99 Problems but a niche ain’t one - invasives inhabit the same geography at home and abroad
Liu, C., Wolter, C., Xian, W. and Jeschke, J.M., 2020. Most invasive species largely conserve their climatic niche. Proceedings of the National Academy of Sciences, 117(38), pp.23643-23651. https://doi.org/10.1073/pnas.2004289117
Written and edited by Suvi Birch, Abigail Guinan, Nicole Read, and Justin Salva
Summary
Our ability to reliably predict invasions into new regions (including range shifts with climate change) relies on an assumption of ‘niche conservatism’. Niche conservatism means that the environmental conditions that define a species’ habitat are the same (conserved) in both the native and introduced ranges. Multiple papers have argued for and against niche conservatism, raising the question: Are niches conserved or do niches shift? Liu et al. (2020) re-analyzed 86 previous studies and found a range of results. However, these different results were likely caused by differences in methods, datasets, and interpretation - in other words, inconsistent models lead to inconsistent results. Liu et al. (2020) retested these datasets using a “gold standard” technique that focuses on measuring overlap between native and introduced niches, unfilling in the native range, and expansion in the introduced range. Their overall results showed that species colonized similar niche space in the native and introduced ranges, but that the size of the niche space (i.e. climatically suitable space) was larger in the native range. Introduced niches tended to be smaller for terrestrial animals, species introduced more recently, and species with more native occurrences. Plants were more likely to fill similar niches between the native and introduced ranges and showed little expansion in the introduced range. In contrast, aquatic species and terrestrial ectotherms showed the most expansion, with up to 20% of the introduced niche unfilled in the native range. This analysis suggests that the climate niche in the native range should be a good predictor of the climate niche in the invaded range, if only we can overcome data and methodological challenges.
Take home points
This paper supports the niche conservatism hypothesis, stating that lack of agreement in the past was likely due to differences in data, approach, and interpretation.
The COUE technique, which uses centroid shift, overlap, unfilling, and expansion to overcome the biases introduced by spatial resolution and sampling efforts, is considered by the authors to be the “gold standard” for testing the niche conservatism hypothesis.
Management implications
Species inhabit broadly similar climatic conditions at home and abroad, suggesting that the native range could effectively predict the invaded range. However, niche similarity can vary between taxa, with plants having much more consistent niche similarity than aquatic species.
Beyond differences across groups of species, there remain a lot of methodological challenges to overcome, which lead to different outcomes and interpretations. So, it might still be too early to trust invasive species risk assessments based only on the geography of the native range.
Keywords
Range shifting; Impact studies; Meta-analysis; Risk assessment; Species distribution models (SDMs); Niche conservatism