3.4 | Ecological Null Modeling
We detected a positive signal over short phylogenetic distances in
relation to sandwort availability (p < 0.05, r =
0.02; Figure S3, Supporting information). Of the physiological,
environmental, and spatial terms considered, only parental status
(p = 0.03) was associated with non-random patterns of
phylogenetic dispersion. Namely mares with foals had higher
|MNTDses| values (Table S6, Supporting
information). Based on between-sample comparisons, communities were more
often phylogenetically conserved (βMNTDses <
0) than they were phylogenetically disparate (βMNTDses> 0) but usually did not deviate in expected phylogenetic
similarity from pairs of randomly assembled communities
(|βMNTDses| < 2).
βMNTDses values were correlated with Julian date
(R2 = 0.03, p < 0.01),
sandwort presence (R2 = 0.07, p <
0.01), beach pea availability (R2 = 0.03,p = 0.02), heathland availability (R2 =
0.03, p = 0.01), and grassland availability
(R2 = 0.02, p = 0.04; Table S7,
Supporting information). In the absence of sandwort,
βMNTDses values appeared to be negatively correlated
with average grassland availability (Figure 5), but positively
correlated with average heath availability (Figure S4A, Supporting
information); conversely, βMNTDses values were greater
when sandwort was present and appeared to be negatively correlated with
average Julian date. In contrast, the absolute magnitude of phylogenetic
deviation from stochastic expectations
(|βMNTDses|) was correlated with beach
pea availability (R2 = 0.05, p< 0.01), longitude (R2 = 0.05, p =
0.04), and parental status (R2 = 0.03, p= 0.03; Table S8, Supporting information). Specifically,
|βMNTDses| values appeared to be
positively correlated with beach pea availability (Figure S4B,
Supporting information) as well as average longitude, and greater among
mares with foals than mares without foals (Figure S4C, Supporting
information). No significant correlation was observed between
longitudinal separation and βMNTDses after controlling
for sandwort presence (partial Mantel test: p = 0.68). Similarly,
no effect of band membership on βMNTDses was observed
(PERMANOVA: p = 0.45).
Approximately 14% of βMNTDses were beyond 2 standard
deviations of the randomized null distributions. Of the remaining
~86% of pairwise comparisons, ~97% had
corresponding RCbray values exceeding 0.95, which
signals greater ASV turnover than expected under ecological drift alone,
a pattern suggestive of dispersal limitation. Based on PERMANOVA
analysis, RCbray values were correlated with longitude
(R2 = 0.02, p < 0.01),
distance from the centre of the population (R2= 0.02, p < 0.01), sandwort presence
(R2 =
0.01, p = 0.04), beach pea availability
(R2 = 0.01, p = 0.04), and Julian date.
(R2 = 0.02, p < 0.01; Table S9,
Supporting information). Additionally, in a univariate PERMANOVA, band
membership was significantly correlated with RCbrayvalues (R2 = 0.65, p < 0.01).
Furthermore, RCbray values were positively correlated
with the distance separating horses even after controlling for
βMNTDses values (partial Mantel test:rpearson = 0.17, p < 0.01;
Figure 6A), but negatively correlated with average longitude and lower
among members of the same band than between members of different bands
(Figure 6B).