Influence of the nurse-protégé interaction on the frugivory pattern of the columnar cactus Pilosocereus leucocephalus.

Nurse plants provide benefits during the early life cycle of the protected plant by reducing the intensity of stressful abiotic conditions. However, nurse plants may influence frugivore visitation and consumption, affecting the initial benefits of this interaction and generating different frugivory patterns during the reproductive phase of the protégé. Despite the importance of nurse plants and frugivory in the structure and composition of ecosystems, they have rarely been evaluated together, and frugivory patterns caused by nurse plants at different spatial and temporal scales are mostly unknown. Pilosocereus leucocephalus produces seeds that are endozoochorically dispersed by birds and mammals, can establish in open spaces devoid of arboreal vegetation (OS), and is associated with the nurse tree Lysiloma acapulcensis. However, the influence of L. acapulcensis on the frugivory patterns of P. leucocephalus is unknown. Therefore, during the fruiting season of P. leucocephalus of 2018, we recorded the visitation rates, effective removal, and removal timescales in 26 individuals located in OS and 15 under L. acapulcensis. Our results indicate that L. acapulcensis increased visits by Euphonia hirundinacea and bats but decreased those of Psilorhinus morio and Campylorhynchus rufinucha. Although L. acapulcensis did not generate differences in fruit removal effectiveness, bats showed the highest effectiveness in OS, followed by birds. L. acapulcensis also had an effect on the fruit removal periods of different frugivorous species at different temporal scales. This shows that the nurse tree generated a complex pattern of frugivory in P. leucocephalus, mainly increasing the initial benefits of the nurse-protégé interaction.

The frugivory network properties of a simplified ecosystem: Birds and plants in a Neotropical periurban park.

Frugivory networks exhibit a set of properties characterized by a number of network theory-derived metrics. Their structures often form deterministic patterns that can be explained by the functional roles of interacting species. Although we know lots about how these networks are organized when ecosystems are in a complete, functional condition, we know much less about how incomplete and simplified networks (such as those found in urban and periurban parks) are organized, which features are maintained, which ones are not, and why. In this paper, we examine the properties of a network between frugivorous birds and plants in a small Neotropical periurban park. We found a frugivory network composed of 29 species of birds and 23 of plants. The main roles in this network are played by four species of generalist birds (three resident, one migratory: Myiozetetes similis, Turdus grayi, Chlorospingus flavopectus, and Dumetella carolinensis) and three species of plants (one exotic, two early successional: Phoenix canariensis, Phoradendron sp., and Witheringia stramoniifolia). When compared to reference data from other locations in the Neotropics, species richness is low, one important network-level metric is maintained (modularity) whereas another one is not (nestedness). Nestedness, a metric associated with network specialists, is a feature this network lacks. Species-level metrics such as degree, species strength, and module roles, are not maintained. Our work supports modularity as the most pervasive network-level metric of altered habitats. From a successional point of view, our results suggest that properties revealed by species-level indices may be developed at a later time, lagging the acquisition of structural elements.

Patterns of frugivory in the columnar cactus Pilosocereus leucocephalus.

In the frugivory networks of many arid and semi-arid Mesoamerican ecosystems, columnar cacti act as keystone species that produce fruits with a high content of water and nutrients attractive to numerous vertebrates. The aim of this investigation was to assess the fruit removal patterns of two guilds of frugivores on the fruits of the woolly torch Pilosocereus leucocephalus. We assessed fruit pulp removal in two ways: by estimating the consumption of seeds given the amount of pulp removed per visit and by estimating the percentage of pulp removal over time. We put exclosures on unripe, intact fruits to keep frugivores from removing material. Once ripe, we removed the exclosures and tracked animal visitation of 69 fruits using camera traps. We obtained a total of 2,162 hr of footage (14:47 hours of them with effective pulp removal). The highest number of visitors is that of diurnal species (n = 12, all birds) versus only four nocturnal (three bats, one rodent). The most effective species in pulp removal are birds. Bats play a modest role in frugivory of this cactus. The significance of this work is twofold: (a) birds and bats consume the fruit pulp of this cactus and likely disperse its seeds, and (b) although bats rank high in pulp removal effectiveness, birds as a guild far outweigh their importance in this system, as they are not only more frequent but also remove more pulp and seeds. Both groups are known to be important in cacti seed dispersal, and our findings are essential in understanding the population dynamics of the woolly torch and in elucidating its seed dispersal ecology.

En las redes de frugivoría de muchos ecosistemas áridos y semiáridos mesoamericanos, los cactus columnares funcionan como especies claves que producen frutos con un alto contenido de agua y nutrientes atractivos a numerosos vertebrados. El propósito de esta investigación fue determinar los patrones de remoción de pulpa de los frutos del cactus viejito Pilosocereus leucocephalus por dos gremios de frugívoros. Determinamos los patrones de remoción de pulpa de dos maneras: estimando el consumo de semillas dada la cantidad de pulpa removida en cada visita y estimando el porcentaje de pulpa removida por unidad de tiempo. Colocamos jaulas de tela de alambre sobre frutos sin madurar para excluir frugívoros. Una vez maduros los frutos, quitamos las jaulas y registramos las visitas de animales en 69 frutos utilizando cámaras­trampa. Obtuvimos un total de 2162 h de video (14.47 h de estas con remoción efectiva de frutos). El mayor número de visitantes fue de especies diurnas (n=12, todos aves) vs. solo cuatro nocturnos (tres murciélagos, un roedor). Las especies más efectivas en la remoción de frutos son aves. Los murciélagos juegan un papel modesto en la frugivoría de este cactus. El significado de este trabajo es doble: (1) aves y murciélagos consumen la pulpa de los frutos de este cactus y muy posiblemente dispersan sus semillas, y (2) aunque los murciélagos se ubican entre los visitantes más efectivos en la remoción de pulpa, las aves les aventajan de lejos en importancia en este sistema dado que no solo son más frecuentes, sino que remueven más pulpa y semillas. Ambos grupos son conocidos por su importancia en la dispersión de semillas de cactus y nuestros hallazgos son esenciales en el entendimiento de la dinámica poblacional del cactus viejito y en dilucidar la ecología de su dispersión de semillas.