Effects of disturbance on the diversity of hard-bottom macrobenthic communities on the coast of Chile

The intermediate disturbance hypothesis (IDH) predicts maximal diversity at intermediate levels of disturbance, but the validity of this hypothesis is controversially discussed. In this study, results of a field experiment, which was conducted on the northern-central Chilean coast, are presented. Fouling communities on artificial settlement substrata were studied. A total of 7 disturbance frequencies were applied to previously established communities, and a single disturbance event resulted in a removal of ~20% of the biomass. Species cover was estimated at the end of the experimental period, and it was found that diversity was strongly affected by disturbance frequency. With high disturbance frequencies the composition of the community was changed, with a decrease in the solitary ascidian Pyura chilensis (Molina 1782). The decrease of P. chilensis resulted in an increase of the colonial ascidian Diplosoma sp. A unimodal relationship between disturbance frequency and species richness was found, supporting the IDH. The results suggest that disturbance sustains diversity by reducing the abundance of the dominant species (e.g. P. chilensis), preventing competitive exclusion of the subordinate species, thus allowing subordinate species to re-emerge when competition is alleviated by disturbance. The results also suggest that these species show a trade-off between competitive and colonizing abilities, pointing to the existence of a competitive hierarchy. Therefore, the presence of competitive exclusion and disturbance-induced suppression of the dominant species remains a crucial mechanism, permitting species coexistence in the context of the IDH in the system studied

High temporal variability in the occurrence of consumer-resource interactions in ecological networks

Ecological networks are theoretical abstractions that represent ecological communities. These networks are usually defined as static entities, in which the occurrence of a particular interaction between species is considered fixed despite the intrinsic dynamics of ecological systems. However, empirical analysis of the temporal variation of trophic interactions is constrained by the lack of data with high spatial, temporal, and taxonomic resolution. Here, we evaluate the spatiotemporal variability of multiple consumer-resource interactions of large marine networks. The tropic interactions of all of the analyzed networks had low temporal persistence, which was well described by a common exponential decay in the rank-frequency relationship of consumer-resource interactions. This common pattern of low temporal persistence was evident despite the dissimilarities of environmental conditions among sites. Between-site rank correlations of frequency of occurrence of interactions ranged from 0.59 to 0.73. After removing the interactions with <50% frequency, the between-site correlations decreased to values between 0.60 and 0.28, indicating that low-frequency interactions accounted for the apparent similarities between sites. Our results showed that the communities studied were characterized by few persistent interactions and a large number of transient trophic interactions. We suggest that consumer-resource temporal asynchrony in addition to varying local environmental conditions and opportunistic foraging could be among the mechanisms generating the observed rank-frequency relationship of trophic interactions. Therefore, our results question the analysis of ecological communities as static and persistent natural entities and stress the need for strengthening the analysis of temporal variability in ecological networks and long-term studies.Comment: 21 pages, 3 figure

Limited predatory effects on infaunal macrobenthos community patterns in intertidal soft-bottom of Arctic coasts

Predation shapes marine benthic communities and affects prey species population dynamics in tropic and temperate coastal systems. However, information on its magnitude in systematically understudied Arctic coastal habitats is scarce. To test predation effects on the diversity and structure of Arctic benthic communities, we conducted caging experiments in which consumers were excluded from plots at two intertidal sedimentary sites in Svalbard (Longyearbyen and Thiisbukta) for 2.5 months. Unmanipulated areas served as controls and partial (open) cages were used to estimate potential cage effects. At the end of the experiment, we took one sediment core from each plot and quantified total biomass and the number of each encountered taxon. At both sites, the experimental exclusion of predators slightly changed the species composition of communities and had negligible effects on biomass, total abundance, species richness, evenness, and Shannon Index. In addition, we found evidence for cage effects, and spatial variability in the intensity of the predation effects was identified. Our study suggests that predators have limited effects on the structure of the studied intertidal macrobenthic Arctic communities, which is different from coastal soft-bottom ecosystems at lower latitudes

Asymmetric competitive effects during species range expansion: an experimental assessment of interaction strength between ‘equivalent’ grazer species in their range overlap.

1. Biotic interactions are central to the development of theory and concepts in community ecology; experimental evidence has shown their strong effects on patterns of population and community organization and dynamics over local spatial scales. The role of competition in determining range limits and preventing invasions at biogeographic scales is more controversial, partly because of the complexity of processes involved in species colonization of novel habitats and the difficulties in performing appropriate manipulations and controls. 2. We examined experimentally whether competition is likely to affect poleward range expansion hindering or facilitating the establishment of the limpet Scurria viridula along the southeastern Pacific rocky shore (30°S, Chile) in the region occupied by the congeneric S. zebrina. We also assessed whether competition with the “invader” or range expanding species could reduce individual performance of the ‘native’ S. zebrina and depress local populations 3. Geographic field surveys were conducted to characterize the abundance and identity of limpets along the south-eastern Pacific coast from 18°S to 41°S, and the micro-scale (few cm) spatial distribution across the range overlap of the two species. Field-based competition experiments were conducted at the southern leading edge of the range of S. viridula (33°S) and at the northern limit of S. zebrina (30°S). 4. Field surveys showed poleward range expansion of S. viridula of ca. 210 km since year 2000, with an expansion rate of 13.1 km year -1. No range shift was detected for S. zebrina. The resident S. zebrina had significant negative effects on the growth rate of the invading juvenile S. viridula, while no effect of the latter was found on S. zebrina. Spatial segregation between species was found at the scale of cms. 5. Our results provide novel evidence of an asymmetric competitive effect of a resident species on an invader, which may hamper further range expansion. No negative effect of the invader on the resident species was detected. This study highlights the complexities of evaluating the role of species interactions in setting range limits of species, but showed how interspecific competition might slow the advance of an invader by reducing individual performance and overall population size at the advancing front

Distribución geográfica y descripción de cuatro especies de cirripedios pelágicos a lo largo de la costa chilena del Pacífico sur este - una aproximación zoogeográfica

The majority of zoogeographic studies along the Chilean Pacific coast have focused on benthic organisms and oceanographic conditions are considered the main factors influencing their distributions. Herein we examined the geographic distribution of pelagic barnacles of the family Lepadidae collected from floating macroalgae at seven sampling areas between 23 and 50&deg; S. Four species were encountered and they are briefly described herein. The most abundant northern species was Lepas anatifera, and it diminished in abundance towards the south (33&deg; S). Moreover, this species was not found in waters with a sea surface temperature (SST) of less than ~18 &ordm;C. Lepas australis, primarily a circumpolar West Wind Drift species, diminished in abundance towards the north (33&deg; S). This species was restricted to waters of &lt; 18 &ordm;C SST. A third species, L. pectinata, was encountered throughout almost the entire study area, but it was most abundant between 29 and 33&deg; S. The fourth species, Dosima fascicularis, was only found at two sampling areas, namely at 27&deg; S and 33&deg; S, and this is the first record of this species from the central coast of Chile. The distributional pattern of the pelagic barnacles found herein corresponds to the three main zoogeographic regions as revealed by the majority of previous studies based on littoral organisms: the northern Peru-Chilean Province, the southern Magellanic Province, and the central Chilean Transition Zone where the two provinces overlap. Even though the present study only considers four species of pelagic barnacles, the results support the hypotheses on the importance of oceanographic conditions (in particular SST) in determining the zoogeographic patterns along the south east Pacific coast of Chile

Short-Interval, Severe Wildfires Alter Saproxylic Beetle Diversity in Andean Araucaria Forests in Northwest Chilean Patagonia

The occurrence of short-interval, severe wildfires are increasing drastically at a global scale, and appear as a novel phenomenon in areas where fire historically returns in large time lapses. In forest ecosystems, these events induce drastic changes in population dynamics, which could dramatically impact species diversity. Here, we studied the effect on diversity of recent short-interval, severe wildfires (SISF), which occurred in rapid succession in the summers of 2002 and 2015 in Chilean Northern Patagonian Araucaria–Nothofagus forests. We analyzed the diversity of deadwood-dependent (i.e., saproxylic) and fire-sensitive beetles as biological indicators across four conditions: 2002-burned areas, 2015-burned areas, SISF areas (i.e., burned in 2002 and again in 2015), and unburned areas. Saproxylic beetles were collected using window traps in 2017 to 2019 summer seasons. To investigate the mechanisms underpinning the fire-related disturbance of the assemblage, we evaluated the effects of post-fire habitat quality (e.g., dead wood decomposition) and quantity (e.g., burned dead wood volume and tree density) on the abundances and species richness of the entire assemblage and also multiple trophic groups. Compared with the unburned condition, SISF drastically reduced species richness, evenness, and Shannon’s diversity and altered the composition of the saproxylic beetle assemblages. The between-condition variation in composition was accounted for by a species replacement (turnover) between SISF and 2015-burned areas, but both species replacement and extinction (nestedness) between SISF and unburned areas. Dead wood decomposition and tree density were the variables with the strongest effects on the abundance and species richness of the entire saproxylic beetle assemblage and most trophic groups. These results suggest that SISF, through degraded habitat quality (dead wood decomposition) and quantity (arboreal density), have detrimental impacts on diversity and population dynamics of saproxylic beetle assemblages. Therefore, habitat loss is a central mechanism underpinning fire-related biodiversity loss in these forest ecosystems.F.T. (Francisco Tello) was financially supported by CONICYT doctoral scholarship no. 21171980. F.T. (Francisco Tello), M.E.G., and A.L. were financially supported by ANID/FONDAP center no. 15110009 (CR2). M.E.G. was financially supported by FONDECYT grant no. 1201528. N.V. was financially supported by FONDECYT grants no. 1190529, no. 1181300, and FONDAP center no. 15150003 (IDEAL)

Formative research: perceptions of communication science students at a peruvian university

Formative research generates different perceptions in undergraduate students, and in order to know more about them, 80 were surveyed, and 12 Communication Science students were interviewed at a national university in Lima (Peru). The results evidence that they conceive of it as: training to conduct scientific research, curricular or extracurricular activities as part of or for scientific research, preparation for conducting research work for graduation or obtaining a qualification, the development of competences for researching in the profession, an instructional strategy to develop research competences, and a strengthening of the research culture, among others. But beyond these varied concepts, the estimation of the majority emerges that formative research has been neglected by the university, thus becoming a challenge to optimize professional training, requiring qualified instructors with pertinent instructional methods, as well as an updated curriculum, which strengthens the research culture, responding to social demands and ensuring resources for the development of research competencesPeer Reviewe

Monitoreo hemodinámico invasivo por catéter de arteria pulmonar Swan-Ganz: conceptos y utilidad

Since its beginnings in the last century, pulmonary artery catheterization (PAC) has evolved into an invasive hemodynamic evaluation technique that can be performed at the patient’s bedside through a Swan-Ganz catheter; this procedure has maintained an intermittent course in terms of its use; however, it has currently demonstrated relevance in specific scenarios. The PAC allows access to the central venous circulation, the right heart and the pulmonary artery; it performs the calculation of hemodynamic variables directly or indirectly by means of established formulas and methods. This makes possible to perform an adequate hemodynamic evaluation and classification, perform specific tests (e.g. vasoreactivity test), which help to define the diagnosis, therapeutic , monitor the response to treatment, evaluation prior to advanced therapies (e.g. cardiac transplantation or mechanical circulatory assistance devices), and prognosis in our patients. In this article we discuss the concepts and usefulness of pulmonary artery catheterization.Desde sus inicios en el siglo pasado, el cateterismo de arteria pulmonar (CAP) ha ido evolucionando hasta ser una técnica de evaluación hemodinámica invasiva que puede realizarse en la cama del paciente a través de un catéter Swan-Ganz; este procedimiento ha mantenido un curso intermitente en cuanto a su uso; no obstante, actualmente ha demostrado relevancia en escenarios específicos. El CAP permite el acceso a la circulación venosa central, el corazón derecho y la arteria pulmonar; realiza el cálculo de variables hemodinámicas de manera directa o indirecta mediante fórmulas y métodos establecidos. Esto hace posible realizar una evaluación y clasificación hemodinámica adecuada, realizar pruebas específicas (p. ej. prueba de vasorreactividad), que ayudan a definir el diagnóstico, la conducta terapéutica, monitorizar la respuesta al tratamiento, la evaluación previa a terapias avanzadas (p. ej. el trasplante cardiaco o dispositivos de asistencia circulatoria mecánica), y el pronóstico en los pacientes. En este artículo profundizamos sobre los conceptos y la utilidad del cateter de arteria pulmonar

Effect of anticomplement agent K-76 COOH in hamster-to-rat and guinea pig- to-rat xenotransplantation

In normal rats, the xenobiotic K76 inhibited the C5 and probably the C2 and C3 steps of complement and effectively depressed classical complement pathway activity, alternative complement pathway activity, and the C3 complement component during and well beyond the drug's 3-hr half-life. It was tested alone and with intramuscular tacrolimus (TAC) and/or intragastric cyclophosphamide (CP) in rat recipients of heterotopic hearts from guinea pig (discordant) and hamster (concordant) donors. Single prevascularization doses of 100 and 200 mg/kg increased the median survival time of guinea pig hearts from 0.17 hr in untreated controls to 1.7 hr and 10.2 hr, respectively; with repeated injections of the 200-mg dose every 9-12 hr, graft survival time was increased to 18.1 hr. Pretreatment of guinea pig heart recipients for 10 days with TAC and CP, with or without perioperative splenectomy or infusion of donor bone marrow, further increased median graft survival time to 24 hr. Among the guinea pig recipients, the majority of treated animals died with a beating heart from respiratory failure that was ascribed to anaphylatoxins. Hamster heart survival also was increased with monotherapy using 200 mg/kg b.i.d.i.v. K76 (limited by protocol to 6 days), but only from 3 to 4 days. Survival was prolonged to 7 days with the addition to K76 of intragastric CP at 5 mg/kg per day begun 1 day before operation (to a limit of 9 days); it was prolonged to 4.5 days with the addition of intramuscular TAC at 2 mg/kg per day beginning on the day of transplantation and continued indefinitely. In contrast to the limited efficacy of the single drugs, or any two drugs in combination, the three drugs together (K76, CP, and TAC) in the same dose schedules increased median graft survival time to 61 days. Antihamster antibodies rapidly increased during the first 5 days after transplantation, and plateaued at an abnormal level in animals with long graft survival times without immediate humoral rejection. However, rejection could not be reliably prevented, and was present even in most of the xenografts recovered from most of the animals dying (usually from infection) with a beating heart. Thus, although effective complement inhibition with K76 was achieved in both guinea pig- and hamster-to-rat heart transplant models, the results suggest that effective interruption of the complement cascade will have a limited role, if any, in the induction of xenograft acceptance