VI.—Some New Points in the Pre-Cambrian Geology of Anglesey

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Vol. 36, No. 2

Labor Relations Collaboration from Start to Finish: A Case Study on a First Contract for Westminster Colorado Firefighters, by Lisa R. Callaway and Rebecca C. Barnard Recent Developmentshttps://scholarship.kentlaw.iit.edu/iperr/1109/thumbnail.jp

SNPMClust: Bivariate Gaussian Genotype Clustering and Calling for Illumina Microarrays

SNPMClust is an R package for genotype clustering and calling with Illumina microarrays. It was originally developed for studies using the GoldenGate custom genotyping platform but can be used with other Illumina platforms, including Infinium BeadChip. The algorithm first rescales the fluorescent signal intensity data, adds empirically derived pseudo-data to minor allele genotype clusters, then uses the package mclust for bivariate Gaussian model fitting. We compared the accuracy and sensitivity of SNPMClust to that of GenCall, Illumina's proprietary algorithm, on a data set of 94 whole-genome amplified buccal (cheek swab) DNA samples. These samples were genotyped on a custom panel which included 1064 SNPs for which the true genotype was known with high confidence. SNPMClust produced uniformly lower false call rates over a wide range of overall call rates

The Advantages of Clonal Integration Under Different Ecological Conditions: a Community-Wide Test

The connectedness of clonal plants has been shown to promote survival and growth in a variety of single-species, single-factor studies, but experiments comparing the relative advantages of clonality across multiple habitats and species are rare, raising the concern that generalizations about the benefits of clonality might be biased by the particular species or habitat studied. We studied the importance of clonal integration in southeastern USA salt marsh plants, using all six of the common clonal species in the community, by following the success of intact and severed clonal fragments invading three habitat treatments. Clonal integration was most important for growth of clonal fragments invading hypersaline salt pans, likely because parent clones supplied salt-stressed fragments with water; of moderate importance for fragments invading the neighbors-clipped treatment, likely because parent clones supplied fragments with resources enabling rapid exploitation of unused patches; and least important when neighbors were present, consistent with suggestions that size-based asymmetrical competition is relatively unimportant in clonal plants. Our results indicate that the importance of clonal integration can differ between habitats and species within a community. We encourage explicit consideration of these potential sources of variability to best understand the importance of clonal integration in the field

Impact of a Parasitic Plant on the Structure and Dynamics of Salt Marsh Vegetation

We investigated the effect of a native parasitic plant, Cuscuta salina, on the structure and dynamics of the plant community in a California salt marsh. Cuscuta was common in the middle marsh zones. The abundance of Cuscuta was positively correlated with the abundance of Limonium californicum at two sampling scales (0.25— and ≈\approx40—m2 quadrats). Sampling at the scale of individual plants indicated that the dominant plant in the marsh, Salicornia virginica, was preferred by Cuscuta as a host over Arthrocnemum subterminale, Limonium californicum, and Frankenia salina. This result was confirmed with host—choice experiments in the field. Based on spatial correlations and host—choice experiments, we hypothesized that Cuscuta indirectly facilitated Limonium and Frankenia, increasing plant diversity and initiating vegetation cycles. This hypothesis was supported by sampling patches with different histories of Cuscuta infection. Patches with recent heavy Cuscuta infection had reduced Salicornia biomass and increased Limonium and Frankenia biomass relative to controls. This effect was most pronounced at higher elevations and in larger, older patches. The hypothesis was also supported by sampling permanent quadrats repeatedly over time. The probability that Cuscuta would invade a quadrat increased with increasing cover of Salicornia. Quadrats containing Cuscuta increased in Limonium and Frankenia cover between censuses relative to quadrats lacking Cuscuta. Our results indicate that parasitic plants can have strong effects on the structure and dynamics of natural vegetation assemblages. However, these effects are mediated by physical and biological gradients across the landscape

Facilitation May Buffer Competitive Effects: Indirect and Diffuse Interactions Among Salt Marsh Plants

Direct interactions among plant species may be highly modified by indirect or diffuse effects within a multispecies community. We investigated the direct and diffuse effects of two salt marsh perennials, Monanthechloe littoralis and Arthrocnemum subterminale, on winter annuals and the perennial herb Limonium californicum in a salt marsh in central California. In permanent plots, Monanthechloe had expanded substantially in the upper marsh over the past 13 yr, while Arthrocnemum and all annual species had decreased. These dynamics suggest that Monanthechloe may directly outcompete most other species in the upper marsh. In contrast, Arthrocnemum is known to facilitate some annual species. In our field experiments, Monanthechloe strongly suppressed Arthrocnemum, all four common annual species, and Limonium in direct interactions. In contrast, Arthrocnemum directly facilitated the winter annuals Parapholis incurva and Lasthenia glabrata, competed with Spergularia marina, and did not have a significant effect on Limonium. However, when the combined effects of Monanthechloe and Arthrocnemum were tested, Arthrocnemum ameliorated the negative effect of Monanthechloe on all four species. Although isolated Arthrocnemum competed with Spergularia and had no direct effects on Limonium, Arthrocnemum in the presence of Monanthechloe facilitated both species. We hypothesize that Arthrocnemum buffered the strong competitive effects of Monanthechloe on Lasthenia and Parapholis via direct positive effects and benefited Spergularia and Limonium through its competitive effect on Monanthechloe. These findings add to the growing body of literature emphasizing the importance of diversity and interdependence in the functioning of plant communities