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Understanding global change from the perspective of the Proteaceae
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By Nicky Allsopp, Karen Esler, Frank Schurr and Jasper Slingsby
There are over 9 000 plant species in the Cape Floristic Kingdom ... so why would scientists focus on studying plants in one family with around 330 species in this area?
Professors Karen Esler (Stellenbosch University) and Frank Schurr (Universities of Montpellier and Potsdam) and Dr Nicky Allsopp (SAEON) set out to explore this phenomenon by organising a symposium and workshop on Proteaceae at this year’s Fynbos Forum. The Proteaceae Symposium was made possible with funding from a German-South African Year of Science award.
Researchers from four continents presented talks on the evolution and ecology of members of the Proteaceae. Scientific presentations at the meeting shed light on the demography of Proteaceae under environmental change, drivers of the group’s extraordinary diversity and interactions between Proteaceae and other organisms, all topics which help inform our understanding of the impacts of global change.
The Protea Atlas
Apart from the attraction of working on a distinctive, beautiful and easily recognisable group, there are several reasons why this interest has developed in the Proteaceae. Foremost among these is the Protea Atlas which provides detailed distribution data on all the Western Cape Proteaceae. This Atlas, initiated by Dr Tony Rebelo (South African National Biodiversity Institute) comprises of thousands of records contributed by citizen scientists.
The Atlas has seen the Proteaceae becoming a classic group for species distribution models in the face of climate change. Detailed work on the evolutionary relationships between members of the Proteaceae has also contributed to turning the Proteaceae into model organisms for biodiversity research since one can trace when specific traits developed in response to past environmental pressures. For example, serotiny (the ability to store seeds in cones to be released only after fire) appears to have developed at least 28 million years ago among some species in the Proteaceae.
Proteas and Global Change
Hope that the Proteaceae may survive higher ambient temperatures in the future was presented by Dr Tony Rebelo, who demonstrated that certain species showed some germination at temperatures 3.5oC above those at present. Jane Carlson and Kent Holsinger (Connecticut, USA) showed that populations from cold and dry environments have the least plastic leaf traits. If this is a general pattern, plants from such extreme environments may have the lowest potential for rapid responses to environmental change.
Another concerning issue was that the results of three surveys by Annelise Schutte-Vlok (CapeNature), Tineke Kraaij (South African National Parks) and Katharina Mayer (Potsdam, Germany) have shown that current fire intervals are frequently too short for slow-maturing, non-sprouting species to set seed.
Predicting vulnerabilities of species to climate change
To assess how native Proteaceae will respond to future changes in climate, land use and fire regimes John Silander (University of Connecticut, USA), Frank Schurr and Jörn Pagel (Universities of Montpellier, France and Potsdam, Germany) presented studies on variation in growth, reproduction and mortality across the geographical ranges of several Fynbos Proteaceae. Plant, leaf and floral traits determine the outcomes of plant-plant and plant-pollinator interactions, how these interactions may in turn determine the reproductive output of individual plants and, hence, future community composition. The hope is that such trait-based demographic studies will improve our understanding of existing communities, and help to predict vulnerabilities of species to climate change.
Fynbos Proteaceae are well suited for such trait-based studies since they show remarkable variation in plant size, leaf form, ability to survive fires and many other functional traits among species and populations which are expected to determine how these species respond to climate change.
Drivers of global change and their impact
An area of concern is how the drivers of global change may impact interactions between species which ensure the survival of individual species and the many diverse natural communities in Fynbos. Proteaceae interact with the animals that pollinate their flowers and disperse or predate their seeds. Some proteas are pollinated by rodents, attracted by musty scents developed in these species, others are pollinated by specific birds and insects which ensure successful seed set.
Anina Heystek (Stellenbosch University), analysing the Protea Atlas data base, showed that Proteaceae with the same pollination syndrome co-occur less frequently than expected by chance, suggesting that pollinator-mediated competition may shape large-scale plant distributions. Other animals also play a role in determining community composition by securing seed banks in the years between fires. We have long known that ants bury the seeds of proteas with elaiosomes on their seeds. These elaiosomes are fatty bodies which the ants harvest for food after they have buried the seed – keeping them safe underground from other predators and the heat of the next fire. Foreign invasive ants threaten this by stealing the elaiosome before they’ve buried the seed.
Yet other members of the Proteaceae aim for the same outcome of getting their seeds safely buried by following a more hazardous route. Ursina Rusch (University of Stellenbosch) showed that the seed-predating Cape Spiny Mouse hides seeds in small caches underground. Not only does the Cape Spiny Mouse forget where it hid some seeds, but another seed-eating Striped Mouse has difficulty finding buried seeds. While many of the seeds get eaten, some remain safely underground to germinate following the next fire.
While it could be validly argued that a great part of the Cape Flora has been ignored in this focus on members of the Proteaceae, it became clear at the Symposium that without this focus on a single taxon, patterns of response to environmental drivers would be less clear and we would be in a weaker position to understand the possible impacts of global change on our environment.
Acknowledgements
The special symposium and workshop on Proteaceae were held in celebration of the German-South African Year of Science at the 2012 Fynbos Forum, and were funded by a grant of the German Federal Ministry of Education and Research (BMBF), the South African Department of Science and Technology and the National Research Foundation (NRF).
