Comparison of trophic function between the globally invasive crayfishes <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> and <Emphasis Type="Italic">Procambarus clarkii</Emphasis>

Impacts of invasive species may manifest most strongly if these organisms are highly distinct functionally from the native species they often replace. Yet, should we expect functional differences between native and invasive species of generalist organisms like freshwater crayfish? Some existing evidence has pointed to native and invasive crayfish species as ecologically equivalent. We contribute to this literature by comparing the trophic niches of the globally invasive crayfishes Pacifastacus leniusculus and Procambarus clarkii, by applying carbon and nitrogen stable isotope analyses to replicated allopatric (alone) and sympatric (together) lake populations in western Washington State, USA, where P. clarkii has been recently introduced and P. leniusculus is presumed native. Our study corrected for potential inherent differences in lake food webs as a consequence of lake abiotic or biotic characteristics using random effects in linear mixed effects models. We found that although overall trophic niche size or area of these species was not significantly different, P. leniusculus was significantly higher in trophic position than P. clarkii when also accounting for the effects of body size, sex, and lakes as random effects. This pattern of increased trophic position of P. leniusculus over P. clarkii was conserved over time in one sympatric lake for which we had data over multiple years. Cumulatively, our findings point to trophic differences between the globally cosmopolitan crayfishes P. leniusculus and P. clarkii, particularly when accounting for the ways that ecosystem context can affect food web structure of communities and the trophic resources available to these consumers.     

Enhanced ecological indication based on combined planktic and benthic functional approaches in large river phytoplankton ecology

Environmental DNA (eDNA) is a powerful method for assessing the presence and distribution of invasive aquatic species. We used this tool to detect and monitor several invasive crayfishes Procambarus clarkii, Orconectes limosus and Pacifastacus leniusculus present in, or likely to invade, the ponds of the Brenne Regional Natural Park. A previous study showed that the eDNA method was not very efficient in detecting P. clarkii. In the present study, we explored new improvements in the detection of invasive crayfish. We designed specific primers for each crayfish species, and set up an experimental mesocosm approach to confirm the specificity of the primers and the sampling protocol. We analysed samples taken from ponds in 2014 and 2015. We compared two qPCR protocols involving either SybrGreen or TaqMan assays. Using these same primers, we were able to detect crayfish eDNA with both assays during the mesocosm experiment. However, crayfish from field samples could only be detected by performing qPCR with a SybrGreen assay. We successfully monitored the presence of three invasive species of crayfish using eDNA. This method is a powerful tool for establishing the presence or absence of invasive species in various freshwater environments.     

Associations between stream habitat characteristics and native and alien crayfish occurrence

Human mediated introductions of non-indigenous crayfish species (NICS) are responsible for their rapid colonisation of European freshwaters. The introduction of North American crayfish is furthermore linked to the spread of crayfish plague and the decline of indigenous crayfish species (ICS). As the management of ICS and NICS have become necessary, a detailed knowledge on their distribution and ecological requirements is needed. We studied the current range of native noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium, as well as alien signal crayfish Pacifastacus leniusculus in Carinthia (Austria) and evaluated environmental and physical habitat features in streams with and without crayfish. Meanwhile, the loss of many ICS populations was recorded and alien P. leniusculus was found to be widespread in this region. Most of the habitat features of streams having crayfish differed significantly from sites lacking crayfish for at least one investigated native or alien species. Furthermore, multivariate and regression analyses showed specific differences in the habitat use of the investigated crayfish. Our results showed that the presence of alien P. leniusculus was associated with larger and smoother sloped lowland rivers, while the occurrence of the two native species was confined to smaller streams either at higher altitudes and with distinct physical habitat conditions (A. torrentium) or with moderate water temperatures (A. astacus). This study helps to identify potential refuge areas for the endangered native species and to predict the further spread of the most common non-native crayfish species in European streams.     

Predatory impacts of alien decapod Crustacea are predicted by functional responses and explained by differences in metabolic rate

Alien predators can have large impacts on prey. It is important that we understand, and ideally predict, these impacts. Here, we compare predatory impacts of size-matched decapod crustaceans—invasive alien Eriocheir sinensis and Pacifastacus leniusculus, and native European Austropotamobius pallipes—and use this case study to inform methods for impact prediction. We quantify functional responses (FRs) on three macroinvertebrate prey species, examine switching behaviour, and measure metabolic rates as a possible mechanistic explanation for differences in predation. FRs show a consistent pattern: attack coefficients and maximum feeding rates are ordered E. sinensis?≥?P. leniusculus?≥?A. pallipes for all prey species. Attack coefficients of E. sinensis are up to 6.7 times greater than those of size-matched crayfish and maximum feeding rates up to 3.0 times greater. FR parameters also differ between the invasive and native crayfish, but only up to 2.6 times. We find no evidence of switching behaviour in crayfish but suggestions of negative switching in E. sinensis. Differences in FR parameters are mirrored by differences in routine, but not standard, metabolic rate. Overall, our data predict strong predatory impacts of E. sinensis, even relative to alien P. leniusculus. Strong impacts of P. leniusculus relative to A. pallipes may be driven more by body size or abundance than per capita effect. FRs vary between prey types in line with existing knowledge of impacts, supporting the use of FRs in quantitative, prey-specific impact predictions. MRs could offer a general mechanistic explanation for differences in predatory behaviour and impacts.     

Bivalve or gastropod? Using profitability estimates to predict prey choice by <Emphasis Type="Italic">P. clarkii</Emphasis>

Recently, a highly invasive alien species, the zebra mussel Dreissena polymorpha, has colonized Italian aquatic ecosystems that had been previously colonized by another highly invasive alien species—the North American crayfish Procambarus clarkii. This was the first time and world region where these two species met. To evaluate the relative importance of their interactions, we studied prey selection according to its length, as well as prey choice by P. clarkii preying on D. polymorpha in the presence and absence of alternative prey—the freshwater snail Physella acuta. We followed an optimability-based approach, by first estimating the most profitable length of each mollusc and then by conducting a prey choice experiment, on which both species were provided simultaneously to a crayfish with different size combinations. Prey selection was dependent on prey length, handling time and crayfish length for both molluscs. According to our profitability estimates, snails should be more profitable than mussels in the length range 7–10 mm, while for lengths over 11.0 mm, mussels should be more profitable. The results of the prey choice experiment indicated that D. polymorpha length, P. acuta length, and the difference in profitability between the offered individuals were all relevant for the choice of one species over the other by P. clarkii. However, the overall tendency was the choice of the smallest prey, regardless of species, and the estimates of prey profitability were not useful to predict prey choice. Our study shows that D. polymorpha represents a novel prey resource for P. clarkii, even in the presence of an alternative prey, and that zebra mussels may be a preferred prey, especially small-sized individuals (5–10 mm).     

Interspecific comparison of movement patterns among bitterling species in an agricultural ditch system

Patterns of movement are related to life history and/or species traits. Understanding movement patterns of multiple species sharing the same niche may clarify coexistence mechanisms. Therefore, the movement patterns of three bitterling species, Acheilognathus tabira erythropterus, Acheilognathus melanogaster, and Rhodeus ocellatus ocellatus, were examined between June and November 2009 in an agricultural ditch system associated with Lake Kasumigaura in central Japan. The mark–recapture method was used with a fixed releasing point in an approximately 5.5 km-long ditch. Movement distances of A. t. erythropterus and A. melanogaster were longer than that of R. o. ocellatus, but the direction of movement was similar among the three species. However, R. o. ocellatus moved to locations with a low dissolved oxygen concentration and deeper water. These results suggest that R. o. ocellatus may adapt better to environmental fluctuations, because its tolerance to hypoxia is the highest of the three species. Compared with R. o. ocellatus, A. t. erythropterus and A. melanogaster may move relatively longer distances to search for suitable habitats following an environmental fluctuation.     

Life cycles of 17 riffle-dwelling mayfly species (Baetidae,Heptageniidae, and Ephemerellidae) in central Japan

We described the life cycles of 17 riffle-dwelling mayfly species in a central Japanese stream. Both species of Baetidae (Alainites yoshinensis Gose and Baetis thermicus Uéno) and two of nine species of Heptageniidae (Ecdyonurus scalaris Kluge and Epeorus latifolium Uéno/l-nigrus Matsumura) in this stream were multivoltine (more than one generation per year). Seven other heptageniid species (two unidentified species of Cinygmula, Epeorus aesculus Imanishi, E. curvatulus Matsumura, E. ikanonis Takahashi, E. napaeus Imanishi, and Rhithrogena japonica Uéno) and all six species of Ephemerellidae [Cincticostella elongatula (McLachlan), C. nigra (Uéno), Drunella basalis (Imanishi), D. ishiyamana Matsumura, D. sachalinensis (Matsumura), and D. trispina (Uéno)] were essentially univoltine.     

Genetic differentiation among natural populations of the lizard complex <Emphasis Type="Italic">Darevskia raddei</Emphasis> as inferred from genome microsatellite marking

The article presents the genetic parameters of the populations of lizards of the Darevskia raddei complex (D. raddei nairensis and D. raddei raddei) and the populations of D. valentini calculated on the basis of the analysis of variability of 50 allelic variants of the three nuclear genome microsatellite-containing loci of 83 individuals. It was demonstrated that the F_st genetic distances between the populations of D. raddei nairensis and D. raddei raddei were not statistically significantly different from the F_st genetic distances between the populations of different species, D. raddei and D. valentini. At the same time, these distances were statistically significantly higher than the F_st distances between the populations belonging to one species within the genus Darevskia. These data suggest deep divergence between the populations of D. raddei raddei and D. raddei nairensis of the D. raddei complex and there arises the question on considering them as separate species.     

Relationships within <Emphasis Type="Italic">Capitotricha bicolor</Emphasis> (Lachnaceae,Ascomycota) as inferred from ITS rDNA sequences,including some notes on the <Emphasis Type="Italic">Brunnipila</Emphasis> and <Emphasis Type="Italic">Erioscyphella</Emphasis> clades

DNA sequences of Capitotricha bicolor from Quercus, Fagus sylvatica, Alnus alnobetula, and Nothofagus, and C. rubi from Rubus idaeus were obtained from apothecia to establish whether specimens from different hosts belong to separate species. The obtained ITS1–5.8S–ITS2 rDNA sequences were examined with Bayesian and parsimony phylogenetic analyses. Intra- and interspecific variation was also investigated based on molecular distances in the ITS region. The phylogenetic analyses supported the specific distinctness of Capitotricha rubi and the Capitotricha from Nothofagus, but also suggest specific distinctness between samples from Quercus, Fagus, and Alnus. The interspecific distances were larger than intraspecific distances for all examined units. The smallest distance was found between the “Alnus alnobetula” and “Fagus sylvatica” units. Two new sequences of Brunnipila are published. Capitotricha, Lachnum, and Erioscyphella are compared to each other based on hair and excipulum characteristics.     

Taxonomic position of Afghan vole (Subgenus <Emphasis Type="Italic">Blanfordimys</Emphasis>) by the sequence of the mitochondrial <Emphasis Type="Italic">cytb</Emphasis> gene

It is rather difficult to construct a system of gray voles of the tribe Microtini by a set of morphological and karyological characters because form generation is mosaic at these organization levels. The sequence of the mitochondrial cytochrome b gene was used to study the phylogenetic relationships and taxonomic position of the Central Asian subgenus Blanfordimys. Afghan vole Microtus (Blanfordimys) afghanus and Bucharian vole M. (Blanfordimys) bucharensis clustered with Pamir vole M. (Neodon) juldaschi, which is conventionally assigned to another subgenus. The last two species proved to be significantly closer to each other than either of them was to M. (Blanfordimys) afghanus, which disagrees with the monophyletic origin accepted for Blanfordimys. The genetic distances between the species of the subgenus Blanfordmys and M. juldaschi were comparable with the distances between the sister subgenera Microtus s. str. and Sumeriomys or Pallasiinus and Alexandromys and with the basal divergence of supraspecific clades in the subgenus Terricola. It was assumed that a special Central Asian group of species exists within the tribe Microtini and includes species of the subgenus Blanfordimys and M. juldaschi and that the subgenera Neodon and Blanfordimys should be revised.     

Insect herbivory on native and exotic aquatic plants: phosphorus and nitrogen drive insect growth and nutrient release

The invasive clam Corbicula fluminea causes severe environmental and economic impacts in invaded sites and fouled water-dependent industries. The biological control of invasive species has potential as an effective, safe and low-cost tool. The potential of using direct (clam consumption) and indirect approaches (predator-avoidance behaviour) to control the pest was evaluated, aiming at establishing a proof-of-principle regarding the suitability of such strategies in confined settings (e.g. pipelines, channels, raw water tanks and other water-dependent facilities). Invertebrate (Procambarus clarkii) and vertebrate (Lepomis gibbosus, Luciobarbus bocagei) predators were examined for their control potential. In feeding experiments, barbels foraged upon C. fluminea but ingested very few clams, and clam consumption by crayfish was only observed in the smallest size class (<1 cm). Additional experiments linked these results to the protective role of the clam’s shell. In practical terms, the potential of the fish species as C. fluminea predators is limited, but crayfish can be important predators of small clams. In a second set of experiments, putative predator avoidance by clams was assessed in dual-choice aquaria. Refuge availability, predator diet and light conditions were taken into account. Clam avoidance was observed under particular conditions, but the amplitude of dislocation was limited.     

Spatial distribution shifts in two temperate fish species associated to a newly-introduced tropical seaweed invasion

The establishment of non-native habitat-forming seaweeds into new areas may trigger important changes in ecosystem functioning, yet their community and ecosystem-level effects remain largely understudied. Here we studied the spatial distribution of two common fish species (Xyrichtys novacula and Bothus podas) which are key components of communities in unconsolidated bottoms of temperate areas regarding the colonization of the newly-introduced tropical seaweed Halimeda incrassata in the Mediterranean Sea. We used a spatially-explicit before-after-control-impact model and a unique data-set formed by 6 years of fine-scale spatial information of fish and seaweed distribution and abundance. We demonstrate a long-term alteration on the spatial distribution of X. novacula characterized by a shift towards non-native H. incrassata beds, while no effect on B. podas. The introduction of the tropical seaweed H. incrassata has led to the re-distribution of X. novacula, potentially by harbouring a greater biodiversity of species at the base of the food-web through adding biogenic structure to an otherwise bare sediment. Our work demonstrates that non-native tropical habitat-forming species have the potential to maintain or even enhance fish abundance in unconsolidated bottoms in temperate areas potentially altering the functioning of native habitats.     

Molecular genetic markers of intra- and interspecific divergence within starfish and sea urchins (Echinodermata)

A fragment of the mitochondrial COI gene from isolates of several echinoderm species was sequenced. The isolates were from three species of starfish from the Asteriidae family (Asterias amurensis and Aphelasterias japonica collected in the Sea of Japan and Asterias rubens collected in the White Sea) and from the sea urchin Echinocardium cordatum (family Loveniidae) collected in the Sea of Japan. Additionally, regions including internal transcribed spacers and 5.8S rRNA (ITS1–5.8S rDNA–ITS2) were sequenced for the three studied starfish species. Phylogenetic analysis of the obtained COI sequences together with earlier determined homologous COI sequences from Ast. forbesii, Ast. rubens, and Echinocardium laevigaster from the North Atlantic and E. cordatum from the Yellow and North Seas (GenBank) placed them into strictly conspecific clusters with high bootstrap support (99% in all cases). Only two exceptions–Ast. rubens DQ077915 sequence placed with the Ast. forbesii cluster and Aph. japonica DQ992560 sequence placed with the Ast. amurensis cluster–were likely results of species misidentification. The intraspecific polymorphism for the COI gene within the Asteriidae family varied within a range of 0.2-0.9% as estimated from the genetic distances. The corresponding intrageneric and intergeneric values were 10.4-12.1 and 21.8-29.8%, respectively. The interspecific divergence for the COI gene in the sea urchin of Echinocardium genus (family Loveniidae) was significantly higher (17.1-17.7%) than in the starfish, while intergeneric divergence (14.6-25.7%) was similar to that in asteroids. The interspecific genetic distances for the nuclear transcribed sequences (ITS1–5.8S rDNA–ITS2) within the Asteriidae family were lower (3.1-4.5%), and the intergeneric distances were significantly higher (32.8-35.0%), compared to the corresponding distances for the COI gene. These results suggest that the investigated molecular-genetic markers could be used for segregation and identification of echinoderm species.     

Factors determining active dispersal capacity of adult Chinese mitten crab <Emphasis Type="Italic">Eriocheir sinensis</Emphasis> (Decapoda,Varunidae)

The Chinese mitten crab (Eriocheir sinensis) is an invasive crustacean with a widespread distribution, sometimes overlapping with the red swamp crayfish (Procambarus clarkii). E. sinensis performs long river migrations, often moving overland to cross obstacles, but the factors affecting its movement are not well known. We studied its movement speed in and out of water, the survival time out of water and also its interaction with the red swamp crayfish during dispersal. At 16°C the LT₅₀ (time to death of 50% of the individuals) was 70 h, with a mean weight loss of 20%, and at 24°C the LT₅₀ was 31 h, with a mean 22% weight loss. In and out of the water, these crabs moved with mean velocities of 0.074 and 0.016 m s^?1, respectively. P. clarkii did not affect the dispersion of E. sinensis. This crab was able to disperse under various environmental conditions and its speed was affected by density, temperature, relative humidity, carapace length, and condition of the individuals (Fulton index). Moreover, we found that this species has a great capacity to resist desiccation. These characteristics give them all the requirements to successfully invade and adapt to new areas.     

Exploring stream communities in a tropical biodiversity hotspot: biodiversity,regional occupancy,niche characteristics and environmental correlates

Exploring and describing biodiversity and the mechanisms structuring it is fundamental to advancing ecology. This is particularly pertinent in understudied biogeographical regions, such as the Afrotropics, that are characterised by strong seasonal climatic shifts. We investigated the characteristics of stream biodiversity in the Niger Delta region of Nigeria, a tropical biodiversity hotspot, by examining patterns in 20 stream invertebrate communities across both the wet and dry seasons. For this, we took a multi-faceted approach accounting for the three levels of biodiversity (α, β and γ), including partitioning the nestedness and turnover components of β diversity, regional occupancy-abundance patterns, niche characteristics, and the environmental drivers of community structure. α diversity was low in these streams, with strong turnover between sites leading to high β diversity contributing to regional biodiversity, but there was little variation in communities between seasons. The proportion of sites occupied by taxa declined with increasing niche position, and decreasing niche breadth. Occupancy was predicted well by a combination of these two factors (niche position and breadth), but not mean local abundance, as the abundance-occupancy link was an upper-limit unimodal relationship. On average, community structure was linked more strongly to environmental variables in the wet season. Our findings demonstrate the clear role of spatial, but not temporal, turnover in assemblages, which likely reflects the environmental heterogeneity of this region. This is further supported by the fact that regional occupancy was mostly related to niche characteristics, particularly niche position. We emphasise the importance of continued basic and applied ecological work in this important biogeographic region to enable better protection of its biodiversity.     

Does Type of Substratum Affects Chironomid Larvae Assemblage Composition? A Study in a River Catchment in Northern Patagonia,Argentina

Chironomid larvae assemblages were investigated at seven sampling stations in relation to stream habitat type in the Challhuaco-Ñireco river system located in the Nahuel Huapi National Park, in the North-Western part of Rio Negro Province, Argentina. A total of 2229 individuals were sampled and 43 Chironomidae taxa were recorded with Orthocladiinae (29) being the best represented subfamily, followed by Diamesinae (5), Tanypodinae (3), Podonominae (3) and Chironominae (3). Stictocladius spF, Cricotopus (Paratrichocladius) sp6, Cricotopus sp2, Cricotopus sp3 and Parapsectrocladius sp2 were the most abundant taxa. Sites near the source of the river system were dominated by Podonomus sp., Limnophyes sp., Parapsectrocladius sp. and Stictocladius spF, whereas sites close to the river mouth were dominated by Diamesinae sp5 and Cricotopus sp. Rank/abundance plots show that all the analysed sites displayed dominance of some species. Stictocladius spF, Cricotopus sp2, Cricotopus sp3, Cricotopus (Paratrichocladius) sp6, Parapsectrocladius sp. and Limnophyes sp. resulted as dominant species, or being part of a group of dominant species, at least in one sample. Eleven taxa were associated with habitats related with riffle areas and stable substrates with filamentous algae. Species–environment relationships were examined using ordination analysis. Elevation was the most significant environmental variable that explained 22% of the total variability of the chironomid assemblages, showing stronger relationships among sites within an altitudinal gradient than among habitat type. Abundance of chironomids increased from headwaters to the outflow in Nahuel Huapi Lake responding to an altitude gradient as well as some environmental factors such as coarse matter and nutrient concentrations.     

Competitive interactions of Persian oak coppice trees (<Emphasis Type="Italic">Quercus brantii</Emphasis> var. <Emphasis Type="Italic">persica</Emphasis>) in a pure dry woodland revealed through point pattern analysis

Understanding intraspecific interactions among Persian oaks is essential to predict the responses of Zagros dry woodlands purely covered by these coppice trees to environmental changes (such as drought) that have direct effects on the sustainability of these woodlands. This investigation attempted to explore the scale-dependent competition among Persian oaks and highlight the impacts of competitive interactions on their biophysical properties (i.e. tree height, diameter at root collar and crown attributes) via point pattern analysis. Structurally different summary statistics were implemented to analyse the spatial pattern of Persian oaks in a pure 9-ha study plot. Nearest neighbour distribution function D(r) indicated that these coppice trees had no nearest neighbours up to the spatial scale of 2 m, and they all had a nearest neighbour at distances shorter than 12 m. Furthermore, pair correlation function g(r) showed the significant dispersion of Persian oaks up to the scale of 5 m, which may be the outcome of intraspecific competition for resources such as soil nutrients and water. As explored by mark variograms γ _m (r), Persian oaks of the same size had significant spatial correlations that illustrated the competitive (not facilitative) interactions of these coppice trees in the study plot. Mark correlation function k _mm (r) additionally revealed negative correlations of height and radial growth up to large spatial scales. Consequently, the outcome of this study highlighted the significant effects of competitive intraspecific interactions among Persian oak coppice trees on their spatial pattern and biophysical properties.     

Spatial patterns of shrub encroachment in neighbouring grassland communities in the Pyrenees: floristic composition heterogeneity drives shrub proliferation rates

We studied the role of floristic composition and associational resistance in shrub dynamics by comparing spatial patterns of shrub cover after prescribed burning in neighbouring grassland communities with different palatability. The study focused on the shrub Cytisus balansae ssp. europaeus (G. López and Jarvis) Muñoz Garmendia. Seven two-dimensional transects (20 × 0.5 m) were established to monitor shrub cover for at least 10 years after prescribed burning. Shrub cover and spatial patterns were assessed in each transect. Floristic similarity between transects and Cytisus associations with different species were estimated. Over an entire transect, shrub cover and shrub scale of pattern and patch size were lowest in the unpalatable Festuca eskia grasslands and highest in F. paniculata grasslands. At short distances, we found negative associations between Cytisus and most of the grasses, except for F. nigrescens and Agrostis capillaris, which showed positive associations with Cytisus. Thus, the effects of associational resistance on shrub encroachment were not as marked as expected, F. eskia grasslands showing the lowest shrub encroachment rates after fire. By contrast, Cytisus was positively associated with the most palatable grasses in the site, namely F. nigrescens and A. capillaris. We conclude that differences in floristic composition drive shrub encroachment rates in these spatially heterogeneous communities.