Spatial–temporal distribution of ornithochorous seeds from an Elaeagnus umbellata community dominating a riparian habitat

Abstract

The dispersal efficiency and potential distribution of ornithochorous seeds of Elaeagnus umbellata in a riparian habitat were evaluated to clarify this species' establishment site in relation to the disturbance regime of the floodplain. Fruit removal by avian frugivores was monitored using fruit bags, and the spatial distribution of excreted seeds was quantified by seed traps set randomly on a gravel bar as an isolated seed source in the Yoshino River throughout an autumn fruiting season. Although more than 45% of the fruits remained on the twigs in the fruit bags, almost all fruits on the control twigs without fruit bags were exploited by the beginning of January. The fruit removal rate and seed dispersal distance were positively correlated with an increase in wintering bird species and their abundance. Intact bird-dispersed seeds of E. umbellata were trapped within a 400-m range and damaged seeds were limited to traps set within 50 m from the seed source. Frugivore behavior, such as feces excretion on rocks near water drinking sites and perching on surrounding woodland, greatly influenced the spatial and temporal dispersal pattern of the seed rain. In the present study, the avian frugivores showed upstream seed dispersal; thus, in years with stochastic autumnal floods, secondary dispersal via hydrochory downstream may be facilitated. The intensive seed dispersal in E. umbellata indicates that the present distribution of parent trees in the restricted elevation range of the gravel bars is the result of survival through disturbance, rather than seed dispersal limitation.

Engaging Birds in Vegetation Restoration after Elwha Dam Removal

“…Although I often observed American robins foraging on bare sediments, almost all birds flying from forest to open sediment landed on elevated perches first. Most scats in LMD were on LWD probably because frugivorous birds often excrete feces as they land on or fly from perches (Kohri et al 2011). Distance from forest had little effect on scat distribution likely because LWD perch sites were limiting; LWD locations rather than distance determined bird flights and scat deposition.…”

Going against the flow: a case for upstream dispersal and detection of uncommon dispersal events

“…common species). Only in special cases can the direction of dispersal be unequivocally established: for instance, where the seed traps are located upstream from the most upstream established population (Kohri et al ., ). Another important limitation of trapping is that it is limited to short dispersal distances [up to hundred(s) of meters at most], due to rapid increases in sampling effort with distance (Bullock & Clarke, ; Bullock, Shea & Skarpaas, ).…”

“…; Table ). Direct observations included two different methods of assessing upstream dispersal: analysis of historical geographic distribution data revealed an upstream population expansion rate of 19 km yr −1 in an invasive weed (Wang et al ., ), and seed defecation by frugivorous birds was observed in seed traps 0.21 and 0.36 km upstream of the fruit source (Kohri et al ., ). Indirect evidence based on molecular methods detected upstream dispersal over much longer distances than these direct observations (Fig.…”

“…Goodson et al ., ; Boedeltje et al ., ; Engström, Nilsson & Jansson, ; Sarneel et al ., ), but as in most cases the source of the trapped seeds could not be identified, such data could not be used to obtain information on direction, frequency, and distance of dispersal. Only one of the 100 studies investigated upstream dispersal directly by trapping seeds (1 mm mesh cloth suspended in the air) in the field (Kohri, Kamada & Nakagoshi, ). However, due to the spatial positions of adult plants and seed traps, upstream dispersal could only be inferred in very few cases.…”