Quantifying the links between land use and population growth rate in a declining farmland bird

Land use is likely to be a key driver of population dynamics of species inhabiting anthropogenic landscapes, such as farmlands. Understanding the relationships between land use and variation in population growth rates is therefore critical for the management of many farmland species. Using 24 years of data of a declining farmland bird in an integrated population model, we examined how spatiotemporal variation in land use (defined as habitats with “Short” and “Tall” ground vegetation during the breeding season) and habitat‐specific demographic parameters relates to variation in population growth taking into account individual movements between habitats. We also evaluated contributions to population growth using transient life table response experiments which gives information on contribution of past variation of parameters and real‐time elasticities which suggests future scenarios to change growth rates. LTRE analyses revealed a clear contribution of Short habitats to the annual variation in population growth rate that was mostly due to fledgling recruitment, whereas there was no evidence for a contribution of Tall habitats. Only 18% of the variation in population growth was explained by the modeled local demography, the remaining variation being explained by apparent immigration (i.e., the residual variation). We discuss potential biological and methodological reasons for high contributions of apparent immigration in open populations. In line with LTRE analysis, real‐time elasticity analysis revealed that demographic parameters linked to Short habitats had a stronger potential to influence population growth rate than those of Tall habitats. Most particularly, an increase of the proportion of Short sites occupied by Old breeders could have a distinct positive impact on population growth. High‐quality Short habitats such as grazed pastures have been declining in southern Sweden. Converting low‐quality to high‐quality habitats could therefore change the present negative population trend of this, and other species with similar habitat requirements.

土地利用可能是栖息于农田等人造景观的物种种群动态的关键驱动因素。因此，厘清土地利用与种群增长率变异之间的关联，对诸多农田物种种群管理至关重要。本研究基于某一衰退农田鸟类的24年监测数据，借助综合种群模型（Integrated Population Model），在考虑生境间个体移动的前提下，探究了土地利用的时空变异（定义为繁殖季地面植被高度为“低矮”与“高大”的生境）以及生境特异性种群参数与种群增长率变异之间的关联。本研究同时采用瞬态生命表响应实验（Transient Life Table Response Experiment, LTRE）与实时弹性分析开展种群增长贡献评估：前者可揭示过往参数变异的贡献程度，后者则可预测改变种群增长率的未来情景。LTRE分析结果显示，低矮生境对种群增长率的年度变异存在显著贡献，该贡献主要源于出飞幼鸟的种群补充；而高大生境则未表现出相关贡献。仅18%的种群增长率变异可通过建模的局域种群过程得到解释，剩余变异则归因于表观迁入（即残余变异）。本研究还探讨了开放种群中表观迁入贡献占比偏高的潜在生物学与方法学原因。与LTRE分析结果一致，实时弹性分析显示，与低矮生境相关的种群参数对种群增长率的影响潜力显著高于高大生境相关参数。尤为关键的是，成年繁殖个体占据的低矮生境比例提升，可对种群增长产生显著的正向影响。在瑞典南部，放牧牧场等优质低矮生境正持续减少。因此，将低质量生境改造为高质量生境，有望扭转该物种及其他具有相似生境需求的物种当前的种群负增长趋势。