What model suits ecosystem-based fisheries management? A plea for a structured modeling process

As tools within ecosystem-based fisheries management (EBFM), a wide range of Ecosystem Models (EMs) have been designed to represent ecosystem complexity, but it is not always clear how the outputs of these models can be applied. We address this debate in a literature review to illustrate how a better understanding of ecosystem modeling within the EBFM framework could facilitate the use of EMs in the decision-making process. We classify EMs according to their complexity, and qualitatively evaluate their level of success with regard to five general goals of EBFM. In principle, no single EM is found to successfully accomplish all the EBFM goals. Therefore, we suggest that the way in which ecosystem modeling can effectively contribute to EBFM is through a structured modeling process, which should be pursued according to the context of each specific area. Within this planning strategy a range of Ems should be considered, from rather simple ones with few parameters, whose outputs are scientifically robust but possibly of limited use within the EBFM, to those which include a large number of ecosystem elements yet at the expense of increased uncertainty. If multiple EMs, despite their different assumptions, leads to consistent and converging results then robust management decisions will be supported. The present paper appears particularly useful to anyone confronted with the selection of modeling tools for the implementation of fisheries management strategies considering the particular situation of the fishery.     

Influence of habitat complexity and landscape configuration on pollination and seed-dispersal interactions of wild cherry trees

Land-use intensification is a major cause for the decline in species diversity in human-modified landscapes. The loss of functionally important species can reduce a variety of ecosystem functions, such as pollination and seed dispersal, but the intricate relationships between land-use intensity, biodiversity and ecosystem functioning are still contentious. Along a gradient from forest to intensively used farmland, we quantified bee species richness, visitation rates of bees and pollination success of wild cherry trees (Prunus avium). We analysed the effects of structural habitat diversity at a local scale and of the proportion of suitable habitat around each tree at a landscape scale. We compared these findings with those from previous studies of seed-dispersing birds and mammals in the same model system and along the same land-use gradient. Bee species richness and visitation rates were found to be highest in structurally simple habitats, whereas bird species richness—but not their visitation rates—were highest in structurally complex habitats. Mammal visitation rates were only influenced at the landscape scale. These results show that different functional groups of animals respond idiosyncratically to gradients in habitat and landscape structure. Despite strong effects on bees and birds, pollination success and bird seed removal did not differ along the land-use gradient at both spatial scales. These results suggest that mobile organisms, such as bees and birds, move over long distances in intensively used landscapes and thereby buffer pollination and seed-dispersal interactions. We conclude that measures of species richness and interaction frequencies are not sufficient on their own to understand the ultimate consequences of land-use intensification on ecosystem functioning.     

Mycorrhizal responsiveness trends in annual crop plants and their wild relatives—a meta-analysis on studies from 1981 to 2010

Background and aims

Year of release of a cultivar reflects the agricultural and breeding practices of its time; we hypothesize that there are differences in mycorrhizal responsiveness of new high yielding and old crop plants and landraces. We evaluated the importance of the year of release on mycorrhizal responsiveness, arbuscular mycorrhizal (AM) fungal root colonization and P efficiency. We also analyzed the effect of experimental treatments, P efficiency (P acquisition and P utilization efficiency) and AM fungal root colonization on a potential mycorrhizal responsiveness trend for year of release.

Methods

We conducted a meta-analysis on 39 publications working on 320 different crop plant genotypes.

Results

New cultivars were less intensely colonized but were more mycorrhiza-responsive (and possibly dependent) compared to ancestral genotypes. This trend was potentially influenced by the moderator variables density, pre-germination, plant, plant type and AMF species. AM root colonization was also important for the mycorrhizal responsiveness trend for year of release, but P efficiency was not.

Conclusions

With the data available we could find no evidence that new crop plant genotypes lost their ability to respond to mycorrhiza due to agricultural and breeding practices.     

Ecophysiological analysis of moss-dominated biological soil crusts and their separate components from the Succulent Karoo, South Africa

Biological soil crusts, formed by an association of soil particles with cyanobacteria, lichens, mosses, fungi and bacteria in varying proportions, live in or directly on top of the uppermost soil layer. To evaluate their role in the global carbon cycle, gas exchange measurements were conducted under controlled conditions. Moss-dominated soil crusts were first analyzed as moss tufts on soil, then the mosses were removed and the soil was analyzed separately to obtain the physiological response of both soil and individual moss stems. Net photosynthetic response of moss stems and complete crusts was decreased by insufficient and excess amounts of water, resulting in optimum curves with similar ranges of optimum water content. Light saturation of both sample types occurred at high irradiance, but moss stems reached light compensation and saturation points at lower values. Optimum temperatures of moss stems ranged between 22 and 27°C, whereas complete crusts reached similar net photosynthesis between 7 and 27°C. Under optimum conditions, moss stems reached higher net photosynthesis (4.0 vs. 2.8 μmol m^?2 s^?1) and lower dark respiration rates (?0.9 vs. ?2.4 μmol m^?2 s^?1). Respiration rates of soil without moss stems were high (up to ?2.0 μmol m^?2 s^?1) causing by far lower absolute values of NP/DR ratios of soil crusts as compared to moss stems. In carbon balances, it therefore has to be clearly distinguished between measurements of soil crust components versus complete crusts. High rates of soil respiration may be caused by leaching of mosses, creating high-nutrient microsites that favor microorganism growth.     

Serotonin signaling is required for Wnt-dependent GRP specification and leftward flow in Xenopus

In vertebrates, most inner organs are asymmetrically arranged with respect to the main body axis [1]. Symmetry breakage in fish, amphibian, and mammalian embryos depends on cilia-driven leftward flow of extracellular fluid during neurulation [2-5]. Flow induces the asymmetric nodal cascade that governs asymmetric organ morphogenesis and placement [1, 6, 7]. In the frog Xenopus, an alternative laterality-generating mechanism involving asymmetric localization of serotonin at the 32-cell stage has been proposed [8]. However, no functional linkage between this early localization and flow at neurula stage has emerged. Here, we report that serotonin signaling is required for specification of the superficial mesoderm (SM), which gives rise to the ciliated gastrocoel roof plate (GRP) where flow occurs [5, 9]. Flow and asymmetry were lost in embryos in which serotonin signaling was downregulated. Serotonin, which we found uniformly distributed along the main body axes in the early embryo, was required for Wnt signaling, which provides the instructive signal to specify the GRP. Importantly, serotonin was required for Wnt-induced double-axis formation as well. Our data confirm flow as primary mechanism of symmetry breakage and suggest a general role of serotonin as competence factor for Wnt signaling during axis formation in Xenopus.     

Bats eavesdrop on the sound of copulating flies

The idea that copulation might increase predation risk is a classic suggestion [1-3], but empirical evidence to support it is surprisingly scarce. While some early work found decreased vulnerability to predation during mating [2], two lab and one very recent field study documented increased predation during mating in freshwater amphipods [4], water striders [5] and locusts [6]. Decreased vigilance, less efficient escape responses, and increased conspicuousness of mating pairs have been suggested as mechanisms that might underpin elevated predation risk during copulation [2]. However, these putative mechanisms have never been investigated empirically. Here we describe a bat-insect system within which copulation greatly increases predation risk. We experimentally demonstrate that wild Natterer's bats (Myotis nattereri) 'eavesdrop' on acoustic cues emanating from copulating flies (Musca domestica) in a cowshed (Figure 1). With this evidence, we pinpoint increased conspicuousness as a relevant mechanism for elevated predation risk during mating.     

Establishment of global patterns of planar polarity during growth of the Drosophila wing epithelium

Epithelial tissues develop planar polarity that is reflected in the global alignment of hairs and cilia with respect to the tissue axes. The planar cell polarity (PCP) proteins form asymmetric and polarized domains across epithelial junctions that are aligned locally between cells and orient these external structures. Although feedback mechanisms can polarize PCP proteins intracellularly and locally align polarity between cells, how global PCP patterns are specified is not understood. It has been proposed that the graded distribution of a biasing factor could guide long-range PCP. However, we recently identified epithelial morphogenesis as a mechanism that can reorganize global PCP patterns; in the Drosophila pupal wing, oriented cell divisions and rearrangements reorient PCP from a margin-oriented pattern to one that points distally. Here, we use quantitative image analysis to study how PCP patterns first emerge in the wing. PCP appears during larval growth and is spatially oriented through the activities of three organizer regions that control disc growth and patterning. Flattening morphogen gradients emanating from these regions does not reduce intracellular polarity but distorts growth and alters specific features of the PCP pattern. Thus, PCP may be guided by morphogenesis rather than morphogen gradients.     

Testing the adjustable threshold model for intruder recognition on Myrmica ants in the context of a social parasite

Social insect colonies are like fortresses, well protected and rich in shared stored resources. This makes them ideal targets for exploitation by predators, parasites and competitors. Colonies of Myrmica rubra ants are sometimes exploited by the parasitic butterfly Maculinea alcon. Maculinea alcon gains access to the ants' nests by mimicking their cuticular hydrocarbon recognition cues, which allows the parasites to blend in with their host ants. Myrmica rubra may be particularly susceptible to exploitation in this fashion as it has large, polydomous colonies with many queens and a very viscous population structure. We studied the mutual aggressive behaviour of My. rubra colonies based on predictions for recognition effectiveness. Three hypotheses were tested: first, that aggression increases with distance (geographical, genetic and chemical); second, that the more queens present in a colony and therefore the less-related workers within a colony, the less aggressively they will behave; and that colonies facing parasitism will be more aggressive than colonies experiencing less parasite pressure. Our results confirm all these predictions, supporting flexible aggression behaviour in Myrmica ants depending on context.     

Diverse pollinator communities enhance plant reproductive success

Understanding the functional consequences of biodiversity loss is a major goal of ecology. Animal-mediated pollination is an essential ecosystem function and service provided to mankind. However, little is known how pollinator diversity could affect pollination services. Using a substitutive design, we experimentally manipulated functional group (FG) and species richness of pollinator communities to investigate their consequences on the reproductive success of an obligate out-crossing model plant species, Raphanus sativus. Both fruit and seed set increased with pollinator FG richness. Furthermore, seed set increased with species richness in pollinator communities composed of a single FG. However, in multiple-FG communities, highest species richness resulted in slightly reduced pollination services compared with intermediate species richness. Our analysis indicates that the presence of social bees, which showed roughly four times higher visitation rates than solitary bees or hoverflies, was an important factor contributing to the positive pollinator diversity–pollination service relationship, in particular, for fruit set. Visitation rate at different daytimes, and less so among flower heights, varied among social bees, solitary bees and hoverflies, indicating a niche complementarity among these pollinator groups. Our study demonstrates enhanced pollination services of diverse pollinator communities at the plant population level and suggests that both the niche complementarity and the presence of specific taxa in a pollinator community drive this positive relationship.