Fluctuations in plant populations: Role of exogenous and endogenous factors

Abstract

Question: What is the role of exogenous and endogenous factors in determining fluctuations in plant populations? Methods: A total of 29 long-term time series from different plant species was analysed. Data were obtained from the literature as well as from our own surveys. For each series we calculated the autocorrelation function to identify the presence of cyclic dynamics. The existence and the order of density-dependent processes were examined by calculating the partial rate correlation function to obtain the global Lyapunov exponent to assess whether populations exhibited chaotic dynamics. To test the effect of exogenous factors on each population, we used regression analyses to relate mean annual temperature and total annual precipitation to population abundance. Finally, we employed a Mann-Whitney U-test to analyse whether populations that showed endogenous regulation occurred in less variable environments. © 2012 International Association for Vegetation Science.