Alpine cushion plants have species–specific effects on microhabitat and community structure in the tropical Andes

Abstract

Question: Species-specific interactions can connect particular species to others, which has important implications for species interdependence and co-existence. 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 co-existing 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 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 with 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 co-existence and emphasizes interdependence among species in alpine plant communities.

Positive plant–plant interactions expand the upper distributional limits of some vascular plant species

“…, Hupp et al. ). Cushion plants may moderate microclimatic conditions by ameliorating soil temperatures, increasing soil moisture, improving soil nutrient status, and enhancing substrate stability (Nyakatya and McGeoch , Hupp et al.…”

Effects of indirect facilitation on functional diversity, dominance and niche differentiation in tropical alpine communities

“…Our study took place in tropical alpine peatland ecosystems of the Cordillera Real, Bolivia. As in most alpine environments (Callaway et al., ), plant communities of tropical alpine environments are strongly driven by positive interactions among plants (Hupp, Llambí, Ramírez, & Callaway, ; Malatesta, Tardella, Piermarteri, & Catorci, ), but the mechanisms underlying those interactions differ (reviewed in Anthelme & Dangles, ).…”

“…co-existence, functional diversity, functional traits, grazing, indirect facilitation, niche, permutation, trait distribution, tropical alpine peatlands | 837 DANET ET Al. et al, 2002), plant communities of tropical alpine environments are strongly driven by positive interactions among plants (Hupp, Llambí, Ramírez, & Callaway, 2017;Malatesta, Tardella, Piermarteri, & Catorci, 2016), but the mechanisms underlying those interactions differ (reviewed in Anthelme & Dangles, 2012).…”

Determining which mechanisms underlie facilitation by tussocks in tropical high mountains and their relative importance

“…Our results suggest a scenario in which the benefactor species exerts positive and 375 negative, direct and indirect effects on its protégé through a multiplicity of environmental 376 modifications. Such complex effects probably depend on the benefactor's identity: whereas 377 facilitation by Festuca seemed independent of soil properties (although our data are not 378 conclusive), these are important when cushion plants are considered (Anthelme and Dangles 379 2012, Hupp et al 2017). In turn, the protégé's tolerance to different stressors may determine its 380 responses to the benefactor (Liancourt et al 2005).…”

“…For instance, the negligible effect of UV 381 radiation on Mexerion performance probably arises from its dense, reflective pubescence, which 382 may confer resistance to UV radiation (Rozema et al 1997). This interplay between amelioration 383 of and tolerance to multiple stressors may explain why facilitative interactions are highly 384 species-specific in nature (Callaway 1998, Hupp et al 2017.…”