Fruiting trees provide fruit and insect resources for four tropical deer species

Fruiting trees provide important fruit and seed resources for various animal species, but rarely are they considered to be rich sources of insects as well. During a study of seed dispersal of Trewia nudiflora (Euphorbiaceae) using camera-traps in Nepal, we observed four tropical deer species (Axis axis, Muntiacus vaginalis, Rusa unicolor, Axis porcinus) foraging for insects, rather than fruits under the trees. These herbivorous deer are proven seed dispersers of Trewia, but 8-38% of video captures (across each species) were of insectivory, rather than frugivory. The deer chased and consumed red cotton bugs (Dysdercus sp. family Pyrrhocoridae), which were seed predators that hoarded Trewia seeds. It is likely that other unidentified insect species were also consumed. Tropical deer species are considered to be fully herbivorous, so our observations extend their known diets and possibly indicate a seasonal requirement for protein. These findings also highlight tri-trophic interactions among deer, insects, and fruits that could have important implications for seedling recruitment if seed predators are being consumed by seed dispersers (in addition to fruit consumption).

Methods
Cameras were set-up under 75 fruiting trees of Trewia nudiflora to obtain information on its terrestrial consumers and seed dispersers. While monitoring the videos we noticed that not all deer feeding interactions were of fruit, and here we report confirmed and unconfirmed observations of insect feeding. Confirmed feeding was noted when the insect could be clearly distinguished in the video. Unconfirmed feeding was noted when the deer was feeding on something other than the easily identifiable fruit or vegetation; in many of these videos insects can be seen moving away from the deer as they forage, but insect-capture could not be confirmed.  A) Camera trapping and b), counted the number of red cotton bugs in one square meter plots (averaged across four plots per tree) for 20 trees (Karar et al., 2020).