The role of the matrix in shaping extinction risk and conservation opportunities for terrestrial mammals

The global biodiversity crisis, driven primarily by habitat loss and fragmentation, has traditionally led conservation efforts to focus almost exclusively on primary habitats. However, the ecological importance of the matrix, defined as areas surrounding primary habitat, has remained largely overlooked. In this dissertation, I used global-scale spatial analyses coupled with statistical modeling to (i) quantify how matrix condition influences the effects of habitat fragmentation on extinction risk for terrestrial mammals, (ii) compare the predictive performance of alternative habitat intactness models (patch-matrix, continuum, and hybrid models) for assessing extinction risk in terrestrial mammals, and (iii) map global patterns of terrestrial mammal species richness within the matrix to identify conservation opportunities beyond primary habitats. My findings demonstrate that matrix condition plays a key mediating role in the relationship between habitat fragmentation and extinction risk, with greater predictive power than habitat loss or habitat amount alone. Moreover, I found that the predictive importance of fragmentation increases as matrix condition deteriorates, suggesting that managing or restoring the matrix represents a strategic conservation action to mitigate the negative effects of fragmentation on biodiversity. Additionally, the hybrid habitat intactness model—which integrates discrete habitat patches with continuous gradients of habitat quality—consistently outperforms traditional patch-matrix and continuum models, regardless of species’ habitat specialization. Notably, the magnitude of the relationship between habitat intactness and extinction risk was greater when using the hybrid model, highlighting that integrating discrete and continuous habitat representations can improve extinction risk analyses and provide valuable insights for conservation. My results further reveal that hotspots of species richness within the matrix occupy only about 1% of Earth's terrestrial surface, yet could support more than half of all terrestrial mammal species. Matrix areas identified as having high conservation potential—based on overlapping richness hotspots—are primarily concentrated in tropical strongholds such as the Amazon Basin, Colombian Tropical Andes, Brazilian Atlantic Forest, and Albertine Rift. Importantly, many of these matrix areas face intense human pressures and remain inadequately represented within existing protected areas and other area-based conservation measures, underscoring their value as strategic opportunities for biodiversity conservation. Collectively, my results highlight an urgent need for a paradigm shift in conservation strategies that explicitly recognize, manage, and restore matrix areas as integral components of global biodiversity conservation. Integrating the matrix into conservation planning closely aligns with international biodiversity frameworks, particularly Target 2 of the Kunming-Montreal Global Biodiversity Framework, which calls for restoring at least 30% of degraded terrestrial ecosystems to enhance ecological integrity and connectivity. Such integration could substantially improve biodiversity outcomes, ecosystem resilience, and landscape connectivity, ultimately making critical contributions toward reversing global biodiversity declines.