SummaryGrowth in seed dispersal studies has been fast-paced since the seed disperser effectiveness (SDE) framework was developed 17 yr ago. Thus, the time is ripe to revisit the framework in light of accumulated new insight. Here, we first present an overview of the framework, how it has been applied, and what we know and do not know. We then introduce the SDE landscape as the two-dimensional representation of the possible combinations of the quantity and the quality of dispersal and with elevational contours representing isoclines of SDE. We discuss the structure of disperser assemblages on such landscapes. Following this we discuss recent advances and ideas in seed dispersal in the context of their impacts on SDE. Finally, we highlight a number of emerging issues that provide insight into SDE. Overall, the SDE framework successfully captures the complexities of seed dispersal. We advocate an expanded use of the term dispersal encompassing the multiple recruitment stages from fruit to adult. While this entails difficulties in estimating SDE, it is a necessary expansion if we are to understand the central relevance of seed dispersal in plant ecology and evolution.

Disperser effectiveness is the contribution a disperser makes to the future reproduction of a plant. Although it is a key notion in studies of seed dispersal by animals, we know little about what determines the effectiveness of a disperser. The role of the present paper is to review the available information and construct a hierarchical framework for viewing the components of disperser effectiveness.Effectiveness has both quantitative and qualitative components. The quantity of seed dispersal depends on (A) the number of visits made to the plant by a disperser and (B) the number of seeds dispersed per visit. The quality of seed dispersal depends on (A) the quality of treatment given a seed in the mouth and in the gut and (B) the quality of seed deposition as determined by the probability that a deposited seed will survive and become an adult. In this paper I review the ways disperser behavior, morphology and physiology can influence these major components of disperser effectiveness, and when data permit present preliminary analyses of relationships among components.

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...

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Seed dispersal determines the conditions that seeds, seedlings, and saplings confront, and thus potentially provides a unifying theme for plant population ecology. This potential is seldom realized, however, because dispersal is infrequently linked effectively with its consequences. We advocate the importance of explicitly designing studies quantifying spatial patterns of dispersal at a variety of scales, causes of those spatial patterns, and consequences of alternative patterns of dispersal for all stages from seed to new adult. It is critical to link this chain of events with thorough investigations of individual dispersal systems rather than continuing to collect small pieces of the story from a multitude of systems. We first present a brief overview of spatial patterns, causes, and consequences of dispersal. We then develop the argument that a correspondence, or lack of correspondence, between patterns of seed arrival and adult recruitment tells little about causal relationships between the two. Finally, we suggest that a combination of observational and experimental approaches taking into account the complexities of recruitment processes will better link dispersal with its consequences. Experimental manipulations of patterns of seed arrival and causal modelling are potentially powerful approaches, but may be limited in application to easily manageable species.Résumé: Les processus par lesquels les graines sont disséminées déterminent les conditions auxquelles les graines, les plantules et les gaules seront éventuellement confrontés et fournissent aux écologistes un thème unificateur potentiel pour l'étude des populations végétales. Les écologistes parviennent rarement à élaborer de façon précise sur ce thème parce que les liens qui existent entre la dissémination des diaspores et les conséquences de cette dernière sont souvent faibles. Nous insistons sur l'importance d'effectuer des études précises permettant de quantifier les patrons spatiaux de dissémination à des échelles variées, de façon à déterminer les causes de ces patrons et leurs conséquences sur tous les stades de la vie d'une plante, c'est-à-dire du stade plantule jusqu'à l'âge adulte. Pour parvenir à ces fins, il est primordial d'étudier en détail chaque système de dissémi-nation de diaspores plutôt que de collecter des bribes d'information provenant d'une multitude de systèmes. Dans cet article, nous présentons en premier lieu une brève revue des patrons spatiaux de dissémination, ainsi que de leurs causes et conséquences sur les populations végétales. Nous développons ensuite la thèse qu'une correspondance, ou l'absence de correspondance, entre les patrons de dissémination des graines et le recrutement des individus qui parviendront à l'âge de la maturité, ne donne que peu d'informations sur les relations de cause à effet qui existent entre les deux phénomènes. Finalement, nous suggérons qu'une approche combinée (observations sur le terrain, expérimentations) tenant compte de la complexité du processus de recrutement est probablement la meille...

An overview of the classes of mechanisms causing recruitment limitation, which includes source limitation, dissemination limitation and establishment limitation, is presented. The three mechanisms of dissemination limitation are discussed in detail with emphasis on how the behaviours and physiologies of animal seed dispersers may lead to dissemination limitation. The different consequences of dissemination limitation for patterns of recruitment in plant populations and how these patterns in turn affect plant community structure are also discussed, including the ways on how dissemination limitation can contribute to the origin and maintenance of species diversity in ecological communities.

To assess how the decimation of large vertebrates by hunting alters recruitment processes in a tropical forest, we compared the sapling cohorts of two structurally and compositionally similar forests in the Rio Manu floodplain in southeastern Peru. Large vertebrates were severely depleted at one site, Boca Manu (BM), whereas the other, Cocha Cashu Biological Station (CC), supported an intact fauna. At both sites we sampled small (!1 m tall, ,1 cm dbh) and large (!1 cm and ,10 cm dbh) saplings in the central portion of 4-ha plots within which all trees !10 cm dbh were mapped and identified. This design ensured that all conspecific adults within at least 50 m (BM) or 55 m (CC) of any sapling would have known locations.We used the Janzen-Connell model to make five predictions about the sapling cohorts at BM with respect to CC: (1) reduced overall sapling recruitment, (2) increased recruitment of species dispersed by abiotic means, (3) altered relative abundances of species, (4) prominence of large-seeded species among those showing depressed recruitment, and (5) little or no tendency for saplings to cluster closer to adults at BM. Our results affirmed each of these predictions.Interpreted at face value, the evidence suggests that few species are demographically stable at BM and that up to 28% are increasing and 72% decreasing. Loss of dispersal function allows species dispersed abiotically and by small birds and mammals to substitute for those dispersed by large birds and mammals. Although we regard these conclusions as preliminary, over the long run, the observed type of directional change in tree composition is likely to result in biodiversity loss and negative feedbacks on both the animal and plant communities. Our results suggest that the best, and perhaps only, way to prevent compositional change and probable loss of diversity in tropical tree communities is to prohibit hunting.

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