Abstract
Fragmentation of natural habitats generally has negative effects on the reproductive success of many plant species; however, little is known about epiphytic plants. We assessed the impact of forest fragmentation on plant–pollinator interactions and female reproductive success in two epiphytic Tillandsia species with contrasting life history strategies (polycarpic and monocarpic) in Chamela, Jalisco, Mexico, over three consecutive years. Hummingbirds were the major pollinators of both species and pollinator visitation rates were similar between habitat conditions. In contrast, the composition and frequency of floral visitors significantly varied between habitat conditions in polycarpic and self-incompatible T. intermedia but not in monocarpic self-compatible T. makoyana. There were no differences between continuous and fragmented habitats in fruit set in either species, but T. makoyana had a lower seed set in fragmented than in continuous forests. In contrast, T. intermedia had similar seed set in both forest conditions. These results indicate that pollinators were effective under both fragmented and continuous habitats, possibly because the major pollinators are hummingbird species capable of moving across open spaces and human-modified habitats. However, the lower seed set of T. makoyana under fragmented conditions suggests that the amount and quality of pollen deposited onto stigmas may differ between habitat conditions. Alternatively, changes in resource availability may also cause reductions in seed production in fragmented habitats. This study adds to the limited information on the effects of habitat fragmentation on the reproductive success of epiphytic plants, showing that even related congeneric species may exhibit different responses to human disturbance. Plant reproductive systems, along with changes in pollinator communities associated with habitat fragmentation, may have yet undocumented consequences on gene flow, levels of inbreeding and progeny quality of dry forest tillandsias.
Highlights
Anthropogenic loss and fragmentation of natural habitats have profound consequences on the structure of biological communities and populations (Fahrig 2004)
Pollinator assemblages and visitation rates Pollinator observations revealed that flowers of T. intermedia and T. makoyana are visited by hummingbirds and bees, but hummingbirds are the predominant pollinators under both landscape conditions
Adding to this diversity of effects, this study showed that, despite differences in life history strategies, most reproductive variables in T. intermedia and T. makoyana did not differ between habitat conditions
Summary
Anthropogenic loss and fragmentation of natural habitats have profound consequences on the structure of biological communities and populations (Fahrig 2004). In terms of habitat fragmentation, most studies on epiphytic plants show that the abundance, diversity, growth, dispersal and genetic parameters of epiphytes are negatively affected by fragmentation (GonzálezAstorga et al 2004; Flores-Palacios and García-Franco 2004; Werner and Gradstein 2008, 2009; Aguirre et al 2010). This has been related to the dependence of epiphytes on their host trees, which makes epiphytes vulnerable to changes in the availability and traits of their phorophytes (Magrach et al 2012; Sáyago et al 2013). The impact of habitat fragmentation on the pollination and reproductive success of vascular epiphytes is poorly known, except for a number of orchid species (e.g. Parra-Tabla et al 2000, 2011; Murren 2002), and few species in the Cactaceae and the Bromeliaceae families (Aizen and Feinsinger 1994)
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