Ecology is undoubtedly the discipline that has had the greatest expansion in association with environmental problems. It could be thought then that the conservation of biodiversity in cities is within the domain of application of the discipline. For this reason, there are authors who affirm that the same laws and theories that ecology uses to understand and explain natural ecosystems can be applied to urban ecosystems. However, within the discipline, there is a strong debate as to whether ecology has mature laws and theories as other areas of science. Currently, the discussion is centered between those who think that ecology is a science lacking mature laws and theories, and on the other hand, authors who in recent years have defended the opposite position, presenting reconstructed theories and their associated laws that have allowed to answer the discussion about its epistemological status. From this state of affairs we propose to discuss whether urban ecosystems, with the patterns and processes of the organisms that inhabit cities, are within the domain of the laws and theories of ecology. We will also analyze whether the concept of ecosystem that is fundamental in ecology today can be applied to cities or urban ecosystems. Finally, we will discuss whether the problems of biodiversity conservation in cities are ecological problems or whether a more complex interdisciplinary approach is needed to establish measures for their preservation.