The experimental study of seed dispersal by fish (ichthyochory)

Abstract

1. 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.