Seagull influence on soil properties, chenopod shrub distribution, and leaf nutrient status in semi-arid Mediterranean islands

Concentration of seagulls in the Chafarinas Islands (three semi‐arid North African islets) induces profound changes in soil properties including eutrophication, salinization, acidification and nutrient imbalances. Soils of heavily seabird‐affected sites have significantly higher soluble K and NO₃ levels (>20‐fold), Zn and Fe availability (>5‐fold), water‐retention capacity (>40% increase) and ¹⁵N enrichment, compared with control sites. These seabird‐induced soil changes are paralleled by (i) different patterns of abundance of the two main chenopod shrubs: Suaeda vera abundance is higher (>30‐fold) in seabird‐affected sites while Salsola oppositifolia largely dominates in low‐affected areas. No differences were found for Atriplex halimus. The abundance of the first two species may be largely explained by changes in soil soluble K‐to‐available Ca ratio whose value depends of the interaction between seabird products and soil constituents; (ii) significant increases in leaf N, P and Zn levels, and in all K ratios, paralelled by a decrease in Ca, in Salsola; but only by increased K/Na and P/Ca ratios in Suaeda leaves. These changes were significantly correlated to changes in species abundances; (iii) an increase of δ¹⁵N, paralleled by a decrease in δ¹³C values, in Salsola leaves but not in Suaeda.
Conjoint analysis of the seabird‐related changes in soil properties, species abundance, leaf composition and differential response to the seabird‐induced fertilization/severity gradient of the two main chenopod shrub species, has led us to propose an explanatory hypothesis of seagull‐soil‐shrub relationships. According to this, the seagull‐induced soil changes, mediated by processes of (in)tolerance‐facilitation, play a main role in determining the abundance and the leaf nutrient status of the studied chenopod shrubs, which have contrasting physiological adaptations.     

Seed removal in two coexisting oak species: ecological consequences of seed size, plant cover and seed-drop timing

Seed predation and dispersal can critically influence plant community structure and dynamics. Inter‐specific differences arising at these early stages play a crucial role on tree recruitment patterns, which in turn could influence forest dynamics and species segregation in heterogeneous environments such as Mediterranean forests. We investigated removal rates from acorns set onto the ground in two coexisting Mediterranean oak species –Quercus canariensis and Q. suber– in southern Spain. We developed maximum likelihood estimators to investigate the main factors controlling probabilities of seed removal and to describe species‐specific functional responses. To account for inter‐specific differences in seed‐drop timing, two experiments were established: a simultaneous exposure of acorns of the two species (synchronous experiments) and a seed exposure following their natural seed‐drop phenology (diachronic experiments). A total of 1536 acorns were experimentally distributed along a wide and natural gradient of plant cover, and removal was periodically monitored for three months at two consecutive years (with contrasting differences in seed production and thus seed availability on the ground). The probability of seed removal increased with plant cover (leaf area index, LAI) for the two oak species. Inter‐specific differences in acorn removal were higher in open areas and disappeared in closed microhabitats, especially during a non‐mast year. Despite later seed‐drop, Q. suber acorns were removed faster and at a higher proportion than those of Q. canariensis. The higher probability of seed removal for this species could be attributed to its larger seed size compared to Q. canariensis, as inter‐specific differences were less pronounced when similar sized acorns were exposed. Inter‐specific differences in seed removal, arising from seed size variability and microsite heterogeneity, could be of paramount importance in oak species niche separation, driving stand dynamics and composition along environmental gradients.     

Impact of control measures and dynamics of sand flies in southern Brazil

We report the results of control measures introduced to reduce the density of sand flies in domiciles and subsequent monitoring of the effects of these measures on the sand fly populations. The most common species of sand flies were Nyssomyia neivai and Nyssomyia whitmani, which are naturally infected by Leishmania. A total of 268,382 (93.4%) sand flies were collected in ecotypes constructed with the aim of attracting sand flies, and 19,091 (6.6%) sand flies were collected in the ecotypes consisting of residences and other buildings. Human actions determine the growth or reduction of the sand fly population in human‐occupied space. Understanding the dynamics of sand flies in this environment can substantially contribute to the prevention of cutaneous leishmaniasis.     

Host–virus interaction and viral evasion

With each infectious pandemic or outbreak, the medical community feels the need to revisit basic concepts of immunology to understand and overcome the difficult times brought about by these infections. Regarding viruses, they have historically been responsible for many deaths, and such a peculiarity occurs because they are known to be obligate intracellular parasites that depend upon the host's cell machinery for their replication. Successful infection with the production of essential viral components requires constant viral evolution as a strategy to manipulate the cellular environment, including host internal factors, the host's nonspecific and adaptive immune responses to viruses, the metabolic and energetic state of the infected cell, and changes in the intracellular redox environment during the viral infection cycle. Based on this knowledge, it is fundamental to develop new therapeutic strategies for controlling viral dissemination, by means of antiviral therapies, vaccines, or antioxidants, or by targeting the inhibition or activation of cell signaling pathways or metabolic pathways that are altered during infection. The rapid recovery of altered cellular homeostasis during viral infection is still a major challenge. Here, we review the strategies by which viruses evade the host's immune response and potential tools used to develop more specific antiviral therapies to cure, control, or prevent viral diseases.     

Modeling temperature variations in a pilot plant thermophilic anaerobic digester

A model that predicts temperature changes in a pilot plant thermophilic anaerobic digester was developed based on fundamental thermodynamic laws. The methodology utilized two simulation strategies. In the first, model equations were solved through a searching routine based on a minimal square optimization criterion, from which the overall heat transfer coefficient values, for both biodigester and heat exchanger, were determined. In the second, the simulation was performed with variable values of these overall coefficients. The prediction with both strategies allowed reproducing experimental data within 5% of the temperature span permitted in the equipment by the system control, which validated the model. The temperature variation was affected by the heterogeneity of the feeding and extraction processes, by the heterogeneity of the digestate recirculation through the heating system and by the lack of a perfect mixing inside the biodigester tank. The use of variable overall heat transfer coefficients improved the temperature change prediction and reduced the effect of a non-ideal performance of the pilot plant modeled.     

Driving factors of the communities of phytophagous and predatory mites in a physic nut plantation and spontaneous plants associated

Seasonal changes in climate and plant diversity are known to affect the population dynamics of both pests and natural enemies within agroecosystems. In Brazil, spontaneous plants are usually tolerated in small-scale physic nut plantations over the year, which in turn may mediate interactions between pests and natural enemies within this agroecosystem. Here, we aimed to access the influence of seasonal variation of abiotic (temperature, relative humidity and rainfall) and biotic (diversity of spontaneous plants, overall richness and density of mites) factors on the communities of phytophagous and predatory mites found in a physic nut plantation and its associated spontaneous plants. Mite sampling was monthly conducted in dicotyledonous and monocotyledonous leaves of spontaneous plants as well as in physic nut shrubs over an entire year. In the dry season there was a higher abundance of phytophagous mites (Tenuipalpidae, Tarsonemidae and Tetranychidae) on spontaneous plants than on physic nut shrubs, while predatory mites (Phytoseiidae) showed the opposite pattern. The overall density of mites on spontaneous plants increased with relative humidity and diversity of spontaneous plants. Rainfall was the variable that most influenced the density of mites inhabiting physic nut shrubs. Agroecosystems comprising spontaneous plants associated with crops harbour a rich mite community including species of different trophic levels which potentially benefit natural pest control due to increased diversity and abundance of natural enemies.     

Metapopulation Dynamics of the Mistletoe and Its Host in Savanna Areas with Different Fire Occurrence

Mistletoes are aerial hemiparasitic plants which occupy patches of favorable habitat (host trees) surrounded by unfavorable habitat and may be possibly modeled as a metapopulation. A metapopulation is defined as a subdivided population that persists due to the balance between colonization and extinction in discrete habitat patches. Our aim was to evaluate the dynamics of the mistletoe Psittacanthus robustus and its host Vochysia thyrsoidea in three Brazilian savanna areas using a metapopulation approach. We also evaluated how the differences in terms of fire occurrence affected the dynamic of those populations (two areas burned during the study and one was fire protected). We monitored the populations at six-month intervals. P. robustus population structure and dynamics met the expected criteria for a metapopulation: i) the suitable habitats for the mistletoe occur in discrete patches; (ii) local populations went extinct during the study and (iii) colonization of previously non-occupied patches occurred. The ratio of occupied patches decreased in all areas with time. Local mistletoe populations went extinct due to two different causes: patch extinction in area with no fire and fire killing in the burned areas. In a burned area, the largest decrease of occupied patch ratios occurred due to a fire event that killed the parasites without, however, killing the host trees. The greatest mortality of V. thyrsoidea occurred in the area without fire. In this area, all the dead trees supported mistletoe individuals and no mortality was observed for parasite-free trees. Because P. robustus is a fire sensitive species and V. thyrsoidea is fire tolerant, P. robustus seems to increase host mortality, but its effect is lessened by periodic burning that reduces the parasite loads.