Crop Size and Fruit Neighborhood Effects on Bird Visitation to Fruiting Schefflera morototoni Trees in Puerto Rico¹

Abstract

Studies of zoochorous seed dispersal systems often consider crop size, yet seldom consider the kinds and amounts of fruits surrounding parent plants (the fruit neighborhood) when attempting to explain among-plant variation in fruit removal. We studied avian frugivory at 24 Schefflera morototoni trees from February to May 1998 in central Puerto Rico. The number of fruits removed by avian seed dispersers per visit was similar among focal trees (typically 2-4). In contrast, visitation rate was highly variable (range: 0-71 visits per 4 h). We used multiple regression analyses to evaluate the relative roles of crop size (focal tree ripe fruit abundance) and fruit neighborhood variables (measured within 30 m of focal trees) in affecting visitation to focal trees by avian frugivores. Visitation rate was positively related to crop size (although this variable was only significant in one of four regression models considered) and negatively related to the presence or abundance of conspecific fruits, suggesting that trees competed intraspecifically for dispersers. Relationships between visitation and heterospecific fruits were mixed-some kinds of fruits appeared to enhance visitation to focal trees, while others seemed to reduce visitation. In most regression models, neighborhood variables had larger effects on visitation than focal tree fruit crop size. Our results highlight the important effects of local fruiting environments on the ability of individual plants to attract seed dispersers. RESUMENLos estudios de sistemas dispersadores de semillas zoocoras por lo general consideran el tamaño de la cosecha, sin embargo, raras veces consideran los tipos y cantidades de frutos en los alrededores de las plantas madres (las frutas del vecindario) cuando intentan explicar entre plantas, la variación de extracción de frutos. Nosotros estudiamos la frugivoria de aves en 24árboles de Schefflera morototoni entre Febrero y Marzo de 1998 en la parte central de Puerto Rico. El número de frutos removidos en cada visita por las aves dispersadoras de semillas fue similar entre losárboles focales (típicamente de 2 a 4). En contraste, la proporción de visitas fué muy variable (intervalo = 0-71 visitas cada 4 horas). Nosotros utilizamos análisis de regresión múltiple para evaluar el rol relativo del tamaño de la cosecha (árboles focales con abundancia de frutos maduros) y variables en frutos del vecindario (medidos dentro de los 30 m de losárboles focales) en el efecto de visitas por aves frugívoras a losárboles focales. La proporción de visitas estuvo positivamente relacionado con el tamaño de la cosecha (aunque esta variable fué solamente significativa en uno de los cuatro modelos considerados) y negativamente relacionado a la presencia y a la abundancia de frutos coespecíficos, sugiriendo que losárboles compitieron intraespecíficamente por los dispersores. Las relaciones entre visitas y frutos heteroespecíficos fue mixta -algunos tipos de frutos parecen promover las visitas a losárboles focales, mientras que otros parecen reducir las visit...

Interactions between frugivorous birds and plants in savanna and forest formations of the Cerrado

“…Rudgea viburnoides and Miconia staminea belong to the two most important families of plants for tropical frugivorous birds (Rubiaceae and Melastomataceae, respectively) and, because their fruits are succulent, they are appreciated by a variety of frugivorous birds, especially the small ones that feed in the lower strata of the vegetation (Snow 1981, Maruyama et al 2013). On the other hand, the fruit of Schefflera morototoni is rich in lipids and proteins (Snow 1971), and therefore also attracts a wide variety of frugivores ranging from the smallest to the largest (Saracco et al 2005, Parrini et al 2013.…”

“…Frugivorous birds represent 56% of the world's avian families and, in Neotropical forests, 25 to 30% of the avifauna includes fruits in their diet (Pizo & Galetti 2010). According to Jordano (1987), studies of frugivory by birds in tropical forests are relatively well reported (e.g., Snow 1981, Jordano 1987, Galetti & Pizo 1996, Medellín & Gaona 1999, Silva & Tabarelli 2000, Bascompte et al 2003, Saracco et al 2005. It is estimated that 50 to 90% of tree species in tropical forests produce zoochorous fruit (Howe & Smallwood 1982).…”

Frugivory by birds on Schefflera morototoni (Araliaceae) in a Cerrado-Amazon orest transition area, eastern Mato Grosso, Brazil

“…Fruit production is continuous with prolonged maturation, though annual fruit volume and maturity may be influenced by climatic factors (Franco and Ferreira 2002). Infructescences are abundant, green-purplish, and occur at the ends of branches, this provides contrast with the leaves and make it easier for the birds to locate those (Saracco et al 2005). Fruits are fleshy drupes with an average width of 4-6 mm and average length 6-10 mm.…”

“…They usually contain two flat seeds each up to 5 mm in length and with a < 1 mmthick protein-and lipid-rich pulp covering (Snow 1971). They are considered an important food source for forest birds throughout the plants Central and South America range (Snow 1981;Sick 1997;Saracco et al 2005;Parrini et al 2013). Given the above, our objectives were: (i) to record the species of birds that consumed Schefflera morototoni fruits; and (ii) to evaluate the potential of these species as dispersers of seeds from this plant species in a Cerrado-Amazon Forest transition area in the state of Mato Grosso, Brazil.…”

Neighborhood effects on seed dispersal by frugivores: testing theory with a mistletoe–marsupial system in Patagonia

“…A fair number of field studies document how fruiting plant neighbors affect fruit-removal rates by creating facilitation or competition among plant neighbors that share frugivores (Manasse and Howe 1983, Sargent 1990, Garcı´a et al 2001, Carlo 2005, Saracco et al 2005, Blendinger and Villegas 2011. As far as we are aware, there are no empirical studies examining how seed dispersal distances are affected by neighborhood and crop size variables, or probing on the effects of neighborhood-mediated dispersal on plant population dynamics.…”