Exotic species occupancy in an urban reserve: Explosion or stability?

Exotic species represent a threat to the native biodiversity of all ecosystems. The negative effects caused by exotic species can be particularly severe in urban areas due to their ecological conditions and the anthropogenic activities that take place inside them. Here, we studied a set of exotic species of plants and animals that inhabit an ecological reserve immersed within Mexico City. We focused on evaluating two hypotheses: (i) the occupancy of the focal exotic species increases over time (throughout four years) in the ecological reserve, and (ii) urban features such as proximity to urban structures, gardening activities, and presence of anthropogenic garbage promote their occupancy. To test these hypotheses, we analyzed detection data, collected throughout four years, using occupancy models to determine the occurrence dynamics of the 10 focal exotic species in the study area. Contrary to our expectations derived from our first hypothesis, we found that all species showed stability in their occupancy, which indicates that their populations are stable within the urban reserve. According to our second hypothesis, urban features consistently promoted the occupancy of five species. In particular, sites near urban structures, with relatively high urban cover, and where gardening activities take place promote the presence of exotic species. In addition, other non-urban features such as high vegetation cover and richness, rock cover, and deep soils also facilitate the presence of some of our focal species. We conclude by proposing the use of sensitivity and elasticity analyses to identify the most vulnerable stages of exotic plant and animal species to inform future control actions. We also suggest monitoring both groups in the medium and long term, focusing removal efforts on periods of greatest vulnerability. Our findings can inform guidelines for effective removal and management efforts to reduce the establishment and impact of these species within this and other ecological reserves.