Vegetative propagation of the red alga Rhodochorton purpureum by means of fragments that escape digestion by herbivores

Intertidal populations of the filamentous red alga Rhodochorton purpureujn (Lightf.) Rosenv. (Nemaliales, Acrochaetiaceae) in the Northern Netherlands grow as dense velvety turfs in the understory of large fucalean algae. The small and rather constant size of the turf (1 to 1.5 mm) and the high percentage of 'decapitated' filaments suggest that the turf is continually 'shorn' by herbivores. Two grazing invertebrates were found on the turf: the gastropod Littorina littorea (L.) and the amphipod Gamrnarus salinus Spooner Differences between the 2 grazers in the size of ingested R. purpureum fragments and in the proportion of ingested fragments with intact apices were attributed to differences in their feeding mechanisms. Both species egested live R. purpureum fragments In their faecal pellets. These fragments had the capacity to regenerate into new filaments when cultured in the laboratory. In the field small tufts of R. purpureurn filaments were found on bare substratum, originating from fragments contained in sticky, detritus-rich envelopes, probably faecal pellets. Experiments in unlalgal cultures showed that the regeneratlve capacity of fragments is very high, as it proceeds over d broad range of temperature and light conditions, even in total darkness We conclude that the capacity of R. purpureum fragments to escape digestion by herbivores probably plays an important role in vegetative propagation of the species

Nothing moves a surface: vacancy mediated surface diffusion

We report scanning tunneling microscopy observations, which imply that all atoms in a close-packed copper surface move frequently, even at room temperature. Using a low density of embedded indium `tracer' atoms, we visualize the diffusive motion of surface atoms. Surprisingly, the indium atoms seem to make concerted, long jumps. Responsible for this motion is an ultra-low density of surface vacancies, diffusing rapidly within the surface. This interpretation is supported by a detailed analysis of the displacement distribution of the indium atoms, which reveals a shape characteristic for the vacancy mediated diffusion mechanism that we propose.Comment: 4 pages; for associated movie, see http://www-lion.leidenuniv.nl/sections/cm/groups/interface/projects/therm

Zorgvuldig vertrouwen!

Politieke besluitvorming over intensieve veehouderij is regelmatig onderwerp van heftige discussies. Aan de orde zijn vele en onderling conflicterende waarden, opvattingen en feiten. Dit essay analyseert een besluitvormingsproces over de vestiging van een megastal. Tijdens dit proces bleken de verschillende belevingswerelden van boeren, burgers, politici en wetenschappers te botsen

Politieke besluitvorming over het Landbouwontwikkelingsgebied Witveldweg in de Gemeente Horst aan de Maas

LOGs (landbouwontwikkelingsgebieden) maken onderdeel uit van het landelijke reconstructiebeleid. Bijzonder voor Horst aan de Maas is dat een aantal agrarische ondernemers heeft aangegeven een zogenaamd Nieuw Gemengd Bedrijf (NGB) in dit gebied te willen vestigen. Hoewel de vergunningen nog niet zijn afgegeven, heeft de goedkeuring van de gebiedsvisie tot veel commotie geleid. In de aanloop naar de besluitvorming heeft vooral de mogelijke vestiging van het NGB tot veel maatschappelijke onrust en protesten geleid. De protesten hadden vooral betrekking op mogelijke gezondheidsrisico’s van fijnstof en MRSA (de ziekenhuisbacterie), de aantasting van het karakter van het landelijk gebied door een dergelijke grootschalige onderneming, de (stank)overlast en toename van verkeer(sonveiligheid). Daarnaast zijn er ook fundamenteel ethische bezwaren tegen het op een grootschalige manier houden van diere

Comparative analysis of foraging and habitat use by the sympatric Caribbean parrotfish Scarus vetula and Sparisoma viride (Scaridae)

On the fringing reef of Bonaire, Netherlands Antilles, a comparative study was made of habitat use, diet selection, foraging behaviour and food acquisition of the parrotfish species Scarus vetula and Sparisoma viride. The species are sympatric and live in the same reef habitats (depth zones). Both species show similar foraging selectivity, but exploit algal resources differently. Preferred food items are turf algae on substrates infested with endolithic algae, whereas crustose corallines are avoided. Foraging preferences are related to yield, i.e. the amount of AFDW (ash-free dry weight), protein and energy that can be harvested per bite. Foraging behaviour differs between the species. S. vetula takes more bites in long forays, has higher bite rates (no, of bites s(-1)), and makes fewer and smaller scars on grazing substrates than S. viride. Furthermore, S. vetula prefers flat substrate surfaces while adult S. viride graze by preference on concave surfaces. Species-specific differences in preference and utilization of grazing substrates are related to feeding mode. S. vetula employs a scraping feeding mode by which mainly epilithic algae are ingested. In contrast, S. viride is an excavating grazer that ingests large amounts of endolithic and crustose algae. Intake and assimilation of algal AFDW, protein and energy were quantified through a combination of laboratory feeding trials and field observations. S. vetula has lower food intake (mg AFDW bite(-1)) than S. viride (0.8 x 10(-3) x fish wet wt, FWW, and 2.3 x 10(-3) x FWW respectively), resulting from smaller (shallower) bites. Assimilation efficiencies of total AFDW, protein and energy by S. vetula were higher than in S. viride grazing on the same dead coral substrates, In spite of different feeding modes and different fractions of the primary production harvested, daily amounts of assimilated nutrients and energy are similar for both species, resulting from higher feeding rates (no. of bites h(-1)) and higher assimilation efficiency in S. vetula.</p

Dynamics of Lennard-Jones clusters: A characterization of the activation-relaxation technique

The potential energy surface (PES) of Lennard-Jones clusters is investigated using the activation-relaxation technique (ART). This method defines events in the configurational energy landscape as a two-step process: (a) a configuration is first activated from a local minimum to a nearby saddle-point and (b) is then relaxed to a new minimum. Although ART has been applied with success to a wide range of materials such as a-Si, a-SiO2 and binary Lennard-Jones glasses, questions remain regarding the biases of the technique. We address some of these questions in a detailed study of ART-generated events in Lennard-Jones (LJ) clusters, a system for which much is already known. In particular, we study the distribution of saddle-points, the pathways between configurations, and the reversibility of paths. We find that ART can identify all trajectories with a first-order saddle point leaving a given minimum, is fully reversible, and samples events following the Boltzmann weight at the saddle point.Comment: 8 pages, 7 figures in postscrip