Counterfactual effect of Colombian protected areas on multispecies functional connectivity

Abstract

Protected areas (PAs) are central to Target 3 of the Kunming-Montreal Global Biodiversity Framework, which calls for ecologically well-connected systems, yet progress is tracked with indicators of connectivity state rather than of what protection achieved. We evaluated whether PAs in Colombia maintained multispecies functional connectivity relative to unprotected counterfactuals from 2000 to 2022 and whether the magnitude of their effects reflected the pressure they faced. We grouped 181 bird and mammal species into 12 emergent functional groups (EFGs) based on movement traits and exposure to human modification, modeled their connectivity with omnidirectional circuit theory, and matched protected and unprotected pixels with propensity scores within 6 regional subsystems. For 135 PAs, we estimated effects on standardized connectivity change ([Delta]Z) and on avoided critical loss (connected pixels that became impeded) and classified PAs by avoided loss relative to control loss. Connectivity changed more favorably in PAs than in controls (median & [Delta]Z effect 0.87, 95% CI 0.36-1.60); 72.6% of PAs had positive effects, which were significant in 4 of 6 regions. Protected areas avoided 1.51 percentage points (pp) of critical loss nationally, and avoided loss was positive in all 12 EFGs and significant in 8. However, the presence of an effect overstated its contribution: only 55% of PAs avoided more than 1 pp, and 30% lost more than their controls. Effectiveness increased with pressure, from 39% of PAs under low pressure to 75% under high pressure, where sustainable-use areas accounted for 29 of the 33 effective PAs. Small PAs contained most of the loss expected without protection (median 70%), and regional and national PAs performed alike under similar pressure. Measuring avoided loss relative to pressure shows where protection secures connectivity and where governance must improve, and offers a replicable indicator for the well-connected component of Target 3.