Vukeya L R, Mokotjomela T M, Malebo N J, Oke S
South Africa National Biodiversity Institute, Free State National Botanical Garden, Free State, Rayton, Dan Pienaar, Danhof, P.O Box 29036, Bloemfontein, 9310, South Africa.
Faculty of Health and Environmental Science, Central University of Technology, Private Bag X20539, Bloemfontein, 9300, South Africa.
Bot Stud. 2021 Jun 10;62(1):10. doi: 10.1186/s40529-021-00317-6.
By transporting and scarifying the seeds during ingestion, avian frugivores reduce the competition with siblings, and may improve the germination which is critical for dispersal effectiveness and population recruitment. However, generally, there is limited knowledge on how deposited seeds interact/compete in the new microsite. We tested the hypothesis that the bird-dispersed seeds benefit from improved germination after their passage through the bird's gut; and we investigated the potential impact of seed density on competition at the microsites by determining whether seed density and species diversity influence germination in the Free State Province, South Africa.
Overall, the results partly supported the hypothesis. Germination trials with defecated seeds of five plant species compared with the manually depulped seeds showed that only Searsia lancea had significantly higher seed germination success and improved germination speed after passage through the bird gut while Ziziphus mucronata only benefited rapid germination. There was a significant correlation between seed size and the germination of bird-ingested seeds except in Olea subsp. africana possibly due to possession of extremely hard protective seed cover. Seed competition experiments pointed to Z. mucronata and O. subsp. africana having significant germination performance that was positively correlated to seed density and seed size while Ehretia rigida did not germinate at all. Seed species diversity in the germination trays did not have a significant impact since the seeds of two former plant species consistently displayed significantly higher germination across the competition levels.
We conclude that different plant species respond differently to seed ingestion by birds, and that further long-term tests for germination physiological responses of the seeds' samples used in this study are required since poor germination observed in other tree/shrub species cannot be attributed to competition solely.
通过在摄食过程中运输和擦伤种子，食果鸟类减少了与同胞种子的竞争，并可能提高发芽率，这对传播效率和种群补充至关重要。然而，总体而言，关于沉积种子在新微生境中如何相互作用/竞争的了解有限。我们测试了这样一个假设，即鸟类传播的种子在通过鸟类肠道后，发芽情况会得到改善；并且我们通过确定种子密度和物种多样性是否会影响南非自由邦省微生境中的发芽情况，来研究种子密度对竞争的潜在影响。
总体而言，结果部分支持了该假设。对五种植物的粪便种子与人工去果肉种子进行的发芽试验表明，只有lancea叶下珠在通过鸟类肠道后，种子发芽成功率显著更高，发芽速度也有所提高，而尖叶枣仅在快速发芽方面受益。除了非洲油橄榄亚种外，种子大小与鸟类摄入种子的发芽之间存在显著相关性，这可能是由于其拥有极其坚硬的保护性种皮。种子竞争实验表明，尖叶枣和非洲油橄榄亚种具有显著的发芽表现，且与种子密度和种子大小呈正相关，而硬叶厚壳树根本不发芽。发芽盘中的种子物种多样性没有显著影响，因为前两种植物的种子在所有竞争水平上始终显示出显著更高的发芽率。
我们得出结论，不同的植物物种对鸟类摄食种子的反应不同，并且由于在本研究中使用的其他树木/灌木物种观察到的发芽不良不能仅归因于竞争，因此需要对本研究中使用的种子样本的发芽生理反应进行进一步的长期测试。
