Effect of seed predation on seed bank size and seedling recruitment of bush lupine (Lupinus arboreus)

Whether seed consumers affect plant establishment is an important unresolved question in plant population biology. Seed consumption is ubiquitous; at issue is whether seedling recruitment is limited by safe-sites or seeds. If most seeds inhabit sites unsuitable for germination, post-dispersal seed consumption primarily removes seeds that would otherwise never contribute to the population and granivory has minimal impacts on plant abundance. Alternatively, if most seeds ultimately germinate before they lose viability, there is greater potential for seed consumption to affect plant recruitment. Of the many studies on seed consumption, few ask how seed loss affects seedling recruitment for species with long-lived seed banks. We examined post-dispersal seed predation and seedling emergence in bush lupine (Lupinus arboreus), a woody leguminous shrub of coastal grasslands and dunes in California. We followed the fate of seeds in paired experimental seed plots that were either protected or exposed to rodent granivores in grassland and dune habitats. Significantly more seeds were removed by rodents in dunes than grasslands. In dunes, where rodent granivory was greatest (65% and 86% of seeds removed from plots by rodents in two successive years), there is a sparse seed bank (6.6 seeds m⁻²), and granivory significantly reduced seedling emergence (in the same two years, 18% and 19.4% fewer seedlings emerged from exposed versus protected plots), suggesting seed rather than safe-site limited seedling recruitment. In contrast, rodents removed an average of 6% and 56% of seeds from grassland plots during the same two years, and the grassland seed bank is 43-fold that of the dunes (288 seeds m⁻²). Even high seed consumption in the second year of the study only marginally influenced recruitment because seeds that escaped predation remained dormant. Burial of seeds in both habitats significantly reduced the percentage of seeds removed by rodents. Results suggest that granivores exert strong but habitat-dependent effects on lupine seed survival and seedling emergence. Received: 24 October 1996 / Accepted: 4 February 1997     

The effect of nitrogen and phosphorus addition on the growth,reproduction, and nutrient dynamics of two ericaceous shrubs

Summary Aboveground growth, reproduction, and foliar nitrogen and phosphorus contents of two ericaceous shrub species were compared over two seasons in (a) an undisturbed shrub bog (pocosin), and (b) a factorial fertilization design in which three levels each of nitrogen and phosphorus were added in all possible combinations. One species, Zenobia pulverulenta, is deciduous whereas the other species, Lyonia lucida, is evergreen. In the nutrient-poor undisturbed pocosin the two species exhibited similar foliar nitrogen and phosphorus concentrations and aboveground growth rates. Neither species flowered. In response to nutrient-addition Zenobia increased growth rates more than Lyonia. Foliar phosphorus concentrations of both species increased in response to enhanced phosphorus availability. in the first season neither species flowered in any treatment. In the second season Zenobia flowered only in the fertilized plots, with the most flowering in the high phosphorus treatments. I conclude that, by virtue of high growth rates and efficient use of nutrients and despite differences in leaf phenology and morphology, both Lyonia and Zenobia are successful in a competitive community under conditions of extremely low phosphorus availability. However, unlike Lyonia, Zenobia can take advantage of temporarily increased nutrient availability, which occurs following fire in the pocosin, to increase growth and reproduction.     

Non-invasive femoropopliteal assessment: is that angiogram really necessary?

A method of non-invasive preoperative assessment of chronically ischaemic legs was developed that used clinical data and data derived from Doppler ultrasonography to produce a numerical score that could be compared with an angiographic score for stenosis of the popliteal artery trifurcation. The two scoring systems were applied retrospectively to 144 legs after femorodistal bypass. A close correlation was observed (r = 0.89, p less than 0.001), and both systems tended to predict the level of grafting undertaken. A prospective comparison was then made in 81 ischaemic legs that were examined by arteriography; the correlation between the two scoring systems remained close (r = 0.89, p less than 0.001), and the level of bypass was correctly predicted by the non-invasive assessment in 44 of 50 legs that were operated on. Use of the non-invasive assessment subsequently greatly reduced the indications for preoperative arteriography in patients requiring femorodistal vascular reconstruction.     

Effects of Caste on the Expression of Genes Associated with Septic Injury and Xenobiotic Exposure in the Formosan Subterranean Termite

As social insects, termites live in densely populated colonies with specialized castes under conditions conducive to microbial growth and transmission. Furthermore, termites are exposed to xenobiotics in soil and their lignocellulose diet. Therefore, termites are valuable models for studying gene expression involved in response to septic injury, immunity and detoxification in relation to caste membership. In this study, workers and soldiers of the Formosan subterranean termite, Coptotermes formosanus, were challenged by bacterial injection or by no-choice feeding with a sublethal concentration (0.5%) of phenobarbital. Constitutive and induced expression of six putative immune response genes (two encoding for lectin-like proteins, one for a ficolin-precursor, one for the Down syndrome cell adhesion molecule, one for a chitin binding protein, and one for the gram-negative binding protein 2) and four putative detoxification genes (two encoding for cytochrome P450s, one for glutathione S-transferase, and one for the multi antimicrobial extrusion protein), were measured via quantitative real time polymerase chain reaction and compared within and among 1) colonies, 2) treatment types and 3) castes via ANOVA. Eight genes were inducible by septic injury, feeding with phenobarbital or both. Colony origin had no effect on inducibility or differential gene expression. However, treatment type showed significant effects on the expression of the eight inducible genes. Caste effects on expression levels were significant in five of the eight inducible genes with constitutive and induced expression of most target genes being higher in workers than in soldiers.     

Iron age to medieval entomogamous vegetation and Rhinolophus hipposideros roost in South-Eastern Wales (UK)

Karst cave systems are well developed in Wales (UK) and, in some instances, constitute important bat roosts. Ogof Draenen, near Blaenavon in south-east Wales, is the most recent major cave discovery (1994) with already > 70 km of passages explored spanning a vertical range of 148 m.With the exception of one small chamber (Siambre Ddu) located directly above the main Ogof Draenen system, very few bats have been noticed inside. Extensive accumulations of guano, attributable to Rhinolophus hipposideros, are however found in parts of the Ogof Draenen system. In places covering many square metres and sometimes building heaps > 0.5 m thick, these represent volumes not yet found in any other cave system in the British Isles.Although the date of the abandonment of the main Ogof Draenen system as a bat roost remains unknown, six radiocarbon dates on guano from Ogof Draenen place the occupation in the Iron Age to Medieval period at least. Palynological analysis was undertaken on ten samples distributed through the cave. Comparisons were made with a moss polster and a lake mud sample from the area to provide a first approximation of the regional modern pollen rain and with two modern guano samples, one from Siambre Ddu and one from Agen Allwedd cave (5 km to the north-west) to provide a temporal comparison with the fossil guano. Agen Allwedd cave currently is one of the largest active roosts for Lesser Horseshoe bats in Britain and lies close to the present northern limit of this endangered species in Europe.The main results are that (1) the cave appears to have been used both as a summer and a winter roost; (2) most of the Ogof Draenen guano is formed within c. 1600 ¹⁴C years and, if the largest heap is continuous, it has accumulated within 750 ¹⁴C years, i. e. 0.16 mm yr^− 1; 3) the fossil guano samples reflect a relatively closed oak forest with more abundant ivy (Hedera) and holly (Ilex) than at present; (4) insect-pollinated plants such as Ilex, Acer, Hedera and Impatiens glandulifera are over-represented in the guano samples; (5) in addition to the usual causes of bat roost decline (pesticides, pollution), in the case of Ogof Draenen, we may add entrance blocked by rock collapse and decline of the local forest cover as well as change in its composition.     

Probing the role of cysteine residues in the CheR methyltransferase

The CheR methyltransferase catalyzes the transfer of methyl groups from S-adenosylmethionine to specific glutamyl residues in bacterial chemoreceptor proteins. Studies with sulfhydryl reagents such as p-chloromercuribenzoate, N-ethylmaleimide, and 5,5'-dithiobis(2-nitrobenzoate) suggest that a cysteine residue is required for enzyme activity. The nucleotide sequence of the cheR gene predicts a 288-amino acid protein with cysteine residues at positions 31 and 229. To ascertain the role of these cysteine residues in the structure and function of the enzyme, oligonucleotide-directed mutagenesis was used to change each cysteine to serine. Whereas the Cys229-Ser mutation had essentially no effect on transferase activity, the Cys31-Ser mutation caused an 80% decrease in enzyme activity. The double mutant in which both cysteines were replaced by serines also had markedly reduced transferase activity. Preincubation of the wild type or Cys229-Ser proteins with either S-adenosylmethionine or beta-mercaptoethanol protected it from inhibition by sulfhydryl reagents, whereas prior incubation with the second substrate, the Tar receptor, gave partial protection. From these studies, Cys31 appears to be necessary for enzyme activity, and it seems to be located in the vicinity of the active site.     

Profile Analysis of Variance as a Tool for Analyzing Correlated Responses in Experimental Ecology

In ecological studies experiments are often designed in which the variables to be compared are not statistically independent. Examples include repeated measures of the same response by the same individual at different times, measurement of several traits on the same individual, and measurements taken from two or more types of organisms present together in the same experimental unit (e.g.) plot, cage, pond, etc.). This type of design violates several assumptions of the standard analysis of variance. These assumptions are examined and profile analysis, a modification of the standard analysis of variance which does not depend upon these assumptions, is presented. Simple instructions for performing profile analysis of variance using two common statistical packages for mainframe computers are provided in an appendix.     

John Marshall: the making of true spectacles.

In 1693 John Marshall of London devised a novel method of grinding batches of identical, good quality, lenses of a specified focal length. Its commendation by the Royal Society led to a trade war between Marshall and rivals in the Worshipful Company of Spectacle Makers. Despite initial opposition the method was rapidly adopted by London opticians and, though much modified, it forms the unrecognised basis of present day practice.     

Multiple forms of the CheB methylesterase in bacterial chemosensing

The methylesterase which catalyzes demethylation of chemotactic membrane receptors in Salmonella typhimurium has been purified and characterized. Two forms of the enzyme have been isolated from cell extracts. One corresponds in molecular weight, Mr = 37,000, and amino acid composition to the predicted product of the structural gene for the methylesterase, cheB. The other is a proteolytic fragment, Mr = 21,000, corresponding to the C-terminal three-fifths of the intact CheB protein. The specific activity of the 21-kDa enzyme is at least 15-fold greater than that of its 37-kDa precursor. We conclude that the CheB protein is composed of at least two structurally distinct portions: a C-terminal catalytic domain, and an N-terminal region which modulates esterase activity.