Habitat heterogeneity has long been shown to be a driver of species richness in ecological systems. Untangling which aspects of habitat heterogeneity are important to a specific system, however, can be more complicated. Habitat heterogeneity operates at both spatial and temporal scales, from micro- to global levels, and can be driven intrinsically or extrinsically. Additionally, these distinctions are not mutually exclusive.
Using 26 years of rodent abundance time series data from the Portal project, an experimental site in southeastern Arizona, we ask how both spatial and temporal habitat heterogeneity affect species and how they view the landscape. The Portal project consist of 24 plots with three different treatments: full rodent access (controls), kangaroo rat (Dipodomys sp.) exclosures, and rodent removals. With multiple treatment types, the system essentially establishes multiple patches within a more-or-less continuous landscape. In the mid-1990s, a novel competitor, Chaetodipus baileyi, colonized at the site; recently, however, C. baileyi has all but disappeared from the system. Here, we investigate how the arrival and disappearance of C. baileyi influences how an abundant smaller congeneric, C. penicillatus, views the patchy landscape.
Results/Conclusions:
Our results demonstrate that C. penicillatus’s view of the landscape has, in fact, changed in response to the arrival and subsequent decline of C. baileyi. Initially, C. penicillatus was found primarily on kangaroo-rat exclosures, as Dipodomys were its main competitors. With the invasion of C. baileyi in the mid-1990s, C. penicillatus became disproportionately more abundant on control plots. Population metrics of C. penicillatus, including immigration of new individuals, apparent survival, and transition probability between plot types, were all affected by the arrival of C. baileyi. Previous research has shown that the arrival of C. baileyi also had profound effects on ecosystem functioning in the kangaroo rat exclosures, which had previously never greater than 33% of the energy use by Dipodomys sp. on control plots. Our results suggest that ecosystem function has decreased through time but not dropped back to pre-invasion levels, suggesting that ecosystem functioning may have been affected by these shifting views of the landscape. Together, our results suggest that even though all patches are experiencing the same extrinsic environment, the intrinsic heterogeneity of patches—in this case, driven by differences in the dominant competitor in the patch types—can influence a species’ patch selection.