Sollmann Rahel, Caro Tim
Department of Ecological Dynamics Leibniz Institute for Zoo and Wildlife Research Berlin Germany.
School of Biological Sciences University of Bristol Bristol UK.
Ecol Evol. 2024 Aug 27;14(8):e70168. doi: 10.1002/ece3.70168. eCollection 2024 Aug.
Species experience a variety of environmental and anthropogenic conditions across their ranges leading to spatial variation in population dynamics. Understanding population dynamics under different conditions is important but it is challenging to allocate limited effort to spatial and temporal subpopulation monitoring. Using GLMMs, we analyze survey data of a metapopulation of coconut crabs spanning 7 years and 15 sites in and near the Pemba archipelago, Zanzibar, to estimate trends in population size (based on catch per unit effort), weight and sex ratio at the meta- and subpopulation level and investigate anthropogenic drivers of these trends. We found that the overall metapopulation has remained stable in terms of size and composition over the survey period, but observed diverging trends in population size and sex ratio at some subpopulations. Formal protection of sites was associated with positive population trends. Of nine sites for which we could estimate site-specific trends, three showed increasing and two decreasing trends, whereas four sites had stable subpopulations. Although anthropogenic factors affected the average weight, and the incidence of small and large individuals, we found no temporal trends in any weight-related measures. Furthermore, there were no apparent patterns between weight-related measures and subpopulation trends. The metapopulation was biased toward males, and exploitation appeared to be associated with declining trends in the proportion of females, likely an artifact of a strong decline in the proportion of females in one of only two exploited sites in the dataset. Educational campaigns implemented in 2020 at six sites were not related to higher population sizes in later surveys. The variable trends in subpopulation sizes and composition highlight the need for spatially replicated monitoring in metapopulations. The analyses further provide a detailed baseline for future subpopulation studies of this vulnerable species in one of its last remaining metapopulations in the Western Indian Ocean.
物种在其分布范围内经历各种环境和人为条件，导致种群动态出现空间变异。了解不同条件下的种群动态很重要，但将有限的精力分配到空间和时间亚种群监测上具有挑战性。我们使用广义线性混合模型（GLMMs）分析了跨越7年、涵盖桑给巴尔奔巴群岛及其附近15个地点的椰子蟹集合种群的调查数据，以估计在集合种群和亚种群水平上的种群大小（基于单位努力捕捞量）、体重和性别比趋势，并调查这些趋势的人为驱动因素。我们发现，在调查期间，总体集合种群在大小和组成方面保持稳定，但在一些亚种群中观察到种群大小和性别比出现了不同的趋势。对地点的正式保护与积极的种群趋势相关。在我们能够估计特定地点趋势的9个地点中，3个显示出增长趋势，2个显示出下降趋势，而4个地点的亚种群数量稳定。尽管人为因素影响了平均体重以及小型和大型个体的发生率，但我们在任何与体重相关的指标中都未发现时间趋势。此外，与体重相关的指标和亚种群趋势之间没有明显的模式。集合种群偏向雄性，开发似乎与雌性比例下降趋势有关，这可能是数据集中仅有的两个被开发地点之一中雌性比例大幅下降的结果。2020年在6个地点开展的教育活动与后期调查中较高的种群数量无关。亚种群大小和组成的可变趋势凸显了对集合种群进行空间重复监测的必要性。这些分析进一步为该脆弱物种在西印度洋最后剩余的集合种群之一中的未来亚种群研究提供了详细的基线。
