Competitive exclusion of a burying beetle by mongoose

Abstract

Competitive exclusion, a mechanism for local extinction of organisms, has been well established among taxonomically related species, including those within the same genus, family, or class in animal communities. This study, however, focuses on competitive exclusion that occurs across phyla, exemplified by the exclusion of a native insect by an invading exotic mammal, where food resources overlap. The hypothesis proposed in this study is that the small Indian mongoose (Urva auropunctata) has caused the local extinction of a burying beetle (Nicrophorus nepalensis) on Okinawa Is., Japan due to competition for carcasses of small vertebrates. To test this hypothesis, a comparison of beetle abundance was conducted between the area intensively controlled for mongoose and the area where mongoose control was weak or nonexistent. The former situated north of the boundary to prevent mongoose from crossing, and the latter located south of the boundary. To determine the user of carcasses on the forest floor, mouse carcasses were laid and their consumers were observed in each area. The results showed that the beetle abundance was clearly higher in the former than in the latter, and no beetles were collected where mongoose have never been controlled. The beetles often buried the mouse carcasses for their reproduction in the former, whereas in the latter, mongoose frequently consumed the mouse carcasses. These results provide evidence of competitive exclusion of the burying beetle by mongoose. This conclusion represents the first demonstration of competitive exclusion across phyla in an animal community.

Appendices

Appendix 1

See Fig. 6.

Fig. 6

Fish-baited hanging trap to collect Nicrophorus nepalensis

The trap consisted of a plastic cup (95 mm in open diameter and 170 mm high) with four 2 mm diameter holes for drainage on the side (50 mm from the top). The cup contained 150 ml propylene glycol and a small plastic cup (42 mm in open diameter and 35 mm high) was fixed to its upper lip with steel wire. Another small plastic cup, containing 15 g of mackerel (Scomber spp.) meat with a perforated lid (having 25 holes, each 1 mm in diameter), was placed into the suspended cup. The trap was hung 100 mm beneath a white plastic plate (230 mm diameter and 20 mm high) using four steel wires to prevent rainwater from entering. The trap mechanism was hung from a tree branch, utilizing fishing line at an approximate height of 1.2 m. Three of the four wires that held the trap were fastened to nearby tree trunks using the fishing line to prevent the trap from rolling.

Appendix 2

See Fig. 7.

Fig. 7

Mechanism for the observation of consumers of mouse carcasses

Two mouse carcasses were used for the observation, with one placed under a steel rack (405×250 mm, 30 mm high) weighed down with a concrete block (390×190 mm, 120 mm high, 11.3 kg) to prevent interference from animal scavengers. For the observations made south of the SF line, the mouse was placed at the center of a plastic bowl (265 mm diameter and 115 mm high), with the bottom of the bowl removed and the bowl buried in the ground, in order to prevent animals from digging to reach the mouse. The hind leg of the mouse was tied to the steel rack with dental floss measuring approximately 40 cm in length to track the position of the mouse buried by N. nepalensis. The other mouse was also tied to the steel rack and placed beside it without cover. An infrared sensor camera with interval photographing capabilities (Ltl-6210MC, Ltl Acorn®) was placed near the mouse carcasses, with the interval period set to every 60 min.

Appendix 3

See Fig. 8.

Fig. 8

A mouse carcass buried and processed by Nicrophorus nepalensis (a), and the adult and larvae in a processed mouse carcass (b)

Appendix 4

See Fig. 9.

Fig. 9

A mongoose shortly before consuming a mouse carcass without the cover (a) and another that is attempting to consume a mouse carcass with the cover (b)