Effects of site‐selection bias on estimates of biodiversity change

Estimates of biodiversity change are essential for the management and conservation of ecosystems. Accurate estimates rely on selecting representative sites, but monitoring often focuses on sites of special interest. How such site‐selection biases influence estimates of biodiversity change is largely unknown. Site‐selection bias potentially occurs across four major sources of biodiversity data, decreasing in likelihood from citizen science, museums, national park monitoring, and academic research. We defined site‐selection bias as a preference for sites that are either densely populated (i.e., abundance bias) or species rich (i.e., richness bias). We simulated biodiversity change in a virtual landscape and tracked the observed biodiversity at a sampled site. The site was selected either randomly or with a site‐selection bias. We used a simple spatially resolved, individual‐based model to predict the movement or dispersal of individuals in and out of the chosen sampling site. Site‐selection bias exaggerated estimates of biodiversity loss in sites selected with a bias by on average 300–400% compared with randomly selected sites. Based on our simulations, site‐selection bias resulted in positive trends being estimated as negative trends: richness increase was estimated as 0.1 in randomly selected sites, whereas sites selected with a bias showed a richness change of −0.1 to −0.2 on average. Thus, site‐selection bias may falsely indicate decreases in biodiversity. We varied sampling design and characteristics of the species and found that site‐selection biases were strongest in short time series, for small grains, organisms with low dispersal ability, large regional species pools, and strong spatial aggregation. Based on these findings, to minimize site‐selection bias, we recommend use of systematic site‐selection schemes; maximizing sampling area; calculating biodiversity measures cumulatively across plots; and use of biodiversity measures that are less sensitive to rare species, such as the effective number of species. Awareness of the potential impact of site‐selection bias is needed for biodiversity monitoring, the design of new studies on biodiversity change, and the interpretation of existing data

Recuperação de campos nativos suprimidos por agricultura no bioma Pampa: manejo versus regeneração natural.

Os valores médios de riqueza nas áreas de regeneração natural foram inferiores aos das áreas manejadas, e em termos de composição, áreas manejadas tiveram maior similaridade às áreas de referência, indicando que o manejo propiciou aumento na riqueza e composição de espécies em relação às áreas de exclusão, e melhor trajetória dere cuperação

Recuperação de campos nativos suprimidos no Bioma Pampa: um estudo de caso em escala de paisagem em Rosário do Sul (RS).

Uma parceria entre Exército Brasileiro, Ibama, Embrapa Pecuária Sul, Unipampa e UFRGS conduziu um Projeto de Recuperação de Área Degradada (Prad) no Campo de Instrução Barão de São Borja, em Rosário do Sul/RS, visando recuperar campos nativos com histórico de uso com lavouras de arroz e soja. A hipótese central trabalhada no Prad é de que o pastejo pode ser um instrumento para restaurar as formações campestres, impedindo que a vegetação evolua para uma fisionomia arbustiva e acelerando a regeneração natural. O gado bovino foi usado como ?roçadeira biológica? e dispersor de sementes, prática complementada por roçadas mecânicas, nivelamento do solo e isolamento temporário da área em recuperação. O monitoramento da estrutura e da riqueza da vegetação norteou o ajuste de carga animal e os períodos de diferimento. Passados cinco anos, a área apresenta fisionomia campestre desejada, tendo sido observado aumento na riqueza de espécies nativas, e composição botânica com maior similaridade à da área de referência, com aumento na cobertura de espécies das famílias Poaceae e Fabaceae. Houve diminuição do solo exposto, com o aumento da cobertura vegetal, e registrado o aumento da cobertura de Eragrostis plana (capim-annoni), gramínea exótica invasora

General statistical scaling laws for stability in ecological systems

Ecological stability refers to a family of concepts used to describe how systems of interacting species vary through time and respond to disturbances. Because observed ecological stability depends on sampling scales and environmental context, it is notoriously difficult to compare measurements across sites and systems. Here, we apply stochastic dynamical systems theory to derive general statistical scaling relationships across time, space, and ecological level of organisation for three fundamental stability aspects: resilience, resistance, and invariance. These relationships can be calibrated using random or representative samples measured at individual scales, and projected to predict average stability at other scales across a wide range of contexts. Moreover deviations between observed vs. extrapolated scaling relationships can reveal information about unobserved heterogeneity across time, space, or species. We anticipate that these methods will be useful for cross-study synthesis of stability data, extrapolating measurements to unobserved scales, and identifying underlying causes and consequences of heterogeneity

Character and environmental lability of cyanobacteria-derived dissolved organic matter

Autotrophic dissolved organic matter (DOM) is central to the carbon biogeochemistry of aquatic systems, and the full complexity of autotrophic DOM has not been extensively studied, particularly by high-resolution mass spectrometry (HRMS). Terrestrial DOM tends to dominate HRMS studies in freshwaters due to the propensity of such compounds to ionize by negative mode electrospray, and possibly also because ionizable DOM produced by autotrophy is decreased to low steady-state concentrations by heterotrophic bacteria. In this study, we investigated the character of DOM produced by the widespread cyanobacteriaMicrocystis aeruginosausing high-pressure liquid chromatography-electrospray ionization-high-resolution mass spectrometry.M. aeruginosaproduced thousands of detectable compounds in axenic culture. These compounds were chromatographically resolved and the majority were assigned to aliphatic formulas with a broad polarity range. We found that the DOM produced byM. aeruginosawas highly susceptible to removal by heterotrophic freshwater bacteria, supporting the hypothesis that this autotroph-derived organic material is highly labile and accordingly only seen at low concentrations in natural settings

Transanal endoscopic microsurgery versus endoscopic mucosal resection for large rectal adenomas (TREND-study)

Background: Recent non-randomized studies suggest that extended endoscopic mucosal resection (EMR) is equally effective in removing large rectal adenomas as transanal endoscopic microsurgery (TEM). If equally effective, EMR might be a more cost-effective approach as this strategy does not require expensive equipment, general anesthesia and hospital admission. Furthermore, EMR appears to be associated with fewer complications. The aim of this study is to compare the cost-effectiveness and cost-utility of TEM and EMR for the resection of large rectal adenomas. Methods/design. Multicenter randomized trial among 15 hospitals in the Netherlands. Patients with a rectal adenoma 3 cm, located between 115 cm ab ano, will be randomized to a TEM- or EMR-treatment strategy. For TEM, patients will be treated under general anesthesia, adenomas will be dissected en-bloc by a full-thickness excision, and patients will be admitted to the hospital. For EMR, no or conscious sedation is used, lesions will be resected through the submucosal plane i

Follow-up of patients with curatively resected colorectal cancer: a practice guideline

BACKGROUND: A systematic review was conducted to evaluate the literature regarding the impact of follow-up on colorectal cancer patient survival and, in a second phase, recommendations were developed. METHODS: The MEDLINE, CANCERLIT, and Cochrane Library databases, and abstracts published in the 1997 to 2002 proceedings of the annual meeting of the American Society of Clinical Oncology were systematically searched for evidence. Study selection was limited to randomized trials and meta-analyses that examined different programs of follow-up after curative resection of colorectal cancer where five-year overall survival was reported. External review by Ontario practitioners was obtained through a mailed survey. Final approval of the practice guideline report was obtained from the Practice Guidelines Coordinating Committee. RESULTS: Six randomized trials and two published meta-analyses of follow-up were obtained. Of six randomized trials comparing one follow-up program to a more intense program, only two individual trials detected a statistically significant survival benefit favouring the more intense follow-up program. Pooling of all six randomized trials demonstrated a significant improvement in survival favouring more intense follow-up (Relative Risk Ratio 0.80 (95%CI, 0.70 to 0.91; p = 0.0008). Although the rate of recurrence was similar in both of the follow-up groups compared, asymptomatic recurrences and re-operations for cure of recurrences were more common in patients with more intensive follow-up. Trials including CEA monitoring and liver imaging also had significant results, whereas trials not including these tests did not. CONCLUSION: Follow-up programs for patients with curatively resected colorectal cancer do improve survival. These follow-up programs include frequent visits and performance of blood CEA, chest x-rays, liver imaging and colonoscopy, however, it is not clear which tests or frequency of visits is optimal. There is a suggestion that improved survival is due to diagnosis of recurrence at an earlier, asymptomatic stage which allows for more curative resection of recurrence. Based on this evidence and consideration of the biology of colorectal cancer and present practices, a guideline was developed. Patients should be made aware of the risk of disease recurrence or second bowel cancer, the potential benefits of follow-up and the uncertainties requiring further clinical trials. For patients at high-risk of recurrence (stages IIb and III) clinical assessment is recommended when symptoms occur or at least every 6 months the first 3 years and yearly for at least 5 years. At the time of those visits, patients may have blood CEA, chest x-ray and liver imaging. For patients at lower risk of recurrence (stages I and Ia) or those with co-morbidities impairing future surgery, only visits yearly or when symptoms occur. All patients should have a colonoscopy before or within 6 months of initial surgery, and repeated yearly if villous or tubular adenomas >1 cm are found; otherwise repeat every 3 to 5 years. All patients having recurrences should be assessed by a multidisciplinary team in a cancer centre