Assessing the relative importance of intrinsic and extrinsic influence on sheep population dynamics on Hirta Island, UK

SummaryIdentifying the relative importance of intrinsic factors and extrinsic environmental variations on population or ecosystem dynamics is important for ecological conservation research. Here, we use a systematic method proposed by De Menezes and Barabási [2004. Separating internal and external dynamics of complex systems. Physical Review Letters, 93, 068701] to reanalyse the long-term monitoring data of Soay sheep population fluctuations and climate variations on Hirta Island, UK. Our results indicate that the climate conditions have a higher impact than internal factors on the fluctuations of sheep population. The sheep population dynamics are internally self-regulating. The scaling relationships between sheep population and external and internal standard deviations are similar. The threshold of the sheep population on this island as determined by our study is around 1197, which is consistent with previous studies by other methods. Our study indicates that this systematic method may help to understand some of the complicated aspects of population dynamics about which detailed knowledge is limited.