Conserved ancestral tropical niche but different continental histories explain the latitudinal diversity gradient in brush-footed butterflies.

The global increase in species richness toward the tropics across continents and taxonomic groups, referred to as the latitudinal diversity gradient, stimulated the formulation of many hypotheses to explain the underlying mechanisms of this pattern. We evaluate several of these hypotheses to explain spatial diversity patterns in a butterfly family, the Nymphalidae, by assessing the contributions of speciation, extinction, and dispersal, and also the extent to which these processes differ among regions at the same latitude. We generate a time-calibrated phylogeny containing 2,866 nymphalid species (~45% of extant diversity). Neither speciation nor extinction rate variations consistently explain the latitudinal diversity gradient among regions because temporal diversification dynamics differ greatly across longitude. The Neotropical diversity results from low extinction rates, not high speciation rates, and biotic interchanges with other regions are rare. Southeast Asia is also characterized by a low speciation rate but, unlike the Neotropics, is the main source of dispersal events through time. Our results suggest that global climate change throughout the Cenozoic, combined with tropical niche conservatism, played a major role in generating the modern latitudinal diversity gradient of nymphalid butterflies.

Vertical differentiation in tropical forest butterflies: a novel mechanism generating insect diversity?

Many tropical fruit-feeding nymphalid butterflies are associated with either the forest canopy or the understorey; however, the exceptions offer insights into the origins of tropical diversity. As it occurs in both habitats of tropical forests in Ecuador and Peru, Archaeoprepona demophon is one such exception. We compared patterns of occurrence of A. demophon in the canopy and understorey and population genomic variation for evidence of ecological and genetic differentiation between habitats. We found that butterfly occurrences in the canopy were largely uncorrelated with occurrences in the understorey at both localities, indicating independent demographic patterns in the two habitats. We also documented modest, significant genome-level differentiation at both localities. Genetic differentiation between habitat types (separated by approx. 20 m in elevation) was comparable to levels of differentiation between sampling locations (approx. 1500 km). We conclude that canopy and understorey populations of A. demophon represent incipient independent evolutionary units. These findings support the hypothesis that divergence between canopy and understorey-associated populations might be a mechanism generating insect diversity in the tropics.

Large-Scale Climate Effects Meet an Amazonian Butterfly: Which Population Parameters Respond to El Niño?

One of the most tangible outcomes of climate change is change in the frequency of El Niño/La Niña events. They have a large impact on rainfall in the Western hemisphere, but their impact on tropical fauna is largely unknown. A decade long capture-mark-recapture study of the widespread Ecuadorian butterfly Nessaea hewitsoni (Felder & Felder) from an intact forest allowed us to analyze patterns of monthly and seasonal population dynamics before, during, and after an El Niño event. El Niño events did not affect long-term population size, but a 5-month delayed El Niño led to temporary emigration of females, with their subsequent return. Increased rainfall correlated with reduced survival in both sexes, but this effect was twice as strong in females. This investigation is the longest, continuous population study on any Neotropical insect species. Though we sampled on a modest scale, the magnitude of El Niño events suggests that our findings likely reflect insect population responses across a much larger portion of Amazonian forests. This study underscores the importance of analyzing multiple, interacting population parameters beyond local abundance in order to understand the biotic responses to El Niño and climate change in tropical systems. Had our analyses not included temporary emigration, no effect would have been detected because El Niño did not affect local population abundance.

Documenting diversity in the Amazonian butterfly genus Bia (Lepidoptera, Nymphalidae).

A comparative study of over 1,000 specimens allowed us to revise the taxonomy of the Amazonian butterfly genus Bia. We redescribed the genus, and used a selected set of characters to define and describe new species and subspecific taxa. We found that male genitalia showed little variation among taxa, and that wing and genitalia characters varied independently across the range of the genus. We also noted that species diversification seems to follow a north-south Amazonian divide, with Bia actorion and decaerulea occupying the northern portion of the genus range while the remaining four species are found in southern Amazonia. As defined here Bia includes six species: B. actorion (Linnaeus), B. actorion ecuatoria DeVries & Penz, NEW SSP., B. actorion occulta Casagrande & Penz, NEW SSP., B. decaerulea Weymer STAT. NOV., B. decaerulea cayana Simonsen & Penz, NEW SSP., B. decaerulea pallida Casagrande & Penz, NEW SSP., B. rebeli Bryk STAT. NOV., B. rebeli aegina Penz & Simonsen, NEW SSP., B. rebeli acreana Casagrande & Penz, NEW SSP., B. rebeli arikeme Penz & Casagrande, NEW SSP., B. rebeli pareci Penz & DeVries, NEW SSP., B. rebeli cuprea Penz & Casagrande, NEW SSP., B. rebeli tapajos Penz & Simonsen, NEW SSP., B. caelestis Penz & DeVries, NEW SP., B. pucallpa Casagrande & Penz, NEW SP., and B. peruana Röber.

Seasonal cycles of species diversity and similarity in a tropical butterfly community.

1. Studies of seasonality in ecological diversity rarely extend over more than a few years, and few studies of seasonal diversity have explicitly investigated the influence of environmental factors on seasonal community composition, especially in tropical communities. 2. Our 10 years of monthly sampling in Amazonian Ecuador yielded 20 996 individuals of 137 fruit-feeding butterfly species. Seasonal cycles of rainfall drive annual cycles in species diversity and community similarity. Undetermined processes operating most strongly during the dry season maintain species diversity and high community similarity across years. 3. Seasonal cycles in community diversity and similarity are superimposed on a gradual decline in similarity between community samples on a decadal time-scale because of long-term changes in species abundances. 4. Monitoring and analysis of changes in community composition over a range of time-scales can be used to refine models of community dynamics by incorporating environmental factors necessary to predict the ecological impact of future climate change.