Biodiversity conservation focuses on species and/or populations, but preserving genetic diversity and structure has received limited attention and even less maintaining species evolutionary potential over generations. Genetic diversity is an essential component of biodiversity enabling species’ persistence, particularly under disturbances. Via sexual reproduction genetic diversity is transmitted across generations and greater outcrossing in parental populations will lead to greater genetic diversity in their offspring. Grazing by exotic large herbivores is one of the main disturbances driving biodiversity loss threatening rangelands sustainability worldwide. We investigated grazing effects on fitness and genetic diversity of parental and offspring cohorts of Prosopis alpataco from Patagonian Monte Desert. We collected fresh leaves and seeds from 10 independent rangelands with different herbivore density, forming a grazing gradient, and estimated genetic parameters from allele frequencies using isoenzymes. We recorded plant size, seed weight, seed set, seedling emergence and mortality as proxies of plant fitness. Applying regression models and path analysis (D-separation) approaches we observed that increasing grazing reduced seed set and seedling emergence, and significantly increased seedling mortality. Parental and offspring suffered from inbreeding. Moreover, we found genetic diversity loss throughout cohorts in all rangelands, however, this loss was relatively lower at intermediate grazing intensities. The introduction of large herbivores in unmanaged rangelands affected vegetation structure, jeopardizing their evolutionary potential and system sustainability. Therefore, natural revegetation may be compromised by aggravated genetic diversity losses along generations that might be deepened in drylands under forecasted climate change. This highlights the importance of evaluating and conserving genetic diversity.

生物多样性保护的重点是物种和/或种群，但是保护遗传多样性和结构受到的关注有限，甚至几代人都没有保持物种进化的潜力。遗传多样性是生物多样性的重要组成部分，能够使物种得以持久存在，特别是在干扰之下。通过有性生殖，遗传多样性可以世代相传，父母群体中更大的异性杂交将导致其后代更大的遗传多样性。大型外来草食动物放牧是驱动生物多样性丧失，威胁全球牧场可持续性的主要因素之一。我们调查了放牧对Prosopis alpataco父母和后代队列的适应性和遗传多样性的影响来自巴塔哥尼亚的蒙特沙漠。我们收集了来自10个不同草食动物密度的独立牧场的新鲜叶子和种子，形成了放牧梯度，并使用同工酶从等位基因频率估算了遗传参数。我们记录了植物大小，种子重量，种子结实，幼苗出苗和死亡率，以此作为植物适应性的指标。应用回归模型和路径分析（D分离）方法，我们观察到放牧减少了结实和幼苗出苗，并显着增加了幼苗死亡率。父母和后代遭受近亲繁殖。此外，我们在所有牧场的整个队列中都发现了遗传多样性丧失，但是在中等放牧强度下这种丧失相对较低。在未管理的牧场中引入大型草食动物会影响植被结构，危害其发展潜力和系统可持续性。因此，沿代的遗传多样性丧失加剧可能会损害自然植被，而在预测的气候变化下干旱地区的遗传多样性可能会加剧。这突出了评估和保护遗传多样性的重要性。