Browsing by Author "Valdivia, Nelson"

Now showing 1 - 12 of 12
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    Asymmetric competitive effects during species range expansion : An experimental assessment of interaction strength between "equivalent" grazer species in their range overlap
    (2019) Aguilera, Moisés A.; Valdivia, Nelson; Jenkins, Stuart; Navarrete C., Sergio; Broitman Rojas, Bernardo Oscar
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    Disentangling the effects of propagule supply and environmental filtering on the spatial structure of a rocky shore metacommunity
    (2015) Valdivia, Nelson; Aguilera, Moisés A.; Navarrete C., Sergio; Broitman Rojas, Bernardo Oscar
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    Food webs over time: evaluating structural differences and variability of degree distributions in food webs
    (2018) López, Daniela N.; Camus Contreras, Patricio A.; Valdivia, Nelson; Estay Cabrera, Sergio Andrés
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    Geographic variation in diversity of wave exposed rocky intertidal communities along central Chile
    (2011) Broitman, Bernardo R.; Veliz, Fredy; Manzur, Tatiana; Wieters, Evie A.; Randall Finke, G.; Fornes, Paulina A.; Valdivia, Nelson; Navarrete, Sergio A.
    Along the coast of central Chile, geographic trends of diversity have been inferred from literature compilations and museum collections based on species range limits for some taxonomic groups. However, spatially-intensive field-based assessments of macrobenthic species richness are largely missing. Over the course of a multiyear study (1998-2005), we characterized latitudinal patterns of rocky intertidal diversity at 18 sites along the coast of central Chile (29-36 degrees S). At each site, the number of sessile and mobile macrobenthic species was quantified in 0.25 m(2) quadrats. Two estimators of local (alpha) diversity were used: observed local species richness, calculated from the asymptote of a species-rarefaction curve, and the Chao2 index, which takes into account the effect of rare species on estimates of local richness. We identified a total of 71 species belonging to 66 genera for a total of 86 taxa. The most diverse groups were herbivorous mollusks (27 taxa) and macroalgae (43 taxa). Diversity showed a complex spatial pattern with areas of high species richness interspersed with areas of low richness. In accordance with previous work, we found no trend in the number of herbivorous mollusks and an inverse and significant latitudinal gradient in the number of algal species. Our results highlight the need for taxonomically diverse assessments of biodiversity of the dominant taxa that conform intertidal communities.
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    Independent Effects of Species Removal and Asynchrony on Invariability of an Intertidal Rocky Shore Community
    (2022) Fica-Rojas, Eliseo; Catalan, Alexis M.; Broitman, Bernardo R.; Perez-Matus, Alejandro; Valdivia, Nelson
    Ecological stability depends on interactions between different levels of biological organization. The insurance effects occur when increasing species diversity leads to more temporally invariable (i.e., more stable) community-level properties, due in part to asynchronous population-level fluctuations. While the study of insurance effects has received considerable attention, the role of dominant species that contribute with particular functional traits across different level of organizations is less understood. Using a field-based manipulative experiment, we investigated how species richness and different types of parameters at the population level, such as the invariability of dominants, population invariability, and population asynchrony, influence the community invariability. The experiment involved the repetitive removal of the canopy forming alga Mazzaella laminarioides (hereafter "Mazzaella") during 32 months in two rocky intertidal sites of northern-central Chile. We predicted that the invariability of dominants enhances community invariability, that the effect of multispecies population-level parameters on community invariability are dependent on species richness, and that subdominant algae are unable to fully compensate the loss of canopies of the dominant species. Biomass of algae and mobile invertebrates was quantified over time. We observed independent effects of Mazzaella removal and community-wide asynchrony on community invariability. While canopy removal reduced community invariability, population asynchrony boosted community invariability regardless of the presence of canopies. In addition, filamentous and foliose algae were unable to compensate the loss of biomass triggered by the experimental removal of Mazzaella. Canopy removal led to a severe decrement in the biomass of macrograzers, while, at the same time, increased the biomass of mesograzers. Asynchrony stemmed from compensatory trophic responses of mesograzers to increased abundances of opportunistic algae. Thus, further work on consumer-resource interactions will improve our understanding of the links between population- and community-level aspects of stability.
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    Integrating species and interactions into similarity metrics: a graph theory-based approach to understanding community similarity
    (2019) Lopez, Daniela N.; Camus, Patricio A.; Valdivia, Nelson; Estay, Sergio A.
    Community similarity is often assessed through similarities in species occurrences and abundances (i.e., compositional similarity) or through the distribution of species interactions (i.e., interaction similarity). Unfortunately, the joint empirical evaluation of both is still a challenge. Here, we analyze community similarity in ecological systems in order to evaluate the extent to which indices based exclusively on species composition differ from those that incorporate species interactions. Borrowing tools from graph theory, we compared the classic Jaccard index with the graph edit distance (GED), a metric that allowed us to combine species composition and interactions. We found that similarity measures computed using only taxonomic composition could differ strongly from those that include composition and interactions. We conclude that new indices that incorporate community features beyond composition will be more robust for assessing similitude between natural systems than those purely based on species occurrences. Our results have therefore important conceptual and practical consequences for the analysis of ecological communities.
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    Limited effects of management and ecological subsidies on the size-spectra of kelp forest fish communities
    (2024) Gartenstein, Simon; Perez-Matus, Alejandro; Heather, Freddie J.; Godoy, Natalio; Torres-Canete, Felipe; Catalan, Alexis M.; Valdivia, Nelson
    Animal body size influences key ecological processes across biological hierarchies. For instance, densities (N) and community biomass (B) are allometric functions of body mass (M). Energetic equivalence predicts that density scales with body size as N proportional to M-0.75 and that biomass scales with body size as B proportional to M0.25. However, the way fish size-spectra are influenced by external processes, such as ecological subsidies (e.g. nutrients from upwelling zones) and fisheries management, is not well understood. We investigated the relationship of body size with density and biomass of reef fishes associated with subtidal kelp forests of Lessonia trabeculata that were influenced by the separate and interactive effects of management (Territorial Use Rights for Fisheries [TURF] or open access) and upwelling regimes (upwelling or non-upwelling zones). Fish densities and lengths were recorded using underwater visual censuses. Within each of 4 locations, paired TURF and open-access sites were surveyed. We surveyed 18 fish species, encompassing 1511 individuals ranging between 2 and 6639 g. We observed that fish size-spectra deviated from energetic equivalence, as N proportional to M-0.32 and B proportional to M2.2, indicating that the contribution of large-sized fishes to community density and biomass was greater than that predicted by energetic equivalence. Multi-model inference suggested that TURF and upwelling scenarios had weak effects on fish size-spectra. Results indicated that fish communities may have access to external food sources beyond local kelp forests. In addition, size-spectra may be a spatially persistent attribute of these fish communities.
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    Predator control of marine communities increases with temperature across 115 degrees of latitude
    (2022) Ashton, Gail, V; Freestone, Amy L.; Duffy, J. Emmett; Torchin, Mark E.; Sewall, Brent J.; Tracy, Brianna; Albano, Mariano; Altieri, Andrew H.; Altvater, Luciana; Bastida-Zavala, Rolando; Bortolus, Alejandro; Brante, Antonio; Bravo, Viviana; Brown, Norah; Buschmann, Alejandro H.; Buskey, Edward; Calderon Barrera, Rosita; Cheng, Brian; Collin, Rachel; Coutinho, Ricardo; De Gracia, Luis; Dias, Gustavo M.; DiBacco, Claudio; Flores, Augusto A., V; Angelica Haddad, Maria; Hoffman, Zvi; Ibanez Erquiaga, Bruno; Janiak, Dean; Jimenez Campean, Anali; Keith, Inti; Leclerc, Jean-Charles; Pedro Lecompte-Perez, Orlando; Ortigara Longo, Guilherme; Matthews-Cascon, Helena; McKenzie, Cynthia H.; Miller, Jessica; Munizaga, Martin; Naval-Xavier, Lais P. D.; Navarrete, Sergio A.; Otalora, Carlos; Palomino-Alvarez, Lilian A.; Gabriela Palomo, Maria; Patrick, Chris; Pegau, Cormack; Pereda, Sandra, V; Rocha, Rosana M.; Rumbold, Carlos; Sanchez, Carlos; Sanjuan-Munoz, Adolfo; Schloder, Carmen; Schwindt, Evangelina; Seemann, Janina; Shanks, Alan; Simoes, Nuno; Skinner, Luis; Yolimar Suarez-Mozo, Nancy; Thiel, Martin; Valdivia, Nelson; Velez-Zuazo, Ximena; Vieira, Edson A.; Vildoso, Bruno; Wehrtmann, Ingo S.; Whalen, Matt; Wilbur, Lynn; Ruiz, Gregory M.
    Early naturalists suggested that predation intensity increases toward the tropics, affecting fundamental ecological and evolutionary processes by latitude, but empirical support is still limited. Several studies have measured consumption rates across latitude at large scales, with variable results. Moreover, how predation affects prey community composition at such geographic scales remains unknown. Using standardized experiments that spanned 115 degrees of latitude, at 36 nearshore sites along both coasts of the Americas, we found that marine predators have both higher consumption rates and consistently stronger impacts on biomass and species composition of marine invertebrate communities in warmer tropical waters, likely owing to fish predators. Our results provide robust support for a temperature-dependent gradient in interaction strength and have potential implications for how marine ecosystems will respond to ocean warming.
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    Stability of rocky intertidal communities, in response to species removal, varies across spatial scales
    (2021) Valdivia, Nelson; Lopez, Daniela N.; Fica-Rojas, Eliseo; Catalan, Alexis M.; Aguilera, Moises A.; Araya, Marjorie; Betancourtt, Claudia; Burgos-Andrade, Katherine; Carvajal-Baldeon, Thais; Escares, Valentina; Gartenstein, Simon; Grossmann, Mariana; Gutierrez, Barbara; Kotta, Jonne; Morales-Torres, Diego F.; Riedemann-Saldivia, Barbara; Rodriguez, Sara M.; Velasco-Charpentier, Catalina; Villalobos, Vicente, I; Broitman, Bernardo R.
    Improving our understanding of stability across spatial scales is crucial in the current scenario of biodiversity loss. Still, most empirical studies of stability target small scales. We experimentally removed the local space-dominant species (macroalgae, barnacles, or mussels) at eight sites spanning more than 1000 km of coastline in north- and south-central Chile, and quantified the relationship between area (the number of aggregated sites) and stability in aggregate community variables (total cover) and taxonomic composition. Resistance, recovery, and invariability increased nonlinearly with area in both functional and compositional domains. Yet, the functioning of larger areas achieved a better, albeit still incomplete, recovery than composition. Compared with controls, smaller disturbed areas tended to overcompensate in terms of total cover. These effects were related to enhanced available space for recruitment (resulting from the removal of the dominant species), and to increasing beta diversity and decaying community-level spatial synchrony (resulting from increasing area). This study provides experimental evidence for the pivotal role of spatial scale in the ability of ecosystems to resist and recover from chronic disturbances. This knowledge can inform further ecosystem restoration and conservation policies.
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    The natural diet of Prolatilus jugularis inhabiting Lessonia trabeculata kelp forests of south-central Chile
    (2024) Gartenstein, Simon; Fica-Rojas, Eliseo; Perez-Matus, Alejandro; Godoy, Natalio; Torres-Canete, Felipe; Valdivia, Nelson
    Kelp forests support species-rich food webs that predator-prey interactions may sustain. Here, we analyze prey availability and stomach contents of the predatory fish Prolatilus jugularis in an unexplored subtidal kelp forest of Lessonia trabeculata in south-central Chile. In the kelp forest, 42 invertebrate taxa and 1016 individuals were observed. In the diet of P. jugularis, 21 taxa and 130 individuals were identified. Crustacea, particularly amphipods, were the dominant and more frequent taxa in the kelp forest and stomach contents. Annelida and Mollusca were also present in the kelp forest and diets but were less abundant. We did not find a statistically significant correlation between kelp forest and stomach-content prey abundances and frequencies. Also, dominance structure significantly differed between kelps and stomach contents. Our results indicate that P. jugularis could feed in other habitats outside the survey area. Seven predatory fish were sampled in the kelp forest. Pinguipes chilensis was the dominant fish, with 65% of the total fish biomass, followed by P. jugularis with 20%.
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    Transient species driving ecosystem multifunctionality: Insights from competitive interactions between rocky intertidal mussels
    (2024) Betancourtt, Claudia; Catalan, Alexis M.; Morales-Torres, Diego F.; Lopez, Daniela N.; Escares-Aguilera, Valentina; Salas-Yanquin, Luis P.; Buchner-Miranda, Joseline A.; Chaparro, Oscar R.; Nimptsch, Jorge; Broitman, Bernardo R.; Valdivia, Nelson
    Anthropogenic biodiversity loss poses a significant threat to ecosystem functioning worldwide. Numerically dominant and locally rare (i.e., transient) species are key components of biodiversity, but their contribution to multiple ecosystem functions (i.e., multifunctionality) has been seldomly assessed in marine ecosystems. To fill this gap, here we analyze the effects of a dominant and a transient species on ecosystem multifunctionality. In an observational study conducted along ca. 200 km of the southeastern Pacific coast, the purple mussel Perumytilus purpuratus numerically dominated the mid -intertidal and the dwarf mussel Semimytilus patagonicus exhibited low abundances but higher recruitment rates. In laboratory experiments, the relative abundances of both species were manipulated to simulate the replacement of P. purpuratus by S. patagonicus and five proxies for ecosystem functions-rates of clearance, oxygen consumption, total biodeposit, organic biodeposit, and excretion-were analyzed. This replacement had a positive, linear, and significant effect on the combined ecosystem functions, particularly oxygen consumption and excretion rates. Accordingly, S. patagonicus could well drive ecosystem functioning given favorable environmental conditions for its recovery from rarity. Our study highlights therefore the key role of transient species for ecosystem performance. Improving our understanding of these dynamics is crucial for effective ecosystem conservation, especially in the current scenario of biological extinctions and invasions.
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    Variation in coastal Antarctic microbial community composition at sub-mesoscale: spatial distance or environmental filtering?
    (2016) Moreno Pino, Mario; De la Iglesia Cabezas, Rodrigo Alonso; Valdivia, Nelson; Henríquez Castillo, Carlos Andrés; Galan, Alexander; Diez Moreno, Beatriz; Trefault Carrillo, Nicole Natalie; Moreno Pino, Mario; De la Iglesia Cabezas, Rodrigo Alonso; Valdivia, Nelson; Henríquez Castillo, Carlos Andrés; Galan, Alexander; Diez Moreno, Beatriz; Trefault Carrillo, Nicole Natalie