Host-specificity of antagonists and mutualists
We find a substantial share of organisms between plant species (Table 1,
Figure 2). In general, organisms at MFS (plot with 4 dominant species)
were less host specific than those at MFJ (Figure 2), with insects at
MFJ showing the highest host-specificity. For example, chewer and sucker
insects showed at MFJ a mean overlap of 28 and 29%, respectively, but
at the MFS plot mean overlap was 52 and 44%, respectively (Figure 2a,
b). In contrast, plant species shared a larger proportion of pathogens
and epiphytes, with mean values of, approximately 56% in MFJ, and 67%
in MFS. Note that we used different methods for species identification
within guilds (i.e., insects vs. fungi), which does not allow for a
robust comparison among these guilds, but for robust comparison between
forest plots.
We found that the mean number of shared organisms within distancer tended to decline with the corresponding proportion of
heterospecifics if the organisms showed relatively strong host
specificity (Figure S1). This relationship was especially marked for
insects at the MFJ plot, which showed the highest level of host
specificity. Interestingly, epiphytes at the MFJ plot and epiphytes and
pathogens at the MFS plot were less host specific, and showed different
patterns (Figure S1).
Shared antagonists and mutualists
between neighbouring
saplings
As expected, the sapling “seedscape” varied between fruit type, but
were similar between plots (see table 1 for expectations). Saplings of
dry-fruited species were generally surrounded by other saplings that
shared fewer than expected organisms of all four types, with weaker
effects for pathogens and epiphytes at the MFJ plot (Figure 3 a-d, grey
lines). The seedscape of saplings of fleshy-fruited species, in
contrast, did not differ significantly from the expectations of the null
model (Figure 3a-d, red lines) (see Table S3 for significant departures
from the null model, and figure S2 for graphs without the
standardisation).
The contrasting patterns between fleshy- and dry-fruited species are
most likely related to two effects. First, saplings of dry fruited
species showed a significantly higher than expected proportion of
heterospecific saplings in their neighbourhood (Figure 4b, d), and
second, they showed very high local dominance of approximately 50%.
This result is consistent with a density-dependent seedling mortality
caused by Janzen-Connell effects. In contrast, saplings of
fleshy-fruited species had approximately 83% (MFJ) and 75% (MFS)
heterospecific neighbours (Figure 4a, c). The high levels of
heterospecific neighbours are consistent with frugivore seed dispersal
of early density-dependent mortality that prevented emergence of
Janzen-Connell effects (see Table 1).
Shared antagonists and mutualists
between saplings and neighbouring
adults
The patterns of similarity in shared organisms between saplings and
neighboured adults strongly differed from that revealed in the
sapling-sapling analysis (Figure 3). Most notably, the strong negative
sapling-sapling effects of dry-fruited species almost completely
disappeared, in accordance with our expectations (see table 1); except
for shared insects at the MFJ plot up to the 1m neighbourhood (Figures
3e, f). This pattern was caused by a significantly lower than expected
proportion of conspecific adults around saplings (Figure 4f), a pattern
which was not found in the other 3 cases (Figures 4e, g, h), but
probably associated with distance-dependent Janzen-Connell effects.
Interestingly, saplings of dry fruited species at the MFS plot were
surrounded by adults sharing significantly more pathogens and epiphytes
than expected (Figures 3g, h), whereas they were surrounded by saplings
sharing significantly less pathogens and epiphytes than expected (Figure
3c, d). This pattern was probably caused by (slightly) fewer than
expected heterospecific neighbours (Figure 4h, Table S3). Thus, the MFS
adult “seedscape” surrounding saplings showed large differences
depending on whether locations close to other saplings or close to
adults are considered. In contrast, at the MFJ plot (the plot with one
dominant species), patterns in pathogens and epiphytes did much less
differ for dry-fruited species between sapling-sapling and the
sapling-adult analysis (i.e., weak or no significant effects). This
suggest that different mechanisms operate at the two plant communities,
which may be a consequence of the differences in species diversity and
dominance (See Figure S3). Similarly, the patterns of fungal guilds for
fleshy-fruited species were for both, sapling-sapling and sapling-adult
analyses basically non-significant (see Table S3 for significant
departures from the null model).
Shared antagonists and mutualists
between neighbouring
adults
The results of the adult-adult analyses differed substantially from that
of the sapling-sapling and sapling-adult analyses. In most analyses we
found that adults of fleshy fruited species shared, consistently between
plots, fewer than expected antagonists with neighbour adults (red curves
in Figure 3i-l); and showed a higher than expected proportion of
heterospecific adults in their neighbourhood (Figure 4i and 4k).
However, no effects were found for dry-fruited species (grey lines in
figure 3i-l). Interestingly, this pattern is opposite to that of found
in the sapling-sapling analysis, and points to the importance of seed
dispersal as modulators of Janzen-Connell effects.