Global anthropogenic activities are responsible for the modification of landscapes, creation of novel environments and movement of species across biogeographic regions. A consequence of this activity is the mixing of native and introduced species and the formation of novel biotic communities. We review the ecological consequences of the mixing of native and introduced species in theCaribbeanIslands especially inPuertoRico and theUS VirginIslands. Here we found documented examples indicating that novel communities of native and naturalized organisms are ubiquitous. The coexistence of species originating from different biogeographical regions raises research questions that demand attention for their ecological and conservation importance. For example: Is animal abundance in novel communities a measure of habitat quality? To what degree are populations in novel communities self‐sustaining? What are the consequences of species eradication? How does an introduced animal's trophic position affect its effects on novel and native communities? We suggest that novel communities that emerge in theCaribbean after deforestation and land abandonment could be harbingers of how the biota might respond elsewhere to rapidly changing environmental conditions, including global and climate change.