Empirical evidence for ecological traps: a two-step model focusing on individual decisions

Ecological traps are poor quality habitats that are preferred by individuals and that cause standard indicators of habitat quality (e. g., density, age structure, order of settlement) to be misleading. A maladaptive choice of habitats may have detrimental effects on individual fitness and long-term population persistence. For conservation purposes, it is therefore critical to identify ecological traps. We discuss a recent review on the relationships between density, reproductive success and productivity at the patch level. We also discuss the concept of ecological traps and definitions of habitat quality and habitat preference. Based on recent literature on ecological traps, we argue that no study shows evidence of an ecological trap in its strict sense, i.e., a preference for sink and an avoidance of source habitat. This lack of evidence is partly due to poor measures of preference and individual fitness, and to an absence of studies at the individual level. We suggest a two-step protocol at the level of individuals to investigate ecological traps by linking: (1) habitat characteristics, i.e., potential cues used by individuals, to fitness, and (2) preference for specific habitat characteristics. This protocol is illustrated by a long-term study on breeding territory selection in Northern Wheatears (Oenanthe oenanthe) in Sweden. Using our protocol, we could determine at least in part why Wheatears show a mismatch between habitat preference and fitness. We conclude that there is an urgent need for more studies on individual habitat-selection decisions before we can find less labour-intensive ways to identify potential trap situations