Machine Learning and Deep Learning -- A review for Ecologists

The popularity of Machine learning (ML), Deep learning (DL), and Artificial intelligence (AI) has sharply risen in recent years. Despite their spike in popularity, the inner workings of ML and DL algorithms are perceived as opaque, and their relationship to classical data analysis tools remains debated. It is often assumed that ML and DL excel primarily at making predictions. Recently, however, they have been increasingly used for classical analytical tasks traditionally covered by statistical models. Moreover, recent reviews on ML have focused exclusively on DL, missing out on synthesizing the wealth of ML algorithms with different advantages and general principles. Here, we provide a comprehensive overview of ML and DL, starting with their historical developments, their algorithm families, their differences from traditional statistical tools, and universal ML principles. We then discuss why and when ML and DL excel at prediction tasks, and where they could offer alternatives to traditional statistical methods for inference, highlighting current and emerging applications for ecological problems. Finally, we summarize emerging trends, particularly scientific and causal ML, explainable AI, and responsible AI that may significantly impact ecological data analysis in the future.