Seed Disperser Effectiveness: The Quantity Component and Patterns of Seed Rain for Prunus mahaleb

Abstract

Abstract.In this paper we analyze the seed dispersal stage of the Prunus mahaleb-frugivorous bird interaction from fruit removal through seed delivery within the context of disperser effectiveness. The effectiveness of a frugivorous species as a seed disperser is the contribution it makes to plant fitness. Effectiveness depends on the quantity of seed dispersed (''quantity component'') and the quality of dispersal provided each seed (''quality component''). For the main frugivores, we studied abundance, visitation rate, and feeding behavior, the major variables influencing the quantity component of effectiveness, and the postforaging microhabitat use and resultant seed shadows, which set the stage for postdispersal factors that will influence the quality component of effectiveness.Legitimate seed dispersers (SD) swallowed fruits whole and defecated or regurgitated intact seeds; pulp consumers (PC) pecked fruits to obtain pulp and dropped seeds to the ground, but some species occasionally dispersed seeds (PCSD species). Overall numbers of fruits removed (i.e., handled) by avian frugivores were similar in the two study years; however, the estimated percentage of seeds dispersed differed significantly, with lower relative dispersal success in the year with greater relative abundance of PC species. Similar numbers of seeds were dispersed in the two years despite nearly a fourfold difference in number of fruits produced. Fruit crop size explained Ͼ80% variance in the number of seeds dispersed per tree.A total of 38 species of birds were recorded during censuses, with frugivores representing 68.8% of them; the relative representation of SD, PC, and PCSD species was 42.2%, 17.2%, and 9.4%, respectively. Individual trees showed extensive variation in visitation rates, ranging from 0.3 to 41.6 visits/10 h in any year. The main visitors were the SD species Phoenicurus ochruros (10.8 visits/10 h), Turdus viscivorus (9.2 visits/10 h), Erithacus rubecula (3.5 visits/10 h), and Sylvia communis (2.6 visits/10 h); and the PC species Fringilla coelebs (16.7 visits/10 h) and Parus ater (4.7 visits/10 h).Species with large quantity components of effectiveness typically had either high visit or high feeding rates, combined with high probability of dispersing a handled seed. Variation among species in fruit-handling behavior, however, was the main factor influencing variation in the quantity component. Visit rate in turn was influenced largely by local abundance. No single frugivore trait, however, can adequately estimate the quantity component of disperser effectiveness. A ''gulper''/''masher'' dichotomy helps explain differences in fruit handling among major frugivore types and shows many correlates with other aspects of frugivore activity that ultimately influence the quantity component.Most species showed marked preferences for microhabitats with plant cover, especially P. mahaleb, midheight shrubs, and Pinus (86.1% of the departure flights) and avoided open microhabitats. Most flights were over short distances (77.5% to perches...

Geographic consistency in the seed dispersal patterns of Taxus baccata L. in the Iberian Peninsula

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“…Both the number of dispersed seeds and the place where they are deposited strongly depend upon the identity and the behavior of the frugivorous animals (Jordano & Schupp, 2000;González-Varo et al, 2014). In temperate ecosystems, the main seed dispersers of fleshy-fruited trees are carnivorous mammals and birds (Guitián & Munilla, 2010;García et al, 2010;Peredo et al, 2013).…”

“…In temperate ecosystems, the main seed dispersers of fleshy-fruited trees are carnivorous mammals and birds (Guitián & Munilla, 2010;García et al, 2010;Peredo et al, 2013). Birds typically account for a large proportion of dispersed seeds (Jordano, 1987;Herrera, 1998;Martínez et al, 2008), depositing them at very short distances from mother trees (Godoy & Jordano, 2001;Jordano et al, 2007;Martínez et al, 2008), and usually under tree canopies as a result of their active selection of forest habitats (Alcántara et al, 2000;Jordano & Schupp, 2000;Martínez et al, 2008;Martínez & García, 2015a). This is the case of yew in the Cantabrian mountains (N Spain), for which birds tend to disproportionately disperse the seeds beneath conspecific adult trees (García et al, 2005b;Martínez et al, 2008), a pattern that may hamper recruitment due to increase predation, pathogen attack, and competition in high-density seed or seedling clumps (JanzenConnell effects;Janzen, 1970;Schupp & Jordano, 2011;Devaney et al, 2014).…”

Differential seed germination of a keystone palm (Euterpe edulis) dispersed by avian frugivores

“…The effectiveness of seed dispersal by vertebrates has been analysed by examining both quantitative and qualitative components (Jordano & Schupp 2000, Schupp et al 2010. While the quantitative component is relatively easily assessed in the field (e.g.…”

Frugivory and seed dispersal of Miconia theaezans (Bonpl.) Cogniaux (Melastomataceae) by birds in a transition palm swamp: gallery forest in Central Brazil

“…According to Jordano and Schupp (2000), the amount of time visitors remained on Miconia theaezans can be considered short (less than 2 minutes). The fact that the number of units ingested by the birds is positively correlated with the time they remained indicates that the visits lasted just enough time for the bird to feed (Francisco and Galetti, 2002a), which reduces the possibility of the seeds being deposited on the mother plant.…”