Competition for dispersal agents among tropical trees: influences of neighbors

Manasse, Robin S.; Howe, Henry F.

doi:10.1007/bf00378836

Cited by 98 publications

(83 citation statements)

References 17 publications

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“…These results, and those of other recent studies (Janzen 1982(Janzen , 1983Manasse and Howe 1983;Herrera 1984c; Manzur and Courtney in press), strongly point to the conclusion that environmental constraints external to the plant-seed disperser interaction usually impose very restrictive limits on the maximum degree of adaptedness attainable by dispersal-related plant traits (see also Howe and Vande Kerckhove 1979;Herrera 1982 a;Janzen 1983). These constraints heavily operate against the feasibility of coevolution between species of plants and vertebrate seed dispersers.…”

Section: Concluding Discussionsupporting

confidence: 52%

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Seed dispersal and fitness determinants in wild rose: Combined effects of hawthorn, birds, mice, and browsing ungulates

Herrera

1984

Oecologia

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Summary.Factors not directly related to either the plants or their avian seed-dispersal agents are ultimately responsible for the sign and magnitude of the average contribution of seed vectors to the fitness of Rosa canina plants in southern Spain. Coexistence with simultaneously fruiting Crataegus monogyna, reproductive depression caused by browsing ungulates, and seed predation by mice, are some of these factors. Disperser behaviour may either enhance, depress, or be neutral to Rosa fitness depending on the relative importance of the reproductive depression caused by browsing ungulates (pre-dispersal) and mice (post-dispersal). The contribution of seed vectors to Rosa fitness is largely independent of their dispersal-related traits and out of the control of the parent plants. Environmental constraints external to the plant -seed disperser interaction seem therefore to impose very restrictive limits on the maximum degree of adaptedness attainable by dispersal-related plant traits, thus operating against coevolution.pressures exerted by dispersers on dispersal-related plant traits could hardly result in observable adaptations if they are offset (or reversed) by stronger pressures from nondisperser organisms influencing plant fitness and/or if dispersal-related determinants of plant fitness are largely nonheritable (Herrera 1984c). These assumptions have not been critically tested to date, but some evidence tends to suggest that they may often be unjustified (Janzen 1982(Janzen , 1983Herrera 1982a Herrera , 1984aManasse and Howe 1983; Manzur and Courtney in press).Seed dispersal of wild rose by frugivorous birds, and its complex relation to browsing mammals, granivorous rodents, and coexisting hawthorn, are investigated in this paper. The objectives are: (1)to compare the relative importance of disperser and non-disperser organisms in determining dispersers' contribution to wild rose fitness; and (2) to evaluate the extent to which observed seed dispersal patterns should be attributed to selection of dispersers on heritable wild rose traits.

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Section: Concluding Discussionsupporting

confidence: 52%

“…These assumptions have not been critically tested to date, but some evidence tends to suggest that they may often be unjustified (Janzen 1982(Janzen , 1983Herrera 1982a Herrera , 1984aManasse and Howe 1983; Manzur and Courtney in press).…”

Section: Discussionmentioning

confidence: 99%

Seed dispersal and fitness determinants in wild rose: Combined effects of hawthorn, birds, mice, and browsing ungulates

Herrera

1984

Oecologia

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“…The competition hypothesis has been best supported within conspecific neighborhoods. Manasse and Howe (1983) found that increasing densities of conspecific fruits within a patch explained a decrease in fruit removal rates from individuals of the tropical shrub Virola surinamensis during peak fruiting seasons. In Puerto Rico, Schefflera morototoni trees also competed intraspecifically for dispersers, lowering overall visitation rates per individual (Saracco et al, 2005).…”

Section: Neighborhood Effectsmentioning

confidence: 99%

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

2017

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Mutualistic interactions between species are crucial for the maintenance and functioning of the community. Current research has shown the importance of not only understanding the structure of these mutualistic interaction networks but also their temporal dynamics. Temporal changes in species abundance, such as those caused by vertebrate resource tracking, may create temporal variability in a network though neighborhood effects and influence the directedness of dispersal. While much research has been done on resource tracking, neighborhood effects, and directed dispersal individually, little research has been done into their interrelationships and, therefore, theory of how resource tracking can influence frugivory and seed dispersal networks remains poorly developed. We use the available literature to show the prevalence of resource tracking by vertebrate frugivores and hypothesize how, through neighborhood effects, resource tracking may influence short-term variation in network properties. We then discuss how resource tracking can influence long-term network properties by altering the dispersal of plant species. Lastly, we use this information to hypothesize how the introductions of new species into a community may alter the influence of resource tracking on frugivory and seed dispersal. While trait matching and links that are not possible between species in a community (i.e., forbidden links) play a large role in determining the structure of a network, temporal change in the abundance of species due to resource tracking may also affect the properties of networks. By increasing our understanding of the role resource tracking has in the temporal variability of frugivory and seed dispersal networks, we can better determine the full extent of species interactions and provide valuable information for the conservation of ecological communities.

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“…Just as isolation can affect herbivory (Evans 1983) and frugivory (Manasse and Howe 1983), so can the extent and type of isolation influence pollination (Rathcke 1983, Thomson 1983, Waser 1983. First, a plant may be distant from the nearest conspecific, relative to pollinators' typical flights, or isolated in the absolute sense.…”

Section: Introductionmentioning

confidence: 99%

Floral Neighborhood and Pollination Success in Four Hummingbird‐Pollinated Cloud Forest Plant Species

Feinsinger¹,

Murray²,

Kinsman³

et al. 1986

Ecology

138

129

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Abstract. In a cloud forest at Monteverde, Costa Rica, we examined pollen loads received by self-compatible flowers of two pairs of plant species pollinated by hummingbirds: Hansteinia blepharorachis and Razisea spicata (Acanthaceae), and Besleria triflora and Drymonia rubra (Gesneriaceae). Each pair consisted of one species (Hansteinia or Besleria) pollinated by short-billed hummingbirds and a related species (Razisea or Drymonia) pollinated by long-billed hummingbirds. At three different times per species, separated by 1-3 mo, we examined flowers on 28-40 focal plants from a wide variety of floral neighborhoods, ranging from plants isolated from conspecifics, either by distance or by other flowering species pollinated by the same hummingbirds, to plants surrounded by conspecifics.Because short-billed hummingbirds often restrict foraging to areas ofhigh flower density, and because short-tubed flowers adapted for hummingbirds often have similar pollen placement, we predicted that short-tubed flowers isolated from conspecifics would receive fewer conspecific grains and more heterospecific grains than short-tubed flowers surrounded by conspecifics. Because long-billed hummingbirds often forage over large areas and because long-tubed flowers adapted for hummingbirds tend to diverge in pollen placement, we predicted that pollination of long-tubed flowers would be relatively unaffected by floral neighborhood.Effects on pollen loads of floral neighborhood (nearness to or isolation from other flowers) followed few patterns consistent with our prediction or with conventional theory. (1) There were no consistent effects of floral neighborhoods on numbers of heterospecific grains deposited on stigmas; in all four species, regardless of corolla length, effects of particular neighborhood variables (as determined with stepwise multiple regression) were as likely to run exactly counter to conventional models as to corroborate models. (2) In none of the 12 sampling runs did increases in absolute densities of neighboring heterospecific flowers adversely affect pollination. (3) However, in two runs, loads of conspecific grains increased with increases in the absolute density of neighboring conspeci:fic flowers, and/or (in three runs) with increases in their relative density (proportion of conspecifics among neighboring flowers). These runs all involved short-flowered species rather than long-flowered species, tending to confirm our initial prediction, but half the sampling runs, even of short-flowered species, failed to show any density-dependent effects from neighboring flowers pollinated by the same hummingbirds.Flowers frequently received fewer conspeci:fic grains than they had ovules to be fertilized. Therefore, the potential existed for floral neighborhoods to affect seed set and fitness of plants. Nevertheless, even though neotropical hummingbird-pollinated flowers have been cited as examples of species whose flowering peaks are displaced through competition for pollination, competitive effects from neighboring heterospeci...

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Competition for dispersal agents among tropical trees: influences of neighbors

Cited by 98 publications

References 17 publications

Seed dispersal and fitness determinants in wild rose: Combined effects of hawthorn, birds, mice, and browsing ungulates

Seed dispersal and fitness determinants in wild rose: Combined effects of hawthorn, birds, mice, and browsing ungulates

Connecting Resource Tracking by Frugivores to Temporal Variation in Seed Dispersal Networks

Floral Neighborhood and Pollination Success in Four Hummingbird‐Pollinated Cloud Forest Plant Species

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