Response of Seedlings and AMF Spores to Vertebrates 297and nearby open plots at 6-month intervals.
In 2001, we assessed AMF spore abundance
and diversity from soil cores collected in 13
of the 14 exclosure–open pairs (Gehringet al.
2002). Faunal censuses indicated that our
study site included three species of marsupi-
als, the long-nosed bandicoot (Perameles nasuta),
musky rat kangaroo (Hypsiprymnodonmoschatus),
and red-legged pademelon (Thylogale stigmatica),
and three species of eutherian rodents, the
bush rat (Rattus fuscipes), fawn-footed melomys
(Melomys cervinipes), and giant white-tailed
rat (Uromys caudimaculatus). Ground-frequenting
birds included the southern cassowary (Casuar-
iuscasuarius), brush turkey (Alecturalathami), and
chowchilla (Orthonyx spaldingii). Of the birds, the
cassowary was completely excluded by the fenc-
ing, while brush turkeys and chowchillas only
occasionally flew over the fences. Monitoring of
tracks and trapping indicated that the ground-
dwelling marsupials were completely excluded
from the exclosures. Bush rats were captured only
once in the exclosures in 300+tra pnights versus
58 captures in open plots. Access by white-tailed
rats was reduced to one third that of the open
plots andMelomysaccess was reduced by more
than 50%.
After 4.5 years of terrestrial vertebrate exclu-
sion, seedling abundance averaged 40% more on
exclosure plots than on open plots (Table 17.1).
These differences were due to both reduced
seedling recruitment and increased seedling mor-
tality on unfenced plots. Seedling species richness
averaged 27% more on exclosure plots than on
open plots. However, we found no significant dif-
ferences in evenness or Shannon’s diversity of the
seedling community (Table 17.1).
Over roughly the same time period, verte-
brates promoted AMF spore abundance, species
richness, species diversity, and inoculum poten-
tial in the soil (Table 17.1). Mean AMF spore
abundance was 51% higher and spore species
richness was 28% higher in soils from open plots
than from terrestrial vertebrate exclosure plots
(Gehringet al. 2002). The species composition
of the spore communities varied between exclo-
sure and open plots, withGlomus rubiforme,a
sporocarp-forming species that might be selec-
tively consumed by terrestrial vertebrates, serving
as the strongest indicator of treatment differences
(Gehringetal. 2002). Another sporocarp-forming
species,Glomus fasciculatum, also was markedly
more abundant on open plots than on exclosure
plots (Gehringet al. 2002). These differences in
spore communities were not associated with indi-
rect effects of terrestrial vertebrates on seedlings
or the soil environment (Gehringet al. 2002). Dif-
ferences in the AMF spore communities of open
and exclosure plots also were not associated with
consistent differences in tree seedling communi-
ties (Figure 17.1). We performed the same ordi-
nation analysis on the seedling communities that
we had done for the spore communities (blocked
multi-response permutation procedure [MRPP],
Gehringet al. 2002) and found no significant
difference between exclosure and open plots in
seedling community composition (A=−0.004,
P=0.497).
The differences in the spore communities that
resulted from vertebrate exclusion were associated
with differences in the AMF inoculum potential
of the soil. Both a standard bioassay plant (corn)
and a rainforest seedling (Flindersia brayleana)
had higher levels (42–50%) of AMF coloniza-
tion when grown in soil cores from open plots
than when grown in soil cores from exclosure
plots, suggesting that the effects of vertebrates
on spore communities had consequences for for-
mation of associations with AMF (Gehringet al.
2002). Subsequent comparisons with seedlings of
another rainforest species,Cryptocarya angulata,
indicated that levels of colonization by AMF also
differed between seedlings naturally establishing
in exclosure versus open plots in the field, demon-
strating that the spore differences are important
at early stages of seedling development even when
other sources of inoculum, such as intact hyphal
networks, are present (Figure 17.2).POTENTIAL REASONS FOR THE
DIFFERENT RESPONSE OF
SEEDLINGS AND AMF SPORES
Our study plots can be viewed as relatively small
islands of space where rates of local coloniza-
tion and extinction differed due to the impacts