Citizen scientist data suggest widespread climate driven changes in North American butterfly communities

Background/Question/Methods

Climate warming is expected to change the distribution and abundance of plant and animal species. Range shifts have been detected in a number of European taxa for which long term government supported survey data are available. In North America such long-term data are rare. Observations made by “citizen scientists”, however, may be an excellent alternative to systematic surveys. Using the list-length analysis method developed by Szabo et al. (2010), we analyzed species lists from 19,779 trips made by amateur naturalists in Massachusetts by the Massachusetts Butterfly Club (MBC) between 1992 and 2010 to estimate changes in abundance of all species in the butterfly community.

 Results/Conclusions

Of the 116 butterflies species reported by the MBC, 100 had a sufficient number of observations to estimate population trends. Estimated population trajectories indicate about half the species were declining and half were increasing. Increases were highest among species near their northern range limits, and declines concentrated in species near their southern range limits. Of the 21 species with ranges that have northerly distributions (areal extent of range centered north of Boston (41.78^o N 70.50^o W) 17 were declining, 1 was increasing, and 3 had no significant change in populations. Permutation tests indicate that this number of declining species in highly significant (p = 0.000275). Other life history traits, including obligate univoltinism and overwintering as egg or unfed neonate larvae were also highly over-represented in declining species (p= 0.0117 and 0.000794, respectively). The results suggest a major, climate-induced, shift of North American butterflies, characterized by northward expansions of warm-adapted and retreat of cold-adapted butterfly species. Our results also suggest that certain evolved life history traits are more sensitive to climate warming than others and may provide predictive value in determining the constituents of future butterfly communities as the climate warms.