Population fluctuations of light-attracted chrysomelid beetles in relation to supra-annual environmental changes in a Bornean rainforest

Abstract

In Southeast Asian tropical rainforests, two events, severe droughts associated with the El Niño-Southern Oscillation and general flowering, a type of community-wide mass flowering, occur at irregular, supra-annual intervals. The relationship between these two supra-annual events and patterns of insect population fluctuations has yet to be clearly elucidated. Leaf beetles (Chrysomelidae) are major herbivores and flower-visitors of canopy trees, affecting their growth and reproduction and, in turn, affected by tree phenology; but their population fluctuations in the Southeast Asian tropics have not been extensively investigated. We examined population fluctuation patterns of the 34 most dominant chrysomelid species in relation to the two supra-annual events by conducting monthly light-trapping over seven years in a lowland dipterocarp forest in Borneo. Our results showed large community variation in population fluctuation patterns and a supra-annual (between-year) variation in abundance for most of the dominant chrysomelids that was significantly larger than the annual (within-year) variation. Specifically, in response to a severe drought in 1998, chrysomelid species exhibited different population responses. These results show that population fluctuations of individual species, rather than the entire assemblage, must be analyzed to determine the effects of changes in environmental conditions on the structure of insect assemblages in the tropics, especially in regions where supra-annual environmental changes are relatively more important than seasonal changes.

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

“…The degree of inter-vs. intra-annual variation in tropical insect communities has rarely been assessed. A short-term study of beetle populations in Borneo found inter-annual variation to greatly exceed intra-annual variation, which supported the characterization of this rainforest as generally aseasonal with a strong ENSO effect (Kishimoto-Yamada et al 2009). …”

“…During the studied years, the highest annual precipitation occurred in 2001 (not coinciding), followed by 2006, 2003, and 2010 (all coinciding with the positive El Niño phases). Previously, the effects of an ENSO event (severe droughts and consequent synchronous flowering and leaf-production in Southeast Asian rainforests) on insect communities have been reported in several short-term studies (Harrison 2000, Intachat et al 2001, Kishimoto-Yamada et al 2009). In Central-America, the ENSO has been associated with increases in the migrating adults of a butterfly species via increased soil moisture and leaf flushing of the host plants (Srygley et al 2010).…”

“…In addition to seasonal changes, natural populations of short lived organisms also experience annual fluctuations in their abundance, and therefore, tropical insect communities can be expected to change at inter-annual time scales as well. Such changes could be caused e.g., by interannual variation in precipitation due to largescale climate processes such as El Niño Southern Oscillation (ENSO; e.g., Kishimoto-Yamada et al 2009). The degree of inter-vs. intra-annual variation in tropical insect communities has rarely been assessed.…”

The value of targeted reforestations for local insect diversity: a case study from the Ecuadorian Andes

“…Huberty and Denno 2004;Kishimoto-Yamada and Itioka 2008;Scherber et al 2013). Conversely, individual species may show a sudden proliferation following a drought (Kishimoto-Yamada et al 2009;van Bael et al 2004). Without data on community composition prior to the event, the impact of such climatic extremes on our results is difficult to judge.…”

Wide Host Ranges of Herbivorous Beetles? Insights from DNA Bar Coding

“…The leaf and flower production of many dipterocarp trees is known to fluctuate synchronously among species at irregular intervals [13, 14, 21–23]. In contrast, the adults of some leaf chewer species emerge constantly throughout the year and fluctuate in abundance independently of dipterocarp tree phenology [23,24], although they have been observed to feed on the young leaves and flowers of dipterocarp trees [25]. This pattern leads us to hypothesize that these leaf chewer species are able to feed on other plant species when the young leaves and flowers of dipterocarp trees are unavailable.…”