Dryobalonops lanceolata

Junker, Robert R., Itioka, Takao, Bragg, Phil E. & Blüthgen, Nico, 2008, Feeding Preferences Of Phasmids (Insecta: Phasmida) In A Bornean Dipterocarp Forest, Raffles Bulletin of Zoology 56 (2), pp. 445-452 : 451

Dryobalonops lanceolata ( Fig. 2 )

Two-way ANOVA: Phasmid + Stratum F 3,41 = 6.95 *** t = 0.7

Stratum F 1,43 = 14.49 *** t = 1.69

Phasmid F 2,42 = 1.49 t = 1.58

Canopy young – sapling young F 1,23 = 15.10 *** t = 11.80 ***

Canopy old – sapling old F 1,21 = 0.01 t = 3.87 ***

Canopy young – sapling old F 1,21 = 1.50 t = 4.71 ***

Canopy old – sapling young F 1,23 = 0.90 t = 3.87 ***

canopy. During our survey we found very few phasmids and observed very little leaf damage in the canopy. Other studies have also shown a much lower overall level of herbivory in the canopy compared to the understorey ( Lowman, 1985; Coley & Barone, 1996).

Three nonexclusive hypotheses are suggested to potentially explain the apparent higher density of phasmids in the understorey: (1) It seems likely that abiotic factors are unfavourable in the canopy. For instance, the microclimate in the upper canopy becomes extremely hot and dry during the daytime (Sakai et al. 1999, measured at the same D. lanceolata tree sampled in this study), where the phasmids would run the risk of desiccation; (2) Understorey plants of different species occur in close proximity, making it easy for generalists to choose from different food plant species. A mixed diet may benefit generalists by providing complementary nutrition and/or reducing the accumulation of specific toxic compounds ( Bernays et al., 1994). Host plant switches in the canopy would require much more effort for flightless phasmids; (3) Apart from feeding, other factors of the life history may require proximity to the ground. For instance, female H. echinata bury their eggs in leaf litter ( Bragg, 2001). These hypotheses merit more detailed investigation in the future.

Figures

Fig. 2. Leaf age preferences between saplings and an old growth canopy tree of the dipterocarp Dryobalanops lanceolata (c = canopy, s =sapling, y = young, o = old). Proportions of consumption of old leaves and canopy leaves were calculated in relation to total consumption. Values above 0.5 indicate preference for old or canopy leaves, respectively. The number of phasmid individuals is provided to the right of each bar.