Recovery and Germination of Dichrostachys cinerea Seeds Fed to Goats (Capra hircus)

Abstract

Goats can act as dispersal agents by consuming seed pods of woody plants and dispersing the seeds in feces. Concerns that goats might thereby promote encroachment by woody plant species such as Dichrostachys cinerea (sickle bush) have not been addressed. The objective of this study was to determine the recovery rate and germination of D. cinerea seeds that pass through the digestive tract of goats. We hypothesized that 1) D. cinerea seeds will remain intact and viable after passage through the digestive tract of goats and that 2) D. cinerea seeds will be scarified by such passage, resulting in improved germination percentages. The first trial measured the recovery rate of 1 500 D. cinerea seeds that were consumed by indigenous goats, either voluntarily after mixing them with feed pellets (mixed) or by force-feeding (gavaged). Seed recovery for the gavaged treatment (32.7%) was significantly higher than for the mixed treatment (9.9%; P , 0.001). The second trial determined germination percentages of D. cinerea seeds recovered from the feces of animals in the two treatments of the first trial as well as scarified and control (untreated) seeds. The germination percentage of mechanically scarified seeds (53.0%) was significantly higher than that of seeds that passed through the digestive system in the mixed (35.5%) or gavaged (31.2%) treatments or were untreated (19.0%; P , 0.001). Seeds that passed through the digestive tract (mixed and gavaged treatments) had a significantly higher germination percentage than untreated seeds (P , 0.001). A nonnegligible proportion of D. cinerea seeds remained intact after ingestive chewing and passage through the digestive system, and their germination percentage was even elevated. This suggests that goats have a potential to facilitate woody plant encroachment through dispersal of viable and scarified seeds. ResumenLas cabras pueden actuar como agentes dispersores de semillas de plantas leñ osas al consumir las vainas de estas. No se ha discutido la preocupación de que las cabras de este modo podrían propiciar la invasión de plantas leñ osas tales como Dichrostachys cinerea (arbusto hoz). El objetivo de este estudio fue determinar la tasa de recuperación y germinación de semillas de D. cinérea que pasan a trave´s del tracto digestivo de las cabras. Planteamos la hipótesis de 1) Las semillas de D. cinerea permanecerán intactas y viables despue´s de haber pasado por el tracto digestivo de las cabras, y 2) Las semillas de D. cinérea serán escarificadas por tal pasaje resultando, en el mejoramiento de el porcentaje de germinación. El primer experimento se midió la tasa de recuperación de 1 500 semillas de D. cine´rea que fueron consumidas por cabras criollas ya sea de manera voluntaria o después de mezclarlas con bolas de alimento o por alimentación forzada. La recuperación de semillas por medio del tratamiento de alimentación forzada (32.7%) fue significativamente mayor que la del tratamiento de la mezcla (9.9%; P , 0.001). El segundo experimento determino el porcentaje de germinació...

The Effects of Seed Ingestion by Livestock, Dung Fertilization, Trampling, Grass Competition and Fire on Seedling Establishment of Two Woody Plant Species

“…However, these results are consistent with those of [ 15 ] in KwaZulu-Natal, South Africa. Even though cattle and untreated seeds were not significantly different in terms of seedling emergence and seedling recruitment, it is clear that acid scarification in the gut of herbivores usually favours seedling emergence [ 14 , 15 ]. Longer retention of seeds ingested by large bodied-animals, e.g.…”

“…All experimental animals were allowed to consume seeds for 24 hours, after which the remaining seeds were collected. Retrieved undamaged seeds following techniques outlined by [ 14 ] were used during the field seedling emergence trial. This study was approved by the Animal Production Institute Ethics Committee (APIEC).…”

“…Grazing herbivores reduce the ability of grasses to compete with tree seedlings for resources through grazing [ 13 ]. Conversely, herbivores disperse viable woody plant seeds [ 14 ], and may increase seedling emergence, seedling establishment and recruitment of woody plant species through gut passage and dung fertilization [ 15 ]. Endozoochory, seedling emergence, seedling establishment and recruitment are crucial processes in plant population dynamics because they usually influence the distribution and abundance of plant species [ 16 , 17 ].…”

“…Furthermore, the distance that seeds may be dispersed depends positively on herbivore retention time and body size [ 24 , 25 ]. However, other factors such as diet quality and seed characteristics (size, hardness and shape) may also affect germination [ 14 , 27 ].…”

Global patterns of seed germination after ingestion by mammals

“…Even cosmopolitan mammals have different effects in each bioregion. For instance, goats feeding on seeds from Fabaceae trees have neutral effects on seed germination in the Nearctic (Kneuper et al 2003) and the Neotropics (Ortega-Baes et al 2002), while in Africa they have negative, positive and neutral effects (Miller 1995;Tjelele et al 2012Tjelele et al , 2015.…”