Geographic range structure in North American landbrids: variation with migratory strategy, trophic level, and breeding habitat

We investigated the relationship between abundance and geographic range structure of 258 North American landbirds. For this purpose we used six measures of range structure based upon fractal geometry and geostatistics, and three ecological characteristics that can influence avian distribution. Permanent residents (PRs) that were abundant showed little fragmentation of their abundance surface at the periphery of their breeding range. Conversely, common Neotropical migrants (NTMs) exhibited low fragmentation of their central populations the abundance surface was smoother for PRs than NTMs or short-distance migrants (SDMs). indicating that changes in abundance occurred more gradually across space for this group. The areas of high abundance for grassland species had little demographic fragmentation, but other populations showed little spatial autocorrelation in abundance. Species that bred in late-successional forests were relatively rare compared to species breeding in other habitat types. Among carnivores. PRs had a higher average abundance than either NTMs or SDMs. Although carnivores had more distributional gaps within their ranges than other trophic groups, the number of gaps did not differ between rare and abundant species, indicating that increased abundance did not change their presence. absence distribution maps. Knowledge of patterns and variations of geographic range structure among species may provide insights into processes that shape and maintain the biodiversity of a continent.     

Modeling mechanical inhomogeneities in small populations of proliferating monolayers and spheroids

Understanding the mechanical behavior of multicellular monolayers and spheroids is fundamental to tissue culture, organism development, and the early stages of tumor growth. Proliferating cells in monolayers and spheroids experience mechanical forces as they grow and divide and local inhomogeneities in the mechanical microenvironment can cause individual cells within the multicellular system to grow and divide at different rates. This differential growth, combined with cell division and reorganization, leads to residual stress. Multiple different modeling approaches have been taken to understand and predict the residual stresses that arise in growing multicellular systems, particularly tumor spheroids. Here, we show that by using a mechanically robust agent-based model constructed with the peridynamic framework, we gain a better understanding of residual stresses in multicellular systems as they grow from a single cell. In particular, we focus on small populations of cells (1–100 s) where population behavior is highly stochastic and prior investigation has been limited. We compare the average strain energy density of cells in monolayers and spheroids using different growth and division rules and find that, on average, cells in spheroids have a higher strain energy density than cells in monolayers. We also find that cells in the interior of a growing spheroid are, on average, in compression. Finally, we demonstrate the importance of accounting for stochastic fluctuations in the mechanical environment, particularly when the cellular response to mechanical cues is nonlinear. The results presented here serve as a starting point for both further investigation with agent-based models, and for the incorporation of major findings from agent-based models into continuum scale models when explicit representation of individual cells is not computationally feasible.     

Water availability,fundamental niches and realized niches: A case study from the Cape flora

The ability of plants to survive drought or waterlogging constitutes an important niche parameter, which might be particularly significant in explaining species coexistence in the species‐rich and seasonally dry Cape Floristic Region of South Africa. However, the degree of physiological adaptation and specialization to these eco‐hydrological parameters (the fundamental niche) cannot be readily inferred from correlative studies based on species distributions and spatial variation in environmental parameters (the realized niche). We used an ex situ greenhouse experiment to compare the fundamental hydrological niches (different mean annual precipitation, rainfall seasonality and soil drainage) of six eco‐hydrologically divergent African Restionaceae species. Juvenile plants were subjected to six different watering treatments, ranging from no watering to waterlogging, to determine drought and waterlogging susceptibility and optimal growth conditions. We used the rate of biomass accumulation and survival rate as response measures. We found that species from dry and mesic (but well‐drained) habitats had optimal or near‐optimal growth at benign conditions (under which most restio species grow well). All species performed worse when droughted and died when not watered. Species from dry habitats tended to perform better (assessed in growth) than species from wet habitats under droughting. Species from wet habitats performed best when waterlogged, whereas species from dry habitats performed very poorly when waterlogged – thus showing that realized and fundamental niches covaried at the wet end of the hydrological gradient. We conclude that eco‐hydrological parameters are part of the fundamental niche, and fundamental and realized species niches are approximately correlated along them. The distribution of wet habitat species appears not to reflect their drought tolerance, suggesting that it may not be predicted by bioclimatic variables, but rather by soil drainage characteristics.     

Two new species of Askidiosperma (Restionaceae) from South Africa

Askidiosperma delicatulum , sp. nov., from the arid margins of the Cold Bokkeveld mountains in the Western Cape Province, South Africa, is described and illustrated. A. chartaceum ssp. alticolum is raised to specific level. A new key to the species in the genus Askidiosperma is provided.     

Food provision to nestlings in the Hoopoe Upupa epops: implications for the conservation of a small endangered population in the Swiss Alps

In an attempt to recognize the possible ecological causes of the decline of a population of Hoopoes Upupa epops in the Swiss Alps, we collected data on resource exploitation. The prey provisioned to nestlings by parents was investigated at four breeding sites using photographs (n = 4353, 80% of which enabled prey identification). Molecrickets Gryllotalpa gryllotalpa and Lepidoptera (larvae and pupae) were dominant in nestling diet (93% frequency; 97% biomass). Although Molecrickets were provisioned less frequently (26%) than Lepidoptera (67%), they represented 68% of the total biomass (vs 29% for Lepidoptera). There was an overall negative relationship between the proportion of Molecricket biomass in the diet and the parents' feeding rate, whereas a comparison between broods showed that a higher provisioning activity did not lead to an increase in the biomass supplied to the chicks. A diet based on Molecrickets therefore appears to be energetically advantageous. As Molecrickets are a traditional prey of Hoopoes in central Europe, this might be relevant to other populations. In the study area, Molecrickets occur only on the intensively cultivated plain, whereas the majority of Hoopoe pairs nest at various altitudes on the foothills adjacent to the plain as the latter provides at present almost no suitable nesting sites. Hoopoes breeding higher up on the foothills seem to experience greater provisioning costs and have, on average, lower breeding success. Providing nest sites on the plain is the main conservation measure proposed for the local Hoopoe population. Further attention should also be paid to Molecrickets as these may be crucial for Hoopoes.     

Adrenomedullin is a novel marker of tumor progression in neuroendocrine carcinomas.

Adrenomedullin is a multi-functional polypeptide hormone. Its involvement in angiogenesis and vasodilator action support the hypothesis that adrenomedullin may be a secretory product of neuroendocrine tumors and contribute to tumor progression. Plasma levels of adrenomedullin were measured by radioimmunoassay in 46 patients with neuroendocrine carcinomas of the gastroenteropancreatic and bronchial system. Tissue expression of adrenomedullin was studied using monoclonal antibodies on pretreated paraffin embedded tissues in a group of 31 patients. Adrenomedullin plasma levels were significantly elevated in patients compared to healthy age-matched controls (p < 0.001). The highest plasma levels were found in patients with neuroendocrine carcinomas of bronchial, midgut and unknown origin. Patients with progressive disease had higher plasma levels than patients with stable disease (p < 0.001). Of the examined tumor samples, 55 % showed cytoplasmic staining for adrenomedullin > 5 % of the total tumor area. Plasma levels and tissue expression of adrenomedullin did not correlate with functional activity of the tumors or presence of the carcinoid syndrome, but did with tumor progression (p < 0.001 and p < 0.014). In conclusion, plasma and tissue expression of the angiogenic peptide adrenomedullin are predictive of tumor progression in patients with neuroendocrine carcinomas. Adrenomedullin might represent a useful prognostic marker in patients with neuroendocrine carcinomas.     

FLUXNET and modelling the global carbon cycle

Measurements of the net CO₂ flux between terrestrial ecosystems and the atmosphere using the eddy covariance technique have the potential to underpin our interpretation of regional CO₂ source–sink patterns, CO₂ flux responses to forcings, and predictions of the future terrestrial C balance. Information contained in FLUXNET eddy covariance data has multiple uses for the development and application of global carbon models, including evaluation/validation, calibration, process parameterization, and data assimilation. This paper reviews examples of these uses, compares global estimates of the dynamics of the global carbon cycle, and suggests ways of improving the utility of such data for global carbon modelling. Net ecosystem exchange of CO₂ (NEE) predicted by different terrestrial biosphere models compares favourably with FLUXNET observations at diurnal and seasonal timescales. However, complete model validation, particularly over the full annual cycle, requires information on the balance between assimilation and decomposition processes, information not readily available for most FLUXNET sites. Site history, when known, can greatly help constrain the model‐data comparison. Flux measurements made over four vegetation types were used to calibrate the land‐surface scheme of the Goddard Institute for Space Studies global climate model, significantly improving simulated climate and demonstrating the utility of diurnal FLUXNET data for climate modelling. Land‐surface temperatures in many regions cool due to higher canopy conductances and latent heat fluxes, and the spatial distribution of CO₂ uptake provides a significant additional constraint on the realism of simulated surface fluxes. FLUXNET data are used to calibrate a global production efficiency model (PEM). This model is forced by satellite‐measured absorbed radiation and suggests that global net primary production (NPP) increased 6.2% over 1982–1999. Good agreement is found between global trends in NPP estimated by the PEM and a dynamic global vegetation model (DGVM), and between the DGVM and estimates of global NEE derived from a global inversion of atmospheric CO₂ measurements. Combining the PEM, DGVM, and inversion results suggests that CO₂ fertilization is playing a major role in current increases in NPP, with lesser impacts from increasing N deposition and growing season length. Both the PEM and the inversion identify the Amazon basin as a key region for the current net terrestrial CO₂ uptake (i.e. 33% of global NEE), as well as its interannual variability. The inversion's global NEE estimate of −1.2 Pg [C] yr⁻¹ for 1982–1995 is compatible with the PEM‐ and DGVM‐predicted trends in NPP. There is, thus, a convergence in understanding derived from process‐based models, remote‐sensing‐based observations, and inversion of atmospheric data. Future advances in field measurement techniques, including eddy covariance (particularly concerning the problem of night‐time fluxes in dense canopies and of advection or flow distortion over complex terrain), will result in improved constraints on land‐atmosphere CO₂ fluxes and the rigorous attribution of mechanisms to the current terrestrial net CO₂ uptake and its spatial and temporal heterogeneity. Global ecosystem models play a fundamental role in linking information derived from FLUXNET measurements to atmospheric CO₂ variability. A number of recommendations concerning FLUXNET data are made, including a request for more comprehensive site data (particularly historical information), more measurements in undisturbed ecosystems, and the systematic provision of error estimates. The greatest value of current FLUXNET data for global carbon cycle modelling is in evaluating process representations, rather than in providing an unbiased estimate of net CO₂ exchange.     

Two Novel Adenovirus Vector Systems Permitting Regulated Protein Expression in Gene Transfer Experiments

Two new adenovirus vector systems based on the tetracycline-regulated Tet-ON- (Gossen, M., et al., Science 268:1766–1769, 1995) and the RU 486-regulated progesterone antagonist (Wang, Y., et al., Proc. Natl. Acad. Sci. USA 91:8180–8184, 1994)-induced gene expression systems are described. We show that both systems permit a tight control of chloramphenicol acetyltransferase reporter gene expression in a variety of cell types, with induction levels of approximately 1,800-fold (Tet-ON system) and 600-fold (RU 486-regulated system), respectively. A significant advantage of our vector systems is that reporter protein expression can be adjusted over a wide range by varying the amount of inducer. The Tet-ON system is also shown to permit an efficient control of reporter gene expression in mice.