Exotic species can rearrange native communities and, in extreme cases, drive local extirpation. Before extirpation occurs, native species may alter where and when they use the landscape in ways that permit temporary coexistence or that presage long-term decline. The authors asked how the invasive axis deer (Axis axis) influences the spatial and temporal use of two native cervids across a gradient of invasion, and whether observed coexistence reflects behavioral adjustment or pre-existing niche differences.
The study used eight years of camera-trap data spanning 2018–2026. Data came from 103 camera stations distributed across Uruguay and totaled 154,590 camera-nights. These long-term and wide-ranging recordings provided the basis to compare sites where the invader is absent, present, or increasing, thereby enabling inference about changes in space and time use across invasion stages.
The two focal native species differ in habitat affinities. The brown brocket (Subulo gouazoubira) is associated with forested environments and relies on understory stratum for its ecological needs. The pampas deer (Ozotoceros bezoarticus) is restricted to grassland habitats. The invader, Axis axis, is expanding through the landscape and can overlap with one or both natives depending on local habitat.
To evaluate spatial and temporal relationships among species, the study combined multiple analytical methods: activity-overlap comparisons, directional-avoidance metrics, hierarchical activity assessments, and two-species occupancy analyses. These complementary approaches aimed to detect co-occurrence, temporal segregation or overlap, directional avoidance or attraction, and how detection and occupancy probabilities covary between pairs of species.
The invader and the brown brocket were found to share forested areas, but coexistence involved clear segregation along structural habitat dimensions. Specifically, they segregated in space and across the understory stratum: the brocket used the understory the brocket requires, whereas the invader tended to avoid that stratum. In addition, the pair exhibited context-dependent shifts in diel activity — the timing of daily activity changed between them depending on local context. The study also reports that understory cover declined with increasing abundance of Axis axis, a pattern consistent with habitat modification by the invader.
By contrast, interactions between the invader and the pampas deer appear primarily driven by intrinsic segregation. The two species favored different habitats and exhibited opposite diel niches, generating separation without evidence that the pampas deer changed its behavior in response to the invader. Analyses provided no support for a detectable shift in pampas deer space or time use attributable to Axis axis.
The same invasive species produced different outcomes with each native cervid. With the brown brocket, coexistence has elements of behavioral adjustment and potential habitat alteration: spatial and vertical segregation, shifts in diel activity, and a decline in understory cover where the invader is more abundant. With the pampas deer, segregation appears to be driven by pre-existing niche differences in habitat and diel patterns, with little evidence of behavioral change by the native.
Across both dyads the detectable behavioral signal was asymmetric: in some contexts the invader, rather than the native, showed the clearer adjustment. The authors caution that the invader is still expanding and populations are not at equilibrium; therefore, observed patterns are best viewed as provisional coexistence and early warning signals of potential community reorganization.
This work is a synthesis of camera-trap observations and multiple statistical comparisons; the authors note limited numbers of shared sites for some pairwise comparisons, which warrants caution in interpreting asymmetric behavioral signals. Because Axis axis remains in an expansion phase, longer-term monitoring and additional sites will be needed to determine whether current segregations persist or lead to further habitat modification or native declines. The study highlights that early behavioral shifts and structural habitat changes can provide useful signals for conservation and management in the face of biological invasions.
Note: this study is reported as a preprint and has not been peer reviewed. Details beyond those presented in the source abstract and article metadata were not reported in the provided text.