Abstract Despite decades of research, controversy has emerged as to whether positive and negative interactions predictably shift with increasing environmental stress. We used projection matrices, to determine growth rate and elasticity and a LTR experiment to quantify the contribution of each matrix elements to the differences in λ observed between sympatric and syntopic sub-populations of globular cactus species in Brazil (Discocactus placentiformis and D. pseudoinsignis). We addressed the following questions: What is the growth rate of the two species when in sympatry and syntopy? What are the relative contributions of survival, growth, and fecundity to population growth? Which life cycle stages have the highest mortality? Do demographic differences between the two species account for observed differences in sub-population sizes? Both species exhibited higher densities when in syntopy than in sympatry. Seedling establishment and survival were high, and fecundity increased as plant diameter increased. Asymptotic population growth rates were significantly greater than one. The highest elasticity values were for stasis for the later ontogenetic stage and for the growths. It seems that the protection provided by the conservation area is efficient, and that the data were collected during a “bonanza” year, with high rainfall, when all or most reproduction and/or recruitment occur.

中文翻译：

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两种球状仙人掌物种的受保护种群是否面临人口爆炸或只是“富矿”年？

摘要 尽管进行了数十年的研究，但关于积极和消极的相互作用是否会随着环境压力的增加而发生可预见的变化的争论已经出现。我们使用投影矩阵来确定增长率和弹性，并使用 LTR 实验来量化每个矩阵元素对巴西球状仙人掌物种（Discocactus placentiformis 和 D. pseudoinsignis）同域和同位亚群之间观察到的 λ 差异的贡献. 我们解决了以下问题：当处于同位和同位时，这两个物种的增长率是多少？生存、成长、成长的相对贡献是什么？和人口增长的繁殖力？哪个生命周期阶段的死亡率最高？两个物种之间的人口差异是否解释了观察到的亚种群大小差异？两个物种在同位时比在同位时表现出更高的密度。成苗率和成活率高，随着株径的增加，繁殖力增加。渐近人口增长率显着大于1。最高的弹性值是后期个体发育阶段和生长的停滞。保护区提供的保护似乎是有效的，并且数据是在“富矿”年收集的，降雨量大，所有或大部分繁殖和/或补充发生。并且随着植株直径的增加，繁殖力增加。渐近人口增长率显着大于1。最高的弹性值是后期个体发育阶段和生长的停滞。保护区提供的保护似乎是有效的，并且数据是在“富矿”年收集的，降雨量大，所有或大部分繁殖和/或补充发生。并且随着植株直径的增加，繁殖力增加。渐近人口增长率显着大于1。最高的弹性值是后期个体发育阶段和生长的停滞。保护区提供的保护似乎是有效的，并且数据是在“富矿”年收集的，降雨量大，所有或大部分繁殖和/或补充发生。