Introduced and cryptogenic species in Port Phillip Bay, Victoria, Australia

Port Phillip Bay (PPB) is a large (1,930 km²), temperate embayment in southern Victoria, Australia. Extensive bay-wide surveys of PPB have occurred since 1840. In 1995/1996 the Commonwealth Scientific and Industrial Research Organization (CSIRO) Centre for Research on Introduced Marine Pests (CRIMP) undertook an intensive evaluation of the region with the aims of developing a comprehensive species list of native and introduced biota and contrasting previous bay-wide assessments with a current field survey in order to detect new incursions and discern alterations to native communities. Two methods were used to meet these aims: a re-evaluation of regional museum collections and published research in PPB to identify and determine the timing of introductions; and field surveys for benthic (infauna, epifauna and encrusting) organisms between September 1995 to March 1996. One hundred and sixty introduced (99) and cryptogenic (61) species were identified representing over 13% of the recorded species of PPB. As expected, the majority of these are concentrated around the shipping ports of Geelong and Melbourne. Invasions within PPB appear to be increasing, possibly due to an increase in modern shipping traffic and an increase in aquaculture (historically associated with incidental introductions); however the records of extensive biological surveys suggest that this may, in part, be an artefact of sampling effort. In contrast to Northern Hemisphere studies, PPB (and Southern Hemisphere introductions in general) have significantly different suites of successfully invading taxa. PPB is presented as one of the most invaded marine ecosystems in the Southern Hemisphere.Communicated by M.S. Johnson, Crawley     

A unified model of avian species richness on islands and continents

How many species in a given taxon should be found in a delimited area in a specified place in the world? Some recent literature suggests that the answer to this question depends strongly on the geographical, evolutionary, and ecological context. For example, current theory suggests that species accumulate as a function of area differently on continents and islands. Species richness-climate relationships have been examined separately on continents and on islands. This study tests the hypotheses that (1) the functional relationship between richness and climate is the same on continents and islands; (2) the species-area slope depends on distance-based isolation; (3) species-area relationships differ among land bridge islands, oceanic islands, and continents; (4) richness differs among biogeographic regions independently of climate and isolation. We related bird species numbers in a worldwide sample of 240 continental parcels and 346 islands to several environmental variables. We found that breeding bird richness varies similarly on islands and on continents as a function of mean annual temperature, an area x precipitation interaction, and the distance separating insular samples from the nearest continent (R2 = 0.86). Most studies to date have postulated that the slope of the species-area relationship depends upon isolation. In contrast, we found no such interaction. A richness-environment relationship derived using Old World sites accurately predicts patterns of richness in the New World and vice versa (R2 = 0.85). Our results suggest that most of the global variation in richness is not strongly context-specific; rather, it reflects a small number of general environmental constraints operating on both continents and islands.     

Quantifying the importance of regional and local filters for community trait structure in tropical and temperate zones

The influence of regional and local processes on community structure is a major focus of ecology. Classically, ecologists have used local-regional richness regressions to evaluate the role of local and regional processes in determining community structure, an approach that has numerous flaws. Here, we implemented a novel trait-based approach that treats local and regional influences as a continuum, rather than a dichotomy. Using hylid frogs (Hylidae), we compared trait dispersion among members of local species assemblages to the trait dispersion in the regional assemblage from which they were drawn. Similarly, we compared trait dispersion in the regional assemblages to dispersion in the continental species pool. We estimated the contributions of local and regional filters, and we compared their strength in temperate and tropical zones. We found that regional and local filters explained 80% of the total variation among local assemblages in community body size dispersion. Overall, regional filters reduced trait dispersion, and local filters increased it, a pattern driven by particularly strong antagonistic effects in temperate zones that reduced the realized total variation by more than 40%. In contrast, local and regional filters acted in concert in tropical regions. Patterns within the tropics did not differ from the random expectation based on a null model, but within the temperate zone, local community filtering was stronger than expected by chance. Furthermore, in temperate regions, antagonistic regional and local filtering masked from 76% to 90% of the total variation in trait dispersion. Together, these results suggest that there are fundamental differences in the scale and identity of the processes determining community structure in temperate and tropical regions.     

Preliminary results of laboratory toxicity tests with the mayfly, Isonychia bicolor (Ephemeroptera: Isonychiidae) for development as a standard test organism for evaluating streams in the Appalachian coalfields of Virginia and West Virginia

Selecting the most appropriate test species for sediment and water column assays has been a primary goal for ecotoxicologists. Standard test organisms and established test guidelines exist, but the USEPA-recommended species may not be the most sensitive organisms to anthropogenic inputs. This paper describes preliminary results of toxicity tests with the mayfly, Isonychia bicolor (Ephemeroptera). Results suggested that Isonychia were moderately sensitive to NaCl after 96 h with an average LC₅₀ value of 3.10 g NaCl per liter. This value decreased after 7 days of exposure, resulting in a mean LC₅₀ value of 1.73 g NaCl per liter. When exposed to a coal-mine-processed effluent, Isonychia generated LC₅₀ values that ranged from 13% to 39% effluent. I. bicolor were more sensitive to the coal processing effluent than Ceriodaphnia dubia with conductivity lowest observable effects concentration (LOEC) values for mayfly survivorship that ranged from 1,508 to 4,101 μS/cm, while LOEC values for C. dubia reproduction ranged from 2,132 to 4,240 μS/cm.     

A new chasmosaurine from northern Laramidia expands frill disparity in ceratopsid dinosaurs

A new taxon of chasmosaurine ceratopsid demonstrates unexpected disparity in parietosquamosal frill shape among ceratopsid dinosaurs early in their evolutionary radiation. The new taxon is described based on two apomorphic squamosals collected from approximately time equivalent (approximately 77 million years old) sections of the upper Judith River Formation, Montana, and the lower Dinosaur Park Formation of Dinosaur Provincial Park, Alberta. It is referred to Chasmosaurinae based on the inferred elongate morphology. The typical chasmosaurine squamosal forms an obtuse triangle in dorsal view that tapers towards the posterolateral corner of the frill. In the dorsal view of the new taxon, the lateral margin of the squamosal is hatchet-shaped with the posterior portion modified into a constricted narrow bar that would have supported the lateral margin of a robust parietal. The new taxon represents the oldest chasmosaurine from Canada, and the first pre-Maastrichtian ceratopsid to have been collected on both sides of the Canada–US border, with a minimum north–south range of 380 km. This squamosal morphology would have given the frill of the new taxon a unique dorsal profile that represents evolutionary experimentation in frill signalling near the origin of chasmosaurine ceratopsids and reinforces biogeographic differences between northern and southern faunal provinces in the Campanian of North America.     

Coal-Mine Hollow Fill and Settling Pond Influences on Headwater Streams in Southern West Virginia, USA

The influences of coal-mine hollow fills and associated settling ponds in three headwater streams were assessed in southern West Virginia, USA. Fill drainage waters had elevated conductivities and metal concentrations, compared to a regional reference. Benthic macroinvertebrate richness was not affected consistently by the hollow fill drainages, relative to a regional reference, although a more tolerant community, lacking in Ephemeroptera taxa at most locations, was evident. Collector-filterer populations were elevated at monitoring stations directly below the settling ponds, indicating that the ponds’ presence influenced macroinvertebrate community structure by means of organic enrichment. Corbicula fluminea growth was enhanced in monitoring locations directly below the settling ponds, also an apparent result of organic enrichment. Results of acute water column toxicity testing with Ceriodaphnia dubia, sediment chronic toxicity testing with Daphnia magna, and in-situ ecotoxicological assessments with C. fluminea demonstrated no mortality or toxic influence at most of the sites tested below the ponds. The settling ponds appear to serve as sinks in collecting some, but not all, trace metals.     

Black yeast symbionts compromise the efficiency of antibiotic defenses in fungus-growing ants

Multiplayer symbioses are common in nature, but our understanding of the ecological dynamics occurring in complex symbioses is limited. The tripartite mutualism between fungus-growing ants, their fungal cultivars, and antibiotic-producing bacteria exemplifies symbiotic complexity. Here we reveal how black yeasts, newly described symbionts of the ant-microbe system, compromise the efficiency of bacteria-derived antibiotic defense in fungus-growing ants. We found that symbiotic black yeasts acquire nutrients from the ants' bacterial mutualist, and suppress bacterial growth. Experimental manipulation of ant colonies and their symbionts shows that ants infected with black yeasts are significantly less effective at defending their fungus garden from Escovopsis, a prevalent and specialized pathogen. The reduction of mutualistic bacterial biomass on ants, likely caused by black yeast symbionts, apparently reduces the quantity of antibiotics available to inhibit the garden pathogen. Success of the ant-fungal mutualism is directly dependent on fungus garden health. Thus our finding that black yeasts compromise the ants' ability to deal with the garden parasite indicates that it is an integral component of the symbiosis. This is further evidence that a full understanding of symbiotic associations requires examining the direct and indirect interactions of symbionts in their ecological community context.     

Evaluation of Ecologically Relevant Bioassays for a Lotic System impacted by a Coal-mine effluent, using Isonychia

Many studies investigating the ecotoxicological impacts of industrial effluents on fresh-water biota utilize standardized test species such as the daphnids, Ceriodaphnia dubia, Daphnia magna, and the fathead minnow, Pimephales promelas. Such species may not be the most predictive or ecologically relevant gauges of the responses of instream benthic macroinvertebrates to certain stressors, such as total dissolved solids. An indigenous species approach should be adopted, using a sensitive benthic collector-filterer following development of practical laboratory bioassays. In the Leading Creek Watershed (southeast Ohio), an aggregated approximately 99% reduction in mean mayfly abundance for all impacted sites was observed below a coal-mine effluent with mean specific conductivity (SC) of 8,109 (7,750-8,750) microS cm(-1). The mayfly, Isonychia, was exposed for 7-days to a simulation of this effluent, in lotic microcosms. Based on lowest observable adverse effect concentrations, Isonychia survival was a more sensitive endpoint to SC (1,562 microS cm(-1)) than were 7-day C. dubia survival and fecundity (3,730 microS cm(-1)). Isonychia molting, a potentially more sensitive endpoint, was also examined. Using traditional test species to assess discharges to surface water alone may not adequately protect benthic macroinvertebrate assemblages in systems impaired by discharges high in SC.     

Effects of Human Activity on Global Extinction Risk

Both natural and anthropogenic factors are important in determining a species' risk of extinction. Little work has been done, however, to quantify the magnitude of current anthropogenic influences on the extinction process. The purpose of this study is to determine the extent to which measures of the intensity of human activity are related to the global variability of two measures of species' susceptibility to extinction. We observed six indices of human activities in 90 countries, and we tested their relationships to the proportion of threatened bird and mammal species in each country, as well as to mammalian population density. After correcting for area effects, latitudinal diversity gradients, and body size (for population density), 28 to 50% of the remaining variation was statistically attributable to anthropogenic variables. Different measures of anthropogenic influence were most closely related to extinction risk in birds and mammals. Human population density was the variable most closely related to the proportion of threatened bird species per country, whereas per capita GNP was more important for mammal species. Mammalian population density strongly correlates with the extent of protected area per country. Contrary to suggestions in earlier literature, our work does not support the hypothesis that habitat loss is a prime contributor to species loss because frequencies of threatened birds and mammals are not closely related to patterns of land use.