Data from: Climatic effects on population declines of a rare wetland species and the role of spatial and temporal isolation as barriers to hybridization

Climate change and climatic extremes may affect species directly or indirectly. While direct climatic effects have been intensively studied, indirect effects, such as increasing hybridization risk, are poorly understood.
The goal of our study was to analyse the impact of climate on population dynamics of a rare habitat specialist, Chorthippus montanus, as well as the fine-scale spatial overlap with a sympatric habitat generalist, Chorthippus parallelus and the dispersion of hybrids. We were particularly interested in the role of spatiotemporal overlap on heterospecific encounter frequencies.
We conducted high-precision mark-recapture studies on two sites over 7 years and genotyped 702 individuals of two C. montanus generations to detect hybrids. We tested the performance of three programs (structure, newhybrids and adegenet) and accepted only hybrids detected by the two best performing programs. We then tested for correlations between yearly population trends and climatic variables. Furthermore, we analysed the spatial dispersion of both taxa and the hybrids to calculate variation in spatial and temporal overlap and infer heterospecific encounter probabilities.
Our results revealed that droughts during the egg phase and rainy weather during nymphal development were strongly correlated with population declines in the habitat specialist. The highest hybridization rate (19·6%) was found in the population with lowest population size. The combined effects of spatial and temporal niche overlap decreased heterospecific encounter probabilities to 4·2–7·6% compared to 20–28% and 11–19% calculated alone from phenology or spatial overlap respectively. Hybrids were detected in areas of higher heterospecific encounter probability, mainly at the edge of the specialists’ occupied habitat in areas with intermediate soil moisture conditions compared to the parental species.
This illustrates that the combination of spatial and temporal segregation provides an effective barrier to hybridization. However, the high hybridization rate in one of the populations suggests that this function may decrease with decreasing population size. This supports the hypothesis that climatic extremes threaten rare species directly by reducing reproductive success and may indirectly increase hybridization risk.

气候变化与极端气候事件可能对物种产生直接或间接影响。尽管学界已针对直接气候效应开展了大量深入研究，但诸如杂交风险上升等间接效应的相关认知仍较为匮乏。
本研究旨在分析气候对稀有生境专性物种（habitat specialist）山地雏蝗（Chorthippus montanus）种群动态的影响，同时探究其与同域分布的生境广适性物种（habitat generalist）平行雏蝗（Chorthippus parallelus）的精细空间重叠格局，以及杂交个体的空间分布特征。本研究尤为关注时空重叠在异种相遇频率中的作用。
研究团队在两个样地开展了为期7年的高精度标记重捕研究，并对两代山地雏蝗共计702个个体进行基因分型以检测杂交个体。我们测试了Structure、NewHybrids与adegenet三款软件的分析性能，仅采信由两款表现最优的软件共同检出的杂交个体。随后，我们检验了年度种群趋势与气候变量间的相关性。此外，我们还分析了两个物种及杂交个体的空间分布格局，以计算时空重叠的变异程度，并推导异种相遇概率。
研究结果显示，卵期干旱与若虫（nymph）发育期的强降雨均与该生境专性物种的种群下降显著相关。在种群规模最小的样地中，观测到最高的杂交率（19.6%）。相较于仅通过物候或空间重叠分别计算得到的20%~28%与11%~19%，时空生态位重叠的联合效应将异种相遇概率降至4.2%~7.6%。杂交个体主要分布在异种相遇概率更高的区域，具体位于山地雏蝗栖息生境的边缘地带，且其土壤湿度条件介于两个亲本物种之间。
这表明时空隔离能够形成有效的杂交障碍。然而，其中一个样地的高杂交率提示，该屏障功能可能随种群规模缩减而减弱。本研究结果支持以下假说：极端气候事件可通过降低繁殖成功率直接威胁稀有物种，同时还可能间接提升杂交风险。