The impact of fisheries on vulnerable habitats: the case of trawling on circa-littoral grounds in the Strait of Sicily (central Mediterranean Sea)

The Council Regulation (EC) no. 1967/2006 introduced the adoption of the 40 mm square-mesh or alternatively a 50 mm diamond-mesh codend for trawlers of EU Member States. In this context, the main aim of the current study was to compare the catch composition of Lampedusa’s shallow-water trawl fishery, in terms of retained and discarded fraction, using the 24 mm square-mesh codend (illegal and supposed unselective) and the 50 mm current diamond-mesh codend (legal and supposed selective). During 2012, 21 hauls were performed, under commercial conditions, with the 24 mm square mesh codend and 27 with the 50 mm diamond mesh codend in an area of the Strait of Sicily at depths from 40 to 80 m. The introduction of a 50 mm diamond-mesh, although not significantly, reduced the CPUEs of retained and discarded fraction compared with the 24 mm mesh. Moreover, for most target species and their size classes (especially immature individuals), the legal mesh recorded a lower mean number of specimens than the banned mesh size. All these advantages aside, the discard of the shallow-water trawl fishery, in Lampedusa, represented a very important part of the total catch (more than three-quarters) by both mesh sizes and a large amount of this was represented by species and habitat of conservation concern. Our results suggest that spatial restrictions, such as no-take zones, could be a more effective management tool to protect this sensitive ecosystem in the area than the technical measures (e.g. reduction of mesh size) imposed today by the EU.     

How fish-helminth associations arise: an example from Arctic charr in Loch Rannoch

Three sympatric morphs of Arctic charr Salvelinus alpinus occur in Loch Rannoch, Scotland, and are identified by their differing head morphology and diet. These are small-headed benthic, large-headed benthic and pelagic morphs. Six species of endoparasitic helminth were found in the fish, but the morphs had different patterns of infection. Overall infections in pelagic charr were heavier than in large-headed benthics, which were in turn heavier than in small-headed benthics, even though benthic charr live longer than pelagics. Pelagic fish had high prevalences and intensities of pseudophyllidean tapeworms, the intermediate hosts of which are copepods. The prevalence and intensity of metacercariae of Diplostomum sp. (the intermediate hosts of which are snails) were high in the benthic morphs. The results are discussed in terms of the effects of ecological factors on transmission of helminth parasites to their hosts and the evolution of host-parasite associations.     

Methane emissions from wetlands and their relationship with vascular plants: an Arctic example

This paper investigates the relationship between vascular plant production and CH₄ emissions from an arctic wet tundra ecosystem in north‐east Greenland. Light intensity was manipulated by shading during three consecutive growing seasons (1998–2000). The shading treatment resulted in lower carbon cycling in the ecosystem as mean seasonal net ecosystem exchange (NEE) decreased from ?336 to ?196 mg CO₂ m^?2 h^?1 and from ?476 to ?212 mg CO₂ m^?2 h^?1 in 1999 and 2000, respectively, and total ecosystem respiration decreased from 125 to 94 mg CO₂ m^?2 h^?1 in 1999 and from 409 to 306 mg CO₂ m^?2 h^?1 in 2000. Seasonal mean CH₄ emissions in controls and shaded plots were, respectively, 6.5 and 4.5 mg CH₄ m^?2 h^?1 in 1999 and 8.3 and 6.2 mg CH₄ m^?2 h^?1 in 2000. We found that CH₄ emission was sensitive to NEE and carbon turnover, and it is reasonable to assume that the correlation was due to a combined effect of vegetative CH₄ transport and substrate quality coupled to vascular plant production. Total above‐ground biomass was correlated to mean seasonal CH₄ emission, but separation into species showed that plant‐mediated CH₄ transport was highly species dependent. Potential CH₄ production peaked at the same depth as maximum root density (5–15 cm) and treatment differences further suggest that substrate quality was negatively affected by decreased NEE in the shaded plots. The concentration of dissolved CH₄ decreased in the control plots as the growing season progressed while it was relatively stable in the shaded plots. This suggests that a progressively better developed root system in the controls increased the capacity to transport CH₄ from the soil to the atmosphere. In conclusion, vascular plant photosynthetic rate and subsequent allocation of recently fixed carbon to below‐ground structures seemed to influence both vegetative CH₄ transport and substrate quality.     

Incipient speciation through niche expansion: an example from the Arctic charr in a subarctic lake

Two reproductive isolated morphs of Arctic charr (Salvelinus alpinus), termed profundal and littoral charr according to their different spawning habitats, co-occur in the postglacial lake Fjellfr?svatn in North Norway. All profundal charr live in deep water their entire life and have a maximum size of 14cm, while the littoral charr grow to 40cm. Some small and young littoral charr move to the profundal zone in an ontogenetic habitat shift in the ice-free season and the rest of the population remains in epilimnic waters. The two morphs had different diet niches in the profundal zone: the profundal charr ate typical soft-bottom prey (chironomid larvae, pea mussels and benthic copepods), while the young littoral charr mainly consumed crustacean zooplankton. In four other lakes without a profundal morph (i.e. monomorphic populations), young charr also performed ontogenetic habitat shifts to the profundal zone and fed on zooplankton. The profundal morph of Fjellfr?svatn therefore utilize a food resource niche that neither the littoral morph nor comparable monomorphic populations exploit. This suggests that intraspecific resource competition has driven incipient ecological speciation of the profundal charr of Fjellfr?svatn. The exploitation of the soft-bottom resources by the profundal charr supports earlier experimental findings that the profundal morph is genetically different in trophic behaviour and morphology. The sympatric ecological divergence within the profundal habitat is possible because unexploited food resources (soft-bottom profundal prey) are available. Apparently, this represents a case of incipient segregation by expansion to new resource types (niche invasion), and not by subdivision of one broad ancestral niche.     

Optimal foraging behavior with an explicit consideration of within-individual behavioral variation: an example of predation

Animal behavior is flexible, and the same individual can exhibit variable expressions under the equivalent ecological situations (i.e., within-individual behavioral variation). This study examines the evolution of within-individual behavioral variation using an individual-based model. A common predation scenario is considered where a predator spends a period h to handle and consume a captured prey. The model assumes the handling time of the predator to be a random variable. The average and within-individual variance of handling time are described by \(\mu _h\) and \(\sigma _h^2\), respectively, where each individual has its own unique \(\mu _h\) and \(\sigma _h^2\). Using a genetic algorithm, the evolution of \(\sigma _h^2\) is traced. The results show that natural selection acts on both \(\mu _h\) and \(\sigma _h^2\), and the optimal behavioral variation depends on the density of prey. In particular, individuals with high behavioral variance \(\sigma _h^2\) are more likely selected when prey density is low. Individual based modeling can be a useful tool for studying the ultimate significance of within-individual behavioral variation and generating empirically testable predictions. The mechanisms of the evolution of within-individual behavioral variation and their ecological implications are discussed.     

Incorrect handling of calibration information in divergence time inference: an example from volcanic islands

Divergence time studies rely on calibration information from several sources. The age of volcanic islands is one of the standard references to obtain chronological data to estimate the absolute times of lineage diversifications. This strategy assumes that cladogenesis is necessarily associated with island formation, and punctual calibrations are commonly used to date the splits of endemic island species. Here, we re-examined three studies that inferred divergence times for different Hawaiian lineages assuming fixed calibration points. We show that, by permitting probabilistic calibrations, some divergences are estimated to be significantly younger or older than the age of the island formation, thus yielding distinct ecological scenarios for the speciation process. The results highlight the importance of using calibration information correctly, as well as the possibility of incorporating volcanic island studies into a formal, biogeographical hypothesis-testing framework.     

DNA barcoding of Arctic bryophytes: an example from the moss genus Dicranum (Dicranaceae,Bryophyta)

The identification of bryophytes from the Arctic is often difficult due to deviating morphologies under the extreme environmental conditions. This is especially true for species-rich and taxonomically complex genera, such as the moss genus Dicranum. DNA barcoding is expected to improve the identification of Arctic bryophyte species, but the optimal combination of barcoding markers for mosses in general, especially for delimiting closely related, is still under discussion. In this paper, we test the discrimination capacity of six potential barcode markers (rps4-trnT _UGU, trnL _UAA-trnF _GAA, trnH _GUG-psbA, rps19-rpl2, rpoB, and nrITS1-5.8S-ITS2) based on phylogenetic reconstructions of 30 Dicranum samples from Spitsbergen (Svalbard, Norway), and reference samples from all ten Dicranum species confirmed for the Svalbard archipelago and six additional Arctic Dicranum species. All 16 species (possibly except D. fuscescens) were distinguishable with bootstrap support >70 % based on the combined sequence data, but none of the individual markers could delimit all included species. All Svalbard collections could be readily assigned to five species, D. acutifolium, D. elongatum, D. laevidens, D. majus, and D. spadiceum, respectively. It is concluded that DNA barcoding improves species identification of Arctic Dicranum plants, but that a combination of several markers is necessary in order to obtain reliable identification results, with the single loci ITS1, trnL-F and rps4-trnT being the most promising regions.     

Parasitism in bivalves from an Arctic ecosystem

In arctic ecosystems parasitism seems less conspicuous than in more diverse tropical ecosystems. However, several host-parasite relations may be a burden in Arctic ecosystems and modify energy-flow patterns. Four different localities of the shallow shelf off Godhavn, West Greenland, were studied with regard to biomass, production and life cycles of selected bivalve and polychaete species. The following important parasite-bivalve associations were found: the athecate hydroidMonobrachium parasitum onMacoma calcarea; the digenetic trematodeGymnophallus somateriae inHiatella byssifera; an unidentified species of turbellarian inHiatella byssifera; and the nemerteanMalacobdella grossa inMya truncata. In the bivalvesMytilus edulis, Serripes groenlandicus andCardium ciliatum only few parasites were detected. Parasitism seems to follow the general trend observed in Arctic ecosystems which exhibit low species diversities and high numbers of individuals.     

Quantifying assemblage distinctness with time: an example using temperate epibenthos

Artificial substrata are an often-used tool in assessing community development; here we quantify the changing presence of functional groups of benthos with replicate, depth, site, and time in order to explain differences in the structure of the surrounding mature communities. We placed replicate, machined slate panels (15×15×1 cm) in the intertidal, 6 and 12 m at two sites of differing flow rates at Lough Hyne, SW Ireland. They were placed at the same time of year and removed after 2, 6, 12, and 24 months from 1999 to 2001, to compare with a similar experiment run from 1997 to 1999. Furthermore, to examine trends of local assemblages older than 24 months, we examined boulders from each depth/site combination. Percentage cover of 13 functional groups, selected in relation to their competitive abilities, was measured using point intercept analysis of high-resolution digital images of the panels. These data were then quantified using our derived measure of distinctness. Replicates became more similar, and sites and depths both became more distinct with time from 2 to 24 months, although there was less distinctness at the high flow site throughout all stages of the study. Principal components analysis (PCA) of data suggested that all site/depth panel combinations only became truly distinct at the 24-month stage of the study. From 2 to 24 months, ‘good’ competitors increased in space, ‘intermediate’ competitors peaked after ≈12 months, and ‘poor’ competitors reduced in their space occupation with increasing time. Both in similarity and space occupation of functional groups, the 1997-1999 and 1999-2001 data showed high levels of pattern convergence. That there was little difference between assemblages at 12 and 24 months validated our upper time limit of period of study, but at 24 months, assemblages still differed from natural substrata and we suggest that many years would have been necessary to eliminate this difference.     

有益真绥螨与巴氏新小绥螨的集团内捕食和同类相残作用

【目的】有益真绥螨Euseius utilis是北方地区广泛分布的一种多食性植绥螨,而巴氏新小绥螨Neoseiulus barkeri目前在我国广泛应用于农业害虫的生物防治中。本研究旨在对巴氏新小绥螨在本地的应用进行风险评估及为与有益真绥螨的联合释放提供依据。【方法】本研究在室内通过一系列实验,比较了实验室饲养的巴氏新小绥螨和采自内蒙古农业大学校园的有益真绥螨的雌成螨对同种或异种未成熟螨的捕食量、存活时间及产卵量的差异,检测了有益真绥螨与巴氏新小绥螨两种植绥螨相互之间的攻击强度以及种内和种间的相互作用。【结果】两种植绥螨都难以刺吸同种或异种植绥螨的卵,而对同种或异种植绥螨幼螨的捕食量最大,其次是对若螨。在无共同食物的情况下,有益真绥螨雌成螨对同种植绥螨幼螨的攻击性比对异种植绥螨幼螨的攻击性强(BreslowDay检验:χ~2=13.84,df=1,P0.001),且有益真绥螨对同种植绥螨幼螨的捕食量(9.10±1.65头)高于对异种植绥螨幼螨的捕食量(5.31±1.43头)(T检验:t=5.487,P0.001),巴氏新小绥螨对异种植绥螨幼螨的捕食量(7.48±0.75头)高于对同种植绥螨幼螨的捕食量(4.75±0.58头)(T检验:t=9.110,P0.05)。【结论】有益真绥螨更倾向于捕食同种幼螨而发生同类相残;巴氏新小绥螨更倾向于捕食异种幼螨而发生集团内捕食。     

Sources of variation in predation rates at high prey densities: an analytic model and a mite example

Some mathematical techniques for the analysis of satiation-based predation models previously developed by the first author are applied in the present paper to a model by the second author for predation by the predatory miteMetaseiulus occidentalis (Nesbitt). It turns out that for this predator the predation rate should keep increasing at high prey densities as the square root of the prey density,x. This particular shape of the functional response is shown to occur if and only if the upper satiation threshold for prey capture coincides with the maximum gut capacity. The functional response predicted by the model, moreover, is in fair quantitative agreement with predation rates observed by the third author in artificial arenas. A further analysis of the model shows that the variance of the catch should also increase as the square root ofx. This prediction is consistent in a qualitative manner with the continued increase in the variance of the catch. However, quantitatively, the observed variances are even too large to be compatible with any model in which the feeding rate is subject to regulation by a negative feedback. Therefore, the difference between predicted and observed variances is hypothesized to be due to nonhomogeneities in the experimental material. The inferred additional variance component proportional tox accords fairly well with the trend apparent in the data.     

The benefits of clustering eggs: the role of egg predation and larval cannibalism in a predatory mite

Many arthropods produce clusters of eggs, but an unambiguous explanation for the evolution of egg clustering is still lacking. We test several hypotheses for the production of egg clusters by the predatory mite Iphiseius degenerans. This predator feeds on pollen, thrips larvae and nectar in flowers, but oviposits in clusters in tufts of leaf hairs (acarodomatia), where eggs run a lower risk of being killed by thrips, the prey of this predatory mite. The observed clustering is not caused by a shortage of oviposition sites; females preferably oviposit in a domatium containing eggs rather than in an empty domatium. To explain this preference, we first examined the effect of egg clusters on the risk of cannibalism. We found that eggs are invulnerable to cannibalism, whereas larvae emerging from single eggs or from clusters were equally vulnerable. Subsequently, we considered the killing of eggs resulting from counter-attacks by prey, i.e. the western flower thrips. We found no indication that a cluster of eggs protects eggs from predation by thrips. However, when eggs were clustered in a domatium rather than scattered over domatia, the proportion of eggs killed by thrips was lower. Hence, oviposition in clusters has no effect on its own and oviposition in domatia reduces predation risk by thrips, but oviposition in clusters in domatia leads to a synergistic effect on the survival of predator eggs. This synergism probably arises because eggs in clusters within tufts of leaf hairs are more difficult for thrips to reach. These experiments highlight a novel explanation of egg clustering, i.e. adaptation to counter-attacking prey. Moreover, they show that plant domatia protect predator eggs from predation.     

Functional characterization of parvalbumin from the Arctic cod (Boreogadus saida): similarity in calcium affinity among parvalbumins from polar teleosts

Calcium dissociation constants (KD) were measured as a function of temperature for parvalbumin, a small acidic protein expressed abundantly in fast-twitch muscle, from the Arctic cod (Boreogadus saida) and compared to values previously determined for Antarctic and temperate zone teleosts. Estimates of KD were derived independently from fluorometric titrations and calorimetry. In addition, the primary structure of B. saida parvalbumin was determined. Calcium KDs for parvalbumin from B. saida were fundamentally similar to those for parvalbumins from Antarctic species (6.68+/-0.59 nM and 7.77+/-0.72 nM at 5 degrees C, respectively), but significantly different from temperate zone species (1.35+/-0.28 nM at 5 degrees C). However, estimates of KD for B. saida parvalbumin at 5 degrees C closely matched values for temperate zone fish at 25 degrees C (6.54+/-0.56 nM), recapitulating the prior observation that calcium affinity of parvalbumin is conserved at the native temperature of teleost fish. Full sequence of B. saida parvalbumin was generated using reverse-phase HPLC and RACE-PCR. The Arctic parvalbumin showed 83% homology to a carp parvalbumin. None of the 16 total substitutions between the two parvalbumins resided in the cation binding sites of the protein, indicating that the structural locus of the thermal sensitivity of function lies outside the active regions.     

Modelling non-additive and nonlinear signals from climatic noise in ecological time series: Soay sheep as an example

Understanding how climate can interact with other factors in determining patterns of species abundance is a persistent challenge in ecology. Recent research has suggested that the dynamics exhibited by some populations may be a non-additive function of climate, with climate affecting population growth more strongly at high density than at low density. However, we lack methodologies to adequately explain patterns in population growth generated as a result of interactions between intrinsic factors and extrinsic climatic variation in non-linear systems. We present a novel method (the Functional Coefficient Threshold Auto-Regressive (FCTAR) method) that can identify interacting influences of climate and density on population dynamics from time-series data. We demonstrate its use on count data on the size of the Soay sheep population, which is known to exhibit dynamics generated by nonlinear and non-additive interactions between density and climate, living on Hirta in the St Kilda archipelago. The FCTAR method suggests that climate fluctuations can drive the Soay sheep population between different dynamical regimes--from stable population size through limit cycles and non-periodic fluctuations.     

Intraguild predation, cannibalism, and microhabitat use in Calopteryx virgo and Somatochlora metallica larvae: a laboratory experiment

Intraguild predation (IGP) and cannibalism among co-occurring lotic odonate species was studied in Central Finland. A laboratory experiment was performed to assess the microhabitat use and cannibalism between intermediate and late instars of Calopteryx virgo larvae and predation by larger Somatochlora metallica larvae on the intermediate C. virgo instars. The experiment was run in small running-water aquaria where the larvae were able to divide their mutual habitat vertically by clinging onto artificial perches or crawling on the bottom. Life span of the small C. virgo larvae and attack rate on them were compared between the cannibalism and IGP treatments. The effect of predation on the activity, habitat use and spatial distribution of the small C. virgo larvae was examined. The IGP rate was 36%. The prey larvae spent the most of their time on the perches, whereas the S. metallica preferred the substrate. The large C.␣virgo larvae did not cannibalise smaller conspecifics. The presence of a predator (S. metallica) had no effect on the habitat use or activity of the prey (C. virgo) larvae. Habitat use differed more between those species than between conspecifics of different size classes of C. virgo. The spatial distribution between S.␣metallica and C. virgo showed a completely random pattern, whereas the two size classes of C. virgo aggregated in the vegetation. Absence of cannibalism and behavioural observations indicate that C. virgo may have a low tendency for intraspecific aggressions.     

Phylofloristics: an example from the Lesser Antilles

Aims The last decade has seen many plant ecologists integrating phylogenetic analysis into ecology to explain patterns of species co-occurrence and compositional similarity across assemblages. Despite the advances in this area, there are still some challenges that need to be addressed. One challenge is that most of the phylogenetic studies of plant assemblages have focused only on a small proportion of all of the vascular plants that co-occur (e.g. woody plants), while much of the remaining co-occurring flora has been ignored.Methods Here we introduce an analytical approach that we term phylofloristics that analyzes the compositional similarity of floras in relation to spatial and environmental gradients to understand their assembly. As an illustration, we assembled a large phylogenetic tree for the flora of the Lesser Antilles and evaluated the patterns of floristic and phylofloristic similarity among the island-specific floras. We analyzed the relationship of these similarities with spatial and environmental distance and compared the results for non-endemic and endemic lineages.Important findings The results show a major influence of environmental heterogeneity on the assembly of island floras and far less evidence for the importance of dispersal limitation of lineages and species. This study highlights the importance of incorporating broader taxonomic sampling to improve our understanding of assembly processes in ecology. We expect future phylofloristic studies will improve the approach we have taken by generating more refined phylogenetic trees and by incorporating phylogeographic information.     

From polar night to midnight sun: photoperiod, seal predation, and the diel vertical migrations of polar cod (Boreogadus saida) under landfast ice in the Arctic Ocean

The winter/spring vertical distributions of polar cod, copepods, and ringed seal were monitored at a 230-m station in ice-covered Franklin Bay. In daytime, polar cod of all sizes (7–95 g) formed a dense aggregation in the deep inverse thermocline (160–230 m, −1.0 to 0°C). From December (polar night) to April (18-h daylight), small polar cod <25 g migrated into the isothermal cold intermediate layer (90–150 m, −1.4°C) at night to avoid visual predation by shallow-diving immature seals. By contrast, large polar cod (25–95 g), with large livers, remained below 180 m at all times, presumably to minimize predation by deep-diving mature seals. The diel vertical migration (DVM) of small polar cod was precisely synchronized with the light/dark cycle and its duration tracked the seasonal lengthening of the photoperiod. The DVM stopped in May coincident with the midnight sun and increased schooling and feeding. We propose that foraging interference and a limited prey supply in the deep aggregation drove the upward re-distribution of small polar cod at night. The bioluminescent copepod Metridia longa could have provided the light needed by polar cod to feed on copepods in the deep aphotic layers.     

Growing large in a low grade environment: size dependent foraging gain and niche shifts to cannibalism in Arctic char

Arctic char ( Salvelinus alpinus ) living in allopatry in lakes often show a distinct size dimorphism where the large char prey upon small char. We studied the relationship between size scaling of energy intake, total metabolic costs and levels of storage energy related to the niche shift from invertebrate feeding to cannibalism in an alpine Arctic char population. Gill-net samples consisted of two distinct size modes, small invertebrate feeding char (92–172 mm total length) and large cannibalistic char (265–606 mm total length). Food consumption was estimated for a one year period using a radioactive tracer (¹³⁷Cs). The energy intake followed a hump-shaped relationship with fish size for invertebrate feeding char and increased monotonically with size for cannibalistic char. Total metabolic costs increased exponentially with size for both groups. Char feeding in the invertebrate niche had a maximum net energy gain at 140 mm total length with an upper size limit for positive net energy gain at 180 mm. For cannibals the relationship between size and net energy gain formed a hump shaped function with maximum net energy gain at 400 mm and a lower size limit for positive net energy gain at 230 mm. The size at maturation for both small and large char was close to the size for maximum energy gain in their respective niches. Immature individuals close to the upper size limit for positive net energy gain in the invertebrate niche had low levels of storage lipids but tended to have high mass specific growth rates. This may imply a reallocation from reversible (stored) energy to structural (length) growth as a strategy to transform into the size-range where the cannibalistic niche successfully could be exploited.     

The parental investment conflict in continuous time: St. Peter's fish as an example

The parental investment conflict considers the question of how much each sex should invest in each brood, thereby characterizing different animal species. Each species usually adopts a certain parental care pattern: female-care only, male-care only, biparental care, or even no parental care at all. The differences in care patterns are usually explained by the different costs and benefits arising from caring for the offspring in each animal species. This paper proposes a game-theoretical model to the parental investment conflict based on the parental behavior of St. Peter's fish. St. Peter's fish exhibit different parental care patterns, allowing the examination of the factors which determine the particular behavior in each mating. We present a continuous time, two-stage, asymmetric game, with two types of players: male and female. According to the model's results, three parental care patterns: male-only care, female-only care and biparental care, are possible evolutionarily stable strategies. The evolutionarily stable parental care pattern in a certain mating depends on a parent's increase in mortality due to parental care, and on its advantage from biparental care. These results may explain the different parental care patterns observed in a variety of animal species, including those found in the St. Peter's fish.