Finding the Missing Link between Landscape Structure and Population Dynamics: A Spatially Explicit Perspective

We construct and explore a general modeling framework that allows for a systematic investigation of the impact of changes in landscape structure on population dynamics. The essential parts of the framework are a landscape generator with independent control over landscape composition and physiognomy, an individual-based spatially explicit population model that simulates population dynamics within heterogeneous landscapes, and scale-dependent landscape indices that depict the essential aspects of landscape that interact with dispersal and demographic processes. Landscape maps are represented by a grid of 50x50 cells and consist of good-quality, poor-quality, or uninhabitable matrix habitat cells. The population model was shaped in accordance to the biology of European brown bears (Ursus arctos), and demographic parameters were adjusted to yield a source-sink configuration. Results obtained with the spatially explicit model do not confirm results of earlier nonspatial source-sink models where addition of sink habitat resulted in a decrease of total population size because of dilution of high-quality habitat. Our landscape indices, which describe scale-dependent correlation between and within habitat types, were able to explain variations in variables of population dynamics (mean number of females with sink home ranges, mean number of females with source home ranges, and mean dispersal distance) caused by different landscape structure. When landscape structure changed, changes in these variables generally followed the corresponding change of an appropriate landscape index in a linear way. Our general approach incorporates source-sink dynamics as well as metapopulation dynamics, and the population model can easily be modified for other species groups.     

Population dynamics, disturbance, and pattern evolution: identifying the fundamental scales of organization in a model ecosystem

We used auto- and cross-correlation analysis and Ripley's K-function analysis to analyze spatiotemporal pattern evolution in a spatially explicit simulation model of a semiarid shrubland (Karoo, South Africa) and to determine the impact of small-scale disturbances on system dynamics. Without disturnities bance, local dynamics were driven by a pattern of cyclic succession, where 'colonizer' and 'successor' species alternately replaced each other. This results in a strong pattern of negative correlation in the temporal distribution of colonizer and successor species. As disturbance rates were increased, the relationship shifted from being negatively correlated in time to being positively correlated-the dynamics became decoupled from the ecologically driven cyclic succession and were increasingly influenced by abiotic factors (e.g., rainfall events). Further analysis of the spatial relationships among colonizer and successor species showed that, without disturbance, periods of attraction and repulsion between colonizer and successor species alternate cyclically at intermediate spatial scales. This was due to the spatial 'memory' embedded in the system through the process of cyclic succession. With the addition of disturbance, this pattern breaks down, although there is some indication of increasing ecological organization at broader spatial scales. We suggest that many of the insights that can be gained through spatially explicit models will only be obtained through a direct analysis of the spatial patterns produced.     

Wooded habitat edges as refugia from microtine herbivory in tallgrass prairies

Meadow voles, Microtus pennsylvanicus , affect the species composition, distribution, and succession of plants in grassland ecosystems, but the effects of voles on herbaceous plants when grasslands are bordered by wooded edges is not known. We investigated the impact of wooded edges on vole distribution and herbivory of relatively palatable and unpalatable native prairie plant species by studying five reconstructed tallgrass prairies with wooded edges in central Iowa. A 50×50 m trapping grid at each site was established to determine the proportion of voles captured at various distances from the edge. We found that meadow voles were less abundant at wooded edges and, in general, increased in number toward the prairie interior. Seedlings of purple prairie clover ( Dalea purpurea ) and Illinois bundleflower ( Desmanthus illinoensis ), a relatively palatable and unpalatable species, respectively, were transplanted onto simulated gopher mounds 2, 5, 10, 20 and 30 m from the edge. The number of plants grazed per species per mound was determined 1 week and 4 weeks after planting. The amount of herbivory on both species was significantly different by distance, with fewer plants eaten 2 m from the edge. Interestingly, the amount of herbivory on relatively unpalatable plants did not differ from more palatable plants. Herbivory on both plant species also varied by site, such that sites with lower vole density tended to have lower amounts of herbivory. These results indicate that wooded edges do have an effect on meadow vole distribution and native prairie seedling herbivory. Because voles avoid wooded edges, seedlings of any species may experience a small refuge from herbivory along wooded edges.     

Competitive Inhibition of Abscisic Acid-Regulated Gene Expression by Stereoisomeric Acetylenic Analogs of Abscisic Acid

The properties of two enantiomeric synthetic acetylenic abscisic acid (ABA) analogs (PBI-51 and PBI-63) in relation to ABA-sensitive gene expression are reported. Using microspore-derived embryos of Brassica napus as the biological material and their responsiveness to ABA in the expression of genes encoding storage proteins as a quantitative bioassay, we measured the biological activity of PBI-51 and PBI-63. Assays to evaluate agonistic activity of either compound applied individually showed a dose-dependent increase in napin gene expression on application of PBI-63. Maximal activity of about 40 [mu]M indicated that PBI-63 was an agonist, although somewhat weaker than ABA. PBI-63 has a similar stereochemistry to natural ABA at the junction of the ring and side chain. In contrast, PBI-51 showed no agonistic effects until applied at 40 to 50 [mu]M. Even then, the response was fairly weak. PBI-51 has the opposite stereochemistry to natural ABA at the junction of the ring and side chain. When applied concurrently with ABA, PBI-63 and PBI-51 had distinctly different properties. PBI-63 (40 [mu]M) and ABA (5 [mu]M) combined gave results similar to the application of either compound separately with high levels of induction of napin expression. PBI-51 displayed a reversible antagonistic effect with ABA, shifting the typical ABA dose-response curve by a factor of 4 to 5. This antagonism was noted for the expression of two ABA-sensitive genes, napin and oleosin. To test whether this antagonism was at the level of ABA recognition or uptake, ABA uptake was monitored in the presence of PBI-51 or PBI-63. Neither compound decreased ABA uptake. Treatments with either PBI-51 or PBI-63 showed an effect on endogenous ABA pools by permitting increases of 5- to 7-fold. It is hypothesized that this increase occurs because of competition for ABA catabolic enzymes by both compounds. The fact that ABA pools did not decrease in the presence of PBI-51 suggests that PBI-51 must exert its antagonistic properties through direct competition with ABA at a hormone-recognition site.     

Increased T lymphocytes and IgMEA-receptor lymphocytes in Hodgkin's disease spleens.

Splenic lymphocytes from 11 patients with Hodgkin's disease were compared to lymphocytes of six spleens from patients with nonlymphoproliferative diseases. T lymphocytes were increased in patients with histological involvement by Hodgkin's disease. Likewise, lymphocytes from spleens with histological involvement showed increased rosette formation with immunologlobulin M-coated sheep red blood cells (IgMEA). A similar increase in T lymphocytes and in IgMEA rosette formation was not observed with normal peripheral blood lymphocytes, control spleens, or with Hodgkin's disease spleens without evidence of histological involvement.     

Renal transplantation in diabetics nephropathy.

Forty diabetics who had developed end-stage renal failure from diabetic nephropathy and underwent renal transplantation have been followed up from one to six years. After one and two years 63% and 42% survived (45% and 33% respectively with functioning kidneys). Older patients, those with coronary and peripheral vascular disease, and those with severe neuropathy are prone to higher postoperative morbidity and mortality. The presence of advanced retinopathy, on the other hand, does not appear to influence the outcome.     

Recombinant NY-ESO-1 cancer antigen: production and purification under cGMP conditions

The cancer-testis antigen, NY-ESO-1, has been engineered into a bacterial expression plasmid which incorporates a His6-tag. The plasmid was transfected into E. coli strain BL21 and Master and Working cell banks generated from this expression system. Three 15-litre fermentations were performed under cGMP (code of Good Manufacturing Practice) conditions and the crude NY-ESO-1 tagged protein isolated as solubilised inclusion bodies. A three-step cGMP chromatography process (immobilised metal affinity, anion exchange, and hydrophobic interaction) was utilised to purify the protein. The purified NY-ESO-1 is being used in early stage human cancer vaccine trials in Australia and the U.S.A.     

The ability of single sex infections of Schistosoma japonicum to induce resistance to reinfection in mice

In four experiments, mice harbouring an average 50, 76 or over 200 Schistosoma japonicum female worms were not resistant when challenged six to eight weeks after infection. The female worms from these single sex infections were stunted and immature (average length 4.6 mm) and induced no overt pathology in the host. Male worm burdens of 60, 135 or 140 also induced little or no resistance to challenge in the host. The males from these single sex infections were fully grown for their age (average length 9 mm) and burdens of 135 or 140 induced distended hepatic portal veins and marked deposition of pigment in the livers of infected mice.