Spatial variation in the fatty acid composition of elaiosomes in an ant-dispersed plant: Differences within and between individuals and populations

Boieiro M., Espadaler X., Gómez C., Eustaquio A. (2012) Spatial variation in the fatty acid composition of elaiosomes in an ant-dispersed plant: Differences within and between individuals and populations. Flora: Morphology, Distribution, Functional Ecology of Plants. 207: 497-502.
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Doi: 10.1016/j.flora.2012.06.007

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Euphorbia characias is a common myrmecochorous plant of the western Mediterranean Basin whose seeds are dispersed by ants following fruit explosion. The variation in elaiosomes' fatty acid composition of this species was studied at three hierarchical levels (sub-individual, individual and population) in four populations from the Iberian Peninsula. We found that differences in fruit location on the inflorescence do not seem to influence the fatty acid composition of elaiosomes, providing to each propagule an equal chance of being dispersed. However, significant differences in elaiosome fatty acid composition between individuals and populations were found for most of the compounds identified. The content of oleic acid, a key mediator in the ant-seed interaction, differed widely between populations, probably reflecting geographic variations in co-adaptation between plants and their dispersers. The finding that the fatty acid composition of E. characias elaiosomes is distinct from that of the seed itself, but very similar to that of elaiosomes from unrelated species, reinforces the idea of convergent evolution in the chemical composition of these structures. © 2012 Elsevier GmbH.

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Seed production and pre-dispersal reproductive losses in the narrow endemic Euphorbia pedroi (Euphorbiaceae)

Boieiro M., Rego C., Serrano A.R.M., Espadaler X. (2012) Seed production and pre-dispersal reproductive losses in the narrow endemic Euphorbia pedroi (Euphorbiaceae). Plant Ecology. 213: 581-590.
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Doi: 10.1007/s11258-012-0023-7

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Euphorbia pedroi is a narrow endemic species with three known populations located in coastal areas of western Portugal. This study focused on the reproductive biology of this species from flowering to dispersal, aiming to identify the factors causing decrease in seed production potential and to assess the spatio-temporal patterns of seed production at the individual and population levels. The abortion of reproductive structures, particularly seeds, represented a major fraction of losses in the potential seed production of E. pedroi. Moth larvae destroyed a variable proportion of cyathia in a large number of plants from the two populations regardless of their degree of isolation. Furthermore, generalist and specialist pre-dispersal seed predators were responsible for temporally variable seed losses unrelated with variables indicative of plant size and fecundity, and showing no consistency at the individual level. Specialist seed-wasps inflicted the highest losses to E. pedroi and their impact was intimately associated with the magnitude of yearly variation in seed production. This finding highlights the role of the inter-annual variation in seed production as a key feature in this plant-seed predator system. The effect of the two groups of seed predators on the reproductive output of E. pedroi was additive and those insects do not seem to exert an important selective pressure on the traits studied. The proportion of intact seeds produced by E. pedroi differed between locations, but not between individuals within each population, highlighting the major contribution of larger plants to the seed pool. © 2012 Springer Science+Business Media B.V.

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Species Richness-Environment Relationships of European Arthropods at Two Spatial Grains: Habitats and Countries

Entling M.H., Schweiger O., Bacher S., Espadaler X., Hickler T., Kumschick S., Woodcock B.A., Nentwig W. (2012) Species Richness-Environment Relationships of European Arthropods at Two Spatial Grains: Habitats and Countries. PLoS ONE. 7: 0-0.
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Doi: 10.1371/journal.pone.0045875

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We study how species richness of arthropods relates to theories concerning net primary productivity, ambient energy, water-energy dynamics and spatial environmental heterogeneity. We use two datasets of arthropod richness with similar spatial extents (Scandinavia to Mediterranean), but contrasting spatial grain (local habitat and country). Samples of ground-dwelling spiders, beetles, bugs and ants were collected from 32 paired habitats at 16 locations across Europe. Species richness of these taxonomic groups was also determined for 25 European countries based on the Fauna Europaea database. We tested effects of net primary productivity (NPP), annual mean temperature (T), annual rainfall (R) and potential evapotranspiration of the coldest month (PETmin) on species richness and turnover. Spatial environmental heterogeneity within countries was considered by including the ranges of NPP, T, R and PETmin. At the local habitat grain, relationships between species richness and environmental variables differed strongly between taxa and trophic groups. However, species turnover across locations was strongly correlated with differences in T. At the country grain, species richness was significantly correlated with environmental variables from all four theories. In particular, species richness within countries increased strongly with spatial heterogeneity in T. The importance of spatial heterogeneity in T for both species turnover across locations and for species richness within countries suggests that the temperature niche is an important determinant of arthropod diversity. We suggest that, unless climatic heterogeneity is constant across sampling units, coarse-grained studies should always account for environmental heterogeneity as a predictor of arthropod species richness, just as studies with variable area of sampling units routinely consider area. © 2012 Entling et al.

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Ecto- and endoparasitic fungi on ants from the Holarctic Region

Espadaler X., Santamaria S. (2012) Ecto- and endoparasitic fungi on ants from the Holarctic Region. Psyche. : 0-0.
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Doi: 10.1155/2012/168478

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The ant-specific fungi Aegeritella, Laboulbenia, Rickia, Hormiscium, and Myrmicinosporidium in the Holarctic regionnine speciesare reviewed. Present knowledge is highly biased geographically, as shows the single record for Holarctic Asia, and this is to solve. The phylogenetic position of Aegeritella, Hormiscium, and Myrmicinosporidium is unknown. Hosts seem to be also skewed phylogenetically although this may be a true pattern. © 2012 Xavier Espadaler and Sergi Santamaria.

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Effects of ant competition and bird predation on the spider assemblage of a citrus grove

Mestre L., Piñol J., Barrientos J.A., Cama A., Espadaler X. (2012) Effects of ant competition and bird predation on the spider assemblage of a citrus grove. Basic and Applied Ecology. 13: 355-362.
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Doi: 10.1016/j.baae.2012.04.002

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Characterizing intraguild interactions is key to improving understanding of food webs because they are major forces in the structuring of communities. Spiders are generalist predators with intermediate positions in the food web that establish intraguild interactions with ants and birds, which respectively compete with and prey on them. Research has also found interactions between birds and ants, potentially resulting in non-additive effects of both groups on arthropod assemblages, although studies of their combined impacts with tests for multiple-predator effects are scarce. We thus aimed to discern the relative effect of ants and birds on the spider assemblage of a citrus grove. We used a split-plot design to factorially exclude these groups over 2. years, preventing ants reaching the canopies by placing sticky bands around tree trunks, and birds by enclosing groups of trees in cages. We sampled spiders from the canopies (beating) and the ground (pitfalls) every 3. months, and we identified them to species. We found a strong influence of ants on the canopy spider assemblage, mainly through a negative effect on the families Araneidae and Theridiidae. Since spiders' weights from ant-excluded and control trees were similar, these results suggest interference competition of ants on spiders rather than competitive exploitation. Bird exclusion did not affect the spider assemblage, contrasting with other studies reporting a marked predatory pressure of birds on spiders; nor were there any non-additive effects of ants and birds. Our findings show that spider assemblages are not uniformly affected by intraguild competitors. © 2012 Gesellschaft für ökologie.

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Eight years of ant-exclusion from citrus canopies: Effects on the arthropod assemblage and on fruit yield

Piñol J., Espadaler X., Cañellas N. (2012) Eight years of ant-exclusion from citrus canopies: Effects on the arthropod assemblage and on fruit yield. Agricultural and Forest Entomology. 14: 49-57.
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Doi: 10.1111/j.1461-9563.2011.00542.x

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1 Ants are important generalist predators in most terrestrial ecosystems. However, because many ant species are also hemipteran mutualists, their role in agriculture has generally been considered to be negative for plants. 2 In the present study, we report an experiment in ant-exclusion from tree canopies in an organic citrus grove with two main objectives: (i) to examine whether the absence of ants increased the abundance of some beneficial arthropods and reduced the attack of some pests such as aphids and (ii) to examine whether ant-exclusion increased the fruit yield of citrus trees. 3 The exclusion of ants from tree canopies had positive effects on the arthropod assemblage and on fruit yield. However, the 8-year duration of the experiment can be divided into two periods with contrasting results. In the first period, the arthropod assemblage was only slightly affected, except for a greater density of aphids in ant-excluded trees; in addition, fruit yield was higher in ant-excluded trees than in the control ones. In the second period, ant-exclusion increased the abundance of most arthropod groups, although the previous positive effect on fruit yield was no longer observed. 4 There are two main conclusions of the present study. First, from an applied perspective, ant-exclusion from tree canopies is not a sound management alternative in citrus plantations in the Mediterranean. Second, the 8-year duration of the experiment highlighted the importance of long-term experiments in community ecology and biological control because the effects observed in the first 4 years of the experiment were very different from what occurred subsequently. © 2011 The Authors. Agricultural and Forest Entomology © 2011 The Royal Entomological Society.

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Long-term changes and ant-exclusion effects on the true bugs (Hemiptera: Heteroptera) of an organic citrus grove

Piñol J., Ribes E., Ribes J., Espadaler X. (2012) Long-term changes and ant-exclusion effects on the true bugs (Hemiptera: Heteroptera) of an organic citrus grove. Agriculture, Ecosystems and Environment. 158: 127-131.
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Doi: 10.1016/j.agee.2012.06.004

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The Heteroptera assemblage of a citrus grove and how it was affected by ant-exclusion was examined during transformation from conventional to organic agriculture. The results showed that the Heteroptera assemblage changed dramatically over the eight years of the study: at first, it mainly consisted of herbivorous lygaeids and predatory anthocorids but became dominated by predatory mirids in 2008-2009. The predator/herbivore ratio increased steadily over the eight years of the study. Ants can form mutualistic relationships with heteropteran pests. However, exclusion of ants from canopies did not affect the Heteroptera assemblage at the beginning of the study, but had a profound effect later on. In particular, ant-exclusion increased the abundance of most predatory Heteroptera, except for the myrmecomorphic mirid Pilophorus perplexus, which was approximately five times more abundant in control than in ant-excluded trees; the analyses showed that the only mimicked ant species was Lasius grandis. © 2012 Elsevier B.V.

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Trophic diversity in a Mediterranean food web-Stable isotope analysis of an ant community of an organic citrus grove

Platner C., Piñol J., Sanders D., Espadaler X. (2012) Trophic diversity in a Mediterranean food web-Stable isotope analysis of an ant community of an organic citrus grove. Basic and Applied Ecology. 13: 587-596.
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Doi: 10.1016/j.baae.2012.09.006

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Ants as generalist predators and mutualists of herbivores can play an important role in relative stable agroecosystems like plantations. The categorization of the diverse life strategies and traits into ecological groups like trophic levels is essential for a better understanding of food web structures and a better prediction of changes in communities. Stable isotope technology provides simultaneously detection of trophic levels and the ultimate C source of many species.We studied a highly diverse Mediterranean ant community in an organic citrus grove in Tarragona, NE Spain, and analyzed stable isotope contents of 17 species of ants together with dominating plants and important spider and aphid species to establish trophic guilds and detect seasonal changes. The results revealed significant differences between species spanning over a huge range in δ15N-values of at least 10.67‰ which is only comparable to a Peruvian tropical forest with a much higher species diversity. The trophic levels of ants reflected most of previous knowledge on predaceous vs. plant feeding habits. Messor harvester ants and Camponotus species had the lowest δ15N-values. Aphids, smaller spider species, and most other ant genera, including the dominating species Formica rufibarbis and Lasius grandis, had intermediate δ15N-levels. The large spider Dysdera crocata and the typical Mediterranean ant Pheidole pallidula had higher δ15N-values, but two specialized predatory ants with very tiny workers had the highest trophic level. We found unexpectedly high δ13C-values with a high seasonality for several ground-living ant species. The possible role of soil fauna as a second main food resource besides the most commonly analyzed green food chain is discussed. Our results support the hypothesis that the strong seasonality intrinsic to Mediterranean climate and the high heterogeneity of different plant resources and microclimatic conditions in the organically managed plantation are reflected by a notably high trophic diversity of the ant community. © 2012 Gesellschaft für Ökologie.

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Abundance, interannual variation and potential pest predator role of two co-occurring earwig species in citrus canopies

Romeu-Dalmau C., Espadaler X., Piñol J. (2012) Abundance, interannual variation and potential pest predator role of two co-occurring earwig species in citrus canopies. Journal of Applied Entomology. 136: 501-509.
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Doi: 10.1111/j.1439-0418.2011.01671.x

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Earwigs are usually considered pest predators in orchards. Because of its worldwide distribution, most research on earwigs focuses on the European earwig Forficula auricularia Linnaeus (Insecta: Dermaptera: Forficulidae). However, very little is known of this species in Mediterranean citrus orchards. Earwigs and aphids were collected monthly during 5years (2006-2010) from citrus canopies. Two species of earwigs were found: F. auricularia and Forficula pubescens Gené (=Guanchia pubescens), with the latter seldom cited in the literature. The goals of this study were (i) to document the abundance of these two earwig species in Mediterranean citrus canopies; (ii) to determine whether they are positively or negatively associated with each other, or randomly distributed; (iii) to measure the interannual variation of the abundance of both species during a 5-year period and (iv) to evaluate the potential role of earwigs as pest predators in citrus canopies. As compared to colder regions, F. auricularia active period in citrus canopies in our study site lasted longer. Both species co-occurred randomly in canopies. In 2006, both species showed approximately the same abundance, but in 2010, F. pubescens abundance in canopies was 28 times greater than that of F. auricularia. The potential role of earwigs as pest predators is higher in the Mediterranean than in other colder regions, because of the longer active period. F. auricularia is a sedentary generalist predator, already present in citrus canopies at the onset of most pest outbreaks, while F. pubescens arrived later to the canopies, but most likely was abundant enough to contribute in the control of citrus pests. © 2011 Blackwell Verlag, GmbH.

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Friend or foe? The role of earwigs in a Mediterranean organic citrus orchard

Romeu-Dalmau C., Piñol J., Espadaler X. (2012) Friend or foe? The role of earwigs in a Mediterranean organic citrus orchard. Biological Control. 63: 143-149.
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Doi: 10.1016/j.biocontrol.2012.06.010

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As earwigs (Insecta: Dermaptera) are considered both effective predators of aphids and pests in their own right in citrus orchards, the aim of the present study was to examine their relative role as pest versus predator. We conducted a two-year experiment of earwig exclusion from citrus canopies and compared aphid infestation, flower survival and fruit yield in trees with earwigs (control trees) with those in trees without earwigs (banded trees). However, as not only earwigs but also all other crawling insects were excluded from the banded trees, we added a third group of trees (earwig trees) where crawling insects were excluded but earwigs were added to the canopy every 1-2. weeks. We hypothesized that if the same results were obtained in control and earwig trees, and both differed from those obtained in banded trees, earwigs would most probably be the cause of these differences. Overall, aphid infestation in trees with earwigs was less severe than aphid infestation in trees without earwigs; we also found that aphid density was negatively related to earwig abundance. Earwigs also negatively influenced flower survival but this effect was no longer observed once trees naturally abscised their own flowers and fruitlets. Finally, we did not find any difference in fruit yield between the treatments, or any relationship between earwig abundance and fruit production. Thus, as earwigs appeared to control aphid populations while not affecting fruit yield, we can conclude that earwigs are beneficial insects in this Mediterranean organic citrus orchard. © 2012 Elsevier Inc.

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