Browsing by Author "Castro, Sergio A."

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    An island biogeography approach for understanding changes in compositional similarity at present scenario of biotic homogenization
    (ELSEVIER, 2011) Vergara, Pablo M.; Pizarro, Jaime; Castro, Sergio A.
    Local extinction of native species and colonization of non-native species are commonly invoked as responsible for changes in species similarity among biotas of different regions. In this study we used a model of species similarity between islands to assess the emergent, and unexplored, effects of changes in colonization by native species, extinction of non-native species, and propagule pressure on species similarity among insular communities. The model predicts that extinction probability of endemic species has a positive but asymptotic effect on species similarity, which is exacerbated by increasing colonization and reducing extinction of non-native species. Species similarity tends to increase with increasing colonization probability by non-native species, however this effect may be reduced, or even reverted, when the islands are exposed to an elevated number of non-native species that are prone to extinction, high levels of endemic species loss, and an initially large number of native species shared between islands. Species similarity was positively affected by the propagule pressure rate of non-native species only when their colonization and extinction probabilities were large and small enough, respectively. A negative effect of propagule pressure rate can be caused by an increase in the pool size of non-native species, which involves the introduction of different species into different islands, promoting biotic differentiation between islands. Our results indicate that the interactions between colonization, extinction and species pool lead to nonlinear responses and unexpected scenarios of biotic change. In order to validate model predictions, future research programs should focus on understanding the dynamics on such complex meta-communities where coexist native, non-native and endemic species. (C) 2011 Elsevier B.V. All rights reserved.
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    Covariation of taxonomic and functional facets of β-diversity in Chilean freshwater fish assemblages: Implications for current and future processes of biotic homogenization
    (2023) Castro, Sergio A.; Rojas, Pablo; Vila, Irma; Jaksic, Fabian M.
    The biodiversity of assemblages that experience the introduction and extinction of species may lead to responses in two important facets: The taxonomic and functional diversity. The way in which these facets are associated may reveal important implications and consequences for the conservation of those assemblages. Considering the critical situation of freshwater fishes in continental Chile (30 degrees - 56 degrees S), we analyzed how the taxonomic (TD beta) and functional (FD beta) facets of beta-diversity, and their components of turnover and nestedness, are associated. We evaluated changes in beta-diversity (Delta TD beta and Delta FD beta), turnover (Delta TDtur and Delta FDtur), and nestedness (Delta TDnes and Delta FDnes) in 20 fish assemblages from their historical (pre-European) to current composition. We also simulated future trends of these changes, assuming that native species with conservation issues would become extinct. Our results show that the fish assemblages studied are in a process of loss of beta-diversity, both in taxonomic and functional facets (Delta TD beta = -3.9%; Delta FD beta = -30.4%); also, that these facets are positively correlated in the assemblages studied (r = 0.617; P < 0.05). Both components showed by loss in nestedness (Delta TDnes = -36.9%; Delta FDnes = -60.9%) but gain in turnover (Delta TDtur = 9.2%; Delta FDtur = 12.3%). The functional beta-diversity decreased more than the taxonomic (Delta FD beta > Delta TD beta), which was caused chiefly by six exotic species of Salmonidae, whose geographical spread was wider and that at the same time shared several morpho-functional traits. Our forecasts, assuming an intensification in the extinction of Endangered and Vulnerable native species, indicate that the process of homogenization will continue, though at a lower rate. Our study shows that the freshwater ichthyofauna of continental Chile is undergoing biotic homogenization, and that this process involves the facets of taxonomic and functional beta-diversity, which are show high correlation between historical and current compositions. Both facets show that process is influenced by nestedness, and while turnover contributes to differentiation (both taxonomic and functional), its importance is overshadowed by nestedness.
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    Differential response of the components of functional diversity in Orestias fishes (Cyprinodontidae) of the High Andean Plateau
    (2024) Rojas, Pablo; Castro, Sergio A.; Vila, Irma; Jaksic, Fabian M.
    Orestias (Cyprinodontiformes, Cyprinodontidae) is a diverse genus of freshwater fish endemic to the high Andean plateau (Altiplano) of the Andes Mountains, South America. Within the Altiplano, Orestias species form assemblages of varying taxonomic richness, exhibiting considerable diversity in morphological forms and sizes, and occupying different habitat types. Here, we investigate the functional diversity of Orestias assemblages in two basins within the Altiplano: Titicaca Lake and the southwestern Altiplano basins. Titicaca Lake is characterized by high species diversity that evolved sympatrically, while the southwestern Altiplano has lower species diversity that evolved allopatrically. Given that taxonomic diversity under sympatric conditions can promote greater functional diversity, we hypothesize that the Titicaca assemblage should display higher indicators of functional diversity. By using traits related to locomotion, food acquisition, and habitat type to quantify functional diversity we used four functional diversity indicators (functional richness, divergence, specialization, and originality) to compare the Orestias assemblages in two basins. We found no difference in functional divergence and originality between the Orestias from two basins. However, functional specialization was higher in the southwestern Altiplano, contrary to our hypothesis. Only functional richness was higher Titicaca assemblage; supporting our hypothesis. The differentiation between assemblages arises primarily from traits associated with locomotion and food acquisition. Several Orestias species are considered endangered and the extinction of any these taxa could impact the functional diversity of these basins.
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    Diversity patterns and composition of native and exotic floras in central Chile
    (2011) Figueroa Ortiz, Javier Alejandro; Castro, Sergio A.
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    Environmental and biotic filters interact to shape the coexistence of native and introduced bees in northern Patagonian forests
    (2023) Vergara, Pablo M.; Fierro, Andres; Carvajal, Mario A.; Alaniz, Alberto J.; Zorondo-Rodriguez, Francisco; Cifuentes, Maria C.; Castro, Sergio A.
    Native and introduced species can coexist in rich ecosystems where competition for resources is less intense; however, native species can be excluded from suitable habitats hosting a high abundance of introduced species. To test these hypotheses, we estimated the probability of introduced bees (buff-tailed bumblebees and honeybees) to co-occur and dominate giant bumblebees in forested landscapes of northern Patagonia. We evaluated the effects of 29 remote-sensing variables of forest ecosystems on bee abundance using data from 56 landscapes. Then, we used a probabilistic Bayesian model to estimate the effects of the most important predictors of bee abundance on their co-occurrence and dominance probabilities. Introduced and native bees exhibited heterogeneous and scale-dependent responses to environmental conditions, with only six variables affecting their cooccurrence and dominance probabilities. A high maximum temperature was associated with both a decreased co-occurrence and an increased dominance of introduced bumblebees, and the opposed pattern was found for vegetation continuous fields, an index of canopy continuity. Similar responses were found for the co-occurrence probability of honeybees and giant bumblebees. Thus, species dominance and co-occurrence changed differently along environmental gradients, with co-occurrence increasing as native and introduced species become more abundant. A high dominance of introduced bees in unsuitable habitats suggests interspecific competition is strengthened as resources become scarcer, thus reinforcing the idea that abiotic and biotic filters interact with each other.
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    Exotic species elicit decoupled responses in functional diversity components of freshwater fish assemblages in Chile
    (2021) Rojas, Pablo; Castro, Sergio A.; Vila, Irma; Jaksic, Fabian M.
    In the freshwater basins of central Chile, 28 exotic species have been introduced, which have contributed to increase taxonomic diversity. Nevertheless, how these species have modified the components of functional diversity in these assemblages, a key aspect in learning about their present and future stability within an ecosystem, is unknown. In this study, we analyzed how the introduction of exotic species affects the functional diversity components of richness (FRic), divergence (FDiv), specialization (FSpe), and functional originality (FOri). Additionally, we simulated the effect of the loss (extinction/extirpation) of threatened native species. To do so, we gathered information on the distribution and functional characters of native and exotic species. Through Principal Coordinates Analysis (PCo), we obtained three independent axes (PCoA1, PCoA2, and PCoA3), which allowed us to define a multidimensional space and then to calculate FRic, FDiv, FSpe, and FOri. Our results indicate that richness and functional originality have increased significantly with the introduction of exotic species (263% and 32%, respectively). In contrast, functional divergence and specialization have remained the same. The possible extinction of threatened native species may promote increases in functional originality, decreases in functional richness and divergence, and unchanged functional specialization. On the other hand, a subset of exotic species presents novel features, while another shows redundant features with native ichthyofauna. We emphasize that the possible extinction of native species currently classified as threatened may lead to the disappearance of unique functional groups, which puts at risk the persistence and stability of these assemblages.
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    Floristic homogenization as a teleconnected trend in oceanic islands
    (2010) Castro, Sergio A.; Jaksic Andrade, Fabián
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    Native trees provide more benefits than exotic trees when ecosystem services are weighted in Santiago, Chile
    (2021) Arcos-LeBert, Gabriela; Aravena-Hidalgo, Tamara; Figueroa, Javier A.; Jaksic, Fabian M.; Castro, Sergio A.
    Urban forests are conformed by a variable representation of native and exotic species. Because these species differ in the morpho-functional traits that possess, they may have a differential participation in the provision of ecosystem services in cities. Here, we compare ecosystem services inferred from morpho-functional traits of native and exotic tree species present in Santiago, Chile. Five traits associated with ecosystem services valuation (V-i) were scored (1 versus 0), and compared between native and exotic tree species, weighting those ecosystem services according to multi-criteria decision analysis procedure (MCDA). We found that native and exotic species did not have significant differences in the ecosystem services provided to urban dwellers (F = 1.2; P > 0.05); but these results were obtained when ecosystem services were not weighted according to their demand in Santiago. When weights were pondered, native species provided more ecosystem services than did exotic trees (F = 7.1; P < 0.008). Complementarily, we also found that the ecosystem services ranked for native and exotic species did not correlate with their spatial distribution (occupancy, O-i). These results highlight the need to use criteria based on ecosystem services to tree planting in Santiago, prioritizing native species because, in comparison to exotic ones, they provide more ecosystem services demanded city dwellers.
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    Partitioning beta-diversity reveals that invasions and extinctions promote the biotic homogenization of Chilean freshwater fish fauna
    (2020) Castro, Sergio A.; Rojas, P.; Vila, I.; Habit, E.; Pizarro-Konczak, J.; Abades T., Sebastián R.; Jaksic Andrade, Fabián
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    Patterns of turnover and floristic similarity show a non-random distribution of naturalized flora in Chile, South America
    (2008) Castro, Sergio A.; Jaksic, Fabian M.
    The current geographical distribution of alien species could be informative of processes involved in the biological invasions facilitated by humans. Because environmental and anthropic factors affect the geographic distribution of alien plants, we hypothesize that naturalized plants have a non-random distribution along extensive geographical ranges. On the basis of a complete and updated database of naturalized plants in Chile, we analyzed their turnover and floristic similarities among regions that encompass a wide latitudinal gradient in South America. Using Moran's index and Mantel's test we characterized the spatial auto-correlation (regional aggregation) and the effect of geographical distance on the index values. Additionally, we used clustering methods and resampling procedures to detect plant assemblages at regional level. Whittaker's index displayed a positive tilt, increasing according to geographical distance and reaching a plateau; conversely, Jaccard's index was negatively associated with geographical distance. Removing the effect of distance, both Whittaker's and Jaccard's values showed no significant trends. Multivariate analysis combined with resampling procedures revealed the existence of three distinctive plant clusters: Northernmost Chile, Central-southern Chile, and Southernmost Chile. These clusters are characterized by naturalized plants that are not present in the others. Based on this evidence, we conclude that the set of naturalized plants in Chile exhibits a non-random geographical distribution, displaying an ordered geographical pattern across regions (latitude). We discuss the role of the environmental variables (climate, latitude) and land use post-European colonization as factors in the distributional patterns here documented.
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    Régimen de incendios y expansión de plantas naturalizadas en Chile central
    (2011) Contreras, T.; Figueroa Ortiz, Javier Alejandro; Castro, Sergio A.
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    The identity of Fuegian and Patagonian "dogs" among indigenous peoples in southernmost South America
    (SOC BIOLGIA CHILE, 2023) Jaksic, Fabián; Castro, Sergio A.
    Background: By using a historical approach we attempt to answer the question of whether the "dogs" of Fuegian and Patagonian peoples are a domesticated dog (Canis lupus familiaris) or a tamed or domesticated Culpeo "fox" (Lycalopex culpaeus), or a cross breed. Methods and results: We reviewed historical chronicles and current scientific papers, and clarified several rather confusing concepts, providing disambiguation for terms such as Magellanic region, Patagonia, and Tierra del Fuego; Fuegian and Patagonian peoples; and Fuegian and Patagonian dogs. We conclude that these dogs belong to two different canid varieties: The smaller domestic dog typical of the "canoe-indians" (Chonos, Kawesqar, and Yahgan peoples) and the larger tamed or domesticated Culpeo "fox" typical of the "foot indians" (Aonikenk, Manek'enk, and Selk'nam peoples, thus proposing the use of Fuegian and Patagonian dog, respectively. Discussion: We think that the original Fuegian dog was indeed a Canis lupus familiaris brought along by the natives after the Bering's crossing and that the Patagonian dog was a tame Culpeo fox Lycalopex culpaeus, which was progressively replaced by the more gregarious, human friendly, and colorful domestic dogs brought by European explorers, adventurers, colonizers, and settlers of Patagonia and Tierra del Fuego during the mid to late 1800s. The possibility that the Patagonian dog was a cross between domestic dog and Culpeo "fox" cannot be ruled out, but the only specimen genetically analyzed was closest to being the latter and not a hybrid.
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    Vascular flora of Punta Arenas city: comparative analysis of composition, life forms, and biogeographic origins
    (2024) Castro, Sergio A.; Rojas, Gloria; Jaksic, Fabián M.
    The composition of the vascular flora in Punta Arenas city, found in the city’s public spaces, was studied. The species were identified and recorded in a database, which was supplemented with information on taxonomic classification, growth habit, Raunkiaer’s life form, origin status (native or exotic), and original continent-level distribution. These data were compared with studies conducted in five other cities in central Chile, together with an analysis of compositional similarity with these cities, by using the additive complement of Simpson’s index (1– βsim). In Punta Arenas, 119 species were identified, showing a higher proportion of Gymnosperms compared to central Chilean cities. The most represented families were Asteraceae (16 species), Fabaceae (14), Rosaceae (14), Poaceae (12), and Pinaceae (10), which together accounted for 55% of the floristic richness. The compositional similarity between Punta Arenas and the other central Chilean cities ranged from 0.187 to 0.315, showing lower similarity than expected by chance (Montecarlo randomization test; P < 0.05). The primary origin distribution of Punta Arenas’ vascular flora was European, unlike central Chilean cities where it was Asian. Finally, the proportion of exotic species (91.6%) and the number of exotic species per native species (16 exotics/native) were the highest documented for cities in Chile and higher than in other 114 cities worldwide. These results indicate that Punta Arenas’ urban flora differs from the flora in central Chilean cities, not only in taxonomic composition but also in growth habit, biogeographical origin, and high level of exoticism. These differences are likely due to the city’s territorial isolation and extreme southern location (53°S), leading to a unique urban flora configuration.