Comparisons of habitat types and host tree species across a threatened Caribbean orchid’s core and edge distribution

Abstract

Tropical forest ecosystems are rich in epiphytes that make up a significant portion of the overall plant diversity. However, epiphytic plants are often understudied due to inaccessibility and the lack of basic ecological information poses challenges to their conservation, particularly in a time of rapid global change. The mule-ear orchid, Trichocentrum undulatum (Orchidaceae), is a large flowering epiphyte found in southern Florida (USA), the Greater, and Lesser Antilles including Cuba. The plant is Florida state-listed as endangered with only one remaining small and declining population in a coastal mangrove forest due to historical extraction and habitat destruction. Currently, there is no systematic understanding of the species’ habitat requirements. To fill this void, we compared the habitat and microhabitat of the species on its northern distribution edge (southern Florida) and the core range (in Cuba). The Florida population has only one host species, Conocarpus erectus, found in one habitat type. This is in sharp contrast to the 92 documented hosts and 5 habitats across 8 provinces in Cuba. Based on our findings from Cuba, we suggest conservation and restoration options in Florida by proposing potential suitable host plants and habitats. Proactive restoration of this species will help to ease the threat from sea-level rise to the species by securing and expanding range margins.

Populations of a tropical epiphytic orchid are destabilized in its peripheral range by hurricane and an exotic herbivore

“…T. undulatum may be pollinated by several species of bees in the genus Centris in Cuba, but there is only one Centris species native in southern Florida (Genaro, 2008; Pascarella et al, 1999). The larger diameter of host trees in Cuba may also support the concept of less branch breakage from wind, which leads to less wind‐caused plant mortality in the core than in peripheral populations (Borrero, Alvarez, et al, 2022; Mondragón & Elliott, 2013). There is only one study on mycorrhizal associations of T. undulatum , in the peripheral population (Liu et al, 2022).…”

“…In general, core populations are host to more diverse set of mutualistic partners as well as ideal habitat characteristics than the potentially more marginal peripheral populations (Martin, 2001; Sexton et al, 2009). In the growing core population of Core 3, there is a higher diversity of host tree species when compared with the Peripheral site (Borrero, Alvarez, et al, 2022). A higher richness of pollinators in the core range is also likely.…”

“…The orchid is not host specific across its range, but is only known to grow on one species, C. erectus , in Florida (Borrero, Alvarez, et al, 2022). The orchid experiences flower‐crippling herbivory on the inflorescence stalks by the fly Melanagromyza miamensis Spencer (Diptera: Agromyzidae) (Higgins & Gann, 2007; Seavey & Seavey, 2006) (Figure 3).…”

“…Logging can also be devastating due to the potential for direct mortality of epiphytes when a tree is felled as well as the reduction of recruits on potential host trees (Barthlott et al, 2001). Epiphytes inherently depend on other species as host plants and are often specialized to particular sites due to host characteristics, for example, bark rugosity, trunk diameter, or mycorrhizal associations (Borrero, Alvarez, et al, 2022; Callaway et al, 2002; McCormick & Jacquemyn, 2014; Sáyago et al, 2013; Yang et al, 2017; Zarate‐García et al, 2020). Populations of epiphytes, orchids in particular, are considered as dynamic due to both their climate‐sensitive physical positions that are prone to disturbance and specialized species interactions (Houlihan et al, 2019; Huston, 1994; Raventós et al, 2015; Zuleta et al, 2016).…”

“…The southern Florida region is the northern latitudinal limit for 59 orchid species, 44 of which are listed as endangered in the state of Florida (Wunderlin et al, 2022). Tailored management strategies are needed for these endangered and threatened populations, to ameliorate threats to population decline and extinction (Borrero, Alvarez, et al, 2022; Liu et al, 2012; Martin, 2001; Münzbergová & Herben, 2004). To this end, we studied the ecology and dynamics of several populations of an epiphytic orchid, Trichocentrum undulatum (Sw.) Ackerman and M. W. Chase across its distribution range, that is, in Cuba the presumptive distribution core and in southern Florida, the northernmost edge.…”