The Great American Biotic Interchange in birds

The sudden exchange of mammals over the land bridge between the previously isolated continents of North and South America is among the most celebrated events in the faunal history of the New World. This exchange resulted in the rapid merging of continental mammalian faunas that had evolved in almost complete isolation from each other for tens of millions of years. Yet, the wider importance of land bridge-mediated interchange to faunal mixing in other groups is poorly known because of the incompleteness of the fossil record. In particular, the ability of birds to fly may have rendered a land bridge unnecessary for faunal merging. Using molecular dating of the unique bird faunas of the two continents, we show that rates of interchange increased dramatically after land bridge completion in tropical forest-specializing groups, which rarely colonize oceanic islands and have poor dispersal abilities across water barriers, but not in groups comprised of habitat generalists. These results support the role of the land bridge in the merging of the tropical forest faunas of North and South America. In contrast to mammals, the direction of traffic across the land bridge in birds was primarily south to north. The event transformed the tropical avifauna of the New World.     

Biotic homogenization can decrease landscape-scale forest multifunctionality

Many experiments have shown that local biodiversity loss impairs the ability of ecosystems to maintain multiple ecosystem functions at high levels (multifunctionality). In contrast, the role of biodiversity in driving ecosystem multifunctionality at landscape scales remains unresolved. We used a comprehensive pan-European dataset, including 16 ecosystem functions measured in 209 forest plots across six European countries, and performed simulations to investigate how local plot-scale richness of tree species (α-diversity) and their turnover between plots (β-diversity) are related to landscape-scale multifunctionality. After accounting for variation in environmental conditions, we found that relationships between α-diversity and landscape-scale multifunctionality varied from positive to negative depending on the multifunctionality metric used. In contrast, when significant, relationships between β-diversity and landscape-scale multifunctionality were always positive, because a high spatial turnover in species composition was closely related to a high spatial turnover in functions that were supported at high levels. Our findings have major implications for forest management and indicate that biotic homogenization can have previously unrecognized and negative consequences for large-scale ecosystem multifunctionality.It is widely established that high local-scale biodiversity increases levels of individual ecosystem functions in experimental ecosystems (1–4), and that biodiversity is even more important for the simultaneous maintenance of multiple functions at high levels (i.e., ecosystem multifunctionality) (5–8). Because the capacity of natural ecosystems to maintain multiple functions and services is crucial for human well-being (9), the positive diversity–multifunctionality relationship is often used as an argument to promote biodiversity conservation (6, 10). However, although society seeks to maximize the delivery of potentially conflicting ecosystem services, such as food production, bioenergy generation, and carbon storage at the landscape scale (11–13), research into the relationship between biodiversity and ecosystem multifunctionality has been largely limited to local-scale studies, where diversity is manipulated in experimental plant communities. Although some studies have focused on more natural communities distributed over larger spatial extents (e.g., 14–16), they examined relationships between local-scale biodiversity and local-scale multifunctionality. The only previous study to investigate multifunctionality at larger scales (17) simulated artificial landscapes using data from experimental grassland communities. It showed that although different aspects of biodiversity affected multifunctionality, local-scale (α-) diversity was a much stronger driver than the turnover of species between sites (β-diversity). However, whether those findings can be extrapolated to real-world (i.e., natural, seminatural) ecosystems, such as forests, is unknown. As a result, we have a poor understanding of how multifunctionality relates to biodiversity at the larger spatial scales that are most relevant to ecosystem managers. This question is of particular concern, given recent findings suggesting that human-driven homogenization of communities [loss of β-diversity (18–21)] may be just as widespread as α-diversity declines (22, 23).Multifunctionality can be measured by a variety of methods, and the most appropriate means of doing so remains unresolved (24–27), particularly at larger scales, where the desired distribution of ecosystem function across the landscape has not been quantified. At local scales, one can quantify ecosystem multifunctionality as the number of ecosystem functions that exceed a given threshold value, where the threshold equals a certain percentage of the maximum observed value of each function (10, 24) (hereafter “threshold-based multifunctionality”; Fig. 1B). This threshold reflects the minimum value of ecosystem functioning that is deemed satisfactory. Because trade-offs between ecosystem functions or services are commonplace (5, 7, 28, 29), it is often impossible to maximize all of the desired functions in a local community (6). However, when different species provide different functions (5, 7) at larger spatial scales, a high spatial turnover in community composition (i.e., a high β-diversity) across the landscape can cause different parts of the landscape to provide different functions at high levels (defined as high threshold-based β-multifunctionality; Fig. 1B). Therefore, high β-diversity might cause all desired ecosystem functions to be provided at high levels in at least one patch within a landscape [and hence promote threshold-based landscape-scale or γ-multifunctionality (30)] (Fig. 1B), but only if (i) species differ in the functions they support and (ii) there is no “superspecies” that supports the majority of functions. This threshold-based γ-multifunctionality may be relevant for cases where forest landscapes are managed for many different services (e.g., timber production, limitation of nutrient runoff, ecotourism), but where each of these services only needs to be provided at high levels in a part of the landscape, not everywhere (31). Alternatively, a manager may seek to promote the total delivery of many summed individual ecosystem functions across a landscape. We define this total delivery as sum-based γ-multifunctionality (Fig. 1B). This metric may be a more appropriate measure of multifunctionality in cases where the benefits of ecosystem services are manifested at large scales, such as carbon sequestration or water purification (32). In this case, β-diversity might only promote sum-based γ-multifunctionality if nonadditive diversity effects, such as resource partitioning, species-environment matching, or spillover effects, operate at relatively large spatial scales (33, 34). It is therefore likely that the importance of β-diversity for γ-multifunctionality varies depending on the desired pattern of ecosystem service provision.Open in a separate windowFig. 1.Quantifying biodiversity and multifunctionality across spatial scales. The light yellow areas represent hypothetical landscapes, consisting of (white) local communities. In these communities, some species are present (colored icons in A and C), whereas others are absent (gray icons). Similarly, some functions are performing above a hypothetical threshold of 0.5 (colored icons in B), whereas others are not (gray icons). Diversity and threshold-based multifunctionality are quantified at (i) the local plot (α-) scale as the number of species present (two and three in A) or functions performing above a given threshold (two and three in B), (ii) the β-scale as the turnover in species composition [ = 1 ? log((a + b + 2c)/(a + b + c)) = 1 ? log((1 + 2 + 2)/(1 + 2 + 1)) = 0.90 in A (49)] or functions [ = 1 ? log((a + b + 2c)/(a + b + c)) = 1 ? log((1 + 2 + 2)/(1 + 2 + 1)) = 0.90 in B (49)] across plots, and (iii) the landscape (γ-) scale as the number of functions (four in B) present in at least one plot. Sum-based γ-multifunctionality is defined as the sum of all standardized ecosystem values in a landscape (= 0.8 + 0.2 + 0.7 + 0.4 + 0.9 + 1.0 + 0.1 + 0.6 = 4.7). In contrast to threshold-based multifunctionality, sum-based multifunctionality is not analogous to biodiversity (where species are either present or absent), and can therefore not be partitioned into α- or β-components. (C) This framework allows investigation of whether γ-multifunctionality is promoted by α- and/or β-diversity.Forests provide many ecosystem services, including wood production, regulation of water quality and climate, and recreation (35, 36). Most present-day European forests and almost all forest plantations worldwide are dominated by only one or a few tree species (15, 37), although their diversity could be promoted relatively easily by planting more species or by encouraging natural regeneration. This fact makes the understanding of diversity–multifunctionality relationships in these ecosystems highly relevant for forest management.We therefore assessed the importance of α- and β-diversity of tree species in driving γ-multifunctionality in mature European forests. To do so, we used data taken from a pan-European forest dataset consisting of 209 forest plots, specifically selected to investigate relationships between tree diversity and ecosystem functioning by maximizing variation in dominant “target” species richness and minimizing (i) variation in other potential drivers of ecosystem function (e.g., soil and climatic conditions) and (ii) covariation between tree α-diversity, species composition, and environmental variables as much as possible (38). Our plot selection therefore aimed to mimic biodiversity experiments to investigate relationships between biodiversity and ecosystem functioning in mature forests, which are difficult to undertake with manipulative approaches due to the longevity of tree species. The plots were widely distributed across six European countries, spanning boreal to Mediterranean zones and representing six major European forest types (38). In each plot, 16 ecosystem processes, functions, or properties (termed “functions” hereafter) were measured. These functions represented a wide range of supporting, provisioning, regulating, and cultural ecosystem services (sensu 9) (SI Appendix, Table S3). Next, we created simulated landscapes by randomly drawing plots from a country to generate a “landscape” of five plots, from which γ-multifunctionality was calculated. We then explored relationships between α- and β-diversity and different measures of γ-multifunctionality: threshold-based γ-multifunctionality, quantified as the number of functions with levels above a threshold [a certain percentage of maximum functioning observed across all plots (10)] in at least one plot of the landscape (quantification is shown in Fig. 1B), and sum-based γ-multifunctionality, quantified as the sum of scaled values of all functions across all plots within a landscape (quantification is shown in Fig. 1B). To demonstrate how α- and β-diversity can promote threshold-based γ-multifunctionality, we also measured the relationships between both α- and β-diversity and threshold-based α- and β-multifunctionality (quantification is shown in Fig. 1B).     

Biotic interactions mediate soil microbial feedbacks to climate change

Decomposition of organic material by soil microbes generates an annual global release of 50–75 Pg carbon to the atmosphere, ∼7.5–9 times that of anthropogenic emissions worldwide. This process is sensitive to global change factors, which can drive carbon cycle–climate feedbacks with the potential to enhance atmospheric warming. Although the effects of interacting global change factors on soil microbial activity have been a widespread ecological focus, the regulatory effects of interspecific interactions are rarely considered in climate feedback studies. We explore the potential of soil animals to mediate microbial responses to warming and nitrogen enrichment within a long-term, field-based global change study. The combination of global change factors alleviated the bottom-up limitations on fungal growth, stimulating enzyme production and decomposition rates in the absence of soil animals. However, increased fungal biomass also stimulated consumption rates by soil invertebrates, restoring microbial process rates to levels observed under ambient conditions. Our results support the contemporary theory that top-down control in soil food webs is apparent only in the absence of bottom-up limitation. As such, when global change factors alleviate the bottom-up limitations on microbial activity, top-down control becomes an increasingly important regulatory force with the capacity to dampen the strength of positive carbon cycle–climate feedbacks.The Earth system models that inform the climate projections of the International Panel on Climate Change incorporate two feedbacks with terrestrial carbon exchanges (1, 2). The CO₂ fertilization effect has the potential to partially offset anthropogenic emissions by the stimulation of primary productivity (1). In contrast, climate-induced increases in soil microbial decomposition are expected to enhance atmospheric warming via the land carbon–climate feedback, although the strength of this positive feedback remains a major uncertainty (1). Soil carbon dynamics are particularly sensitive to climate change in forest ecosystems (3), which contain ∼40% (787 Pg carbon) of the global soil carbon pool (2). These soils are generally dominated by basidiomycete fungi (4), which govern the rate-limiting steps in organic matter decomposition via the production of various hydrolytic and oxidative enzymes (5, 6). Elevated temperature is expected to stimulate growth and enzyme production of large, cord-forming basidiomycetes (7, 8), driving functional shifts in soil decomposer communities (9) and enhancing carbon losses from forest sinks (10). Simultaneously, global nitrogen deposition is predicted to double by 2050 (11), and the potential for interactive effects with warming on the activity of belowground communities is well recognized (3, 12, 13). Although the direct effects of these abiotic processes have been studied exhaustively in recent decades (3, 13), the stabilizing effects of biotic interactions are rarely considered in global studies. Indeed, recent advances in our mechanistic understanding of microbial feedbacks to climate change have been generated predominantly from ex situ studies, which use sieved soil that excludes fungal cords and interacting soil biota (10, 14, 15).In recent years, a growing body of work highlights the potential for biotic interactions to override the initial effects of global change factors on aboveground plant communities (16, 17). Grazing of shrubs by musk oxen and caribou, for example, has been shown to mitigate the warming-induced increases in plant biomass within arctic ecosystems (18). In belowground systems, the grazing of fungal mycelia by soil invertebrates is an analogous trophic interaction, but the functional consequences of this process are poorly understood. Contemporary food web theory asserts that the complexity of the detrital food web will dampen the effects of any top-down interactions in soil, relative to aboveground systems (19), but laboratory-based studies suggest that the selective removal of dominant microbial groups by large invertebrates (isopods in particular) can be an important regulatory force (20). Indeed, simplified (two-species) model systems highlight the potential for interactive effects of warming and invertebrate grazing on fungal cord growth (7, 9), but it remains unclear whether these effects are relevant within natural, complex soil food webs. Despite their potential relevance for the land carbon–climate feedback, the capacity for animal–microbial interactions to mediate decomposition responses to global change remains untested. The failure to incorporate animals and their interactions with microbial communities into global decomposition models has been highlighted as a critical limitation in our understanding of carbon cycling under current and future climate scenarios (21, 22).In this study, we explore the potential of grazing soil invertebrates to mediate the interactive effects of soil warming and nitrogen enrichment on microbial (fungal and bacterial) biomass and functioning (extracellular enzyme production and wood decomposition rates) in temperate forest soil. The study was conducted in a multifactor global change experiment (Fig. 1A) established 8 y ago at the Harvard Forest Long-Term Ecological Research (LTER) site. Experimental treatments include two levels of soil warming and nitrogen addition (ambient and elevated), each replicated six times across a fully factorial design, that reflect values predicted by worst-case climate scenarios for the year 2100 (2). We then manipulated soil communities, establishing four biotic treatment chambers within each plot: −fungal cords,−isopods, with isopods and fungal cords removed; +fungal cords,−isopods; −fungal cords,+isopods; and +fungal cords,+isopods (Fig. 1B) to explore whether top-down control of cord-forming fungi by isopod grazers can mediate the direct effects of the abiotic global change factors. We tested the specific hypotheses that (i) the combined global change factors will stimulate soil microbial biomass, enzyme production, and wood decomposition by enhancing the growth of cord-forming basidiomycete fungi, but (ii) by grazing on fungal cords, soil animals will limit increases in fungal growth, thus dampening the direct effects of these abiotic global change factors on the rates of soil nutrient processes.Open in a separate windowFig. 1.Digital images showing (A) the Harvard Forest warming plots (although the study was conducted in the fall, this image was captured in winter to delineate the warming plots clearly); (B) the arrangement of biotic treatment mesocosms within each abiotic plot; (C) the surface of the soil (under the litter layer) within a warming+nitrogen addition plot in the absence of isopods; and (D) the surface of the soil within a warming+nitrogen addition plot in the presence of grazing isopods.     

Fish Species Distribution in Seagrass Habitats of Chesapeake Bay are Structured by Abiotic and Biotic Factors

Abstract

Seagrass habitats have long been known to serve as nursery habitats for juvenile fish by providing refuges from predation and areas of high forage abundance. However, comparatively less is known about other factors structuring fish communities that make extensive use of seagrass as nursery habitat. We examined both physical and biological factors that may structure the juvenile seagrass-associated fish communities across a synoptic-scale multiyear study in lower Chesapeake Bay. Across 3 years of sampling, we collected 21,153 fish from 31 species. Silver Perch Bairdiella chrysoura made up over 86% of all individuals collected. Nine additional species made up at least 1% of the fish community in the bay but were at very different abundances than historical estimates of the fish community from the early 1980s. Eight species, including Silver Perch, showed a relationship with measured gradients of temperature or salinity and Spot Leiostomus xanthurus showed a negative relationship with the presence of macroalgae. Climate change, particularly increased precipitation and runoff from frequent and intense events, has the potential to alter fish–habitat relationships in seagrass beds and other habitats and may have already altered the fish community composition. Comparisons of fish species to historical data from the 1970s, our data, and recent contemporary data in the late 2000s suggests this has occurred.

Received September 4, 2012; accepted May 5, 2013     

Biotic and abiotic determinants of seroprevalence of antibodies against Trypanosoma cruzi in Palmar de Bravo, Puebla, Mexico

OBJECTIVE: To establish the relationship between seroprevalence for antibodies against Trypanosoma cruzi and its relationship with biotic and abiotic factors. MATERIAL AND METHODS: A cross-sectional study was conducted between August 2000 and September 2001. The study population consisted of a simple random sample of 390 volunteers residing in Palmar de Bravo, Puebla, Mexico. Sample and data collection procedures included assaying antibodies against T. cruzi with validated assays, and searching for domestic reservoirs and triatomine bugs. The relationship between biotic and abiotic factors with seropositivity was assessed. Statistical analysis was conducted using Kappa values for diagnostic tests; statistical significance was assessed with 2 x 2 tables, chi-squared test with Yates' correction, Fisher exact test, and odds ratios. RESULTS: The seroprevalence of T. cruzi infection in humans was 4%; in domestic reservoirs (horses, pigs, and dogs) only 10% of canine reservoirs were positive. Vector species recognized were T. borberi and T. pallidipennis, with a Dispersion Area Index and a Colonization Index of 55% and 40%, respectively. The most important risk factors associated with positive serology were altitude (>2,150 and <2,180 meters above sea level), presence of triatomines, age, time of residence, and participation in a social assistance program. CONCLUSIONS: T. cruzi infection was identified in human beings, vectors, and possibly in domestic reservoirs, in communities located over 2,000 meters above sea level.     

Nucleation time and growth time in patients with cholesterol gallstone--factors affecting nucleation time and growth time and effect of UDCA and CDCA

Nucleation time (NT) and growth time (GT) were measured in gallbladder bile of patients with cholesterol gallstones. NT was significantly shortened (NT less than 10 days) in pure cholesterol stones but was moderately shortened (11 less than or equal to NT less than or equal to 21) in mixed and combination stones. GT also was accelerated (GT less than 7 days) in cholesterol stones. NT was shortened in increased biliary total protein, but on the contrary, was shortened in decreased apo A-I. NT of bile by UDCA therapy but not CDCA was extended. This suggests that increased apo A-I during UDCA therapy might imply extension of NT. The strong negative correlation between GT and CSI of bile suggests that CSI plays an important role in crystal growth.     

Physical time and personal biological time in gerontologic research

Beside the reversible t-time of physics is introduced an irreversible logarithmical tau-time as a second time. This time is determined by growth, vitality, and reliability of an organism. Using the tau-time it is possible to divide the lifespan of an organism into four parts. Each segment is of approximately the same duration, namely a quarter of the lifespan. There is an analogy between tau-time and physical entropy.     

Primary percutaneous coronary intervention in acute myocardial infarction: time, time, and time!

Longer door-to-balloon times, total duration of ischaemia, and time of presentation relative to symptom onset all have an impact on outcome following primary percutaneous coronary intervention.     

Laboratory controls of heparin therapy with thrombin time, partial thromboplastin time and activated recalcification time

For the laboratory control of a heparin therapy thrombin time, partial thromboplastin time and activated recalcification time are used. On account of distinct differences in the heparin sensitivity of these reactions an indication-related application is necessary. The ability of evidence and the possibility of establishing test-specific therapeutic regions are restricted by differences caused by reagents, individual variability and influence by accompanying haemostasiological changes. The own approach, taking into consideration the so-called heparin resistance, it presented.