Soil selenium concentration and Kashin-Beck disease prevalence in Tibet, China

In order to investigate the correlation between the prevalence of Kashin-Back disease (KBD) and Se concentrations, natural soil samples and cultivated soil samples were collected from southeastern Tibet, China; and the soil Se concentrations were measured by atomic fluorescent spectrophotometer. It was found that the mean Se concentrations of natural soil samples in KBD areas, from the first layer to the third layer, were 0.17 mg/kg, 0.11 mg/kg, and 0.10 mg/kg, respectively, and in nondisease areas were 0.21 mg/kg, 0.24 mg/kg, and 0.13mg/kg, respectively. The mean Se concentrations of cultivated soil samples were 0.10 mg/kg in KBD areas and 0.23 mg/kg in non-disease areas, respectively. Soil Se concentrations in KBD areas were lower than that in non-disease areas, and the mean concentrations of soil Se in Tibet were lower than the average of China (0.29 mg/kg). Therefore, there is a close relationship between soil Se concentrations and KBD in Tibet. More studies should be concentrated on the impacts of Se deficiency in soils and its relationship with Se concentrations in food-grain and the human body in Tibet areas.     

The fitting of general force-of-infection models to wildlife disease prevalence data

Researchers and wildlife managers increasingly find themselves in situations where they must deal with infectious wildlife diseases such as chronic wasting disease, brucellosis, tuberculosis, and West Nile virus. Managers are often charged with designing and implementing control strategies, and researchers often seek to determine factors that influence and control the disease process. All of these activities require the ability to measure some indication of a disease's foothold in a population and evaluate factors affecting that foothold. The most common type of data available to managers and researchers is apparent prevalence data. Apparent disease prevalence, the proportion of animals in a sample that are positive for the disease, might seem like a natural measure of disease's foothold, but several properties, in particular, its dependency on age structure and the biasing effects of disease-associated mortality, make it less than ideal. In quantitative epidemiology, the "force of infection," or infection hazard, is generally the preferred parameter for measuring a disease's foothold, and it can be viewed as the most appropriate way to "adjust" apparent prevalence for age structure. The typical ecology curriculum includes little exposure to quantitative epidemiological concepts such as cumulative incidence, apparent prevalence, and the force of infection. The goal of this paper is to present these basic epidemiological concepts and resulting models in an ecological context and to illustrate how they can be applied to understand and address basic epidemiological questions. We demonstrate a practical approach to solving the heretofore intractable problem of fitting general force-of-infection models to wildlife prevalence data using a generalized regression approach. We apply the procedures to Mycobacterium bovis (bovine tuberculosis) prevalence in bison (Bison bison) in Wood Buffalo National Park, Canada, and demonstrate strong age dependency in the force of infection as well as an increased mortality hazard in positive animals.     

Factors influencing movement probabilities of big brown bats (Eptesicus fuscus) in buildings.

We investigated movements of female big brown bats (Eptesicus fuscus) roosting in maternity colonies in buildings in Fort Collins, Colorado (USA), during the summers of 2002, 2003, and 2005. This behavior can be of public health concern where bats that may carry diseases (e.g., rabies) move among buildings occupied by people. We used passive integrated transponders (PIT tags) to mark individual bats and hoop PIT readers at emergence points to passively monitor the use of building roosts by marked adult females on a daily basis during the lactation phase of reproduction. Multi-strata models were used to examine movements among roosts in relation to ambient temperatures and ectoparasite loads. Our results suggest that high ambient temperatures influence movements. Numbers of mites (Steatonyssus occidentalis) did not appear to influence movements of female bats among building roosts. In an urban landscape, periods with unusually hot conditions are accompanied by shifting of bats to different buildings or segments of buildings, and this behavior may increase the potential for contact with people in settings where, in comparison to their more regularly used buildings, the bats may be more likely to be of public concern as nuisances or health risks.     

Species‐level persistence probabilities for recovery and conservation status assessment

Recovery planning for species listed under the U.S. Endangered Species Act has been hampered by a lack of consistency and transparency, which can be improved by implementing a standardized approach for evaluating species status and developing measurable recovery criteria. However, managers lack an assessment method that integrates threat abatement and can be used when demographic data are limited. To help meet these needs, we demonstrated an approach for evaluating species status based on habitat configuration data. We applied 3 established persistence measures (patch occupancy, metapopulation capacity, and proportion of population lost) to compare 2 conservation strategies (critical habitat designated by the U.S. Fish and Wildlife Service and the Forest Service's Carbonate Habitat Management Strategy) and 2 threat scenarios (maximum limestone mining, removal of all habitat in areas with mining claims; minimum mining, removal of habitat only in areas with existing operations and high‐quality ore) against a baseline of existing habitat for 3 federally listed plant species. Protecting all area within the designated critical habitat maintained a similar level (83.9–99.9%) of species persistence as the baseline, whereas maximum mining greatly reduced persistence (0.51–38.4% maintained). The 3 persistence measures provided complementary insights reflecting different aspects of habitat availability (total area, number of patches, patch size, and connectivity). These measures can be used to link recovery criteria developed following the 3 R principles (representation, redundancy, and resilience) to the resulting improvements in species viability. By focusing on amount and distribution of habitat, our method provides a means of assessing the status of data‐poor species to inform decision making under the Endangered Species Act.     

Network inclusion probabilities and Horvitz-Thompson estimation for adaptive simple Latin square sampling

Consider a survey of a plant or animal species in which abundance or presence/absence will be recorded. Further assume that the presence of the plant or animal is rare and tends to cluster. A sampling design will be implemented to determine which units to sample within the study region. Adaptive cluster sampling designs Thompson (1990) are sampling designs that are implemented by first selecting a sample of units according to some conventional probability sampling design. Then, whenever a specified criterion is satisfied upon measuring the variable of interest, additional units are adaptively sampled in neighborhoods of those units satisfying the criterion. The success of these adaptive designs depends on the probabilities of finding the rare clustered events, called networks. This research uses combinatorial generating functions to calculate network inclusion probabilities associated with a simple Latin square sample. It will be shown that, in general, adaptive simple Latin square sampling when compared to adaptive simple random sampling will (i) yield higher network inclusion probabilities and (ii) provide Horvitz-Thompson estimators with smaller variability.     

Space-time Bayesian small area disease risk models: development and evaluation with a focus on cluster detection

This paper extends the spatial local-likelihood model and the spatial mixture model to the space-time (ST) domain. For comparison, a standard random effect space-time (SREST) model is examined to allow evaluation of each model’s ability in relation to cluster detection. To pursue this evaluation, we use the ST counterparts of spatial cluster detection diagnostics. The proposed criteria are based on posterior estimates (e.g., misclassification rate) and some are based on post-hoc analysis of posterior samples (e.g., exceedance probability). In addition, we examine more conventional model fit criteria including mean square error (MSE). We illustrate the methodology with a real ST dataset, Georgia throat cancer mortality data for the years 1994–2005, and a simulated dataset where different levels and shapes of clusters are embedded. Overall, it is found that conventional SREST models fair well in ST cluster detection and in goodness-of-fit, while for extreme risk detection the local likelihood ST model does best.     

Estimates of sex- and age-class-specific survival probabilities for a southern Great Barrier Reef green sea turtle population

Sex- and age-class-specific survival probabilities of a southern Great Barrier Reef green sea turtle population were estimated using a capture–mark–recapture (CMR) study and a Cormack–Jolly–Seber (CJS) modelling approach. The CMR history profiles for 954 individual turtles tagged over a 9-year period (1984–1992) were classified into three age classes (adult, subadult, juvenile) based on somatic growth and reproductive traits. Reduced-parameter CJS models, accounting for constant survival and time-specific recapture, fitted best for all age classes. There were no significant sex-specific differences in either survival or recapture probabilities for any age class. Mean annual adult survival was estimated at 0.9482 (95% CI: 0.92–0.98) and was significantly higher than survival for either subadults or juveniles. Mean annual subadult survival was 0.8474 (95% CI: 0.79–0.91), which was not significantly different from mean annual juvenile survival estimated at 0.8804 (95% CI: 0.84–0.93). The time-specific adult recapture probabilities were a function of sampling effort but this was not the case for either juveniles or subadults. The sampling effort effect was accounted for explicitly in the estimation of adult survival and recapture probabilities. These are the first comprehensive sex- and age-class-specific survival and recapture probability estimates for a green sea turtle population derived from a long-term CMR program.Communicated by M.S. Johnson, Crawley     

A new satellite-based methodology for continental-scale disturbance detection.

The timing, location, and magnitude of major disturbance events are currently major uncertainties in the global carbon cycle. Accurate information on the location, spatial extent, and duration of disturbance at the continental scale is needed to evaluate the ecosystem impacts of land cover changes due to wildfire, insect epidemics, flooding, climate change, and human-triggered land use. This paper describes an algorithm developed to serve as an automated, economical, systematic disturbance detection index for global application using Moderate Resolution Imaging Spectroradiometer (MODIS)/Aqua Land Surface Temperature (LST) and Terra/MODIS Enhanced Vegetation Index (EVI) data from 2003 to 2004. The algorithm is based on the consistent radiometric relationship between LST and EVI computed on a pixel-by-pixel basis. We used annual maximum composite LST data to detect fundamental changes in land-surface energy partitioning, while avoiding the high natural variability associated with tracking LST at daily, weekly, or seasonal time frames. Verification of potential disturbance events from our algorithm was carried out by demonstration of close association with independently confirmed, well-documented historical wildfire events throughout the study domain. We also examined the response of the disturbance index to irrigation by comparing a heavily irrigated poplar tree farm to the adjacent semiarid vegetation. Anomalous disturbance results were further examined by association with precipitation variability across areas of the study domain known for large interannual vegetation variability. The results illustrate that our algorithm is capable of detecting the location and spatial extent of wildfire with precision, is sensitive to the incremental process of recovery of disturbed landscapes, and shows strong sensitivity to irrigation. Disturbance detection in areas with high interannual variability of precipitation will benefit from a multiyear data set to better separate natural variability from true disturbance.     

Spatial analysis of semi-arid patchy vegetation by the cumulative distribution of patch boundary spacings and transition probabilities

The vegetative cover in semi-arid lands typically occurs as patches of individual species more or less separated from one another by bare ground. We have adapted two methods to quantify the spatial pattern of such cover from measurements across patches on transects.Transects were laid in several directions across digital maps of the land surface or across the land itself, and the distances between successive patch boundaries were measured. The distances were ranked in order, and their cumulative distributions were computed and modeled with gamma functions. The parameters of the model provided estimates of the mean distance across patches. The means for different directions were further tested for anisotropy. Transitions between classes on the transects estimate the probabilities with which the different species occur next to others (and to bare ground) and so describe the arrangement of the patches occupied by the different species.The methods were tested with data from mosaic patterns at three semi-arid sites dominated by the tussock grass Stipa tenacissima. The differences in the estimated mean boundary spacings from site to site accorded with prior qualitative assessment, as did the estimated anisotropy. The transition matrices and the estimated proportions of cover showed the dominance of the bare soil with which all the individual species are intimately associated. The transitions also suggest the presence of both positive and negative relations among the main species. Those between Stipa tenacissima and Brachypodium retusum seem to be facilitative, as do those between this grass and the shrub Anthyllis cytisoides. In contrast, Globularia alypum seems to inhibit the other species.We also estimated transition probabilities geostatistically by summing the indicator variograms of the individual species. Standard variogram models were then fitted to describe the ordered series of values, and these again produced results that accorded with visual impressions.     

Satellite detection of bird communities in tropical countryside.

The future of biodiversity hinges partly on realizing the potentially high conservation value of human-dominated countryside. The characteristics of the countryside that promote biodiversity preservation remain poorly understood, however, particularly at the fine scales at which individual farmers tend to make land use decisions. To address this problem, we explored the use of a rapid remote sensing method for estimating bird community composition in tropical countryside, using a two-step process. First, we asked how fine-grained variation in land cover affected community composition. Second, we determined whether the observed changes in community composition correlated with three easily accessible remote sensing metrics (wetness, greenness, and brightness), derived from performing a tasseled-cap transformation on a Landsat Enhanced Thematic Mapper Plus image. As a comparison, we also examined whether the most commonly used remote sensing indicator in ecology, the Normalized Difference Vegetation Index (NDVI), correlated with community composition. We worked within an agricultural landscape in southern Costa Rica, where the land comprised a complex and highly heterogeneous mosaic of remnant native vegetation, pasture, coffee cultivation, and other crops. In this region, we selected 12 study sites (each < 60 ha) that encompassed the range of available land cover possibilities in the countryside. Within each site, we surveyed bird communities within all major land cover types, and we conducted detailed field mapping of land cover. We found that the number of forest-affiliated species increased with forest cover and decreased with residential area across sites. Conversely, the number of agriculture-affiliated species using forest increased with land area devoted to agricultural and residential uses. Interestingly, we found that the wetness and brightness metrics predicted the number of forest- and agriculture-affiliated species within a site as well as did detailed field-generated maps of land cover. In contrast, NDVI and the closely correlated greenness metric did not correlate with land cover or with bird communities. Our study shows the strong potential of the tasseled-cap transformation as a tool for assessing the conservation value of countryside for biodiversity.     

Survival and remigration probabilities for loggerhead turtles (Caretta caretta) nesting in the eastern Gulf of Mexico

Few long-term mark-recapture tagging datasets exist to estimate population parameters for loggerhead sea turtle (Caretta caretta) recovery units. Using a two-state open robust design model, we analyzed a 20-year (1990–2009) mark-recapture dataset from the Keewaydin Island loggerhead nesting assemblage off the southwest coast of Florida (USA) in the eastern Gulf of Mexico. For this analysis, 2,292 turtle encounters were evaluated, representing 841 individual nesting turtles. Survival was estimated at 0.73 (95 % CI 0.69–0.76). This estimate is comparable with survival estimates elsewhere in the Peninsular Florida subpopulation and is among the lowest estimates for the Northwest Atlantic loggerhead population. We documented no changes in remigration rates or clutch frequency over time. These are the first survival and remigration probabilities estimated for a loggerhead nesting assemblage in the eastern Gulf of Mexico.     

Sampling design trade-offs in occupancy studies with imperfect detection: examples and software.

Researchers have used occupancy, or probability of occupancy, as a response or state variable in a variety of studies (e.g., habitat modeling), and occupancy is increasingly favored by numerous state, federal, and international agencies engaged in monitoring programs. Recent advances in estimation methods have emphasized that reliable inferences can be made from these types of studies if detection and occupancy probabilities are simultaneously estimated. The need for temporal replication at sampled sites to estimate detection probability creates a trade-off between spatial replication (number of sample sites distributed within the area of interest/inference) and temporal replication (number of repeated surveys at each site). Here, we discuss a suite of questions commonly encountered during the design phase of occupancy studies, and we describe software (program GENPRES) developed to allow investigators to easily explore design trade-offs focused on particularities of their study system and sampling limitations. We illustrate the utility of program GENPRES using an amphibian example from Greater Yellowstone National Park, U.S.A.     

Transport of brine shrimps via the digestive system of migratory waders: dispersal probabilities depend on diet and season

Waterbirds are known to disperse invertebrate propagules that survive gut passage, but there is very little information about how the probability of dispersal changes at different times of the annual cycle when birds move in different directions, or how it is affected by changes in diet. We studied internal transport of brine shrimp Artemia cysts by migratory waders in the Odiel saltworks in south-west Spain. Viable cysts of parthenogenetic Artemia were abundant in the faeces and regurgitated pellets of redshank Tringa totanus, pellets of spotted redshank T. erythropus, and faeces of black-tailed godwit Limosa limosa during spring and/or autumn migrations in 2001–2002, but were not recorded during winter. Godwits did not produce pellets, and spotted redshank faeces were not sampled. Significant correlations between the number of cysts in a pellet or faecal sample and the proportion of that sample constituted by Artemia adults suggested that most cysts were ingested while in the ovisacs of gravid females. The proportion of cysts destroyed during digestion increased when accompanied by harder food items or grit, and when fewer cysts were ingested. The median number of intact cysts was higher in redshank faeces than in their pellets, but cysts extracted from pellets were more likely to hatch. A higher proportion of redshank pellets contained Artemia cysts in spring than in autumn, but more redshank migrated through the area in autumn. Significantly fewer cysts were recorded in redshank pellets in winter than in spring or autumn. Our results confirm that there is potential for long-distance dispersal of Artemia cysts via waders during both northwards (spring) and southwards (autumn) migrations.     

The fish fauna of a seasonally closed Australian estuary. Is the prevalence of estuarine-spawning species high?

The fish at sites located throughout the large, seasonally closed Wilson Inlet, on the southern coast of Western Australia, were sampled bimonthly between September 1987 and April 1989. Seine nets were used to sample nearshore shallow waters, while gill nets were employed in slightly more offshore and deeper waters. Twenty species were recorded in the shallows, of which the three species of atherinid and the three species of goby comprised >97% of the total catch. In terms of number of individuals, the 27 species recorded in gill nets in the deeper waters were dominated by Cnidoglanis macrocephalus and Platycephalus speculator, and to a lesser extent Engraulis australis, Aldrichetta forsteri, Sillaginodes punctata and Arripis georgianus. Fifty-five percent of the species recorded in the nearshore shallow waters and 18% of those in offshore deeper waters spawn within Wilson Inlet; these species contributed 98.5 and 63.0%, respectively, to the total catches in those waters. Classification and ordination showed that the composition of the fauna in the shallows was similar at all sites throughout the large basin and did not change conspicuously with season. However, the composition of catches taken in offshore waters differed between the lower part of the basin and the middle and upper regions of the basin, which in turn differed from those in the saline reaches of a tributary river. The four diagnostic species of the lower estuary were all marine species, while the three diagnostic species in the river included a marine species (Mugil cephalus) that often penetrates far upstream in other systems, and a species which was confined to the rivers (Acanthopagrus butcheri). The composition of the fish fauna in the offshore waters of the lower estuary between the middle of spring and middle of autumn was different in 1987/1988 (when the estuary mouth was open for only the first two months of that period) from that in 1988/1989 (when the mouth was open for the whole of that period). This difference is related to the greater number of marine species that were retained in the first of these years, when the estuary was open to the ocean for only a short period. The greater retention of marine species in 1987/1988 than in 1988/1989 probably reflects a far lower level of freshwater flusing and/or a less marked decline in salinity.     

Using habitat suitability index and particle dispersion models for early detection of marine invaders.

Eradication and control of invasive species are often possible only if populations are detected when they are small and localized. To be efficient, detection surveys should be targeted at locations where there is the greatest risk of incursions. We examine the utility of habitat suitability index (HSI) and particle dispersion models for targeting sampling for marine pests. Habitat suitability index models are a simple way to identify suitable habitat when species distribution data are lacking. We compared the performance of HSI models with statistical models derived from independent data from New Zealand on the distribution of two nonindigenous bivalves: Theora lubrica and Musculista senhousia. Logistic regression models developed using the HSI scores as predictors of the presence/absence of Theora and Musculista explained 26.7% and 6.2% of the deviance in the data, respectively. Odds ratios for the HSI scores were greater than unity, indicating that they were genuine predictors of the presence/ absence of each species. The fit and predictive accuracy of each logistic model were improved when simulated patterns of dispersion from the nearest port were added as a predictor variable. Nevertheless, the combined model explained, at best, 46.5% of the deviance in the distribution of Theora and correctly predicted 56% of true presences and 50% of all cases. Omission errors were between 6% and 16%. Although statistical distribution models built directly from environmental predictors always outperformed the equivalent HSI models, the gain in model fit and accuracy was modest. High residual deviance in both types of model suggests that the distributions realized by Theora and Musculista in the field data were influenced by factors not explicitly modeled as explanatory variables and by error in the environmental data used to project suitable habitat for the species. Our results highlight the difficulty of accurately predicting the distribution of invasive marine species that exhibit low habitat occupancy and patchy distributions in time and space. Although the HSI and statistical models had utility as predictors of the likely distribution of nonindigenous marine species, the level of spatial accuracy achieved with them may be well below expectations for sensitive surveillance programs.     

Same-sex sexual behavior in insects and arachnids: prevalence, causes, and consequences

Same-sex sexual (SSS) behavior represents an evolutionary puzzle: whilst associated costs seem obvious, positive contributions to fitness remain unclear. Various adaptive explanations have been proposed and thorough reviews exist for vertebrates, but a thorough synthesis of causes for SSS behavior in invertebrates is lacking. Here we provide evidence for such behavior in ~110 species of insects and arachnids. Males are more frequently involved in SSS behavior in the laboratory than in the field, and isolation, high density, and exposure to female pheromones increase its prevalence. SSS behavior is often shorter than the equivalent heterosexual behavior. Most cases can be explained via mistaken identification by the active (courting/mounting) male. Adaptive explanations, such as sperm transfer of the mounting male via the mounted one or gaining experience by young males, are of limited general significance. The passive (being courted/mounted) male is sometimes responsible for this “mistake” by releasing sex pheromones or carrying female pheromones that were attached to his cuticle during prior mating activity. Passive males often resist courting/mating attempts. SSS behavior in arthropods is predominantly based on mistaken identification and is probably maintained because the cost of rejecting a valid opportunity to mate with a female is greater than that of mistakenly mating with a male. Many species exhibiting SSS behavior also mate with related species, another case of mistaken identification. Future research should focus on uncovering the situations/contexts in which mistaken identification is more or less costly for males.     

Dynamics of prion disease transmission in mule deer.

Chronic wasting disease (CWD), a contagious prion disease of the deer family, has the potential to severely harm deer populations and disrupt ecosystems where deer occur in abundance. Consequently, understanding the dynamics of this emerging infectious disease, and particularly the dynamics of its transmission, has emerged as an important challenge for contemporary ecologists and wildlife managers. Although CWD is contagious among deer, the relative importance of pathways for its transmission remains unclear. We developed seven competing models, and then used data from two CWD outbreaks in captive mule deer and model selection to compare them. We found that models portraying indirect transmission through the environment had 3.8 times more support in the data than models representing transmission by direct contact between infected and susceptible deer. Model-averaged estimates of the basic reproductive number (R0) were 1.3 or greater, indicating likely local persistence of CWD in natural populations under conditions resembling those we studied. Our findings demonstrate the apparent importance of indirect, environmental transmission in CWD and the challenges this presents for controlling the disease.     

Spatial correlation between the prevalence of transmissible spongiform diseases and British soil geochemistry

Transmissible spongiform encephalopathies (TSEs) are a group of fatal neurological conditions affecting a number of mammals, including sheep and goats (scrapie), cows (BSE), and humans (Creutzfeldt-Jakob disease). The diseases are widely believed to be caused by the misfolding of the normal prion protein to a pathological isoform, which is thought to act as an infectious agent. Outbreaks of the disease are commonly attributed to contaminated feed and genetic susceptibility. However, the implication of copper and manganese in the pathology of the disease, and its apparent geographical clustering, have prompted suggestions of a link with trace elements in the environment. Nevertheless, studies of soils at regional scales have failed to provide evidence of an environmental risk factor. This study uses geostatistical techniques to investigate the correlations between the distribution of TSE prevalence and soil geochemical variables across the UK according to different spatial scales. A similar spatial pattern in scrapie and BSE occurrence is identified, which may be linked with increasing pH and total organic carbon, and decreasing iodine concentration. However, the pattern also resembles that of the density of dairy farming. Nevertheless, despite the low spatial resolution of the TSE data available for this study, the fact that significant correlations are detected indicates there is a possibility of a link between soil geochemistry, scrapie, and BSE. It is suggested that further investigations of the prevalence of TSE and environmental exposure to trace metals should take into account the factors affecting their bioavailability.     

Predator detection and avoidance: Ornamentation of tube-caps of Diopatra spp. (Polychaeta: Onuphidae)

One strategy for predator avoidance involves the creation of a structural refuge. Onuphid polychaetes characteristically ornament above-sediment portions of their tubes (=tube-caps) with shell and algal debris. These species feed on the sediment surface through an opening in the tube-cap, and thus the ability to detect a surface predator while feeding would be advantageous. An investigation of the function of the ornamentation in Diopatra spp. suggests that ornamentation facilitates predator detection and avoidance. Three intensities of mechanical disturbance were applied directly to D. ornata tube-caps. When ornamented tube-caps were stimulated, the response of worms to the three intensities were significantly different, and increased in duration with greater intensities. In contrast, when no ornamentation was present, the responses were not significantly different, and were similar to the low-intensity response when ornamentation was present. This suggests that ornamentation should allow a worm to distinguish between harmful (high intensity due to mobile epifaunal predators) and profitable (low intensity due to drift algae) disturbances, and furthermore, worms with ornamented tube-caps should be more successful in escaping surface predators. Densities of intertidal populations of D. cuprea at Tom's Cove, Virginia, USA, correlated with the amount of tube ornamentation, consistent with this predator detection and avoidance hypothesis. Final tube-cap lengths of laboratory D. ornata and field D. cuprea were inversely related to the size of attached debris. When large debris was attached, cap formation ceased earlier and caps were shorter than when small debris or no debris was attached. Cryptic and food-catching functions would predict that highly ornamented tubes would be most advantageous, while only a few large debris would be required for disturbance transmission. Laboratory specimens showed no selectivity between 0.5 or 1.5 cm² shell; or 1.0 cm² or 3 to 8 cm² algae, and utilized shell and algae when available and according to relative abundance. Tube-caps of field specimens also showed positive correlations between shell attached and shell abundance in the local sediment. While such lack of selectivity may enhance cryptic properties of the tube-cap, it is argued that conditions seldom exist which would permit selectivity of debris size or of specific material. These data are consistent with the hypothesis that ornamentation functions as a created refuge for predator detection and avoidance and further suggest that the availability of ornamental debris in the environment indirectly can affect these species' distributions and abundances.     

Hotspot detection and clustering: ways and means

This paper reviews the development of methods for the analysis of hotspots and clustering. Discussion focusses on different data types and the usefulness of density estimation, scan testing and model-based approaches to clustering. Various application areas are considered ranging from ecology, over health mapping to genomics and landscape analysis. A discussion of software availability is also provided.