The Magdalena river valley as an example of pervasive degradation of natural ecosystems and biological communities

The Magdalena river basin in Colombia, concentrates approximately 77% of the country´s population and is responsible for 80% of its economy. The basin provides most of the country´s hydroelectric power and almost 70% of the... [ view full abstract ]

The Magdalena river basin in Colombia, concentrates approximately 77% of the country´s population and is responsible for 80% of its economy. The basin provides most of the country´s hydroelectric power and almost 70% of the nation’s agricultural products are produced within this region, which comprises only one fourth of Colombia’s geographic extension. None the less, natural ecosystems in the Magdalena river basin have been widely transformed and to date less than 20% of natural ecosystems exist, most of them with a high degree of fragmentation and degradation. Here, we assess the current threats, challenges and opportunities that these ecosystems face at a regional scale and evaluate the impacts of anthropogenic disturbance on keystone species, and specially on large bodied mammals. We combined an assessment of the extent of natural forests from 1990, 2000, 2005 and 2010 combined with maxent modelling (for endemic taxa) in order to estimate the rates of habitat loss and fragmentation. We compiled secondary information to address the extent of habitat degradation associated with extensive cattle ranching, large oil palm monocultures, legal and illegal mining and major infrastructure development in the basin. Finally, we used occupancy models (through camera trapping) for medium and large mammals to better understand the vulnerability of large and emblematic animals to environmental changes from current patterns of land use and management. Based on our models, The Magdalena river valley has lost over 82% of its natural habitats, and rates of degradation have increased dramatically in the last decade. Although historical processes associated with extensive cattle ranching account for the vast majority of transformed areas, in the last decade large palm oil plantations have been the major driver of the transformation of natural forests into economically productive areas. Large predators (e.g., jaguars and pumas) and large herbivores and omnivores (e.g., tapirs and white-lip peccaries) are the most sensitive species to habitat loss and degradation and had a negative relation with the extent of forest cover and proximity to human settlements and access routes (roads, rivers, amongst others). We conclude that even though the Magdalena river valley is considerably degraded, current trends of habitat transformation are still not decreasing. In fact, the agricultural, and extractive industries continue to grow and increase their area of influence in this region. The disruption of biological processes through the potential local extinction of large predators and herbivores, might also derive in unpredictable changes in the diversity and dynamics of the remaining forests in the region. In conclusion, the Magdalena river basin is facing a critical moment in which large inter-institutional efforts will need to reconcile Colombia´s development plans with the conservation of natural ecosystems end in order to guarantee their integrity and the goods and services they provide.