Hapca Simona, Crawford John W, Young Iain M
SIMBIOS Centre, University of Abertay Dundee, Dundee DD1 1HG, UK.
J R Soc Interface. 2009 Jan 6;6(30):111-22. doi: 10.1098/rsif.2008.0261.
The characterization of the dispersal of populations of non-identical individuals is relevant to most ecological and epidemiological processes. In practice, the movement is quantified by observing relatively few individuals, and averaging to estimate the rate of dispersal of the population as a whole. Here, we show that this can lead to serious errors in the predicted movement of the population if the individuals disperse at different rates. We develop a stochastic model for the diffusion of heterogeneous populations, inspired by the movement of the parasitic nematode Phasmarhabditis hermaphrodita. Direct observations of this nematode in homogeneous and heterogeneous environments reveal a large variation in individual behaviour within the population as reflected initially in the speed of the movement. Further statistical analysis shows that the movement is characterized by temporal correlations and in a heterogeneously structured environment the correlations that occur are of shorter range compared with those in a homogeneous environment. Therefore, by using the first-order correlated random walk techniques, we derive an effective diffusion coefficient for each individual, and show that there is a significant variation in this parameter among the population that follows a gamma distribution. Based on these findings, we build a new dispersal model in which we maintain the classical assumption that individual movement can be described by normal diffusion, but due to the variability in individual dispersal rates, the diffusion coefficient is not constant at the population level and follows a continuous distribution. The conclusions and methodology presented are relevant to any heterogeneous population of individuals with widely different diffusion rates.
对非同质个体群体扩散的特征描述与大多数生态和流行病学过程相关。在实际中，通过观察相对较少的个体并求平均值来量化移动，以估计整个群体的扩散速率。在此，我们表明，如果个体以不同速率扩散，这可能会导致群体预测移动出现严重误差。我们受寄生线虫雌雄同体拟丽突线虫的移动启发，开发了一个异质群体扩散的随机模型。在同质和异质环境中对这种线虫的直接观察揭示了群体内个体行为的巨大差异，最初体现在移动速度上。进一步的统计分析表明，移动具有时间相关性，并且在异质结构环境中出现的相关性与同质环境中的相比范围更短。因此，通过使用一阶相关随机游走技术，我们为每个个体推导了一个有效扩散系数，并表明该参数在群体中存在显著差异，且遵循伽马分布。基于这些发现，我们构建了一个新的扩散模型，其中我们保留了个体移动可由正态扩散描述的经典假设，但由于个体扩散速率的变异性，扩散系数在群体水平上不是恒定的，而是遵循连续分布。所呈现的结论和方法适用于任何扩散速率差异很大的异质个体群体。
