Interpopulation Variability in Dietary Traits of Invasive Bleak Alburnus alburnus (Actinopterygii, Cyprinidae) Across the Iberian Peninsula

The bleak Alburnus alburnus is native to most of Europe. This cyprinid fish is a successful invader in the Iberian Peninsula. No studies exist on its foraging strategies on a large scale for this ecoregion. The aim of the present study was to compare dietary traits of invasive bleak among the main Iberian rivers and a ‘reference’ native bleak population from France. Bleak were sampled during May–June 2019 from the Iberian Rivers Ebro, Tagus, Guadiana, Segura and Guadalquivir and the River Saône (France). Diptera larvae and zooplankton were common food categories in the River Saône. Insect nymphs were more important in the River Ebro. The intake of plant material was higher in the River Tagus. Flying insects were more consumed in the River Guadiana. Nektonic insects were important in the River Guadalquivir. Detritus was a frequent food category for all populations, in terms of occurrence and mass. Dietary parameters followed a unimodal response in relation to the latitudinal gradient, with the maximum values for the Tagus and Guadiana populations. Overall, results suggest that this wide interpopulation variability will contribute to the species’ successful establishment throughout Mediterranean Europe, which poses a serious risk to its highly valuable native fish fauna.

Hidden similarities in the dynamics of a weakly synchronous marine metapopulation

Populations of many marine species are only weakly synchronous, despite coupling through larval dispersal and exposure to synchronous environmental drivers. Although this is often attributed to observation noise, factors including local environmental differences, spatially variable dynamics, and chaos might also reduce or eliminate metapopulation synchrony. To differentiate spatially variable dynamics from similar dynamics driven by spatially variable environments, we applied hierarchical delay embedding. A unique output of this approach, the “dynamic correlation,” quantifies similarity in intrinsic dynamics of populations, independently of whether their abundance is correlated through time. We applied these methods to 17 populations of blue crab (Callinectes sapidus) along the US Atlantic coast and found that their intrinsic dynamics were broadly similar despite largely independent fluctuations in abundance. The weight of evidence suggests that the latitudinal gradient in temperature, filtered through a unimodal response curve, is sufficient to decouple crab populations. As unimodal thermal performance is ubiquitous in ectotherms, we suggest that this may be a general explanation for the weak synchrony observed at large distances in many marine species, although additional studies are needed to test this hypothesis.

Edaphic properties as key drivers for woody species distributions in tropical savannic and forest habitats

Edaphic gradients can explain plant species distribution at a local scale in the neotropics and elsewhere, but few studies have evaluated the individual responses of species to such gradients. We collected data on species and soils in open savannic and forest formations (totalling five habitats in each formation), aiming to evaluate the importance of edaphic factors on the distribution of woody plant species in tropical habitats. Logistic regression was used to test the influence of predictor variables (soil texture and fertility) on plant occurrence (presence or absence). Most species (73%) responded to the edaphic gradients. However, the edaphic gradients did not explain the distribution of the remaining 27% of species, which implies the existence of other factors determining their occurrence. Soil fertility (nutritional status) was the major factor in forest habitats (65% of the species which showed significant response), while soil texture was the most explanatory factor for species occurrence in open habitats (55% of the species that showed a significant response). Thus, nutrient status was less limiting and soil texture was more limiting in savannic formations, whereas the opposite was observed for forest formations. Most species showing a relationship with edaphic gradients had a unimodal response, which is in accordance with the literature. Our study showed that soil properties largely regulate the distribution of plant species in tropical habitats, despite other factors not investigated here also having an effect on several of the studied species. Models of species distribution that take into account environmental heterogeneity are key for the elaboration of strategies for the conservation and restoration of ecosystems.

Ordenación de las poblaciones silvestres de pitayo y cardón en la Cuenca de Sayula, Jalisco

The ecological relationships of "pitayo" and "cardón" were studied in the Sayula, Jalisco Basin. A multivariate approach was used considering three sets of explanatory variables: geographical (FG), edaphic (E) and biotic (B). Three columnar cacti species Stenocereus queretaroensis, and S. dumortieri and Pachycereus grandis were found. According to a detrended correspondence analysis the length of the gradient was 3.59 S.D., which justifies the use of unimodal response model for the species data. Also the results of a correspondence analysis showed a sites and species pattern related to a supposed moisture gradient. Due to the presence of outliers in some variables, it was necessary to use certain passive sites in the canonical correspondence analysis. The selected variables were: a] geographical: latitude, longitude, elevation and exposure; b] edaphic: potassium content, cation exchange capacity and sand percentage. Of these components of species data variation, the first explains 28.94% and the second one 23.66%, while the interaction of both explains only 8.23%. At the biotic level, the accompanying shrubs and tree species data were related to "pitayo" and "cardón" attributes in two ways: a] as three separated populations, or b] as a complex. The better selected attributes were total cover and average height of individual in the complex, or else S. dumortieri and P. grandis, respectively, for the species strategy. However, there was a poor relation for the species (17.4%), with the variation of the associated shrub and tree species.

Subalpine grassland carbon balance during 7 years of increased atmospheric N deposition

Air pollution agents interact when affecting biological sinks for atmospheric CO2, e.g., the soil organic carbon (SOC) content of grassland ecosystems. Factors favoring plant productivity, like atmospheric N deposition, are usually considered to favor SOC storage. In a 7-year experiment in subalpine grassland under N- and O3-deposition treatment, we examined C fluxes and pools. Total N deposition was 4, 9, 14, 29 and 54 kg N ha−1 yr−1 (N4, N9, etc.); annual mean phytotoxic O3 dose was 49, 65 and 89 mmol m−2 projected leaf area. We hypothesized that between years SOC of this mature ecosystem would not change in control treatments and that effects of air pollutants are similar for plant yield, net ecosystem productivity (NEP) and SOC content, leading to SOC content increasing with N deposition. Cumulative plant yield showed a significant N and N × N effect (+38 % in N54) but no O3 effect. In the control treatment SOC increased significantly by 9 % in 7 years. Cumulative NEP did show a strong, hump-shaped response pattern to N deposition with a +62 % increase in N14 and only +39 % increase in N54 (N effect statistically not significant, N × N interaction not testable). SOC had a similar but not significant response to N, with highest C gains at intermediate N deposition rates, suggesting a unimodal response with a marginal (P = 0.09) N × N interaction. We assume the strong, pollutant-independent soil C sink developed as a consequence of the management change from grazing to cutting. The non-parallel response of SOC and NEP compared to plant yield under N deposition is likely the result of increased respiratory SOC losses, following mitigated microbial N-limitation or priming effects, and a shift in plant C allocation leading to smaller C input from roots.

Atmospheric N deposition causes carbon balance gains in a seven year field experiment in subalpine grassland

Air pollution agents interact when affecting biological sinks for atmospheric CO2, e.g. the soil organic carbon (SOC) content of grassland ecosystems. Factors favoring plant productivity, like atmospheric N deposition, are usually considered to favor SOC storage. In a seven year experiment in subalpine grassland under N- and O3-deposition treatment, we examined C-fluxes and -pools. Total N deposition was 4, 9, 14, 29 and 54 kg N ha−1 yr−1 (N4, N9, etc.), annual mean phytotoxic O3 dose was 49, 65 and 89 mmol m−2 projected leaf area. We hypothesized that SOC of this mature ecosystem would not change in control treatments, but that effects of air pollutants on plant yield, net ecosystem productivity (NEP) and SOC content would develop in parallel, leading to SOC content to increase with N deposition. In the control treatment SOC increased significantly by 9 % in seven years. Cumulative plant yield showed a highly significant N effect (+38 % in N54), but no O3-effect. Cumulative NEP did show a strong, yet statistically insignificant, hump shaped response pattern to N deposition with a +62 % increase in N14, and only +39 % increase in N54. SOC had a similar response to N, with highest gains at intermediate N deposition rates (9 and 14 kg N ha−1 yr−1), suggesting an unimodal response, too. We assume the strong, pollutant-independent soil C sink developed as a consequence of the management change from grazing to cutting. The non-parallel response of SOC and NEP compared to plant yield under N deposition is likely the result of increased respiratory SOC losses, following mitigated microbial N-limitation or priming effects, and a shift in plant C allocation leading to smaller C input from roots.