COS 248-4 - Extinction debt of species and interactions in a fragmented landscape

Abstract: Addressing the worldwide biodiversity crisis in fragmented landscapes must consider both present species extinctions and those yet to come. This extinction debt emerges as a consequence of past environmental disturbances such as habitat loss and habitat fragmentation. As species interact locally in ecological networks, biotic int­eractions themselves may be threatened by habitat destruction, creating delayed extinction of interactions—an extinction debt of interactions. However, the extent to which extinction debts of interactions happen in natural systems has received little attention. To fill this gap, we studied the response of plants, herbivores, parasitoids, and their trophic interactions to long-term habitat loss and fragmentation in 14 habitat fragments of a dryland landscape in central-western Argentina. Using maps of present and historical landscape cover over a period of 30 years, we distinguished old habitat fragments (stable habitats) and young (unstable habitats) according to fragmentation age (origin of fragment before or after 2003), independently of area or connectivity loss. Assuming a paid debt in old habitat fragments, we examined the potentially unpaid extinction debt in young habitats as the difference between the current richness of species and interactions and the expected richness for area and connectivity relationships in old habitat fragments. We found a greater species and interaction debt for connectivity than for area, except for plants, for which area loss caused more delayed extinctions than connectivity loss. Furthermore, when considering connectivity loss, we found the greatest debt for parasitoids and their interactions with herbivores, followed by herbivores and their interactions with plants, and finally plants themselves. In contrast, for area loss, herbivores and their trophic interactions had a lower extinction debt. Ignoring extinction debts in natural habitats underestimate the biodiversity crisis and its potential consequences for humanity. Estimating the magnitude of the debt for both species and interactions confers the opportunity to preserve and restore habitats before extinctions occur and mitigate negative effects on ecosystems. Our analytical methods and findings contribute to improving the way to estimate extinction debts of species and biotic interactions in fragmented landscapes.