Limitations and future directions
Using the ‘pulse’ and ‘press’ traits to describe the environmental
stressors helped to introduce the mechanisms, and highlight the
similarities, that may result in biodiversity change, regardless of the
GC they are associated with. However, the lack of consistency in results
may be due to the simplistic nature of using just a single trait for
each stressor. Indeed, proposed 30 different traits to characterize
environmental stressors, a classification scheme that they found worked
well when applied to a soil microbial experiment. further stated that
stressors should not only be classified based on their traits but also
sources, temporal overlap, mode of action, and co-tolerance to determine
their similarities and aid predictions. Unfortunately, there is
currently no classification scheme that assigns environmental stressors
to such a wide range of different traits, which would be needed to fully
realise the benefits of this approach.
As not all GCs and environmental stressors had enough data to enable in
depth investigation, further questions remain as to the specific impacts
of habitat fragmentation and invasive species on soil fauna. It would be
expected that both habitat fragmentation and invasive species alter the
soil enough to impact many soil organisms . Alternatively, more
moderators may be needed to capture the heterogeneity (e.g., habitat
type; ), and/or more complex interactions between the moderators .
The breadth of this meta-analysis provides us with insight and
comparisons that have previously not been possible. However, it also
reduces our ability to ‘zoom’ into specific effects, such as different
doses of GCs (stressor concentrations, amounts), temporal aspects or
community composition shifts. Therefore, further experimental work is
needed to elucidate variations in exposure to different GCs and their
influences on soil biodiversity, as well as more specific meta-analyses.
Although this meta-analysis contained a large number of data points,
there still was a lack of data for specific questions, for example,
habitat fragmentation and invasive species as discussed above, different
pollutant types, and better representation of taxonomic groups. An
additional focus on additional diversity indices, such as community
composition and beta diversity metrics, may also be insightful. We hope
that by highlighting the relative lack of data, these gaps may be
overcome in the future with additional studies.
One aspect of the study of global change that is being highlighted in
the scientific literature as an important avenue of research is the
potential impact of two or more GCs simultaneously . Many meta-analyses
that looked at the additive and interactive effects of GCs on
biodiversity have found that the interactions between GCs are important
. Although it might be anticipated that the interaction between GCs may
result in greater negative impacts than expected based on the singular
GCs , there is the potential for the presence of two GCs to result in
less of a negative impact than expected . Given the changing world that
we are in, and that GCs rarely act singularly on biodiversity , this
would be the most important avenue to study further, and is indeed
possible within a meta-analysis framework when factorial data are
present .