Abstract:
Environmental stressors and changes in land use have led to rapid and dramatic species losses. As such,
we need effective monitoring programs that alert us not only to biodiversity losses, but also to functional
changes in species assemblages and associated ecosystem processes. Ants are important components
of terrestrial food webs and a key group in food web interactions and numerous ecosystem processes. Their sensitive and
rapid response to environmental changes suggests that they are a suitable indicator group for the monitoring of abiotic,
biotic, and functional changes. We tested the suitability of the incidence (i.e. the sum of all species occurrences
at 30 baits), species richness, and functional richness of ants as indicators of ecological responses to environmental change, forest degradation, and of the
ecosystem process predation on herbivorous arthropods. We sampled data along an elevational gradient
(1000–3000 m a.s.l.) and across seasons (wetter and drier period) in a montane rainforest in south-
ern Ecuador. The incidence of ants declined with increasing elevation but did not change with forest
degradation.
Ant incidence was higher during the drier season. Species richness was highly correlated
with incidence and showed comparable results. Functional richness also declined with increasing ele-
vation and did not change with forest degradation. However, a null-model comparison revealed that
the functional richness pattern did not differ from a pattern expected for ant assemblages with ran-
domly distributed sets of traits across species. Predation on arti?cial caterpillars decreased along the
elevational gradient; the pattern was not driven by elevation itself, but by ant incidence (or inter-
changeable by ant richness), which positively affected predation. In spite of lower ant incidence (or
ant richness), predation was higher during the wetter season and did not change with forest degrada-
tion and ant functional richness. We used path analysis to disentangle the causal relationships of the
environmental factors temperature (with elevation as a proxy), season, and habitat degradation with
the incidence and functional richness of ants, and their consequences for predation. Our results would
suggest that the forecasted global warming might support more active and species-rich ant assem-
blages, which in turn would mediate increased predation on herbivorous arthropods. However, this
prediction should be made with reservation, as it assumes that the dispersal of ants keeps pace with
the climatic changes as well as a one-dimensional relationship between ants and predation within a
food-web that comprises species interactions of much higher complexity. Our results also suggested
that degraded forests in our study area might provide suitable habitat for epigaeic, ground-dwelling ant
assemblages that do not differ in incidence, species richness, functional richness, composition, or predation
on arthropods from assemblages of primary forests. Most importantly, our results suggest that
the occurrence and activity of ants are important drivers of ecosystem processes and that changes in the
incidence and richness of ants can be used as effective indicators of responses to temperature changes
and of predation within mega-diverse forest ecosystems
