Stemle Leyna R, Sorfleet Julie M, Moore Chelsea L, Christie Jack T, Searcy Christopher A, Rothermel Betsie B
Department of Biology University of Miami Coral Gables Florida USA.
Archbold Biological Station Venus Florida USA.
Ecol Evol. 2024 Nov 3;14(11):e70509. doi: 10.1002/ece3.70509. eCollection 2024 Nov.
Juvenile growth rate is a critical demographic parameter, as it shortens the time to maturity and often dictates how long individuals remain vulnerable to predation. However, developing a mechanistic understanding of the factors determining growth rates can be difficult for wild populations. The gopher tortoise () is an ecosystem engineer threatened by habitat loss and deficient management of pinelands in the southeastern United States. We investigated the factors governing immature gopher tortoise growth and explored the use of drone-based imagery for habitat assessment by comparing predictive models based on ground-based plant surveys versus drone-derived data. From 2021 to 2022, we tracked and measured immature tortoises in native sandhill and human-modified, ruderal habitat in south-central Florida. Using quarterly, high-resolution drone imagery, we quantified plant cover types and vegetation indices at each occupied burrow and measured the frequency of occurrence of forage species by hand. Annual growth rates of immature tortoises in ruderal habitat were higher than those in sandhill and were the highest published for this species. Models based on drone-derived data were able to explain similar proportions of variation in growth as ground-collected measures of forage, especially during the late dry season when both types of models were most predictive. Habitat differences in forage nitrogen content were also more pronounced during this season, when dominant ground cover in ruderal habitat (bahiagrass) had much higher nitrogen content than dominant ground cover in sandhill (wiregrass). Despite concerns about potential growth-survival trade-offs, tortoises in ruderal habitat did not exhibit lower apparent survival. Our findings indicate that habitat dominated by nutritious non-native grass can provide a valuable supplement to native sandhill through the mechanism of increased growth rates due to higher forage quality. Finally, our study demonstrates that drone technology may facilitate management by providing less labor-intensive ways to assess habitat quality for this and other imperiled herbivores.
幼年生长率是一个关键的种群统计学参数，因为它缩短了成熟时间，并且常常决定个体易受捕食影响的时间长短。然而，对于野生种群而言，要从机制上理解决定生长率的因素可能具有挑战性。地鼠龟（）是一种生态系统工程师，受到美国东南部栖息地丧失和松林管理不善的威胁。我们研究了影响未成熟地鼠龟生长的因素，并通过比较基于地面植物调查与无人机获取数据的预测模型，探索了利用无人机图像进行栖息地评估的方法。2021年至2022年，我们在佛罗里达州中南部的原生沙丘和人类改造的杂草丛生栖息地追踪并测量了未成熟的地鼠龟。利用每季度的高分辨率无人机图像，我们量化了每个占据洞穴处的植物覆盖类型和植被指数，并手工测量了觅食物种的出现频率。杂草丛生栖息地中未成熟地鼠龟的年生长率高于沙丘栖息地中的生长率，且是该物种已发表的最高生长率。基于无人机获取数据的模型能够解释与地面收集的觅食测量数据相似比例的生长变化，尤其是在旱季后期，此时两种类型的模型预测性最强。在这个季节，觅食氮含量的栖息地差异也更为明显，此时杂草丛生栖息地中的优势地被植物（巴哈雀稗）的氮含量远高于沙丘栖息地中的优势地被植物（线茅草）。尽管担心潜在的生长 - 生存权衡，但杂草丛生栖息地中的地鼠龟并未表现出较低的表观存活率。我们的研究结果表明，以营养丰富的非本地草为主的栖息地可以通过因较高的觅食质量而提高生长率的机制，为原生沙丘提供有价值的补充。最后，我们的研究表明，无人机技术可以通过提供劳动强度较低的方式来评估该物种和其他濒危食草动物的栖息地质量，从而促进管理工作。
