La dinàmica temporal de les xarxes ecològiques

Els estudis de xarxes tenen una llarga tradició en ecologia i amb els anys s'ha anat veient que hi ha una sèrie de propietats comunes que s'observen reiteradament en tots els sistemes ecològics. Per exemple les xarxes ecològiques són sempre asimètriques, és a dir, unes poques espècies concentren un gran nombre d'interaccions i ocupen un lloc central en el fluxe d'energia mentre que la resta es situa en posicions més perifèriques i tenen un nombre més reduït d'interaccions. Un estudi presentat per un equip de la UAB demostra que l'estructura de les xarxes depèn alhora de diversos processos, ecològics i evolutius, que varien amb diferents ritmes temporals, incloent alhora variacions estacionals en el comportament de les espècies i canvis morfològics adaptatius que requereixen moltes generacions.Los estudios de redes tienen una larga tradición en ecología y con los años se ha ido viendo que hay una serie de propiedades comunes que se observan en todos los sistemas ecológicos. Por ejemplo, las redes ecológicas son siempre asimétricas; es decir, unas pocas especies concentran un gran número de interacciones y ocupan un lugar central en el flujo de energía mientras que el resto se sitúa en posiciones más periféricas y tienen un número más reducido de interacciones. Un estudio presentado por un equipo de la UAB demuestra que la estructura de las redes depende a la vez de diversos procesos, ecológicos y evolutivos, que varían con diferentes ritmos temporales, incluyendo variaciones estacionales en el comportamiento de las especies y cambios morfológicos adaptativos que requieren muchas generaciones

La necessitat de descarbonitzar la societat

Aquest article estudia la dependència dels recursos fòssils en la nostra societat com a motor del seu creixement, i considera la necessitat de desempallegar-se d'aquest vell model de creixement tecnològic i social. Ja sigui per interessos ecològics, econòmics o laborals, les possibilitats que ofereix un canvi de règim energètic són desitjables i beneficioses, sempre i quan estiguem disposats a adaptar sectors com el del transport o l'energètic.Este artículo estudia la dependencia de los recursos fósiles en nuestra sociedad como motor de su crecimiento, y considera la necesidad de deshacerse de este viejo modelo de crecimiento tecnológico y social. Ya sea por intereses ecológicos, económicos o laborales, las posibilidades que ofrece un cambio de régimen energético son deseables y beneficiosas, siempre y cuando estemos dispuestos a adaptar sectores como el del transporte o el energético

The temporal dynamics of resource use by frugivorous birds: a network approach

Ecological network patterns are influenced by diverse processes that operate at different temporal rates. Here we analyzed whether the coupled effect of local abundance variation, seasonally phenotypic plastic responses, and species evolutionary adaptations might act in concert to shape network patterns. We studied the temporal variation in three interaction properties of bird species (number of interactions per species, interaction strength, and interaction asymmetry) in a temporal sequence of 28 plant frugivore interaction networks spanning two years in a Mediterranean shrubland community. Three main hypotheses dealing with the temporal variation of network properties were tested, examining the effects of abundance, switching behavior between alternative food resources, and morphological traits in determining consumer interaction patterns. Our results demonstrate that temporal variation in consumer interaction patterns is explained by short-term variation in resource and bird abundances and seasonal dietary switches between alternative resources (fleshy fruits and insects). Moreover, differences in beak morphology are associated with differences in switching behavior between resources, suggesting an important role of foraging adaptations in determining network patterns. We argue that beak shape adaptations might determine generalist and specialist feeding behaviors and thus the positions of consumer species within the network. Finally, we provide a preliminary framework to interpret phylogenetic signal in plant animal networks. Indeed, we show that the strength of the phylogenetic signal in networks depends on the relative importance of abundance, behavioral, and morphological variables. We show that these variables strongly differ in their phylogenetic signal. Consequently, we suggest that moderate and significant phylogenetic effects should be commonly observed in networks of species interactions. Read More: http://www.esajournals.org/doi/abs/10.1890/07-1939.

The consecutive Disparity index, D: a measure of temporal variability in ecological studies

Temporal variability in ecological processes has attracted the attention of many disciplines inecology, which has resulted in the development of several quantitative indices. The coefficient of variation(CV=standard deviation9mean 1) is still one of the most commonly used indices to assess temporalvariability, despite being known to present several problems on its assessment (e.g., mean dependence orhigh sensitivity to rare events). The proportional variability (PV) index was developed to solve some of theCV's drawbacks, but, so far, no variability index takes into account the chronological order of the values intime series. In this paper, we introduce the consecutive disparity index (D), a temporal variability indexthat takes into account the chronological order of the values, assessing the average rate of change betweenconsecutive values. We used computer simulations and empirical data for fruit production in trees, birdcounts, and rodent captures to compare the behavior ofD, PV, and CV under different scenarios.Dwassensitive to changes in temporal autocorrelation in the negative autocorrelation range, and CV and PVwere sensitive in the positive autocorrelation range despite not considering the chronological order of thevalues. The CV, however, was highly dependent on the mean of the time series, whileDand PV were not.Our results demonstrate that, like PV,Dsolves many of the problems of the CV index while taking intoaccount the chronological order of values in time series. The mathematical and statistical features ofDmake it a suitable index for analyzing temporal variability in a wide range of ecological studies

Contrasting trait syndromes in angiosperms and conifers are associated with different responses of tree growth to temperature on a large scale

Recent large-scale studies of tree growth in the Iberian Peninsula reported contrasting positive and negative effects of temperature in Mediterranean angiosperms and conifers. Here we review the different hypotheses that may explain these trends and propose that the observed contrasting responses of tree growth to temperature in this region could be associated with a continuum of trait differences between angiosperms and conifers. Angiosperm and conifer trees differ in the effects of phenology in their productivity, in their growth allometry, and in their sensitivity to competition. Moreover, angiosperms and conifers significantly differ in hydraulic safety margins, sensitivity of stomatal conductance to vapor-pressure deficit (VPD), xylem recovery capacity or the rate of carbon transfer. These differences could be explained by key features of the xylem such as non-structural carbohydrate content (NSC), wood parenchymal fraction or wood capacitance. We suggest that the reviewed trait differences define two contrasting ecophysiological strategies that may determine qualitatively different growth responses to increased temperature and drought. Improved reciprocal common garden experiments along altitudinal or latitudinal gradients would be key to quantify the relative importance of the different hypotheses reviewed. Finally, we show that warming impacts in this area occur in an ecological context characterized by the advance of forest succession and increased dominance of angiosperm trees over extensive areas. In this context, we examined the empirical relationships between the responses of tree growth to temperature and hydraulic safety margins in angiosperm and coniferous trees. Our findings suggest a future scenario in Mediterranean forests characterized by contrasting demographic responses in conifer and angiosperm trees to both temperature and forest succession, with increased dominance of angiosperm trees, and particularly negative impacts in pines

Butterfly diversity in the Montseny Mountains : patterns and processes

Aim: To describe spatial patterns of Mediterranean butterfly species richness by functional groups, analyze their main landscape and climatic drivers, test the existence of extinction debt effects, and predict past species richness distributions using past climatic and landscape data. Location: A transect of 186 1-km2 quadrats in the Montseny region and surrounding plains in the area of Catalonia (NE Spain), located between the Mediterranean Sea and the Pyrenees mountains. Methods: From 2003 to 2010 we systematically recorded the presence of butterfly species in each quadrat for a total 123 different butterfly species. Times series data were analyzed for average monthly temperature and average monthly precipitation to determine significant trends in climate. Proportions of landscape types per quadrat were calculated for years 1956, 1993 and 2005. Using these geographic, climatic and landscape data for each quadrat, a generalized linear model was built to determine the significant factors affecting butterfly species richness patterns. Results: Butterfly species richness followed a hump-shaped pattern along the altitudinal gradient. The highest species richness occurred at an average elevation range between 600 and 800 m. Of the landscape and climatic data, species richness was best explained by the interaction of temperature and precipitation (quadratic effect) as well as the amount of artificial unproductive land (negative effect), natural unproductive land (positive effect), and meadows and pastures present (positive effect). No extinction debt was found using past climatic and landscape data from the 1950s and 1990s. Main conclusions: Significant increases in temperature and large increases in artificial unproductive land may be attributable for the change in the predicted distribution of species from 1956 to 2005. These effects could also be filtering out certain functional groups, selecting for species most suited to higher temperatures and urbanized areas (i.e. species with high temperature preference, high dispersal ability and most generalist in habitat specialization), particularly at lower elevations

Factors influencing the foliar elemental composition and stoichiometry in forest trees in Spain

Concentrations of nutrient elements in organisms and in the abiotic environment are key factors influencing ecosystem structure and function. We studied how concentrations and stoichiometries of nitrogen (N), phosphorus (P) and potassium (K) in leaves of forest trees are related to phylogeny and to environmental factors (mean annual precipitation, mean annual temperature, forest type, and nitrogen deposition). Using data for 4691 forest plots from across Spain, we tested the following hypotheses: (i) that foliar stoichiometries of forest trees are strongly influenced by phylogeny, (ii) that climate, as an important driver of plant uptake and nutrient use efficiency, affects foliar stoichiometry, (iii) that long-term loads of N influence N, P and K concentrations and ratios in natural vegetation, and (iv) that sympatric species are differentiated according to their foliar stoichiometry, thereby reducing the intensity of resource competition. Our analyses revealed that several factors contributed to interspecific variation in elemental composition and stoichiometry. These included phylogeny, forest type, climate, N deposition, and competitive neighborhood relationships (probably related to niche segregation effect). These findings support the notion that foliar elemental composition reflects adaptation both to regional factors such as climate and to local factors such as competition with co-occurring species

Foliar and soil concentrations and stoichiometry of N and P across European Pinus sylvestris forests: relationships with climate, N deposition and tree growth

1. This study investigated the factors underlying the variability of needle and soil elemental composition and stoichiometry and their relationships with growth in Pinus sylvestris forests throughout the species' distribution in Europe by analyzing data from 2245 forest stands. 2. Needle N concentrations and N:P ratios were positively correlated with total atmospheric N deposition, whereas needle P concentrations were negatively correlated. These relationships were especially pronounced at sites where high levels of N deposition coincided with both higher mean annual temperature and higher mean annual precipitation. Trends toward foliar P deficiency were thus more marked when high N deposition coincided with climatic conditions favorable to plant production. 3. Atmospheric N deposition was positively correlated with soil-solution NO3-, SO42-, K+, P, and Ca2+ concentrations, the soil-solution NO3-:P ratio, total soil N, and the total soil N:Olsen P ratio, and negatively correlated with soil Olsen P concentration. 4. Despite these nutrient imbalances, during the period studied (1990-2006), N deposition was positively related with Pinus sylvestris absolute basal diameter (BD) growth, although only accounting for the 10% of the total variance. However, neither N deposition nor needle N concentration were related with relative annual BD growth. In contrast, needle P concentration was positively related with both absolute and relative annual BD growth. 5. These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition and unveil a trend toward increased nutrient losses in runoff as a consequence of higher soil-solution N concentrations. Overall, the data show increasing ecosystem nutrient imbalances with increasingly limiting roles of P and other nutrients such as K in European P. sylvestris forests, especially in the center of their distribution where higher levels of N deposition are observed. Thus, although the data show that N deposition has had an overall positive effect on P. sylvestris growth, the effect of continuous N deposition, associated with decreasing P and K and increasing N:P in leaves and in soil, may in the future become detrimental for the growth and competitive ability of P. Sylvestris trees

Foliar and soil concentrations and stoichiometry of N and P across European Pinus sylvestris forests : relationships with climate, N deposition and tree growth

1. This study investigated the factors underlying the variability of needle and soil elemental composition and stoichiometry and their relationships with growth in Pinus sylvestris forests throughout the species' distribution in Europe by analyzing data from 2245 forest stands. 2. Needle N concentrations and N:P ratios were positively correlated with total atmospheric N deposition, whereas needle P concentrations were negatively correlated. These relationships were especially pronounced at sites where high levels of N deposition coincided with both higher mean annual temperature and higher mean annual precipitation. Trends toward foliar P deficiency were thus more marked when high N deposition coincided with climatic conditions favorable to plant production. 3. Atmospheric N deposition was positively correlated with soil-solution NO3-, SO42-, K+, P, and Ca2+ concentrations, the soil-solution NO3-:P ratio, total soil N, and the total soil N:Olsen P ratio, and negatively correlated with soil Olsen P concentration. 4. Despite these nutrient imbalances, during the period studied (1990-2006), N deposition was positively related with Pinus sylvestris absolute basal diameter (BD) growth, although only accounting for the 10% of the total variance. However, neither N deposition nor needle N concentration were related with relative annual BD growth. In contrast, needle P concentration was positively related with both absolute and relative annual BD growth. 5. These results thus indicate a tendency of European P. sylvestris forests to store N in trees and soil in response to N deposition and unveil a trend toward increased nutrient losses in runoff as a consequence of higher soil-solution N concentrations. Overall, the data show increasing ecosystem nutrient imbalances with increasingly limiting roles of P and other nutrients such as K in European P. sylvestris forests, especially in the center of their distribution where higher levels of N deposition are observed. Thus, although the data show that N deposition has had an overall positive effect on P. sylvestris growth, the effect of continuous N deposition, associated with decreasing P and K and increasing N:P in leaves and in soil, may in the future become detrimental for the growth and competitive ability of P. Sylvestris trees

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

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