Spatial structure of reproductive success infers mechanisms of ungulate invasion in Nearctic boreal landscapes

Abstract

Landscape change is a key driver of biodiversity declines due to habitat loss and fragmentation, but spatially shifting resources can also facilitate range expansion and invasion. Invasive populations are reproductively successful, and landscape change may buoy this success.We show how modeling the spatial structure of reproductive success can elucidate the mechanisms of range shifts and sustained invasions for mammalian species with attendant young. We use an example of white-tailed deer (deer; Odocoileus virginianus) expansion in the Nearctic boreal forest, a North American phenomenon implicated in severe declines of threatened woodland caribou (Rangifer tarandus).We hypothesized that deer reproductive success is linked to forage subsidies provided by extensive landscape change via resource extraction. We measured deer occurrence using data from 62 camera traps in northern Alberta, Canada, over three years. We weighed support for multiple competing hypotheses about deer reproductive success using multistate occupancy models and generalized linear models in an AIC-based model selection framework.Spatial patterns of reproductive success were best explained by features associated with petroleum exploration and extraction, which offer early-seral vegetation resource subsidies. Effect sizes of anthropogenic features eclipsed natural heterogeneity by two orders of magnitude. We conclude that anthropogenic early-seral forage subsidies support high springtime reproductive success, mitigating or exceeding winter losses, maintaining populations. Synthesis and Applications. Modeling spatial structuring in reproductive success can become a key goal of remote camera-based global networks, yielding ecological insights into mechanisms of invasion and range shifts to inform effective decision-making for global biodiversity conservation.

Keywords: camera trapping; fitness; invasive species; landscape change; multistate occupancy models; range shifts; reproduction.

Figure 1

Occurrence of white‐tailed deer was surveyed at 62 camera sites (large block dots, scaled to deer relative abundance) in the boreal forest of northeast Alberta, Canada. Anthropogenic landscape features are widespread across this landscape, including forest harvesting cutblocks (gray polygons), well sites (square dots), seismic lines (gray), and roads and trails (dark gray and colored lines). Lakes are in blue

Figure 2

In the boreal forest of Alberta, Canada, camera traps quantified sites with white‐tailed deer fawns—characterized by their small size, and for younger animals, the presence of spots. Sites with fawns appearing in a survey month were recorded as “fawning” for that month

Figure 3

Spatial variation in white‐tailed deer reproductive success in the oil sands of the western Nearctic boreal forest of Alberta, Canada, was best explained by the post hoc stepAIC model (#31) which included petroleum extraction features—conventional seismic lines, 3D seismic lines, and pipelines—as well as upland deciduous forest. Gray shading represents 95% confidence intervals. Abscissae are scaled to the range maximum for that variable

Figure 4

The probability of white‐tailed deer reproduction across Alberta's northeast boreal forest oil sands' region. Beta coefficients from the best‐supported generalized model explaining spatial variation in fawn occurrence were extrapolated across the region using the same spatial data from which the models were derived