Differences in the genomic diversity, structure, and inbreeding patterns in wild and managed populations of Agave potatorum Zucc. used in the production of Tobalá mezcal in Southern Mexico.

Agave potatorum Zucc. locally known as Tobalá, is an important species for mezcal production. It is a perennial species that takes 10 to 15 years to reach reproductive age. Because of high demand of Tobalá mezcal and the slow maturation of the plants, its wild populations have been under intense anthropogenic pressure. The main objective of this study was to estimate the genome-wide diversity in A. potatorum and determine if the type of management has had any effect on its diversity, inbreeding and structure. We analyzed 174 individuals (105 wild, 42 cultivated and 27 from nurseries) from 34 sites with a reduced representation genomic method (ddRADseq), using 14,875 SNPs. The diversity measured as expected heterozygosity was higher in the nursery and wild plants than in cultivated samples. We did not find private alleles in the cultivated and nursery plants, which indicates that the individuals under management recently derived from wild populations, which was supported by higher gene flow estimated from wild populations to the managed plants. We found low but positive levels of inbreeding (FIS = 0.082), probably related to isolation of the populations. We detected low genetic differentiation among populations (FST = 0.0796), with positive and significant isolation by distance. The population genetic structure in the species seems to be related to elevation and ecology, with higher gene flow among populations in less fragmented areas. We detected an outlier locus related to the recognition of pollen, which is also relevant to self-incompatibility protein (SI). Due to seed harvest and long generation time, the loss of diversity in A. potatorum has been gradual and artificial selection and incipient management have not yet caused drastic differences between cultivated and wild plants. Also, we described an agroecological alternative to the uncontrolled extraction of wild individuals.

Changes in bee functional traits at community and intraspecific levels along an elevational gradient in a Mexical-type scrubland.

Understanding the causes of morphological variation of organisms along climatic gradients has been a central challenge in ecological research. We studied the variation of community weighted mean (CWM) and two functional diversity metrics (Rao-Q and functional richness) computed for five morphological traits of wild bees (Hymenoptera: Apoidea) related to thermal performance (namely body size, relative appendage length and hairiness), at community and interspecific levels, along an elevation gradient in a Mexical-type scrubland. At the community level we found a decreasing CWM of body size pattern with increasing elevation which is consistent with the species-energy theory (and contrary to Bergmann's rule). We also found an increase in the CWM of relative tibia length, which is contrary to Allen's rule. Additionally, we found an increase in the CWM of relative hair length towards high levels of elevation, which would be consistent with the hypothesis that hairiness plays an important role as thermal insulation. We found that functional diversity was larger at low elevations with respect to high elevation for body size and hair length, which could imply that highland communities were more sensitive towards environmental changes than lowland communities. Overall, at intraspecific level, most of species showed no pattern for any of the traits along the elevation gradient. Future research should provide further evidence on the possible behavioral or physiological mechanisms behind it.

Changes in the structure and composition of the 'Mexical' scrubland bee community along an elevational gradient.

'Mexical' scrubland is a sclerophyllous evergreen Mediterranean-like vegetation occurring in the leeward slopes of the main Mexican mountain ranges, under tropical climate. This biome occupies an elevational range approximately from 1900 to 2600 meters above sea level, which frequently is the upper-most part of the mountains range. This puts it at risk of extinction in a scenario of global warming in which an upward retraction of this type of vegetation is expected. The Mexical remains one of the least studied ecosystems in Mexico. For instance, nothing is known about pollinator fauna of this vegetation. Our main objective is to make a first insight into the taxonomic identity of the bee fauna that inhabits this biome, and to study how it is distributed along the elevational gradient that it occupies. Our results highlight that elevation gradient negatively affects bee species richness and that this relationship is strongly mediated by temperature. Bee abundance had no significant pattern along elevational gradient, but shows a significant relationship with flower density. Interestingly, and contrary to previous works, we obtained a different pattern for bee richness and bee abundance. Bee community composition changed strongly along elevation gradient, mainly in relation to temperature and flower density. In a global warming scenario, as temperatures increases, species with cold preferences, occupying the highest part of the elevation gradient, are likely to suffer negative consequences (even extinction risk), if they are not flexible enough to adjust their physiology and/or some life-story traits to warmer conditions. Species occupying mid and lower elevations are likely to extend their range of elevational distribution towards higher ranges. This will foreseeably cause a new composition of species and a new scenario of interactions, the adjustment of which still leaves many unknowns to solve.

Phenotypic structure of plant facilitation networks.

Identifying the plant traits that determine the outcome of facilitation interactions is essential to understand how communities are assembled and can be restored. Plant facilitation networks are phylogenetically structured but which traits are behind such a pattern is unknown. We sampled plant interactions in stressful ecosystems from south-eastern Spain to build seedling and adult facilitation networks. We collected 20 morphological and ecophysiological traits for 151 species involved in interactions between 879 nurse individuals benefiting 24 584 seedlings and adults. We detected a significant phenotypic signal in the seedling facilitation network that was maintained in the adult network, whereby functionally similar nurses tended to facilitate functionally similar species whose traits differ from those of their nurses. We provide empirical evidence to support a long-lasting theoretical postulate stating that facilitation networks are phenotypically structured. Trait matching through which nurse and facilitated species avoid phenotypic overlap, and consequently competition, is the main linkage rule shaping plant facilitation networks.

Tectono-stratigraphic basin evolution in the Tehuacán-Mixteca highlands, south western México.

The morphological evolution of the basins in the Sierra Madre del Sur (SMS), southern México is poorly understood. This work explains for the first time the geomorphological development of the tectonic, fluvially-interconnected SMS basins named San Juan Raya (SJRb) and Zapotitlán (ZAPb). The evolution of the SJRb and ZAPb are analysed within the context of the transformations of the well-studied Tehuacán basin (TEHb). A new interpretation of a series of tectonic features of the TEHb valley area is also presented. Published geological data and extensive field work provided the basis for our geomorphological and evolutionary interpretation of basin evolution of this part of Mesoamerica during the late Cenozoic. Stratigraphic and sedimentary records suggest that after the late Cretaceous-early Cenozoic orogeny the TEHb and ZAPb were closed basins, and that the TEHb graben system was activated during the Paleogene as a response to the dominant regional NW-SE trending faults. We propose that the ZAPb and SJRb formed sequentially during the Neogene as a result of new E-W, N-S and NE-SW faults. The continuation of the TEHb extension during the Oligocene widened its lowland area and allowed the formation of an extensive lake. No alluvial or fluvial records of this interval are found in the ZAPb and SJRb. No sedimentation rather than formation and subsequent erosion of such sediments is supported by the basin morphology and by the absence of re-worked alluvial deposits at the outlet area where both connect to the TEHb. By middle to late Miocene the TEHb lost its endorheic configuration, ending the lake-type deposition while new faults initiated the opening of the ZAPb. Intensive tectonics, alluvial deposition and the confinement of the Tehuacán lake to the north sector of this basin characterised the Pliocene. During the late Pliocene to the early Pleistocene the formation of the SJRb was initiated. Quaternary faulting related to basin extension along the north watershed of the SJRb and ZAPb is supported by independent data on the biogeography of the cactus Mammillaria pectinifera. We introduce the idea that the departure from the regional NW-SE fault alignment that formed the major Miocene basins to a more local E-W trend that formed Neogene-Quaternary basins was probably a response to the latest post-orogenic relaxation of the crust in the Mixteca terrane.

Incorporating phylogenetic metrics to microbial co-occurrence networks based on amplicon sequences to discern community assembly processes.

Co-occurrence network analysis based on amplicon sequences is increasingly used to study microbial communities. Patterns of co-existence or mutual exclusion between pairs of taxa are often interpreted as reflecting positive or negative biological interactions. However, other assembly processes can underlie these patterns, including species failure to reach distant areas (dispersal limitation) and tolerate local environmental conditions (habitat filtering). We provide a tool to quantify the relative contribution of community assembly processes to microbial co-occurrence patterns, which we applied to explore soil bacterial communities in two dry ecosystems. First, we sequenced a bacterial phylogenetic marker in soils collected across multiple plots. Second, we inferred co-occurrence networks to identify pairs of significantly associated taxa, either co-existing more (aggregated) or less often (segregated) than expected at random. Third, we assigned assembly processes to each pair: patterns explained based on spatial or environmental distance were ascribed to dispersal limitation (2%-4%) or habitat filtering (55%-77%), and the remaining to biological interactions. Finally, we calculated the phylogenetic distance between taxon pairs to test theoretical expectations on the linkages between phylogenetic patterns and assembly processes. Aggregated pairs were more closely related than segregated pairs. Furthermore, habitat-filtered aggregated pairs were closer relatives than those assigned to positive interactions, consistent with phylogenetic niche conservatism and cooperativism among distantly related taxa. Negative interactions resulted in equivocal phylogenetic signatures, probably because different competitive processes leave opposing signals. We show that microbial co-occurrence networks mainly reflect environmental tolerances and propose that incorporating measures of phylogenetic relatedness to networks might help elucidate ecologically meaningful patterns.

Plant facilitation through mycorrhizal symbiosis is stronger between distantly related plant species.

The tendency of closely related plant species to share natural enemies has been suggested to limit their co-occurrence and performance, but we lack a deep understanding on how mutualistic interactions such as the mycorrhizal symbiosis affect plant-plant interactions depending on the phylogenetic relatedness of the interacting plants. We hypothesise that the effect of the mycorrhizal symbiosis on plant-plant facilitative interactions depends on the phylogenetic distance between the nurse and facilitated plants. A recently published meta-analysis compiled the strength of plant facilitative interactions in the presence or absence (or reduced abundance) of mycorrhizal fungi. We use phylogenetically informed Bayesian linear models to test whether the effect size is influenced by the phylogenetic distance between the plant species involved in each plant facilitative interaction. Conspecific facilitative interactions are more strongly enhanced by mycorrhizal fungi than interactions between closely related species. In heterospecific interactions, the effect of the mycorrhizal symbiosis on plant facilitation increases with the phylogenetic distance between the nurse and facilitated plant species. Our result showing that the effect of mycorrhizal symbiosis on the facilitation interactions between plants depends on their phylogenetic relatedness provides new mechanisms to understand how facilitation is assembling ecological communities.

Nurse plants transfer more nitrogen to distantly related species.

Plant facilitative interactions enhance co-occurrence between distant relatives, partly due to limited overlap in resource requirements. We propose a different mechanism for the coexistence of distant relatives based on positive interactions of nutrient sharing. Nutrients move between plants following source-sink gradients driven by plant traits that allow these gradients to establish. Specifically, nitrogen (N) concentration gradients can arise from variation in leaf N content across plants species. As many ecologically relevant traits, we hypothesize that leaf N content is phylogenetically conserved and can result in N gradients promoting N transfer among distant relatives. In a Mexican desert community governed by facilitation, we labelled nurse plants (Mimosa luisana) with 15 N and measured its transfer to 14 other species in the community, spanning the range of phylogenetic distances to the nurse plant. Nurses established steeper N source-sink gradients with distant relatives, increasing 15 N transfer toward these species. Nutrient sharing may provide long-term benefits to facilitated plants and may be an overlooked mechanism maintaining coexistence and increasing the phylogenetic diversity of plant communities.

Are invasive plants more competitive than native conspecifics? Patterns vary with competitors.

Invasive plants are sometimes considered to be more competitive than their native conspecifics, according to the prediction that the invader reallocates resources from defense to growth due to liberation of natural enemies ['Evolution of Increased Competitive Ability' (EICA) hypothesis]. However, the differences in competitive ability may depend on the identity of competitors. In order to test the effects of competitors, Ageratina adenophora plants from both native and invasive ranges competed directly, and competed with native residents from both invasive (China) and native (Mexico) ranges respectively. Invasive A. adenophora plants were more competitive than their conspecifics from native populations when competing with natives from China (interspecific competition), but not when competing with natives from Mexico. Invasive A. adenophora plants also showed higher competitive ability when grown in high-density monoculture communities of plants from the same population (intrapopulation competition). In contrast, invasive A. adenophora plants showed lower competitive ability when competing with plants from native populations (intraspecific competition). Our results indicated that in the invasive range A. adenophora has evolved to effectively cope with co-occurring natives and high density environments, contributing to invasion success. Here, we showed the significant effects of competitors, which should be considered carefully when testing the EICA hypothesis.

Integrating novel chemical weapons and evolutionarily increased competitive ability in success of a tropical invader.

The evolution of increased competitive ability (EICA) hypothesis and the novel weapons hypothesis (NWH) are two non-mutually exclusive mechanisms for exotic plant invasions, but few studies have simultaneously tested these hypotheses. Here we aimed to integrate them in the context of Chromolaena odorata invasion. We conducted two common garden experiments in order to test the EICA hypothesis, and two laboratory experiments in order to test the NWH. In common conditions, C. odorata plants from the nonnative range were better competitors but not larger than plants from the native range, either with or without the experimental manipulation of consumers. Chromolaena odorata plants from the nonnative range were more poorly defended against aboveground herbivores but better defended against soil-borne enemies. Chromolaena odorata plants from the nonnative range produced more odoratin (Eupatorium) (a unique compound of C. odorata with both allelopathic and defensive activities) and elicited stronger allelopathic effects on species native to China, the nonnative range of the invader, than on natives of Mexico, the native range of the invader. Our results suggest that invasive plants may evolve increased competitive ability after being introduced by increasing the production of novel allelochemicals, potentially in response to naïve competitors and new enemy regimes.

Abiotic stress tolerance and competition-related traits underlie phylogenetic clustering in soil bacterial communities.

Soil bacteria typically coexist with close relatives generating widespread phylogenetic clustering. This has been ascribed to the abiotic filtering of organisms with shared ecological tolerances. Recent theoretical developments suggest that competition can also explain the phylogenetic similarity of coexisting organisms by excluding large low-competitive clades. We propose that combining the environmental patterns of traits associated with abiotic stress tolerances or competitive abilities with phylogeny and abundance data, can help discern between abiotic and biotic mechanisms underlying the coexistence of phylogenetically related bacteria. We applied this framework in a model system composed of interspersed habitats of highly contrasted productivity and comparatively dominated by biotic and abiotic processes, i.e. the plant patch-gap mosaic typical of drylands. We examined the distribution of 15 traits and 3290 bacterial taxa in 28 plots. Communities showed a marked functional response to the environment. Conserved traits related to environmental stress tolerance (e.g. desiccation, formation of resistant structures) were differentially selected in either habitat, while competition related traits (e.g. organic C consumption, formation of nutrient-scavenging structures) prevailed under high resource availability. Phylogenetic clustering was stronger in habitats dominated by biotic filtering, suggesting that competitive exclusion of large clades might underlie the ecological similarity of co-occurring soil bacteria.

Plant phylodiversity enhances soil microbial productivity in facilitation-driven communities.

The classical relationship between biodiversity and ecosystem functioning can be better understood when the phylogenetic component of biodiversity is considered. We linked plant phylodiversity and ecosystem functioning in a water-limited gypsum ecosystem driven by plant facilitation. We tested whether (1) plant facilitation relaxes the abiotic filter imposed by gypsum, allowing the establishment of non-gypsophyte plant species, and consequently increasing plant phylodiversity, and (2) plant phylodiversity influences soil microbial productivity. Our data revealed that the gypsophyte Ononis tridentata spatially determines a macrophytic mosaic, ameliorates the microenvironment, and maximizes plant richness and phylodiversity through facilitating non-gypsophyte species. Beyond the direct effect of the nurse plant on soil microbial biomass, activity, and respiration, the analyses suggest a direct effect of plant phylodiversity (MPD) on these general indicators of soil microbial productivity. Plant diversity (Shannon index) neither correlated with the mentioned parameters nor with specific indicators of C, N and P cycling. This is the first report of a relationship between producer phylodiversity and decomposer productivity, which supports phylogenetic diversity as a relevant player of the ecosystem functioning.

The evolution of increased competitive ability, innate competitive advantages, and novel biochemical weapons act in concert for a tropical invader.

There are many non-mutually exclusive mechanisms for exotic invasions but few studies have concurrently tested more than one hypothesis for the same species. Here, we tested the evolution of increased competitive ability (EICA) hypothesis in two common garden experiments in which Chromolaena odorata plants originating from native and nonnative ranges were grown in competition with natives from each range, and the novel weapons hypothesis in laboratory experiments with leachates from C. odorata. Compared with conspecifics originating from the native range, C. odorata plants from the nonnative range were stronger competitors at high nutrient concentrations in the nonnative range in China and experienced far more herbivore damage in the native range in Mexico. In both China and Mexico, C. odorata was more suppressed by species native to Mexico than by species native to China. Species native to China were much more inhibited by leaf extracts from C. odorata than species from Mexico, and this difference in allelopathic effects may provide a possible explanation for the biogeographic differences in competitive ability. Our results indicate that EICA, innate competitive advantages, and novel biochemical weapons may act in concert to promote invasion by C. odorata, and emphasize the importance of exploring multiple, non-mutually exclusive mechanisms for invasions.

Trait divergence and indirect interactions allow facilitation of congeneric species.

BACKGROUND: Plant facilitation occurs when the presence of a plant (i.e. a nurse plant) modifies the environment, making it more favourable for the establishment and survival of other species (i.e. facilitated plants), which can germinate and grow nearby. Facilitative associations can be maintained or turned into competition as the facilitated seedling grows. According to the competition-relatedness hypothesis that suggests that closely related species tend to compete more, facilitation turns into competition between phylogenetically close species. However, some examples of facilitation between congeneric species, which are supposed to be closely related species, have been found in nature. SCOPE: In this work, some examples of congeneric facilitation and subsequent coexistence are reviewed and an attempt is made to explain those exceptions to the competition-relatedness hypothesis. CONCLUSIONS: Two mechanisms are proposed that can switch the facilitation-competition balance: trait divergence and indirect interactions. When traits have diverged within the genus, the niche overlap is reduced and competition relaxed, thus allowing the coexistence of congeneric species. The presence of third interplayers (mycorrhizal fungi, seed dispersers, pollinators or pathogens) participating in the interaction between plants can alleviate the competition or enhance the reproduction and allow the coexistence of species that could not coexist in their absence.

Phylogenetic relatedness as a tool in restoration ecology: a meta-analysis.

Biotic interactions assembling plant communities can be positive (facilitation) or negative (competition) and operate simultaneously. Facilitative interactions and posterior competition are among the mechanisms triggering succession, thus representing a good scenario for ecological restoration. As distantly related species tend to have different phenotypes, and therefore different ecological requirements, they can coexist, maximizing facilitation and minimizing competition. We suggest including phylogenetic relatedness together with phenotypic information as a predictor for the net effects of the balance between facilitation and competition in nurse-based restoration experiments. We quantify, by means of a Bayesian meta-analysis of nurse-based restoration experiments performed worldwide, the importance of phylogenetic relatedness and life-form disparity in the survival, growth and density of facilitated plants. We find that the more similar the life forms of neighbouring plants are the greater the positive effect of phylogenetic distance is on survival and density. This result suggests that other characteristics beyond life form are also contained in the phylogeny, and the larger the phylogenetic distance, the less is the niche overlap, and therefore the less is the competition. As a general rule, we can maximize the success of the nurse-based practices by increasing life-form disparity and phylogenetic distances between the neighbour and the facilitated plant.

Volatile chemicals from leaf litter are associated with invasiveness of a neotropical weed in Asia.

Some invasive plant species appear to strongly suppress neighbors in their nonnative ranges but much less so in their native range. We found that in the field in its native range in Mexico, the presence of Ageratina adenophora, an aggressive Neotropical invader, was correlated with higher plant species richness than found in surrounding plant communities where this species was absent, suggesting facilitation. However, in two nonnative ranges, China and India, A. adenophora canopies were correlated with much lower species richness than the surrounding communities, suggesting inhibition. Volatile organic compound (VOC) signals may contribute to this striking biogeographical difference and the invasive success of A. adenophora. In controlled experiments volatiles from A. adenophora litter caused higher mortality of species native to India and China, but not of species native to Mexico. The effects of A. adenophora VOCs on seedling germination and growth did not differ between species from the native range and species from the nonnative ranges of the invader. Litter from A. adenophora plants from nonnative populations also produced VOCs that differed quantitatively in the concentrations of some chemicals than litter from native populations, but there were no chemicals unique to one region. Biogeographic differences in the concentrations of some volatile compounds between ranges suggest that A. adenophora may be experiencing selection on biochemical composition in its nonnative ranges.

Species-specificity of nurse plants for the establishment, survivorship, and growth of a columnar cactus.

PREMISE OF THE STUDY: Seedling establishment and early survivorship are crucial steps for the regeneration of plant populations because both have long-lasting effects on plant population dynamics. For species recruiting through facilitation, species-specific facilitative effects might affect early fitness, an overlooked aspect in studies of facilitation considering groups of nurse species. • METHODS: We experimentally evaluated the roles of 10 nurse species and open space on the early performance of the columnar cactus Neobuxbaumia mezcalaensis. We measured establishment, survivorship, and growth of individuals over 3 years. Moreover, to study an extended period of the ontogeny of the interaction between this cactus and its nurse plants, we also monitored survivorship and growth rates of individuals between 3 to 12 cm tall during a 3-year period. • KEY RESULTS: Neobuxbaumia mezcalaensis performance varied significantly among nurse species, and only six yielded positive effects on early fitness. Densely canopied plants were the best nurses for this cactus. However, even among densely canopied species, some produced negative effects on the early fitness of N. mezcalaensis, indicating that similar nurse plants may elicit either facilitative or interference effects on beneficiary species. • CONCLUSIONS: Our results emphasize the importance of species-specific facilitative interactions in the crucial early stages in the life cycle of N. mezcalaensis and how different nurse species modify the effect of seed-rain and contribute significantly to the population dynamics of the species.

Neighborhood phylodiversity affects plant performance.

Facilitation and competition are ecological interactions that are crucial for the organization of plant communities. Facilitative interactions tend to occur among distantly related species, while the strength of competition tends to decrease with phylogenetic distance. The balance between both types of interactions will ultimately determine the specific composition of multispecies associations. Although multispecies patches are the arena in which coexistence develops among different phylogenetic groups within communities, the specific processes that occur across life stages have not been explored. Here we study how different species, in composing discrete patches in central Mexico, exert competitive or facilitative effects on seeds and seedlings. We relate these interactions to phylogenetic relationships among nurse species and beneficiary species, and among members of the patches. Survivorship and growth rates of the columnar cactus Neobuxbaumia mezcalaensis were highly positively related to increasing phylogenetic distance to different nurse species, to the presence of related species in patches, and to mean phylogenetic distances to the rest of the species in the patch. Each of these three elements influenced N. mezcalaensis differently, with different nurse species varying substantially in their early effects on emergence, and the nearest relatives and species composition of patches varying in their late effects on survival and growth. Our results emphasize that evolutionary relationships among co-occurring species in vegetation clumps exert direct and indirect effects on plants, affecting individual performance and species coexistence.

Functional and evolutionary correlations of steep leaf angles in the mexical shrubland.

In the evergreen shrubland vegetation of Mexico (mexical), most of the species are sclerophyllous woody plants with steep leaf angles. This architectural pattern has been interpreted as a strategy to cope with water shortages and high radiation. However, the current association between evergreenness and steep leaf angles across mexical plant species could be the result of an adaptive association achieved through correlated evolutionary change between both traits or, alternatively, may be the result of common evolutionary ancestry. In this study, we quantified leaf angle in 28 dominant species under a phylogenetic framework and evaluated the functional implications of the observed range of leaf angles in terms of leaf temperature, water potentials and transpiration by combining manipulative experiments restraining leaves horizontally with microclimatic and stomatal conductance measurements in selected species and energy balance calculations. Horizontally restrained leaves exhibited reduced water potentials and stomatal conductances, and significantly increased temperatures and transpiration rates. Steeply inclined leaves operated near air temperatures and could sustain relatively high stomatal conductances during the dry season since they were associated with low transpiration rates. Phylogenetic analyses showed that steep leaf angles evolved in a correlated fashion in evergreen species. The functional consequences of leaf angle together with the phylogenetic analysis indicate the adaptive nature of this trait which allows the evergreen species to cope with arid conditions and therefore to persist within the mexical community.

Don't diss integration: a comment on Ricklefs's disintegrating communities.

Ricklefs's recent call to investigate ecological processes at large scales helps focus ecologists' attention on an undoubtedly important topic. However, we believe that some of his accompanying arguments for the primacy of such work and, in particular, for the need to "disintegrate" the local community concept are flawed. We revisit Ricklefs's main tenets and demonstrate that research on local communities is a vital part of understanding processes and diversity across a range of spatial and temporal scales. The integration of research across spatial scales expands our horizons and understanding of ecology and evolution, and this should not be unnecessarily constrained to one extreme or the other.