A Unified Approach to Multi‐item Reliability

Summary The reliability of multi‐item scales has received a lot of attention in the psychometric literature, where a myriad of measures like the Cronbach's α or the Spearman–Brown formula have been proposed. Most of these measures, however, are based on very restrictive models that apply only to unidimensional instruments. In this article, we introduce two measures to quantify the reliability of multi‐item scales based on a more general model. We show that they capture two different aspects of the reliability problem and satisfy a minimum set of intuitive properties. The relevance and complementary value of the measures is studied and earlier approaches are placed in a broader theoretical framework. Finally, we apply them to investigate the reliability of the Positive and Negative Syndrome Scale, a rating scale for the assessment of the severity of schizophrenia.     

The scales of salticid spiders

The form and location of the scales of salticid spiders, as revealed by light and scanning electron microscopy, provide useful diagnostic characters for the separation of species, the assignment of species to genera, and a further understanding of the relationships between salticid genera. Partly on the basis of distinctions provided by scale structure, the new genus Platycryptus , type-species Aranea undata De Geer, 1778, is defined. Metaphidippus vitis Cockerell, 1894, is placed in the genus Sassacus Peckham, 1895, and Paromaevia michelsoni (Barnes), 1955, is returned to the genus Maevia . The placement of Eris, Hentzia, Icius, Metaphidippus, Phidippus , and Sassacus in the subfamily Dendryphantinae is substantiated; Tutelina and Zygoballus are added to this group. On the basis of common scale structure, Evarcha, Habrocestum, Menememerus, Phlegra, Platycryptus , and Sitticus are tentatively assigned to the subfamily Habrocestinae. Scales of Anasntis, Corythalia, Cosmophasis, Hyllus, Marpissa, Metacyrba, Pellenes, Plexippus, Salticus, Sarinda, and Thiodina are also described.     

How to compute the effective size of spatiotemporally structured populations using separation of time scales

Calculations to derive effective population size become highly complicated when complex population structure is considered. We provide an easy method of computing the effective size of a subdivided population with overlapping generations (a spatiotemporally structured population) using an approximation based on separation of time scales. We also numerically compute the effective size to verify the accuracy of the derived formula. Various interesting quantities, including moments of coalescent time, are readily derived using this approach.     

Sustained oscillations via coherence resonance in SIR

Sustained oscillations in a stochastic SIR model are studied using a new multiple scale analysis. It captures the interaction of the deterministic and stochastic elements together with the separation of time scales inherent in the appearance of these dynamics. The nearly regular fluctuations in the infected and susceptible populations are described via an explicit construction of a stochastic amplitude equation. The agreement between the power spectral densities of the full model and the approximation verifies that coherence resonance is driving the behavior. The validity criteria for this asymptotic approximation give explicit expressions for the parameter ranges in which one expects to observe this phenomenon.     

Molecular phylogeny, scale evolution and taxonomy of centrohelid heliozoa

Heliozoa are ubiquitous, unicellular phagotrophs with slender radiating axopodia for trapping prey. We sequenced 18S rRNA genes from 35 cultured centrohelid heliozoa (18 studied by electron microscopy) and 28 environmental libraries (18 freshwater, 10 marine), yielding 97 new sequences, this exceeding described species. Phylogenetic analyses show two major groups and that ancestral centrohelids probably had inner plate-like tangential and distinct outer radial silica scales, the latter diverging early into contrasting scale types seen in extant Pterocystis/Choanocystis and Acanthocystis/Raphidiophryidae. Scales were lost at least thrice. Pterocystis is paraphyletic, as was the classical family Acanthocystidae; Heterophrys was polyphyletic. Using scale morphology and rRNA sequences, we establish new families Pterocystidae (Pterocystis, Raineriophrys, Chlamydaster), Marophryidae (type Marophrys (Heterophrys) marina gen. et comb. nov.) and Choanocystidae, new suborders Pterocystina (Pterocystidae, Choanocystidae, Heterophryidae) and Acanthocystina (Acanthocystidae, Raphidiophryidae, Marophryidae), and ten new Pterocystis, Acanthocystis and Choanocystis species. Most clades are exclusively freshwater or exclusively marine; evolutionary transitions between these habitats have been rare.     

Predation Hot Spots: Large Scale Impact of Local Aggregations

Abstract   Broad scale survey distributions of fish are dominated by some extremely high catches. With a novel survey design we resolved the small-scale fish distribution in the spatio-temporal vicinity of these extreme hauls and showed that in the North Sea they generally do not occur in isolation. An additional case study where stomach contents of fish predators were analyzed revealed that they actually indicate aggregations of piscivorous fish predators on prey aggregations. We show that the predation impact can reach immense dimensions, an aggregation of more than 50 million juvenile cod (Gadus morhua) was entirely wiped out in 5 days by predatory whiting (Merlangius merlangus), aggregating on these juveniles in an area of approximately 18 km². The consumption of only 32 hot spots of similar magnitude as observed in our study adds up to the average size of an incoming North Sea cod year class. These findings support the hypothesis of predation as the major source of mortality in young-of-the-year demersal fish species and questions the generality of fish aggregation as an effective anti-predator strategy. This study highlights the system-wide structuring force of small-scale predation hot spots and further points to the importance of a more realistic implementation of local high-intensity predation events in food web models. Electronic supplementary material:   The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Plant traits respond to the competitive neighbourhood at different spatial and temporal scales

Background and Aims Clonal plants can plastically modify their traits in response to competition, but little is known regarding the spatio-temporal scale at which a competitive neighbourhood determines the variability in species traits. This study tests the hypothesis that the local neighbourhood can be expected to influence the processes that are involved in competition tolerance and avoidance, and that this effect depends on organ lifespan.Methods Fragments of the rhizomatous Elytrigia repens (Poaceae) were sampled in 2012 in experimental plant communities that varied in species identity and abundance. These communities had been cultivated since 2009 in mesocosms in a common garden. Fragment performance, shoot and clonal traits were measured, and the effects of past and present local neighbourhoods of five different radius sizes (5–25 cm) were examined. Past and present local neighbourhood compositions were assessed in 2011 and 2012, respectively.Key Results Most of the measured traits of E. repens responded to the local neighbourhood (5–10 cm radius), with an additional effect of the larger neighbourhood (20–25 cm radius) on ramet height, leaf dry matter content, maximal internode length and specific rhizome mass. Contrary to the expectation of the hypothesis, the temporal influence was not due to the organ lifespan. Indeed, five of the eight traits studied responded to both the past and present neighbourhoods. With the exception of specific rhizome mass, all trait responses were explained by the abundance of specific species.Conclusions This study demonstrates that the traits of a single clonal individual can respond to different competitive environments in space and time. The results thus contribute to the understanding of competition mechanisms.     

Limited influence of local and landscape factors on finescale gene flow in two pond‐breeding amphibians

Dispersal and gene flow within animal populations are influenced by the composition and configuration of the landscape. In this study, we evaluated hypotheses about the impact of natural and anthropogenic factors on genetic differentiation in two amphibian species, the spotted salamander (Ambystoma maculatum) and the wood frog (Lithobates sylvaticus) in a commercial forest in central Maine. We conducted this analysis at two scales: a local level, focused on factors measured at each breeding pond, and a landscape level, focused on factors measured between ponds. We investigated the effects of a number of environmental factors in six categories including Productivity, Physical, Land Composition, Land Configuration, Isolation and Location. Embryos were sampled from 56 spotted salamander breeding ponds and 39 wood frog breeding ponds. We used a hierarchical Bayesian approach in the program GESTE at each breeding pond and a random forest algorithm in conjunction with a network analysis between the ponds. We found overall high genetic connectivity across distances up to 17 km for both species and a limited effect of natural and anthropogenic factors on gene flow. We found the null models best explained patterns of genetic differentiation at a local level and found several factors at the landscape level that weakly influenced gene flow. This research indicates multiscale investigations that incorporate local and landscape factors are valuable for understanding patterns of gene flow. Our findings suggest that dispersal rates in this system are high enough to minimize genetic structuring and that current forestry practices do not significantly impede dispersal.     

KELP PATCH DYNAMICS IN THE FACE OF INTENSE HERBIVORY: STABILITY OF AGARUM CLATHRATUM (PHAEOPHYTA) STANDS AND ASSOCIATED FLORA ON URCHIN BARRENS1

The brown alga Agarum clathratum (Dumortier) is the only large, perennial, fleshy macrophyte commonly found on urchin‐dominated barrens in the northwestern North Atlantic. We examined the spatial and temporal stability of A. clathratum stands and their impact on algal recruitment in the Mingan Islands, northern Gulf of St. Lawrence. The stands were highly stable in space and time, with only small intersite variations. The percent cover of A. clathratum in 144‐m² areas increased by 6.5%–11.4% over a 2‐year period, and most changes in abundance occurred at the edge of the stands. The surface area of small (<13 m²) single stands of A. clathratum increased by approximately 1.8%·month^?1, although marked increases (>95%) occurred during winter, largely because adjacent stands merged into larger single stands. Mature stands of A. clathratum appear to enhance algal recruitment, as juvenile A. clathratum and the understory red alga Ptilota serrata (Kützing) were orders of magnitude more abundant inside than outside the stands. The experimental removal of the A. clathratum canopy (1‐m² portions) had no long‐term effect on the abundance of A. clathratum, which within 14 months had recolonized most of the cleared areas. In contrast to juvenile A. clathratum, the abundance of P. serrata rapidly decreased after canopy removal. Our results demonstrate that A. clathratum stands are a stable component of urchin barrens in spite of the heavy grazing that typically occurs there. Maintenance and expansion of A. clathratum stands and associated flora appear to depend on positive interactions with self‐defended adult A. clathratum.