Scale-specific spatial density-dependence in parasitoids: a multi-factor meta-analysis

1. Within a landscape, the risk of an insect being attacked by a parasitoid varies with the local density of the host species. This relationship should be strongest when observed at medium extents and resolutions with respect to the parasitoids’ foraging range, and turn negative at fine resolutions. The relationship is also hypothesised to depend on certain traits of the host and parasitoid taxa – e.g. being more positive for more specialised hosts or parasitoids and more negative for mobile hosts or gregarious parasitoids. Building on earlier literature reviews, it is now possible to investigate these hypotheses using meta-analysis. 2. We performed a multi-factor meta-analysis on 151 analyses of parasitism rates with respect to host densities at specified scales, from 61 empirical studies published from 1988 to 2012. We explored how the correlation between host density and parasitism rate may be related to the explanatory variables already mentioned, plus parasitoid body-size and various other characteristics of both hosts and parasitoids. 3. Correlations (Pearson’s r) between host density and parasitism rate ranged from –0.88 to 0.98 (mean 0.16, standard deviation 0.39). The correlation was more often negative where the host was exotic or in the orders Lepidoptera or Diptera, where the parasitoid was larger or exotic, or where the study was conducted at a finer grain-size. Hymenoptera and Homoptera were the most likely host orders to reveal positive associations, with Coleoptera and Diptera intermediate. 4. The fact that increased observational grain-size had similar effects to decreased parasitoid body length could be taken as evidence that parasitoids’ foraging ranges increase with their body-length. However, the hypothesis about scale-specific foraging was not supported by studies that compared multiple scales. 5. We conclude that parasitism most commonly produces positive (compensatory) spatial density-dependence, but ecological context is all-important. These findings should help improve the design and interpretation of field experiments on parasitism as well as their application to the modelling of population dynamics and the practice of biological control

Soil and plant response to three subsoiling implements

Many Southeastern Coastal Plain soils require deep (>0.45 m) inrow tillage or subsoiling to disrupt dense tillage/traffic pans and/ or eluvial (E) horizons. Three subsoiling implements [Super Seeder (SS), ParaTill (PT), and Kelly (KE)] were compared on Norfolk (Typic Paleudult) loamy sand to assess their effectiveness in developing and maintaining a proper rooting environment for corn (Zen mays L.). Soil strength (cone index) for the implements was evaluated with and without conventional surface tillage (disking). All three subsoiling implements effectively disrupted the E horizon regardless of surface tillage, but the 67% stand establishment in nondisked treatments was significantly lower than for disked treatments (92%). However, yields were not significantly different. Significant differences in soil strength were measured among subsoiling implements at the beginning of each growing season. In 1985 mean profile soil strength was lower (P 0.10) for SS and PT than for KE. In 1986, soil strength was lower (P 0.10) for SS than either PT or KE. The consistent difference between SS and KE occurred because SS disrupted a larger area than the thinner-shanked KE. Nondisked treatments had mean soil strength that was 0.32 MPa lower within the row than disked treatments, but disked treatments had mean soil strength that was 0.37 MPa lower between the rows. Soil strength results suggest that Coastal Plain soils, which have been subsoiled, are less likely to restrict root development regardless of implement with, or without, prior surface tillage

Neighbouring-group composition and within-group relatedness drive extra-group paternity rate in the European badger (Meles meles)

Extra-group paternity (EGP) occurs commonly among group-living mammals and plays an important role in mating systems and the dynamics of sexual selection; however, socio-ecological and genetic correlates of EGP have been underexplored. We use 23 years of demographic and genetic data from a high-density European badger (Meles meles) population, to investigate the relationship between the rate of EGP in litters and mate availability, mate incompatibility and mate quality (heterozygosity). Relatedness between within-group assigned mothers and candidate fathers had a negative quadratic effect on EGP, whereas the number of neighbouring-group candidate fathers had a linear positive effect. We detected no effect of mean or maximum heterozygosity of within-group candidate fathers on EGP. Consequently, EGP was associated primarily with mate availability, subject to within-group genetic effects, potentially to mitigate mate incompatibility and inbreeding. In badgers, cryptic female choice, facilitated by superfecundation, superfoetation and delayed implantation, prevents males from monopolizing within-group females. This resonates with a meta-analysis in group-living mammals, which proposed that higher rates of EGP occur when within-group males cannot monopolize within-group females. In contrast to the positive meta-analytic association, however, we found that EGP associated negatively with the number of within-group assigned mothers and the number of within-group candidate fathers; potentially a strategy to counter within-group males committing infanticide. The relationship between the rate of EGP and socio-ecological or genetic factors can therefore be intricate, and the potential for cryptic female choice must be accounted for in comparative studies

Do fragment size and edge effects predict carbon stocks in trees and lianas in tropical forests?

Summary Tropical forests are critical for protecting global biodiversity and carbon stores. While forest degradation and fragmentation cause negative impacts on trees, many woody lianas benefit, with associated negative effects on carbon storage. Here, we focus on the key question of how abiotic environmental changes resulting from tropical forest fragmentation mediate the allocation of carbon into trees and lianas. We focus on the globally threatened Brazilian Atlantic Forest, in forest fragments spanning 13–23 442 ha in area and at fragment edges and interiors. Within each fragment, we established two transects: one at the edge and one in the interior. Each transect consisted of ten 10 × 10 m plots spaced at 20 m intervals. Within each plot, we sampled living trees with diameter ≥4·8 cm at 1·3 m above ground, living lianas with diameter ≥1·6 cm at 10 cm above ground, and several microclimatic and soil variables. Fragmentation changed a broad suite of abiotic environmental conditions recognized as being associated with forest carbon stocks: edges and smaller fragments were hotter, windier, and less humid, with more fertile and less acid soils at edges. Tree carbon stocks were thus higher in forest interiors than at edges, and were positively related to fragment size in interiors, but were not impacted by fragment size at edges. Trees and lianas showed different responses to fragmentation: in interiors of small fragments, tree carbon stocks declined whereas liana carbon stocks increased; and at edges, tree carbon stocks were not affected by fragment size, whereas liana carbon stocks were highest in smaller fragments. These patterns were strongly related to changes in abiotic environmental conditions. We conclude that the abiotic changes across the fragmentation gradient, rather than liana proliferation, were more likely to reduce tree carbon stocks. Cutting of lianas is frequently promoted for restoring forest carbon in human-modified tropical forests. However, this approach may not be effective for restoring forest carbon stocks in fragmented forests

Herbivore effect traits and their impact on plant community biomass: an experimental test using grasshoppers

1. Using trait-based approaches to study trophic interactions may represent one of the most promising approaches to evaluate the impact of trophic interactions on ecosystem functioning. To achieve this goal, it is necessary to clearly identify which traits determine the impact of one trophic level on another.2. Using functionally contrasting grasshopper species, we tested the ability of multiple traits (morphological, chemical and biomechanical) to predict herbivore impact on the biomass of a diverse plant community. We set up a cage experiment in an old species rich grassland field and evaluated how multiple candidate grasshopper effect traits mediated herbivore impact on plant biomass.3. Grasshoppers had different impact on plant community biomass (consuming up to 60 % of plant community biomass). Grasshopper impact was positively correlated with their incisive strength while body size or grasshopper C:N ratio exhibited low predictive ability. Importantly, the strong relationship between the incisive strength and the impact was mediated by the grasshopper feeding niche, which was well predicted in our study by two simple plant traits (leaf dry matter content, leaf C:N ratio). Feeding niche differences between grasshoppers were explained by differences in incisive strength, highlighting the fundamental linkage between grasshopper effect traits and their niche.4. Our study contributes to the development of the trait-based approach in the study of trophic interactions by providing a first experimental test of the relationship between herbivore effect traits, their impact on plant community biomass, and in a larger extent on ecosystem functioning. By comparing the relative importance of multiple interacting grasshopper traits, our study showed that incisive strength was a key effect trait which determined grasshopper feeding niche and its relative impact on plant community biomass

Optimal data partitioning, multispecies coalescent and Bayesian concordance analyses resolve early divergences of the grape family (Vitaceae)

Evolutionary rate heterogeneity and rapid radiations are common phenomena in organismal evolution and represent major challenges for reconstructing deep-level phylogenies. Here we detected substantial conflicts in and among data sets as well as uncertainty concerning relationships among lineages of Vitaceae from individual gene trees, supernetworks and tree certainty values. Congruent deep-level relationships of Vitaceae were retrieved by comprehensive comparisons of results from optimal partitioning analyses, multispecies coalescent approaches and the Bayesian concordance method. We found that partitioning schemes selected by PartitionFinder were preferred over those by gene or by codon position, and the unpartitioned model usually performed the worst. For a data set with conflicting signals, however, the unpartitioned model outperformed models that included more partitions, demonstrating some limitations to the effectiveness of concatenation for these data. For a transcriptome data set, fast coalescent methods (STAR and MP-EST) and a Bayesian concordance approach yielded congruent topologies with trees from the concatenated analyses and previous studies. Our results highlight that well-resolved gene trees are critical for the effectiveness of coalescent-based methods. Future efforts to improve the accuracy of phylogenomic analyses should emphasize the development of newmethods that can accommodate multiple biological processes and tolerate missing data while remaining computationally tractable. (C) The Willi Hennig Society 2017.National Natural Science Foundation of China [NNSF 31500179, 31590822, 31270268]; National Basic Research Program of China [2014CB954101]; National Science Foundation [DEB0743474]; Smithsonian Scholarly Studies Grant Program and the Endowment Grant Program; CAS/SAFEA International Partnership Program for Creative Research Teams; Laboratory of Analytical Biology of the National Museum of Natural History, Smithsonian Institution; Science and Technology Basic Work [2013FY112100]info:eu-repo/semantics/publishedVersio

Variability in the area, energy and time costs of wintering waders responding to disturbance

Birds’ responses to human disturbance are interesting due to their similarities to anti-predator behaviour, and understanding this behaviour has practical applications for conservation management by informing measures such as buffer zones to protect priority species. To understand better the costs of disturbance and whether it will impact on population size, studies should quantify time-related responses as well as the more commonly reported flight initiation distance (FID). Using waders wintering on an estuarine area, we experimentally disturbed foraging birds on the Wash Embayment, UK, by walking towards them and recording their responses (FID, alert time, time spent in flight, time taken to resume feeding, and total feeding time lost). We present data for 10 species of conservation concern: Curlew Numenius arquata, Oystercatcher Haematopus ostralegus, Bar-tailed Godwit Limosa lapponica, Grey Plover Pluvialis squatarola, Redshank Tringa totanus, Knot Calidris canutus, Turnstone Arenaria interpres, Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Dunlin Calidris alpina. Larger species responded more strongly, response magnitude was greater under milder environmental conditions, and responses varied over both small and large spatial scales. The energetic costs of individual responses, however, were low relative to daily requirements and disturbance events were unlikely to be frequent enough to seriously limit foraging time. We suggest, therefore, that wintering wader populations on the Wash are not currently significantly negatively impacted by human disturbance during the intertidal foraging period. This is also likely to be the case at other estuarine sites with comparable access levels, visitor patterns, invertebrate food availability and environmental conditions