Phylogenetic patterns of species loss in Thoreau's woods are driven by climate change

Abstract

Climate change has led to major changes in the phenology (the timing of seasonal activities, such as flowering) of some species but not others. The extent to which flowering-time response to temperature is shared among closely related species might have important consequences for community-wide patterns of species loss under rapid climate change. Henry David Thoreau initiated a dataset of the Concord, Massachusetts, flora that spans approximately 150 years and provides information on changes in species abundance and flowering time. When these data are analyzed in a phylogenetic context, they indicate that change in abundance is strongly correlated with flowering-time response. Species that do not respond to temperature have decreased greatly in abundance, and include among others anemones and buttercups [Ranunculaceae pro parte (p.p.)], asters and campanulas (Asterales), bluets (Rubiaceae p.p.), bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales), mints (Lamiaceae p.p.), orchids (Orchidaceae), roses (Rosaceae p.p.), saxifrages (Saxifragales), and violets (Malpighiales). Because flowering-time response traits are shared among closely related species, our findings suggest that climate change has affected and will likely continue to shape the phylogenetically biased pattern of species loss in Thoreau's woods.

Fig. 1.

Composite phylogeny of 429 flowering plant species from the Concord flora depicting changes in abundance from 1900 to 2007. Change in abundance ranged on an integer scale from −5 to +4, and was calculated as the difference in abundance for each taxon in 1900 and 2007 based on 7 abundance categories (0 to 6; see Materials and Methods). Branch color indicates parsimony character state reconstruction of change in abundance. For simplicity, we have indicated this reconstruction by using 4 colors: red (major decline, −5 to −3), pink (moderate decline, −2), gray (little to no change, −1 to +1), and blue (increase, +2 to +4). For the complete character reconstruction and taxon labels see Fig. S1. Average decline in abundance was calculated for all internal nodes as the mean change in abundance of descendant nodes weighted with branch length information ascertained from divergence time estimates. An average decline of 2.5 or greater corresponds to a decline in abundance of 50% or greater, based on our most conservative scoring using 6 abundance categories (0 to 5; see Materials in Methods). Clades exhibiting these major declines are indicated with black dots. Each of the most inclusive clades exhibiting these declines are indicated in pink and referenced numerically to their clade name. Subclades in major decline that are nested within more widely recognized clades are labeled with the more familiar name followed by pro parte (p.p.). These clades include some of the most charismatic wildflower species in New England, such as anemones and buttercups (Ranunculaceae p.p.), asters, campanulas, goldenrods, pussytoes, and thistles (Asterales), bedstraws and bluets (Rubiaceae p.p.), bladderworts (Lentibulariaceae), dogwoods (Cornaceae), lilies (Liliales), louseworts and Indian paintbrushes (Orobanchaceae), mints (Lamiaceae p.p.), orchids (Orchidaceae), primroses (Onograceae p.p.), roses (Rosaceae p.p.), saxifrages (Saxifragales), Indian pipes (Ericales p.p.), and St. John's worts and violets (Malpighiales).