The impact of specialist and generalist pre-dispersal seed predators on the reproductive output of a common and a rare Euphorbia species

Boieiro M., Rego C., Serrano A.R.M., Espadaler X. (2010) The impact of specialist and generalist pre-dispersal seed predators on the reproductive output of a common and a rare Euphorbia species. Acta Oecologica. 36: 227-233.
Enllaç
Doi: 10.1016/j.actao.2010.01.001

Resum:

Pre-dispersal seed predators can have a severe impact on the reproductive output of their hosts, which can translate into negative effects on population dynamics. Here we compared the losses due to specialist and generalist insect seed predators in two Euphorbia species, a rare (Euphorbia welwitschii) and a common one (Euphorbia characias). Pre-dispersal losses to specialist seed-wasps (Eurytoma jaltica) and generalist hemipterans (Cydnus aterrimus and Dicranocephalus agilis) were on average higher for the rare E. welwitschii than for its widespread congener. In both Euphorbia species, the variation in losses to specialist and generalist seed predators was not related with traits indicative of plant size, fecundity, or isolation. Nevertheless, the temporal variation in losses to seed-wasps seemed to be intimately associated with the magnitude of yearly variation in fruit production. The impact of seed-wasps and hemipterans on the reproductive output of both Euphorbia species was additive, though there was evidence for infochemical-mediated interference at the fruit level. The moderate levels of seed predation in E. welwitschii, together with the results from the comparative analysis with its widespread congener, suggest that insect seed predation is not a causal effect of plant rarity. © 2010 Elsevier Masson SAS. All rights reserved.

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Plant fecundity and pre-dispersal reproductive losses in a common and a rare Euphorbia species (Euphorbiaceae)

Boieiro M., Serrano A.R.M., Rego C., Espadaler X. (2010) Plant fecundity and pre-dispersal reproductive losses in a common and a rare Euphorbia species (Euphorbiaceae). Ecological Research. 25: 447-456.
Enllaç
Doi: 10.1007/s11284-009-0674-6

Resum:

Comparative studies on the reproductive biology of closely related plant species have provided valuable information to understand the causes and consequences of common-rare differences with possible applications for the management of threatened populations. The magnitude and spatiotemporal variability of seed production and pre-dispersal reproductive losses were studied for 3 years in the rare endemic Euphorbia welwitschii and in its widespread congener E. characias. The factors responsible for a decrease in potential seed production in these species were the lack of a functional ovary in the cyathium, ovary and fruit abortion, seed predation by insects and seed abortion. In E. characias, the moth Acroclita subsequana was also responsible for minor reproductive losses. The proportion of male cyathia varied significantly between seasons, populations and species, being consistently higher in E. characias than in E. welwitschii. Reproductive losses that resulted in ovary, fruit and seed abortion affected mostly the endemic species and were heavier in the populations located near the sea due to local adverse climatic conditions. Seed predators inflicted higher reproductive losses to the endemic species than to its widespread congener and their impact was particularly heavy at Risco. The two Euphorbia species differed markedly in cyathia production, with E. welwitschii producing systematically a lower number of cyathia than its widespread congener and this, together with higher levels of ovary, fruit and seed abortion, seemed to be the main reasons for the low reproductive output of this rare species. © The Ecological Society of Japan 2009.

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Dispersal mechanisms of the narrow endemic Polygala vayredae: Dispersal syndromes and spatio-temporal variations in ant dispersal assemblages

Castro S., Ferrero V., Loureiro J., Espadaler X., Silveira P., Navarro L. (2010) Dispersal mechanisms of the narrow endemic Polygala vayredae: Dispersal syndromes and spatio-temporal variations in ant dispersal assemblages. Plant Ecology. 207: 359-372.
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Doi: 10.1007/s11258-009-9679-z

Resum:

This study assesses the dispersal mechanisms of the narrow endemic Polygala vayredae, analysing the functioning of its dispersal syndromes (anemochory and myrmecochory), the spatio-temporal variability of the disperser assemblage, foraging behaviour and dispersal ability, and the role of the elaiosome in ant attraction and seed germination. The dispersion of diaspores begins when either (1) capsules or seeds fall beneath the mother plant (barochory) or (2) the seeds are directly collected in the suspended capsules by ants (myrmecochory). As capsules frequently open and expose/disseminate seeds before leaving the mother plant, the adaptation for anemochory appears to be reduced and rarely functional, possibly with only occasional events of long-distance dispersal (e. g. under extreme weather conditions). P. vayredae is essentially myrmecochorous and a diverse array of ant species are involved in seed manipulation, with the elaiosome playing a major role in ant attraction. From the plant's perspective for dispersal, the majority of ant species had a positive interaction with the seeds, but negative and potential neutral interactions were also observed. Overall, dispersal distances were limited and were mainly determined by ant body size. The frequency of interactions and the ant assemblage varied significantly both spatially and temporally, and these factors may have an effect on directing or disrupting the selection of plant traits. Low seed predation and similar germination rates of intact seeds compared with seeds without elaiosome indicate that seed predator avoidance and seed germination improvement after ant manipulation are not among the selective advantages of myrmecochory operating at present. Dispersal mechanisms that enhance seed dispersal within the population and only occasionally lead to long-distance dispersal events, along with the rarity and patchiness of suitable habitats, may be the main factors explaining the actual density and narrow distribution of this species. © Springer Science+Business Media B.V. 2009.

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Ant versus bird exclusion effects on the arthropod assemblage of an organic citrus grove

Piñol J., Espadaler X., Cañellas N., MartíNez-Vilalta J., Barrientos J.A., Sol D. (2010) Ant versus bird exclusion effects on the arthropod assemblage of an organic citrus grove. Ecological Entomology. 35: 367-376.
Enllaç
Doi: 10.1111/j.1365-2311.2010.01190.x

Resum:

Predation-exclusion experiments have highlighted that top-down control is pervasive in terrestrial communities, but most of these experiments are simplistic in that they only excluded a single group of predators and the effect of removal was evaluated on a few species from the community. The main goal of our study was to experimentally establish the relative effects of ants and birds on the same arthropod assemblage of canopy trees. We conducted 1-year long manipulative experiments in an organic citrus grove intended to quantify the independent effects of bird and ant predators on the abundance of arthropods. Birds were excluded with plastic nets whereas ants were excluded with sticky barriers on the trunks. The sticky barrier also excluded other ground dwelling insects, like the European earwig Forficula auricularia L. Both the exclusion of ants and birds affected the arthropod community of the citrus canopies, but the exclusion of ants was far more important than the exclusion of birds. Indeed, almost all groups of arthropods had higher abundance in ant-excluded than in control trees, whereas only dermapterans were more abundant in bird-excluded than in control trees. A more detailed analysis conducted on spiders also showed that the effect of ant exclusion was limited to a few families rather than being widespread over the entire diverse spectrum of spiders. Our results suggest that the relative importance of vertebrate and invertebrate predators in regulating arthropod populations largely depends on the nature of the predator-prey system. © 2010 The Authors. Journal compilation © 2010 The Royal Entomological Society.

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Nuevos casos y hospedadores de Myrmicinosporidium durum Hölldobler, 1933 (Fungi).

García F, Espadaler X (2010) Nuevos casos y hospedadores de Myrmicinosporidium durum Hölldobler, 1933 (Fungi). Iberomyrmex 2: 5-11.

Citas nuevas o interesantes de hormigas (Hymenoptera, Formicidae) para Marruecos.

Taheri A,Reyes-López J, Espadaler X (2010) Citas nuevas o interesantes de hormigas (Hymenoptera, Formicidae) para Marruecos. Boletín de la Sociedad entomológica Aragonesa 47: 299-300.

Hormigas (Hymenoptera, Formicidae) de los acantilados de l'Avenc de Tavertet (Osona).

García F, Espadaler X, Echave P, Vila R (2010) Hormigas (Hymenoptera, Formicidae) de los acantilados de l'Avenc de Tavertet (Osona). Boletín de la Sociedad entomológica Aragonesa 47: 33-37.

First record of Lasius paralienus Seifert, 1992 (Hymenoptera : Formicidae) from France and Andorra.

Bernadou A, Galkowski C, Le Goff A, Fourcassié V, Espadaler X (2010) First record of Lasius paralienus Seifert, 1992 (Hymenoptera : Formicidae) from France and Andorra. Myrmecological News 13: 111-113.

Formigues de les Planes de Son i mata de València.

Espadaler X, Roig X, Gómez K, García F (2010) Formigues de les Planes de Son i mata de València. Treballs de la Institució Catalana d'Història Natural 16: 609-627.

. The impact of pre-dispersal seed predators on the reproductive output of two Euphorbia.

Boieiro M, Rego C, Serrano A, Espadaler X (2010) . The impact of pre-dispersal seed predators on the reproductive output of two Euphorbia. Acta Oecologica 36: 227-233.

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