DSpace Angular :: Browsing by Author "Jaksic, Fabian M."

Browsing by Author "Jaksic, Fabian M."

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An Eltonian proxy for restoring a lost browser-tree interaction
(2024) Root-Bernstein, Meredith; Guerrero-Gatica, Matias; Rossle, Andoni Elorrieta; Fleming, Jory; Aguillar, Jorge Ramos; Rochefort, Benjamin Silva; Charles-Dominique, Tristan; Armesto, Juan; Jaksic, Fabian M.
Many South American dry woodlands lack good historical or paleoecological baseline data to inform restoration and conservation. However, functionalist approaches such as those popularized by rewilding suggest that functional interactions producing target ecosystem processes are valid even without data confirming compositionalist values such as a long coevolutionary histories or known historical range overlaps of target species. In central Chile, the guanaco (Lama guanicoe) has been extirpated but is known to browse trees in other regions of South America, and the tree Vachellia [Acacia] caven shows adaptations to browsing but has no extant browsers within its Chilean range. Both species are native to Chile but there are no data to assess their historical levels of interaction. Here we test the hypothesis that they can act as mutual "Eltonian proxy" species: interacting species for which we lack sufficient data (the Eltonian shortfall) to prove they are not proxies. Specifically we predict that they have complementary adaptations such that guanacos will browse Vachellia [Acacia] caven and the latter will show adaptive responses to their browsing. We introduced five guanacos into an enclosure of Vachellia [Acacia] caven "espinal" woodland, and over two years measured the growth responses of individual branches, compared to branches of trees in an area without browsing. We predicted that Vachellia [Acacia] caven would show compensatory growth in response to guanaco browsing resulting in an increase in branching. Guanacos browsed throughout the two years. In the presence of guanaco browsing, Vachellia [Acacia] caven branches grew longer, grew more sub-branches, and showed more densely streamlined branch architectures. These results indicate that guanacos could be used to substitute anthropogenic pruning as a restoration and management technique in Vachellia [Acacia] caven "espinal" woodlands. However, other extinct megaherbivores or extirpated deer may also be key components of a past herbivore community to which Vachellia [Acacia] caven was adapted. Further attention to a network of multiple interacting browsers, and their indirect and nontrophic effects, is an area for further research.
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.
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.
Does thermal physiology explain the ecological and evolutionary success of invasive species? Lessons from ladybird beetles
(2018) Boher, Francisca; Jaksic, Fabian M.; Martel, Sebastian I.; Orellana, Maria J.; Bozinovic, Francisco
Background: Several hypotheses have been proposed to explain invasive species success. Much of the research in this field has been conducted at the ecosystem or community level. Physiological traits are usually ignored, although they may play a role. As invasiveness has been correlated with species range expansion, it has been assumed - but scarcely tested - that species with greater physiological thermotolerances could be more invasive and colonize more habitats.
Effect of prolonged exposition to pulp mill effluents on the invasive aquaticplant Egeria densa and other primary producers
(2008) Palma, Alvaro T.; Silva, Marcelo G.; Munoz, Carlos A.; Cartes, Carolina; Jaksic, Fabian M.
The recent disappearance of the aquatic plant Egeria densa, a Brazilian native invasive species, from a wetland in southern Chile prompted several efforts to unveil the origin of this phenomenon. Because these changes occurred by the time a newly built pulp mill started its operations in the area, a reasonable doubt for a cause-effect relationship is plausible. We implemented a mesocosm approach to directly evaluate the effect of treated pulp mill effluents (PMEs) on several growth-related parameters of E. densa as well as other primary producers. We hypothesize that effluent, at a dilution similar to that detected in the zone of the wetland where the negative environmental impacts were evident, has a significant negative effect on this aquatic plant as well as on other primary producers inside a mesocosm system. After a prolonged (months) exposure to both 0% PME with pure river water and a 4 to 5% (v/v) dilution of treated PME, no effect on E. densa was measured. Furthermore, plants exposed to effluent exhibited a significantly greater general growth rate. Coincidently, chlorophyll a concentration in the water column and periphyton biomass also changed over time, but without any pattern attributable to the effluent. Values of the autotrophic index obtained from the periphyton growth pattern did not suggest enrichment of the system with organic matter. Our results only refer to the direct effect of mill effluents on several biotic responses, but they represent an important advance toward generation of the scientific knowledge necessary to understand how the ecosystem functions while receiving this and other unquantified sources of water.
EVIDENCE OF HIGH CONSUMPTION OF WASTE BY THE ANDEAN CONDOR (VULTUR GRYPHUS) IN AN ANTHROPIZED ENVIRONMENT OF CHILE
(2019) Pavez, Eduardo F.; Duclos, Melanie; Rau, Jaime R.; Sade, Soraya; Jaksic, Fabian M.
Anthropogenic food subsidies and waste disposals have become a new food resource for wildlife, including the Andean Condor (Vultur gryphus), a situation that implies benefits and health risks. To increase understanding of Andean Condor feeding habits in the most anthropized area in Chile, we analyzed 280 pellets collected during 2016 from one roost in the Metropolitan Region, central Chile. We identified the main diagnostic elements microscopically and expressed them as percentage of occurrence (percentage of each item in relation to all pellets). We found 12 prey categories (including mammals, birds, and plant material) and 9 waste categories. Condors fed mainly on mammals (99%); livestock was their main feeding source (52%), followed by native (22%) and exotic wild species (19%). Birds were detected less frequently (8%). We found a high occurrence of waste (31%), of which plastic remains were the main item (27%). According to our results, landfills serve as a complementary food source for condors, probably a low-quality but easily accessible, and which exposes them to a variety of health and mortality risks. Despite the fact that Andean Condors can reach distant places in foraging flights to find food resources, a high proportion of the population is attracted to rubbish dumps and landfills. Despite the spatio-temporal limitations of our results, this is the first record that describes and quantifies a high presence of waste as a component of the Andean Condor diet. We recommend a more comprehensive study to assess their feeding habits and habitat preferences in a broader spatio-temporal context, and to determine the possible impact of the use of waste disposals on Andean Condor populations.
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.
Exploring the influence of density-dependence and weather on the spatial and temporal variation in common vole (Microtus arvalis) abundance in Castilla y León, NW Spain
(2024) Caminero-Saldana, Constantino; Correa-Cuadros, Jennifer Paola; Banos-Herrero, Ana; Riquelme, Carlos; Pallavicini, Yesica; Fernandez-Villan, Mercedes; Plaza, Javier; Perez-Sanchez, Rodrigo; Sanchez, Nilda; Mougeot, Francois; Luque-Larena, Juan Jose; Jaksic, Fabian M.; Garcia-Ariza, Maria Carmen
BACKGROUND: The common vole has invaded the agroecosystems of northwestern Spain, where outbreaks cause important crop damage and management costs. Little is yet known about the factors causing or modulating vole fluctuations. Here, we used 11 years of vole abundance monitoring data in 40 sites to study density-dependence and weather influence on vole dynamics. Our objective was to identify the population dynamics structure and determine whether there is direct or delayed density-dependence. An evaluation of climatic variables followed, to determine whether they influenced vole population peaks. RESULTS: First- and second-order outbreak dynamics were detected at 7 and 33 study sites, respectively, together with second-order variability in periodicity (2-3 to 4-5-year cycles). Vole population growth was explained by previous year abundance (mainly numbers in summer and spring) at 21 of the sites (52.5%), by weather variables at 11 sites (27.5%; precipitation or temperature in six and five sites, respectively), and by a combination of previous abundance and weather variables in eight sites (20%). CONCLUSIONS: We detected variability in vole spatiotemporal abundance dynamics, which differs in cyclicity and period. We also found regional variation in the relative importance of previous abundances and weather as factors modulating vole fluctuations. Most vole populations were cyclical, with variable periodicity across the region. Our study is a first step towards the development of predictive modeling, by disclosing relevant factors that might trigger vole outbreaks. It improves decision-making processes within integrated management dealing with mitigation of the agricultural impacts caused by voles. (c) 2023 Society of Chemical Industry.
Fire Severity Causes Temporal Changes in Ground-Dwelling Arthropod Assemblages of Patagonian Araucaria-Nothofagus Forests
(2022) Zuniga, Alfredo H.; Rau, Jaime R.; Fierro, Andres; Vergara, Pablo M.; Encina-Montoya, Francisco; Fuentes-Ramirez, Andres; Jaksic, Fabian M.
Fire is one of the main drivers of anthropogenic disturbances in temperate forest ecosystems worldwide, with multiple effects spread across ecological networks. Nevertheless, the biodiversity effects of fire are poorly known for species-diverse groups such as arthropods. In this research, we used a burn gradient generated two and three years after a large fire event to assess how different levels of fire severity affect arthropod diversity in the forest with the main forest forming long-living tree species Araucaria araucana, in southern Chile. The species richness and abundance of arthropods among trophic guilds was estimated annually in four fire-severity levels. We found that arthropods responded differently to fire severity levels, depending on their trophic guilds and years after fire (two and three years after fire). During the second year after fire, zoophages, phytophages, and parasitoids were more diverse in areas with high fire severity within the second year after fire, as compared to those in areas with low severity or unburned stands. In the third year after fire, a change in this trend was observed, where the abundance of all groups dropped significantly, with positive changes in the diversity in zoophages, phytophages, polyphages and saprophages, which is more noticeable in sites with high severity. These results indicate that annual variation in environmental conditions triggers bottom-up cascading effects for arthropods. Forests stands severely impacted by fires support highly fluctuating and possibly unstable arthropod assemblages. Hence, restoration efforts should be focused on recovering microhabitat conditions in these stands to allow the persistence of arthropods.
FOOD HABITS AND TROPHIC ATTRIBUTES OF THE MAGELLANIC HORNED OWL (BUBO MAGELLANICUS) IN THE PATAGONIAN STEPPE, SOUTHERNMOST CHILE
(2020) Martinez, David R.; Alvarez-Cortez, Gabriela; Jaksic, Fabian M.
For most of southern South America, the food habits of Magellanic Horned owls (Bubo magellanicus) are well known. In Chile, several researchers have reported the owl's diet in northern xerophytic environments, as well as subpolar forests; however, other than a short note on the owls' summer diet in Punta Dungeness (Martinez 2018), no major studies have documented the food habits of Magellanic Horned owls in the Chilean Patagonian steppe. Based on 278 fresh pellets, we reported the food habits of owls inhabiting two sites located at > 52 degrees S in the southernmost Patagonian steppe in continental Chile, and compared our findings with those reported for owls inhabiting eight localities from 39 to 52 degrees S in the Argentinean Patagonian steppe. Our results indicate that in Patagonian steppe environments of both Argentina and Chile, the Magellanic Horned Owl is a generalist predator, which consumes whatever prey available, ranging in size from invertebrates to introduced juvenile lagomorphs. Because all five major vertebrate prey here reported (Abrothrix olivacea, Loxodontomys micropus, Microcavia australis, Reithrodon auritus, Lepus europaeus) are broadly distributed in the Argentinean Patagonian steppe and occur abundantly from 36 degrees S southwards to the Strait of Magellan and Isla Grande de Tierra del Fuego, their generalized occurrence as prey does not allow for expression of latitudinal trends in species composition in the owl's diet.
Habitat and food preferences of European rabbits in core and edge populations along the invasion front Patagonia-Monte, Argentina
(2023) Yasmin Bobadilla, Sabrina; Dacar, Maria A.; Jaksic, Fabian M.; Ojeda, Ricardo A.; Fernanda Cuevas, Maria
The European rabbit Oryctolagus cuniculus is an exotic herbivorous mammal undergoing an active phase of geographical expansion in the arid ecosystems of Argentina. The Adaptive Flexibility Hypothesis states that populations at the range edge (new populations) will exhibit greater flexibility in the use of resources compared with populations located in the range core (older populations). The objective of this work was to compare the rabbit's use of spatial and trophic resources in relation to the establishment time of their populations. The sampling was carried out for 2 years (2017 and 2018) in sites with different establishment times for rabbit populations. Random sampling stratified by type of habitat was applied using 115 fixed strip transects of 1,000 m(2) laid out across the study areas. Fresh rabbit signs were recorded in each transect, and environmental and anthropic variables were measured. Our results show that the individuals from the range edge are more selective in the use of habitat than those from the range core. At the microhabitat level, we observed a pattern in the particular components of habitat use by rabbits mainly linked to food availability and proximity to water. From a trophic perspective, rabbits could show flexible adjustment to novel conditions and environments in the range edge. The variability in resource use by the European rabbit confirms its ecological flexibility, pivotal for their advance toward new environments in Argentina.
Historical account and current knowledge of the southernmost Chiropterofauna in the world: the Magellanic/Fuegian bats
(2023) Jaksic, Fabian M.; Martinez, David R.
A depauperate Chiropterofauna consisting of essentially three bat species (the year-round residents Histiotus magellanicus and Myotis chiloensis, and the apparently migratory Lasiurus varius), exists in the challenging cold and windy environment of the Magellanic/Fuegian region, which encompasses territories in Argentina and Chile, both continental and insular. Knowledge of that bat fauna benefitted from earlier explorers and naturalists visiting such southerly and isolated geographical confines, but still lacks a comprehensive scientific study, particularly in face of expected green-energy projects using aerogenerators known to cause bat fatalities elsewhere. Currently, there is a paucity of information on the fine-scale geographic distribution, local abundance, and migration patterns of those bats that needs to be remedied as soon as possible. Our review may aid orienting and focusing such a research program, which should hopefully be binational, on account of the artificial nature of the border between Argentina and Chile in Tierra del Fuego.
Historical ecology and current status of the European hare Lepus europaeus in South America: a new species in new countries
(2024) Jaksic, Fabian M.
With a historical perspective, I reviewed the peer-reviewed scientific literature (and some gray literature, as needed) on European hare (Lepus europaeus) in the six countries already invaded by it: Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. I covered the following topics: (a) Introduction, spread, and current distribution; (b) Life history, reproduction, and population dynamics; (c) Interactions with predators other than humans; (d) Interactions with scavengers; (e) Interactions with plants and herbivorous competitors; (f) Interactions with parasites and diseases; (g) Interactions with humans, including hunting, exports, and interference. Notoriously missing is the coverage of hare genetics and population dynamics and modeling. Another eyesore is the lack of an ecosystem approach to this invader, including not only biological aspects but the social-economic and cultural contexts that harbors it.
Invasive African clawed frog Xenopus laevis in southern South America: key factors and predictions
(2013) Lobos, Gabriel; Cattan, Pedro; Estades, Cristian; Jaksic, Fabian M.
The African clawed frog Xenopus laevis is one of the most widely distributed amphibians in the world. It has invaded an area of approximately 21,200 km(2) since its naturalization in Chile in the early 1980s. Currently, there is scant knowledge on the factors and processes underlying its distributional pattern. We constructed a bioclimatic niche model considering areas susceptible to be invaded (coarse model). At a local scale, we explored topographic, ecological, and anthropic variables, to identify which of these have the greatest predictive power for the expansion of this African species in southern South America. Not surprisingly, the projection of the distribution of Xenopus laevis laevis in southern Africa had the highest probabilities associated with the mediterranean area of the Cape region. From the habitat projection on southern South America, we predict high habitat suitability for this species in the mediterranean region of Chile. Nonetheless, the coastal desert of northern Chile, the Atlantic coasts of Argentina (32 degrees to 54 degrees S), Uruguay, southern Brazil, the north-central part of Argentina (22 degrees to 35 degrees S) and the central-southern region of Bolivia, are potentially suitable as well. At a local scale, we confirm that lentic aquatic environments, with slow drainage and murky waters, highly connected, human-disturbed, and part of an irrigation system of small streams and canals, account for the highest probabilities of successful establishment of X. laevis within the area of invasion. Based on our habitat suitability models, we expect the African clawed frog to invade farther north and farther south in Chile. We warn that the pet trade and subsequent release of African clawed frog to the wild pose a serious invasion risk to other countries of the southern cone of South America.
Long-term research in Bosque Fray Jorge National Park: Twenty years studying the role of biotic and abiotic factors in a Chilean semiarid scrubland
(2010) Gutierrez, Julio R.; Meserve, Peter L.; Kelt, Douglas A.; Engilis, Andrew, Jr.; Previtali, M. Andrea; Milstead, W. Bryan; Jaksic, Fabian M.
Since 1989, we have conducted a large-scale ecological experiment in semiarid thorn scrub of a national park in north-central Chile. Initially, we focused on the role of biotic interactions including predation, interspecific competition, and herbivory in small mammal and plant components of the community. We utilized a reductionist approach with replicated 0.56 ha fenced grids that selectively excluded vertebrate predators and/or larger small mammal herbivores such as the degu, Octodon degas. Although we detected small transitory effects of predator exclusions on degu survival and numbers, other species failed to show responses. Similarly, interspecific competition (i.e., degus with other small mammals) had no detectable numerical effects (although some behavioral responses occurred), and degu-exclusions had relatively small effects on various plant components. Modeling approaches indicate that abiotic factors play a determining role in the dynamics of principal small mammal species such as O. degas and the leaf-eared mouse (Phyllotis darwini). In turn, these are mainly related to aperiodic pulses of higher rainfall (usually during El Nino events) which trigger ephemeral plant growth; a food addition experiment. in 1997-2000 verified the importance of precipitation as a determinant of food availability. Since 2004, we have expanded long-term monitoring efforts to other important community components including birds and insects in order to understand effects of abiotic factors on them; we report some of the first results of comprehensive surveys on the former in this region. Finally, we recently shifted focus to documenting effects of exotic lagomorphs in the park. We installed additional treatments selectively excluding small mammals, lagomorphs, or both, from replicated grids in order to evaluate putative herbivore impacts. In conjunction with increased annual rainfall since 2000, we predict that introduced lagomorphs will have increasing impacts in this region, and that more frequent El Ninos in conjunction with global climatic change may lead to marked changes in community dynamics. The importance of long-term experimental studies is underscored by the fact that only now after 20 years of work are some patterns becoming evident.
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.
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.
Spatial and trophic niche of an assemblage of native and non-native herbivores of arid Argentina
(2022) Bobadilla, S. Yasmin; Dacar, Maria A.; Jaksic, Fabian M.; Ojeda, Ricardo A.; Cuevas, Maria F.
The coexistence of ecologically similar species is facilitated by differential use of resources along habitat, diet, and/or temporal niche axes. We used feces of non-native rabbit (Oryctolagus cuniculus), hare (Lepus europaeus), goat (Capra hircus), and the native plains viscacha (Lagostomus maximus) to compare the utilization of spatial and trophic resources in an arid ecosystem of Argentina. We expected herbivores to present differential responses in the use of at least one of the niche axes (habitat and/or trophic) associated with seasonal changes in resource availability and according to the origin of the species (native, non-native). We evaluated habitat use and selection through Chi-squared goodness-of-fit tests and Bonferroni confidence intervals, and factors shaping habitat selection (particular components of the habitat type) using generalized linear mixed-effects models. We analyzed the seasonal compositions of diets, breadth of trophic niches, and dietary overlaps. The assemblage of herbivores did not segregate markedly in spatial resource use, showing that hares and goats were more generalist than rabbits and plains viscacha in the utilization of different habitat types. Native and non-native herbivores overlapped markedly in the trophic niche dimension but segregated to some degree in the use of space during wet and dry seasons. The four herbivores shared a similar diet composition. Among dietary items, grasses contributed high percentages during the wet season. Under conditions of resource limitation (dry season), the native plains viscacha differed in feeding strategy from the non-native herbivores. These results deepen our understanding of likely underlying mechanisms that allow coexistence of native and non-native herbivores in an arid ecosystem.
The currently known distribution of the Austral Patagonian and Fuegian bats
(2024) Jaksic, Fabian M.; Martinez, David R.
We report the currently existing 31 records for Austral Patagonian and Fuegian bats spanning from 1866 to 2022. The Vespertilionidae were: Myotis chiloensis , Histiotus magellanicus , and Lasiurus varius , and the Molossidae was Tadarida brasiliensis . The former two species were recorded at forested sites along a swath that runs NW-SE for about 670 km from Torres del Paine in continental Magallanes to Tierra del Fuego and Navarino islands. Those forests were Coihue-Canelo (Nothofagus betuloides-Drymis winteri) , Coihue-Lenga (N. betuloides-N. pumilio ), Lenga ( N. pumilio-Maytenus disticha ), or & Ntilde;irre shrubland ( N. antarctica-Chiliotrichum difussum ). Only one record for each of Lasiurus varius , Histiotus magellanicus, and Tadarida brasiliensis were located in steppe environments of Festuca gracillima-Chiliotrichum difussum but were centered at human habitations and surrounding orchards or plantations, and their presence therein may be deemed accidental.
The ecological roles of the European rabbit in the Magellanic/Fuegian ecosystem of southernmost Chile
(2024) Mann-Vollrath, Francisca; Correa-Cuadros, Jennifer Paola; Avila-Thieme, M. Isidora; Duclos, Melanie; Jaksic, Fabian M.
The European rabbit has invaded numerous ecosystems worldwide, but rarely steppes. Since its various introduction attempts into the ecosystems of the Magallanes/Fuegian region, the rabbit has become a key player, interacting with species at different trophic levels and generating impacts on ecosystems. To better understand the role of the rabbit in steppe and scrub ecosystems, we characterised the food web in the Magallanes/Fuegian region to understand the identity of their interacting species, the mechanisms and complexities of their interactions to demonstrate that rabbit management may become more complex than just controlling a single species. Based on a bibliographic review and wildlife specialists' opinions, we built the Magellanic/Fuegian food web, evaluated their topological properties and performed a rabbit extinction simulation to assess the possible short-term ecological mechanisms operating in the community. We found that the network had 206 nodes (64% native, 13% exotic, and 22% mixed) and 535 links among nodes. The European rabbit was the most connected node of the food web, had the second largest dietary breadth, and ranked as the seventh prey item with more predators. A rabbit extinction simulation shows a possible release of herbivory pressure on plants, including that on several native plants (e.g., Gunnera tinctoria, Pratia repens, Gavilea lutea, Tetroncium magellanicus), and a possible release of competition for some herbivores that share resources with the rabbit (e.g., Ovis aries, Lama guanicoe, Bos taurus). Although rabbit predators have a broad and generalist diet, some such as the native Galicitis cuja, could face a 20% reduction in their trophic width and could intensify predation on alternative prey. These results show that the European rabbit is strongly embedded in the Magellanic/Fuegian ecosystem and linked to several native species. Therefore, rabbit management should consider ecosystem approaches accompanied by monitoring programs on native fauna and experimental pilot studies on native flora to conserve the Chilean Patagonia community.

Browsing by Author "Jaksic, Fabian M."

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