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A number of distinct β-amyloid (Aβ) variants or multimers have been implicated in Alzheimer's disease (AD), and antibodies recognizing such peptides are in clinical trials. Humans have natural Aβ-specific antibodies, but their diversity, abundance, and function in the general population remain largely unknown. Here, we demonstrate with peptide microarrays the presence of natural antibodies against known toxic Aβ and amyloidogenic non-Aβ species in plasma samples and cerebrospinal fluid of AD patients and healthy controls aged 21-89 years. Antibody reactivity was most prominent against oligomeric assemblies of Aβ and pyroglutamate or oxidized residues, and IgGs specific for oligomeric preparations of Aβ1-42 in particular declined with age and advancing AD. Most individuals showed unexpected antibody reactivities against peptides unique to autosomal dominant forms of dementia (mutant Aβ, ABri, ADan) and IgGs isolated from plasma of AD patients or healthy controls protected primary neurons from Aβ toxicity. Aged vervets showed similar patterns of plasma IgG antibodies against amyloid peptides, and after immunization with Aβ the monkeys developed high titers not only against Aβ peptides but also against ABri and ADan peptides. Our findings support the concept of conformation-specific, cross-reactive antibodies that may protect against amyloidogenic toxic peptides. If a therapeutic benefit of Aβ antibodies can be confirmed in AD patients, stimulating the production of such neuroprotective antibodies or passively administering them to the elderly population may provide a preventive measure toward AD.

Spatial structure in metacommunities and their relationships to environmental gradients have been linked to opposing theories of community assembly. In particular, while the species sorting hypothesis predicts strong environmental influences, the neutral theory, the mass effect, and the patch dynamics frameworks all predict differing degrees of spatial structure resulting from dispersal and competition limitations. Here we study the relative influence of environmental gradients and spatial structure in bird assemblages of the Chilean temperate forest. We carried out bird and vegetation surveys in South American temperate forests at 147 points located in nine different protected areas in central Chile, and collected meteorological and productivity data for these localities. Species composition dissimilarities between sites were calculated, as well as three indices of bird local diversity: observed species richness, Chao estimate of richness, and Shannon diversity. A stepwise multiple regression and partial regression analyses were used to select a small number of environmental factors that predicted bird species diversity. Although diversity indices were spatially autocorrelated, environmental factors were sufficient to account for this autocorrelation. Moreover, community dissimilarities were not significantly related to distance between sites. We then tested a multivariate hypothesis about climate, vegetation, and avian diversity interactions using a structural equation modeling (SEM) approach. The SEM showed that climate and area of fragments have important indirect effects on avian diversity, mediated through changes in vegetation structure. Given the scale of this study, the metacommunity framework provides useful insights into the mechanisms driving bird assemblages in this region. Taken together, the weak spatial structure of community composition and diversity, as well as the strong environmental effects on bird diversity, support the interpretation that species sorting has a predominant role in structuring avian assemblages in the region.

In the northeastern Pacific, intertidal zones of the most wave-beaten shores receive more energy from breaking waves than from the sun. Despite severe mortality from winter storms, communities at some wave-beaten sites produce an extraordinary quantity of dry matter per unit area of shore per year. At wave-beaten sites of Tatoosh Island, WA, sea palms, Postelsia palmaeformis, can produce >10 kg of dry matter, or 1.5 × 108J, per m2in a good year. Extraordinarily productive organisms such as Postelsia are restricted to wave-beaten sites. Intertidal organisms cannot transform wave energy into chemical energy, as photosynthetic plants transform solar energy, nor can intertidal organisms ``harness'' wave energy. Nonetheless, wave energy enhances the productivity of intertidal organisms. On exposed shores, waves increase the capacity of resident algae to acquire nutrients and use sunlight, augment the competitive ability of productive organisms, and protect intertidal residents by knocking away their enemies or preventing them from feeding.

In an experimental test of plant community invasibility, we introduced seeds of a native ruderal, California poppy (Eschscholzia californica), at fixed density into experimental plots in a California winter annual grassland. Each of the 42 plots, which ranged in size from 2 m^2 to 32 m^2, had been studied for 4 yr previous to the introduction, with the common observation that a subset of plots of each size consistently held more species than others. It was primarily in these more species-rich plots that establishment and reproduction by the experimental invader occurred. Success of the invader per plot, measured as the total number of plants germinating, producing seeds, or perennating, varied with plot size, but the statistical contribution of plot size was secondary to that of local species number. Contributing variables were the extent of small mammal disturbance (positive) and the degree to which a single resident plant species (in particular, Bromus diandrus) dominated a plot (negative). In contrast to theories of competitive exclusion via niche partitioning, species-rich plots were more invasible.

Benthic marine invertebrates with planktonic larvae may exhibit Allee effects in reproduction or recruitment. Hydrodynamic considerations and experimental evidence suggest that species broadcasting gametes suffer greatly reduced fertilization efficiencies as densities decline. There is also evidence for some species, including the red sea urchin, that post-dispersal recruitment success declines at low densities of adults, if adults provide shelter from predators or other sources of mortality. Species displaying strong Allee effects may be susceptible to catastrophic population collapses with slight increases in mortality due to harvesting or natural causes. A simple two patch logistic model suggests that the establishment of a harvest refuge is necessary to prevent collapses and maintain sustainable catches at high levels of harvesting effort. A more detailed, age structured model based on the biology of the red sea urchin, Strongylocentrotus franciscanus produces similar results. Effects of harvesting strategies are sensitive to Allee effects caused by both fertilization efficiency and the disruption of adult spine canopies. Theoretical requirements for the size and spacing of marine reserves depends upon the dispersal abilities of the target species. Multiple reserves, spaced more closely than the average larval dispersal distance, appear to be an effective and conservative strategy for maintaining healthy populations and sustainable levels of harvest.

This GIS-based study analyzes the distribution and management of woody riparian vegetation in California's Sacramento Valley and discusses the prospects for its conservation. Although forests were the predominant floodplain vegetation prior to extensive settlement, only 3.3% of floodplain was covered by forest in the late 1980s. This remaining forest was fragmented into 2607 patches with an average area of 3.1 ha. Only 180 patches were 10 ha, with three patches 100 ha. Despite over two decades of conservation efforts, these forests are essentially unpreserved: Only 14.5% of extant forests are in public ownership or on land managed primarily for biological conservation. Some privately owned forests represent opportunities for preservation, but owing to their small size and scattered distribution, reforestation would be necessary to obtain a high cover of forest over large areas. Additionally, high property values, existing land uses, and regulated hydrology constrain conservation efforts. As a consequence of these constraints, and current distribution and ownership patterns, preservation or restoration of substantial areas of riparian forest would be extremely expensive and would divert conservation resources from other habitats in this rapidly developing state. Therefore, efforts to conserve these forests should satisfy two criteria: (1) that the specific goals are attainable with available funding and existing human uses, and (2) funding the effort will result in more effective regional conservation than would funding the conservation of other habitats.

Estimators of the number of additional species expected in the next Δn samples offer a potentially important tool for improving cost-effectiveness of species inventories but are largely untested. We used Monte Carlo methods to compare 11 such estimators, across a range of community structures and sampling regimes, and validated our results, where possible, using empirical data from vascular plant and beetle inventories from Glacier National Park, Montana, USA. We found that B. Efron and R. Thisted's 1976 negative binomial estimator was most robust to differences in community structure and that it was among the most accurate estimators when sampling was from model communities with structures resembling the large, heterogeneous communities that are the likely targets of major inventory efforts. Other estimators may be preferred under specific conditions, however. For example, when sampling was from model communities with highly even species-abundance distributions, estimates based on the Michaelis-Menten model were most accurate; when sampling was from moderately even model communities with S = 10 species or communities with highly uneven species-abundance distributions, estimates based on Gleason's (1922) species-area model were most accurate. We suggest that use of such methods in species inventories can help improve cost-effectiveness by providing an objective basis for redirecting sampling to more-productive sites, methods, or time periods as the expectation of detecting additional species becomes unacceptably low.

Many natural populations are subdivided among partially isolated habitat patches, but the influence of habitat patchiness per se on species immigration, extinction, and the resulting patterns of species diversity, has received virtually no experimental study. In an experiment designed to test the effects of habitat subdivision on local community structure, we compare the diversity and annual turnover of flowering plant species in 3 treatments of the same total area, but subdivided to different degrees. We experimentally fragmented a California winter annual grassland into isolated plots, two of 32 m2, eight of 8 m2, and 32 of 2 m2, each treatment representing a combined area of 64 m2. Insularization of the experimental habitat fragments is provided by grazing sheep. The effects of plot area on species diversity, extinction, and turnover are consistent with the MacArthur-Wilson model. Species richness increases with the degree of habitat subdivision. Extinction, immigration, and turnover, however, are relatively independent of the degree of subdivision. These experimental results contrast with predictions that habitat subdivision necessarily results in greater rates of extinction accompanied by reduced species diversity.

(1) Numerous species-area studies indicate that diversity should be maximized in single contiguous areas, whereas patch models often predict regional coexistence and thus enhanced total diversity, resulting from spatial subdivision of habitat. We investigated this problem experimentally in a California annual grassland by isolating experimental areas of 64 m2, subdivided into 2, 8 and 32 subunits. The areas between plots were intensively grazed by sheep. Unfenced plots measured grazing effects. (2) Species richness and species evenness (J') of flowering plants increased with increasing subdivision, with approximately 40% more species in the most subdivided treatment than in the least. Mean species richness was highest in large plots; both grazed and ungrazed and species-area curves were similar to those derived from mainland habitat islands. (3) Above-ground interspecific competition appears to be an important causal mechanism. There is evidence of strong `priority effects' in which dominant species preempt particular plots and prevent the establishment of competitors. Late-emerging and low-growing species occur primarily on plot edges and the greater relative perimeter of the more subdivided treatments may contribute substantially to their greater diversity.