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

Abstract

Aim Temporal dynamics of biodiversity along tropical elevational gradients are unknown. We studied seasonal changes of Lepidoptera biodiversity along the only complete forest elevational gradient in the Afrotropics. We focused on shifts of species richness patterns, seasonal turnover of communities and seasonal shifts of species’ elevational ranges, the latter often serving as an indicator of the global change effects on mountain ecosystems. Location Mount Cameroon, Cameroon. Taxon Butterflies and moths (Lepidoptera). Methods We quantitatively sampled nine groups of Lepidoptera by bait‐trapping (16,800 trap‐days) and light‐catching (126 nights) at seven elevations evenly distributed along the elevational gradient from sea level (30 m a.s.l.) to timberline (2,200 m a.s.l.). Sampling was repeated in three seasons. Results Altogether, 42,936 specimens of 1,099 species were recorded. A mid‐elevation peak of species richness was detected for all groups but Eupterotidae. This peak shifted seasonally for five groups, most of them ascending during the dry season. Seasonal shifts of species’ elevational ranges were mostly responsible for these diversity pattern shifts along elevation: we found general upward shifts in fruit‐feeding butterflies, fruit‐feeding moths and Lymantriinae from beginning to end of the dry season. Contrarily, Arctiinae shifted upwards during the wet season. The average seasonal shifts of elevational ranges often exceeded 100 m and were even several times higher for numerous species. Main conclusions We report seasonal uphill and downhill shifts of several lepidopteran groups. The reported shifts can be driven by both delay in weather seasonality and shifts in resource availability, causing phenological delay of adult hatching and/or adult migrations. Such shifts may lead to misinterpretations of diversity patterns along elevation if seasonality is ignored. More importantly, considering the surprising extent of seasonal elevational shifts of species, we encourage taking account of such natural temporal dynamics while investigating the global climate change impact on communities of Lepidoptera in tropical mountains.

Does rainforest biodiversity stand on the shoulders of giants? Effect of disturbances by forest elephants on trees and insects on Mount Cameroon

“…Belonging to the biodiversity hotspot, Mount Cameroon harbor numerous endemics (e.g., Cable and Cheek, 1998; Ustjuzhanin et al , 2018, 2020). With >12,000 mm of yearly precipitation, foothills of Mount Cameroon belong among the globally wettest places (Maicher et al , 2020). Most of the rain falls during the wet season (June–September) with monthly precipitation >2,000 mm, whilst the dry season (late December–February) lacks any strong rains (Maicher et al , 2020).…”

“…With >12,000 mm of yearly precipitation, foothills of Mount Cameroon belong among the globally wettest places (Maicher et al , 2020). Most of the rain falls during the wet season (June–September) with monthly precipitation >2,000 mm, whilst the dry season (late December–February) lacks any strong rains (Maicher et al , 2020). Since 2009, most of its rainforests have become protected by the Mount Cameroon National Park.…”

“…All plots were established in high canopy forests (although sparse in the undisturbed sites), any larger clearings were avoided. In the disturbed forest sites, eight plots were selected to follow a linear transect among 16 plots previously used for a study of elevational diversity patterns (Hořák et al , 2019; Maicher et al , 2020), without looking at their diversity data. In the undisturbed forest sites, plots were established specifically for this study.…”

“…They also substantially differ in the usage of habitats, and together can be considered as useful biodiversity indicators. Within each sampling plot, fruit-feeding lepidopterans were sampled by five bait traps (four in understory, one in canopy) baited by fermented bananas (see Maicher et al , 2020 for details). All fruit-feeding butterflies and moths (hereinafter referred as butterflies and fruit-feeding moths ) were removed daily from the traps for ten consecutive days and identified to (morpho)species.…”

“…These plots were selected to characterize the local heterogeneity of forest habitats and separated by a few hundred meters from each other. Moths were attracted by light (see Maicher et al , 2020 for details) during six complete nights per elevation (i.e., two nights per plot). Six target moth groups (Lymantriinae, Notodontidae, Lasiocampidae, Sphingidae, Saturniidae, and Eupterotidae; hereafter referred as light-attracted moths ) were collected manually and identified into (morpho)species.…”