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64
BULLETIN OF THE UNIVERSITY OF NEBRASKA STATE MUSEUM
size, prior reproductive history of the parents,
and possibly a “prediction” of future reproductive
opportunities for the offspring.
In the 1980s, entomologists documented
the decreasing abundance of N. americanus
across North America (Davis 1980, Anderson
1982a, Kozol et al. 1988). Since that
time, beetles of this species have not been
collected or sighted in the United States
except for the known and widely separated
populations previously mentioned. Because
of the precipitous decline in the distribution
of this species, it was included in the IUCN
Invertebrate Red Book as an endangered
species (Wells et al. 1983). It was proposed as
an endangered species in the United States
Federal Register in 1988 (Recce 1988) and
was placed on the Endangered Species List
on 14 August 1989.
Scott et al. (1987) noted that Nicrophorus
species diversity is highest at northern
latitudes, and it is likely that congeneric
competition would be greatest where species
diversity is highest. Kozol et al. (1988)
observed that body size appears to be the
most important determinant of success in
competition for securing carrion; the largest
individuals invariably displace smaller burying
beetles. Because N. americanus are the
largest carrion beetles in North America and
even the smallest N. americanus overlap in
size only slightly with the largest N. orbicollis
and N. marginatus, it seems unlikely that
N. americanus have been outcompeted by
other Nicrophorus species. However, factors
other than size that might affect the outcome
of competition remain to be examined.
Kozol et al. (1994) studied genetic variation
within and between two populations of
N. americanus, one from Rhode Island (Block
Island) and the other from Oklahoma and
Arkansas. They used the polymerase chain
reaction RAPD-PCR with single short primers
to randomly amplify polymorphic DNA.
Comparable low levels of genetic variation
were observed in both the island and distantly
removed mainland populations. These
populations were not differentiated, and this
suggested that no genetic isolation had yet
occurred as a result of the relatively recent
geographic isolation.
The prevailing theory explaining the
disappearance of the American burying
beetle involves habitat fragmentation.
Fragmentation of large expanses of natural
habitat changed the species composition and
lowered the reproductive success of prey species
required by the American burying beetle
for optimum reproduction. Fragmentation
also resulted in an increase in edge habitat
that supported and increased the occurrence
and density of vertebrate predators
and scavengers such as crows, raccoons,
foxes, opossums and skunks, all of which
compete with burying beetles for available
carrion. Fragmented habitats not only support
fewer or lower densities of indigenous
species that historically may have supported
burying beetle populations, but there is also
now a great deal more competition for those
limited resources among the “new” predator/
scavenger community.
Determining a single cause for the decline
of the American burying beetle would
simplify and facilitate its recovery. Unfortunately,
the decline is probably the result of an
interplay of several complex factors that may
include (1) artificial lighting that decreases
populations of nocturnally active insects,
(2) changing sources of carrion because of
habitat alteration, (3) isolation of preferred
habitat because of land use changes, (4)
increased edge effect harboring more vertebrate
competitors for carrion and (5) the
possibility of reduced reproduction because of
some genetic characteristic of the species.
The U.S. Fish and Wildlife Service, in
cooperation with the scientific community,
has formulated a recovery plan that is now
being implemented. Surveys at several
places in the United States are being conducted
to find remnant populations so they
can be protected.
Beetles are being reintroduced in
Massachusetts from a laboratory colony at
Boston University, and other introductions
are planned. Life history studies are being
conducted in order to determine possible