The development of sessile epifaunal communities in Kylesalia,Kilkieran bay (west coast of Ireland)

Test panels, which were suspended horizontally at three sites in a shallow inlet on the west coast of Ireland, were sampled monthly over a period of one year to investigate the development of epifaunal communities. In addition, the current regime and sedimentation at these sites were measured. The deposited materials, of high organic value, may enhance the food supply to the sessile organisms through resuspension. Heavy deposition at one site interrupted the study. At the other two sites, however, the experiment was not affected. At one site, initial settlement by colonial bryozoans, followed by solitary ascidians, was noted on the panels over the period studied. In the competition for space, the dense aggregations during settlement, the relative large size, and the rapid growth of these solitary animals may occlude the colonization by colonial bryozoan mats underneath. At the other site, a more diversified community with co-existence of many sedentary polychaete and colonial bryozoan species was recorded on the panels. The continuing availability of free space on the panels suggests that the development of sessile communities at this site may be hindered by the relatively slow current flow and heavy deposition and resuspension. Whilst differences in community development were observed on the panels at these two sites, it would be difficult, through such a short study period, to ascertain whether stable climax states had been reached.     

Spatial distribution of algae and invertebrates in the rocky intertidal zone of the Strait of Magellan: are patterns general?

Spatial variability in the distribution of macroalgae and invertebrates was examined at a number of sites in the Strait of Magellan. Two main predictions of models of zonation were tested in this study: (1) consistency in patterns of vertical distribution among sites one to tens of kilometers apart, and (2) homogeneity between areas at the same level on the shore, tens to hundreds of meters apart. Two types of habitat were considered: continuous rocky shores and blocks of rock in gravel beaches. In the former habitat, percent cover estimates of sessile organisms (algae and mussels) were obtained from three replicated plots (0.5 × 0.5 m) sampled non-destructively in each of three random areas (stretches of shore about 20 m long) at each of three levels on the shore: high, middle and low intertidal zone. This procedure was repeated at six different sites along the Chilean coast of the Strait of Magellan. Blocks of rock were sampled at two sites about 1 km apart. Estimates of the abundance of sessile (barnacles and mussels) and mobile (limpets) organisms were obtained for six blocks at each of two levels on the shore (high and low intertidal zone) at each site. At each level on the shore, three blocks were sampled on the top and three on the vertical sides. A single plot was sampled on each block. This design allowed a test of the null hypothesis of no interactive effects between position on the blocks and level on the shore. Both the predictions were falsified: (1) there were large between-site differences in the vertical structure of assemblages and (2) variability between areas at the same level on the shore was large for some of the most common algae. In contrast, the null hypothesis of no interactive effects of position on the blocks and level on the shore was retained. The results of this study show that vertical position on the shore alone is not a good predictor of the structure of assemblages of benthic organisms in the rocky intertidal of the Strait of Magellan. Received: 9 December 1996 / Accepted: 2 May 1997     

Temporal variation and succession in an algal-dominated high intertidal assemblage

We determined whether temporal variation and succession were similar among sites with similar species composition by sampling unmanipulated and cleared plots in a high intertidal assemblage dominated by Endocladia muricata and Mastocarpus papillatus. Sampling was done for 6 years at six sites spanning over 4° of latitude in California. Ten 1×2-m permanent plots were chosen in the central portion of the assemblage at each site. Four of these served as unmanipulated controls, three were cleared (scraped and burned) in the spring of 1985, and three were cleared in the fall of 1985. The cover of sessile and density of motile species were determined by subsampling within the plots from 1985 until 1991. Recovery of the clearings was determined by their similarity to the controls. The algae E. muricata, M. papillatus, and Fucus gardneri, and the barnacle Balanus glandula, were the most abundant sessile organisms in the control plots, although the latter never exceeded 12% cover at any site. The grazing gastropods Littorina scutulata/plena, various limpets, and Tegula funebralis were the most common mobile organisms. The species composition of the common species remained constant in the control plots over the study period and there were few large changes in relative abundance. Significant seasonal variation was detected in 11 species but variation was commonly site-specific.Ephemeral algae were abundant during early succession at only two of the six sites, and barnacle cover was low (<15% cover) at four sites and moderate (15-50% cover) at the remaining two throughout succession. Recovery rate varied considerably among sites and between times of clearing (1-10%/month). Correlations between ephemeral algae and grazer abundance, and between these variables and recovery rate were not significant. The effects of grazers on recovery rate were only evident at one site where they appeared to reduce an initially high cover of ephemeral algae and delay the establishment of perennials. Some of the largest differences in recovery rate were between clearing times, associated with differences in the phenology of the dominant perennial algae. In spite of these differences, most plots recovered by the end of the study period.These results indicate that the assemblages in the control plots at each site were relatively stable and, while successional pathways and processes varied, the assemblage at most sites still recovered. Current models, based largely on biological interactions, that attempt to explain within assemblage structure and succession were not broadly applicable.     

The role of the physical structure of Spartina densiflora Brong. in structuring macroinvertebrate assemblages

In Patagonian rocky salt marshes, the presence of the austral cordgrass Spartina densiflora provide habitat for diverse faunal assemblages. Two different mechanisms may influence the distribution and abundance patterns of these associated organisms: those generated by the biological properties of cordgrasses and those caused or mediated by the physical structure supplied by the plants. The aims of this study were: (1) to determine the effect of cordgrasses on macroinvertebrate assemblages dominating a rocky marsh and (2) to determine how much of this effect is caused by the physical structure supply by the plants. In order to achieve these objectives, we conducted two field manipulative experiments. In the first one, we manipulated the presence of defaunated transplants of cordgrass, and in the second one, we did the same with plastic cordgrass mimics simulating the architecture of Spartina densiflora. In both experiments, sessile and mobile assemblages were separately examined to evaluate whether they respond in the same way or not. Abundance and richness of mobile and sessile organisms were higher in transplant and mimic cordgrass plots compared to the controls, indicating that the presence of cordgrasses, either transplanted or artificial, has a positive effect on sessile and mobile assemblages. Furthermore, we found that the composition of mobile and sessile macroinvertebrates assemblages did not differ between transplants and mimics. Therefore, the physical structure of cordgrass was found to be the major factor influencing macroinvertebrates assemblages in the studied Patagonia rocky salt marshes. Within the period of 1 year, mobile and sessile fauna colonized several times more abundantly transplant and artificial cordgrass than the control unvegetated plots, highlighting the key role of cordgrasses in optimizing the colonization rate of macroinvertebrate communities in this rocky bottom environment. Since Spartina densiflora is invading different regions worldwide, our study may help to predict its potential effect on the invaded communities.     

Computational Analysis of the Predicted Evolutionary Conservation of Human Phosphorylation Sites

Protein kinase-mediated phosphorylation is among the most important post-translational modifications. However, few phosphorylation sites have been experimentally identified for most species, making it difficult to determine the degree to which phosphorylation sites are conserved. The goal of this study was to use computational methods to characterize the conservation of human phosphorylation sites in a wide variety of eukaryotes. Using experimentally-determined human sites as input, homologous phosphorylation sites were predicted in all 432 eukaryotes for which complete proteomes were available. For each pair of species, we calculated phosphorylation site conservation as the number of phosphorylation sites found in both species divided by the number found in at least one of the two species. A clustering of the species based on this conservation measure was concordant with phylogenies based on traditional genomic measures. For a subset of the 432 species, phosphorylation site conservation was compared to conservation of both protein kinases and proteins in general. Protein kinases exhibited the highest degree of conservation, while general proteins were less conserved and phosphorylation sites were least conserved. Although preliminary, these data tentatively suggest that variation in phosphorylation sites may play a larger role in explaining phenotypic differences among organisms than differences in the complements of protein kinases or general proteins.     

ADAPTIVE PLASTICITY OF THE PENIS IN A SIMULTANEOUS HERMAPHRODITE

Acorn barnacles are important model organisms for the study of sex allocation. They are sessile, nonselfing hermaphrodites that copulate with penises that have been suggested to be phenotypically plastic. On wave-exposed shores, Semibalanus balanoides develop penises with relatively greater diameter whereas in wave-protected sites they are thinner. A reciprocal transplant experiment between wave-exposed and protected sites tested whether these exposure-specific morphologies have adaptive value. Mating success was compared over a range of distances to compare the ability of barnacles to reach mates. Barnacles that grew in the wave-protected site and mated in the wave-protected site fertilized more broods at increasing distances than those transplanted to the wave-exposed site. For barnacles that developed in the wave-exposed site, there was no difference in the ability to fertilize neighbors between sites of differing exposure. This study demonstrates the adaptive value of plasticity in penis morphology. The results suggest a trade-off between development of a penis adapted to wave exposure and the ability to fertilize distant mates. Barnacles in different physical environments are limited by different factors, which may limit numbers of potential mates, constrain optimal sex allocation strategies and alter reproductive behavior.     

A histopathological survey of shore crab (Carcinus maenas) and brown shrimp (Crangon crangon) from six estuaries in the United Kingdom

Invertebrates show considerable potential as sentinel organisms for the monitoring of the health status of aquatic systems. They are generally small, abundant, relatively sessile, and may readily bioaccumulate toxins. Cascade-like stress responses can occur following acute or chronic exposures to contaminated environments and as such, the overall health status of individuals within those environments, both in terms of histopathological lesions and the presence of infecting organisms, may ultimately reflect the general health status of these sites. The current study provides baseline multi-organ histopathological data for two common crustacean species, the shore crab (Carcinus maenas) and the brown shrimp (Crangon crangon) collected from six UK estuarine sites. Changes in the metabolic condition of crustaceans from these sites (measured in terms of connective tissue storage cell status) were interpreted in relation to other health measures (including parasite load and the presence of microbial pathogens). The relative ease at which a holistic assessment of health can be made using histopathology and the suitability of these species as environmental sentinels provide support for the inclusion of crustaceans as indicators of aquatic environmental health. Studies linking disease status to burdens of industrial contamination in these environments are now required.     

Biomass changes and bentho-pelagic transfers throughout the Benthic Boundary Layer in the English Channel

One hundred and eight suprabenthic hauls were taken from sixsites in the English Channel with a modified Macer-GIROQ sledgethat permitted the sampling of three kinds of organisms in thebenthic boundary layer: mesozooplankton, macrozooplankton andsuprabenthos. A complete annual cycle was sampled in the Bayof Saint-Brieuc but only spring and autumn samplings were takenfrom the other sites. Meso- and macrozooplankton biomasses wereusually higher at every site during the daytime than at night;in contrast, suprabenthic biomasses were lower during the daythan at night. However, at site 5, on pebble substrates, everyfaunistic group showed a higher biomass during the day thanat night, while at site 2 the opposite occurred. Meso- and macrozooplanktonbiomasses were at their maximum during spring whereas the highestbiomass of suprabenthos was observed from summer to autumn.Daytime exchanges were by mesozooplanktonic organisms and night-timeexchanges were by suprabenthic species, especially amphipods,mysids and large decapods. Daily transfers showed the same patternfor every faunistic group, and transfers were higher in autumnthan in spring, except at site 1 where it was similar duringboth seasons. Three groups of sites were identified from theirannual transfers: sites 1 and 3, on the Brittany coasts, withlowest annual transfers; site 2, offshorePlymouth, with thehighest transfer, and the three eastern sites (4, 5 and 6) showingsimilar annual transfers. The rate between macrobenthic productionand annual transfers was high at coarse sand and pebble siteswhere the benthic macrofauna was endobenthic and sessile, suggestinga concentration of carbon in the bottom. On the other hand,this rate was low on medium sand substrates where the benthicmacrofauna was vagile, suggesting that carbon remained concentratedin the benthic boundary layer where exchanges were most importantby the migration of both pelagic and benthic organisms in thiscompartment.     

Effects of commercial trawling activities in the diet of the flat fish Citharus linguatula (Osteichthyes: Pleuronectiformes) and the starfish Astropecten irregularis (Echinodermata: Asteroidea)

This study assesses the effects of commercial trawling on benthic fauna, by analysing differences in the population structure and diet of benthic organisms inhabiting fishing grounds. The study is focused on two epifaunal species collected from a fishing ground in the north-western Mediterranean, which included a portion of un-trawled seabed used as a reference of undisturbed community. The selected species were the flatfish Citharus linguatula, more abundant at the undisturbed site and previously characterised as a surface predator and vulnerable to trawling, and the starfish Astropecten irregularis, which dominated the epibenthic community and had been characterised as an opportunistic species with low vulnerability to trawling. Both species were selective feeders and ingested similar prey species at each of the two sites, although differences in the relative prey abundance found in the stomachs occurred between sites. A. irregularis at the fished site mainly ingested gastropods, whereas higher proportion of bivalves was ingested at the undisturbed site. C. linguatula diet mainly composed of crustaceans at both sites, but there was an increase in the ingestion of small fish at the fished site. Moreover, prey ingestion of these two species generally increased with fishing activity. Trawling appears to modify the diet of these two species in terms of relative abundance of ingested prey, nevertheless, increased opportunism due to trawling disturbance was not detected and the density of these predators over fishing grounds was more closely related to their vulnerability to trawling.     

Reef fish community structure in the Tropical Eastern Pacific (Panamá): living on a relatively stable rocky reef environment

We compared the community structure of reef fish over different physical complexities in 12 study zones of Bahía Honda, Gulf of Chiriquí (BH-GCH), Tropical Eastern Pacific (TEP), Panama, aiming at an analysis of the importance of the physical structure provided by corals, rocks and benthic sessile organisms. This was the first region that emerged in the Isthmus of Panama; it exhibits the oldest benthic fauna and has constant conditions in terms of temperature and salinity. Two hundred and eighty-eight visual fish censuses were conducted on 48 benthic transects from February to July 2003. One hundred and twenty-six fish species of 44 families were found. Plankton feeding pomacentrids and labrids along with haemulids that feed on mobile invertebrates were the most abundant, particularly in shallow areas. Fourteen species showed size-segregations between zones, suggesting ontogenetic migrations (smaller fishes in shallow high-complexity zones, larger-sized fishes in deeper habitats). Highly mobile and site-attached genera were abundant in most shallow, wave-exposed zones particularly on exposed rocky substrates. Planktivores were the most abundant, followed by carnivores, feeders on mobile invertebrate and piscivores. Herbivores and feeders on sessile invertebrate were lower in abundance. Species richness exceeds that of any other studied region close to the mainland in the TEP and correlates with substrate diversity, increasing size-heterogeneity of holes and structural complexity. Species diversity increases with habitat complexity and benthic diversity. It seems that water current strength, tides and waves which select for swimming, play an important role in the community organization. The study region has been proposed as a refuge-centre in the TEP, where reef fishes that evolved on coral reefs have shifted their distribution onto rocky reef habitats.     

Community Structure of Fishes and Habitat Complexity on a Tropical Rocky Shore

The relationship between the variables of reef fish community structure (fish richness, fish diversity and total number of fishes) and those of habitat complexity (total surface area, substratum diversity, topographic complexity, number of holes, percent cover of turf algae, zoanthids, millepores, massive corals, bare rock, encrusting calcareous algae, urchins, other sessile organisms and Sargassum) were examined on three different rocky shores (FA, FB and FT) at Arraial do Cabo, a tropical region located on Brazilian southeastern coast (23° S, 42° W). Fish abundance and vertical distribution were assessed by a visual census technique using strip transects. Percentage cover of benthic organisms and other substratum types were calculated by replicated transects using a chain laid down on the substratum. Topographic complexity was determined by the chain link method and number of holes were estimated by direct counts on replicated transects. More than 91 fishes belonging to 37 families were seen in all study sites during one year of visual census effort. FA and FB sites had similar fish community structure and habitat complexity characteristics, while FT showed different habitat characteristics and higher fish diversity and richness, plus total number of fishes. Vertical distribution of fishes along the rocky shores studied seemed to be predictable and was determined by factors such as feeding habits and behavior, availability of refuges and social interactions. The habitat variables that best explained the higher diversity and number of fishes observed in FT site were total surface area of rocky shores and the abundance of benthic sessile invertebrates; these conditions were typical of rocky shores more exposed to wave surge.     

PCR-based identification of thermotolerant free-living amoebae in Italian hot springs

Several thermal areas, also used for leisure purposes, may represent suitable habitats for free-living amoebae (FLAs), but few studies have been carried out in search for these organisms. The aim of this study was to assess the presence and distribution of FLAs by culture detection and molecular identification, over a one year-round sampling of two sites in Central Italy. Two geothermal springs (Site A and Site B) were investigated for a total of 36 water samples. Four sets of primers were used to amplify FLA DNA from all cultures positive for amoebic growth at both 37 °C and 45 °C. Overall, 33 (91.6%) water samples produced PCR amplification. Eleven taxa were identified. The array of identified species varied over the sampling period, and differed between the two hot springs, Site A harbouring 11 taxa compared to 5 of site B. However, both sites were characterized by the most common species Vermamoeba vermiformis and Naegleria australiensis. Acanthamoeba genotypes T4 and T15 were found at low frequency. Differences in the composition between the two sites could reflect environmental changes in biotic and chemical/physical parameters. From a public health perspective, the detection of potentially pathogenic amoebae could unveil a potential risk for humans.     

Estimating site occupancy rates for aquatic plants using spatial sub-sampling designs when detection probabilities are less than one

Estimation of site occupancy rates when detection probabilities are <1 is well established in wildlife science. Data from multiple visits to a sample of sites are used to estimate detection probabilities and the proportion of sites occupied by focal species. In this article we describe how site occupancy methods can be applied to estimate occupancy rates of plants and other sessile organisms. We illustrate this approach and the pitfalls of ignoring incomplete detection using spatial data for 2 aquatic vascular plants collected under the Upper Mississippi River's Long Term Resource Monitoring Program (LTRMP). Site occupancy models considered include: a naïve model that ignores incomplete detection, a simple site occupancy model assuming a constant occupancy rate and a constant probability of detection across sites, several models that allow site occupancy rates and probabilities of detection to vary with habitat characteristics, and mixture models that allow for unexplained variation in detection probabilities. We used information theoretic methods to rank competing models and bootstrapping to evaluate the goodness-of-fit of the final models. Results of our analysis confirm that ignoring incomplete detection can result in biased estimates of occupancy rates. Estimates of site occupancy rates for 2 aquatic plant species were 19–36% higher compared to naive estimates that ignored probabilities of detection <1. Simulations indicate that final models have little bias when 50 or more sites are sampled, and little gains in precision could be expected for sample sizes >300. We recommend applying site occupancy methods for monitoring presence of aquatic species.     

Sperm motility parameters and spermatozoa morphometric characterization in marine species: A study of swimmer and sessile species

The biodiversity of marine ecosystems is diverse and a high number of species coexist side by side. However, despite the fact that most of these species share a common fertilization strategy, a high variability in terms of the size, shape, and motion of spermatozoa can be found. In this study, we have analyzed both the sperm motion parameters and the spermatozoa morphometric features of two swimmer (pufferfish and European eel) and two sessile (sea urchin and ascidian) marine species. The most important differences in the sperm motion parameters were registered in the swimming period. Sessile species sperm displayed notably higher values than swimmer species sperm. In addition, the sperm motilities and velocities of the swimmer species decreased sharply once the sperm was activated, whereas the sessile species were able to maintain their initial values for a long time. These results are linked directly to the species-specific lifestyles. Although sessile organisms, which show limited or no movement, need sperm with a capacity to swim for long distances to find the oocytes, swimmer organisms can move toward the female and release gametes near it, and therefore the spermatozoa does not need to swim for such a long time. At the same time, sperm morphology is related to sperm motion parameters, and in this study an in-depth morphometric analysis of ascidian, sea urchin, and pufferfish spermatozoa, using computer-assisted sperm analysis software, has been carried out for the first time. A huge variability in shapes, sizes, and structures of the studied species was found using electron microscopy.     

Variations in holdfast attachment mechanics with developmental stage, substratum-type, season, and wave-exposure for the intertidal kelp species Hedophyllum sessile (C. Agardh) Setchell

Biomechanical models that describe physical and biological interactions on wave-exposed shores typically assume that a species' attachment properties are similar between seasons and sites. We tested this assumption using Hedophyllum sessile to investigate how macroalgal biomechanical attachment properties vary with developmental stage, substratum-type, season, and wave-exposure. Hedophyllum sessile is an intertidal kelp species that is able to survive in wave-exposed areas in the Northeast Pacific. For both juveniles and adults, holdfast attachment force and strength were measured at a wave-exposed and wave-protected site in Barkley Sound, British Columbia, Canada. Substratum and wave-exposure effects on attachment properties were tested in juvenile populations. Adult populations were sampled prior to (in July 1996) and after (in November 1996) a series of storms. Site and seasonal wave-exposure effects on attachment properties were tested in these adult populations. Comparisons to known attachment properties of other temperate macroalgal species were also made. Causes for these patterns are discussed but were not isolated in these studies. Juveniles' attachment properties differed on different substrata types and between wave-exposures, with the highest attachment forces and the most attached juveniles in articulated coralline algal turfs. Adult attachment is firm ( approximately 100 N), but relatively weak ( approximately 0.07 MNm(-2)). Adult attachment did not vary with site wave-exposure, but there was a shift within each site to more resistant holdfasts after a series of early winter storms. Seasonal increases in storm swells correlated to more thallus tattering and selected against large, loose holdfasts. The data presented here suggest that results from holdfast attachment field studies in one season cannot be extrapolated to another due to a complex set of dynamics. This is the first documentation of seasonal patterns in macroalgal attachment properties.     

Coexistence of arbuscular mycorrhizae and dark septate endophytic fungi in an undisturbed and a disturbed site of an arid ecosystem

Effect of disturbance on root colonization and vertical distribution of arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) was investigated at two adjacent sites of Lal Suhanra Biosphere Reserve, Pakistan. Disturbance clearly affected AMF and DSE colonization, vertical distribution of AMF and plant community structure. Mean colonization of AMF and DSE was slightly less at the disturbed site. Average spore densities, diversity and richness of AMF and DSE were higher at the undisturbed site. A study of the vertical distribution of AMF associated with the five plant species most common to each study site indicated that beside AMF and DSE colonization disturbance may affect AMF species composition. Correlation of AMF with DSE is also discussed.     

Assessment of concordance among genealogical reconstructions from various mtDNA segments in three species of Pacific salmon (genus Oncorhynchus)

Seven segments of mitochondrial DNA (mtDNA), comprising 97% of the mitochondrial genome, were amplified by polymerase chain reaction (PCR) and examined for restriction site variation using 13 restriction endonucleases in three species of Pacific salmon: pink (Oncorhynchus gorbuscha), chum (O. keta) and sockeye (O. nerka) salmon. The distribution of variability across the seven mtDNA segments differed substantially among species. Little similarity in the distribution of variable restriction sites was found even between the mitochondrial genomes of the even- and odd-year broodlines of pink salmon. Significantly different levels of nucleotide diversity were detected among three groups of genes: six NADH-dehydrogenase genes had the highest; two rRNA genes had the lowest; and a group that included genes for ATPase and cytochrome oxidase subunits, the cytochrome b gene, and the control region had intermediate levels of nucleotide diversity. Genealogies of mtDNA haplotypes were reconstructed for each species, based on the variation in all mtDNA segments. The contributions of variation within different segments to resolution of the genealogical trees were compared within each species. With the exception of sockeye salmon, restriction site data from different genome segments tended to produce rather different trees (and hence rather different genealogies). In the majority of cases, genealogical information in different segments of mitochondrial genome was additive rather than congruent. This finding has a relevance to phylogeographic studies of other organisms and emphasizes the importance of not relying on a limited segment of the mtDNA genome to derive a phylogeographic structure.     

Salmonella, Campylobacter and Enterococcus spp.: Their Antimicrobial Resistance Profiles and their Spatial Relationships in a Synoptic Study of the Upper Oconee River Basin

Rivers may serve as reservoirs for enteric organisms. Very little is known about the boundaries of microbial communities in moving bodies of water so this study was undertaken to find the limits of distribution of some bacteria, focusing on enteric organisms. The presence of Salmonella, Campylobacter, and Enterococcus spp. and the antimicrobial resistance phenotypes carried by these organisms was evaluated for the Upper Oconee River basin, a small river in the lower Piedmont of northeastern Georgia, USA. Samples were obtained from 83 sites during a 3-h period on a spring day (April 2005) in an approximately 30 × 20 km region. Campylobacter spp. was isolated at 12 sites. The Campylobacter isolates from three sites were resistant to tetracycline. Of the five short-variable region (SVR) subtypes of Campylobacter that were found, three were found at more than one site, two types were found twice, and one subtype was found three times. Enterococcus was isolated at 71 sites. E. casseliflavus was the most common species. Based on species identification and antimicrobial resistance patterns, 24 types of Enterococcus were found. Salmonella was isolated from 62 sites. Of the 19 Salmonella serovars that were isolated, serovar Muenchen accounted for about 20% of the isolates. The next three most common serovars isolated, Rubislaw, Hartford, and Give, accounted for about 44% of the river isolates. Antimicrobial resistance profiling offered limited differentiation of Salmonella isolates because only seven isolates were resistant to any antimicrobial. The sites at which Salmonella, Campylobacter, or Enterococcus were isolated did not correlate with each other or with the total coliform number or Escherichia coli count for the site. However, isolates of some of the same species and type occurred in clusters that were restricted to areas within 5 to 6 km.     

Effects of conspecific and heterospecific residents on patterns of immigration in two species of voles

Studies with birds have shown that presence and density of resident conspecifics and heterospecifics can influence patterns of habitat selection. There have been few studies on the effects of social cues on rates of immigration in mammals. We report results from a long-term live trapping study of immigration in two species of voles, Microtus ochrogaster Wagner, 1842 and Microtus pennsylvanicus Ord, 1815, in bluegrass habitat in east-central Illinois, USA. We compare immigration into control sites from which no individuals of either species were removed with immigration into experimental sites from which either conspecifics or heterospecifics were removed. We focus on characteristics of immigrants and rates of immigration in relation to density in destination habitats. Within each species, immigrants into control and removal sites were similar with respect to body mass and reproductive condition, indicating no major differences in the physical condition of immigrants into sites with established populations and sites without established populations. For both species, density of conspecifics at a site positively influenced rate of immigration at that site. Density of heterospecifics at destination sites did not significantly influence rate of immigration for either species. These results suggest that site selection by dispersing M. ochrogaster and M. pennsylvanicus is characterized by conspecific attraction.