A Checklist for historical studies of species’ responses to climate change

Biologists have been widely involved in our understanding of global climate change since the early 1980s. The vast majority of work includes studies that attempt to predict future biological changes in response to future climatic change. These studies range from speculation of range shifts and changes in species interactions based on assumptions that species’ distributions and behaviors are broadly controlled by temperature, to highly detailed bioclimatic mapping models that identify the climatic variables most important in determining species’ ranges and then map future species’ distributions based on expected changes in these variables. Such studies cover a broad spectrum of biological systems, including terrestrial plants (Woodward, 1992; Beerling, 1993), infectious disease (Patz et al., 1996), insects (Rubenstein, 1992), other invertebrates (Bhaud et al., 1995), birds (Root, 1993), freshwater fishes (Scott and Poynter, 1991), algae (Breeman, 1990), marine fishes (Frank et al., 1990), coastal marine communities (Fields et al., 1993; Lubchenco et al., 1993), and native human populations (Langdon, 1995). The vast majority of these studies consider climate change solely in terms of its future signal as predicted by large-scale global circulation models. The significant warming trend seen during the 20th century (Intergovernmental Panel on Climate Change, 2001) and its effects on natural populations is largely ignored by these treatments. Recently, however, a growing number of studies have shown long-term biological changes during this century that are argued to be correlated with warming trends over the same time period. These studies, like their more speculative antecedents, cover a wide range of taxa including butterflies (Parmesan, 1996; Parmesan et al., 1999), birds (Thomas and Lennon, 1999), reptiles and amphibians (Pounds et al., 1999), fish (Holbrook et al., 1997), and marine invertebrates (Barry et al., 1995; Sagarin et al., 1999). These studies are largely examples of “historical science” (Francis and Hare, 1994) rather than strict experimental procedures. While experimental studies of species’ responses to climate change have an essential role in determining important mechanisms that will drive species’ responses (Chapin et al., 1995) or reveal unexpected indirect effects (Davis et al., 1998; Sanford, 1999), they are largely inadequate or impractical for tracking species’ responses to climate change in the present (Sagarin, 2001).