Dr. De Leo is a theoretical ecologist by formation, generally interested in investigating factors and processes driving the dynamics of natural and harvested populations and in understanding how to use this knowledge to inform practical management.

In recent years, Dr. De Leo has been particularly interested in investigating factors and processes that provide resilience of natural or managed population to natural and anthropogenic stressors, environmental shocks and climate change. He studies resilience from two very different points of view: on the one hand, he has focused his attention on populations that prove to be resilient despite our effort to control or eradicate them, namely parasitic and infectious diseases. On the other hand, he has been working extensively to understand how to increase resilience of population of commercial or conservation interest to extensive harvesting, environmental shocks, climate change and land use change.

Dr. De Leo has been working on a number of theoretical and applied problems ranging from the conservation of the European eel to the sustainable management of the abalone fishery in Baja California in the face of climate change, the biocontrol of schistososmiasis in west Africa and the relationship between resource exploitation, infectious diseases and poverty traps.