Coexistence and competitive exclusion in mutualism

The competitive exclusion principle is fundamental to understanding coexistence. Well-established theories predict the conditions for coexistence in consumer-resource interactions. Given that species often compete for commodities offered by mutualists, competitive exclusion theory should also be critical to understanding how mutualisms function. We explicitly apply the competitive exclusion principle to mutualism and derive a rule analogous to Tilman's R* rule for exploitative competition. Coexistence is impossible when competitors compete solely for a shared partner-provided commodity because superior competitors deplete that commodity sufficiently to exclude inferior competitors. We then investigate how competition between two guild members for a partner-provided commodity and a resource external to the mutualism affects competitor coexistence. There are three key results. First, coexistence is possible via partitioning of a partner-provided commodity and another resource. Second, unlike in classic R* Theory, competitive outcomes are influenced both by species' abilities to obtain commodities and their mutualisms with the shared commodity-providing partner, which can indirectly alleviate competitors' commodity limitation. Third, the outcome of competition has important consequences for the commodity-providing partner, which depend on the type of mutualism and the competitive abilities of competing mutualists. This theory provides a novel framework for investigating how competitors for mutualistic commodities coexist in nature.Science Foundation Arizona Grant [BSP0528-13]; ETH Zurich Center for Adaptation to a Changing EnvironmentThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

An Herbivore’s Thermal Tolerance is Higher Than That of the Ant Defenders in a Desert Protection Mutualism

In North American deserts, many species of cactus attract ants to their extrafloral nectaries; the ants actively defend the food source, and hence the plant, against herbivores. In thermally extreme environments, however, networks of positive and negative interactions like these are likely to be sensitive to the thermal limitations of each of the interacting species. We compared the thermal tolerance of a common phytophagous cactus bug, Narnia pallidicornis (Hemiptera: Coreidae), to that of the ants that defend the cactus Ferocactus wislizeni in the Sonoran Desert, USA. We used flow-through respirometry to experimentally determine the thermal limit of the herbivore and compared this to the thermal limits of the ant defenders, determined previously. In the field, we recorded herbivore frequency (proportion of plants with N. pallidicornis) and abundance (the number of N. pallidicornis per plant) in relation to ambient temperature, ant species presence and identity, and fruit production. We show that N. pallidicornis has a higher thermal tolerance than the four most common ant mutualists, and in the laboratory can survive very high temperatures, up to 43°C. Herbivore frequency and abundance in the field were not related to the daily high temperatures observed. Plants that were not defended by ants were occupied by more N. pallidicornis, although they showed no reduction in fruit set. Therefore, herbivory is likely to continue on fishhook barrel cacti even at high temperatures, especially those temperatures beyond the thermal tolerance of the ant defenders. The consequences of increased herbivory, however, remain unclear. Mutualisms are essential for ecosystem functioning; it is important to understand the thermal sensitivity of these interactions, especially in light of expected increases in global temperature regimes

Contextual organismality: Beyond pattern to process in the emergence of organisms

Biologists have taken the concept of organism largely for granted. However, advances in the study of chimerism, symbiosis, bacterial-eukaryote associations, and microbial behavior have prompted a redefinition of organisms as biological entities exhibiting low conflict and high cooperation among their parts. This expanded view identifies organisms in evolutionary time. However, the ecological processes, mechanisms, and traits that drive the formation of organisms remain poorly understood. Recognizing that organismality can be context dependent, we advocate elucidating the ecological contexts under which entities do or do not act as organisms. Here we develop a "contextual organismality" framework and provide examples of entities, such as honey bee colonies, tumors, and bacterial swarms, that can act as organisms under specific life history, resource, or other ecological circumstances. We suggest that context dependence may be a stepping stone to the development of increased organismal unification, as the most integrated biological entities generally show little context dependence. Recognizing that organismality is contextual can identify common patterns and testable hypotheses across different entities. The contextual organismality framework can illuminate timeless as well as pressing issues in biology, including topics as disparate as cancer emergence, genomic conflict, evolution of symbiosis, and the role of the microbiota in impacting host phenotype.John Templeton FoundationVersion of record online: 27 October 2016; published open access.This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Servus pauperum Christi: the Hospitallers’ Services to Pilgrims in the Latin East, XI-XIII Centuries

Dos rasgos principales caracterizan el renacimiento religioso del siglo XI: un crecimiento de la peregrinación a los lugares santos y un nuevo énfasis en la actividad apostólica y evangelizadora. La combinación de los dos lleva a la creación de una de las instituciones religiosas más originales del Este: el Hospital de San Juan, establecido poco antes de 1071 como hospicio para los peregrinos pobres y enfermos que llegaban a Jerusalén. Este artículo analiza sus orígenes y actividades en cuanto organización internacional establecida para el servicio de los peregrinos y de los pobres en el Oriente Latino desde el siglo XI al siglo XIII. ----------------------------------------------------------- Two major features characterized the religious revival of the eleventh century: a growth in pilgrimage to holy places and a new emphasis on apostolic and evangelical activity. The combination of the two lead to the creation of one of the most original religious institutions in the East: The Hospital of St. John, established some time before 1071 as a hospice for poor and sick pilgrims coming to Jerusalem. This paper analyses its origins and it activities as an international order established for the service of pilgrims and the poor in the Latin East from the XIth to the XIIIth centuries

Diversity and evolution of a trait mediating ant-plant interactions: insights from extrafloral nectaries in Senna (Leguminosae)

Background and Aims Plants display a wide range of traits that allow them to use animals for vital tasks. To attract and reward aggressive ants that protect developing leaves and flowers from consumers, many plants bear extrafloral nectaries (EFNs). EFNs are exceptionally diverse in morphology and locations on a plant. In this study the evolution of EFN diversity is explored by focusing on the legume genus Senna, in which EFNs underwent remarkable morphological diversification and occur in over 80 % of the approx. 350 species. Methods EFN diversity in location, morphology and plant ontogeny was characterized in wild and cultivated plants, using scanning electron microscopy and microtome sectioning. From these data EFN evolution was reconstructed in a phylogenetic framework comprising 83 Senna species. Key Results Two distinct kinds of EFNs exist in two unrelated clades within Senna. ‘Individualized' EFNs (iEFNs), located on the compound leaves and sometimes at the base of pedicels, display a conspicuous, gland-like nectary structure, are highly diverse in shape and characterize the species-rich EFN clade. Previously overlooked ‘non-individualized' EFNs (non-iEFNs) embedded within stipules, bracts, and sepals are cryptic and may represent a new synapomorphy for clade II. Leaves bear EFNs consistently throughout plant ontogeny. In one species, however, early seedlings develop iEFNs between the first pair of leaflets, but later leaves produce them at the leaf base. This ontogenetic shift reflects our inferred diversification history of iEFN location: ancestral leaves bore EFNs between the first pair of leaflets, while leaves derived from them bore EFNs either between multiple pairs of leaflets or at the leaf base. Conclusions EFNs are more diverse than previously thought. EFN-bearing plant parts provide different opportunities for EFN presentation (i.e. location) and individualization (i.e. morphology), with implications for EFN morphological evolution, EFN-ant protective mutualisms and the evolutionary role of EFNs in plant diversificatio

Phenological overlap of interacting species in a changing climate: an assessment of available approaches

Abstract Concern regarding the biological effects of climate change has led to a recent surge in research to understand the consequences of phenological change for species interactions. This rapidly expanding research program is centered on three lines of inquiry: (1) how the phenological overlap of interacting species is changing, (2) why the phenological overlap of interacting species is changing, and (3) how the phenological overlap of interacting species will change under future climate scenarios. We synthesize the widely disparate approaches currently being used to investigate these questions: (1) interpretation of longterm phenological data, (2) field observations, (3) experimental manipulations, (4) simulations and nonmechanistic models, and (5) mechanistic models. We present a conceptual framework for selecting approaches that are best matched to the question of interest. We weigh the merits and limitations of each approach, survey the recent literature from diverse systems to quantify their use, and characterize the types of interactions being studied by each of them. We highlight the value of combining approaches and the importance of longterm data for establishing a baseline of phenological synchrony. Future work that scales up from pairwise species interactions to communities and ecosystems, emphasizing the use of predictive approaches, will be particularly valuable for reaching a broader understanding of the complex effects of climate change on the phenological overlap of interacting species. It will also be important to study a broader range of interactions: to date, most of the research on climateinduced phenological shifts has focused on terrestrial pairwise resourceconsumer interactions, especially those between plants and insects