Habitat type controls microarthropod community changes across a Magellanic sub-Antarctic elevation gradient

Elevation gradients are often used
as a proxy for climate change as they allow
comparisons of ecological responses over much larger temporal and spatial
scales than is possible through experimental manipulations. Here, we tested how
microarthropod communities (Collembola and Acari) are affected by climatic differences
between sea level and 600 m a.s.l. on Navarino Island, in the Magellanic
sub-Antarctic ecoregion of southern Chile (mean annual temperatures of 5.6 vs
3.1 °C, respectively). We quantified
microarthropod abundance, richness and community trait characteristics in dominant
moss (Racomitrium lanuginosum and Polytrichum strictum)and
lichen (Usnea trachycarpa, Pseudocyphellaria freycinetii and Stereocaulon
alpinum) vegetation growing at both elevations.
These moss and lichen genera are characterised by large morphological
differences and allow testing of how habitat characteristics affect
microarthropod community response across elevation gradients.

Collembola and Acari community
composition differed between the low and high elevation sites. Total abundance
levels of Acari were maintained in each habitat across elevation, whereas Collembola
richness strongly declined
(50%) at high elevation in the moss habitats. Acari community differences
across elevation were driven by relative abundance changes whereas the Collembola
community lost species at higher elevation. An anticipated decline of smaller
eudaphic Collembola at high elevation was only observed in the moss Racomitrium,
reflecting potentially lower temperature buffering capacity and shelter options
compared to Polytrichum.Lichens mostly supported larger epigeic species irrespective of elevation.
There were no consistent patterns linking microarthropod communities with
habitat water holding capacity or water loss rates across the studied habitats
and elevation. Habitat type and the genus of moss or lichen were associated
with microarthropod community changes across elevation, including examples of
declines, increases and no change. These findings highlight that community
responses across gradients may not always relate to the generally hypothesized
environmental variables (e.g. temperature variability) and that habitat
characteristics should be taken into account when using elevation as a proxy
for climate change.