Currently, introduced mammals (rodents and cats) are considered among the main threats to wildlife, mainly in island ecosystems due to voracity of their diet, high reproductive rates and, in the case of cats, for their ability to support long periods with limitation of fresh water. At Galapagos Islands several studies have documented a predation effect of rodents and cats on various native species. The understanding of the population dynamics of these species, the influence of environmental variability on their diet and their interrelations with the native and endemic flora and fauna of the Galapagos contribute to improving the management and control actions of introduced species. Our projects try to understand the biology, trophic ecology and population dynamics of introduced rodents and cats and evaluate their impacts on endemic and native marine sea birds in priority conservation areas on Galapagos Islands.