Spatial co-occurrence of exotic species in an urban reserve in Mexico City

Abstract

Exotic species can interact positively or negatively with other exotic species. The patches of original vegetation immersed within some urban centers may be vulnerable to invasion by exotic species, which may compromise the value of these urban ecological reserves for the conservation of native biodiversity. We used four years of data to examine potential spatial interactions between different exotic plant and animal species, employing two-species, multi-season occupancy models in an ecological reserve immersed within a megacity. We tested the hypothesis that the human activities taking place in the urbanized areas that surround the reserve should promote spatial co-occurrence (aggregation). Conversely, the conservation areas may represent biotic barriers for exotic species and, hence, antagonistic processes (lack of co-occurrence) should occur in these areas. We detected 10 positive and two negative spatial interactions. Eucalyptus camaldulensis , Schinus molle , and Passer domesticus were the species that had the greatest influence on other exotic species. All spatial interactions between animal species were positive. Many of the observed spatial interactions occurred during the warm-dry season. We did not find evidence supporting the hypothesis that aggregation should occur in the periphery of the reserve where humans provide resources to exotic species. In addition, we did not detect negative spatial associations between exotic species in the conservation areas. Given the potential synergistic effects that may result from the observed co-occurrence between distinct exotic species, we emphasize the importance of their early detection and management to prevent facilitation processes between them that could increase their spread within urban reserves.