Propagule pressure and land cover changes as main drivers of red and roe deer expansion in mainland Portugal

© 2017 John Wiley & Sons Ltd Aim: The management of the rapid expansion of wild ungulate populations is a challenging task and a societal priority. Using a progressive database of red (Cervus elaphus) and roe (Capreolus capreolus) deer colonization over the last three decades, we estimate the range expansion rates and the underlying mechanisms involved in the expansion patterns of red and roe deer populations at the south-western edge of its European distribution. Location: Mainland Portugal. Methods: We compiled and grouped historical red and roe deer distribution data in three time periods (1981–1990, 1991–2000 and 2001–2010). We used generalized linear mixed models to evaluate how biotic and abiotic drivers determine the expansion patterns of red and roe deer. Results: We reported a significant expansion of red and roe deer populations during the last three decades. The significant interaction between propagule pressure and land cover suggests that the effects of propagule pressure vary along environmental gradients. We found that the influence of livestock on red and roe deer expansion is idiosyncratic. Contrary to red deer, roe deer expansion was also influenced by climatic conditions. We did not detect any significant effect of human factors on the red and roe deer expansion. Main conclusions: The synergistic effects between variables should be taken into account when studying the patterns of species expansion. Our study emphasize that policy makers should consider the spatial, temporal, ecological and societal nuances of species expansion in order to prioritize management measures and to allocate management budgets. Although concerted strategies to curtail species spread should mitigate red and roe deer economic and ecological impacts, these effects can be neutralized by a continuous rural exodus and the consequent forest and shrub encroachment.