Aim
To assess the changes in the elevational distribution of 151 butterfly species over a period of 22 years (1988–2011) and investigate whether these changes are related to regional global warming and land use change.
Location
Sierra de Juárez, Oaxaca, Mexico.
Methods
Butterflies were surveyed at eight sites spanning elevations ranging from 117 m to 3000 m in 1988, and the same sites were resurveyed in 2010–2011. Changes in the elevational distribution of species and the structure and composition of species assemblages were compared between surveys. The results were interpreted in the context of land use and climate change in the region.
Results
Butterfly species had shifted their distributions uphill by approximately 145 m on average. Significantly more species (78) showed an uphill shift in their distributions than a downhill shift (32 species). Species occurring above 1000 m elevation had shifted their distribution to an extent that matched the range shift expected under the recorded temperature changes. However, for species occurring below 1000 m elevation, and for all species combined, uphill range shifts were significantly less than expected based solely on the increase in temperature. Land use change over the study period was more pronounced at low elevations, and these butterfly assemblages are now dominated by generalist species.
Main conclusions
Our results represent the first concrete evidence of shifts in elevation distribution of a large Neotropical butterfly community, attributable to increased regional temperatures. At high elevations, land use change is minimal and climate change appears to be the main driver of changes to distributions and assemblages, and the main conservation threat. However, extensive land use change has been the main driver of changes to butterfly communities at lower elevations.
Despite high diversity levels of beetles inhabiting dung and carcasses, very few studies have attempted a comparative assessment of copro-necrophile beetle communities in relation to spatio-temporal variations, particularly in the tropics where the vast majority of beetles occur. We compared beetle assemblages attracted to pads of cattle dung and rat carcasses in four contrasting vegetation types associated with oak forest. In a total of 52 transects including 3,952 dung pad days and 2,600 carcass-trap days we recorded 14,989 beetles representing 406 species and 33 families. Necrophiles (323 species and 33 families) were considerably more diverse than coprophiles (172 species and 16 families). Staphylinidae were taxonomically and numerically dominant, comprising 45% of species and 66% of individuals, respectively. Species estimators (Chao 2) suggested that the observed beetle richness represented 68% of coprophile and 56% of necrophile species richness, with rare species constituting the majority of the species: singletons and doubletons = 89 species (52%) of coprophiles and 166 species (51%) of necrophiles. Beetle assemblages varied in diversity and composition as regards to vegetation type and season: samples from less disturbed vegetation types (continuous oak forest and ravines) had higher beetle diversity, and a strong seasonality effect was recorded for necrophiles, but not for coprophiles. In addition, an indicator value analysis (IndVal), showed that relatively preserved vegetation types recorded more indicator species as compared to disturbed sites. Our studies clearly demonstrates that the least fragmented oak forest and ravine are the most valuable areas for necrophile and coprophile beetles in Neotropical Mexico, especially for specialist beetles.
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