Modelling the spatial and temporal dynamics of upland birds in Scotland

Abstract

Population numbers change in space and time. The construction of models to investigate the spatial and temporal dynamics of populations may offer a means to identify the processes driving this change. In this thesis, we make use of models to examine the population ecology of three species of upland birds: red grouse, meadow pipit and capercaillie. Populations of red grouse in the British Isles exhibit cyclic fluctuations in abundance. Time series data from 287 grouse moors across the United Kingdom were analysed to investigate co-variation in these fluctuations. Results indicate high levels of synchrony between populations on neighbouring moors, with synchrony declining with increasing intermoor distance. At distances greater than 100km, populations exhibit only weak synchrony. Synchrony is shown to be a product of strong coupling events, which occur on average every one in six years. In the absence of such events, synchrony is shown to dissipate within three years. Further, we present evidence which suggests this coupling is driven (at least in part) by dispersal between populations. The density dependent structures are also found to be sufficiently homogeneous to allow correlations in climate to synchronise dynamics, but examination of three climate variables failed to detect a relationship. We also studied the population dynamics of meadow pipits in upland grassland ecosystems. Data, collected as part of an ongoing grazing field experiment, were analysed to construct a Bayesian model of population growth, and predict the effect of grazing intensity on meadow pipit populations. Results suggest grazing has a significant impact on population growth. Grazing may act to improve meadow pipit foraging efficiency and thus productivity. Finally, a spatially explicit population viability model was constructed to predict changes in the future abundance and distribution of capercaillie. Published estimates of key demographic variables were drawn from the literature to parameterise the model. The spatial structure of the population was inferred from spatial data, documenting the extent and configuration of remnant pine woodlands in Scotland. The model predicts a low probability of extinction for capercaillie in the future, and offers insights into key processes affecting the distribution and abundance of this species. The development of these models has advanced our understanding of the environmental processes driving changes in the spatial and temporal dynamics of these species. The results of these studies may be useful in anticipating the future consequences of various drivers of change on the ecology of upland species