Biogeography of the ithomiine and heliconiine butterflies near Tarapoto, Peru
The eastern slopes of the tropical Andes harbour the highest diversity of organisms on Earth, and butterflies are no exception. Not only are the forested foothills of the Andes characterised by a very high species richness in every locality, but geographical differenciation is also high. Indeed, regions 100-200km apart often show totally different species or subspecies assemblages. On top of that, butterfly communities also change a lot with altitude, e.g. between with lowland, montane, and cloud forest, form 120m to 2500m above sea level.
Tarapoto (San Martín, Peru) is situated in the valley of the Río Mayo at 350m, characterised by dry, non-seasonal tropical forest. Nearby is the Cordillera Azul, the Easternmost Andean mountain ridge, which reaches ~1600-2000m, with wet montane forest and cloud forest near the top. On the other side of the Cordillera Azul (locally called Cerros Escalera) are the Amazonian Lowlands and the lower Río Huallaga region at ~150m and with lush, wet, lowland forest. Many species of Heliconiinae and Ithomiinae butterflies (Nymphalidae) have different races in these three different regions, and usually form large area-specific mimicry rings. For instance, many of the races found in the high-altitude forest switch to a black and orange mimicry ring, while many Amazonian lowland races bear a yellow-tip tiger pattern. See also the orange-tip mimicry ring and the small white transparent mimicry ring.
The origin of these biogeographic segregation is still under debate: some claim this pattern is the consequence of past (Quaternary) forest refugia, others think present ecological processes are more important. Alaine Whinnet, Jim Mallet, Fraser Simpson, kanchon Dasmahapatra, Lisa Leadbeater and I (and others) have been collecting Ithomiines in the area and Kanchon and Fraser are now getting sequence data looking for patterns of divergence consistent with one scenario or the other. (see also Jim Mallet's webpage)
Below is a link to the Guide to Ithomiinae for the area, with photographs for all species recorded from the region of San Martín. I compiled this guide in collaboration with Gerardo Lamas at the Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima, where all specimens pictured here are conserved. One must remember that much of Ithomiine taxonomy is still unstable, particularly in the genera Oleria, Pteronymia and Hyalaris. Mullerian mimicry is very prevalent in these groups of chemically-defended butterflies, so identification based on colour pattern is often tricky (but that's what makes it fun!). Ithomiines genera are defined by their hind-wing venation.