Collapse of the invasive garden ant, Lasius neglectus, populations in four European countries

Tartally A., Antonova V., Espadaler X., Csősz S., Czechowski W. (2016) Collapse of the invasive garden ant, Lasius neglectus, populations in four European countries. Biological Invasions. : 1-5.
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Doi: 10.1007/s10530-016-1227-x

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The invasive garden ant Lasius neglectus (Hymenoptera: Formicidae) has been spreading rapidly in Europe ever since the 1990s. This ant established enormous supercolonies in many European cities and poses a serious threat to the local native faunas. The spread of this species has not slowed down in the last decades, but in the recent years the sizes of the known L. neglectus populations have generally been declining or have stagnated. For 29 supercolonies checked in four countries, in 10 cases L. neglectus individuals have not been found on the former area of their occurrence. On the other hand, only two supercolonies have expanded. In this paper, we summarize these monitoring data collected by the personal independent, diligent monitoring activities of myrmecologists on populations of the invasive garden ant in Bulgaria, Hungary, Poland and Spain. The reasons for this collapse are thought to be: (1) depletion of the local resources, (2) gradation of pathogens and (social)parasites, (3) climatic factors, (4) intra-population mechanisms, (5) confrontation with highly competitive native species, and (6) lack of suitable nesting microhabitats. As similar phenomena were observed in the cases of supercolonies of other invasive ant species, it seems that they decline more generally than has been thought. © 2016 Springer International Publishing Switzerland

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Discovered just before extinction? The first endemic ant from the Balearic Islands (Lasius balearicus sp. nov.) is endangered by climate change

Talavera G., Espadaler X., Vila R. (2015) Discovered just before extinction? The first endemic ant from the Balearic Islands (Lasius balearicus sp. nov.) is endangered by climate change. Journal of Biogeography. 42: 589-601.
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Doi: 10.1111/jbi.12438

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Aim: We analyse the taxonomic status, phylogenetic relationships, distribution and age of a newly discovered ant taxon found in the mountaintops of the island of Mallorca (Spain). We also consider the potential impact of short-term climate change on the survival of this ant and make proposals on its conservation status, risks and management. Location: Balearic Islands (Spain). Methods: We used morphological, molecular and ecological evidence to assess the specific status of the potential new species. We gathered distribution data to conduct climate-based distribution modelling of present and future occupancy under several SRES emission scenarios. Results: The existence of a new non-cryptic species of ant (Lasius balearicus Talavera, Espadaler & Vila, sp. nov.) is described from the island of Mallorca. Its distribution was found to be extremely restricted (Serra de Tramuntana) and elevationally constrained to island summits (between 800 and 1400 m a.s.l.). Molecular dating indicated that this species diverged about 1.51 million years ago from its nearest relatives, from which it can be distinguished based on several morphological traits. Ecological niche modelling shows a dramatic reduction of areas with suitable climatic conditions under the different scenarios studied. Main conclusions: Lasius balearicus represents the first endemic ant to be described in the Balearic Islands, as well as the first endemic Lasius species in the Mediterranean islands. Distribution modelling predictions, the low intraspecific genetic diversity observed, and the geographical and elevational isolation of the populations indicated a low probability for the survival of the species in the short term, thus making it a potential model to study real-time climate-based biodiversity loss. As a consequence, we strongly recommend including L. balearicus in the IUCN Red List of Threatened Species under the category 'Endangered'. This case illustrates that a fraction of biodiversity remains unexplored even within Europe, arguably the best-studied region of the planet, and that the available time-window for us to study and protect it may be in some instances notably narrow. © 2014 John Wiley & Sons Ltd.

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Rapid increase of the parasitic fungus Laboulbenia formicarum in supercolonies of the invasive garden ant Lasius neglectus

Tragust S., Feldhaar H., Espadaler X., Pedersen J.S. (2015) Rapid increase of the parasitic fungus Laboulbenia formicarum in supercolonies of the invasive garden ant Lasius neglectus. Biological Invasions. 17: 2795-2801.
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Doi: 10.1007/s10530-015-0917-0

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A key feature among invasive ant species is their ability to dominate vast areas by forming dense networks of connected nests in contrast to the smaller and discrete, spatially dispersed colonies of most social insects. However, it was recently proposed that such supercolonies are more vulnerable to infection by parasites and diseases as they would serve as large targets with high rates of transmission from nests to nest. We studied the invasive garden ant Lasius neglectus, a pest species currently spreading throughout Europe. Several populations are infected with an ectoparasitic fungus, Laboulbenia formicarum, itself an introduced species, yielding a new host–parasite relationship. Long-term monitoring of the prevalence and intensity of infection in two populations (supercolonies) over 4–10 years revealed epizootic spread of the parasite with a 14 % annual increase in prevalence until ca. 80 % of all ants were infected. In contrast, no other local ant species with discrete colonies carried the parasite, although a local species (Lasius niger) proved susceptible in a cross-infection experiment. These results support the hypothesis that supercolonies potentially face an important challenge from parasites and diseases, with interesting perspectives for biological control of such ant species. © 2015, Springer International Publishing Switzerland.

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Evaluating the importance of trophobiosis in a Mediterranean ant community: a stable isotope analysis

Brewitt K., Pinol J., Werner C., Beyschlag W., Espadaler X., Perez Hidalgo N., Platner C. (2014) Evaluating the importance of trophobiosis in a Mediterranean ant community: a stable isotope analysis. Insectes Sociaux. : 0-0.
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Doi: 10.1007/s00040-014-0375-1

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Trophobiosis between aphids (Aphididae, Hemiptera) and ants (Formicidae, Hymenoptera) is considered to provide an important source of nutrition for ants by aphid honeydew and aphids themselves used as prey. However, little is known about nutrient fluxes and the relative importance of trophobiosis for different ant species. Combining direct contact observations between ants and aphids with stable isotope analyses of distinct multitrophic sample sets (soil, plant, aphid, and ant), we aimed at disentangling the importance of trophobiosis in a Mediterranean food web and possible feedbacks on the functional diversity of ants in a species-rich organic Citrus plantation. We analyzed δ13C- and δ15N-values of sample sets for fertilized and natural soil, using the fertilizer as natural isotope label. The results showed trophic relationships between 18 host plant species, 22 aphid species, and 7 ant species. Direct observation revealed at least 40 different plant–aphid combinations and 25 aphid–ant combinations with a marked range of δ15N-values. However, the δ13C and δ15N isotope ratios still reflected the trophic levels. A significant correlation occurred between the isotope ratios of aphids and their host plants. However, no relationship was found between aphids and ants or between plants and ants revealing that many ant species do not exhibit a close relationship with their trophobiotic partners. Isotopic data allowed us to separate ant species into trophic functional groups and showed the relevance of other food resources. The applied fertilizer shifted the isotopic baseline for the whole trophic system. By combining the stable isotope analysis with the exact origin of the samples, we avoided a misleading interpretation of the high isotopic range of species. Thus, we emphasize the importance of considering a baseline in stable isotope food web studies.

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Reorientation patterns in central-place foraging: Internal clocks and klinokinesis

Campos D., Bartumeus F., Mendez V., Espadaler X. (2014) Reorientation patterns in central-place foraging: Internal clocks and klinokinesis. Journal of the Royal Society Interface. 11: 0-0.
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Doi: 10.1098/rsif.2013.0859

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We study central-place foraging patterns of Aphaenogaster senilis ants at a population level by video framing individual ant trajectories in a circular arena with a nest connected to its centre. The ants naturally leave and enter the nest and forage generating non-trivial movement patterns around the nest. Our data analysis indicated that the trajectories observed can be classified into two strategies: the risk-averse strategy, which involves wandering around the nest without departing far from it and the riskprone strategy, which involves long exploration paths with periodic returns to the central region, nearby the nest. We found that both risk-prone and risk-averse strategies exhibit qualitatively the same reorientation patterns, with the time between consecutive reorientations covering a wide range of scales, and fitting a stretched exponential function. Nevertheless, differences in the temporal scales and the time variability of such reorientation events differ, together with other aspects of motion, such as average speed and turns. Our results give experimental evidence that the internal mechanisms driving reorientations in ants tend to favour frequently long relocations, as theory predicts for efficient exploration in patchy landscapes, but ants engaged in central-place foraging can modulate such behaviour to control distances from the nest. Previous works on the species support the idea that risk-prone and risk-averse strategies may reflect actual differences between individuals age and experience; these factors (age and experience) should be then relevant in modulating the internal reorientation clocks. To support the validity of our findings, we develop a random-walk model combining stretched exponential reorientation clocks with klinokinesis that fits the time length and the travelled distance distributions of the observed trajectories. © 2013 The Author(s) Published by the Royal Society. All rights reserved.

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Rickia lenoirii, a new ectoparasitic species, with comments on world Laboulbeniales associated with ants

Santamaria S., Espadaler X. (2014) Rickia lenoirii, a new ectoparasitic species, with comments on world Laboulbeniales associated with ants. Mycoscience. : 0-0.
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Doi: 10.1016/j.myc.2014.06.006

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A new species of the genus Rickia is described on ants of the genus Messor based on collections from Greece and France. Rickia lenoirii is distinguished from Rickia wasmannii by the smaller size of the thallus and by the fewer number of cells in each of the three series, as well by other characteristics. The newly described species belongs to the perlata morphological group and because of its diminutive thallus may be compared with similar small species, mostly on mites; therefore it could be included among acarophilous forms according to an old Thaxter definition. The database of ant-Laboulbenial interactions consists of 43 species, 10 genera, and three subfamilies of ants documented as hosts for the six Laboulbeniales known from ants worldwide. Some ant Laboulbenial species show a low host phylogenetic specificity while other species are much restricted in their host range. The highly biased known distribution of ant Laboulbeniales is probably an artifact and the database is far from being complete. © 2014 The Mycological Society of Japan.

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Invasive and socially parasitic ants are good bioindicators of habitat quality in Mediterranean forest remnants in northeast Spain

Bernal V., Espadaler X. (2013) Invasive and socially parasitic ants are good bioindicators of habitat quality in Mediterranean forest remnants in northeast Spain. Ecological Research. 28: 1011-1017.
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Doi: 10.1007/s11284-013-1083-4

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We surveyed ants in 16 forest remnants in the Vallès lowlands north of Barcelona, Spain: eight with invasive exotic ants (IE = Linepithema humile and/or Lasius neglectus) present, seven with native parasitic ants (P = Lasius meridionalis, Lasius carniolicus, Plagiolepis xene, Chalepoxenus muellerianus, and/or Polyergus rufescens) present, and one remnant with both invasive exotic and parasitic ants present. Forest remnants with IE ants were smaller, more isolated, had greater perimeter/area, lower ant species density, and lower ant species richness than remnants with P ants. The community composition was also significantly different, with greater dissimilarity within remnants with alien, invasive species. The presence of some species is bio-indicator of low disturbance, whereas others are indicative of high disturbance. Our findings underscore the value of different types of ants as bio-indicators of fragmentation and habitat quality. © 2013 The Ecological Society of Japan.

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Bird predation affects diurnal and nocturnal web-building spiders in a Mediterranean citrus grove

Mestre L., Garcia N., Barrientos J.A., Espadaler X., Piñol J. (2013) Bird predation affects diurnal and nocturnal web-building spiders in a Mediterranean citrus grove. Acta Oecologica. 47: 74-80.
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Doi: 10.1016/j.actao.2013.01.001

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Spiders and birds can greatly decrease insect populations, but birds also limit spider densities in some habitats. Bird predation is thought to be one of the causes behind nocturnal activity in spiders, so night-active spiders that hide in retreats during the day should be less affected by bird foraging than day-active spiders. However, this hypothesis has not yet been tested. We investigated the importance of bird predation on the spider community of a Mediterranean organic citrus grove. We excluded birds by placing net cages over the trees and we conducted visual searches in the canopies to sample web-building spiders. As there are many nocturnal species in the family Araneidae, we conducted searches both by day and by night to compare the abundance of active araneids in these two time periods. We sampled the tree trunks with cardboard bands to collect hunting spiders. In bird-excluded canopies there were more spiders of the families Araneidae and Theridiidae. There were higher numbers of active Araneidae at night, but these were just as negatively affected by bird predation as day-active Araneidae, so there was no evidence of nocturnal activity serving as an anti-predator strategy. We did not find any negative impact of birds on hunting spiders. Our results contrast with other studies reporting a negative effect of birds on hunting but not on web-building spiders. © 2013.

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Ant exclusion in citrus over an 8-year period reveals a pervasive yet changing effect of ants on a Mediterranean spider assemblage

Mestre L., Pinol J., Barrientos J.A., Espadaler X. (2013) Ant exclusion in citrus over an 8-year period reveals a pervasive yet changing effect of ants on a Mediterranean spider assemblage. Oecologia. 173: 239-248.
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Doi: 10.1007/s00442-013-2594-y

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Ants and spiders are ubiquitous generalist predators that exert top-down control on herbivore populations. Research shows that intraguild interactions between ants and spiders can negatively affect spider populations, but there is a lack of long-term research documenting the strength of such interactions and the potentially different effects of ants on the diverse array of species in a spider assemblage. Similarly, the suitability of family-level surrogates for finding patterns revealed by species-level data (taxonomic sufficiency) has almost never been tested in spider assemblages. We present a long-term study in which we tested the impact of ants on the spider assemblage of a Mediterranean citrus grove by performing sequential 1-year experimental exclusions on tree canopies for 8 years. We found that ants had a widespread influence on the spider assemblage, although the effect was only evident in the last 5 years of the study. During those years, ants negatively affected many spiders, and effects were especially strong for sedentary spiders. Analyses at the family level also detected assemblage differences between treatments, but they concealed the different responses to ant exclusion shown by some related spider species. Our findings show that the effects of experimental manipulations in ecology can vary greatly over time and highlight the need for long-term studies to document species interactions. © 2013 Springer-Verlag Berlin Heidelberg.

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Trophic structure of the spider community of a Mediterranean citrus grove: A stable isotope analysis

Mestre L., Pinol J., Barrientos J.A., Espadaler X., Brewitt K., Werner C., Platner C. (2013) Trophic structure of the spider community of a Mediterranean citrus grove: A stable isotope analysis. Basic and Applied Ecology. 14: 413-422.
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Doi: 10.1016/j.baae.2013.05.001

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Spiders are dominant terrestrial predators that consume a large variety of prey and engage in intraguild predation. Although the feeding habits of certain species are well known, the trophic structure of spider assemblages still needs to be investigated. Stable isotope analysis enables characterisation of trophic relationships between organisms because it tracks the energy flow in food webs and indicates the average number of trophic transfers between a given species and the base of the web, thus being a useful tool to estimate the magnitude of intraguild predation in food webs. Using this technique, we studied the trophic groups of spiders and their links within the arthropod food web of a Mediterranean organic citrus grove. We assessed the trophic positions of the 25 most common spider species relative to other arthropod predators and potential prey in the four seasons of the year, both in the canopy and on the ground. The analyses showed great seasonal variation in the isotopic signatures of some arthropod species, as well as the existence of various trophic groups and a wide range of trophic levels among spiders, even in species belonging to the same family. Differences in δ15N between spiders and the most abundant prey in the grove usually spanned two trophic levels or more. Our findings provide field evidence of widespread intraguild predation in the food web and caution against using spider families or guilds instead of individual species when studying spider trophic interactions. © 2013 Gesellschaft für Ökologie.

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