Epizootiology of Sin Nombre and El Moro Canyon hantaviruses, southeastern Colorado, 1995-2000

Sin Nombre virus (SNV) is an etiologic agent of hantavirus pulmonary syndrome. To better understand the natural history of this virus we studied population dynamics and temporal pattern of infection of its rodent hosts in southeastern Colorado (USA) from 1995 to 2000. We present evidence for the presence of two hantaviruses, SNV in deer mice (Peromyscus maniculatus) and El Moro Canyon virus in western harvest mice (Reithrodontomys megalotis), at our study sites. Sin Nombre virus appeared only sporadically in deer mouse populations; overall prevalence of antibody to SNV was 2.6%. El Moro Canyon virus was enzootic: seroconversions occurred throughout the year; antibody prevalence (11.9% overall) showed a delayed-density-dependent pattern, peaking as relative abundance of mice was declining. Males of both host species were more frequently infected than were females. An apparently lower mean survivorship (persistence at the trapping site) for SNV antibody-positive deer mice could indicate a detrimental effect of SNV on its host, but might also be explained by the fact that antibody-positive mice were older when first captured.     

Composition and dynamics of a highly diverse diatom assemblage in a limestone stream

The algal assemblages of a small limestone stream were studied for a year at monthly intervals. Algal standing crop was permanently high (mean concentration of 158 mg Chl-a · m^–2), but it reached the maximum values in spring and summer. Diatoms were dominant in the algal assemblages throughout this time, and more than one hundred species were recorded during the survey. Most of them are characteristic of hard waters, but others, mainly occurring in summer, have been observed elsewhere in moderately halophile waters.A striking succession was observed in the diatom assemblage in the stream in each season. This succession, with a maximum in summer, was mainly related with the lessening in flow and the increase in water mineralization. Moreover, the diversity of the samples increased sharply from April 1982 to July 1983. In fact, a progressive increase in salinity tolerant species could be observed from winter and spring to summer. Nitzschia sociabilis, Navicula gregaria, Navicula lanceolata and Gomphonema olivaceum were the most abundant species in winter, whereas Achnanthes minutissima reached its maximum in spring and Navicula schroeterii, Nitzschia thermaloides and Cyclotella meneghiniana were some of the most abundant in summer.     

Mosquitoes of field and forest: the scale of habitat segregation in a diverse mosquito assemblage

Knowledge of the distribution of arthropod vectors across a landscape is important in determining the risk for vector‐borne disease. This has been well explored for ticks, but not for mosquitoes, despite their importance in the transmission of a variety of pathogens. This study examined the importance of habitat, habitat edges, and the scale at which mosquito abundance and diversity vary in a rural landscape by trapping along transects from grassland areas into forest patches. Significant patterns of vector diversity and distinct mosquito assemblages across habitats were found. The scale of individual species' responses to habitat edges was often dramatic, with several species rarely straying even 10 m from the edge. The present results suggest blood‐seeking mosquito species are faithful to certain habitats, which has consequences for patterns of vector diversity and risk for pathogen transmission. This implies that analysts of risk for pathogen transmission and foci of control, and developers of land management strategies should assess habitat at a finer scale than previously considered.     

Population dynamics of two suspension-feeding bivalves on a sheltered beach in southeastern Brazil

The population biology and secondary production of the bivalves Anomalocardia brasiliana (Gmelin, 1791) and Diplodonta punctata (Say, 1822) were studied on a sheltered beach on the southeast coast of Brazil (Flexeiras Beach) between December 2006 and February 2009. Six transects were established perpendicular to the shoreline. Along each transect, sampling units (SUs) were extracted every 3?m, with a 0.04?m² metal sampler and to a depth of 25?cm, from the base of the boulder wall until 9?m below the waterline during low tide. The abundances of A. brasiliana and D. punctata were inversely correlated over time. The populations differed in several aspects: (1) A. brasiliana occupied mainly the upper levels, whereas D. punctata occupied the lower level of the beach; (2) total abundance, growth rate, and production were higher for A. brasiliana; and (3) mortality and turnover rate were higher for D. punctata. The differences in growth, mortality, and production parameters may be associated with a difference in the species’ abilities to exploit resources.     

Population dynamics of autotrophic picoplankton in a southeastern U.S. Reservoir

Reservoirs typically exhibit a gradient along their longitudinal axis in turbidity, nutrient flux, and algal biomass. We utilized these characteristics to examine factors influencing temporal and spatial patterns in abundance, biomass, composition, and production of epilimnetic autotrophic picoplankton (APP) in Sardis Reservoir, Mississippi, USA. Over a 18-month period, APP abundance varied between about 15,000 and 700,000 cells ml⁻¹. Both APP abundance and APP biomass were closely linked to APP production and temperature. On an annual basis, the contribution of APP to total algal biomass and light-standardized production ranged between 15–47%, and 5–40%, respectively. Prokaryotes comprised more than 95% of all APP in summer, but eukaryotes dominated the APP community in winter. During the nutrient-depleted summer period, APP decreased in number but tended to increase in the percentage of total algal biomass and production, from the uplake riverine zone to the downlake lacustrine zone. Only in the second year of the study, when reservoir water residence time was more than four times greater than in the first year, were there significant differences in biomass and productivity of APP between the uplake and downlake regions. We suggest that, particularly in years or at times of the year when water-flow through the reservoir is slow, the importance of APP in Sardis Reservoir reflects a spatial and temporal gradient in nutrient availability.     

Seasonal dynamics of a glycan-degrading flavobacterial genus in a tidally mixed coastal temperate habitat

Coastal marine habitats constitute hotspots of primary productivity. In temperate regions, this is due both to massive phytoplankton blooms and dense colonisation by macroalgae that mostly store carbon as glycans, contributing substantially to local and global carbon sequestration. Because they control carbon and energy fluxes, algae-degrading microorganisms are crucial for coastal ecosystem functions. Environmental surveys revealed consistent seasonal dynamics of alga-associated bacterial assemblages, yet resolving what factors regulate the in situ abundance, growth rate and ecological functions of individual taxa remains a challenge. Here, we specifically investigated the seasonal dynamics of abundance and activity for a well-known alga-degrading marine flavobacterial genus in a tidally mixed coastal habitat of the Western English Channel. We show that members of the genus Zobellia are a stable, low-abundance component of healthy macroalgal microbiota and can also colonise particles in the water column. This genus undergoes recurring seasonal variations with higher abundances in winter, significantly associated to biotic and abiotic variables. Zobellia can become a dominant part of bacterial communities on decaying macroalgae, showing a strong activity and high estimated in situ growth rates. These results provide insights into the seasonal dynamics and environmental constraints driving natural populations of alga-degrading bacteria that influence coastal carbon cycling.     

Local and regional rarity in a diverse tropical fish assemblage

Because most species in an ecological assemblage are rare, much of the species richness we value is due to taxa with few individuals or a restricted distribution. It has been apparent since the time of ecological pioneers such as Bates and Darwin that tropical systems have disproportionately large numbers of rare species, yet the distribution and abundance patterns of these species remain largely unknown. Here, we examine the diversity of freshwater fish in a series of lakes in the Amazonian várzea, and relate relative abundance, both as numbers of individuals and as biomass, to the occurrence of species in space and time. We find a bimodal relationship of occurrence that distinguishes temporally and spatially persistent species from those that are infrequent in both space and time. Logistic regression reveals that information on occurrence helps distinguish those species that are rare in this locality but abundant elsewhere, from those that are rare throughout the region. These results form a link between different approaches used to evaluate commonness and rarity. In doing so, they provide a tool for identifying species of high conservation priority in poorly documented but species rich localities.     

Population dynamics and dispersal of Lepthyphantes tenuis in an ephemeral habitat

The population dynamics of Lepthyphantes tenuis (Blackwall) were investigated in two fields of winter wheat in Sussex, England, with the aim of attributing the major factors controlling population fluctuations. Continuous measures of changes in density, reproductive rate and dispersal were obtained using a range of methodologies, including laboratory analysis, suction trapping, rotary sampling of the aerial fauna, caging, and detailed density estimations. The resulting data were then used to determine the major causes of the observed population fluctuations and to describe the processes of dispersal and reproduction in this population.Population densities were initially very low following ploughing operations, but increased throughout the season as a result of high reproductive rates. Investigation of the reproductive potential of the spiders showed that the number of eggs per egg-sac did not vary with season, and that egg development was temperature related. There was no evidence that the number of viable eggs per egg-sac varied during the season. There were three peaks of hatchling production per year suggesting two to three generations of spiders. Dispersal was not responsible for the major changes in field density throughout the season although dispersal activity was high for this species. Dispersal activity increased with age and was highest in females. Dispersal activity as a ratio of activity/field density for females, males, sub-adults, immatures and hatchlings was 4:2:3:1:1.Aerial dispersal is only possible under suitable weather conditions. It was found that female dispersal was correlated with weather conditions far more strongly than other population groups. Calculations showed that under suitable weather conditions (e.g., 25% of the time being suitable for dispersal), almost 4% of the adult females could be expected to leave the population daily. The overall effect is therefore to displace individuals from the population but to have little effect on densities. Dispersal in other stages was controlled by the suitability of weather conditions but also by other, undetermined factors. It is postulated that L. tenuis has a life history strategy whereby suitable habitats act as sources of spiders, mainly females, which are continually involved in dispersal. Dispersal in other population groups may be triggered by factors such as the avoidance of adverse conditions. This type of life-history strategy is typical of organisms, such as weeds, that are successful in ephemeral habitats and may indicate that this species originally evolved in unpredictable habitats such as dry river beds or coastal areas.     

Inter-specific association and habitat use in a farmland passerine assemblage

We studied the pattern of inter-specific association of breeding territories in a passerine assemblage of dry cereal farmland in central Spain and evaluated the role of the presence of heterospecifics in the habitat use patterns exhibited by different species. Bird territories showed a non-random inter-specific spatial aggregation pattern. We studied territory abundance variation in the three more abundant species: the corn bunting, the crested lark, and the fan-tailed warbler. Crested lark and fan-tailed warbler territories were more abundant in plots where corn bunting territories were present and vice versa, while their respective abundances did not vary with the breeding presence of the other species. We used landscape and agricultural management variables to analyze the relationships between habitat and each species?? breeding territories by means of classification trees. While the corn bunting showed a marked pattern of nesting habitat use, the crested lark and the fan-tailed warbler exhibited a much more generalist one. Corn Bunting presence was affected negatively by intensification-related variables, such as field size and percent cover of cereal crops. Similarly, the presence of crested larks was negatively related to high yielding areas. However, when the presence of hetero-specific territories was considered, the presence of corn bunting territories was the most important variable explaining the occurrence of breeding fan-tailed warblers, and the second most important in the case of the crested lark. These results suggest that inter-specific attraction could play a role in the formation of farmland bird assemblages, while adding further evidence for the detrimental effect of agricultural intensification at the community level.     

Population dynamics of a generalist rodent in relation to variability in pulsed food resources in a fragmented landscape

1. Pulsed food resources are often considered equivalent in their potential impact on the reproduction and population dynamics of consumers, but differences in the attributes of food pulses and their distribution in the landscape may cause differences in their effects. 2. We tested whether a perishable pulsed resource (periodical cicadas, Magicicada spp.) had similar effects on the population dynamics of a generalist forest rodent, Peromyscus leucopus, as have been reported for a cacheable pulsed resource (acorn mast). 3. Because the availability of periodical cicadas may vary between edge and interior habitat, we also tested whether habitat type (edge vs. interior) and fragment size affected the abundance of cicadas and P. leucopus. 4. Nearly 90% of the variation in the relative population densities of P. leucopus was explained by the variation in the relative densities of periodical cicadas, and fragments with more cicadas tended to have more reproductive female mice and litters. 5. We found more cicadas and more P. leucopus in edge than interior habitat, but no differences in the relative densities of either in relation to fragment size. 6. Data from a non-emergence year revealed no differences other than the presence of periodical cicadas that could explain the 50% higher relative densities of P. leucopus in the emergence year. 7. At the beginning of the emergence of periodical cicadas, the three fragments with the highest numbers of emergence holes had three times more mice than the fragments with the lowest numbers of emergence holes, suggesting that P. leucopus is able to anticipate the emergence of periodical cicadas and increase reproduction prior to the pulse. 8. Hence, despite differences in perishability, seasonal timing and nutritional quality of pulsed food resources in a fragmented landscape, they appear to have similar positive effects on the population dynamics of the generalist rodent, P. leucopus and, in fact, P. leucopus may be able to anticipate resource pulses.     

Population dynamics of coniferous and broad-leaved trees in a Japanese temperate mixed forest

The growth and survival of coniferous and broad-leaved trees were followed over a 5-yr period in a temperate old-growth mixed forest in Japan, and dynamic features of the forest were studied in relation to the life history of the dominants, the coniferous Abies homolepis and the broad-leaved Fagus crenata. During this period, the gap formation rate was 31m² ha^?1yr^?1, the mortality of trees > 2m high was 1.7%/yr, and the rate of loss in basal area 1.4%/yr. These values were much higher than the recruitment, 0.3%/yr, and the total growth of surviving and new trees, 0.6%/yr, owing to the inhibition of regeneration by understorey dwarf bamboo (Sasa borealis). A transition matrix model based on DBH size classes predicts that the basal area of the forest will decrease by 14% in 50 yr, but that the DBH distribution of trees > 10 cm diameter will change little. Equilibrium DBH distributions assuming recruitment being equal to mortality, were quite different between broad-leaved and coniferous trees, reflecting different survivorship curves of the two dominants. The composition and structure of the forest may change depending on the pattern and frequency of disturbances, or episodic events, notably the synchronous death of Sasa borealis.     

Diversity and seasonal dynamic of a lizard assemblage in a Neotropical semiarid habitat

We assessed the lizard assemblage from a priority conservation Caatinga area from northeastern Brazil, through a pluriannual ecological approach, to expand the understanding on biodiversity patterns of Neotropical semiarid habitats. The studied area presented one of the richest lizard faunas among Caatinga sites, being composed primarily by species typical from open landscapes. The local species composition was more similar to assemblages from adjacent Caatinga ecoregions than to those from other areas within the same ecoregion. The inventoried lizard assemblage consisted of a few common species and a majority of low abundance ones, and its overall richness and abundance did not differ between rainy and dry months. Our findings demonstrated that the composition of lizard assemblages did not match with the current proposed Caatinga ecoregions, and revealed that the studied assemblage followed a lognormal species-abundance distribution, showing no significant seasonal fluctuation in richness and abundance.     

Fulu biota,a new exceptionally-preserved Cambrian fossil assemblage from the Longha Formation in southeastern Yunnan

A new exceptionally-preserved Cambrian biota, with fossils belonging to multiple phyla, has recently been found from the middle part of the Longha Formation, near Fulu Village, southeastern Yunnan, South China, and is named the Fulu biota. Groups recovered so far include polymerid trilobites, agnostoids, large bivalved arthropods, bradoriid arthropods, echinoderms, brachiopods, priapulids (worms), hyoliths, macroscopic algae, and trace fossils. The arthropods dominate the biota and are highly diverse with echinoderms second in diversity. The associated agnostoids provide a precise late Guzhangian Age (late Miaolingian Epoch) for the biota, indicating that the biota occurs stratigraphically about halfway between the occurrences of the Kaili and the Guole biotas of South China, from both of which the new Fulu biota differs significantly in faunal components. Guzhangian biotas preserving poorly mineralized tissues and complete echinoderms have been previously unknown in Gondwana until now; thus, the discovery of Fulu biota provides a unique window into life at this critical time interval.     

Differential influence of a monotypic and diverse native aquatic plant bed on a macroinvertebrate assemblage; an experimental implication of exotic plant induced habitat

Aquatic plants mediate ecological processes in aquatic habitats, specifically predator–prey (bluegill sunfish (Lepomis macrochirus Rafinesque)-macroinvertebrate) interactions. Macroinvertebrate colonization is directly and indirectly influenced by substrate heterogeneity, interstitial space, and surface complexity. Exotic invasive plant species, such as Hydrilla verticillata L.F. Royle, may alter the available structure in aquatic habitat by creating a shift to a homogeneous habitat, thus affecting the macroinvertebrate community. Since macroinvertebrates provide a food base for young phytophilic fishes, changes in their density and abundance may alter food webs. We investigated the hypothesis that macroinvertebrate community structure is influenced by differences in habitat heterogeneity by measuring difference between a heterogeneous native aquatic plant bed, homogenous hydrilla plant bed, and habitat with no plants. Studies were conducted in the field (pond) and the experimental treatments were: (1) no plants, (2) monotypic bed of hydrilla, and (3) diverse native plants. Aquatic plants, regardless of species, supported greater macroinvertebrate abundance, richness, and biomass. Macroinvertebrate abundance, richness, and biomass in a hydrilla-dominated habitat did not differ significantly from a diverse plant habitat, except for richness in October. Indicator taxa did differ significantly between respective treatments, suggesting a change in species composition. However, no significant effect of fish predation on macroinvertebrate populations and/or community structure was documented. The data suggest that a shift from a natural mosaic of vegetated habitat to a highly complex monotypic habitat (e.g., exotic hydrilla) may reduce spatial heterogeneity important to structuring a macroinvertebrate assemblage. Handling editor: S. M. Thomaz