Terrestrial orchids in a tropical forest: best sites for abundance differ from those for reproduction

Abstract

Abstract. Suitable habitat for a species is often modeled by linking its distribution patterns with landscape characteristics. However, modeling the relationship between fitness and landscape characteristics is less common. In this study we take a novel approach towards species distribution modeling (SDM) by investigating factors important not only for species occurrence, but also abundance and physical size, as well as fitness measures. We used the Neotropical terrestrial orchid Prescottia stachyodes as our focal species, and compiled geospatial information on habitat and neighboring plants for use in a two-part conditional SDM that accounted for zero inflation and reduced spatial autocorrelation bias. First, we modeled orchid occurrence, and then within suitable sites we contrasted habitat characteristics important for orchid abundance as compared to plant size. We then tested possible fitness implications, informed by analyses of allometric scaling of reproductive effort and lamina area, as well as size-density relationships in areas of P. stachyodes co-occurrence. We determined that orchid presence was based on a combination of biotic and abiotic factors (indicator species, diffuse solar radiation). Within these sites, P. stachyodes abundance was higher on flat terrain, with fine, moderately well-drained soil, and areas without other native orchids, whereas plant size was greater in less rocky areas. In turn, plant size determined reproductive effort, with floral display height proportionate to lamina area (more photosynthates); however, allometric scaling of flower quantity suggests a higher energy cost for production, or maintenance, of flowers. Overall, habitat factors most important for abundance differed from those for size (and thus reproductive effort), suggesting that sites optimal for either recruitment or survival may not be the primary source of seeds. For plots with multiple P. stachyodes plants, size-density relationships differed depending on the size class examined, which may reflect context-dependent population dynamics. Thus, ecological resolution provided by SDM can be enhanced by incorporating abundance and fitness measures.

Linking habitat suitability to demography in a pond-breeding amphibian

“…reproductive success [ 5 , 13 , 14 ] and apparent survival [ 15 , 16 ], has rarely been evaluated. Such tests are important because several studies did not find the expected link between habitat suitability and species occurrence or demography [ 9 , 11 , 17 ]. Species may not occur in suitable patches when structured as a metapopulation [ 18 ] or they may be found in unsuitable patches (i.e.…”

Characterization of mycorrhizal fungi of the genus <em>Tulasnella (Tulasnellaceae, Basidiomycota)</em> in the genus of orchids <em>Bletia</em> from Barranca del Cupatitzio Natural Reserve, Mexico

“…2016). However, a large number of these species is included in some risk extinction category because of direct or indirect human activities (Whitman & Ackerman 2015). The species of this family stablish associations with other organisms during some critical stages of their life cycle, such as pollinators at flowering and symbiotic fungi during germination stages (Rasmussen & Rasmussen 2007;Schatz & al.…”