67 research outputs found
Functional Effects of Parasites on Food Web Properties during the Spring Diatom Bloom in Lake Pavin: A Linear Inverse Modeling Analysis
This study is the first assessment of the quantitative impact of parasitic chytrids on a planktonic food web. We used a carbon-based food web model of Lake Pavin (Massif Central, France) to investigate the effects of chytrids during the spring diatom bloom by developing models with and without chytrids. Linear inverse modelling procedures were employed to estimate undetermined flows in the lake. The Monte Carlo Markov chain linear inverse modelling procedure provided estimates of the ranges of model-derived fluxes. Model results support recent theories on the probable impact of parasites on food web function. In the lake, during spring, when ‘inedible’ algae (unexploited by planktonic herbivores) were the dominant primary producers, the epidemic growth of chytrids significantly reduced the sedimentation loss of algal carbon to the detritus pool through the production of grazer-exploitable zoospores. We also review some theories about the potential influence of parasites on ecological network properties and argue that parasitism contributes to longer carbon path lengths, higher levels of activity and specialization, and lower recycling. Considering the “structural asymmetry” hypothesis as a stabilizing pattern, chytrids should contribute to the stability of aquatic food webs
Shedding Light on Vampires: The Phylogeny of Vampyrellid Amoebae Revisited
With the advent of molecular phylogenetic techniques the polyphyly of naked filose amoebae has been proven. They are interspersed in several supergroups of eukaryotes and most of them already found their place within the tree of life. Although the ‘vampire amoebae’ have attracted interest since the middle of the 19th century, the phylogenetic position and even the monophyly of this traditional group are still uncertain. In this study clonal co-cultures of eight algivorous vampyrellid amoebae and the respective food algae were established. Culture material was characterized morphologically and a molecular phylogeny was inferred using SSU rDNA sequence comparisons. We found that the limnetic, algivorous vampyrellid amoebae investigated in this study belong to a major clade within the Endomyxa Cavalier-Smith, 2002 (Cercozoa), grouping together with a few soil-dwelling taxa. They split into two robust clades, one containing species of the genus Vampyrella Cienkowski, 1865, the other containing the genus Leptophrys Hertwig & Lesser, 1874, together with terrestrial members. Supported by morphological data these clades are designated as the two families Vampyrellidae Zopf, 1885, and Leptophryidae fam. nov. Furthermore the order Vampyrellida West, 1901 was revised and now corresponds to the major vampyrellid clade within the Endomyxa, comprising the Vampyrellidae and Leptophryidae as well as several environmental sequences. In the light of the presented phylogenetic analyses morphological and ecological aspects, the feeding strategy and nutritional specialization within the vampyrellid amoebae are discussed
A multivariate model of stalking behaviours
In order to reveal the variations that exist among stalkers in terms of actual stalking
behaviours the range of offence actions that should be examined was derived from theoretical
accounts of the differences between offenders. Four distinct thematic foci were
hypothesised characterised by sexual, intimate, possessive and aggressive-destructive
modes of offender-victim interaction. To test these hypotheses 50 offences were content
analysed into 24 behavioural categories. The occurrence of these categories of
behaviour across all offences was examined using SSA-I. A modulating facet was proposed,
by analogy with previous studies, of violent sexual assaults that reflected the
intensity of personal contact the stalker imposes upon the victim, with the most intense
being the most differentiated and least frequent. The results lend support to the existence
of a intensity facet that modulates all four aspects identified from the published
literature, providing further evidence for a radex of criminality. This radex model is
used to indicate biases in the current sample of cases by postulating implicit elements
for future study. The implication of the radex model of stalking for the management of
and interventions in stalking are also considered as the basis for future explorations
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