174 
Psyche 
[Vol. 95 
captured in traps on Block Island was 7.98 to 12.63 mm. Females 
are reproductively capable immediately upon leaving a brood. 
Laboratory studies with N. americanus showed that reproductive 
success, measured by total brood weight and by the number of 
tenerals eclosed, is significantly correlated with carcass size as has 
also been demonstrated in laboratory broods of N. orbicollis (Wil- 
son and Fudge 1984). The significant negative correlation between 
the number of adults eclosed per brood and their average weight 
suggests that N. americanus individuals rearing broods may make a 
tradeoff between a large number of small offspring or a small 
number of large offspring. The outcome of this tradeoff may depend 
on carcass size, prior reproductive history of the parents, and possi- 
bly a prediction of future reproductive opportunities for the 
offspring. 
Collection records from the Museum of Comparative Zoology at 
Harvard University indicate that N. americanus was found in the 
following states at the early part of this century: Kansas, Illinois, 
Minnesota, Wisconsin, Virginia, New York, Pennsylvania, Connec- 
ticut, New Hampshire, and Massachusetts. Davis (1980) reported 
additional collections in Tennessee (29 individuals in 1952) and 
Kentucky (1974). Anderson (1982b) located collection records of N. 
americanus after 1950 only in Ontario, Arkansas, Illinois, Michi- 
gan, Missouri, and Tennessee. Ten N. americanus individuals have 
been collected at light traps in Oklahoma (near Tenkiller Ferry 
Resevoir and in Latimer County) between 1979 and 1988 (L. Mas- 
ter, personal communication). Why has N. americanus suffered 
such a severe decline in what appears to be a relatively short period 
of time? Studies in enclosures with another species suggest it is 
unlikely that N. americanus has been outcompeted at least in direct 
confrontation by congeners. Studies with N. orbicollis have shown 
that the preferred carcass size is 20-60 grams and that carcasses over 
60 grams are difficult to bury (Scott unpublished data). N. orbicollis 
may not be a major competitor of N. americanus because of a lack 
of overlap in the size frequency distribution of suitable carcasses 
and frequent loss in contest competition. 
Nicrophorus species diversity is highest at northern latitudes 
(Scott et al. 1987) and it is likely that congeneric competition would 
be greatest where species diversity is highest. Size appears to be the 
most important determinant of success in competition for securing 
carrion; the largest individuals invariably displace smaller burying 
