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Fremontodendron decumbensgrows in a single county in central California, USA. Prior research showed that its elaiosome-bearing seeds are dispersed by the harvester ant Messor andrei. I tested several hypotheses regarding the positive role of ant-mediated dispersal to F. decumbens: (1) Does ant-mediated seed dispersal facilitate seed escape from rodent predation?; (2) Does ant processing of seeds stimulate germination?; (3) Are ant middens more suitable microsites for seed or seedling survival in unburned chaparral areas?; and (4) Do survival benefits of dispersal occur post-fire in the form of differences in seedling survival probabilities and, if so, why? Results of tests of each hypothesis were: (1) similar percentages of seeds placed on ant middens and under F. decumbens shrub canopies were destroyed by rodents, but seeds from which elaiosomes had been removed were more likely to escape rodent predation; (2) seeds processed by ants did not germinate more readily than seeds removed directly from shrub branches; (3) seedling predation was a major cause of mortality in unburned chaparral on both ant middens and under shrubs, and overall seedling survival did not differ between the two microsites; (4) post-burn seedling survival was significantly greater for seedlings dispersed away from F. decumbens shrub canopies, because dispersed seedlings were both less likely to be killed by predators and more likely to be growing in a gap created by the fire-caused death of an established shrub. I concluded that the major ecological benefit toF. decumbens of ant-mediated seed dispersal was elevated post-fire seedling survival resulting from enhanced escape by dispersed seedlings from both predation and competition.

Fremontodendron decumbens grows in a single county in central California, USA. Prior research showed that its elaiosome-bearing seeds are dispersed by the harvester ant Messor andrei. I tested several hypotheses regarding the positive role of ant-mediated dispersal to F. decumbens: (1) Does ant-mediated seed dispersal facilitate seed escape from rodent predation?; (2) Does ant processing of seeds stimulate germination?; (3) Are ant middens more suitable microsites for seed or seedling survival in unburned chaparral areas?; and (4) Do survival benefits of dispersal occur post-fire in the form of differences in seedling survival probabilities and, if so, why? Results of tests of each hypothesis were: (1) similar percentages of seeds placed on ant middens and under F. decumbens shrub canopies were destroyed by rodents, but seeds from which elaiosomes had been removed were more likely to escape rodent predation; (2) seeds processed by ants did not germinate more readily than seeds removed directly from shrub branches; (3) seedling predation was a major cause of mortality in unburned chaparral on both ant middens and under shrubs, and overall seedling survival did not differ between the two microsites; (4) post-burn seedling survival was significantly greater for seedlings dispersed away from F. decumbens shrub canopies, because dispersed seedlings were both less likely to be killed by predators and more likely to be growing in a gap created by the fire-caused death of an established shrub. I concluded that the major ecological benefit to F. decumbens of ant-mediated seed dispersal was elevated post-fire seedling survival resulting from enhanced escape by dispersed seedlings from both predation and competition.

Premise of the study Phenological mismatch has received attention in plant-pollinator interactions, but less so in seed dispersal mutualisms. We investigated whether the seasonal availability of myrmecochorous seeds is well matched to the seasonal activity patterns of seed-dispersing ants. Methods We compared seasonal timing of seed removal by a keystone seed-dispersing ant, Aphaenogaster rudis, and fruit dehiscence of several species of plants whose seeds it disperses in a deciduous forest in southern Ontario, Canada. We examined the timing of elaiosome "robbing" by the nonnative slug Arion subfuscus and tested whether seed removal by ants declines in response to supplementation with additional elaiosome-bearing seeds (ant "satiation"). Key results Seed removal from experimental depots peaked early in the season for all plant species and correlated with temperature. In contrast, elaiosome robbing by slugs increased late in the season and thus may disproportionately affect plants with late-dehiscing fruits. Ant colonies removed seeds at similar rates regardless of seed supplementation, indicating that satiation likely does not impact seasonal patterns of seed dispersal in this system. Fruits of the five myrmecochorous plant species in our study dehisced at discrete intervals throughout the season, with minimal overlap among species. Peak dehiscence did not overlap with peak seed removal for any plant species. Conclusions Fruit dehiscence of myrmecochorous plants and peak ant seed dispersal activity occur asynchronously. Whether future climate warming will shift ant and plant phenologies in ways that have consequences for seed dispersal remains an open question.

Premise of the study Comparing ecological attributes of endemic species with related, widespread species can reveal differences accounting for rarity. Forests of the southeastern United States are home to many range-restricted endemic and widespread species of Trillium, a genus of ant-dispersed herbs. Evidence suggests that aspects of seed-related life history stages are often correlated with plant rarity, but few studies have tested whether the process of seed dispersal differs for endemic and widespread species. To address this question, we compared aspects of seed dispersal effectiveness (SDE) for three sympatric, widespread endemic Trillium species pairs. Methods We observed seed dispersal for Trillium species pairs by ants at eight sites, recorded numbers of seeds dispersed and dispersal distances, and described disperser interactions. To test disperser preference, we presented seeds of each pair to captive colonies of Aphaenogaster picea, a keystone disperser. Seeds were assigned scores based on worker behavior, and we recorded proportions of seeds dispersed after 1 h and 24 h. Key results Field observations yielded some significant within-pair differences. Ants dispersed more seeds of widespread species for all pairs, although dispersal distances did not differ. In laboratory experiments, after 24 h, ants dispersed more seeds of widespread species into nests. Conclusions Endemic Trillium species had lower overall SDE than did their widespread congeners. These findings add to the list of ecological and demographic challenges that face endemic plants when compared to common congeners. Lower SDE may negatively impact reproductive rates and the colonization of new habitats, which may contribute to patterns of endemism.

Studies on embryology and seed morphology are complementary to molecular phylogenetics and of special value at the genus level. This paper discusses the delimitation and evolutionary relationships of genera within the tribe Hydrophylleae of the Boraginaceae. The seven Nemophila species characterized by a conspicuous seed appendage are similar in embryology and seed structure. The ovule is tenuinucellate and unitegmic with a meristematic tapetum. The embryo sac penetrating the nucellar apex is of the Polygonum type, has short-lived antipodal cells, and an embryo sac haustorium. The endosperm is cellular, producing two terminal endosperm haustoria, of which the chalazal has a lateral branch. Embryogeny is of the Chenopodiad type (as in Pholistoma). The seed coat is formed from the small-celled inner epidermis of the integument. The large-celled outer epidermis of the integument disintegrates into scattered cells. Seed pits evolve from irregularly placed inner epidermal cells of the integument. The chalazal part of the ovule produces a cucullus, that functions as an ant-attracting elaiosome. Those species of Nemophila with a conspicuous cucullus form a natural genus. Nemophila is most closely related to Pholistoma. The integumentary seed pits of Nemophila might have evolved from ovular seed pits similar to those in Pholistoma.

Myrmecochores are plants with seeds adapted for ant dispersal. This specialized dispersal syndrome may provide Erythronium americanum seeds with protection from predators within the eastern deciduous forests. To determine the adaptive significance of myrmecochory in E. americanum, seed removal rates and seed predation in relation to seed release date and location along the Potomac River in Langley, Virginia, were examined. The number of seeds removed from four exclosure treatments were monitored two times in 1992 and three times in 1993 within floodplain and hilltop populations of E. americanum. Overall, seed removal was greatest from control depots, and E. americanum seeds were removed at nearly the same rate from predator-exclusion depots, indicating that removal from open depots is largely due to ant removal. Ants removed significantly more seeds than predators in the first 48 h of seed exposure and could potentially remove all E. americanum seeds before nightfall. Aphaenogaster rudis was identified as the primary disperser of E. americanum. Seeds placed in depots after the natural seed release period were discovered more quickly and removed by ants at a significantly higher rate than seeds released at the natural date. These results suggest that ant dispersal of E. americanum seeds reduces the likelihood of seed predation.

Seed predation, an omnipresent phenomenon in tropical rain forests, is an important determinant of plant recruitment and forest regeneration. Although seed predation destroys large amounts of the seed crop of numerous tropical species, in many cases individual seed damage is only partial. The extent to which partial seed predation affects the recruitment of new individuals in the population depends on the type and magnitude of alteration of the germination behavior of the damaged seeds. We analyzed the germination dynamics of 11 tropical woody species subject to increasing levels of simulated seed predation (0–10% seed mass removal). Germination response to seed damage varied considerably among species but could be grouped into four distinct types: (1) complete inability to germinate under damage ≥1%, (2) no effect on germination dynamics, (3) reduced germination with increasing damage, and (4) reduced final germination but faster germination with increasing damage. We conclude that partial seed predation is often nonlethal and argue that different responses to predation may represent different proximal mechanisms for coping with partial damage, with potential to shape, in the long run, morphological and physiological adaptations in tropical, large-seeded species.

Two tropical herbaceous plant species, Calathea microcephala and Calathea ovandensis, exhibit morphological adaptations for seed dispersal by ants. In the field, 21 ant species are attracted to the arils of the seeds. Previously known as predatory carnivores, the ponerine ants Odontomachus laticeps, 0. minutus, Pachycondyla harpax, and P. apicalis carry the seeds toward their nests, behaving as though they were carrying prey. These ants remove the aril in the nest, and seeds without arils germinate more readily than seeds with arils. Ant foraging distances can account for seedling distributions. Myrmecochory may be far more common in tropical rain forests than has been previously suspected. THIS iS the first well-documented case of myrmecochory, seed dispersal by ants, for wet tropical rain forest floor herbs. Many cases of myrmecochory have been reported from temperate latitude mesic forests (see reviews in Ridley, 1930; van der Pijl, 1971; see examples Handel, 1976; Culver and Beattie, 1978). Only a few scattered reports come from the tropical latitudes, and, of these, the majority refer to ant-garden epiphytes high in the branches of trees (Ule, 1905, 1908; Bequaert, 1922; van Leeuwen, 1929; van Steenis and van Steenis, 1934; van der Pijl, 1951, 1955; Kleinfeldt, 1978). In subtropical Australia, a large number of myrmecochores have recently been found, but these were from dry sclerophyllous shrub vegetation, not from mesic forest herbs (Berg, 1976). The study of myrmecochory in a tropical forest bears on three evolutionary questions: 1) Does a mutualism such a myrmecochory imply an equivalent amount of evolutionary 1 Received for publication 15 May 1979; revision accepted 11 September 1979. We thank the following: Refugio Cedillo Trigos, Xavier Ramirez, Gabino Perez Garcia and other staff of the Estaci6n de Biologia Tropical de Los Tuxtlas, M6xico; Enrique Gonzalez, Dr. Jos6 Sarukhan, Dra. Ana Luisa Anaya, of the Instituto de Biologia, UNAM, M6xico; Diane L. Marshall and Dr. L. E. Gilbert, of the University of Texas, Austin; Dr. Stephen Bullock, of La Jolla, California; Dr. David C. Culver and Dr. E. Raymond Heithaus, of Northwestern University. Travel funds were provided by Special Dissertation Research Grant Committee, Northwestern University, awarded to C. C. Horvitz, and by a grant to A. J. Beattie and D. C. Culver (NSF DEB 76-02227). A pilot trip leading to this project was supported by a grant to Dr. L. I. Nevling, Field Museum of Natural History (NSF BMS 73-07061 A02). We thank him for his encouragement and Dr. Arturo G6mez-Pompa and field assistant Juan Ismael Calzada, of INIREB, Xalapa. adaptation for all species involved in the interaction (Vandermeer and Boucher, 1978; Gilbert, 1978)? 2) What are the effects of ant seed dispersal systems on germination and seedling distributions of plant populations (Grant, 1958; Sarukhan, 1974; McKey, 1975)? 3) What is the frequency of seed-ant interactions in tropical rain forests and how might such inconspicuous plant-animal interactions affect tropical ecosystem diversity (Farnsworth and Golley, 1973; Baker, 1973; GomezPompa et al., 1976; Howe, 1977; Gilbert, 1980)? This work is part of a study of the demographic consequences of myrmecochory in two herbaceous perennial plant species, Calathea microcephala (P. & E.) Koernicke sens. lat. and C. ovandensis Matuda (Marantaceae).2 These plants occur in primary high evergreen tropical rain forests (Gomez-Pompa, 1973) and in secondary forests in the region of Los Tuxtlas, Veracruz, Mexico. MATERIALS AND METHODS-Morphological adaptations for myrmecochory-Two hundred fifty individuals of C. microcephala and 150 individuals of C. ovandensis in permanent quadrats were monitored during the fruiting season, May-October, 1977-1978, in the field. The C. microcephala study site was in the Biological Reserve of the Universidad Nacional Autonoma de Mexico at Los Tuxtlas at an elevation of 160 m. There were two study sites for C. ovandensis, one at Los Chorros approaching Cerro Amarillo and the other at 2 Voucher specimens deposited at the Field Museum of Natural History, and the National Herbarium of Mexico (UNAM). Generous determinations and advice were provided by Dr. Helen Kennedy, Lyon Arboretum, University of Hawaii.

Experimental plantings of the seeds of the two species Viola odorata and V. hirta were carried out to determine relative importance of three effects of myrmecochory: 1) clumping of seeds, 2) scarification of the testa and elaiosome removal, and 3) relocation into ant nests. The study site was a beech-larch wood in southern England. Data show that clumping slightly reduces seedling emergence, scarification and elaiosome removal slightly enhances it, while the nest environment significantly increases the rate of seedling emergence. Only the last effect is statistically significant. Seedlings from nests have larger first adult leaves. The possible impact of ant manipulation of seeds on seedling recruitment into myrmecochorous populations is discussed. THE PHENOMENON of ant dispersal of diaspores (myrmecochory) has been extensively documented both by studies of morphological adaptation of diaspores for dispersal (Sernander, 1906; Berg, 1975), and observations of ants carrying diaspores that were placed within their foraging areas (Sernander, 1906; Culver and Beattie, 1978; Beattie, Culver, and Pudlo, 1979). A considerable proportion of the vernal flora of cool temperate forests apparently is ant-dispersed, but there has been no direct documentation of the advantage of myrmecochory to plants. Handel (1978) gives strong, but indirect, evidence that myrmecochores escape competition, and Culver and Beattie (1978) give indirect evidence that myrmecochores escape seed predation. In this paper we provide direct evidence of the effect ant dis

The reproductive ecology of Jeffersonia diphylla (L.) Pers. (Berberidaceae) was investigated by studying its breeding system, ovule production, seed set, seed dispersal by ants and seed predation by rodents. This species flowers early in the spring and is facultatively autogamous. In a typical year fruit and seed set is high (90%), however, freezing temperatures from late spring frosts in 1983 and 1985 resulted in low fruit set (7% and 20%, respectively), and reduced seed set in those flowers that produced fruit. No differences in seed set between selfed and outcrossed flowers were observed over a two-yr period (1983-84). Ovule number per capsule increased with plant size as measured by leaf number. Seed set and seed wt were unaffected by leaf number unless leaves were removed after flowering was initiated. Jeffersonia diphylla is myrmecochorous. Ants removed seeds faster when seeds were placed in areas where J. diphylla plants were absent, suggesting that dispersal within J. diphylla populations is ant limited. Moreover, fresh (1 day old) seeds were removed by ants faster than 3 day old seeds. Seed predation by rodents prior to dehiscence from capsules is heavy in large populations (85-90%), and apparently negligible in small populations. Predation of seeds that are released from capsules is heavy (approx. 66%), particularly at night. Overall, seed predators consume about 96% of the seed crop in well established populations, but probably much less in small young populations. Hence, seedling recruitment is likely to be higher in small populations, whereas ramet production from rhizomes is the primary mode of propagation in large ones. The evolution of autogamy, early flowering, and myrmecochory are discussed in light of the results of this study.

All Vancouveria species are habitual myrmecochores of the Viola odorata type. The anatropous, bitegmic seed develops an unusual elaiosome in the form of a large, empty, folded and lobed sac of epidermal tissue. The thin-walled assimilating capsule dehisces along an oblique weak zone that probably represents the suture between two fused and unequal carpels. In V. hexandra the capsule opens early to expose immature assimilating seeds. Decurved pedicels, down-turned fruits, and weak funiculi produce tachyspory. The related Epimedium, Jeffersonia, and Plagiorhegma have appendaged seeds and other possible myrmecochorous features resembling those of Vancouveria. Myrmecochory was probably established in the early or middle Tertiary period. The Vancouveria-Epimediumn complex indicates that enormous plant migrations may be accomplished -by means of ants. VANCOUVERIA has been included in a survey of ant-dispersed North American plants and their myrmecochorous adaptations (Berg, 1958, 1959, 1966, 1969) because all its species have a white, spongy seed appendage that, according to Stearn (1938), probably is attractive to ants. The related epimediums of the Old World also have seed appendages, and E. alpinum was believed by Sernander (1906) to be myrmecochorous. The purpose of this study is: first, to investigate the function of this appendage; second, to describe the Vancouveria seed and its appendage in detail; and third, to relate appendage function to certain aspects of general structure, habit, evolution, and distribution of the genus. Vancouveria is a genus of three species endemic

A B S T R A C T Both species of Dendromecon are diplochorous, that is, the seeds are first scattered from the mother plant by violently dehiscing capsules and then transported further away by ants, which are strongly attracted to the e]aiosome at the micropylar end of the seed. The tensions that cause the capsule to explode develop between the two carpels and also between lateral and central fiber strands in the capsular valves. The elaiosome is unusual in that it contains large quntities of starch in addition to the commonly present fatty oils and that it is more drought resistant than most known elaiosomes. Seed dispersal is very efficient over short distances, but migration barriers a few hundred meters or more cannot be crossed except by chance dispersal. Dendromecon differs strikingly from most ant-dispersed plants in being woody and xerophytic; so far, D. rigida is the only chaparral plant known to be habitually dispersed by ants. The presence of an autochorous-myrmecochorous type of seed dispersal in D. rigida may partly explain the polymorphism of this species, since this type of seed dispersal tends to keep local populations isolated. The nearly complete correspondence, anatomically, morphologically, and functionally, between the fruit of Dendromecon and that of Eschscholzia strongly supports the idea of a close taxonomic relationship between these two genera. The seed appendage is believed to be a "recent" specialization in Dendroniecon, phylogenetically independent from seed appendages facilitating dispersal by ants in other genera of the Papaveraceae. DISPERSAL ECOLOGY, the study of dispersal processes and mechanisms, is an underdeveloped, mostly neglected sector of botany, despite the fact that ecologists, evolutionists, plant geographers, and evolutionary taxonomists all would profit from increased teaching and research activity in this classical field. A particularly interesting and rewarding aspect for study is myrmecochory, i.e., seed dispersal by ants. Only a very few plants in North America are known to be regularly dispersed by ants: Uvularia grandiflora Sm. (Robertson, 1897), Sanguinaria canadensis L. (Robertson, 1897; Kerner, 1898

Carex pedunculata is the first North American species of the Cyperaceae that is identified as a myrmecochore. Many morphological and phenological features of this species and its breeding system are interpreted as adaptive for seed dispersal by ants. In laboratory tests, workers of the ant species Aphaenogaster rudis carry the diaspores to the nest, eat the elaiosomes, carry larvae to the elaiosomes to feed, and deposit diaspores whose elaiosomes have been eaten with other nest debris. The achenes then germinate. Achenes will also germinate without any handling by ants. Workers will also transport diaspores with uneaten elaiosomes when the nest is disturbed. Greenhouse tests show that seedling growth is greatly inhibited if a diaspore remains near the parent plant and cohort seedlings. Field studies of natural populations identify rotting logs (the location of ant nests) as forest floor microsites for colonization of C. pedunculata and other myrmecochores. Ant nesting behavior may pattern much of the herb stratum. This species is self-compatible, and single seeds may start successful new populations. Three processes contribute to population growth: vegetative growth, germination of untransported diaspores, and germination of ant-transported diaspores. THE GENUS CAREX has had a remarkable evolutionary radiation, with hundreds of species recognized in America (Mackenzie, 1935; Hermann, 1974) and Eurasia (Kuikenthal, 1909). Despite this, little is known about the distribution or ecology of most species, perhaps because the superficial vegetative similarities of these sedges make identification difficult. As part of a study of the comparative popula

A B S T R A C T persal systems. The majority of species, the diplochores, have evolved a system which com- bines ballistic and ant seed dispersal with predator avoidance. Diplochory itself may be a re- sponse to predation pressure. The minority of species are purely myrmecochorous, possibly highly coevolved with specific ant species, thus limiting the distribution of the Viola species concerned.