Aguade D., Poyatos R., Rosas T., Martinez-Vilalta J. (2015) Comparative drought responses of Quercus ilex L. and Pinus sylvestris L. In a montane forest undergoing a vegetation shift. Forests. 6: 2505-2529.LinkDoi: 10.3390/f6082505
Different functional and structural strategies to cope with water shortage exist both within and across plant communities. The current trend towards increasing drought in many regions could drive some species to their physiological limits of drought tolerance, potentially leading to mortality episodes and vegetation shifts. In this paper, we study the drought responses of Quercus ilex and Pinus sylvestris in a montane Mediterranean forest where the former species is replacing the latter in association with recent episodes of drought-induced mortality. Our aim was to compare the physiological responses to variations in soil water content (SWC) and vapor pressure deficit (VPD) of the two species when living together in a mixed stand or separately in pure stands, where the canopies of both species are completely exposed to high radiation and VPD. P. sylvestris showed typical isohydric behavior, with greater losses of stomatal conductance with declining SWC and greater reductions of stored non-structural carbohydrates during drought, consistent with carbon starvation being an important factor in the mortality of this species. On the other hand, Q. ilex trees showed a more anisohydric behavior, experiencing more negative water potentials and higher levels of xylem embolism under extreme drought, presumably putting them at higher risk of hydraulic failure. In addition, our results show relatively small changes in the physiological responses of Q. ilex in mixed vs. pure stands, suggesting that the current replacement of P. sylvestris by Q. ilex will continue. © 2015 by the authors.
Aizpurua O., Cantu-Salazar L., San Martin G., Biver G., Brotons L., Titeux N. (2015) Reconciling expert judgement and habitat suitability models as tools for guiding sampling of threatened species. Journal of Applied Ecology. : 0-0.LinkDoi: 10.1111/1365-2664.12515
Up-to-date knowledge on species distribution is needed for efficient biodiversity conservation and management decision-making. Implementing efficient sampling strategies to identify previously unknown locations of species of conservation-concern is therefore a key challenge. Both structured expert judgement and habitat suitability models may help target sampling towards areas where chances to find the species are highest. However, practitioners often object to the use of models and believe they do not result in better decisions than the subjective opinion of experts, thus potentially constraining an optimal use of available methods and information. To illustrate the potential of habitat suitability models for guiding sampling strategies, we evaluated and compared the ability of experts and models to identify important areas for the conservation of a bird species (Lanius collurio) in Luxembourg. We conducted extensive fieldwork to find as many unknown bird territories as possible according to three independent sampling strategies: (i) a sampling strategy based on structured expert judgement, (ii) a sampling strategy based on the predictions of a habitat suitability model and (iii) a general-purpose stratified random sampling strategy used as a baseline reference. Both the expert-based and the model-based sampling strategies substantially outperformed the general-purpose sampling strategy in identifying new species records. In addition, the model-based sampling strategy performed significantly better than the expert-based sampling strategy. Synthesis and applications. This study explicitly shows that habitat suitability models can efficiently guide field data collection towards suitable areas for species of conservation-concern. Results may facilitate the involvement of practitioners in the development of habitat suitability models with the objective of maximizing the robustness of modelling applications in conservation practice and management decision-making. © 2015 British Ecological Society.
Ameztegui A., Coll L. (2015) Herbivory and seedling establishment in Pyrenean forests: Influence of micro- and meso-habitat factors on browsing pressure. Forest Ecology and Management. 342: 103-111.LinkDoi: 10.1016/j.foreco.2015.01.021
Browsing damage is among the most determinant factors that limit the establishment of tree seedlings in forests. In some areas, this process leads to massive mortalities that can reduce or even completely prevent the regeneration of some tree species. Mediterranean mountain forests have undergone during the last decades important changes in land-uses that have significantly altered the type and abundance of herbivore populations. In this study we assessed the impact of current grazing conditions in forest regeneration using a set of experimental plantations established in the Eastern Pyrenees in areas visited by domestic livestock (cattle and horses) and wild ungulates (mainly roe deer and chamois). We analyzed during 4. years the role of seedling species and size, mesohabitat (elevation and type of forest cover) and microhabitat (herbaceous cover, distance to shrub, and light availability) on the browsing-induced mortality of more than 500 seedlings of Pinus sylvestris, Pinus uncinata, Betula pendula and Abies alba, the most common tree species in the study area. Browsing-induced mortality for the three conifer species was much lower (40%) and depended on both microhabitat - mainly on the distance to protective elements such as shrubs; and mesohabitat, with an interaction between the elevational belt (site) and the type of forest cover (gaps vs. understory). In the subalpine belt, browsing on A. alba and P. uncinata was higher during summer at plots located in the forest understory whereas, during winter, it was higher at plots located in gaps. The study shows that both mesohabitat and microhabitat can exert an effect on the patterns of plant damage by herbivores, providing useful information to adapt forest management in areas particularly exposed to them. © 2015 Elsevier B.V.
Ameztegui A., Coll L., Messier C. (2015) Modelling the effect of climate-induced changes in recruitment and juvenile growth on mixed-forest dynamics: The case of montane-subalpine Pyrenean ecotones. Ecological Modelling. 313: 84-93.LinkDoi: 10.1016/j.ecolmodel.2015.06.029
Most predictive models forecast significant upward displacement of forest species due to increases in temperatures, but not all the species respond in the same way to changes in climate. In temperate or mountain systems, biotic competitive interactions drive species distributions, and responses to climate change will ultimately depend upon productive and demographic processes such as growth, recruitment and mortality. We parameterized and used an individual-based, spatially explicit model of forest dynamics (SORTIE-ND) to investigate the role of species-specific differences in juvenile performance induced by climate change (juvenile growth and recruitment ability) in the dynamics of mixed forests located in the montane-subalpine ecotone of the Pyrenees. We assessed this role for two types of forests composed of three species with differing light requirements and sensitivity to climate change: (1) a mixed forest with two shade-intolerant pines (Pinus uncinata and Pinus sylvestris) and (2) a mixed forest composed by a shade-intolerant pine and a shade-tolerant fir (Abies alba). Our results show that for species with similar light requirements (i.e., both pines), small differences in sapling growth response to climate change can lead to significant differences in future species composition (an increase in P. sylvestris growth of 10% leads to an increase in its abundance from 42% to 50.3%). Conversely, in pine-fir forests, shade-tolerance results more decisive than climate-induced changes in growth in driving the future forest composition. © 2015 Elsevier B.V.
Arellano L., Fernandez P., Fonts R., Rose N.L., Nickus U., Thies H., Stuchlik E., Camarero L., Catalan J., Grimalt J.O. (2015) Increasing and decreasing trends of the atmospheric deposition of organochlorine compounds in European remote areas during the last decade. Atmospheric Chemistry and Physics. 15: 6069-6085.LinkDoi: 10.5194/acp-15-6069-2015
Bulk atmospheric deposition samples were collected between 2004 and 2007 at four high-altitude European sites encompassing east (Skalnaté Pleso), west (Lochnagar), central (Gossenköllesee) and south (Redòn) regions, and analysed for legacy and current-use organochlorine compounds (OCs). Polychlorobiphenyls (PCBs) generally showed the highest deposition fluxes in the four sites, between 112 and 488 ng m-2 mo-1, and hexachlorobenzene (HCB) the lowest, a few ng m-2 mo-1. Among pesticides, endosulfans were found at higher deposition fluxes (11-177 ng m-2 mo-1) than hexachlorocyclohexanes (HCHs) (17-66 ng m-2 mo-1) in all sites except Lochnagar that was characterized by very low fluxes of this insecticide. Comparison of the present measurements with previous determinations in Redòn (1997-1998 and 2001-2002) and Gossenköllesee (1996-1998) provided for the first time an assessment of the long-term temporal trends in OC atmospheric deposition in the European background areas. PCBs showed increasing deposition trends while HCB deposition fluxes remained nearly constant. Re-emission of PCBs from soils or as a consequence of glacier melting and subsequent precipitation and trapping of the volatilized compounds may explain the observed PCB trends. This process does not occur for HCB due to its high volatility which keeps most of this pollutant in the gas phase. A significant decline of pesticide deposition was observed during this studied decade (1996-2006) which is consistent with the restriction in the use of these compounds in most of the European countries. In any case, degassing of HCHs or endosulfans from ice melting to the atmosphere should be limited because of the low Henry's law constants of these compounds that will retain them dissolved in the melted water. Investigation of the relationship between air mass trajectories arriving at each site and OC deposition fluxes showed no correlation for PCBs, which is consistent with diffuse pollution from unspecific sources as the predominant origin of these compounds in these remote sites. In contrast, significant correlations between current-use pesticides and air masses flowing from the south were observed in Gossenköllesee, Lochnagar and Redòn. In the case of Redòn, the higher proportion of air masses from the south occurred in parallel to higher temperatures, which did not allow us to discriminate between these two determinant factors of pesticide deposition. However, in Gossenköllesee and Lochnagar, the relationship between pesticide concentration and southern air masses was univocal, reflecting the impact of regions with intensive agricultural activities. © Author(s) 2015.
Armenteras D., Rodríguez N., Retana J. (2015) National and regional relationships of carbon storage and tropical biodiversity. Biological Conservation. 192: 378-386.LinkDoi: 10.1016/j.biocon.2015.10.014
Tropical forests host the highest levels of biodiversity and maintain some of the largest carbon stocks of all terrestrial ecosystems. Policies resulting from the United Nations Framework Convention on Climate Change (UNFCC) for forest-based climate change mitigation (e.g., Reducing Emissions from Deforestation and forest Degradation (REDD. +)) have been considered win-win solutions for both C storage and biodiversity conservation. Win-win solutions are indeed apparent when there is geographical overlap of high carbon density forests with high biodiversity, as suggested by many global studies. However, strong congruence between high carbon storage and biodiversity at the national and subnational levels is less obvious. To improve national policies and expectations of REDD. + outcomes, it is necessary to account for the potential risks of relocating deforestation activities from high-carbon areas to low-carbon areas, as such relocation may negatively affect high-biodiversity habitats. Using a combined dataset of global and national biodiversity and C storage, we examined whether the optimization of carbon and biodiversity is, as suggested, a win-win situation. We identified hotspots of C storage and of biodiversity within Colombia and the demographic and land use factors that affect the spatial distribution of the current patterns of biodiversity and C. We also identified and mapped two additional forest carbon and biodiversity relationships (areas with high carbon and low biodiversity and areas with low carbon and high biodiversity) that represented relevant conservation trade-offs at national and subnational levels. Our results suggest that, although C storage and biodiversity hotspots still overlap nationally and subnationally, the relationship between these two types of hotspots is weaker than that at the global level. Additionally, areas where high carbon and high biodiversity do not overlap are more extensive than potential win-win areas. Simultaneous carbon and biodiversity conservation is not as straightforward as it appears to be at the global level. Countries must swiftly identify areas where unintentional negative biodiversity consequences may result from national REDD. + strategies, and future research should identify the factors that affect C storage and biodiversity both at the national and subnational levels. © 2015 Elsevier Ltd.
Arnan X., Cerdá X., Retana J. (2015) Partitioning the impact of environment and spatial structure on alpha and beta components of taxonomic, functional, and phylogenetic diversity in European ants. PeerJ. 2015: 0-0.LinkDoi: 10.7717/peerj.1241
We analyze the relative contribution of environmental and spatial variables to the alpha and beta components of taxonomic (TD), phylogenetic (PD), and functional (FD) diversity in ant communities found along different climate and anthropogenic disturbance gradients across western and central Europe, in order to assess the mechanisms structuring ant biodiversity. To this aim we calculated alpha and beta TD, PD, and FD for 349 ant communities, which included a total of 155 ant species; we examined 10 functional traits and phylogenetic relatedness. Variation partitioning was used to examine how much variation in ant diversity was explained by environmental and spatial variables. Autocorrelation in diversity measures and each trait's phylogenetic signal were also analyzed.We found strong autocorrelation in diversity measures. Both environmental and spatial variables significantly contributed to variation in TD, PD, and FD at both alpha and beta scales; spatial structure had the larger influence. The different facets of diversity showed similar patterns along environmental gradients. Environment explained a much larger percentage of variation in FD than in TD or PD. All traits demonstrated strong phylogenetic signals. Our results indicate that environmental filtering and dispersal limitations structure all types of diversity in ant communities. Strong dispersal limitations appear to have led to clustering of TD, PD, and FD in western and central Europe, probably because different historical and evolutionary processes generated different pools of species. Remarkably, these three facets of diversity showed parallel patterns along environmental gradients. Trait-mediated species sorting and niche conservatism appear to structure ant diversity, as evidenced by the fact that more variation was explained for FD and that all traits had strong phylogenetic signals. Since environmental variables explained much more variation in FD than in PD, functional diversity should be a better indicator of community assembly processes than phylogenetic diversity. © 2015 Arnan et al.
Bagaria G., Helm A., Rodà F., Pino J. (2015) Assessing coexisting plant extinction debt and colonization credit in a grassland–forest change gradient. Oecologia. 179: 823-834.LinkDoi: 10.1007/s00442-015-3377-4
Changes in species richness along the ecological succession gradient may be strongly determined by coexisting extinction debts of species from the original habitats and colonization credits of those from the replacing habitats. The magnitude of these processes and their causes remain largely unknown. We explored the extinction debt and colonization credit for grassland and forest specialist plants, respectively, and the local and landscape factors associated to the richness of these species groups in a 50-year process of forest encroachment into semi-natural Mediterranean grasslands. A set of sampling plots of persistent grasslands and forests and their transitional habitat (wooded grasslands) was selected within fixed-area sites distributed across the landscape. Our results confirm the extinction debt and suggest colonization credit (according to observed trends and model predictions) in wooded grasslands when compared to persistent forests, despite wooded grasslands and persistent forests having similar tree cover. Grassland connectivity and solar radiation had opposing effects on the richness of both grassland and forest specialists, and it is possible that the availability of seed sources from old forests may have accelerate the payment of colonization credit in the wooded grasslands. These results suggest that extinction debt and colonization credit have driven species turnover during the 50 years of forest encroachment, but at different rates, and that local and landscape factors have opposing effects on these two phenomena. They also highlight the importance of documenting biodiversity time lags following habitat change when they are still in progress in order to timely and adequately manage habitats of high conservation value such as the grasslands studied here. © 2015, Springer-Verlag Berlin Heidelberg.
Bartrons M., Einarsson A., Nobre R.L.G., Herren C.M., Webert K.C., Brucet S., Olafsdottir S.R., Ives A.R. (2015) Spatial patterns reveal strong abiotic and biotic drivers of zooplankton community composition in Lake Mývatn, Iceland. Ecosphere. 6: 0-0.LinkDoi: 10.1890/ES14-00392.1
Spatial patterns in the abundance of species are determined by local abiotic and biotic conditions, and by the movement of individuals among localities. For species distributed among discrete habitat "islands", such as zooplankton distributed among lakes, local conditions within lakes often dominate low movement rates among lakes to determine the composition of communities. Here, we ask whether the same abiotic and biotic environmental conditions can generate spatial patterns in the distribution of zooplankton within a lake where there are high horizontal movement rates. We conducted three spatial surveys of zooplankton communities in Lake Mývatn, Iceland, a moderately sized (37 km2) shallow lake with a high outflow rate. The pelagic zooplankton community showed strong spatial structure (spatial autocorrelation), with species composition varying with spatial variation in chlorophyll-a, the abundance of Anabaena (cyanobacteria), lake depth, light extinction coefficient, and temperature. These factors are known from other studies to be strong drivers of among-lake variation in freshwater zooplankton communities. However, in contrast with among-lake studies, fish (stickleback) abundance had no measureable effect on the abundance or species composition of the zooplankton community, although high local stickleback abundance was associated with low zooplankton:phytoplankton biomass ratios. Finally, a parallel study of the underlying benthic crustacean community showed much finer spatial variation (spatial autocorrelation to a range ≤0.6 km vs. 9 km for pelagic zooplankton), suggesting that the stationary character of the benthos allows finer grained spatial patterns. Given the high flow rate of water in Mývatn (>200 m/d), the generation of spatial patterns suggests very strong effects of variation in abiotic and biotic environmental conditions on the population dynamics of zooplankton in the lake. © 2015 Bartrons et al.
Bartrons M., Gratton C., Spiesman B.J., Zanden M.J.V. (2015) Taking the trophic bypass: Aquatic-terrestrial linkage reduces methylmercury in a terrestrial food web. Ecological Applications. 25: 151-159.LinkDoi: 10.1890/14-0038.1
Ecosystems can be linked by the movement of matter and nutrients across habitat boundaries via aquatic insect emergence. Aquatic organisms tend to have higher concentrations of certain toxic contaminants such as methylmercury (MeHg) compared to their terrestrial counterparts. If aquatic organisms come to land, terrestrial organisms that consume them are expected to have elevated MeHg concentrations. But emergent aquatic insects could have other impacts as well, such as altering consumer trophic position or increasing ecosystem productivity as a result of nutrient inputs from insect carcasses. We measure MeHg in terrestrial arthropods at two lakes in northeastern Iceland and use carbon and nitrogen stable isotopes to quantify aquatic reliance and trophic position. Across all terrestrial focal arthropod taxa (Lycosidae, Linyphiidae, Acari, Opiliones), aquatic reliance had significant direct and indirect (via changes in trophic position) effects on terrestrial consumer MeHg. However, contrary to our expectations, terrestrial consumers that consumed aquatic prey had lower MeHg concentrations than consumers that ate mostly terrestrial prey. We hypothesize that this is due to the lower trophic position of consumers feeding directly on midges relative to those that fed mostly on terrestrial prey and that had, on average, higher trophic positions. Thus, direct consumption of aquatic inputs results in a trophic bypass that creates a shorter terrestrial food web and reduced biomagnification of MeHg across the food web. Our finding that MeHg was lower at terrestrial sites with aquatic inputs runs counter to the conventional wisdom that aquatic systems are a source of MeHg contamination to surrounding terrestrial ecosystems. ï¿½ 2015 by the Ecological Society of America
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