Interacting trophic forcing and the population dynamics of herring

Small pelagic fish occupy a central position in marine ecosystems worldwide, largely by determining the energy transfer from lower trophic levels to predators at the top of the food web, including humans. Population dynamics of small pelagic fish may therefore be regulated neither strictly bottom-up nor top-down, but rather through multiple external and internal drivers. While in many studies single drivers have been identified, potential synergies of multiple factors, as well as their relative importance in regulating population dynamics of small pelagic fish, is a largely unresolved issue. Using a statistical, age-structured modeling approach, we demonstrate the relative importance and influence of bottom-up (e.g., climate, zooplankton availability) and top-down (i.e., fishing and predation) factors on the population dynamics of Bothnian Sea herring (Clupea harengus) throughout its life cycle. Our results indicate significant bottom-up effects of zooplankton and interspecific competition from sprat (Sprattus sprattus), particularly on younger age classes of herring. Although top-down forcing through fishing and predation by grey seals (Halichoerus grypus) and Atlantic cod (Gadus morhua) also was evident, these factors were less important than resource availability and interspecific competition. Understanding key ecological processes and interactions is fundamental to ecosystem-based management practices necessary to promote sustainable exploitation of small pelagic fish.     

Species' traits predict phenological responses to climate change in butterflies

How do species' traits help identify which species will respond most strongly to future climate change? We examine the relationship between species' traits and phenology in a well-established model system for climate change, the U.K. Butterfly Monitoring Scheme (UKBMS). Most resident U.K. butterfly species have significantly advanced their dates of first appearance during the past 30 years. We show that species with narrower larval diet breadth and more advanced overwintering stages have experienced relatively greater advances in their date of first appearance. In addition, species with smaller range sizes have experienced greater phenological advancement. Our results demonstrate that species' traits can be important predictors of responses to climate change, and they suggest that further investigation of the mechanisms by which these traits influence phenology may aid in understanding species' responses to current and future climate change.     

Specialization and interaction strength in a tropical plant-frugivore network differ among forest strata

The degree of interdependence and potential for shared coevolutionary history of frugivorous animals and fleshy-fruited plants are contentious topics. Recently, network analyses revealed that mutualistic relationships between fleshy-fruited plants and frugivores are mostly built upon generalized associations. However, little is known about the determinants of network structure, especially from tropical forests where plants' dependence on animal seed dispersal is particularly high. Here, we present an in-depth analysis of specialization and interaction strength in a plant-frugivore network from a Kenyan rain forest. We recorded fruit removal from 33 plant species in different forest strata (canopy, midstory, understory) and habitats (primary and secondary forest) with a standardized sampling design (3447 interactions in 924 observation hours). We classified the 88 frugivore species into guilds according to dietary specialization (14 obligate, 28 partial, 46 opportunistic frugivores) and forest dependence (50 forest species, 38 visitors). Overall, complementary specialization was similar to that in other plant-frugivore networks. However, the plant-frugivore interactions in the canopy stratum were less specialized than in the mid- and understory, whereas primary and secondary forest did not differ. Plant specialization on frugivores decreased with plant height, and obligate and partial frugivores were less specialized than opportunistic frugivores. The overall impact of a frugivore increased with the number of visits and the specialization on specific plants. Moreover, interaction strength of frugivores differed among forest strata. Obligate frugivores foraged in the canopy where fruit resources were abundant, whereas partial and opportunistic frugivores were more common on mid- and understory plants, respectively. We conclude that the vertical stratification of the frugivore community into obligate and opportunistic feeding guilds structures this plant-frugivore network. The canopy stratum comprises stronger links and generalized associations, whereas the lower strata are composed of weaker links and more specialized interactions. Our results suggest that seed-dispersal relationships of plants in lower forest strata are more prone to disruption than those of canopy trees.     

UV-radiation versus grazing pressure: long-term floating of kelp rafts (<Emphasis Type="Italic">Macrocystis pyrifera</Emphasis>) is facilitated by efficient photoacclimation but undermined by grazing losses

Large quantities of floating macroalgae are traveling in coastal waters of the SE Pacific and in other temperate climate zones. While afloat, these algae are potentially exposed to full solar radiation, including UVA and UVB, which can have profound effects on their physiological and growth performance. Latitudinal variations in UV-radiation (UVR) are hypothesized to affect floating algae differently with higher impacts at low latitudes than at high latitudes. In addition, UVR together with grazing might accelerate the demise of floating kelps. This hypothesis was tested with outdoor laboratory experiments in which sporophytes of the giant kelp Macrocystis pyrifera (L.) C. Agardh were exposed to a combination of different UVR regimes (PAR only, PAR + UV) and grazing at three sites along the Chilean coast (20°S, 30°S, and 40°S). A latitudinal trend in irradiance was detected with increasing values from 40°S to 20°S. Surprisingly, floating M. pyrifera responded with a high acclimation potential within this latitudinal UVR gradient. At 20°S, floating kelps were slightly sensitive to UVR, which was reflected in reduced blade growth. At 30°S, physiological responses were hardly affected by the prevailing irradiance but sporophyte growth and thus persistence mainly depended on the presence or absence of amphipod grazers. At high latitudes, grazing had only minor impacts on algal biomass and blade growth, and kelps thrived well under all tested environmental conditions. Overall, our results reveal that floating M. pyrifera was only slightly affected by UVR and that sporophytes can efficiently acclimate over a latitudinal UVR gradient that spans from 20°S to 40°S. Given this high acclimation potential, we suggest that these (and possibly other) positively buoyant algae are important dispersal agents over a wide range of temperate latitude conditions.     

Mitochondrial DNA sequence variation in spiny lobsters: population expansion,panmixia, and divergence

To investigate population differentiation in a comparative and historical context, segments of the mitochondrial cytochrome c oxidase subunit I gene and the control region were sequenced in Panulirus argus from nine sites along approximately 1,500 km of the Northern Caribbean Sea (n = 326) and analyzed with respect to available panulirid data. A mismatch analysis and Fu’s F _S test uncovered a signature of historical population expansion around the time of the Last Glacial Maximum. Significant population structure was not detected in the area. The data supported a hypothesis of panmixia resulting from ongoing larval transport by ocean currents and historical population expansion. Despite high intraspecific divergence levels at COI within Panulirus argus and several other Panulirus species, genetic species identification through DNA barcoding was feasible using either a modified distance threshold or a character-based approach.     

Size-selective sampling of particulates using a physiologic sampling pump

Recent laboratory research indicates physiologic sampling of gas and vapor may provide more representative estimates of personal exposures than traditional methods. Modifications to the physiologic sampling pump (PSP) used in that research are described which extend its usefulness to size-selective sampling of particulates. PSPs used in previous research varied motor speed to keep sampling proportional to the subject's inhalation. This caused airflow and particle velocities through the collection device to continually change making those pumps unsuitable for sampling particulates. The modified implementation of the PSP pulls a constant airflow into and through a cyclone, then uses valves to either direct the airflow through, or divert the airflow around, the sampling filter. By using physiologic inputs to regulate the fraction of each second that air flows through the sampling filter, samples may be collected in proportion to inhalation rate. To evaluate the performance of a functional prototype 5 different sizes of monodisperse aerosols of ammonium fluorescein were generated by a vibrating orifice aerosol generator and introduced into a calm air chamber. To simulate different inhalation rates the valves of the PSP were energized using 9 different duty cycles. Efficiency curves are presented and compared to a standard respirable convention by bias mapping. The performance of the modified cyclone used in the PSP sampling head compared favorably with a commercially available cyclone of the same model, operating at a constant airflow (± 10% over almost all the size distributions of concern). The new method makes physiologic sampling of the respirable fraction of particulates feasible.     

European Farmland Bird Distribution Explained by Remotely Sensed Phenological Indices

Birds are important components of biodiversity conservation since they are capable of indicating changes in the general status of wildlife and of the countryside. The Pan-European Common Bird Monitoring Scheme (PECBM) has been launched by the BirdLife Partnership in Europe, where the European Bird Census Council has been collecting data from 20 independent breeding bird survey programs across Europe over the last 25 years. These data show dramatic declines in European farmland birds. We suggest that seasonal characteristics of vegetation cover derived from high temporal resolution remote sensing images could facilitate the monitoring the suitability of farmland bird habitats, and that these indicators may be a better choice for monitoring than climate data. We used redundancy analysis to link the PECBM data of the estimated number of farmland birds in Europe to a set of phenological and climatic indicators and to the biogeographic regions of Europe. Variance partitioning was used to account for the variation explained by the phenological and climate variables and by the area of the environmental strata individually, to define the pure effect of the variables, and to extract the total explained variance. The analysis revealed high statistical significance (p < 0.001) of the correlations between species and environment. Phenological indices explained 38% of the variance in community composition of the 23 farmland bird species, whereas climate explained 30% of the variance. After partitioning the other variables as covariables, the pure effect of phenology, climate, and environmental strata were 16%, 8%, and 16%, respectively. Based on the probability results, we suggest that phenological indicators derived from remote sensing may supply better indicators for continental scale biodiversity studies than climate only. In addition, these indicators are cost and time effective, are on continuous scale, and are readily repeatable on a large spatial coverage while supplying standardized results.     

Contrasting temporal trends and relationships of total organic carbon, black carbon, and polycyclic aromatic hydrocarbons in rural low-altitude and remote high-altitude lakes

Historical records of total organic carbon (TOC), black carbon (BC), and polycyclic aromatic hydrocarbons (PAHs) were reconstructed in dated sediment cores from four nearby lakes in central Switzerland. In the sub-Alpine Lake Thun, located at 558 m a.s.l., the proximity to anthropogenic emission sources is reflected in higher input of BC and PAHs into sediments with fluxes only slightly decreasing during the last decades. PAH/BC ratios are relatively high and correlation between levels of total PAHs and BC is almost inexistent in Lake Thun, probably due to the presence of less condensed forms of the BC spectrum (char BC) that is underestimated with the chemothermal oxidation method applied in this study. The sediment profiles of TOC, BC, and PAHs are noticeably different in the mountain lakes located around 2000 m a.s.l. In Lake Engstlen, the PAH/BC ratios, as well as the correlation between PAHs and BC, point towards appreciable amounts of predominantly light soot particles. Light soot particles have higher mobility and can, therefore, be efficiently transported to this remote site. The proglacial Lake Oberaar is shown to be a receptor of BC and PAHs released by the fast melting adjacent glacier acting as a secondary source for these conservative species temporarily stored in the glacier ice. Finally, Lake Stein is in strong contrast to all other lakes. High flux of BC into Lake Stein, combined with constant temporal evolutions of BC and PAHs, and in particular BC/TOC ratios approaching 100% are all strong indications for a geogenic presence of graphite in its catchment area.     

Cadmium, copper, lead, and zinc in Mugil cephalus from seven coastal lagoons of NW Mexico

The increasing order of the mean concentrations of Cd, Cu, and Zn in the tissues of Mugil cephalus of seven coastal lagoons of Sinaloa State (NW Mexico) was liver > gills > muscle, while for Pb it was gills > muscle ≥ liver. There were no differences between the mean concentrations of Cd and Pb of the three tissues determined in the samples of the seven lagoons and, although there were some significant differences, there was no indication of a latitude-related trend in the distribution of Cu and Zn: the Cu content of the muscle tended to be higher in the northern than in the southern lagoons, although in the case of the gills the highest and lowest mean values indicated an opposite trend, with the highest and lowest values in one southern and one northern lagoon. In the case of the liver, there were no differences and no indication of a regional trend. There were no differences in the mean Zn contents of muscle and gills; in the case of the liver, one of the lagoons of the central part of the state had a significantly higher value than one of the southern lagoons and all the rest had similar values. In addition, there was no clear indication of season-related differences in any of the three tissues. According to our results, the metal contents of the muscle of this species are not of concern for human health, since the allowable ingestion would be in the order of 0.9 kg/day.     

Eutrophication induced changes in benthic community structure of a flow-restricted tropical estuary (Cochin backwaters), India

The influence of anthropogenic loading on the distribution of soft bottom benthic organisms of a tropical estuary (Cochin backwaters) was examined. The industrial activities were found to be high in the northern and central part of the estuary, where dissolved inorganic nitrogen (DIN > 210 ??M) and phosphorus (DIP > 6.5 ??M) have caused high abundance of chlorophyll a (up to 73 mg m^???3) and accumulation of organic carbon in sediments (up to 5%). Principal component analysis distinguished three zones in the estuary. The central zone (Z1) was characterized by organic enrichment, low species diversity, and increased number of pollution tolerant species. Long-term deterioration of the estuary is indicated by an increase in the nutrients and chlorophyll a levels by sixfold during the last few decades. Flow restrictions in the lower estuary have lead to a fourfold increase in sediment organic carbon over the period of three decades. The reduced benthic diversity followed by an invasion of opportunistic polychaetes (Capitella capitata), are indicative of a stress in the estuary.