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Question Species-specific interactions can connect particular species to others, which has important implications for species interdependence and coexistence. However, species-specific effects of ecosystem engineers remain little explored, particularly in the alpine tropics. We investigated the effects of two cushion plants with subtle differences in morphological traits in a tropical Andean ecosystem. We asked whether these foundation species differed in their effects on local abiotic factors, species richness and the structure of plant assemblages growing within them. Location La Culata National Park, northern tropical Andes, Venezuela. Methods We determined shallow soil temperature, soil organic matter and water content within two coexisting cushion species, the larger and more compact Azorella julianii and the smaller and denser Arenaria musciformis, and in adjacent open areas. We also recorded the total number of plant species growing within both cushion species, and in paired open areas at three sites. We then compared local species richness, total plant abundance, and the abundance of each species within cushions and outside using the Relative Interaction Index (RII), and community dissimilarity patterns using non-metric multidimensional scaling (NMDS) ordination. We also compared species accumulation curves across sites between the cushions and open areas. Results Both cushions had similar positive effects on soil organic matter, but soil water content was increased only by Azorella. Both cushions had a positive effect on local species richness and total plant abundance. In addition, both species significantly modified species abundance patterns, showing a positive association with several species, many of them grasses. However, facilitative effects on other species were generally stronger for Azorella than Arenaria. Moreover, community structure of plants growing within the two cushion plants differed. The exotic invader Rumex acetosella increased in abundance within Azorella but not Arenaria. Conclusions We found evidence for species-specific effects of ecosystem engineers in the alpine tropics; two cushion species with subtly contrasting traits had different effects on microhabitat conditions and plant assemblages. This could in turn increase abiotic and biotic heterogeneity and promote species coexistence and emphasizes interdependence among species in alpine plant communities. This article is protected by copyright. All rights reserved.

Digital cameras can provide a consistent view of vegetation phenology at fine spatial and temporal scales that are impractical to collect manually and are currently unobtainable by satellite and most aerial based sensors. This study links greenness indices derived from digital images in a network of rangeland and forested sites in Montana and Idaho to 16-day normalized difference vegetation index (NDVI) from NASA&rsquo, s Moderate Resolution Imaging Spectroradiometer (MODIS). Multiple digital cameras were placed along a transect at each site to increase the observational footprint and correlation with the coarser MODIS NDVI. Digital camera phenology indices were averaged across cameras on a site to derive phenological curves. The phenology curves, as well as green-up dates, and maximum growth dates, were highly correlated to the satellite derived MODIS composite NDVI 16-day data at homogeneous rangeland vegetation sites. Forested and mixed canopy sites had lower correlation and variable significance. This result suggests the use of MODIS NDVI in forested sites to evaluate understory phenology may not be suitable. This study demonstrates that data from digital camera networks with multiple cameras per site can be used to reliably estimate measures of vegetation phenology in rangelands and that those data are highly correlated to MODIS 16-day NDVI.

Understanding how habitat and nutritional condition affect ungulate populations is necessary for informing management, particularly in areas experiencing carnivore recovery and declining ungulate population trends. Variations in forage species availability, plant phenological stage, and the abundance of forage make it challenging to understand landscape-level effects of nutrition on ungulates. We developed an integrated spatial modeling approach to estimate landscape-level elk (Cervus elaphus) nutritional resources in two adjacent study areas that differed in coarse measures of habitat quality and related the consequences of differences in nutritional resources to elk body condition and pregnancy rates. We found no support for differences in dry matter digestibility between plant samples or in phenological stage based on ground sampling plots in the two study areas. Our index of nutritional resources, measured as digestible forage biomass, varied among land cover types and between study areas. We found that altered plant composition following fires was the biggest driver of differences in nutritional resources, suggesting that maintaining a mosaic of fire history and distribution will likely benefit ungulate populations. Study area, lactation status, and year affected fall body fat of adult female elk. Elk in the study area exposed to lower summer range nutritional resources had lower nutritional condition entering winter. These differences in nutritional condition resulted in differences in pregnancy rate, with average pregnancy rates of 89% for elk exposed to higher nutritional resources and 72% for elk exposed to lower nutritional resources. Summer range nutritional resources have the potential to limit elk pregnancy rate and calf production, and these nutritional limitations may predispose elk to be more sensitive to the effects of harvest or predation. Wildlife managers should identify ungulate populations that are nutritionally limited and recognize that these populations may be more impacted by recovering carnivores or harvest than populations inhabiting more productive summer habitats.

Facilitation by nurse plants has received considerable attention, but the feedback effects of beneficiaries on the benefactor fitness remain comparatively unexplored. In particular, to our knowledge there have been no studies of feedback effects of exotic species on nurse plants. Furthermore, there have been few studies of how exotic plants interact with native beneficiaries, potentially generating indirect effects on the nurse. Here, through spatial association analyses, we estimate the reciprocal interactions between the cushion nurse-plant Arenaria musciformis, native beneficiaries, and the dominant exotic Rumex acetosella (a fast growing heliophile species) in a tropical alpine ecosystem of the Venezuelan Andes, locally known as páramos. We recorded the density of natives and the exotic within Arenaria cushions and in paired open areas at three sites and calculated Relative Interaction Indices (RII) to explore the effects of the cushion. Then, we analyzed the feedback effects of Rumex and the natives on the density of flowers produced by Arenaria. Finally, we analyzed how Rumex abundance is related to the abundance of native species inside and outside cushions. RIIs indicated a facilitative effect of cushions on the abundance of native plants, but no effect on Rumex. We found a negative relationship between the density of natives and cushion flower density, but no such relationship for Rumex. However, at high densities, Rumex was negatively correlated with the abundance of the natives both inside and outside of cushions. Our results suggest the possibility of complex reciprocal interactions between nurses, natives and exotics, and that native and exotic plants can differ in their feedback effects on nurse cushions. Native plants appeared to be facilitated by cushions and then develop a parasitic relationship with their nurses. In contrast, the exotic Rumex had a neutral interaction with the nurse, but competitive effects on the native beneficiary community, which could indirectly modulate the feedback effects of natives on the nurse. These results highlight the importance of analyzing direct and indirect reciprocal interactions and the impacts of exotic invaders for understanding alpine community assembly. Fil: Llambí, Luis D.. Universidad de Los Andes; Venezuela Fil: Hupp, Nicole. University of Montana; Estados Unidos Fil: Sáez, Agustín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; Argentina Fil: Callaway, Ragan. University of Montana; Estados Unidos

International audience; Facilitative effects of some species on others are a major driver of biodiversity. These positive effects of a benefactor on its beneficiary can result in negative feedback effects of the beneficiary on the benefactor and reduced fitness of the benefactor. However, in contrast to the wealth of studies on facilitative effects in different environments, we know little about whether the feedback effects show predictable patterns of context dependence. We reanalyzed a global data set on alpine cushion plants, previously used to assess their positive effects on biodiversity and the nature of the beneficiary feedback effects, to specifically assess the context dependence of how small- and large-scale drivers alter the feedback effects of cushion-associated (beneficiary) species on their cushion benefactors using structural equation modelling. The effect of beneficiaries on cushions became negative when beneficiary diversity increased and facilitation was more intense. Local-scale biotic and climatic conditions mediated these community-scale processes, having indirect effects on the feedback effect. High-productivity sites demonstrated weaker negative feedback effects of beneficiaries on the benefactor. Our results indicate a limited impact of the beneficiary feedback effects on benefactor cushions, but strong context dependence. This context dependence may help to explain the ecological and evolutionary persistence of this widespread facilitative system.