Effects of seed traits on the potential for seed dispersal by fish with contrasting modes of feeding

Abstract

SUMMARY1. For aquatic and riparian plants, the important role of fish in seed dispersal is increasingly recognised. While the propensity of seeds to disperse is known to be a function of morphological, physical and chemical traits of the seed, in the case of fish-mediated seed dispersal (ichthyochory), it is largely unknown how seed traits modulate the potential for seed ingestion and their subsequent survival through the gut. Furthermore, which seed traits are important may vary among fish species. 2. To evaluate the role of both seed and fish traits in ichthyochory, we fed seeds of 19 aquatic and riparian plant species to fish with differing feeding mechanisms. Cyprinus carpio (common carp) has a pharyngeal 'mill', which it uses physically to crush hard food, while Oreochromis mossambicus (Mozambique tilapia) has only tiny oral and pharyngeal teeth and instead relies more on chemical digestion. 3. A number of seed traits, including hardness, size and shape, were important determinants of the potential of seeds for ichthyochory. Certain traits (e.g. seed dimensions) were more important during ingestion, whereas other traits were more important for seed survival and subsequent germination (e.g. seed hardness, mucilaginous coat). Compared to controls, germination of retrieved seeds in carp was lower in 10 and higher in two plant species, whereas for tilapia, it was lower in seven and higher in three species. Overlap between these plant species was low, indicating clear difference between the fish studied in their potential for seed dispersal. Carp increased in size during the experiment and concomitant decreases in seed survival and retrieval were found, suggesting that body size and the correlated bite force is an important fish trait in ichthyochory. 4. Overall, seed hardness, size and shape appear crucial for the survival of seeds passing through the guts of carp and tilapia. Beyond this general pattern, a greater complexity of trait-performance relationships appeared: different seed traits are involved during each of the stages of ichthyochory. Moreover, the importance of seed traits differed between carp and tilapia, with some traits having interactive and contrasting effects in both fish species. Aquatic plants with floating seeds adapted to hydrochorous dispersal were less likely to be dispersed by tilapia than plants with non-floating seeds, suggesting a dispersal trade-off between ichthyochory and hydrochory. Thus, depending on their seed characteristics, fish may offer an additional dispersal route to aquatic and riparian plants.

Fishing‐down within populations harms seed dispersal mutualism

“…(), 2) Boedeltje et al . (), 3) Kubitzki & Ziburski (), 4) Lucas (), 5) Anderson et al . (), 6) Anderson et al .…”

“…In only one case, increases in individual size led to a decrease in seed dispersal effectiveness. In a feeding experiment, Boedeltje et al (2015) found that, as carps (Cyprinus carpio) grew, increased bite force reduced seed survival. Therefore, seed dispersal efficiency may not only depend on gape size, but also on other morphological and physiological traits that covary with body size (e.g., dentition and jaw morphology, bite force, digestive capability); this is an important aspect that should be investigated in future studies.…”

Consistent individual differences in seed disperser quality in a seed-eating fish

“…Their fruits (hereafter called seeds) are released in autumn. They remain dormant during the winter during which they are dispersed by water currents (Boedeltje et al 2004; Pollux et al 2009b), fish (Ridley 1930; Pollux et al 2007b; Boedeltje et al 2015) and waterfowl (Pollux et al 2005; Soons et al 2016), until they germinate in the following spring. Ripe seeds were collected during October 2003 from natural populations in The Netherlands (Pollux et al 2006).…”

Floods affect the abundance of invasive Impatiens glandulifera and its spread from river corridors

“…The plants flower from late July until the first frost and set seed from late August until November and the seed rain density is 5000-6000 seeds m À2 (Beerling & Perrins, 1993); Koenis & Glava c (1979) found a maximum of 32,000 seeds m À2 in Germany. The seeds are also dispersed with soil by logging machinery or animals along forest roads and clearings, as well as by ants and small rodents (Beerling & Perrins, 1993), birds (Heintze, 1932) and maybe even fish (Boedeltje et al, 2015). The seeds are also dispersed with soil by logging machinery or animals along forest roads and clearings, as well as by ants and small rodents (Beerling & Perrins, 1993), birds (Heintze, 1932) and maybe even fish (Boedeltje et al, 2015).…”