Insects and recent climate change

Abstract

Insects have diversified through more than 450 million y of Earth's changeable climate, yet rapidly shifting patterns of temperature and precipitation now pose novel challenges as they combine with decades of other anthropogenic stressors including the conversion and degradation of land. Here, we consider how insects are responding to recent climate change while summarizing the literature on long-term monitoring of insect populations in the context of climatic fluctuations. Results to date suggest that climate change impacts on insects have the potential to be considerable, even when compared with changes in land use. The importance of climate is illustrated with a case study from the butterflies of Northern California, where we find that population declines have been severe in high-elevation areas removed from the most immediate effects of habitat loss. These results shed light on the complexity of montane-adapted insects responding to changing abiotic conditions. We also consider methodological issues that would improve syntheses of results across long-term insect datasets and highlight directions for future empirical work.

Keywords: Anthropocene; climate change; extinction; extreme weather; population decline.

Fig. 1.

Overview of geography and major trends for the Northern California case study. (A) Map of Northern California with focal sites, also shown in elevational profile in B with two-letter site abbreviations and the year when continuous sampling started at each site (SM, Suisun Marsh; GC, Gates Canyon; WS, West Sacramento; NS, North Sacramento; RC, Rancho Cordova; WA, Washington; LC, Lang Crossing; DP, Donner Pass; CP, Castle Peak; SV, Sierra Valley). (C and D) Standardized population indices (means across species by site) for mountain sites (C) and low-elevation sites (D), with site colors the same as in B and brackets above x axes to indicate major drought years from 2011 to 2015. Density plots in C, Inset and D, Inset show the distribution of year coefficients across species in the two regions (high and low elevations), with vertical dotted lines marking zero, such that observations to the left of the line represent species with negative trends across time. (E–G) Histograms summarize changes in elevation between different 9-y windows of time; for example, E is the change in mean elevation per species between the earliest years (1977 to 1985) and years immediately before the megadrought (2002 to 2010). Colors in histograms are for visualization, with darker orange corresponding to more negative (downward) shifts and darker blue being more positive (upslope) shifts (SI Appendix, Fig. S1 shows additional details). Mean shifts (in meters; with SEs) and results from one-sample t tests (against the null of mean elevational shift being zero) are as follows: (E) 85.5 (±22.4), t₁₁₆ = 3.82, P < 0.001; (F) −40.9 (±25.6), t₁₁₆ = −1.59, P = 0.12; and (G) 38.1 (±23.4), t₁₁₈ = 1.63, P = 0.11.

Fig. 2.

Traits associated with population trends at four montane monitoring sites. Points represent a species at a site (any individual species can have between one and four points), and those in the top half are generally increasing, while bottom half points are generally declining. Points are colored according to coefficients associated with years (i.e., “trend” or change through time), and those coefficients as well as climate sensitivities were estimated in separate Bayesian models. Traits represented include life history traits and sensitivities to climatic variables, specifically precipitation (PPT Sens.), average daily maximum temperatures (MaxT Sens.), and average daily minimum temperatures (MinT Sens.). Life history traits include overwintering states, geographic range (Geo. Range), phenology (average date of first flight), elevational range (Elev. Range), elevational shift (as in Fig. 1 E–G), voltinism, body size (wingspan), breadth of habitat association (generalism), and weedy status (the text and SI Appendix have more details). Percentage of constrained variation explained is shown in parentheses after each axis label. Four species are illustrated (clockwise from the upper left): Boloria epithore, Epargyreus clarus, Strymon melinus, and Pontia occidentalis (Illustrations credit: M.L.F.). RDA, redundancy analysis.