Effects of gut treatment on recovery and germinability of bovine and ovine ingested seeds of four woody species from the Sudanian savanna in West Africa

Passage rate through the digestive tracts of zebu cattle and sheep, and subsequent germination of egested seeds of four woody species from the Sudanian savanna, Acacia dudgeoni, Acacia seyal, Burkea africana and Prosopis africana, were studied. The result indicates large differences in passage rate among woody species, as well as between animals. The values ranged from 46% to 87% for seeds ingested by cattle while the lowest passage rate was 2.3% and the highest being 74% for seeds ingested by sheep. Among plant species, seeds of Prosopis africana had the highest passage rate through the digestive tract of both cattle and sheep. Seed passage through the gut showed a significant positive correlation with seed mass and thickness for cattle and sheep, respectively. The gut treatment and the retention time in the gut did not improve germination capacity and the speed of germination of dormant seeds. For non-dormant seeds of Acacia dudgeoni, the germination capacity was higher for seeds ingested by cattle than sheep. The speed of germination was also significantly higher for egested seeds than the control. It can be concluded that large herbivores could play an essential role in long distance dispersal of seeds. Gut treatment alone was not effective in breaking seed coat-imposed dormancy, although it enhanced the rate of germination of non-dormant seeds. To get a complete picture of the effect of frugivore on the release of seed dormancy, the combined effect of initial mastication and subsequent gut treatment needs to be investigated.     

Post‐Dispersal Seed Removal and Germination Selected Tree Species Dispersed by Cebus capucinus on Barro Colorado Island,Panama1

Dispersal quality, an important component of seed disperser effectiveness, may strongly affect the rate of plant recruitment. Here we evaluated the quality of Cebus monkey dispersal by comparing the secondary removal fate and germination of fresh and Cebus‐ingested seeds of nine tree species on Barro Colorado Island, Panama. Overall, rates of secondary seed removal by vertebrates were low, with most Cebus defecations remaining undisturbed for extended periods on the forest floor. Only four of 30 feces were completely buried by dung beetles, and we found significantly higher vertebrate removal of defecated seeds than control seeds for only one species, Cordia bicolor. Seed germination varied greatly between plant taxa. Seeds of 3 out of 9 species showed significantly higher percent germination after monkey gut passage than control fresh seeds. Germination times tended to be shorter for defecated than for control seeds but were significantly different only for one of nine species, Cecropia insignis. Low rates of seed removal from Cebus feces, coupled with high germination probabilities, suggest high dispersal effectiveness for Cebus and contrasts strongly with patterns of post‐dispersal seed fate recorded for other primate species.     

Seed dispersal effectiveness of the western lowland gorilla (Gorilla gorilla gorilla) in Gabon

The quantitative and qualitative aspects of seed dispersal by the western lowland gorilla (Gorilla gorilla gorilla) were investigated in Gabon. Fresh faeces were collected and washed to identify and count the seeds. Seed germinability after gut passage was estimated with trials in a nursery at the study site. To assess the impact of gut passage on germination success and delay, comparative trials were run with four treatments: (i) gut passed seeds cleaned of faeces, (ii) gut passed seeds within a faecal matrix, (iii) seeds from fresh fruits surrounded by pulp, and (iv) seeds from fresh fruits cleaned of pulp. The analysis of 180 faecal units resulted in the identification of 58 species of seed. Germination trials were realized for 55 species and the mean germination success reached 46%. The impact of gut passage was investigated for Santiria trimera and Chrysophyllum lacourtianum; both species displayed higher germination success after ingestion. This study shows that gorillas effectively disperse seeds of numerous plant species, many of which provide timber or nontimber forest products or are typical of Gabonese forests. Considering the high‐quality of gorilla deposition sites, gorillas is thought to play a unique role in the dynamics of Central African forest.     

Gut passage effect of the introduced red‐whiskered bulbul (Pycnonotus jocosus) on germination of invasive plant species in Mauritius

In Mauritius, many of the worst invasive plant species have fleshy fruits and rely on animals for dispersal. The introduced red‐whiskered bulbul (Pycnonotus jocosus) feeds on many fleshy‐fruited species, and often moves from invaded and degraded habitats into higher quality native forests, thus potentially acting as a mediator of continued plant invasion into these areas. Furthermore, gut passage may influence seed germination. To investigate this, we fed fleshy fruits of two invasive plant species, Ligustrum robustum and Clidemia hirta, to red‐whiskered bulbuls. Gut passage times of seeds were recorded. Gut‐passed seeds were sown and their germination rate and germination success compared with that of hand‐cleaned seeds, as well as that of seeds in whole fruits. Gut passage and hand‐cleaning had significant positive effects on germination of both species. Gut‐passed seeds of both C. hirta and L. robustum germinated faster than hand‐cleaned seeds. However, for L. robustum, this was only true when compared with hand‐cleaned seeds with intact endocarp; when compared with hand‐cleaned seeds without endocarp, there was no difference. For overall germination success, there was a positive effect of gut passage for C. hirta, but not for L. robustum. For both C. hirta and L. robustum, no seeds in intact fruits geminated, suggesting that removal of pulp is essential for germination. Our results suggest that, first, the initial invasion of native forests in Mauritius may not have happened so rapidly without efficient avian seed dispersers like the red‐whiskered bulbul. Second, the bulbul is likely to be a major factor in the continued re‐invasion of C. hirta and L. robustum into weeded and restored conservation management areas.     

Introduced galliforms as seed predators and dispersers in Hawaiian forests

In altered communities, novel species’ interactions may critically impact ecosystem functioning. One key ecosystem process, seed dispersal, often requires mutualistic interactions between frugivores and fruiting plants, and functional traits, such as seed width, may affect interaction outcomes. Forests of the Hawaiian Islands have experienced high species turnover, and introduced galliforms, the largest of the extant avian frugivores, consume fruit from both native and non-native plants. We investigated the roles of two galliform species as seed dispersers and seed predators in Hawaiian forests. Using captive Kalij Pheasants (Lophura leucomelanos) and Erckel’s Francolins (Pternistis erckelii), we measured the probability of seed survival during gut passage and seed germination following gut passage. We also examined which seeds are being dispersed in forests on the islands of O’ahu and Hawai’i. We found that galliforms are major seed predators for both native and non-native plants, with less than 5% of seeds surviving gut passage for all plants tested and in both bird species. Gut passage by Kalij Pheasants significantly reduced the probability of seeds germinating, especially for the native plants. Further, larger-seeded plants were both less likely to survive gut passage and to germinate. In the wild, galliforms dispersed native and non-native seeds at similar rates. Overall, our results suggest the introduced galliforms are a double-edged sword in conservation efforts; they may help reduce the spread of non-native plants, but they also destroy the seeds of some native plants. Broadly, we show mutualism breakdown may occur following high species turnover, and that functional traits can be useful for predicting outcomes from novel species’ interactions.

     

Effects of ant behaviour and presence of extrafloral nectaries on seed dispersal of the Neotropical myrmecochore Turnera ulmifolia L. (Turneraceae)

This paper describes the myrmecochory system of Turnera ulmifolia in a coastal sand dune matorral in Mexico. Turnera ulmifolia has elaiosome‐bearing seeds and extrafloral nectaries (EFNs). In ten quadrants (4 × 15 m) ant–seed interaction was monitored, and an interaction intensity index calculated and correlated with the number of seedlings. Seed removal rates by ants were surveyed every 2 h for 24 h, the ants being observed both on and beneath the plants. The role of the elaiosome in seed removal was evaluated by offering seeds with and without elaiosomes, and elaiosomes only. Finally, the effect of ant manipulation in seed germination was evaluated. There were 25 ant species associated with seeds and/or EFNs, the most frequently recorded being Monomorium cyaneum and Forelius analis. There was a positive correlation between the intensity index and seedling number per quadrant. There was significantly higher mean seed removal during the day than during the night (19.3% and 12.3%, respectively), and from beneath than on the plant (21.9% and 9.5%, respectively). The preference for elaiosomes only was also greater during the diurnal period, and when gathered on, rather than beneath, the plant. Seed manipulation by F. analis enhanced germination by T. ulmifolia. Seed removal, dispersal distances, seed predation and germination were largely determined by ant behaviour. The presence of EFNs may be influencing seed removal on the plant by attracting a specific assemblage of omnivorous ants. Among such assemblages associated with T. ulmifolia we encountered a variety of behaviours, with ant species either good at defending plants but bad at dispersing seeds, or vice versa. We discuss the way in which these two rewards, and the processes involved (defence and dispersion), could have interacted with each other and evolved. © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86 , 67–77.     

Helophyte germination in a Mediterranean salt marsh: Gut‐passage by ducks changes seed response to salinity

Question: In seeds which are regularly consumed by waterbirds in the field, how does gut‐passage modify their response to salinity gradients? Location: Doñana National Park salt marsh, south‐west of Spain. Methods: Seeds of Scirpus litoralis and Scirpus maritimus were collected and force fed to mallards (Anas platyrhynchos). Both the ingested seeds (passage) and non‐ingested seeds (controls) were exposed, in germination chambers, to a salinity range similar to that observed in the field (0–32 dS/m). After 30 days, the total percentage germination, the duration of the dormancy period and the germination speed were computed. The response of the different germination parameters to ingestion and salinity was analyzed using generalized lineal models. Recovery tests on seeds that did not germinate in the various treatments and tests of the effect of ingestion on the intrinsic variability in seed response were also performed. Results: An increase in salinity reduced germinability and increased the length of dormancy, while gut pas sage increased the intrinsic variability of the temporal seed response in both species. In S. litoralis there was a significant interaction between the effects of salinity and passage on germination rate. Passage increased germination rate at low salinities (≤2 dS/m) but decreased it at high salinities (≥4 dS/m). Conclusion: Gut‐passage by ducks significantly changes seed response to salinity. The outcome of plant‐animal interactions can be influenced by environmental gradients. Studies of germination in response to gut passage that do not take such gradients into account may produce misleading results.     

How do primates affect seed germination? A meta‐analysis of gut passage effects on neotropical plants

Biotic seed dispersal is a key process maintaining biodiversity in tropical forests where most trees produce vertebrate‐dispersed seeds. Existing meta‐analyses suggest an overall positive effect of vertebrate gut passage on seed germination, but no significant effects for non‐flying mammals. However, previous meta‐analyses combined rodents (seed predators) and primates (seed dispersers) into the non‐flying mammals category, which may confound specific effects of each group on seed germination. However positive effects of monkeys on germination had previously been found in some studies. Here we disentangle the role of Neotropical primates as contributors to seed dispersal in tropical forests by running a meta‐analysis to determine the overall magnitude of gut passage effects on seed germination percentage and mean time to germination. We also compare effect sizes as a function of different feeding guilds, gut complexities, and seed size. Our results show a strong, positive effect of primates on seed germination percentage and on the number of days to first germination. Strictly frugivorous monkeys, the group most threatened by extinction, showed the highest dispersal quality, increasing germination percentage by 75%. Primates that include insects in their diets had no average effect on germination percentage or time. Gut passage had different outcomes on seeds with different sizes; both large and small seeds showed similar increases in germination percentages after gut passage, but only large seeds germinated faster than control seeds after gut passage. Our results show a relevant role for primates in providing high seed dispersal quality and as drivers of forest regeneration. The combined effects of defaunation and forest fragmentation may result in decreased regeneration of trees, which has the potential to affect negatively both forest structure and ecosystem processes. Finally, we provide general guidelines for standardizing research on seed dispersal by primates. Synthesis Consuming fleshy fruits and dispersing seeds is the main ecological service provided by vertebrates to plants. Vertebrate increases seed germination due to treatment given during digestive system passage. Previous meta‐analyses suggest an overall positive effect of vertebrate gut passage on germination, but no insights are available on its variation among different functional groups of mammals. Our analyses indicated that gut passage by Neotropical primates increased seed germination. Strict frugivores, the ones most threatened by extinction, were the most efficient. Our results show a relevant role for primates in providing high seed dispersal quality and as drivers of forest regeneration, which can be meaningful for conservation in a community scale.     

Asian Tapirs Are No Elephants When It Comes To Seed Dispersal

The elimination of the largest herbivores (elephants and rhinoceroses) from many forests in tropical East Asia may have severe consequences for plant species that depend on them for seed dispersal. We assessed the capacity of Malayan tapirs Tapirus indicus—the next largest nonruminant herbivore in the region—as a substitute for the lost megafauna in this role by studying their ability to disperse the seeds of nine fleshy‐fruited plants with seeds 5–97 mm in length. We combined information from feeding trials, germination tests, and field telemetry to assess the effect of tapir consumption on seed viability and to estimate how far the seeds would be dispersed. The tapirs (N=8) ingested few seeds. Seed survival through gut passage was moderately high for small‐seeded plants (e.g., 36.9% for Dillenia indica) but very low for medium‐ (e.g., 7.6% for Tamarindus indica) and large‐seeded (e.g., 2.8% for Artocarpus integer) plants. Mean seed gut passage times were long (63–236 h) and only the smallest seeds germinated afterwards. Using movement data from four wild tapirs in Peninsular Malaysia we estimated mean dispersal distances of 917–1287 m (range=22–3289 m) for small‐seeded plants. Malayan tapirs effectively dispersed small‐seeded plants but acted as seed predators for the large‐seeded plants included in our study, suggesting that they cannot replace larger herbivores in seed dispersal. With the absence of elephants and rhinos many megafaunal‐syndrome plants in tropical East Asia are expected to face severe dispersal limitation problems.     

Effects of gut passage,feces, and seed handling on latency and rate of germination in seeds consumed by capuchins (Cebus capucinus)

One of the key measures of the effectiveness of primary seed dispersal by animals is the quality of seed dispersal (Schupp: Plant Ecol 107/108 [1993] 15–29). We present data on quality of seed dispersal by two groups of white‐faced capuchins (Cebus capucinus) in Costa Rica to test the hypothesis that capuchin seed handling results in effective primary dispersal for some fruit species they consume. We examined seed handling for 27 plant species, and germination rates of 18 species consumed by capuchins. For five of the most commonly swallowed seed species, we determined germination rates and average time to germination (latency) for seeds ingested and defecated by capuchins and compared these to seeds removed directly from fruit and planted. For the same five species, we compared germination rates and latency for passed seeds planted in capuchin feces to those cleaned of feces and planted in soil. For three of five species, differences in proportion of germinated seeds were significantly higher for gut passed seeds than for controls. For four of five species, germination latency was significantly faster for gut passed seeds than for controls. Feces had either no effect on seed germination rate or precluded germination. Data presented here support the hypothesis that white‐faced capuchins are effective primary dispersers. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Seed traits and bird species influence the dispersal parameters of wetland plants

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Does seed ingestion by bats enhance germination? A new meta‐analysis 15 years later

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White‐tailed deer as the last megafauna dispersing seeds in Neotropical dry forests: the role of fruit and seed traits

Endozoochory is a prominent form of seed dispersal in tropical dry forests. Most extant megafauna that perform such seed dispersal are ungulates, which can also be seed predators. White‐tailed deer (Odocoileus virginianus) is one of the last extant megafauna of Neotropical dry forests, but whether it serves as a legitimate seed disperser is poorly understood. We studied seed dispersal patterns and germination after white‐tailed deer gut passage in a tropical dry forest in southwest Ecuador. Over 23 mo, we recorded ca 2000 seeds of 11 species in 385 fecal samples. Most seeds belonged to four species of Fabaceae: Chloroleucon mangense, Senna mollissima, Piptadenia flava, and Caesalpinia glabrata. Seeds from eight of the 11 species dispersed by white‐tailed deer germinated under controlled conditions. Ingestion did not affect germination of C. mangense and S. mollissima, whereas C. glabrata showed reduced germination. Nevertheless, the removal of fruit pulp resulting from ingestion by white‐tailed deer could have a deinhibition effect on germination due to seed release. Thus, white‐tailed deer play an important role as legitimate seed dispersers of woody species formerly considered autochorous. Our results suggest that more research is needed to fully understand the ecological and evolutionary effects of the remaining extant megafauna on plant regeneration dynamics in the dry Neotropics.     

Functional diversity in fruit‐frugivore interactions: a field experiment with Mediterranean mammals

Using field seed sowings, we assessed how four mammal species (Meles meles, Vulpes vulpes, Sus scrofa, and Oryctolagus cuniculus) influenced seed germination in three fleshy‐fruited Mediterranean shrubs (Corema album, Pyrus bourgaeana, and Rubus ulmifolius). We predicted that gut passage and removal away from mother plants would enhance the quantity, speed, and asynchrony of seed germination. Results showed that percent germination was altered by gut passage, but that the magnitude and even the direction of such effects varied according to plant and disperser species. Likewise, dispersal away from mother plants affected the percentage and germination speed in some species but not others. Gut passage increased asynchrony of germination in Rubus and Pyrus, and removal from the mother plant increased asynchrony in Rubus, which likely enhances plant fitness in unpredictable environments. Gut passage generally had a stronger effect on germination than removal away from mother plants, but for some species both factors were similarly influential. Therefore, the combined effects of both seed dispersal services varied individually among fruit and frugivore species, leading to unusually high functional diversity in this seed dispersal mutualism.     

Role of Brycinus lateralis (Teleostei: Alestidae) in dispersal and germination of Nymphaea nouchali (Angiospermae: Nymphaeaceae) seeds on a seasonal floodplain of the Okavango Delta,Botswana

Seed passage through the gut of vertebrates can be important for seed dispersal, but might influence seed viability. The ability of seeds to germinate after ingestion by seed-eating fish is important for the population dynamics of some plant species, and significant in the evolution of plant–fish interactions. Certain fish in the Okavango Delta, Botswana, are fruit- and seed-eaters and could act as seed dispersers. We sampled 14 fish species in 2013, finding Nymphaea nouchali var. caerulea seeds in the digestive tracts of eight, most commonly in the striped robber Brycinus lateralis. Seeds extracted from the gut of this species had an overall mean germination success of 11.7%. This fish species might well be a legitimate seed disperser, having a positive effect on seed dispersal from parent plants in the Okavango Delta. The current study represents one of the first investigations of the likelihood of seed dispersal by fish on the African continent.     

The role of Rhytidoponera metallica (Hymenoptera,Formicidae) in facilitating post‐fire seed germination of three ant‐dispersed legume species

The fire avoidance hypothesis proposes that a benefit of seed dispersal by ants (myrmecochory) is to protect seeds from being killed during fire and to facilitate post‐fire germination of seeds that require heat shock to break their physical dormancy. The aim of this study was to quantify the effect of fire and seed burial by a predominant seed‐dispersing ant, Rhytidoponera metallica (subfamily: Ectatomminae) on germination levels of three ant‐dispersed legume species (Pultenaea daphnoides, Acacia myrtifolia and Acacia pycnantha). Experimental burial of seeds within aluminium cans at a site prior to being burnt and at an adjacent unburnt site showed that fire increased germination levels, particularly for seeds buried at 1‐ and 2‐cm deep and that overall, germination levels differed among the three plant species. To quantify seed burial depths and post‐fire germination levels facilitated by R. metallica ants, seeds were fed to colonies prior to fire at the burnt and unburnt sites. Of the seeds buried within nests that were recovered, between 45% and 75% occurred within the upper 6 cm of the soil profile, although unexpectedly, greater percentages of seeds were recovered from the upper 0–2 cm of nests in the unburnt site compared with nests in the burnt site. Germination levels of buried seeds associated with R. metallica nests ranged from 21.2% to 29.5% in the burnt site compared with 3.1–14.8% in the unburnt site. While increased seed germination levels were associated with R. metallica nests following fire, most seeds were buried at depths below those where optimal temperatures for breaking seed dormancy occurred during the fire. We suggest that R. metallica ants may provide fire avoidance benefits to myrmecochorous seeds by burying them at a range of depths within a potential germination zone defined by intra‐ and inter‐fire variation in levels of soil heating.     

Seed dispersal of Diospyros virginiana in the past and the present: Evidence for a generalist evolutionary strategy

Several North American trees are hypothesized to have lost their co‐evolved seed disperser during the late‐Pleistocene extinction and are therefore considered anachronistic. We tested this hypothesis for the American persimmon (Diospyros virginiana) by studying the effects of gut passage of proposed seed dispersers on seedling survival and growth, natural fruiting characteristics, and modern animal consumption patterns. We tested gut passage effects on persimmon seeds using three native living species, the raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), and coyote (Canis latrans), and two Pleistocene analogs; the Asian elephant (Elephas maximus) and alpaca (Vicugna pacos). Persimmon seeds excreted by raccoons, coyotes, and elephants survived gut transit. Gut passage did not affect sprouting success, but did tend to decrease time to sprout and increase seedling quality. Under field conditions, persimmon fruits were palatable on the parent tree and on the ground for an equal duration, but most fruits were consumed on the ground. Seven vertebrate species fed upon persimmon fruits, with the white‐tailed deer (Odocoileus virginianus)—a species not capable of dispersing persimmon seeds—comprising over 90% of detections. Conversely, potential living seed dispersers were rarely detected. Our results suggest the American persimmon evolved to attract a variety of seed dispersers and thus is not anachronistic. However, human‐induced changes in mammal communities could be affecting successful seed dispersal. We argue that changes in the relative abundance of mammals during the Anthropocene may be modifying seed dispersal patterns, leading to potential changes in forest community composition.     

Seed dispersal effectiveness by a large‐bodied invasive species in defaunated landscapes

Animal‐dispersed plants are increasingly reliant on effective seed dispersal provided by small‐bodied frugivores in defaunated habitats. In the Neotropical region, the non‐native wild pig (Sus scrofa) is expanding its distribution and we hypothesized that they can be a surrogate for seed dispersal services lost by defaunation. We performed a thorough analysis of their interaction patterns, interaction frequencies, seed viability, and characteristics of the seed shadows they produce. We found 15,087 intact seeds in 56% of the stomachs and 5,186 intact seeds in 90% of the scats analyzed, 95% of which were smaller than 10 mm in diameter. Wild pigs were the third most effective disperser among 21 extant frugivore species in a feeding trail experiment in terms of quantity of seeds removed. Gut retention time was 70 ± 23 hr, indicating wild pigs can promote long‐distance seed dispersal. Seed survival after seed handling and gut passage by wild pigs was positively related with seed size, but large seeds were spat out and only smaller seeds were defecated intact, for which we observed a positive or neutral effect on germination relative to manually de‐pulped seeds. Finally, deposition of seeds was four times more frequent in unsuitable than suitable sites for seedling recruitment and establishment. Seed dispersal effectiveness by wild pigs is high in terms of the quantity of seeds dispersed but variable in terms of the quality of the service provided. Our study highlights that negative and positive effects delivered by non‐native species should be examined in a case by case scenario. Abstract in Portuguese is available with online material.     

The potential for birds to disperse the seeds of Acacia cyclops,an invasive alien plant in South Africa

Rooikrans Acacia cyclops is an aggressive invasive tree that threatens natural resources in South Africa. The seeds of A. cyclops have a prominent aril which attracts birds that ingest the seeds and disperse them endozoochorously. Two biological control agents, a Seed Weevil Melanterius servulus and a Flower‐galling Midge Dasineura dielsi, were released on A. cyclops in 1991 and 2002, respectively. Together these agents have substantially reduced seed production and generally far lower numbers of seeds are now available to birds. A consequence of this transition from historically bounteous quantities of seeds to scanty seed availability is that birds may no longer associate with the trees and seed dispersal may be disproportionately reduced. To assess whether this has happened, seed attrition was measured by comparing the amount of seeds that disappeared from two groups of branches, one available to birds and the other enclosed in bird netting. Other types of granivores (mainly field mice) were excluded from both groups of branches with a plastic funnel placed around the stems. Mature seeds were also harvested and fed to caged bird species to determine gut retention times and germination rates of ingested seeds. Attrition rates of seeds showed that birds continue to remove seeds but that only a proportion of the crop is taken. Only two frugivorous species (Knysna Turaco Tauraco corythaix and Red‐winged Starling Onychognathus morio) and two granivorous species (Red‐eyed Dove Streptopelia semitorquata and Laughing Dove Streptopelia sengalensis) ingested A. cyclops seeds during feeding trials. Ingestion by birds enhanced seed germination except for those ingested by Laughing Doves. There were no apparent effects of length of gut passage time and avian body size on seed germination rates. Despite the diminished seed resource due to biological control agents, birds continue to disperse A. cyclops seeds.     

The effect of seed morphology on the potential dispersal of aquatic macrophytes by the common carp (Cyprinus carpio)

1. The potential for seed dispersal by fish (ichthyochory) will vary among aquatic plants because of differences in seed size and morphology. 2. To examine how seed morphology influences the probability of dispersal by the common carp (Cyprinus carpio), we studied seed ingestion, retention time and subsequent egestion and germination of seeds of Sparganium emersum and Sagittaria sagittifolia, two aquatic plant species with similar sized but morphologically different seeds. 3. We compared dispersal probabilities between the two plant species, in which the probability of dispersal is assumed to be a function of the probabilities of seed ingestion, egestion and germination, and the dispersal distance is assumed to be a function of seed egestion rate over time. 4. We found that, although the soft seeds of S. sagittifolia had an approximately 1.5 times higher probability of being ingested by the carp than the hard seeds of S. emersum (83.15% ± 1.8% versus 56.16% ± 2.7%, respectively), the latter had an almost twofold higher probability of surviving the passage through the digestive tract (38.58% ± 2.7% versus 20.97% ± 1.5%, respectively). Patterns of seed egestion over time did not differ between the two plant species, despite the difference in seed morphology. Gut passage had a different effect on seed germination between plant species. Compared with non‐ingested controls, seeds of S. emersum showed a 12.6% increase in germination and a 2.1 day acceleration in germination rate, whereas seeds of S. sagittifolia displayed a 47.3% decrease and 5.1 day delay, respectively. 5. Our results suggest that seed morphology affects the dispersal probability and postdispersal establishment, but not the dispersal distance, of aquatic plants that are dispersed by fish.