Orchestrated Flowering and Interspecific Facilitation: Key Factors in the Maintenance of the Main Pollinator of Coexisting Threatened Species of Andean Wax Palms (Ceroxylon spp.)

Abstract

Solitary, dioecious, and mostly endemic to Andean cloud forests, wax palms (Ceroxylon Bonpl. ex DC. spp.) are currently under worrisome conservation status. The establishment of management plans for their dwindling populations rely on detailed biological data, including their reproductive ecology. As in the case of numerous other Neotropical palm taxa, small beetles are assumed to be selective pollinators of wax palms, but their identity and relevance in successful fruit yield were unknown. During three consecutive reproductive seasons we collected data on population phenology and reproductive and floral biology of three syntopic species of wax palms native to the Colombian Andes. We also determined the composition of the associated flower-visiting entomofauna, quantifying the extent of the role of individual species as effective pollinators through standardized value indexes that take into consideration abundance, constancy, and pollen transport efficiency. The studied populations of C. parvifrons (Engel) H. Wendl., C. ventricosum Burret, and C. vogelianum (Engel) H. Wendl. exhibit seasonal reproductive cycles with marked temporal patterns of flower and fruit production. The composition of the associated flower-visiting entomofauna, comprised by ca. 50 morphotypes, was constant across flowering seasons and differed only marginally among species. Nonetheless, a fraction of the insect species associated with pistillate inflorescences actually carried pollen, and calculated pollinator importance indexes demonstrated that one insect species alone, Mystrops rotundula Sharp, accounted for 94%–99% of the effective pollination services for all three species of wax palms. The sequential asynchronous flowering of C. parvifrons, C. ventricosum, and C. vogelianum provides an abundant and constant supply of pollen, pivotal for the maintenance of large populations of their shared pollinators, a cooperative strategy proven effective by high fruit yield rates (up to 79%). Reproductive success might be compromised for all species by the population decline of one of them, as it would tamper with the temporal orchestration of pollen offer.

Phenology of the endangered palm Ceroxylon quindiuense (Arecaceae) along an altitudinal gradient in Colombia

“…Since palms present a structure composed of successive leaf-inflorescence-internode modules (Henderson, 2002), the development of each of their reproductive structures (buds, inflorescences, and infructescences) can be followed individually. As floral anthesis lasts only 2-3 days (personal observation from 2005 through 2018; Carreño-Barrera et al, 2013;Carreño-Barrera, Núñez-Avellaneda, Sanín, & Campos, 2020), and our observations were bimonthly, the probability of finding an inflorescence at anthesis during the observation period was low. For this reason, for each reproductive structure, the month of its flowering was interpolated between the last observation in which it was found in bud and the appearance of a structure with early developing fruits.…”

“…To maintain pollinator populations, palms of the genus Ceroxylon have developed strategies that allow them to have a constant supply of pollen for the beetles. Where several Ceroxylon species co-occur, one of these strategies is the asynchronous flowering of the different Ceroxylon species along the gradient, so that there is a steady offer of flowers over a long period of time (Carreño-Barrera et al, 2020).…”

Fine‐scale temporal dynamics of flower visitors sheds light on insect‐assemblage overlap between sexes in a dioecious Ecuadorian palm

“…Despite this large diversity of visitors shared by both floral sexes, a core of 16 morphospecies totalized 99% of visits. Species abundance in a community is an important factor to predict their relative effectiveness for pollination (Ollerton, 2017) and is commonly used to identify palm pollinators, among other variables such as pollen load (Carreño‐Barrera et al, 2020; Núñez‐Avellaneda & Rojas‐Robles, 2008). Nevertheless, the very limited knowledge of the biology of these morphospecies and the absence of data on the individual performance of pollination considerably limit the identification of efficient pollinators (Ne'eman et al, 2009).…”

“…Although the arthropod fauna and the ecological role of individual flower‐visiting species have thoroughly been studied for several palm species (e.g., Ceroxylon sp. ; Carreño‐Barrera et al (2020); Kirejtshuk & Couturier, 2009, and Mauritia flexuosa ; Mendes et al (2017), our knowledge of the insect communities interacting with most dioecious palm flowers, and their fluctuations in abundance and composition during the flowering remains fragmentary.…”

“…monly used to identify palm pollinators, among other variables such as pollen load(Carreño-Barrera et al, 2020;Núñez-Avellaneda & Rojas-Robles, 2008). Nevertheless, the very limited knowledge of the biology of these morphospecies and the absence of data on the individual performance of pollination considerably limit the identification of efficient pollinators(Ne'eman et al, 2009).…”