Marina Wolowski

Community-wide assessment of pollen limitation in hummingbird-pollinated plants of a tropical montane rain forest.

BACKGROUND AND AIMS Although pollen limitation of reproduction (PL) has been widely studied, our understanding of its occurrence in tropical communities, especially for bird-pollinated plants, is underdeveloped. In addition, inclusion of both quantity and quality aspects in studies of PL are generally lacking. Within hummingbird-pollinated plants, a prediction was made for higher PL for the quality than quantity aspects and a minor effect of temporal variation because hummingbirds are constant and efficient pollen vectors but they may transfer low quality pollen. METHODS Field hand and open pollination experiments were conducted on 21 species in a tropical montane rain forest over 2 years. The quantity (fruit set and seeds per fruit) and quality (seed weight and germination) aspects of reproduction were assessed as the response to open pollination relative to outcross hand pollination. The relationships between the effect size of quantity and quality aspects of reproduction and predictive plant features (self-incompatibility, autogamy, density and pollinator specialization level) were assessed with phylogenetic generalized linear models. KEY RESULTS Just over half of all the species expressed PL for one or more response variables. On average, the severity of PL was strong for one quality variable (seed germination; 0·83), but insignificant for another (seed weight; -0·03), and low to moderate for quantity variables (0·31 for seeds per fruit and 0·39 for fruit set). There was only a minor contribution of temporal variation to PL within the studied species. Common predictors of PL, i.e. phylogenetic relatedness, self-incompatibility, autogamy, plant density and pollinator specialization level, did not adequately explain variation in PL within this community. CONCLUSIONS Despite the measurable degree of PL within these hummingbird-pollinated plants, the causes of pollen quality and quantity insufficiency are not clear. Variables other than those tested may contribute to PL or causes of PL may vary among species and cannot adequately be accounted for when assessed from the within-community perspective.

Plant–flower visitor networks in a serpentine metacommunity: assessing traits associated with keystone plant species

Consistent topology of plant–pollinator networks across space may be due to substitutability of the plant species most important for community function (keystone species). It is unclear, however, whether keystone species identity varies within a community type and what traits underlie this variation. Using a network biology approach, we assess whether keystone plant species vary across a metacommunity of five serpentine seeps in California and determine the features that predict their identity. We define keystone species as those with high strength, low node specialization index (NSI), and/or low d′ and determine whether these parameters are predicted by floral traits (flower biomass, number of open flowers per plant, symmetry, or stamen number) and/or ecological features (variation in local floral abundance, endemism) within seeps and across the metacommunity. Keystone species identity varied among seeps and was associated with local flower abundance: mean floral abundance correlated positively with strength but negatively with NSI within most seeps as well as across the metacommunity. For the metacommunity, flower biomass correlated negatively with NSI while variation in flower abundance correlated negatively with strength. Across the metacommunity, the d′ metric was associated with flower biomass, whereby plants with smaller flowers interacted with the most abundant pollinators across the metacommunity. Results suggest that connectance and interaction evenness may not be greatly influenced by community composition turnover due to substitution of keystone plant species across space. Keystone species can be predicted by functional traits but which trait (flower abundance or size) depended on the metric used and the level observed.

Influence of plant-pollinator interactions on the assembly of plant and hummingbird communities

Summary Understanding how ecological processes structure species assemblages is a central issue in community ecology. While the influence of plant-pollinator interactions on each others evolution is well recognized, their role in the assembly of interdependent communities of plants and pollinators is still unclear. Using data from seven communities of hummingbirds and plants that they pollinate from two tropical rainforest types (lowland and montane), we evaluated phylogenetic relationships and signal of functional traits, over space and time, to test predictions on the main processes (environmental filtering, facilitation or competition) that are driving these hummingbird-plant assemblages. Our findings suggest that the main processes driving these assemblages varied between hummingbirds and plants and between habitats, and even among communities at the same habitat. The non-conserved floral trait and the phylogenetic patterns (even or random) give support to the hypothesis of facilitation or competition as processes regulating the composition of plant assemblages. Moreover, the positive relationship between fitness and flowering synchrony suggests facilitation as the most important mechanism for montane plant communities. Distinctively, for lowland plant communities, the combination of non-conserved traits and clustered phylogenetic patterns may be a result of either adaptive radiation or biotic filtering driven by a particular pollinator species that plays a main role as plant community organizer. Lastly, evidence of trait conservatism, together with clustered or even phylogenetic patterns, suggest that facilitation or competition may drive the assembly of montane hummingbird communities, despite the predominance of random phylogenetic patterns. Synthesis. Overall we present a pathway to identify central ecological processes that may drive the assembly of plant-pollinator communities. We show that different processes related with pollination that vary in space and time may contribute to the assembly of the interdependent tropical communities of plants and pollinators. These findings highlight the importance of considering ecological interactions when evaluating community assembly processes. This article is protected by copyright. All rights reserved.

Breeding system and pollination of Senna multijuga (Fabaceae) in a montane Atlantic Forest

Abstract Knowledge of reproductive biology and pollination of Neotropical tree species has been increasing in recentdecades. However, this is still incipient in the Atlantic Forest, and many questions remain, for instance, aboutthe prevalence of self-incompatibility. We studied the floral biology, breeding system and floral visitors ofSenna multijuga in order to verify the occurrence of self-incompatibility and determine its pollinators. This speciesbears the typical floral traits of the genus, such as asymmetry, enantiostily, heteranthery and poricid anthers.Anthesis is diurnal and pollen viability did not differ among the morphs of anthers. Pollinators were bees of thegenera Bombus, Epicharis, Centris and Xylocopa and smaller bees acted as pollen thieves. Sexual reproductionof Senna multijuga depends on the transfer of pollen by pollinators, as no fruit was formed by either apomixisor self-pollination. The latter result may be due to inbreeding depression or by a mechanism of late-acting self-incompatibility, as we observed after self-pollination both penetration of pollen tubes in the ovules anduniform abortion of pistils. Differences on fertility after manual crossings and under natural conditionsindicate that female fitness is affected by pollen limitation, as well as by the availability of resources.Key words: inbreeding depression, late-acting self-incompatibility, pollen flower, pollination.