Testing the predictive capabilities of ecological niche models: a case study examining Red‐bellied Woodpeckers

Abstract

As humans continue to alter natural habitats indirectly and directly, species’ geographic ranges may change as they track shifting climate regimes or changing landscapes. Ecological niche models (ENMs) are frequently used to show modern ranges and forecast future range changes. These models, however, assume that a species will exhibit niche conservatism, though this is rarely tested. Here, we examine a woodpecker species with a well‐documented recent range expansion to assess the effectiveness of predictive models by comparing the pre‐ and post‐expansion climate/habitat niche using ENMs and multivariate principal components analysis. Occurrence data for the Red‐bellied Woodpecker (Melanerpes carolinus) were obtained from the pre‐expansion (1910–1939; n = 299) and post‐expansion (1980–2009; n = 868) time periods. Ecological niche models were constructed using GIS layers describing climate data and crop cover for the pre‐ and post‐expansion time periods. We then used the pre‐expansion ENM to forecast the distribution of Red‐bellied Woodpeckers into the post‐expansion time period, and vice versa, and calculated the niche overlap of the projected distributions and the actual distributions in those time periods to determine whether pre‐ and post‐expansion niches were similar. Predictive ENMs did not closely match the actual distributions in the pre‐ and post‐expansion time periods, respectively, and the pre‐expansion and post‐expansion niches were significantly different from each other (Schoener's D = 0.745, P < 0.001). Multivariate analyses revealed that the present‐day niche encompasses the past niche and that Red‐bellied Woodpeckers today have broader temperature and precipitation tolerances and are found in both more‐ and less‐forested areas than they were in the pre‐expansion era. Our analyses reveal that Red‐bellied Woodpeckers are not exhibiting climate or habitat niche conservatism, explaining why predictive ENMs for this species could not effectively track their range shift. This study emphasizes that predictive models may not be effective for species undergoing niche changes.

Red-bellied Woodpecker (Melanerpes carolinus) has increased in abundance at a western range margin

“…Thus, it might be that Red-bellied Woodpecker has increased near its western limit in our study area simply as part of a broader pattern of increase range-wide. That long-term trend might be related to increased productivity and/or survivorship from increasingly milder winters, nutritional supplementation at suburban bird feeders, competitive release, or an expansion of niche space (FitzGerald et al 2018). In our study area of the central and western Great Plains there is good reason to suspect that Red-bellied Woodpecker has increased in abundance as more suitable habitat has spread across the region.…”

“…The Red-bellied Woodpecker is nonmigratory and largely philopatric, which increases confidence that any detected expansion indicates a persistent change in distribution rather than a stochastic change in occupancy. Red-bellied Woodpecker is known to have expanded northward, as warming temperatures at northern limits of the distribution have allowed birds to colonize higher latitudes (Jackson and Davis 1998, Kirchman and Schneider 2014, FitzGerald et al 2018). Although this northward expansion is well documented and there is some evidence of a westward expansion (Kirchman and Schneider 2014), considerably less is known about dynamics at the western range margins.…”

Genetic evidence for widespread population size expansion in North American boreal birds prior to the Last Glacial Maximum

“…Recent findings, however, suggest that the magnitude of range expansion estimated by SDMs may not be correlated with the magnitude of N e changes inferred from genetic data [8]. One potential explanation for the decoupling of range size versus N e throughout time is that SDMs assume niche conservation through time [95–97]. Predictions from SDMs do not always match fossil or pollen records, suggesting that niches can change throughout time [96,98].…”