Effect of protected areas on four indices of bird diversity in eight biodiversity hotspots

Coefficients correspond to the estimates of GAM models. Asterisks represent P value (***<0.001 **<0.01 *<0.05). Vertical error bars show 95% confidence interval. Data from Cazalis et al. (2020)

Tropical regions host a disproportionately large share of the world’s biodiversity, but also suffer from rapid habitat loss and degradation. Evaluating the effectiveness of protected area networks in these regions is vital, but can be particularly challenging as large, detailed biodiversity datasets are often unavailable. Cazalis et al. (2020) used data from the world’s largest citizen science programme – eBird – to quantify the effect of protected areas on bird species diversity in eight tropical forest biodiversity hotspots across three continents. Using such a large dataset allowed the comparison of protected and unprotected sites while controlling for location biases (differences between protected and unprotected sites prior to protected area designation).

Although there was no consistent evidence that protected areas increased overall bird species richness, they were effective at retaining three groups of conservation concern: forest-dependent birds (species richness on average 17.8% higher in protected sites than unprotected areas), endemics (77.6% higher species richness in protected sites), and threatened or Near Threatened species (19.0% higher species richness in protected sites). These results suggest that protected areas are effective at avoiding the replacement of species of conservation concern with more generalist species following ecosystem alteration – a pattern which has been recorded previously and leads to little or no change in overall species richness (Hillebrand et al. 2018, Dornelas et al. 2014).

Cazalis et al. (2020) also found that protected sites had on average a 17.8% higher probability of being forested and 46.7% lower deforestation rates than comparable non-protected sites. Forested sites had, on average, higher species richness of the three groups of conservation concern (forest specialists, endemics, and threatened or Near Threatened species), suggesting that the effectiveness of protected areas at retaining these species is primarily driven by their effectiveness at mitigating forest loss.

Mitigation of loss of forest quality in protected areas also contributed towards the conservation of species of concern. When comparing protected areas with unprotected areas, canopy height was on average 4.8% higher, contiguity 2.6% higher, and wilderness 5.7% higher in protected areas. Each of these metrics of forest quality, as well as the residual effect of protection when controlling for these variables, were positively correlated with richness in species of conservation concern.

These results indicate that by mitigating against forest loss and degradation, protected areas make a measurable difference to the conservation of species of concern in tropical biodiversity hotspots. The results also illustrate the value of citizen science data on birds for evaluating conservation outcomes.