Do habitat corridors provide connectivity?

Skeptics have questioned the empirical evidence that corridors provide land scape connectivity. Some also have suggested dangers of corridors. We revie wed published studies that empirically addressed whether corridors enhance or diminish the population viability of species in habitat patches connecte d by corridors. A randomized and replicated experimental design has not bee n used-and we argue is not required-to make inferences about the conservati on value of corridors. Rather, studies can use observational or experimenta l analyses of parameters of target populations or movements of individual a nimals Two of these approaches hold the greatest promise for progress, espe cially if the shortcomings of previous studies are remedied. First, experim ents using demographic parameters as dependent variables-even if unreplicat ed-can demonstrate the demographic effects of particular corridors in parti cular landscapes Such studies should measure demographic traits before and after treatment in both the treated area (corridor created or destroyed) an d an untreated area (habitat patches isolated from one another). This appro ach is superior to observing the demographic conditions in various landscap es because of the tendency for corridor presence to be correlated with othe r variables, such as patch size, that can confound the analysis. Second, ob servations of movements by naturally dispersing animals in fragmented lands capes can demonstrate the conservation value of corridors more convincingly than can controlled experiments on animal movement. Such field observation s relate directly to the type of animals (e.g., dispersing juveniles of tar get species) and the real land scapes that are the subject of decisions abo ut corridor preservation. Future observational studies of animal movements should attempt to detect extra-corridor movements and focus on fragmentatio n-sensitive species for which corridors are likely to be proposed Fewer tha n half of the 32 studies we reviewed provided persuasive data regarding the utility of corridors other studies were inconclusive, largely clue to desi gn flaws. The evidence from well-designed studies suggests that corridors a ve valuable conservation tools. Those who would destroy the last remnants o f natural connectivity should bear the burden of proving that corridor dest ruction will not harm target populations.