Latitudinal variation in the diversity-disturbance relationship demonstrates the context-dependency of disturbance impacts

Aim: The shape of the diversity-disturbance relationship is
context-dependent, but the mechanisms driving this context-dependency are
unclear due to limited standardised empirical assessments across different
environmental and ecological settings. At seven sites and over 20o of
latitude, spanning both temperate and tropical systems, we measured
community response to a fine-scale experimental disturbance gradient in
communities of benthic invertebrates. Location: East coast of Australia
(16.48oS – 36.43oS) Time period: 66 weeks (August 2012 – November 2013)
Major taxa studied: Benthic marine invertebrates Methods: Communities were
grown on acrylic tiles and subjected to four experimental disturbance
events over a 66-week period. At the end of this period, the effect of
increasing disturbance extent (0-100% community clearance) on alpha and
beta-diversity measures were assessed. Results: In the tropics, richness
and diversity increased with disturbance as the creation of free space
allowed for the colonisation of new recruits. In temperate communities,
increasing disturbance led to a monotonic loss in species richness and a
more hump-shaped relationship in evenness and diversity. In the tropics
compositional change with increasing disturbance was driven by changes in
species identities and abundances as the cover of rare species increased.
In temperate regions, however, changes in species abundances were
primarily responsible for compositional changes, reflecting the shift to
algal dominance under conditions of high disturbance. Main conclusions:
The shape of the diversity-disturbance relationship changed over latitude
indicating that the concept of “intermediate” disturbance differs amongst
these communities. Faster rates of increases in bare space, loss of
species richness and a shift to algal dominance suggest that, in these
systems, higher latitude communities are more susceptible to negative
outcomes of high levels of disturbance than lower latitude communities. We
discuss how differences in community dynamics, including competition,
regional diversity and availability of propagules, help explain this
pattern.