The spatial scaling of species interaction networks

Galiana N., Lurgi M., Claramunt-López B., Fortin M.-J., Leroux S., Cazelles K., Gravel D., Montoya J.M. (2018) The spatial scaling of species interaction networks. Nature Ecology and Evolution. 2: 782-790.
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Doi: 10.1038/s41559-018-0517-3

Resum:

Species-area relationships (SARs) are pivotal to understand the distribution of biodiversity across spatial scales. We know little, however, about how the network of biotic interactions in which biodiversity is embedded changes with spatial extent. Here we develop a new theoretical framework that enables us to explore how different assembly mechanisms and theoretical models affect multiple properties of ecological networks across space. We present a number of testable predictions on network-area relationships (NARs) for multi-trophic communities. Network structure changes as area increases because of the existence of different SARs across trophic levels, the preferential selection of generalist species at small spatial extents and the effect of dispersal limitation promoting beta-diversity. Developing an understanding of NARs will complement the growing body of knowledge on SARs with potential applications in conservation ecology. Specifically, combined with further empirical evidence, NARs can generate predictions of potential effects on ecological communities of habitat loss and fragmentation in a changing world. © 2018 The Author(s).

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Taphonomic signature of golden eagles (Aquila chrysaetos) on bone prey remains

Lloveras L., Cosso A., Solé J., Claramunt-López B., Nadal J. (2017) Taphonomic signature of golden eagles (Aquila chrysaetos) on bone prey remains. Historical Biology. : 1-20.
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Doi: 10.1080/08912963.2017.1319830

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The golden eagle (Aquila chrysaetos) is one of the most important birds of prey in the Northern Hemisphere. This raptor is used to building large nests in high cliffs to which they return for several breeding years accumulating important amounts of their prey skeletal remains. This makes the golden eagle one of the major predators able to accumulate faunal remains in archaeological sites. Despite this fact, the taphonomic signature of golden eagles has not been properly characterized. Here we present the analysis of ingested and non-ingested faunal remains predated and accumulated by this raptor in two different nesting areas from the Iberian Peninsula. Results show how the faunal taxonomic record may vary depending on the ecological zone. Leporids and terrestrial carnivores are the best represented. The observed anatomical representation, breakage and bone surface modification patterns are discussed for different taxa. The taphonomic pattern varies depending on the type of prey and the origin of skeletal materials (non-ingested vs. pellets). Finally, after comparing our results with marks left by other predators, several characteristic features are noted to recognise golden eagles as agents of animal bones accumulations in the fossil record. © 2017 Informa UK Limited, trading as Taylor & Francis Group

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Multiple geographic origins and high genetic differentiation of the Alpine marmots reintroduced in the Pyrenees

Bichet C., Sauzet S., Averty L., Dupont P., Ferrandiz-Rovira M., Ferrari C., Figueroa I., Tafani M., Rézouki C., López B.C., Cohas A. (2016) Multiple geographic origins and high genetic differentiation of the Alpine marmots reintroduced in the Pyrenees. Conservation Genetics. : 1-13.
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Doi: 10.1007/s10592-016-0851-4

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Reintroductions inherently involve a small number of founders leading reintroduced populations to be prone to genetic drift and, consequently, to inbreeding depression. Assessing the origins as the genetic diversity and structure of reintroduced populations compared to native populations are thus crucial to foresee their future. Here, we aim to clarify the origins of the Alpine marmots reintroduced in the Pyrenees and to evaluate the genetic consequences of this reintroduction after almost 30 years without monitoring. We search for the origins and compare the genetic structure and the genetic variability of three reintroduced Pyrenean and eight native Alpine populations using pairwise genetic distances, Bayesian clustering method and multivariate analyses. Our results reveal that the Alpine marmots reintroduced in the Pyrenees originated both from the Northern and the Southern Alps, and that, despite these multiple origins, none of the current Pyrenean marmots are admixed. The reintroduction led to a strong genetic differentiation and to a decrease in genetic diversity. This pattern likely results from the small number of founders and the low dispersal capacities of Alpine marmots and thus, highlight the necessity to consider both genetic characteristics and natural history when reintroducing a species. © 2016 Springer Science+Business Media Dordrecht

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Do pre- and post-copulatory sexually selected traits covary in large herbivores?

Ferrandiz-Rovira M., Lemaitre J.-F., Lardy S., Lopez B.C., Cohas A. (2014) Do pre- and post-copulatory sexually selected traits covary in large herbivores?. BMC Evolutionary Biology. 14: 0-0.
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Doi: 10.1186/1471-2148-14-79

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Background: In most species, males compete to gain both matings (via pre-copulatory competition) and fertilizations (via post-copulatory competition) to maximize their reproductive success. However, the quantity of resources devoted to sexual traits is finite, and so males are predicted to balance their investment between pre- and post-copulatory expenditure depending on the expected pay-offs that should vary according to mating tactics. In Artiodactyla species, males can invest in weapons such as horns or antlers to increase their mating gains or in testes mass/sperm dimensions to increase their fertilization efficiency. Moreover, it has been suggested that in these species, males with territory defence mating tactic might preferentially increase their investment in post-copulatory traits to increase their fertilization efficiency whereas males with female defence mating tactic might increase their investment in pre-copulatory sexually selected traits to prevent other males from copulating with females. In this study, we thus test the prediction that male's weapon length (pre-copulatory trait) covaries negatively with relative testes size and/or sperm dimensions (post-copulatory traits) across Artiodactyla using a phylogenetically controlled framework. Results: Surprisingly no association between weapon length and testes mass is found but a negative association between weapon length and sperm length is evidenced. In addition, neither pre- nor post-copulatory traits were found to be affected by male mating tactics. Conclusions: We propose several hypotheses that could explain why male ungulates may not balance their reproductive investment between pre- and post-copulatory traits. © 2014Ferrandiz-Rovira et al.; licensee BioMed Central Ltd.

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Invasions cause biodiversity loss and community simplification in vertebrate food webs

Galiana N., Lurgi M., Montoya J.M., Lopez B.C. (2014) Invasions cause biodiversity loss and community simplification in vertebrate food webs. Oikos. 123: 721-728.
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Doi: 10.1111/j.1600-0706.2013.00859.x

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Global change is increasing the occurrence of perturbation events on natural communities, with biological invasions posing a major threat to ecosystem integrity and functioning worldwide. Most studies addressing biological invasions have focused on individual species or taxonomic groups to understand both, the factors determining invasion success and their effects on native species. A more holistic approach that considers multispecies communities and species' interactions can contribute to a better understanding of invasion effects on complex communities. Here we address biological invasions on species-rich food webs. We performed in silico experiments on empirical vertebrate food webs by introducing virtual species characterised by different ecological roles and belonging to different trophic groups. We varied a number of invasive species traits, including their diet breadth, the number of predators attacking them, and the bioenergetic thresholds below which invader and native species become extinct. We found that simpler food webs were more vulnerable to invasions, and that relatively less connected mammals were the most successful invaders. Invasions altered food web structure by decreasing species richness and the number of links per species, with most extinctions affecting poorly connected birds. Our food web approach allows identifying the combinations of trophic factors that facilitate or prevent biological invasions, and it provides testable predictions on the effects of invasions on the structure and dynamics of multitrophic communities. © 2014 The Authors.

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Drought-induced mortality selectively affects Scots pine trees that show limited intrinsic water-use efficiency responsiveness to raising atmospheric CO2

Heres A.-M., Voltas J., Lopez B.C., Martinez-Vilalta J. (2014) Drought-induced mortality selectively affects Scots pine trees that show limited intrinsic water-use efficiency responsiveness to raising atmospheric CO2. Functional Plant Biology. 41: 244-256.
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Doi: 10.1071/FP13067

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Widespread drought-induced tree mortality has been documented around the world, and could increase in frequency and intensity under warmer and drier conditions. Ecophysiological differences between dying and surviving trees might underlie predispositions to mortality, but are poorly documented. Here we report a study of Scots pines (Pinus sylvestris L.) from two sites located in north-eastern Iberian Peninsula where drought-associated mortality episodes were registered during the last few decades. Time trends of discrimination against 13C (Δ13C) and intrinsic water-use efficiency (WUEi) in tree rings at an annual resolution and for a 34 year period were used to compare co-occurring now-dead and surviving pines. Results indicate that both surviving and now-dead pines significantly increased their WUEi over time, although this increase was significantly lower for now-dead individuals. These differential WUEi trends corresponded to different scenarios describing how plant gas exchange responds to increasing atmospheric CO2 (Ca): the estimated intercellular CO2 concentration was nearly constant in surviving pines but tended to increase proportionally to Ca in now-dead trees. Concurrently, the WUEi increase was not paralleled by a growth enhancement, regardless of tree state, suggesting that in water-limited areas like the Mediterranean, it cannot overcome the impact of an increasingly warmer and drier climate on tree growth. © 2014 CSIRO.

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Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality

Hereş A.-M., Camarero J.J., López B.C., Martínez-Vilalta J. (2014) Declining hydraulic performances and low carbon investments in tree rings predate Scots pine drought-induced mortality. Trees - Structure and Function. 28: 1737-1750.
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Doi: 10.1007/s00468-014-1081-3

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Key message: The retrospective analysis of wood anatomical features evidences how a long-term deterioration of hydraulic performance and carbon use portend drought-induced mortality in Scots pine.Abstract: Widespread episodes of drought-induced tree mortality are predicted to become more frequent as climate becomes warmer and drier. Nevertheless, growth trends and their links to changes in wood anatomy before tree dies are still poorly understood. Wood anatomical features provide valuable information that can be extracted to infer the mechanisms leading to tree death. In this study, we characterize drought-induced mortality affecting two Scots pine (Pinus sylvestris) sites (Prades and Arcalís) located in the North Eastern Iberian Peninsula. Co-occurring now-dead and living Scots pine trees were sampled and their wood anatomical features were measured and compared. We aimed to detect differences in anatomical features between living and dead trees, and to infer past physiological performances that might have determined their subsequent death or survival. Now-dead trees showed lower tracheid and resin duct production, and smaller radial lumen diameters than co-occurring living trees. At the more xeric Prades site, these anatomical differences were larger and chronic, i.e. were observed over the three studied decades, whilst they were less pronounced at the other, more mesic Arcalís site, where tree mortality episodes were more recent. This indicates that dead trees’ hydraulic conductivity was severely affected and that carbon investment in xylem formation and resin duct production was constrained prior to tree death. Our findings show that both hydraulic deterioration and low carbon allocation to xylem formation were associated to drought-induced mortality in Scots pine. Nevertheless, the temporal dynamics of these processes differed between populations as a function of site climatic conditions. © 2014, Springer-Verlag Berlin Heidelberg.

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Fine-root turnover rates of European forests revisited: An analysis of data from sequential coring and ingrowth cores

Brunner I., Bakker M.R., Björk R.G., Hirano Y., Lukac M., Aranda X., Børja I., Eldhuset T.D., Helmisaari H.S., Jourdan C., Konôpka B., López B.C., Miguel Pérez C., Persson H., Ostonen I. (2013) Fine-root turnover rates of European forests revisited: An analysis of data from sequential coring and ingrowth cores. Plant and Soil. 362: 357-372.
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Doi: 10.1007/s11104-012-1313-5

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Background and Aims: Forest trees directly contribute to carbon cycling in forest soils through the turnover of their fine roots. In this study we aimed to calculate root turnover rates of common European forest tree species and to compare them with most frequently published values. Methods: We compiled available European data and applied various turnover rate calculation methods to the resulting database. We used Decision Matrix and Maximum-Minimum formula as suggested in the literature. Results: Mean turnover rates obtained by the combination of sequential coring and Decision Matrix were 0. 86 yr-1 for Fagus sylvatica and 0. 88 yr-1 for Picea abies when maximum biomass data were used for the calculation, and 1. 11 yr-1 for both species when mean biomass data were used. Using mean biomass rather than maximum resulted in about 30 % higher values of root turnover. Using the Decision Matrix to calculate turnover rate doubled the rates when compared to the Maximum-Minimum formula. The Decision Matrix, however, makes use of more input information than the Maximum-Minimum formula. Conclusions: We propose that calculations using the Decision Matrix with mean biomass give the most reliable estimates of root turnover rates in European forests and should preferentially be used in models and C reporting. © 2012 The Author(s).

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Influence of tree size, reduced competition, and climate on the growth response of Pinus nigra Arn. salzmannii after fire

Valor T., Pique M., Lopez B.C., Gonzalez-Olabarria J.R. (2013) Influence of tree size, reduced competition, and climate on the growth response of Pinus nigra Arn. salzmannii after fire. Annals of Forest Science. 70: 503-513.
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Doi: 10.1007/s13595-013-0284-x

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Context: After wildfire, surviving trees are of major ecological importance as they can help in the post-fire regeneration process. Although these trees may be damaged, they may also benefit from reduced fuel hazard and competition. However, little is known about the long-term growth response of surviving trees. Aims: This study aims to explain short- to long-term variations in the postfire growth of surviving black pines in an area burnt in 1994, focusing on levels of fire severity and tree sizes. Methods: Relative basal area increments were used to detect time-course variations in postfire radial tree growth depending on fire severity. Linear mixed-effects models were used to describe the factors affecting postfire ring growth. Results: In the short term, fire caused stronger reduction in growth in small trees with increasing bole char height. However, as time since fire increased, a positive effect of fire on growth due to reduced competition counteracted the short-term fire impacts. Indeed, small surviving trees demonstrated a surge in growth 15 years after the fire. Conclusion: It was concluded that reduced competition might offset the short-term negative effects of fire in surviving black pines. © 2013 INRA and Springer-Verlag France.

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The age of monumental olive trees (Olea europaea) in northeastern Spain

Arnan X., López B.C., Martínez-Vilalta J., Estorach M., Poyatos R. (2012) The age of monumental olive trees (Olea europaea) in northeastern Spain. Dendrochronologia. 30: 11-14.
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Doi: 10.1016/j.dendro.2011.02.002

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Trees can reach ages that in some cases amount to thousands of years. In the Mediterranean region, olive trees (Olea europaea) have traditionally been considered a particularly long-lived species. The main objective of this study was to assess the age of large olive trees considered to be millenarian and classified as monumental trees in northeastern Spain. We extracted cores of 14 individuals and obtained 8 sections of trees which had already been cut in the area where the largest olive trees in the northeastern Iberian Peninsula are found. The age of the sampled olive trees was assessed by counting the number of annual growth rings. Tree rings did not cross-date well, neither within nor between individuals, but boundaries between likely annual rings were clearly distinct. We found a linear relationship between DBH and tree age (in years) (Age=2.11×diameter(cm)+88.93, R2=0.80), which was used to estimate the age of unsampled olive trees. The maximum estimated age (627±110 years) is among the greatest ages reported for olive trees around the world (700 years) and among the oldest trees in Mediterranean ecosystems. © 2011 Istituto Italiano di Dendrocronologia.

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