Pollination specialization and time of pollination on a tropical Venezuelan plain: variations in time and space

Abstract

Levels of specialization of the pollination systems were evaluated in 155 plant species from the Venezuelan Central Plain. In all, 29 pollination systems were found, resulting from various combinations of nine pollen-vector types or pollinating agent classes. The number of pollen-vector types composing a pollination system ranged from one to five. Ninety-one species were pollinated by only a single pollen-vector type; the frequency of pollination systems fell monotonically with increasing number of constituent pollen-vector types. Some 30-40 per cent of bee-, moth-, beetle-and bat-pollinated species were pollinated by that group of vectors alone. The highest incidence of co-occurrence between pollen-vector types was found for the combinations fly-wasp, butterfly-wasp, butterfly-fly, and to a lesser extent bird-butterfly, bat-bird, bat-moth and butterfly-moth. The average number of pollen-vector types per plant species was significantly higher for trees and shrubs than for lianas and perennial herbs. The distribution of polyphily, oligophily, monophily and anemophily was significantly associated with life form and habitat. The relative frequencies of these types varied least through the year in the forest-savannah ecotone and in the vegetation as a whole, reflecting the combination of life forms. There were significantly fewer night-pollinated than day-pollinated species. Daypollinated species tended to be polyphilous, and most of the night-pollinated species were monophilous or oligophilous. Time of pollination activity was related to habitat. The relative importance of night pollination among life forms decreased from trees to perennial herbs. Plant species exclusively pollinated during the night reached a peak during the rainy season (May to November) for trees, lianas and perennial herbs. The data as a whole show that the relative frequency of polyphily, oligophily, monophily and anemophily, and the time of pollination activity are influenced by community structure and plant species richness, and may change from season to season.

Plant sexual systems, dichogamy, and herkogamy in the Venezuelan Central Plain

“…However, polyphilous animal pollination seems to be associated with the evolution of dioecy from an ancestral hermaphrodite sexual system. The temporal frequency distribution of pollination indicated that polyphily tends to increase during the dry-rainy transition period in the forest and the community level (Ramı´rez, 2004b). Under such circumstances, polyphily is phenologically biased, and consequently, seems to act as a selective force for evolution of dioecy during the dry-rainy transition period.…”

“…Information about plant pollination systems was established according to two criteria of specialization examined previously: qualitative and quantitative forms (Ramı´rez, 2004b). Plant species were categorized dealing principally with the character of visits received (lightly modified from Faegri and Van der Pijl, 1979, p. 48).…”

Floral resources used by insects in a grassland community in Southern Brazil

“…Since bees depend exclusively on floral resources for their survival, they are the most frequent visitors found on flowers, and were reported as the most diverse and abundant group of floral visitors, as well as the main pollinators in several plant communities (Ramirez 1989, Barbosa 1997, Momose et al 1998, Oliveira & Gibbs 2000, Machado & Lopes 2004, Ramirez 2004, Freitas & Sazima 2006. Flies and wasps, after bees, were the predominant floral visitors recorded in this study, as well as in cerrado and high-altitude grasslands (Barbosa 1997, Freitas & Sazima 2006, while beetles and lepidopterans were less represented in all three communities.…”

Atributos florais em um sistema de polinização especializado: Calathea cylindrica (Roscoe) K. Schum. (Marantaceae) e abelhas Euglossini

“…Atualmente existe vasta literatura indicando que os sistemas de polinização das angiospermas se distribuem em um contínuo entre os extremos de generalização e especialização (Fenster et al 2004, Ramírez 2004, Freitas & Sazima 2006, Waser & Ollerton 2006 e uma das questões que emerge desse cenário é o entendimento dos fatores que estão ligados ao surgimento e manutenção de sistemas de polinização com alto grau de especialização (Westerkamp 1997, Aigner 2001, Fenster et al 2004, Cane & Sipes 2006. De acordo com o princípio de Stebbins (1970) do polinizador mais efetivo, uma planta deve especializarse no polinizador mais eficaz e mais abundante quando a disponibilidade deste é confiável.…”