Few plants and one dominant fly shape a unique pollination network in a Neotropical mangrove

Abstract

Mangroves are unique ecosystems supported by very small plant assemblages. Those few plants tend to be insect-pollinated and make generalized interactions, which leads to competition for pollinators. Mangroves are poorly studied in terms of pollination ecology, and we still do not know how those interactions scale up to form networks. We described the pollination network of a Neotropical mangrove to understand how plant species share pollinators and to gain insight into network assembly in a species-poor ecosystem. We assessed year-round pollination interactions in a mangrove in north-eastern Brazil comprising three entomophilous plant species and described the topology of the resulting network in terms of nestedness, specialization, and modularity. We also assessed the relative importance and niche breadth of different pollinator groups using centrality metrics. The network had highly imbalanced node classes, comprising three zoophilous plant species and 29 insect species from the orders Diptera, Hymenoptera, and Lepidoptera. Pollinator species were mostly peripheral and rarely interacted with all plants, while plant species formed a generalized core. A single dominant fly species, Palpada albifrons, visited all plants and made most interactions, softening the separation between modules. The network was nonetheless moderately specialized due to several exclusive interactions with a taxonomic signal. These taxon-specific interaction patterns point to idiosyncrasies in mangrove pollination systems instead of the expected generalized interactions with non-selective insects. However, the mangrove’s reproductive dynamics seems to be dominated by a single pollinator species, and its network topology is heavily influenced by the low plant richness resultant from strong environmental filters.