The use of corridors as a conservation strategy is increasing despite a lack of scientific consensus on their efficacy. More specifically, whether corridors enhance the movement of animals and plants between habitat fragments has only been addressed on a case-by-case basis with mixed results. Recently, there have been a growing number of well-designed experiments addressing this question, making the topic ripe for a meta-analytical review. We conducted a meta-analysis to determine 1) if corridors enhance movement, 2) whether there is a difference in the effectiveness of corridors by different organisms, 3) whether the effectiveness of corridors is restricted to manipulative experiments, or whether they work in real-world landscapes, and 4) how recent changes in the design of corridors studies has influenced the findings.
We analyzed 86 comparisons from 31 different studies using a highly conservative Bayes model, which accounted for sampling and hierarchical dependence within and across studies. We found that corridors do enhance movement; the result was highly significant and had a mean effect size of 0.58. We also found evidence that corridors are more likely to be important in the movement of invertebrates, non-flying vertebrates, and plants as opposed to birds. Natural experiments, those conducted using existing corridors instead of creating corridors, showed significantly more movement than manipulative experiments. Finally, several recent methodological advances in corridor experiments, including controlling for increased area and controlling for distance, which are typically viewed as more conservative approaches, do not seem to be important in influencing whether corridors enhance movement. The results of this meta-analysis suggest that existing corridors enhance movement of animal and plant species in fragmented landscapes, even more than some manipulative experiments have suggested. Our results suggest that efforts spent on creating corridors in real-world landscapes to assist in the movement and prevent the eventual extinction of populations are likely succeeding.