Journal
ECOGRAPHY
Volume 37, Issue 12, Pages 1267-1281Publisher
WILEY
DOI: 10.1111/ecog.00845
Keywords
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Categories
Funding
- Danish Council for Independent Research \ Natural Sciences [10-085056]
- NSF [1046328, 1137366]
- European Research Council under European Community [281422]
- Swiss National Science Foundation [CRS113-125240, PBZHP3_147226]
- Australian Research Council [FT0991640]
- Swiss National Science Foundation (SNF) [PBZHP3_147226] Funding Source: Swiss National Science Foundation (SNF)
- Direct For Biological Sciences
- Emerging Frontiers [1137366, 1137364] Funding Source: National Science Foundation
- Australian Research Council [FT0991640] Funding Source: Australian Research Council
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Species distribution models (SDMs) are widely used to explain and predict species ranges and environmental niches. They are most commonly constructed by inferring species' occurrence-environment relationships using statistical and machine-learning methods. The variety of methods that can be used to construct SDMs (e.g. generalized linear/additive models, tree-based models, maximum entropy, etc.), and the variety of ways that such models can be implemented, permits substantial flexibility in SDM complexity. Building models with an appropriate amount of complexity for the study objectives is critical for robust inference. We characterize complexity as the shape of the inferred occurrence-environment relationships and the number of parameters used to describe them, and search for insights into whether additional complexity is informative or superfluous. By building 'under fit' models, having insufficient flexibility to describe observed occurrence-environment relationships, we risk misunderstanding the factors shaping species distributions. By building 'over fit' models, with excessive flexibility, we risk inadvertently ascribing pattern to noise or building opaque models. However, model selection can be challenging, especially when comparing models constructed under different modeling approaches. Here we argue for a more pragmatic approach: researchers should constrain the complexity of their models based on study objective, attributes of the data, and an understanding of how these interact with the underlying biological processes. We discuss guidelines for balancing under fitting with over fitting and consequently how complexity affects decisions made during model building. Although some generalities are possible, our discussion reflects differences in opinions that favor simpler versus more complex models. We conclude that combining insights from both simple and complex SDM building approaches best advances our knowledge of current and future species ranges.
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