Protected wildlife habitats provide valuable stepping stones for species that shift their distributions in response to climatic and other environmental changes, but they might also aid the spread of invasive alien species. Here, we quantify the use of protected areas (PAs) by both introduced and natural wetland colonists in the UK to analyse patterns of colonization and examine the propensity of invaders to use PAs.
We calculate PA associations for six species of wetland birds deliberately introduced to the UK and compare these with eight others that have recently colonized the UK naturally. We assess PA associations at three different stages of establishment – first breeding in each county, early establishment of a population (4–6 years after initial breeding) and subsequent consolidation (14–16 after initial breeding) – and analyse changes in PA association over time.
Introduced wetland bird species were less associated with PAs than natural colonists at each stage of establishment. During the later stages of colonization, the PA association of introduced species tended to increase. In contrast, natural colonists usually colonized PAs first, and their established populations subsequently spread into non-PA sites.
The United Kingdom PA network did not facilitate the invasion of introduced species during the initial stages of their colonization, but was vulnerable to colonization as populations established. This is in contrast to natural colonists, which are more reliant on PAs during initial colonization but become less dependent as they establish. During a period of rapid environmental change, PAs have facilitated expansions of natural colonists, without acting as the prime sites for invasion by introduced species.