Sadiki Kantakwa Grégoire, Yessoufou Kowiyou, Suinyuy Terence N
Department of Geography, Environmental Management and Energy Studies University of Johannesburg Johannesburg South Africa.
School of Biology and Environmental Sciences, Faculty of Agriculture and Natural Sciences University of Mpumalanga Mbombela South Africa.
Ecol Evol. 2024 Aug 27;14(8):e70209. doi: 10.1002/ece3.70209. eCollection 2024 Aug.
The genus is entirely endemic to Africa, and like most cycad species, the genus is at risk of extinction. One of the threats jeopardising the future of the genus is reproduction failure, a failure that is still poorly understood. Our objective was to investigate what predisposes species to seed damages through predation, a potential cause of reproduction failure. We collected functional traits of 430 individuals of , as well as data on pre-dispersal seed predation, habitat type and elevation in the Origi Gorge Nature Reserve, South Africa. Then, we analysed our data by fitting a structural equation model. We found that plants tend to be taller when moving from open to close habitat, whereas plant height tends to increase along elevation. In addition, taller plants tend to have more leaves, and plant canopy size shows significant positive relationship with elevation, plant height and number of leaves. These findings suggest a leaf height-canopy dimension strategy perhaps in response to environmental stresses imposed by elevation. We tested the effects of habitat types on seed production. Although there were significantly more seeds in open habitats, open habitats showed the lowest proportion of predated seeds. Finally, we tested the effects of elevation on seed production. We found that seed production decreases along elevation while the proportion of predated seeds increases. Under the resource concentration hypothesis, these findings (where there are more resources, predation is low) are unexpected, suggesting rather that it is the resource dilution effect that matches the pre-dispersal seed predation patterns in our study area. We suggest that anthropogenic pressures at lower elevation due to easy access may cause seed predators to shift towards higher elevation where they cause heavier damage to seed, thus perhaps contributing to the extinction risk of the genus Encephalartos.
该属植物完全原产于非洲，与大多数苏铁科物种一样，该属面临灭绝风险。危及该属未来的威胁之一是繁殖失败，而这种失败目前仍知之甚少。我们的目标是调查是什么因素使该属物种易受种子被捕食的损害，这是繁殖失败的一个潜在原因。我们收集了南非奥里吉峡谷自然保护区430株该属植物的功能性状，以及关于种子传播前被捕食情况、栖息地类型和海拔的数据。然后，我们通过拟合结构方程模型来分析数据。我们发现，从开阔栖息地到封闭栖息地，植物往往会更高，而植物高度往往会随着海拔升高而增加。此外，较高的植物往往有更多的叶子，植物冠层大小与海拔、植物高度和叶子数量呈显著正相关。这些发现表明，可能存在一种叶高 - 冠层维度策略，也许是为了应对海拔带来的环境压力。我们测试了栖息地类型对种子产量的影响。虽然开阔栖息地的种子明显更多，但开阔栖息地的种子被捕食比例最低。最后，我们测试了海拔对种子产量的影响。我们发现，种子产量随着海拔升高而下降，而被捕食种子的比例增加。根据资源集中假说，这些发现（资源越多，捕食越低）是出乎意料的，这表明在我们的研究区域，是资源稀释效应与种子传播前的捕食模式相匹配。我们认为，由于容易到达，低海拔地区的人为压力可能会导致种子捕食者转向更高海拔地区，在那里它们对种子造成更严重的损害，从而可能导致该属植物面临灭绝风险。
