Consistent individual differences in seed disperser quality in a seed-eating fish
Pollux, Bart J.A. - \ 2017
Oecologia 183 (2017)1. - ISSN 0029-8549 - p. 81 - 91.
Ichthyochory - Intra-specific variation - Long-distance dispersal - Seed retention time - Zoochory
Animal-mediated seed dispersal (zoochory) is considered to be an important mechanism regulating biological processes at larger spatial scales. To date, intra-specific variation in seed disperser quality within seed-dispersing animals has not been studied. Here, I employed seed feeding trials to quantify individual differences in disperser quality within the common carp (Cyprinus carpio) using seeds of two aquatic plants: unbranched bur-reed (Sparganium emersum, Sparganiaceae) and arrowhead (Sagittaria sagittifolia, Alismataceae). I found substantial variation among carp individuals in their propensity to ingest seeds and their ability to digest them, resulting in up to 31-fold differences in the probability of seed dispersal. In addition, there were significant differences in the time that seeds are retained in their digestive systems, generating a twofold difference in the maximum distance over which they can potentially disperse seeds. I propose that seed-eating animal species consist of individuals that display continuous variation in disperser quality, with at one end of the continuum individuals that are likely to eat seeds, pass them unharmed through their digestive tract and transport them over large distances to new locations (i.e. high-quality seed dispersers) and at the other end individuals that rarely eat seeds, destroy most of the ones they ingest and transport the few surviving seeds over relatively short distances (low-quality seed dispersers). Although individual differences in seed dispersal quality could be the result of a variety of factors, these results underline the ecological and evolutionary potential of such variation for both plants and animals.
Interspecific associations in seed arrival and seedling recruitment in a Neotropical forest
Wright, S.J. ; Calderón, Osvaldo ; Hernandéz, Andrés ; Detto, Matteo ; Jansen, Patrick A. - \ 2016
Ecology 97 (2016)10. - ISSN 0012-9658 - p. 2780 - 2790.
Anemochory - Barro Colorado Island - Contagious seed dispersal - Fruiting phenology - Seed production - Seed rain - Seedling recruitment - Zoochory
Contagious seed dispersal refers to the tendency for some sites to receive many dispersed seeds while other sites receive few dispersed seeds. Contagious dispersal can lead to interspecifc associations in seed arrival, and this in turn might lead to interspecifc associations in seedling recruitment. We evaluate the extent of spatially contagious seed arrival, the frequency of positive interspecifc associations in seed arrival, and their consequences for seedling recruitment at the community level in a tropical moist forest. We quantifed seed arrival to 200 passive seed traps for 28 yr of weekly censuses and seedling recruitment to 600 1-m2 quadrats for 21 yr of annual censuses on Barro Colorado Island, Panama. We assessed whether spatially contagious seed dispersal was more important among zoochorous species than among anemochorous species, increased in importance with similarity in fruiting times, and led to interspecifc associations in seed arrival and seedling recruitment. We controlled adult seed source associations statistically to evaluate predicted relationships. We found that spatially contagious seed arrival was widespread among zoochorous species, but also occurred among anemochorous species when the strong, consistent trade winds were present. Signifcant interspecifc associations in seed arrival were more likely for pairs of species with zoochorous seeds and similar fruiting times and persisted through seedling recruitment. Thus, interspecifcally contagious seed dispersal affects local species composition and alters the mixture of interspecifc interactions through the seed, germination, and early seedling stages in this forest. Future investigations should consider the implications of interspecifc association at the regeneration stages documented here for later life stages and species coexistence.
The experimental study of seed dispersal by fish (ichthyochory)
Pollux, B.J.A. - \ 2011
Freshwater Biology 56 (2011)2. - ISSN 0046-5070 - p. 197 - 212.
Retention time - Seed ingestion - Seed survival - Seed viability - Zoochory
The last few years have seen an increased interest in the experimental study of seed dispersal by fish (ichthyochory). This paper reviews such experiments, aiming to determine what functional aspects of ichthyochory have been investigated, what experimental designs have been used and what the potential pitfalls are.2.The process of seed dispersal by fish can be divided into six discrete stages, each with its own probability of occurrence and each individually quantifiable in seed feeding trials: (i) seed uptake, (ii) ingestion, (iii) retention time, (iv) survival, (v) germination probability and (vi) germination rate after gut passage.3.Inter- and intraspecific variation in seed traits (e.g. size, coat hardness, coat morphology, colour, presence and chemical composition of fruit pulp) and characteristics of fish (e.g. gape width, jaw morphology, presence of teeth, length of the digestive tract and digestive capability) can significantly affect the probability of one or more of the six stages of ichthyochory, thereby affecting the probability and distance of seed dispersal by fish.4.To date only seven studies, which together investigated a total of nine fish species and 25 plant species, have used feeding experiments to study one or more of these quantifiable stages in the ichthyochory process. There is a clear bias in the research questions towards assessing seed survival during passage through the gut and subsequent viability. Only a few studies focus on seed retention in the digestive tract and germination rate, and even fewer address seed ingestion.5.There is also considerable variation in experimental design among studies: Some have used groups of fish, while others used fish that are individually housed; some have fed seeds to hungry fish, while others used sated fish; some studied germination of seeds dissected from the alimentary tract, rather than seeds recovered from the faeces.6.I present a number of recommendations for a more standardised protocol for future experimental studies of zoochory in general, and ichthyochory in particular, and highlight areas of interest for future research.
Gene flow and genetic structure of the aquatic macrophyte Sparganium emersum in a linear unidirectional river
Pollux, B.J.A. ; Luteijn, A. ; Groenendael, J.M. Van; Ouborg, N.J. - \ 2009
Freshwater Biology 54 (2009)1. - ISSN 0046-5070 - p. 64 - 76.
Assignment tests - Asymmetric bidirectional dispersal - Hydrochory - One-dimensional ecosystems - Zoochory
1. River systems offer special environments for the dispersal of aquatic plants because of the unidirectional (downstream) flow and linear arrangement of suitable habitats. 2. To examine the effect of this flow on microevolutionary processes in the unbranched bur-reed (Sparganium emersum) we studied the genetic variation within and among nine (sub)populations along a 103 km stretch of the Niers River (Germany-The Netherlands), using amplified fragment length polymorphisms. 3. Genetic diversity in S. emersum populations increased significantly downstream, suggesting an effect of flow on the pattern of intrapopulation genetic diversity. 4. Gene flow in the Niers River is asymmetrically bidirectional, with gene flow being approximately 3.5 times higher in a downstream direction. The observed asymmetry is probably caused by frequent hydrochoric dispersal towards downstream locations on the one hand, and sporadic zoochoric dispersal in an upstream direction on the other. The spread of vegetative propagules (leaf and stem fragments) is probably not an important mode of dispersal for S. emersum, suggesting that gene flow is mainly via seed dispersal. Realized dispersal distances exceeded 60 km, revealing a potential for long-distance dispersal in S. emersum. 5. There was no correlation between geographical and genetic distances among the nine S. emersum populations (i.e. no isolation by distance), which may be due to the occurrence of long-distance dispersal and/or colonization and extinction dynamics in the Niers River. 6. Overall, the genetic population structure and regional dispersal patterns of S. emersum in the Niers River are best explained by a linear metapopulation model. Our study shows that flow can exert a strong influence on population genetic processes of plants inhabiting stream systems.
Reproductive strategy, clonal structure and genetic diversity in populations of the aquatic macrophyte Sparganium emersum in river systems
Pollux, B.J.A. ; Jong, M.D.E. ; Steegh, A. ; Verbruggen, E. ; Groenendael, J.M. Van; Ouborg, N.J. - \ 2007
Molecular Ecology 16 (2007)2. - ISSN 0962-1083 - p. 313 - 325.
Dispersal - Hydrochory - Sexual reproduction - Vegetative reproduction - Waterfowl - Zoochory
Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.
Differences in endozoochorous dispersal between aquatic plant species, with reference to plant population persistence in rivers
Pollux, B.J.A. ; Santamaria, L. ; Ouborg, N.J. - \ 2005
Freshwater Biology 50 (2005)2. - ISSN 0046-5070 - p. 232 - 242.
Aquatic plants - Birds - Drift-paradox - Population persistence - Upstream dispersal - Zoochory
1. In river ecosystems, populations are continuously subjected to unidirectional downstream currents resulting in a downstream movement of populations. To ensure long-term population persistence in rivers, organisms must have a mechanism for upstream dispersal, which allows them to re-colonise upstream areas. 2. In this study we assessed differences in the potential for endozoochorous seed dispersal of Sparganium emersum and Sagittaria sagittifolia, two aquatic plant species with different seed morphologies, by mallard (Anas platyrhynchos) and teal (Anas crecca), two duck species with different body weights. 3. We found no significant differences in seed retrieval (the proportion of ingested seeds retrieved after gut passage) and seed retention time (time between seed ingestion and retrieval), between mallard and teal, despite the difference in body weights. We did find a significantly higher germination (%) over retention time of S. emersum seeds retrieved from teal compared with mallard, most likely related to a more efficient removal of the seed coat during passage through the gut of teal. 4. There were large differences between S. emersum versus S. sagittifolia in: (i) seed retrieval (22.65 ± 20.8% versus 1.60 ± 2.4%, respectively); (ii) seed retention time in duck gut, with a maximum of 60 h versus 12 h; (iii) the effect of gut passage on seed germination, with an increase of approximately 35% versus a decrease of 25%; and (iv) the effect of gut passage on seed germination rate, with an acceleration of 10 days versus a delay of 3 days on average. The results show that S. emersum has a higher potential for endozoochorous dispersal by ducks and postdispersal establishment than S. sagittifolia. 5. We propose that, in rivers, bird-mediated seed dispersal may promote re-colonisation of upstream areas, enabling long-term plant population persistence.