Climate warming drives divergence of montane butterfly communities in Southern Italy

Abstract

Because of climate change, many insect species are shifting their altitudinal and latitudinal ranges, including Mediterranean butterflies, particularly in mountainous regions. In this study, we evaluated changes in butterfly communities over time, sampled in 1975, 2004, and 2012, in relation to their altitude and two indices representing the climate envelopes of species within a given community: CTI (Community Temperature Index) and CPI (Community Precipitation Index). The study took place in a protected area where we found strong changes in community compositions over the 37-year study period. There was no vertical stratification of communities in 1975, but became significantly so in 2004 and 2012. Likewise, CTI and CPI were correlated with altitude only in 2004 and 2012. Over time, CTI increased at lower altitudes, indicating an increase in species associated with higher temperatures, and was stable or decreased at higher altitudes. CPI showed opposing trends, decreasing at lower altitude of communities and increasing in higher altitude communities. This resulted in asymmetric changes along the altitudinal gradient. The highest elevations (>1900 m) shifted towards butterfly species that are more associated with colder, wetter habitats, and lower elevations shifted towards species more associated with hotter, drier habitats. In conclusion, changes in butterfly communities were consistent with expectations from observed changes of temperatures and precipitations at low altitudes and mid-altitudes, but not at the highest altitudes. This counter-intuitive result may be due to land-use changes following creation of a national park in 1993 that encompassed the sample sites, but we lack the data to test this hypothesis.

A comparison between time‐constrained counts and line transects as methods to estimate butterfly diversity and monitor populations in tropical habitats

“…Time-constrained counts (henceforth, 'timed counts') is an alternative visual-count method for conducting butterfly surveys and population monitoring (Beneš et al, 2003;Kadlec et al, 2012;Kral-O'Brien et al, 2021;Naik et al, 2022aNaik et al, , 2022bSantorufo et al, 2021;Taron & Ries, 2015). In timed counts, effort is standardised by time rather than by length/area as done in line or belt transects.…”

“…Timed counts also offer flexibility to navigate difficult terrain because a uniform pace and linear paths are not required, but they can still record the spatial and temporal distribution of butterflies or their resources in a standardised and comparable format. Timed counts may be especially advantageous in complex, dynamic landscapes, and even in smaller habitat fragments (Kadlec et al, 2012;Santorufo et al, 2021;Scalercio et al, 2007;Taron & Ries, 2015). Similar to line transects, timed counts assume that: (a) detectability is certain on the path, (b) counts are exact, (c) variation in the number of individuals counted at different sites or in different seasons truly reflect differences in their population sizes, and (d) butterflies are detected at their initial location (Glennie et al, 2015;Taron & Ries, 2015).…”