Carrion reduction by animals in contrasting tropical habitats

Decomposition of lizard (Iguana iguana, Ctenosaura similis) and toad (Bufo marinus) carrion open to arthropods was studied in a tropical dry and a tropical wet forest in Costa Rica. Carcass fates, feeding interactions of necrophagous animals and their predators, temporal succession patterns, and species compositions differed between sites. More than 170 species representing 49 families were associated with the carrion baits; calliphorid and sarcophagid larvae and adults and adult Formicidae and Scarabaeidae were most important in reducing carcasses to the dry skin stage. The significance of these results is discussed in relation to nutrient cycles and the decomposition submodel of a tropical forest ecosystem. SYNTHESES OF ENERGY and elemental transfers in tropical forest ecosystems are now available (Golley et al. 1969, McGinnis et al. 1969, Odum and Pigeon 1970, Malaisse et al. 1972, Fittkau and Klinge 1973). The grazing and detritus food chains are the two major pathways for the movement of nutrients in such ecosystems (Odum and de la Cruz 1963, Wiegert and Owen 1971). Nutrients enter the decomposer subsystem via such detritus pathways as annual leaf fall (de la Cruz 1964); total plant death (Richards 1952); seed and fruit drop (Smythe 1970); animal defecation (Watling 1963, Nicholson, Bocock, and Heal 1966); and animal death (Heatwole 1971). Nutrients tied up in dead animals of various sizes are released in large part by activities of necrophagous bacteria, fungi, and animals. Research on carrion bacteria and fungi is scant (Okafor 1966), but this is not true for investigations of the role of scavenger birds (Chapman 1938, Stager 1964), omnivorous mammals (Koepcke and Koepcke 1952), and arthropods (Chapman and Sankey 1955, Reed 1958). In addition, Fuller (1934), Bornemissza (1957), Payne (1965), and Payne and Crossley (1966) report results of studies on faunas associated with carrion. More specialized research discusses carrion-associated Coleoptera (Pessoa and Lane 1941, Howden 1950, Halffter and Matthews 1966, Shubeck 1969, Payne and King 1969a); Diptera (Hepburn 1943); and Lepidoptera (Payne and King 1969b). These investigations have increased our understanding of the intricate food webs, temporal patterns, and identity of arthropods associated with the carrion microcosm in temperate regions of the world. Virtually nothing is known about similar phenomena in tropical environments. The purpose of this research is (1) to document relative durations of the various stages of lizard and toad decomposition in two different tropical forests; (2) to structure preliminary trophic interactions and discuss them in terms of resource partitioning; (3) to detail temporal succession patterns; and (4) to establish an inventory of species attending these carriotn. Information about the carrion microcosm will be useful in elucidating detritus compartments of the above-mentioned models of ecosystems. SITES, MATERIALS AND METHODS This research was conducted at a tropical dry lowland forest at Finca La Pacifica, 5 km N of Las Cafias, Guanacaste Prov. , Costa Rica, and a tropical wet lowland forest 5 km W of Rincon de Osa, Puntarenas Prov. , Costa Rica, in the dry season during parts of February and March 1968. From February 8 to February 17 temperatures measured at ground level at the Guanacaste site ranged from 21.8 to 38.50 C with a typical daily fluctuation from 240 C (0400 hr) to 340 C (1300 hr). Ten-year averages of rainfall at Las Cafias (Scott 1966) ranged from a low of 5 mm in January and March, through an average of 17 mm during February to a high of 375 mm in October. In February, the soil was rather dry and loose, and the depth of the dry leaf litter, where existent, averaged 5 cm. The Osa site exhibited temperature extremes of 22.0 and 28.50 C at ground level for the period February 29 to March 9; typical daily fluctuations ranged from 23 to 270 C. Rainfall profile by ten-year averages for nearby Coto, Puntarenas Prov. , ranged from 39 mm (February) to 579 mm (October) with 60 mm as the average for March (Scott 1966). The soil was moist, somewhat compact and rocky. Litter depth averaged 1 Present address: Battelle-Columbus Laboratories, 505 King Avenue, Columbus, Ohio 43201 U.S.A. This study was conducted under the auspices of the Organization for Tropical Studies, Inc., Apartado 16, Universidad de Costa Rica, C. A. BIOTROPICA 6(1): 51-63 1974 51 This content downloaded from 157.55. 39.104 on Sun, 19 Jun 2016 06:46:14 UTC All use subject to http://about.jstor. org/terms 4 cm. Minimal selective cutting of large trees had occurred at both forest sites within the last 20 years. Both study areas were at least 200 m from remote human habitations. Animals native to the respective forests were killed and served as carrion baits: two Bufo marinui m4rinus (Linnaeus) (1 ? , 61 g (wet weights taken immediately after death), 90 mm (snout to vent); 1 ? , 303 g, 130 mm) and two medium-sized Ctenosama similis similis Gray ( 3, 88 g, 145 mm; ? , 124 g, 168 mm) were studied at Guanacaste; two medium-sized Igzana igaana iguana Linnaeus ( 3, 261 g, 210 mm; 3', 291 g, 180 mm) and two B. m. marinus (3', 71 g, 95 mm; 3', 222 g, 115 mm) were used at Osa. At the sites it was impossible to locate lizard and toads whose sizes exactly matched. Toads were hand retrieved and pithed. Lizards were either noosed and strangled or shot from a tree with a shotgun; there were a few, small perforations in the skin of the latter specimens. Each carcass was placed at the center of a 1 m2 square area. The area was cleared of most leaf and twig litter to facilitate observations at the lizardground interface as has been done in other carrion studies (Payne 1963, 1965). It was assumed that the carrion fauna was not affected by the partial clearing of such a small area on the forest floor. Individual plots were at least 35 m apart at each site. Carcasses were protected from molestation by vertebrate scavengers by small bottomless wire cages (2 cm x 3 cm mesh size), which permitted large cockroaches and beetles access to the rotting animals. One lizard and one toad were killed and placed in the field on day one, another pair readied on day four; this staggered placement schedule permitted over 100 hours of observation for the total study and maximized observation time per carcass during the first 3 days of the decay sequence. Numerous observations were made daily at each carcass primarily between 0600 and 1900 hr; several night observations were made also. Each observation lasted from 5 to 180 min with an average of ca. 70 min per observation. The study was conducted at Guanacaste during the following dates in February: 8-15, lizard 1; 11-16, lizard 2; 8-14, toad 1; 11-14, toad 2. Osa dates are as follows: February 29-March 9, lizard 3; March 5-March 12, lizard 4; February 29March 8, toad 3; March 5-March 12, toad 4. During observation times the cage was lifted away from the carcass. Once placed, carcasses were not moved. The following phenomena were scrutinized at each carrion: decay state of carcass; arrivals, abundances during residency and departures of arthropod taxa; feeding habits by animals on carcass proper and on each other. One feeding observation represents either the removal of flesh or fluid from the carcass or the capture and ingestion of one organism by a predator(s). Ants and fly larvae ate holes through the body walls of some dead toads and lizards; these breaks permitted observation of the abundances of necrophagous animals inside the carcasses. Activities also were noted as maggots en masse undulated under the skin and body walls. Limited voucher specimens of each recognized morpho-species associated with each kind of carcass were collected and labelled daily.