Browsing by Author "Farina, Jose Miguel"

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    Coexistence of Ambrosia chamissonis and Ammophila arenaria in coastal dunes in the Nuble Region, Chile
    (2024) Cerda-Paredes, Jose Miguel; Ginocchio, Rosanna; Farina, Jose Miguel
    Coastal dunes are unique ecosystems distributed worldwide. They share coastline-to-inland abiotic stress gra-dients determining their plant ' s spatial distribution and biological interactions. Ambrosia chamissonis and Ammophila arenaria dominate coastal dunes in Chile, but there is scarce ecological information about their in-teractions and spatial distribution. The aim of this study was to characterize the coexistence of these two species and to evaluate the effect of stress gradients on their spatial distribution and performance. The study was carried out in three coastal dunes of the N similar to uble Region, Chile; two dunes in which each species dominates and one in which they coexist. In each dune, sampling sites were defined along study transects perpendicular to the coast, where both soil characteristics (pH, salinity, contents of water, organic matter, nitrogen, phosphorus, and po-tassium) and biological variables of each species (cover, height, water content, content of foliar macronutrients) were measured. Variation of each abiotic variable with the distance from the high tide level was correlated to determine environmental stress gradients. A Canonical Correspondence Analysis (CCA) was performed to determine soils characteristics that better explained changes in plant abundance. The Relative Interaction In-tensity index was calculated from biological variables and compared intraspecifically to determine dominant interactions along the dunes. Our results showed two soil stress gradients (soil salinity and available potassium) which decreased inland and may define in part, the spatial distribution of the species, as shown by the CCA. Our results support the idea that dune plants do not always follow the stress gradient hypothesis suggesting a modification of the hypothesis.
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    Osmoregulatory capacity and the ability to use marine food sources in two coastal songbirds (Cinclodes
    (2006) Sabat, Pablo; Maldonado, Karin; Farina, Jose Miguel; del Rio, Carlos Martinez
    Cinclodes nigrofumosus and C. oustaleti are two closely related songbirds that inhabit the northern Chilean coast during the austral fall and winter. This stretch spans a dramatic north to south latitudinal gradient in rainfall and temperature. Whereas C. nigrofumosus lives exclusively on coastal environments, C. oustaleti shifts seasonally from coastal environments to inland freshwater ones. We used the delta C-13 of these two species' tissues to investigate whether the reliance on marine versus terrestrial sources varied from the hyperarid north to the wet south. We also investigated latitudinal variation in the renal traits that mediate how these birds cope with dehydration and a salty marine diet. Both species increased the incorporation of terrestrial carbon, as measured by 613 C, as terrestrial productivity increased southwards. However, C. nigrofumosus had consistently more positive (i.e. more marine) and less variable delta C-13 values than C. oustaleti. The osmoregulatory traits of both species varied with latitude as well. Urine osmolality decreased from extremely high values in the north to moderate values in the south, while C. nigrofumosus produced more concentrated urine than C. oustaleti. In both species, the proportion of kidney devoted to medullary tissue decreased from north to south, and kidney size increased significantly with latitude. Cinclodes nigrofumosus had larger kidneys with larger proportions of medullary tissue than C. oustaleti. C. nigrofumosus and C. oustaleti are terrestrial organisms subsidized by a rich marine environment where it is adjacent to an unproductive terrestrial. Variation in the reliance on marine food sources seems to be accompanied by adjustments in the osmoregulatory mechanisms used by these birds to cope with salt and dehydration.
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    Responses of plant-arthropod communities to nutrient enrichment in hyper-arid and semi-arid zones
    (2022) Coccia, Cristina; Farina, Jose Miguel
    Excessive nutrient loading in coastal wetlands is threatening biodiversity and altering ecosystem functioning worldwide. Nonetheless, fertilization studies have focused mainly on temperate, continental and humid climates, while little is known about the effects of nutrient enrichment in more arid environments.This study examines the responses of salt marsh plants and two dominant arthropod communities (Isopoda and Coleoptera) to short-term nutrient addition in hyper-arid (HA) and semi-arid (SA) zones of Chile. We experi-mentally increased nitrogen (N) and phosphorous (P) to examine how enrichment alters primary producers and consumer taxonomic and non-taxonomic (size-based) structure. Both N and P increased plant biomass in the HA, while in the SA, N addition increased biomass but P addition had no significant effects. N and P addition affected arthropod community and size structure differentially in HA and SA. N addition changed Coleoptera composition in HA, while P addition had large contrasting effect sizes on Isopoda and Coloeptera size evenness. In SA, N addition had large and negative effect sizes on Isopoda size evenness and Coleoptera mean body size, while P addition had large, positive effect sizes on total arthropod abundance and changed the composition of both Coleoptera and Isopoda. Although nutrient additions did not significantly affect arthropod productivity, struc-tural equation models suggested that increases in vegetation biomass with fertilization in HA could mediate positively the effects of fertilization on arthropod biomass, but not in SA where Coleoptera body size reduced. In conclusion, this study revealed that over a short time frame the effects of nutrient additions flow through the food webs more disproportionately in SA than in HA.