Pacific Science (1975), Vol. 29, No.1, p. 31-50 Printed in Great Britain Distribution and Ecology of the Marine Toad, Dufo marinus, in Papua New Guinea I GEORGE R. ZUG,2 ERIC LINDGREN,3 AND JOHN R. PIPPET4 ABSTRACT: Bufo marinus was introduced into the New Guinea region in the late 1930s. Its present distribution in Papua New Guinea is mapped. In the Port Mores­ by area, the population ofBufo marinus is capable ofreproduction at any time ofthe year. Sampling at a rain forest and a savann~ site near Port Moresby showed that the density of savanna toads is 10 times that of rain forest toads but that the rain forest toads are longer and heavier. This size difference probably results from the greater amounts of food and a larger proportion of proteinaceous food in the stomachs ofrain forest toads. No native frogs appear to have been displaced by the successful invasion of the toad. Similarly, no native animals have become apparent toad predators. The literature on Bufo marinus ecology is summarized. THE PROPENSITY of the marine toad (Bufo DISTRIBUTION marinus) for insects and savannas has caused Following the early success ofBufo marinus as man to introduce this species into many South a biological control agent on Oahu, the Pacific islands. The toad was primarily intro­ Hawaiian Sugar Planters' Association actively duced to control insects associated with sugar­ distributed this toad throughout the other cane and has been fairly successful in reducing Hawaiian Islands and made it available to their insect damage to this crop (Wolcott 1937). Pacific neighbors (Oliver 1949). The initial in­ While reducing the frequency of insect pests, troduction into Papua New Guinea at Keravat, the toads have multiplied and have themselves East New Britain, occurred in February 1937 reached pest proportions in many areas. This (Commonwealth of Australia 1938: 79-80) and superabundance is apparent in the urban and the toads are purported to have been received human-exploited areas of Papua New Guinea directly from the Hawaiian Islands. The toads and has provided us with the opportunity to were introduced to control the sweet potato study their ecology. moth, Hippe/ion ce/erio, which was a serious pest Through our present investigation, we pro­ in New Guinea at that time. Apparently, some posed to document the toad's current distribu­ measure of success was achieved as the 1939 tion in order to follow accurately its expansion Report to the League of Nations (Common­ or contraction of range. We also wished to ob­ wealth of Australia 1940: 80) says that, "The tain basic ecological data on toads in Papua Giant Toad, Bufo marinus, is being distributed New Guinea. With these data we can deduce to various parts of the Territory to control this the factors permitting successful invasion and pest." Because the territories of New Guinea the possibility of native faunal displacement. and Papua were administered separately prior to, Ws;:\rld:Wa,r II, this report implies that the introductions were limited to the Territory of I Manuscript received 18 May 1974. New Guinea. 2 Division ofReptiles/Amphibians, National Museum of Natural History, Washington, D.C. 20560, U.S.A. We have been unable to document accurately 3 WilalifeLaboratory, Department of Agriculture, the date or place of the first introduction of the Stock and Fisheries, P.O. Box 2417, Konedobu, Papua toad 0,11 the main island of New Guinea. Hear­ New Guinea. say evidence relates an attempt to use the toads 4 Wildlife Laboratory, Department of Agriculture, Stock and Fisheries, P.O. Box 2417, Konedobu, Papua for human pregnancy tests at the Port Moresby New Guinea. Hospital in 1938, and, when they were found to 3 31 II PS 29 32 PACIFIC SCIENCE, Volume 29, January 1975 1--------.;>-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- _. -- -- -- -- --.- -- -. -- -- -- -- -- ---------------------.---------. ·, ·, , , , , , , · , , , , , , i '. ",.• __ • .J ';~'/' ,- 0 -. -- -- -- -- -- -- -- -- -- -- -- -. -- --'-----. , , '% ,: , ·, .~ ·i : , ~~ : ~--------------------------------------- -- ------------- -- -- -_ . .! FIGURE 1. Distribution ofBufo mari/lus in Papua New Guinea in 1972. Solid circle, presence of toad; open circle, absence; thin line, 300-m contour. be unsatisfactory, they were either released or natural range in Central and South America, escaped. although there have been no ecological studies The distribution of B. marinus as of 1972 is of the marine toad to document the observa­ mapped in Figure 1. Both the toad's presence tions. Our current knowledge of marine toad and absence from a locality (see also Appendix 1 biology has been obtained predominantly from for detailed district list) have been plotted to introduced populations. Because of this, we provide a documented base for future studies lack the necessary base for the comparison of of the dispersal of the toad. These data were our data. obtained by sending a circular to all agricultural field staff, all local government councils, and all ANALYSIS OF ECOLOGICAL DATA schools in Papua New Guinea. Apart from very Materials and Methods few records, all localities for B. marinus are below or adjacent to the 300-m contour. The To estimate the possible effect of Bufo major areas of occurrence are centered around marinus on the native New Guinean frogs, we towns such as Lae, Port Moresby, or Rabaul. collected data on reproduction, food habits, Population densities are high in urban areas and and relative abundance. Two sampling localities rapidly decrease as the habitats become less were selected in the Port Moresby area (Figure disturbed. B. mat'inus also inhabits primary low­ 2): (1) a eucalyptus savanna habitat was repre­ land rainforest, for single individuals have been sented by a site-at the Moitaka sewage plant and seen in the rain forest near Port Moresby, Garu associated road, approximately 14 km north of village on West New Britain, and Madang. This Port Moresby; (2) a rain forest habitat was pattern of abundance in Papua New Guinea represented by a section of the Brown River seems to be the same as that within toad's Road approximately 24 to 34 km north of Port Bufo marinus in Papua New Guinea-ZuG, LINDGREN, AND PIPPET 33 1 Daru 2 Port Moresby 3 Wariarata ~ Talasea ~, ,~, \ \ \ \ I J RAIN FOREST / TRANSECT ... / ttl/tllti Rirer \, I 0,1 ·r\D / ~ Appro•. RoJn F....' I SoYaMA JunctJoli SEWAGE PONOS, :/ SAYANNA ~t"III 1-------To SOIC,i PORT MORESBY TIlANSECl \1 and / Wariorato ENVIRONS ,./// ---,' FIGURE 2. Sampling localities of present study. 34 PACIFIC SCIENCE, Volume 29, Jan~ary 1975 180 • 160 W • ...J 0- 140 :::?: <l: en • a:: 120 12 W 0- Il en ...J 100 10 <l: :::> 0 III 9 0 i IIIII · ::0 :;: 80 8 ~ 0 z Z IIIIII:I~' 7 ~ lJ.. 60 " 6 r 0 • r a:: 5 W (=) al III ' i I s:: ~ 40 4 :::> 'I z III·' iI 3 20 /'. 2 1 1 / ".-. iilllll~IIII"IIIl:II I~' III,~ • ~IIIII•...,.!.,....... ,,'II~III'a '. 0 '''11 11 " ... •• ."",,_ 0 II 27 10 26 10 25 8 23 7 21 8 21 6 20 6 19 4 18 3 18 2 16 31 15 29 OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG SEP SAMPLING DATES FIGURE 3. Toad census data and total amount of rainfall in 2 weeks preceding the sampling date. Circle, savanna count; square, rain forest count; vertical lines, rainfall. Moresby. Biweekly samples and counts were collected at the savanna site in October, Febru­ taken at each site. Dates of sampling were set ary, June, and August for size analyses. Samples to coincide with nights of the quarter moon in were also collected at Daru (Western District), order to have all samples collected under ap­ Talasea (West New Britain District), and proximately equal lightintensity and at approxi­ Wariarata (Central District) (see Figure 2). mately the same level of activity if toads were At the rain forest site, toads were both following a lunar cycle. All collections at both counted and collected along a 9.6-km section sites were made at night, usually around 2000 ofthe road. This sampling without replacement hours. The toads were frozen on the night of was done principally on the first 3.2 km of road collection or on the following morning. as toads were rarely seen beyond this initial At the savanna site, the number oftoads on a section of rain forest road. Although the road 1.6 km (= 1 mile) section of road leading into was patrolled, no toads were obtained from the the sewage plant was counted. Ten 1l?'ales and rain forest site from June to September 1972. 10 females were collected from the vicinity of Even though both census transects were the sewage settling ponds at each sampling along unpaved roads, the toad counts represent period. During the dry season (April through censuses of the bordering habitats and not of September), 50 toads were collected and the the road, since the toads were from adjacent first 10 males and 10 females were processed, areas and were using the roads only as a feeding this technique being used because of ~he diffi­ area. Brattstrom (1962) showed that toads fed culty in distinguishing the sexes in the field. at sites other than their diurnal resting sites. Larger samples of 50 to 100 individuals were The bordering habitats represent a little-dis- Bufo marinus in Papua New Guinea-ZuG, LINDGREN, AND PIPPET 35 turbed eucalyptus savanna and a seasonal rain TABLE 1 forest. The savanna transect did not include the MONTHLY RAINFALL (IN CM) FOR THREE METEORO­ sewage plant as the terminus ofthe transect was LOGICAL STATIONS IN THE PORT MORESBY AREA, nearly 100 m from the plant. One section (0.4 CENTRAL DISTRICT, OCTOBER 1971 TO km) ofthe rain forest transect passed through a SEPTEMBER 1972 maturing-teak plantation. The following data were obtained from each PORT MT.