Disturbance and the (surprising?) role of ecosystem engineering in
explaining spatial patterns of non-native plant establishment
Abstract
The Intermediate Disturbance Hypothesis is widely considered to be wrong
but is rarely tested against alternative hypotheses. It predicts that
soil disturbances and herbivory have identical impacts on species
richness via identical mechanisms (reduction in biomass and in
competition). An alternative hypothesis is that the specific traits of
disturbance agents (small mammals) and plants differentially affects
richness or abundance of different plant groups. We tested these
hypotheses on a degu (Octodon degus) colony in central Chile. We ask
whether native and non-native forbs respond differently to degu
bioturbation on runways vs. herbivory on grazing lawns. We ask whether
this can explain the increase in non-native plants on degu colonies. We
found that biopedturbation did not explain the locations of non-native
plants. We did not find direct evidence of grazing increasing non-native
herbs either, but a grazing effect appears to be mediated by grass,
which is the dominant cover. Further, we provide supplementary evidence
to support our interpretation that a key mechanism of non-native spread
is the formation of dry soil conditions on grazing lawns. Thus ecosystem
engineering (alteration of soil qualities) may be an outcome of
disturbances, which each interact with specific plant traits, to create
the observed pattern of non-native spread in the colony. Based on these
results we propose to extend Jentsch & White’s (2019) concept of
combined pulse/ disturbance events to the long-term process duality of
ecosystem engineering/ disturbance.