Data analysis
Because ants are colonial organisms and the presence of multiple
individuals in a single trap likely represents individuals from a single
colony, only the presence or absence of each ant species was quantified
in each Winkler sack (frequency of occurrence ranging from zero to 10 in
each patch). For each patch, we created a patch × species matrix (26
rows × 251 columns) filled with species occurrence frequencies in
Winkler extractors. These data were used to estimate the occupancy and
detection of individual species in each patch and the effect of
predictor variables (patch and landscape area, connectivity, and cattle
presence) on species detection and occupancy. Because true presence
(occupancy) of individual species in patches determines community-level
patterns (e.g. species richness), we indirectly estimated the effects of
the covariates on local ant diversity (alpha), and on the composition of
ant species (beta-diversity) through their effects on individual species
occupancy. If all species were perfectly detected, this approach would
provide the same results as regression models directly associating
species diversity with predictor variables.
Occupancy models require a hierarchical structure for data sampling and
organization. In our study, we estimated species occupancy at the patch
level (higher level) and used replication within patches (Winkler
extractions; lower level) to estimate detection probabilities. It is
important to acknowledge that at the replication scale (within a patch),
detection can be influenced by various factors, such as species rarity,
aggregation patterns, and behaviour (Iknayan et al. , 2014).
Therefore, differences in detectability among patches are not solely
attributable to sampling limitations but also reflect biological
processes.
Similar to other studies using occupancy models with temporal bird
surveys (Guillera‐Arroita et al. 2018) or camera traps for mammals (Van
der Weyde 2018), which do not incorporate covariates at the replication
level, our model assumes that all Winkler extractions within a patch
(but not among patches or species) have a similar probability of
capturing a given species. This assumption is reasonable considering
that leaf-litter ants have a limited foraging range (Hölldobler and
Wilson 1990) and that the similarity between neighbouring extractions as
close as 5 meters apart is extremely low (Fisher et al. 1990).