What goes on below?

The above-ground diversity of plants in the Cape Floristic Region is legion.  But what about arthropods?  And what about below-ground?

Several years ago at the start of my postgraduate research training and career, I was part of a team of researchers from Stellenbosch University who were fascinated simply by how life works and how it is structured in the natural world. My interest in springtails was piqued on a research trip to sub-Antarctic Marion Island. Where my collaborators were absorbed by insects, I became fascinated with Collembola: how many species were there on the island? What were the differences between invasive and indigenous species, and what were these differences?

Image: Collembola such as the Seira species pictured above, show high turnover in the Cape Floristic Region. Photo by Amy Liu.

FROM THE COVER: read the article on which this post is based …
Janion-Scheepers C, Bengtsson J, Duffy, GA, Deharveng L, Leinaas HP, Chown SL (2020) High spatial turnover in springtails of the Cape Floristic Region. Journal of Biogeography, 47:1007–1018. https://doi.org/10.1111/jbi.13801

So I set about learning how to find out, with help from Steven Chown and Hans Petter Leinaas. Naturally, as soon as I had completed this work for my Masters thesis I asked another seemingly simple question: ‘How many species of springtails are in South Africa and what do they do?’ In the Cape Floristic Region, this question is almost inevitably also accompanied by speculation about whether any groups other than plants have also shown spectacular radiation. So my Ph.D. project and the rich collaboration with my co-authors were born, and the research that led to this paper.

The extraordinary diversity of plants across the Cape Floristic Region is characterized by considerable species turnover among sites. Studies so far on phytophagous insects show similarly high turnover, but their patterns are closely coupled to those of their hosts. Thus, if the mechanisms underlying high plant turnover are not unique to plants, similar patterns of turnover should also be seen in non-herbivorous arthropod groups. In this study, we tested this hypothesis for the Collembola fauna of the Fynbos biome. Thus, our research is testing major diversification ideas using an independent group to do so.

Diversity of environment and flora in the Cape Floristic Region

Most studies to date on alpha and beta diversity of the Cape Floristic Region have been on above-ground plants and invertebrates such as insects, showing there is extremely high turnover. This is the first study to investigate if this high turnover is also true for below-ground organisms. We foundthe alpha diversity of Fynbos Collembola assemblages is quite similar to that elsewhere, given energy availability and so on. By contrast, beta diversity is really high, and in particular considering the small distances among sites. That beta diversity is also characterized predominantly by species turnover. We were simply astounded by the high turnover we found for Collembola. Every site had new species, and some genera were extremely rich in diversity, with most species being undescribed. These patterns of unremarkable alpha diversity, but high turnover among sites are comparable to many Fynbos plant groups. The mechanisms giving rise to high beta diversity of the plants have probably led to high diversity in springtails independently of any host association. That’s an awesome finding!

This unexpected level of diversity in Collembola made clear one of the knottiest problems I had to overcome: Taxonomy. The world really needs more taxonomists. I have now had over a decade of training by arguably the world leader in Collembola taxonomy, Dr. Louis Deharveng from the Museum National d’Histoire Naturelle in Paris, France. This also led to more collaborations with other Collembola taxonomists specialising on certain families. So I am one more person that knows the systematics, at least partially, although we still need more. This problem is global and is a real barrier to finding out how our world works and what makes it work.

(This image, above, and below) Development and habitat change mean trouble for all of biodiversity in the Cape Floristic Region. The gems are both obvious and subtle, and all of them need conservation.
Photos by Steven L. Chown.

Reflecting on the whole process, one of the major outcomes of the project has been an affirmation of my fascination in the drivers of turnover and the idea that some groups, other than plants and host-specific arthropods, have responded to the history and conditions of the Cape Floristic region to become highly diverse.

This project was also the start of several international collaborations with soil ecologists and taxonomists, and as mentioned above sparked my interest in taxonomy. This project also prompted our team to start using DNA barcoding to aid in species identification, and we now have a database of almost 2,500 sequences for Collembola in South Africa (www.boldsystems.org). These collaborations have led to several long-lasting partnerships and friendships.

Following this study, we now have several ongoing projects which have evolved from this one using Collembola as model organisms, sampling over a wider region, exploring their physiology, diet, taxonomic and molecular diversity, and their functional roles in the fynbos and other ecosystems in South Africa. Through this multidisciplinary approach, we hope to understand what the mechanistic drivers behind these shared above-below ground diversity patterns are. Our knowledge is certainly growing, although I still wonder: how many species of springtails are in South Africa and what do they do?

Written by:
Charlene Janion-Scheepers – Lecturer, University of Cape Town, South Africa

Additional information:
@cjanion; @grant_duffy; @steven.chown1

For additional images of Collembola, see chaosofdelight.org.

Acknowledgements: I am thankful to SLC and GD for comments on this blog post.


Published by Biogeography.news

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