The story of this article started already some three years ago at the BES symposium Demography beyond populations organised by Rob Salguero-Gómez and colleagues. Two of us were sitting in the auditorium and listening to talks, when almost simultaneously we had the same idea. “Do clonal species differ in their demographic characteristics? They definitely should, given their completely different way of growth! It must be quite easy to find out; we just merge CLO-PLA (the database of plant clonal traits) and COMPADRE.” Therefore, we started to work enthusiastically on the task even in the auditorium. Upon return from the in many aspects great Symposium, we met with Tomáš and told him of our idea and he said that he had had a very much the same idea for some time as well. The three of us set out to work and in a couple of months, we assembled the core of analyses of demographic characteristics of Central European clonal and non-clonal plant species.
So far, the story of the article had been very much as if narrated by a university PR department, yet here, the problems started to emerge. Results of our analyses indicated several effects of clonality and shoot ontogeny type on demographic characteristics, but taken together they did not enable us to come up with a coherent discussion of our paper. Jitka and Zdeněk started to suspect that there must have been at work biases in demographers’ choices of study species. They went through the original works, which the matrix population models (hereafter MPM) in COMPADRE are based on, and found that there are at least three fundamental ways how demographers study demography of clonal species (Fig. 1). Some researchers did not incorporate clonal propagation into MPMs at all. Others treated clonal propagation as a part of mother plant’s growth, while yet others saw clonal propagation as another reproductive pathway similar to generative reproduction. Interestingly and unfortunately as well, there indeed had been a bias in demographers’ decisions (Table 1). Clonal propagation of species with monocyclic shoot ontogeny type was more likely to be neglected, while in species with polycyclic shoot ontogeny type, i.e. overlapping shoot cohorts, clonality was often considered a part of mother plant’s growth. Only clonal propagation of species with monopodial shoot ontogeny type, which typically possess distinct leaf rosettes, was seen as means of reproduction.
At this point, the three of us ended many times in a debate, which of these three approaches is the right one to treat clonal propagation. Finally, during one such heated debate, Tomáš reached out into the bookshelf for now-classical Population biology of plants by J.L. Harper. Harper tackled the problem of defining an individual in the clonal plant’s population by defining a ramet, i.e. such rooted part of the genetic individual, which can live through all life-cycle stages. Reviewing existing demographic studies of clonal species through this prism indicated that in most species clonal propagation needs to be viewed as another mode of reproduction albeit with different genetic and evolutionary consequences. Treating clonal propagation as reproduction does not seem to be a suitable option only in species with very strong integration of ramets (e.g. Carex humilis).
As we were reviewing the original literature on demography of clonal species, a huge wealth of mainly practical MPM applications unfolded to us and we definitely see this as one of the main assets of MPMs. By drawing recommendations of the ways of clonal propagation incorporation into MPMs, we hope to help to raise the utility of MPMs also for asking general questions about plant demography and evolutionary biology.
Zdeněk Janovský, Jitka Klimešová and Tomáš Herben
The resulting publication of this initiative can be found here:
Janovský, Klimešová & Herben. Accounting for clonality in comparative plant demography growth or reproduction? Folia Geobotanica 1-10