of all sites were probably reduced by acidicdeposition. Because the majority of Ca in the forest floor isin a readily leachable form, and Ca inputs to the forest floor from the mineral soil and atmospheric deposition have beendecreasing in recent decades, the previously documented decreasesin Ca concentrations in the forest floor over previous decades mayextend into the future.     

The ecology of lizards on Praslin Island, Seychelles

Ecological studies of five species of lizards were carried out on the island of Praslin, central Seychelles between July and September 1976. Quadrat sampling within four vegetation types revealed distinct habitat preferences between species. Phelsuma sundbergi occurred at highest densities in coastal vegetation, particularly coconuts Cocos nucifera , whilst Phelsuma astriata occurred at highest densities in intermediate forest, particularly in endemic palms such as Lodoicea maldivica. Within each vegetation type, both species preferred particular tree species. In coastal coconuts and Lodoicea in intermediate forest, the two species tended to occur in different sized trees. Calculations of niche breadth indicated greatest values for P. sundbergi in coastal vegetation and for P. astriata in intermediate forest. Both Phelsuma species showed a diurnal pattern of activity with some indication of temporal displacement between species in lowland and intermediate forest. Ailuronyx sechellensis was nocturnal with a relict distribution on Praslin, occurring in the quadrats on only three endemic palm species in intermediate forest. Mabuya sechellensis was by far the commonest and most widespread of the two skink species, with highest density in intermediate forest where it was probably favoured by the high proportion of palm leaf litter. Scelotes gardineri was only recorded in lowland and intermediate forest, where it occurred at low densities. Both species were diurnal, although the latter was never recorded after midday. Intermediate forest had the highest lizard biomass and species diversity whilst eroded land had the lowest. The possible origins and relationships of the two closely related Phelsuma species are discussed, together with the roles that habitat modification, predation, and interspecific competition may play.     

Review The ecology of ticks transmitting Lyme borreliosis

The main vectors of Borrelia burgdorferi sensu lato, the cause of Lyme borreliosis, are ixodid ticks of the Ixodes persulcatus species complex. These ticks, which occur throughout the northern temperate zone, have very similar life cycles and ecological requirements. All are three-host ticks, with the immature stages mainly parasitizing small to medium-sized mammals and birds and the adult females parasitizing large mammals such as deer, cattle, sheep and hares. The host-seeking stages show a distinct seasonality, which is regulated by diapause mechanisms and there appear to be major differences in this respect between the Old World and New World species. Most cases of human borreliosis are transmitted in the summer by the nymphal stages, with the exception of the Eurasian species, I. persulcatus, in which the adult females are mainly responsible. The ticks acquire the spirochaetes from a wide variety of mammals and birds but large mammals do not seem to be infective, so that t icks that feed almost exclusively on large mammals, for example in some agricultural habitats, are rarely infected. The greatest tick infection prevalences occur in deciduous woodland harbouring a diverse mix of host species and the diversity of the different genospecies of B. burgdorferi s.l. is also greatest in such habitats. There is evidence that these genospecies have different host predilections but, apart from the fact that I. persulcatus does not seem to be infected by B. burgdorferi sensu stricto, they do not seem to be adapted to different tick strains or species. © Rapid Science Ltd. 1998     

Analysis of Weather Effects on Variability in Lyme Disease Incidence in the Northeastern United States

In this study, variability in reported Lyme disease incidence between 1993 and 2001 was analyzed in seven states in the northeastern part of the USA. Positive significant correlations at p < 0.05 were found in all states between early summer disease incidence and the June moisture index in the region two years prior. These correlations may reflect an enhanced nymphal Ixodes scapularis survival under wetter conditions. In some states, significant correlations were observed related to warmer winter weather a year and a half prior to disease incidence, which may have been due to higher survival and activity levels of the white-footed mouse, an important host for I. scapularis ticks. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular identification and analysis of Borrelia burgdorferi sensu lato in lizards in the southeastern United States

Lyme borreliosis (LB) group spirochetes, collectively known as Borrelia burgdorferi sensu lato, are distributed worldwide. Wild rodents are acknowledged as the most important reservoir hosts. Ixodes scapularis is the primary vector of B. burgdorferi sensu lato in the eastern United States, and in the southeastern United States, the larvae and nymphs mostly parasitize certain species of lizards. The primary aim of the present study was to determine whether wild lizards in the southeastern United States are naturally infected with Lyme borreliae. Blood samples obtained from lizards in Florida and South Carolina were tested for the presence of LB spirochetes primarily by using B. burgdorferi sensu lato-specific PCR assays that amplify portions of the flagellin (flaB), outer surface protein A (ospA), and 66-kDa protein (p66) genes. Attempts to isolate spirochetes from a small number of PCR-positive lizards failed. However, PCR amplification and sequence analysis of partial flaB, ospA, and p66 gene fragments confirmed numerous strains of B. burgdorferi sensu lato, including Borrelia andersonii, Borrelia bissettii, and B. burgdorferi sensu stricto, in blood from lizards from both states. B. burgdorferi sensu lato DNA was identified in 86 of 160 (54%) lizards representing nine species and six genera. The high infection prevalence and broad distribution of infection among different lizard species at different sites and at different times of the year suggest that LB spirochetes are established in lizards in the southeastern United States.     

Mapping amphibian contact zones and phylogeographical break hotspots across the United States

Identifying congruence in the geographical position of lineage breaks and species range limits across multiple taxa is a focus of the field of comparative phylogeography. These regions are biogeographical hotspots for investigations into the processes driving divergence at multiple phylogenetic levels. We used spatially explicit statistical methods to identify these regions for amphibians across the United States. Significant clustering occurred in the Appalachian Mountains and in the general area of Alabama - a region underappreciated as an important amphibian hotspot. When the orders Caudata and Anura were examined separately, spatial clustering was still found in Alabama for both. However, in Caudata the Appalachians and California were also important, and for Anura, the Great Lakes region was highlighted. When species richness was statistically controlled, cluster hotspots shifted out of Alabama and the Appalachians and moved to broader swaths of the Great Lakes region, southwestern United States and California. The exact location of particular suture zones is probably a result of complex interactions between historical and ecological factors including physiography, climate and distance from glacial refugia. These contact zone and phylogeographical break hotspots are ideal arenas in which to test alternative speciation hypotheses and examine the extent of reproductive isolation using novel, integrative approaches combining modern methods in statistical phylogeography, ecological niche modelling and genomics.     

A review of vertebrate community composition in seasonal forest pools of the northeastern United States

Seasonally-flooded wetlands occur throughout the world and provide important foraging, resting, and breeding habitat for a broad array of organisms. This review summarizes our current understanding of vertebrate community composition at seasonal forest pools in the northeastern United States. These wetlands typically have hydroperiods that range from temporarily flooded to intermittently exposed, which reduces densities of many potential predators (e.g., fish). Current research has shown that pool hydroperiod, canopy closure, vegetation structure within pools, presence of potential predators, and landscape structure surrounding pools are the key factors determining vertebrate diversity at seasonal forest pools. Of 25 species of amphibians in the region, frogs (10 of 12 species) are more likely to breed in seasonal forest pools than salamanders (6 of 13 species). Seven of 10 amphibian species that breed in seasonal forest pools are state-listed as threatened or endangered. Among 27 species of reptiles, 3 of 15 species of snakes, and 6 of 12 species of turtles utilize seasonal pools during at least one stage of their annual cycle. Seasonal forest pools are important foraging and basking habitat for three species of turtles listed as threatened or endangered. Compared to other vertebrate taxa, most species of mammals are habitat generalists, with 50 of 63 mammal species potentially foraging at seasonal pools during part of their annual cycle. Chiroptera (bats; all 9 species) are believed to actively forage at seasonal pools and some Insectivora, particularly Sorex palustris Richardson and S. fumeus (Miller) and Condylura cristata (L.), are detected regularly at seasonal pools. Breeding birds are less likely to utilize seasonal pools than other vertebrate taxa, although 92 of 233 species might forage or breed near seasonal pools. Several species of Anatidae, Rallidae, and some Passeriformes use seasonally flooded pools. All vertebrates that use seasonal forest pools use other habitats during some stage in their life cycle; thus gaining a clear understanding of their habitat requirements is critical to their long-term persistence.     

Effects of Landscape Fragmentation and Climate on Lyme Disease Incidence in the Northeastern United States

Lyme disease is the most frequently reported vector borne illness in the United States, and incidences are increasing steadily year after year. This study explores the influence of landscape (e.g., land use pattern and landscape fragmentation) and climatic factors (e.g., temperature and precipitation) at a regional scale on Lyme disease incidence. The study area includes thirteen states in the Northeastern United States. Lyme disease incidence at county level for the period of 2002–2006 was linked with several key landscape and climatic variables in a negative binomial regression model. Results show that Lyme disease incidence has a relatively clear connection with regional landscape fragmentation and temperature. For example, more fragmentation between forests and residential areas results in higher local Lyme disease incidence. This study also indicates that, for the same landscape, some landscape variables derived at a particular scale show a clearer connection to Lyme disease than do others. In general, the study sheds more light on connections between Lyme disease incidence and climate and landscape patterns at the regional scale. Integrating findings of this regional study with studies at a local scale will further refine understanding of the pattern of Lyme disease as well as increase our ability to predict, prevent, and respond to disease.     

Relating fish biomass to habitat and chemistry in headwater streams of the northeastern United States

Stream pH and stream habitat have both been identified as important environmental features influencing total fish biomass in streams, but few studies have evaluated the relative influence of habitat and pH together. We measured total fish biomass, stream habitat, and stream pH in sixteen sites from three tributary systems in the northeastern United States. The habitat metrics included total pool area, a cover score, large wood frequency, and stream temperature. We created and compared nine linear models relating total fish biomass in summer to stream pH and stream habitat using Akaike’s Information Criterion (AIC) analysis. The best (most parsimonious) models included pool area and stream pH. These results and a separate comparison of three regressions (low-flow pH, pool area, and these two metrics together versus total fish biomass) suggest that both habitat and stream buffering capacity affect the total biomass of fish in northeastern US headwater streams. When stream pH is adequate (low-flow pH greater than at least 5.7), physical habitat is likely to be more important, but under lower pH conditions, habitat is likely to be less effective in accounting for the total biomass of fish in these streams. This work demonstrates the continued effects of stream acidification in the northeastern US and more generally, it illustrates the importance of considering both physical and chemical conditions of a stream when evaluating the factors influencing fish communities.