Flying between raindrops: Strong seasonal turnover of several Lepidoptera groups in lowland rainforests of Mount Cameroon

Abstract

Although seasonality in the tropics is often less pronounced than in temperate areas, tropical ecosystems show seasonal dynamics as well. Nevertheless, individual tropical insects’ phenological patterns are still poorly understood, especially in the Afrotropics. To fill this gap, we investigated biodiversity patterns of Lepidoptera communities at three rainforest localities in the foothills of Mount Cameroon, West Africa, one of the wettest places in the world. Our multitaxa approach covered six lepidopteran groups (fruit‐feeding butterflies and moths, the families Sphingidae, Saturniidae, and Eupterotidae, and the subfamily Arctiinae of Erebidae) with diverse life strategies. We sampled adults of the focal groups in three distinct seasons. Our sampling included standardized bait trapping (80 traps exposed for 10 days per locality and season) and attraction by light (six full nights per locality and season). Altogether, our dataset comprised 20,576 specimens belonging to 559 (morpho)species of the focal groups. The biodiversity of Lepidoptera generally increased in the high‐dry season, and either increased (fruit‐feeding moths, Arctiinae, Saturniidae) or decreased (butterflies, Sphingidae) in the transition to the wet season in particular groups. Simultaneously, we revealed a strong species turnover of fruit‐feeding Lepidoptera and Arctiinae among the seasons, indicating relatively high specialization of these communities for particular seasons. Such temporal specialization can make the local communities of butterflies and moths especially sensitive to the expected seasonal perturbations caused by the global change. Because of the key role of Lepidoptera across trophic levels, such changes in their communities could strengthen this impact on entire tropical ecosystems.

Seasonal shifts of biodiversity patterns and species’ elevation ranges of butterflies and moths along a complete rainforest elevational gradient on Mount Cameroon

“…Species richness patterns of most focal groups differed among the sampled seasons. On Mount Cameroon, species richness of most lepidopteran groups in lowland and mid‐elevations increased during the dry season and until the transition to the wet season, as already described in Maicher et al (). These latter authors mostly explained this phenology by the locally extreme precipitation during the wet season constraining all life cycle stages, and the consequent emergence of most adults towards the dry season (Maicher et al, ).…”

“…On Mount Cameroon, species richness of most lepidopteran groups in lowland and mid‐elevations increased during the dry season and until the transition to the wet season, as already described in Maicher et al (). These latter authors mostly explained this phenology by the locally extreme precipitation during the wet season constraining all life cycle stages, and the consequent emergence of most adults towards the dry season (Maicher et al, ). By extending the sampling to the complete rainforestelevational gradient, we have now shown that these increases in species richness differed seasonally among elevations, altogether causing the observed seasonal shifts of diversity peaks.…”

“…We found that the phenological patterns of diversity, previously described for six lepidopteran groups in the lowland rainforest of Mount Cameroon (Maicher et al, ), change along elevations: the species richest communities occur sooner during the annual cycle at lower elevations, and only later on at the higher sites (Figure ). We thus hypothesize that the seasonal shifts of both species richness and species’ elevational ranges should be related to a phenological delay of some crucial conditions between the beginning and end of the dry season.…”

“…Despite the historical concept of 'aseasonal' tropics, tropical insect biodiversity is known to be strongly seasonal (Kishimoto-Yamada & Itioka, 2015;Wolda, 1988). Such phenological changes of tropical lepidopteran communities are often driven by wet and dry season cycles influencing availability of resources for both caterpillars and adult butterflies and moths (Grøtan, Lande, Chacon, & DeVries, 2014;Grøtan, Lande, Engen, Saether, & DeVries, 2012;Maicher et al, 2018;Valtonen et al, 2013). In contrast, montane insect phenology is crucially driven by seasonal changes of temperature (Bishop, Robertson, van Rensburg, & Parr, 2014;Boulter, Lambkin, & Starick, 2011;Wardhaugh, Stone, & Stork, 2018).…”

“…Ashton et al, 2016;Brehm & Fiedler, 2003). Nevertheless, seasonality is known to strongly affect distribution, abundance and diversity of lepidopteran communities in many tropical ecosystems (Grøtan et al, 2014(Grøtan et al, , 2012Maicher et al, 2018;Valtonen et al, 2013). Therefore, it remains questionable how the described elevational range shifts might be related to natural seasonal dynamics together with potential sampling biases arising from the lack of temporal replicates.…”