Tropical phenology: bi‐annual rhythms and interannual variation in an Afrotropical butterfly assemblage

Anu Valtonen,Heikki Roininen,Matthew P Ayres,James R Carey,Freerk Molleman,Colin A Chapman

doi:10.1890/es12-00338.1

Abstract

Temporal variation and phenology of tropical insect communities and the role of environmental factors controlling this variation is poorly understood. A better understanding is needed, for example, to predict the effects of climate change on tropical insect communities and to assess the long‐term persistence of tropical communities. We studied seasonal and inter‐annual variation in tropical fruit‐feeding butterflies by exploiting a unique 137‐month abundance time series of >100 species, sampled at 22 locations in the medium altitude montane rain forest of Kibale National Park, western Uganda. Precipitation peaked twice per year, about 20 d after each equinox. Vegetation greenness peaked approximately 33 d later. Species richness and abundance of butterflies peaked about 2 and 3 months, respectively, after the greenness peak. Furthermore, temporal shifts in peaks of butterfly abundances of each 6‐month cycle positively correlated with temporal shifts in peaks of vegetation greenness approximately three months before. The butterfly assemblages of ENSO warm phase years differed significantly from assemblages of the other years. To our knowledge this is the first elucidation of bi‐annual rhythms in butterfly assemblages. Host plant availability could explain the seasonal cycles in butterfly abundance and species richness, because the 3‐month lag observed matches with the egg‐to‐adult development time in the studied species.

Highlights

Knowledge of phenology and inter-annual variation of tropical communities is essential to predict and measure effects of climate change, impacting e.g., biodiversity, forestry, agriculture, human health and ecosystem level processes
Seasonal patterns in environment Annual or bi-annual seasonal patterns were revealed in monthly time-series of average daily maximum and minimum temperature, precipitation and Enhanced Vegetation Index (EVI) (Fig. 1)
Our results showed that one or two years of study could be too short to capture the nature of seasonal patterns in tropical insect communities, which can be more subtle than in systems that go from green to brown annually, and can be obscured by extensive inter-annual variation

Summary

Introduction

Knowledge of phenology and inter-annual variation of tropical communities is essential to predict and measure effects of climate change, impacting e.g., biodiversity, forestry, agriculture, human health and ecosystem level processes (including carbon cycling). Phenology, the study of seasonal timing of periodic life cycle events (Rathcke and Lacey 1985), has become an important field of study in tropical systems, addressing both species level phenomena, e.g., leaf phenology (Reich et al 2004) or timing of reproduction in insects (Frederickson 2006) as well as community level events, e.g., changes in vegetation greenness (Pau et al 2010), or insect assemblage structure (Ahrens et al 2009). High abundance, and species richness, insect model systems are well suited to address the temporal dynamics and phenology of tropical communities. Tropical insects show remarkable variation in their seasonal patterns (Wolda 1988). There are some long-lived tropical insect species that seem to keep remarkably stable (adult) population sizes over multiple generations (Owen and Chanter 1972)

Methods

Results

Discussion

Conclusion