Predictive models in spatially and temporally variable freshwater systems

Abstract This paper discusses the relationships between scaling and predictability in ecosystems. The logical basis of ecosystem modelling is explored using ideas first developed in complexity theory and analogies with the behaviour of complex adaptive systems. Any ecological model is a scale-dependent entity and both empirical and dynamic models of freshwater systems have their strengths and weaknesses. The logical basis of modelling using functional groups is explored. I conclude that such an approach can be justified and that such models have predictive power. Any predictive model of freshwater systems must take the major scales of external (atmospheric and catchment) forcing into account as well as the scales of key processes in the ecosystem itself. The importance of so-called ‘pink noise’ spectra, which arise both from external forcing and the internal dynamics of dynamic systems, is noted. The key scales of pattern and process in freshwater ecosystems are discussed in relation to the properties of the major functional groups. In order to have predictive power, I conclude that models of freshwater systems must include sediment exchanges and the properties of aquatic macrophytes as well as water column interactions and the pelagic components. When viewed at the scale of functional groups and the major biogeochemical processes, freshwater ecosystems may not be as complex as is often assumed.     

The viability of seeds of rainforest species after experimental soil burials under tropical wet lowland forest in north-eastern Australia

Seed samples of 50 rainforest species representative of all successional stages from tropical lowland forests in north-eastern Australia were buried in nylon material bags under rainforest for periods up to 2 years. The seed samples were exhumed after 6 weeks, 6 months, 1 year and 2 years, and their viabilities assessed. Substantial portions of the samples of 31 species of pioneer and early and late secondary species retained viability for 2 years in the buried samples, and germinated immediately they were exposed to greenhouse conditions. In approximately one-third of these species, the dormancy was completely enforced by the burial conditions since fresh, mature seed germinated immediately in the greenhouse. The remainder of the long-lived seeds showed some evidence of variable initial periods of innate dormancy produced by their hard, impermeable coats. There was no indication that the burial conditions enforced or induced any dormancy in the seeds of primary forest trees. The mean viability of the primary forest seeds examined was 10% after 6 months burial. The soft-coated seeds were obligate immediate germinators; they germinated or died. The remainder showed variably delayed germination, and this was interpreted as a mechanical dormancy produced by their leathery, fibrous, or stony endocarps. The group of late secondary species sampled contained both obligate immediate germinators and seeds with well developed dormancy mechanisms. Many of the buried 'seedlings’ of primary forest species remained alive for a year or more attached to seeds, demonstrating the ability of the larger primary seeds to sustain seedlings under conditions adverse to photosynthesis and growth. Some seedlings of Castanospermum australe were alive and were transplanted successfully after 2 years burial. This enables primary forest species to stock seedlings on the forest floor in contrast to the secondary species which store seed in the soil.     

Uptake and Accumulation of {alpha}-Naphthalene Acetic Acid by Cell Suspensions of Galium mollugo L.

Fidgeon, C. and Wilson, G. 1988. Uptake and accumulation ofa-naphthalene acetic acid by cell suspensions of Galium mollugoL.—J. exp. Bot. 39: 241-249. Galium mollugo cell suspensions require -NAA for continued growthand cell division. The kinetics of -NAA uptake from the medium(B₅) by Galium cells was assessed using 1-¹⁴C -NAA in a standardratio of cells to medium (0.25 g: 2.5 cm³). It was found thatthe uptake of -NAA was rapid, over 90% being taken up within4 h. Cells which had accumulated -NAA for 4 h or more did notrelease it back into the medium. It was found that Galium cellsaccumulated -NAA against a significant concentration gradient;suggesting the participation of an active component in the uptakemechanism. The effect of free-space and surface adsorption onthe uptake of -NAA was determined by means of a repeated washtechnique. These two factors were found to be of importanceonly during the first hour of uptake. Neither dead cells norplasmolysed cells absorbed -NAA. It is clear that, in the normal growth cycle, Galium cells cantake up the available -NAA within 3 or 4 h of inoculation andthat this can stimulate a cell division response of 3-4 generationsover the subsequent 14 d. Key words: Galium, cell suspension, -naphthalene acetic acid     

Pollination ecology of Christmas Bells (Blandfordia nobilis): Patterns of standing crop of nectar

Standing crop of nectar (both volume and sugar concentrations) was measured from flowers in a population of Blandfordia nobilis. Nectar in this honeyeater-pollinated species was extremely viscous during one flowering season and averaged approximately 95% sugar, while it averaged only 25% sugar two seasons later. Nectar volume was significantly and negatively correlated with sugar concentration on nine often sampling dates. There was no significant relationship between either nectar volume or sugar concentration and a number of measures of plant size (inflorescence height, numbers of open flowers, buds, spent flowers and total flowers). Similarly, no consistent relationship was found between measures of flower size and reward level. There were significant positive correlations between the reward (both volume and sugar concentration) offered by blossoms on the same plant. The nectar volume of flowers from nearest neighbouring inflorescences were significantly and positively correlated with one another on three of six occasions while the sugar concentrations of those blossoms were significantly correlated on just two of six sampling dates. There was no significant difference in reward (both volume and sugar concentration) between open flowers and those bagged to exclude pollinators. There was significant heterogeneity in the nectar volumes offered by plants to pollinators during a single flowering season.     

A quantitative analysis of habitat preferences of Woodcock Scolopax rusticola in the breeding season

In Britain, prior to breeding, Woodcock Scolopax rusticola switch from feeding on pastures by night to feeding in woodland by day. Their major food is earthworms (Lumbricidae). In April and May 1985, vegetation structure and composition and soil parameters including earthworm numbers (30 habitat variables) were recorded for quadrats containing 50 feeding locations of six radio-tagged birds, seven nests and 50 random locations in Whitwell Wood, northeast Derbyshire.
Significantly different mean values between feeding and random sites were found for 11 habitat variables. Feeding sites were in younger stands, with a higher percentage ground cover of dog's mercury Mercurialisperennis and consistently high values for pH. Earthworm biomass was on average 82% greater than in random plots. Areas of beech Fagus sylvaticus were avoided. A discriminant function based on six habitat variables correctly classified 85-5% of the feeding and random sites; 70% of the feeding locations were correctly classified by a jack-knife procedure. The important factors determining where feeding occurs are probably safety from avian predators and high availability of earthworms.
Discriminant analysis of the habitats used for feeding by solitary birds, broods and for nesting produced significant functions which correctly classified 84% of sites. Nests were in areas with a high percentage cover of brambles Rubus spp. and more open ground vegetation. Broods and solitary birds used similar areas characterized by denser ground vegetation than nest sites.
The results of this study indicate that both habitat structure and food availability influence the distribution of Woodcock in the breeding season.     

The phylogeny and systematics of European predacious Syrphidae (Diptera) based on larval and puparial stages

The external larval morphology of predacious Syrphidae is examined and compared with that of other groups of syrphids. Predacious larvae form a distinctive, monophyletic group. Relationships among 29 of the 34 European genera and subgenera are analysed using cladistic methods based on larval and puparial characters. Interpretation of the cladogram suggests that, within Syrphinae, a system of five tribes can be recognized and that a major trend has been a shift from ground layer to arboreal larval habitats, with an increasing degree of obligate dependence on soft-bodied Homoptera as prey. Generic diagnoses with biological and taxonomic notes are given and a key to genera based on larvae and puparia is provided.     

Transformation of blueberry without antibiotic selection

Transformation of the blueberry cultivar North Country (Vaccinium corymbosum × V. angustifolium) was achieved using the disarmed Agrobacterium tumefaciens isolate LBA4404, containing a binary vector with an intron-containing β-glucuronidase (GUS) marker gene. Plant regeneration was carried out in the absence of antibiotics due to their toxicity to blueberry explants. Agrobacterium contamination was controlled by dipping the explants in antibiotics and rinsing in sterile distilled water. Once regeneration had been achieved, the plantlets were placed on to medium containing the antibiotic ticaricillin at 250 mg litre^-1 to control and try to eliminate any remaining Agrobacterium. Selection of regenerating explants expressing GUS was achieved by growing the plant material for 2 days on a medium containing 4-methyl umbelliferyl glucuronide (MUG), and examining the medium under UV light to detect fluorescent activity. From the 19 explants showing signs of regeneration, seven produced fluorescent patches on MUG medium. From the selected explants, five plantlets were found to express the GUS gene as detected by fluorometric and histochemical analysis. PCR was used to confirm the presence of the GUS and/or NPTII marker genes after 2 years in culture. Bacterial contamination isolated from plant material (which appeared free of contamination) was examined for GUS activity and analysed using PCR with GUS and NPTII specific primers, but no positive results were obtained.     

Trypanosoma gerrhonoti n. sp., and Extrinsic Development of Lizard Trypanosomes in California Sandflies

Trypanosoma gerrhonoti n. sp. is described from southern alligator lizards Gerrhonotus multicarinatus of central California. It is the 2nd trypanosome species described from western North America. Extrinsic development of T. gerrhonoti and T. scelopori of western fence lizards was observed in phlebotomine sandflies Lutzomyia vexatrix occidentis, the probable natural vector. Both trypanosomes establish dense anterior midgut infections composed of long, thin epimastigotes.