Exploring the links between forest transition and landscape changes in the Mediterranean. Does forest recovery really lead to better landscape quality?

Marull J., Otero I., Stefanescu C., Tello E., Miralles M., Coll F., Pons M., Diana G.L. (2015) Exploring the links between forest transition and landscape changes in the Mediterranean. Does forest recovery really lead to better landscape quality?. Agroforestry Systems. : 0-0.
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Doi: 10.1007/s10457-015-9808-8

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A growing number of studies argue that forest transition should be enhanced by policymakers given its potential benefits, for instance in slowing climate change through carbon sequestration. Yet the effects of forest transition in landscape heterogeneity and biodiversity remain poorly understood. In this paper we explore the relationships between the forest transition and the landscape changes occurred in a Mediterranean mountain area. Historical land-use maps were built from cadastral cartography (1854; 1956; 2012). Metrics on land-cover change, landscape structure, and landscape functioning were calculated. Multiyear data on butterfly assemblages from two transects (1994–2012) was used as indicator of land-use change effects on biodiversity. Results show a forest expansion process in former cereal fields, vineyards and pasturelands along with rural out-migration and land abandonment. Such forest transition involved large changes in landscape structure and functioning. As peasant management of integrated agrosilvopastoral systems disappeared, landscape became less diverse. Even if forest area is now larger than in mid-nineteenth century, ecological connectivity among woodland did not substantially improve. Instead, ecological connectivity across open habitats has greatly decreased as cereal fields, vineyards, meadows and pasturelands have almost disappeared. Butterfly assemblages under changing land-uses highlights the importance of agro-forest mosaics not only for these species but for biodiversity at large in the last decades. Our work emphasizes that conservation of landscapes with a long history of human use needs to take into account the role of humans in shaping ecological features and biodiversity. Hence the suitability of forest transitions should be critically examined in relation to context and policy objectives. © 2015 Springer Science+Business Media Dordrecht

Llegeix més

Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances

Carnicer J., Sardans J., Stefanescu C., Ubach A., Bartons M., Asensio D., Penuelas J. (2014) Global biodiversity, stoichiometry and ecosystem function responses to human-induced C-N-P imbalances. Journal of Plant Physiology. : 0-0.
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Doi: 10.1016/j.jplph.2014.07.022

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Global change analyses usually consider biodiversity as a global asset that needs to be preserved. Biodiversity is frequently analysed mainly as a response variable affected by diverse environmental drivers. However, recent studies highlight that gradients of biodiversity are associated with gradual changes in the distribution of key dominant functional groups characterized by distinctive traits and stoichiometry, which in turn often define the rates of ecosystem processes and nutrient cycling. Moreover, pervasive links have been reported between biodiversity, food web structure, ecosystem function and species stoichiometry. Here we review current global stoichiometric gradients and how future distributional shifts in key functional groups may in turn influence basic ecosystem functions (production, nutrient cycling, decomposition) and therefore could exert a feedback effect on stoichiometric gradients. The C-N-P stoichiometry of most primary producers (phytoplankton, algae, plants) has been linked to functional trait continua (i.e. to major axes of phenotypic variation observed in inter-specific analyses of multiple traits). In contrast, the C-N-P stoichiometry of higher-level consumers remains less precisely quantified in many taxonomic groups. We show that significant links are observed between trait continua across trophic levels. In spite of recent advances, the future reciprocal feedbacks between key functional groups, biodiversity and ecosystem functions remain largely uncertain. The reported evidence, however, highlights the key role of stoichiometric traits and suggests the need of a progressive shift towards an ecosystemic and stoichiometric perspective in global biodiversity analyses.

Llegeix més

Determinants of extinction-colonization dynamics in Mediterranean butterflies: The role of landscape, climate and local habitat features

Fernandez-Chacon A., Stefanescu C., Genovart M., Nichols J.D., Hines J.E., Paramo F., Turco M., Oro D. (2014) Determinants of extinction-colonization dynamics in Mediterranean butterflies: The role of landscape, climate and local habitat features. Journal of Animal Ecology. 83: 276-285.
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Doi: 10.1111/1365-2656.12118

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Many species are found today in the form of fragmented populations occupying patches of remnant habitat in human-altered landscapes. The persistence of these population networks requires a balance between extinction and colonization events assumed to be primarily related to patch area and isolation, but the contribution of factors such as the characteristics of patch and matrix habitats, the species' traits (habitat specialization and dispersal capabilities) and variation in climatic conditions have seldom been evaluated simultaneously. The identification of environmental variables associated with patch occupancy and turnover may be especially useful to enhance the persistence of multiple species under current global change. However, for robust inference on occupancy and related parameters, we must account for detection errors, a commonly overlooked problem that leads to biased estimates and misleading conclusions about population dynamics. Here, we provide direct empirical evidence of the effects of different environmental variables on the extinction and colonization rates of a rich butterfly community in the western Mediterranean. The analysis was based on a 17-year data set containing detection/nondetection data on 73 butterfly species for 26 sites in north-eastern Spain. Using multiseason occupancy models, which take into account species' detectability, we were able to obtain robust estimates of local extinction and colonization probabilities for each species and test the potential effects of site covariates such as the area of suitable habitat, topographic variability, landscape permeability around the site and climatic variability in aridity conditions. Results revealed a general pattern across species with local habitat composition and landscape features as stronger predictors of occupancy dynamics compared with topography and local aridity. Increasing area of suitable habitat in a site strongly decreased local extinction risks and, for a number of species, both higher amounts of suitable habitat and more permeable landscapes increased colonization rates. Nevertheless, increased topographic variability decreased the extinction risk of bad dispersers, a group of species with significantly lower colonization rates. Our models predicted higher sensitivity of the butterfly assemblages to deterministic changes in habitat features rather than to stochastic weather patterns, with some relationships being clearly dependent on the species' traits. © 2013 British Ecological Society.

Llegeix més

Latitudinal gradients in butterfly population variability are influenced by landscape heterogeneity

Oliver T.H., Stefanescu C., Paramo F., Brereton T., Roy D.B. (2014) Latitudinal gradients in butterfly population variability are influenced by landscape heterogeneity. Ecography. : 0-0.
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Doi: 10.1111/ecog.00608

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The variability of populations over time is positively associated with their risk of local extinction. Previous work has shown that populations at the high-latitude boundary of species' ranges show higher inter-annual variability, consistent with increased sensitivity and exposure to adverse climatic conditions. However, patterns of population variability at both high- and low-latitude species range boundaries have not yet been concurrently examined. Here, we assess the inter-annual population variability of 28 butterfly species between 1994 and 2009 at 351 and 18 sites in the United Kingdom and Catalonia, Spain, respectively. Local population variability is examined with respect to the position of the species' bioclimatic envelopes (i.e. whether the population falls within areas of the 'core' climatic suitability or is a climatically 'marginal' population), and in relation to local landscape heterogeneity, which may influence these range location - population dynamic relationships. We found that butterfly species consistently show latitudinal gradients in population variability, with increased variability in the more northerly UK. This pattern is even more marked for southerly distributed species with 'marginal' climatic suitability in the UK but 'core' climatic suitability in Catalonia. In addition, local landscape heterogeneity did influence these range location - population dynamic relationships. Habitat heterogeneity was associated with dampened population dynamics, especially for populations in the UK. Our results suggest that promoting habitat heterogeneity may promote the persistence of populations at high-latitude range boundaries, which may potentially aid northwards expansion under climate warming. We did not find evidence that population variability increases towards southern range boundaries. Sample sizes for this region were low, but there was tentative evidence, in line with previous ecological theory, that local landscape heterogeneity may promote persistence in these retracting low-latitude range boundary populations. © 2014 The Authors.

Llegeix més

A unified framework for diversity gradients: The adaptive trait continuum

Carnicer J., Stefanescu C., Vila R., Dincǎ V., Font X., Peñuelas J. (2013) A unified framework for diversity gradients: The adaptive trait continuum. Global Ecology and Biogeography. 22: 6-18.
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Doi: 10.1111/j.1466-8238.2012.00762.x

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Aim Adaptive trait continua are axes of covariation observed in multivariate trait data for a given taxonomic group. These continua quantify and summarize life-history variation at the inter-specific level in multi-specific assemblages. Here we examine whether trait continua can provide a useful framework to link life-history variation with demographic and evolutionary processes in species richness gradients. Taking an altitudinal species richness gradient for Mediterranean butterflies as a study case, we examined a suite of traits (larval diet breadth, adult phenology, dispersal capacity and wing length) and species-specific habitat measures (temperature and aridity breadth). We tested whether traits and species-specific habitat measures tend to co-vary, whether they are phylogenetically conserved, and whether they are able to explain species distributions and spatial genetic variation in a large number of butterfly assemblages. Location Catalonia, Spain. Methods We formulated predictions associated with species richness gradients and adaptive trait continua. We applied principal components analyses (PCAs), structural equation modelling and phylogenetic generalized least squares models. Results We found that traits and species-specific habitat measures covaried along a main PCA axis, ranging from multivoltine trophic generalists with high dispersal capacity to univoltine (i.e. one generation per year), trophic specialist species with low dispersal capacity. This trait continuum was closely associated with the observed distributions along the altitudinal gradient and predicted inter-specific differences in patterns of spatial genetic variability (FST and genetic distances), population responses to the impacts of global change and local turnover dynamics. Main conclusions The adaptive trait continuum of Mediterranean butterflies provides an integrative and mechanistic framework to: (1) analyse geographical gradients in species richness, (2) explain inter-specific differences in population abundances, spatial distributions and demographic trends, (3) explain inter-specific differences in patterns of genetic variation (FST and genetic distances), and (4) study specialist-generalist life-history transitions frequently involved in butterfly diversification processes. © 2012 Blackwell Publishing Ltd.

Llegeix més

Distinguishing between anticipatory and responsive plasticity in a seasonally polyphenic butterfly

Esperk T., Stefanescu C., Teder T., Wiklund C., Kaasik A., Tammaru T. (2013) Distinguishing between anticipatory and responsive plasticity in a seasonally polyphenic butterfly. Evolutionary Ecology. 27: 315-332.
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Doi: 10.1007/s10682-012-9598-7

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Seasonal generations of short-lived organisms often differ in their morphological, behavioural and life history traits, including body size. These differences may be either due to immediate effects of seasonally variable environment on organisms (responsive plasticity) or rely on presumably adaptive responses of organisms to cues signalizing forthcoming seasonal changes (anticipatory plasticity). When directly developing individuals of insects are larger than their overwintering conspecifics, the between-generation differences are typically ascribed to responsive plasticity in larval growth. We tested this hypothesis using the papilionid butterly Iphiclides podalirius as a model species. In laboratory experiments, we demonstrated that seasonal differences in food quality could not explain the observed size difference. Similarly, the size differences are not likely to be explained by the immediate effects of ambient temperature and photoperiod on larval growth. The qualitative pattern of natural size differences between the directly developing and diapausing butterflies could be reproduced in the laboratory as a response to photoperiod, indicating anticipatory character of the response. Directly developing and diapausing individuals followed an identical growth trajectory until the end of the last larval instar, with size differences appearing just a few days before pupation. Taken together, various lines of evidence suggest that between-generation size differences in I. podalirius are not caused by immediate effects of environmental factors on larval growth. Instead, these differences rather represent anticipatory plasticity and are thus likely to have an adaptive explanation. It remains currently unclear, whether the seasonal differences in adult size per se are adaptive, or if they constitute co-product of processes related to the diapause. Our study shows that it may be feasible to distinguish between different types of plasticity on the basis of empirical data even if fitness cannot be directly measured, and contributes to the emerging view about the predominantly adaptive nature of seasonal polyphenisms in insects. © 2012 Springer Science+Business Media B.V.

Llegeix més

Forces driving the composition of butterfly assemblages in Andorra

Komac B., Stefanescu C., Caritg R., Domenech M. (2013) Forces driving the composition of butterfly assemblages in Andorra. Journal of Insect Conservation. 17: 897-910.
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Doi: 10.1007/s10841-013-9571-y

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Despite the impact that human presence has on the area, Andorra in the eastern Pyrenees still harbours a rich butterfly fauna and is a potentially excellent area for studying the effects of global change on biodiversity. The aim of this study was to identify and understand the factors that are inducing observed patterns of butterfly richness in Andorra. We used data collected between 2006 and 2010 from six transects of the Andorran Butterfly Monitoring Scheme that lie at heights from 1,000 to 2,400 m a.s.l. These transects are divided into 44 discrete sections and during the study period 18,603 individuals belonging to 126 butterfly species were recorded. The effects of elevation and habitat composition on species richness and abundance were analyzed, as was the presence of spatial structure in the butterfly assemblages. We found a clear tendency for species richness to decrease as elevation increased and also identified a major faunal turnover. Habitat composition seems to have little effect on species richness and butterfly abundance. A spatial structure was observed in the dataset, with a positive spatial autocorrelation at section scale that reflects a clear effect of altitudinal gradient on species assemblages. Finally, a cluster analysis enabled us to define two main faunistic groups, corresponding to lower (generally in closed habitats) and higher sites (generally in subalpine meadows and grasslands). We thus conclude that the elevation gradient is the principal factor driving butterfly distribution and abundance in Andorra. © 2013 Springer Science+Business Media Dordrecht.

Llegeix més

Host-associated genomic differentiation in congeneric butterflies: Now you see it, now you do not

Mikheyev A.S., McBride C.S., Mueller U.G., Parmesan C., Smee M.R., Stefanescu C., Wee B., Singer M.C. (2013) Host-associated genomic differentiation in congeneric butterflies: Now you see it, now you do not. Molecular Ecology. 22: 4753-4766.
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Doi: 10.1111/mec.12423

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Ecotypic variation among populations may become associated with widespread genomic differentiation, but theory predicts that this should happen only under particular conditions of gene flow, selection and population size. In closely related species, we might expect the strength of host-associated genomic differentiation (HAD) to be correlated with the degree of phenotypic differentiation in host-adaptive traits. Using microsatellite and Amplified Fragment Length Polymorphism (AFLP) markers, and controlling for isolation by distance between populations, we sought HAD in two congeneric species of butterflies with different degrees of host plant specialization. Prior work on Euphydryas editha had shown strong interpopulation differentiation in host-adapted traits, resulting in incipient reproductive isolation among host-associated ecotypes. We show here that Euphydryas aurinia had much weaker host-associated phenotypic differentiation. Contrary to our expectations, we detected HAD in Euphydryas aurinia, but not in E. editha. Even within an E. aurinia population that fed on both hosts, we found weak but significant sympatric HAD that persisted in samples taken 9 years apart. The finding of significantly stronger HAD in the system with less phenotypic differentiation may seem paradoxical. Our findings can be explained by multiple factors, ranging from differences in dispersal or effective population size, to spatial variation in genomic or phenotypic traits and to structure induced by past histories of host-adapted populations. Other infrequently measured factors, such as differences in recombination rates, may also play a role. Our result adds to recent work as a further caution against assumptions of simple relationships between genomic and adaptive phenotypic differentiation. © 2013 John Wiley & Sons Ltd.

Llegeix més

Multi-generational long-distance migration of insects: Studying the painted lady butterfly in the Western Palaearctic

Stefanescu C., Páramo F., Åkesson S., Alarcón M., Ávila A., Brereton T., Carnicer J., Cassar L.F., Fox R., Heliölä J., Hill J.K., Hirneisen N., Kjellén N., Kühn E., Kuussaari M., Leskinen M., Liechti F., Musche M., Regan E.C., Reynolds D.R., Roy D.B., Ryrholm N., Schmaljohann H., Settele J., Thomas C.D., van Swaay C., Chapman J.W. (2013) Multi-generational long-distance migration of insects: Studying the painted lady butterfly in the Western Palaearctic. Ecography. 36: 474-486.
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Doi: 10.1111/j.1600-0587.2012.07738.x

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Long-range, seasonal migration is a widespread phenomenon among insects, allowing them to track and exploit abundant but ephemeral resources over vast geographical areas. However, the basic patterns of how species shift across multiple locations and seasons are unknown in most cases, even though migrant species comprise an important component of the temperate-zone biota. The painted lady butterfly Vanessa cardui is such an example; a cosmopolitan continuously-brooded species which migrates each year between Africa and Europe, sometimes in enormous numbers. The migration of 2009 was one of the most impressive recorded, and thousands of observations were collected through citizen science programmes and systematic entomological surveys, such as high altitude insect-monitoring radar and ground-based butterfly monitoring schemes. Here we use V. cardui as a model species to better understand insect migration in the Western Palaearctic, and we capitalise on the complementary data sources available for this iconic butterfly. The migratory cycle in this species involves six generations, encompassing a latitudinal shift of thousands of kilometres (up to 60 degrees of latitude). The cycle comprises an annual poleward advance of the populations in spring followed by an equatorward return movement in autumn, with returning individuals potentially flying thousands of kilometres. We show that many long-distance migrants take advantage of favourable winds, moving downwind at high elevation (from some tens of metres from the ground to altitudes over 1000 m), pointing at strong similarities in the flight strategies used by V. cardui and other migrant Lepidoptera. Our results reveal the highly successful strategy that has evolved in these insects, and provide a useful framework for a better understanding of long-distance seasonal migration in the temperate regions worldwide. © 2012 The Authors. Journal compilation © 2012 Nordic Society Oikos.

Llegeix més

Biogeography of species richness gradients: Linking adaptive traits, demography and diversification

Carnicer J., Brotons L., Stefanescu C., Peñuelas J. (2012) Biogeography of species richness gradients: Linking adaptive traits, demography and diversification. Biological Reviews. 87: 457-479.
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Doi: 10.1111/j.1469-185X.2011.00210.x

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Here we review how adaptive traits contribute to the emergence and maintenance of species richness gradients through their influence on demographic and diversification processes. We start by reviewing how demographic dynamics change along species richness gradients. Empirical studies show that geographical clines in population parameters and measures of demographic variability are frequent along latitudinal and altitudinal gradients. Demographic variability often increases at the extremes of regional species richness gradients and contributes to shape these gradients. Available studies suggest that adaptive traits significantly influence demographic dynamics, and set the limits of species distributions. Traits related to thermal tolerance, resource use, phenology and dispersal seem to play a significant role. For many traits affecting demography and/or diversification processes, complex mechanistic approaches linking genotype, phenotype and fitness are becoming progressively available. In several taxa, species can be distributed along adaptive trait continuums, i.e. a main axis accounting for the bulk of inter-specific variation in some correlated adaptive traits. It is shown that adaptive trait continuums can provide useful mechanistic frameworks to explain demographic dynamics and diversification in species richness gradients. Finally, we review the existence of sequences of adaptive traits in phylogenies, the interactions of adaptive traits and community context, the clinal variation of traits across geographical gradients, and the role of adaptive traits in determining the history of dispersal and diversification of clades. Overall, we show that the study of demographic and evolutionary mechanisms that shape species richness gradients clearly requires the explicit consideration of adaptive traits. To conclude, future research lines and trends in the field are briefly outlined. © 2011 The Authors. Biological Reviews © 2011 Cambridge Philosophical Society.

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