Genetic diversity and ecosystem recovery; there is more to biodiversity than species count.
It is widely agreed upon that Earth’s ecosystems are enduring a period of unparalleled assault. While exact, research based extinction rates are hard to come by, the focus of the world of conservation ecology seems to be the protection of species level diversity. While I do not disagree that this is an area of importance (there is plenty of research demonstrating the effects of species loss to given ecosystems), I think it is important to keep in mind that a good many ecosystems are relatively species poor and rely upon a dominant primary producer species to supply not only food but shelter and environmental stabilisation crucial for organisms at higher trophic levels. Examples of such ecosystems are fir forests, various marshes, kelp forests and seagrass meadows.
Considering this it is prudent not to ignore the importance of genetic diversity within these primary producer species as diversity at the genetic level provides sufficient phenotypic richness to increase the likelihood of successful resistance and/or resilience to disturbance (both natural and anthropogenic). This is something I loosely term ‘biological future proofing’. From a conservation perspective, this means not only maintaining species count but ensuring there is sufficient genetic diversity within important species to ‘future proof’ them against both predicted and unpredicted environmental change.
A small but very interesting body of research in this area has accumulated using Zostera marina (‘eelgrass’) ecosystems as models. The various observational and experimental studies have demonstrated that there is a positive correlation between genotype level richness and recovery from disturbance. The disturbances studied included grazing by geese, experimental clipping (simulation of grazing), climate warming (both artificial and natural) and the presence of a macroalgal bloom.
While the results are very compelling, I do have some concerns about the use of microsatellite markers as a measure of genetic diversity in this context. The problem is that microsatellite markers, as the science stands, are considered neutral and are thus not tied to any given phenotype that can exert real world effects. Hopefully in future further studies will be able to take advantage of further advances in molecular biology and genetics to measure diversity by directly comparing the sequences responsible for given phenotypes. It’s only a matter of time.
I have written a review of this research and its consequences, the abstract for which can be seen below. The full review with citations is available in pdf format via the link at the bottom of this post.
Zostera marina seagrass meadows as a model for the consequences of genetic diversity at the ecosystem level
While much work has been done to establish the consequences of species level loss for ecosystem function, comparatively little research has been done to establish a link between genetic diversity and ecosystem level functions. The last decade has seen a small body of research accumulate on the impacts of genetic diversity on responses to ecosystem disturbances in seagrass ecosystems based on the primary producer species Zostera marina. This research seems to indicate that a positive correlation exists between increased levels of genetic diversity and rate of recovery from various types of disturbance. A positive link is also demonstrated between periods of recovery in genetically diverse plots and increases in abundance of fauna dependent on Z. marina. While this research is of value as a starting block from which to launch further studies, the reliance of these studies upon neutral microsatellite sequences to assess levels of genetic diversity reduces the validity of the assumptions that can be made based upon these models. This is due to a lack of connection between neutral markers and phenotypes capable of influencing ecosystem level responses to disturbance.