McCauley Edward, Nelson William A, Nisbet Roger M
Ecology and Evolution Group, Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada.
Nature. 2008 Oct 30;455(7217):1240-3. doi: 10.1038/nature07220.
A long-standing issue in ecology is reconciling the apparent stability of many populations with robust predictions of large-amplitude population cycles from general theory on consumer-resource interactions. Even when consumers are decoupled from dynamic resources, large-amplitude cycles can theoretically emerge from delayed feedback processes found in many consumers. Here we show that resource-dependent mortality and a dynamic developmental delay in consumers produces a new type of small-amplitude cycle that coexists with large-amplitude fluctuations in coupled consumer-resource systems. A distinctive characteristic of the small-amplitude cycles is slow juvenile development for consumers, leading to a developmental delay that is longer than the cycle period. By contrast, the period exceeds the delay in large-amplitude cycles. These theoretical predictions may explain previous empirical results on coexisting attractors found in Daphnia-algal systems. To test this, we used bioassay experiments that measure the growth rates of individuals in populations exhibiting each type of cycle. The results were consistent with predictions. Together, the new theory and experiments establish that two very general features of consumers--a resource-dependent juvenile stage duration and resource-dependent mortality--combine to produce small-amplitude resource-consumer cycles. This phenomenon may contribute to the prevalence of small-amplitude fluctuations in many other consumer-resource populations.
生态学中一个长期存在的问题是，如何使许多种群的明显稳定性与基于消费者 - 资源相互作用的一般理论对大幅度种群周期的有力预测相协调。即使消费者与动态资源解耦，理论上，许多消费者中存在的延迟反馈过程也会产生大幅度周期。在这里，我们表明，消费者中依赖资源的死亡率和动态发育延迟会产生一种新型的小幅度周期，这种周期与耦合的消费者 - 资源系统中的大幅度波动共存。小幅度周期的一个显著特征是消费者的幼体发育缓慢，导致发育延迟长于周期时长。相比之下，大幅度周期的周期时长超过延迟时间。这些理论预测可能解释了之前在水蚤 - 藻类系统中发现的共存吸引子的实证结果。为了验证这一点，我们使用了生物测定实验来测量呈现每种周期类型的种群中个体的生长速率。结果与预测一致。新理论和实验共同表明，消费者的两个非常普遍的特征——依赖资源的幼体阶段持续时间和依赖资源的死亡率——共同作用产生了小幅度的资源 - 消费者周期。这种现象可能导致许多其他消费者 - 资源种群中普遍存在小幅度波动。
