Browsing by Author "Armesto, Juan"

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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.
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    Disturbance and the (surprising?) role of ecosystem engineering in explaining spatial patterns of non-native plant establishment
    (2021) Root-Bernstein, Meredith; Munoz, Cesar; Armesto, Juan
    Different conceptions of disturbance differ in the degree to which they appeal to mechanisms that are general and equivalent, or species-, functional group-, or interaction-specific. Some concepts of disturbance, for example, predict that soil disturbances and herbivory have identical impacts on species richness via identical mechanisms (reduction in biomass and in competition). An alternative hypothesis is that the specific traits of disturbance agents (small mammals) and plants differentially affect the richness or abundance of different plant groups. We tested these hypotheses on a degu (Octodon degus) colony in central Chile. We ask whether native and non-native forbs respond differently to degu bioturbation on runways versus herbivory on grazing lawns. We ask whether this can explain the increase in non-native plants on degu colonies. We found that biopedturbation did not explain the locations of non-native plants. We did not find direct evidence of grazing increasing non-native herbs either, but a grazing effect appears to be mediated by grass, which is the dominant cover. Further, we provide supplementary evidence to support our interpretation that a key mechanism of non-native spread is the formation of dry soil conditions on grazing lawns. Thus, ecosystem engineering (alteration of soil qualities) may be an outcome of disturbances, in which each interacts with specific plant traits, to create the observed pattern of non-native spread in the colony. Based on these results, we propose to extend Jentsch and White (Ecology, 100, 2019, e02734) concept of combined pulse/ disturbance events to the long-term process duality of ecosystem engineering/ disturbance.
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    Genetic divergence in the endangeredfrog Insuetophrynus acarpicus (Anura: Leptodactylidae)
    (2006) Mendez, Marco A.; Torres-Perez, Fernando; Correa, Claudio; Soto, Eduardo R.; Nunez, Jose J.; Veloso, Alberto; Armesto, Juan
    Insuetophrynus acarpicus is a poorly known frog restricted to the temperate forests of the coastal range of Chile (39 degrees 25' S, 73 degrees 10' W). Until recently, this species was known only from one type locality since its original description in 1970. However, in 2002 two new localities were reported, extending its distribution range to about 40 km(2). In order to evaluate genetic divergence, provide a preliminary evaluation of the genetic diversity of this species and the phylogenetic relationships among individuals from the three known populations, we analyzed the nucleotide variation of a fragment of the mitochondrial gene cytochrome b. We sampled just two or four individuals per population of this endangered frog. We found a low nucleotide divergence among populations suggesting a genetic homogeneity across the entire range. This highlights the need for further studies to define the conservation status of this endangered frog.
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    Wildfire management in Mediterranean-type regions: paradigm change needed
    (2020) Moreira, Francisco; Ascoli, Davide; Safford, Hugh; Adams, Mark A.; Moreno, Jose M.; Pereira, Jose M. C.; Catry, Filipe X.; Armesto, Juan; Bond, William; Gonzalez, Mauro E.; Curt, Thomas; Koutsias, Nikos; McCaw, Lachlan; Price, Owen; Pausas, Juli G.; Rigolot, Eric; Stephens, Scott; Tavsanoglu, Cagatay; Vallejo, V. Ramon; Van Wilgen, Brian W.; Xanthopoulos, Gavriil; Fernandes, Paulo M.
    During the last decades, climate and land use changes led to an increased prevalence of megafires in Mediterranean-type climate regions (MCRs). Here, we argue that current wildfire management policies in MCRs are destined to fail. Focused on fire suppression, these policies largely ignore ongoing climate warming and landscape-scale buildup of fuels. The result is a 'firefighting trap' that contributes to ongoing fuel accumulation precluding suppression under extreme fire weather, and resulting in more severe and larger fires. We believe that a 'business as usual' approach to wildfire in MCRs will not solve the fire problem, and recommend that policy and expenditures be rebalanced between suppression and mitigation of the negative impacts of fire. This requires a paradigm shift: policy effectiveness should not be primarily measured as a function of area burned (as it usually is), but rather as a function of avoided socio-ecological damage and loss.