Habitat diversity promotes and structures orchid diversity and orchid-host tree interactions

Abstract

At the regional scale, abiotic environmental heterogeneity related to elevation and climatic profiles influences patterns of diversity and species composition. At the local scale, little is known about the influence of biotic environmental heterogeneity (habitat diversity) on the diversity, composition, and networks of interspecific interactions (epiphyte-host tree) of plant families with species of epiphytic and terrestrial habit. As a study model, we selected the orchids of a tropical landscape in central Veracruz, Mexico, which comprises natural habitats of tropical oak forest (TOF), semi-humid deciduous forest (SDF), and tropical dry forest (TDF), as well as shaded coffee plantation (SCP). In this landscape, we recorded a total of 635 individual orchids, belonging to 51 species (80% of epiphytic habit). The TOF and SDF, with 36 and 30 orchid species, respectively, were at least twice as diverse than TDF and SCP, and also presented greater similarity in terms of species composition. The TDF presented a particular composition of orchids comprising species that are morphologically adapted to conditions of drought, and also presented more species of terrestrial habit than the other habitats. The SCP hosted a subset of the species of TOF. The structure and specialization of the network of orchid-host tree interactions (at the landscape level) was less nested, and more modular and specialized than has been reported previously for commensalist networks of vascular epiphytes. The most abundant and tallest tree species favored the orchid-host tree interactions. For this reason, at the landscape scale, the particular tree community of different habitats promotes the great diversity and acts to structure the composition and interactions of one of the most representative plant families of the Neotropics.