Functional diversity and spatial association analyses at different spatial scales reveal no changes in community assembly processes along an aridity gradient in the Atacama Desert.

The structuring of plant assemblages along environmental gradients is typically explained by shifts from competition (limiting similarity) to environmental filtering as the environment becomes more stressful. However, facilitation, weaker-competitor exclusion, environmental heterogeneity, and the colonization-competition tradeoff can also structure plant assemblages along gradients. These assembly processes act on different plant traits and organs, and their prevalence varies with respect to the spatial scale. Using patterns of functional diversity, coupled with patterns of species association at two spatial scales, here we discern the assembly processes that structure shrub communities in four localities along an aridity gradient of the Atacama Desert. At each site, we calculated functional dispersion indexes for above- and below-ground traits, and patterns of species association at a patch and neighborhood scale. Our results revealed that at the patch scale in intermediate levels of aridity, the dominant assembly process was within-site environmental heterogeneity. At the neighborhood scale, communities are assembled mainly through random processes. Nonetheless, in some communities, the dominant assembly process was competition via limiting similarity or exclusion of the weaker competitor, and these did not change along the gradient. Together, these results reveal that environmental heterogeneity and competition are the main drivers of plant community assembly in a hyper-arid environment.

Widespread synchronous decline of Mediterranean-type forest driven by accelerated aridity.

Large-scale, abrupt ecosystem change in direct response to climate extremes is a critical but poorly documented phenomenon1. Yet, recent increases in climate-induced tree mortality raise concern that some forest ecosystems are on the brink of collapse across wide environmental gradients2,3. Here we assessed climatic and productivity trends across the world's five Mediterranean forest ecosystems from 2000 to 2021 and detected a large-scale, abrupt forest browning and productivity decline in Chile (>90% of the forest in <100 days), responding to a sustained, acute drought. The extreme dry and warm conditions in Chile, unprecedented in the recent history of all Mediterranean-type ecosystems, are akin to those projected to arise in the second half of the century4. Long-term recovery of this forest is uncertain given an ongoing decline in regional water balance. This dramatic plummet of forest productivity may be a spyglass to the future for other Mediterranean ecosystems.

Biodiversity in Times of COVID-19 and its Relationship with the Socio-Economic and Health Context: A Look from the Digital Media.

The COVID-19 pandemic has caused a pause in people's activities and a socio-economic crisis worldwide due to confinement. This situation is an unprecedented opportunity to understand how these changes may impact biodiversity and its conservation, as well as to study human-nature interaction. Biodiversity plays an essential role in conservation and economic activities, and in countries with greater inequality and low gross domestic product (GDP), biodiversity could have a low priority. Moreover, how biodiversity is prioritized in a society impacts how the citizens view it, and digital news tends to shape biodiversity narratives. The aim of this work was to determine the main trends in biodiversity-related news categories during the COVID-19 pandemic in countries with terrestrial and marine hotspots and relate them to the socioeconomic and public health context of each country. For this, we searched for news on biodiversity and Covid-19 in the first 6 months of the pandemic and related them to GDP, Gini-index, deaths, and infections by Covid-19. Results showed that conservation, public policies, and use of natural resources stood out as the main news categories across countries, with a positive narrative and mostly related to terrestrial rather than marine environments. On the other hand, the socio-economic and public health characteristics of each country had an influence on which aspect of the biodiversity was reflected in the media. For example, countries with greater inequality were associated with tourism news, additionally, countries with low GDP, high cases, and deaths by Covid-19 were associated with news about cultural diversity. In contrast, countries with high GDP and low inequality were associated with news about zoonosis, research and development, public policies, and alien and invasive species.

Isolation and cross-amplification of the first set of polymorphic microsatellite markers of two high-Andean cushion plants.

In the southern Andes mountains (27-39◦S) Azorella madreporica and Laretia acaulis, two Apiaceae cushion plant species commonly known as yaretas, conform a well-established altitudinal vegetation belt along the lower Andean zone. These species have been considered as fundamental components of several ecological dynamics within their communities; however, high mountain ecosystems are increasingly threatened worldwide by natural and anthropogenic pressures and the southern Andes are not the exception. Recognizing that genetic information is crucial for the success of any conservation or restoration initiative inwild populations, we developed and cross-amplified 28 specifically designed microsatellite markers (14 in A. madreporica and 14 in L. acaulis), and also tested the cross amplification of 25 markers from the related species Azorella selago. In a region which is particularly vulnerable to global change trends, this new polymorphic microsatellite loci will be useful in the study of the genetic diversity of these high-mountain cushion plants, which are pivotal in the structuring of their native ecosystems.

Landscape connectivity among remnant populations of guanaco (Lama guanicoe Müller, 1776) in an arid region of Chile impacted by global change.

Connectivity between populations plays a key role in the long-term persistence of species in fragmented habitats. This is of particular concern for biodiversity preservation in drylands, since water limited landscapes are typically characterized by little suitable habitat cover, high habitat fragmentation, harsh matrices, and are being rapidly degraded at a global scale. In this study, we modelled landscape connectivity between 11 guanaco Lama guanicoe populations in Chile's arid Norte Chico, a region that supports the last remnant coastal populations of this emblematic herbivore indigenous to South America. We produced a habitat suitability model to derive a regional surface resistance map, and used circuit theory to map functional connectivity, investigate the relative isolation between populations, and identify those that contribute most to the patch connectivity network. Predicted suitable habitat for L. guanicoe represented about 25% of the study region (i.e., 29,173 km2) and was heterogeneously distributed along a continuous stretch along the Andes, and discontinuous patches along the coast. As a result, we found that high connectivity current flows in the mid and high Andes formed a wide, continuous connectivity corridor, enabling connectivity between all high Andean populations. Coastal populations, in contrast, were more isolated. These groups demonstrate no inter-population connectivity between themselves, only with higher altitude populations, and for two of them, animal movement was linked to the effectiveness of wildlife crossings along the Pan-American highway. Our results indicate that functional connectivity is an issue of concern for L. guanicoe in Chile's Norte Chico, implying that future conservation and management plans should emphasize strategies aimed at conserving functional connectivity between coastal and Andean populations, as well as the protection of habitat patches likely to act as stepping stones within the connectivity network.

Conspecific plants are better 'nurses' than rocks: consistent results revealing intraspecific facilitation as a process that promotes establishment in a hyper-arid environment.

Harsh environmental conditions in arid ecosystems limit seedling recruitment to microhabitats under nurse structures, such as shrubs or rocks. These structures, however, do not necessarily afford the same benefits to plants because nurse rocks provide only physical nurse effects, whereas nurse plants can provide both physical and biological nurse effects. Nevertheless, if the nurse plant is a conspecific, the benefits it provides may be outweighed by higher mortality due to negative density-dependent processes; consequently, negative density-dependence is expected to limit plants from acting as nurses to their own seedlings. The degree to which an abiotic nurse may be more beneficial than a conspecific one remains largely unexplored. Here, we examine the role and elucidate the mechanisms by which conspecific plants and rocks promote plant establishment in a hyper-arid desert. For 4 years, we examined establishment patterns of Myrcianthes coquimbensis (Myrtaceae), a threatened desert shrub that recruits solely in rock cavities and under conspecific shrubs. Specifically, we characterized these microhabitats, as well as open interspaces for comparison, and conducted germination, seed removal and seedling survival experiments. Our results revealed that conspecific shrubs and nurse rocks modified environmental conditions in similar ways; soil and air temperatures were lower, and water availability was higher than in open interspaces. We found no evidence on negative density-dependent recruitment: seed removal was lowest and seedling emergence highest under conspecific plants, moreover seedling survival probabilities were similar in rock cavities and under conspecific plants. We conclude that the probability of establishment was highest under conspecific plants than in other microhabitats, contrasting what is expected under the Janzen-Connell recruitment model. We suggest that for species living in stressful environments, population regulation may be a function of positive density-dependence and intraspecific facilitation may be a process that promotes the persistence of some plant species within a community.

The importance of scale-dependent ravine characteristics on breeding-site selection by the Burrowing Parrot, Cyanoliseus patagonus.

In birds, the environmental variables and intrinsic characteristics of the nest have important fitness consequences through its influence on the selection of nesting sites. However, the extent to which these variables interact with variables that operate at the landscape scale, and whether there is a hierarchy among the different scales that influences nest-site selection, is unknown. This interaction could be crucial in burrowing birds, which depend heavily on the availability of suitable nesting locations. One representative of this group is the burrowing parrot, Cyanoliseus patagonus that breeds on specific ravines and forms large breeding colonies. At a particular site, breeding aggregations require the concentration of adequate environmental elements for cavity nesting, which are provided by within ravine characteristics. Therefore, intrinsic ravine characteristics should be more important in determining nest site selection compared to landscape level characteristics. Here, we assess this hypothesis by comparing the importance of ravine characteristics operating at different scales on nest-site selection and their interrelation with reproductive success. We quantified 12 characteristics of 105 ravines in their reproductive habitat. For each ravine we quantified morphological variables, distance to resources and disturbance as well as nest number and egg production in order to compare selected and non-selected ravines and determine the interrelationship among variables in explaining ravine differences. In addition, the number of nests and egg production for each reproductive ravine was related to ravine characteristics to assess their relation to reproductive success. We found significant differences between non-reproductive and reproductive ravines in both intrinsic and extrinsic characteristics. The multidimensional environmental gradient of variation between ravines, however, shows that differences are mainly related to intrinsic morphological characteristics followed by extrinsic variables associated to human disturbance. Likewise, within reproductive ravines, intrinsic characteristics are more strongly related to the number of nests. The probability of producing eggs, however, was related only to distance to roads and human settlements. Patterns suggest that C. patagonus mainly selects nesting sites based on intrinsic morphological characteristics of ravines. Scale differences in the importance of ravine characteristics could be a consequence of the particular orography of the breeding habitat. The arrangement of resources is associated to the location of the gullies rather than to individual ravines, determining the spatial availability and disposition of resources and disturbances. Thus, nest selection is influenced by intrinsic characteristics that maximize the fitness of individuals. Scaling in nest-selection is discussed under an optimality approach that partitions patch selection based on foraging theory.

Fruit Size Determines the Role of Three Scatter-Hoarding Rodents as Dispersers or Seed Predators of a Fleshy-Fruited Atacama Desert Shrub.

Scatter-hoarding rodents can act as both predators and dispersers for many large-seeded plants because they cache seeds for future use, but occasionally forget them in sites with high survival and establishment probabilities. The most important fruit or seed trait influencing rodent foraging behavior is seed size; rodents prefer large seeds because they have higher nutritional content, but this preference can be counterbalanced by the higher costs of handling larger seeds. We designed a cafeteria experiment to assess whether fruit and seed size of Myrcianthes coquimbensis, an endangered desert shrub, influence the decision-making process during foraging by three species of scatter-hoarding rodents differing in body size: Abrothrix olivaceus, Phyllotis darwini and Octodon degus. We found that the size of fruits and seeds influenced foraging behavior in the three rodent species; the probability of a fruit being harvested and hoarded was higher for larger fruits than for smaller ones. Patterns of fruit size preference were not affected by rodent size; all species were able to hoard fruits within the entire range of sizes offered. Finally, fruit and seed size had no effect on the probability of seed predation, rodents typically ate only the fleshy pulp of the fruits offered and discarded whole, intact seeds. In conclusion, our results reveal that larger M. coquimbensis fruits have higher probabilities of being harvested, and ultimately of its seeds being hoarded and dispersed by scatter-hoarding rodents. As this plant has no other dispersers, rodents play an important role in its recruitment dynamics.

Enhanced facilitation at the extreme end of the aridity gradient in the Atacama Desert: a community-level approach.

Plant facilitation is now recognized as an important process in severe environments. However, there is still no agreement on how facilitation changes as conditions become increasingly severe. The classic stress gradient hypothesis (SGH) predicts a monotonic increase in facilitation, which rises in frequency as conditions approach the extreme end of the environmental gradient. However, few studies have evaluated the validity of the SGH at the community level, the level at which it was formulated. Moreover, few studies have tested the SGH at either extreme of the gradient, and very few have excluded the effect of livestock on community response to stress. In line with the SGH, we hypothesized that several spatial pattern summary statistics would change monotonically from the least to the most arid sites, indicating increasingly aggregated patterns. In this study, we performed an evaluation of the SGH both within communities of shrub species and across a large portion of the Atacama Desert, and we isolated the abiotic component of the SGH. Our environmental gradient covered an extreme aridity gradient (< 20-130 mm annual precipitation). To perform point pattern analysis, we established 13 sites with environmental conditions representing four distinct levels of this gradient. Further, we conducted species co-occurrence analyses at 19 sites along the gradient. Both sets of analyses showed stronger positive spatial associations among plants at the most extreme end of the gradient. This was true regardless of whether we included all individuals, only small individuals located around large ones, or individuals in species pairs. Moreover, species tended to show greater co-occurrence as environmental severity increased. This increase in aggregation in the plant community seems to correlate with an increase in the strength of positive interspecific interactions, rather than greater clustering within each species. These monotonic increases in species co-occurrence and spatial association in more severe environments are consistent with some of the predictions of SGH, and collectively these results suggest that as the climate becomes more arid, positive species pairs interactions tend to be prevalent in the community.

Contrasting responses to water-deficit among Encelia canescens populations distributed along an aridity gradient.

PREMISE OF THE STUDY: Drought is the most limiting factor for plant growth and recruitment in arid environments. For widespread species, however, plant responses to drought can vary across populations because environmental conditions can vary along the range of the species. Here, we assessed whether plants of Encelia canescens from different populations along an aridity gradient in the Atacama Desert respond differently to water-deficit conditions. METHODS: We conducted a common-garden experiment using plants grown from seeds from three populations distributed along an aridity gradient to test for differences in relative growth rate (RGR), biomass, root to shoot ratios, and photosynthesis between watered and water-deficit plants. Additionally, we examined the relationship between root to shoot ratios with RGR and total plant biomass along the gradient. KEY RESULTS: Water deficit affected root to shoot ratios, biomass, and RGR, but not photosynthesis. Populations varied in RGR and biomass; plants from the most arid population had higher RGRs, but lower biomass than those from the least arid population. In watered conditions, root to shoot ratios did not vary with RGR or biomass. Conversely, with the water deficit, root to shoot ratios were negatively and positively related to biomass and RGR, respectively. CONCLUSIONS: Response to water deficit differed among E. canescens populations; plants from the lowest rainfall environment adjusted root to shoot ratios, which may have allowed for equal biomass production across treatments. In contrast, plants from the wettest population did not adjust root to shoot ratios, but were reduced in biomass. These morphological and physiological changes to water availability showed that populations can use different strategies to cope with water deficit.

Bottom-up control of consumers leads to top-down indirect facilitation of invasive annual herbs in semiarid Chile.

The abundance of exotic plants is thought to be limited by competition with resident species (including plants and generalist herbivores). In contrast, observations in semiarid Chile suggest that a native generalist rodent, the degu (Octodon degus), may be facilitating the expansion of exotic annual plants. We tested this hypothesis with a 20-year data set from a World Biosphere Reserve in mediterranean Chile. In this semiarid environment, rainfall varies annually and dramatically influences cover by both native and exotic annual plants; degu population density affects the composition and cover of exotic and native annual plants. In low-rainfall years, cover of both native and exotic herbs is extremely low. Higher levels of precipitation result in proportional increases in cover of all annual plants (exotic and native species), leading in turn to increases in degu population densities, at which point they impact native herbs in proportion to their greater cover, indirectly favoring the expansion of exotic plants. We propose that bottom-up control of consumers at our site results in top-down indirect facilitation of invasive annual herbs, and that this pattern may be general to other semiarid ecosystems.

Hydraulic lift through transpiration suppression in shrubs from two arid ecosystems: patterns and control mechanisms.

Hydraulic lift (HL) is the passive movement of water through the roots from deep wet to dry shallow soil layers when stomata are closed. HL has been shown in different ecosystems and species, and it depends on plant physiology and soil properties. In this study we explored HL patterns in several arid land shrubs, and developed a simple model to simulate the temporal evolution and magnitude of HL during a soil drying cycle under relatively stable climatic conditions. This model was then used to evaluate the influence of soil texture on the quantity of water lifted by shrubs in different soil types. We conducted transpiration suppression experiments during spring 2005 in Chile and spring 2008 in Spain on five shrub species that performed HL, Flourensia thurifera, Senna cumingii and Pleocarphus revolutus (Chile), Retama sphaerocarpa and Artemisia barrelieri (Spain). Shrubs were covered with a black, opaque plastic fabric for a period of 48-72 h, and soil water potential was recorded at different depths under the shrubs. While the shrubs remained covered, water potential continuously increased in shallow soil layers until the cover was removed. The model output indicated that the amount of water lifted by shrubs is heavily dependent on soil texture, as shrubs growing in loamy soils redistributed up to 3.6 times more water than shrubs growing on sandy soils. This could be an important consideration for species growing in soils with different textures, as their ability to perform HL would be context dependent.

Cold resistance mechanisms in high desert Andean plants.

Freezing tolerance and freezing avoidance were studied, during the growing season, in plant species from two different elevations (3200 m and 3700 m) in a desert region of the high Andes (29° 45'S, 69° 59'W) in order to determine whether there was a relationship between plant height and cold resistance mechanisms. Freezing injury and supercooling capacity were determined in plants of different height, from ground-level (<20 cm tall) to tall shrubs (27-90 cm). All ground-level plants showed freezing tolerance as the main mechanism for resistance to freezing temperatures. Tall shrubs avoided freezing temperatures, mainly through supercooling. Supercooling was only present in plants occupying the lower elevation (i.e., 3200 m). Both avoidance and tolerance mechanisms are present in a single genus (i.e., Adesmia).