Leftovers in seed dispersal: ecological implications of partial seed consumption for oak regeneration

Abstract

Summary1. Successful seed dispersal by animals is assumed to occur when undamaged seeds arrive at a favourable microsite. Most seed removal and dispersal studies consider only two possible seed fates, predation or escape intact. Whether partial consumption of seeds has ecological implications for natural regeneration is unclear. We studied partial consumption of seeds in a rodent-dispersed oak species. 2. Fifteen percent of dispersed acorns were found partially eaten in a field experiment. Most damage affected only the basal portion of the seeds, resulting in no embryo damage. Partially eaten acorns had no differences in dispersal distance compared to intact acorns but were recovered at farther distances than completely consumed acorns. 3. Partially eaten acorns were found under shrub cover unlike intact acorns that were mostly dispersed to open microhabitats. 4. Partially eaten acorns were not found buried proportionally more often than intact acorns, leading to desiccation and exposure to biotic agents (predators, bacteria and fungi). However, partial consumption caused more rapid germination, which enables the acorns to tolerate the negative effects of exposure. 5. Re-caching and shrub cover as microhabitat of destination promote partial seed consumption. Larger acorns escaped predation more often and had higher uneaten cotyledon mass. Satiation at seed level is the most plausible explanation for partial consumption. 6. Partial consumption caused no differences in root biomass when acorns experienced only small cotyledon loss. However, root biomass was lower when acorns experienced heavy loss of tissue but, surprisingly, they produced longer roots, which allow the seeds to gain access sooner to deeper resources. 7. Synthesis. Partial consumption of acorns is an important event in the oak regeneration process, both quantitatively and qualitatively. Most acorns were damaged non-lethally, without decreasing both dispersal distances and the probability of successful establishment. Faster germination and production of longer roots allow partially eaten seeds to tolerate better the exposure disadvantages caused by the removal of the pericarp and the non-buried deposition. Consequently, partially consumed seeds can contribute significantly to natural regeneration and must be considered in future seed dispersal studies.

Predation and aridity slow down the spread of 21-year-old planted woodland islets in restored Mediterranean farmland

“…Rodents and magpies are both predators and dispersers of acorns (Waite 1985), but rabbits and hares, which are abundant in our field site, are only predators (Zamora et al 1985;Díaz et al 1996;Leiva and Fernández 2003;Guzmán et al 2008). We have clear evidence of acorn predation in situ for a small fraction of the unprotected acorns but suspect that most of the unfound acorns were either entirely consumed immediately after removal or re-cached and consumed later in other sites (Perea et al 2011), as the farmland environment where our woodland islets are embedded may exacerbate predation. For instance, found in the Sierra Nevada Mountains (SE Spain) that most caches were recovered and consumed, and only 1.3 % of the original experimental acorns were found alive in caches the following spring.…”

Predation and dispersal of Parah tree ( ) seeds by red spiny rats ( ) in Khao Nan National Park, Thailand Elateriospermum tapos Maxomys

“…Seed predation by predators cause severe loss of seed crops (Kurkjian ., 2016), but it has been proved that seed predators act as keystone species in some habitats (Brown and Heske, 1990). Seed predators contribute to seed germination by manipulating seeds (e.g., removing pericarp and seed coats), which may enhance germination if the prepared seeds are only partially, and not fully predated, or are dispersed far away or buried (Perea ., 2011;Yang and Yi, 2012). Seed dispersal is another important factor for the life cycles of most plants, as dispersal process includes 'departure of a diaspore (e.g.…”

“…Seedling establishment is also significantly affected by heavy partial consumption by rodents (Perea ., 2011). A few studies have observed that partially consumed acorns ( spp.)…”

“…A few studies have observed that partially consumed acorns ( spp.) germinate more rapidly than intact ones (Perea ., 2011;Yang and Yi, 2012). Moreover, Wada and Kamata (2003) observed that seedlings developed from partially cotyledonremoved acorns showed a higher relative growth rate than those from intact ones (Wada and Kamata, 2003).…”

“…Normally, partially consumed seeds germinate more rapidly, and with a higher rate of success, than intact seeds (Pérez ., 2008;Perea ., 2011;Yang and Yi, 2012), though we did not test the seed germination rate of partially predated Parah seeds. Probably, the germination process is accelerated when seeds are damaged, as this process has been attributed to some physiological responses, due to removal of seed coat or other barriers to imbibition (Pérez ., 2008).…”