Spatial distribution and packing of xylem conduits.

Martinez-Vilalta J, Mencuccini M, Alvarez X, Camacho J, Loepfe J, Pinol J (2012) Spatial distribution and packing of xylem conduits. 7th Plant Biomechanics International Conference, Clermont-Ferrand, France, 20-24 August 2012. (Comunicació oral).

Management alternatives to offset climate change effects on Mediterranean fire regimes in NE Spain

Loepfe L., Martinez-Vilalta J., Piñol J. (2012) Management alternatives to offset climate change effects on Mediterranean fire regimes in NE Spain. Climatic Change. 115: 693-707.
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Doi: 10.1007/s10584-012-0488-3

Resum:

Fire regime is affected by climate and human settlements. In the Mediterranean, the predicted climate change is likely to exacerbate fire prone weather conditions, but the mid- to long-term impact of climate change on fire regime is not easily predictable. A negative feedback via fuel reduction, for instance, might cause a non-linear response of burned area to fire weather. Also, the number of fires escaping initial control could grow dramatically if the fire meteorology is just slightly more severe than what fire brigades are prepared for. Humans can directly influence fire regimes through ignition frequency, fire suppression and land use management. Here we use the fire regime model FIRE LADY to assess the impacts of climate change and local management options on number of fires, burned area, fraction of area burned in large fires and forest area during the twenty-first century in three regions of NE Spain. Our results show that currently fuel-humidity limited regions could suffer a drastic shift of fire regime with an up to 8 fold increase of annual burned area, due to a combination of fuel accumulation and severe fire weather, which would result in a period of unusually large fires. The impact of climate change on fire regime is predicted to be less pronounced in drier areas, with a gradual increase of burned area. Local fire prevention strategies could reduce but not totally offset climate induced changes in fire regimes. According to our model, a combination of restoring the traditional rural mosaic and classical fire prevention would be the most effective strategy, as a lower ignition frequency reduces the number of fires and the creation of agricultural fields in marginal areas reduces their extent. © 2012 Springer Science+Business Media B.V.

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Spatial distribution and packing of xylem conduits

Martínez-Vilalta J., Mencuccini M., Álvarez X., Camacho J., Loepfe L., Piñol J. (2012) Spatial distribution and packing of xylem conduits. American Journal of Botany. 99: 1189-1196.
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Doi: 10.3732/ajb.1100384

Resum:

Premise of the study: The hydraulic properties of the xylem determine the ability of plants to transport water from the soil to the leaves and to cope with important stress factors such as frost and drought. Hydraulic properties have usually been studied as a function of the anatomy of xylem conduits and their pits, but recent studies have proposed that system-level properties, related to the topology of the xylem network, may also play a role. Here we study how the spatial arrangement of conduits in xylem cross sections affects the relationship between mean conduit lumen area and conduit density (packing function) across species.Methods: Point pattern analysis was used to describe the spatial distribution of xylem conduits in 97 woody species. The effect of conduit aggregation on the packing function was tested using phylogenetic generalized least squares. A hydraulic model with an explicit description of the topology of the xylem network was used to interpret the functional significance of our findings.Key results: The spatial arrangement of conduits affected the packing function across species, so that species with aggregated distributions tended to have lower conduit densities for a given conduit size and lower conduit lumen fractions. According to our modeling results, the higher conduit-to-conduit connectivity of species with aggregated distributions allows them to achieve higher hydraulic conductivity. Species with aggregated conduits, however, pay a cost in terms of increased vulnerability to embolism.Conclusions: The spatial arrangement of conduits affects the fundamental structural and functional attributes of the xylem. © 2012 Botanical Society of America.

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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

Resum:

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

Resum:

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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Detecting aphid predation by earwigs in organic citrus orchards using molecular markers

Romeu-Dalmau C., Piñol J., Agustí N. (2012) Detecting aphid predation by earwigs in organic citrus orchards using molecular markers. Bulletin of Entomological Research. 102: 566-572.
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Doi: 10.1017/S0007485312000132

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Aphids (Hemiptera: Aphidoidea) can damage citrus trees via direct damage to leaves and flowers or via the indirect transmission of viruses. Predators such as the European earwig, Forficula auricularia Linnaeus (Dermaptera: Forficulidae), may assist in keeping aphid populations under control in citrus orchards. Group-specific primers were developed to detect aphid DNA in earwigs, in order to determine earwig predation rates in aphids in Mediterranean organic citrus trees. These primers were designed in accordance with the alignment of comparable sequences of aphids and earwigs, and they amplified a 224 bp fragment of the mitochondrial cytochrome c oxidase subunit I (COI) region. Following the consumption of three to five Aphis spiraecola Patch, aphid DNA was still detectable in 50% of earwigs one day after the ingestion. When predation was evaluated in the field, aphid DNA was detected in earwigs in May, June and July but not in April and August. The most interesting result is that of May, when aphid abundance was very low but 30% of the earwigs tested positive for aphid DNA. This finding suggests that earwigs are important aphid predators in citrus orchards, as they probably alter aphid dynamics as a result of early seasonal pressure on this pest. Copyright © 2012 Cambridge University Press.

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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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