Last week I attended the 8th Biennial conference of the International Biogeography Society in Tucson, Arizona (U.S.A.). The conference included symposia on modelling large scale ecological and evolutionary dynamics, experimental macroecology and building up biogeography from process to pattern. I presented the first results of my work on what may happen to megafaunal-fruited palm lineages under rapid global environmental change. These species with anachronistic fruits (> 4 cm in length) suffer from dispersal limitation because of recent extinctions of their large-bodied (megafauna) fruit and seed dispersers, such as gomphotheres, ground sloths and glyptodonts. However, we do not know how these palms have survived and evolved in the past – and whether they have suffered from extinction previously, during Quaternary climate change for example. In this talk I showed how over the last 2.6 million years (the Quaternary) these megafaunal-fruited palm lineages have experienced increasing extinction rates, but only in the Americas, and how they have evolved smaller fruits in Southeast Asia and Australasia. These smaller fruits may be adaptations to bird-dispersal in these dynamic island systems.
In a recent study, published in the journal Global Ecology and Biogeography, we investigate the evolution of leaf morphologies and climatic niches in the Proteaceae family. Proteaceae is a Southern Hemisphere family famous especially in Australia and South Africa for their impressive flowers and leaves. They are also tasty – the macademia nut belongs to the Proteaceae as well. Species in the Proteaceae family occur in all kinds of habitats, from montane forests to dry heathlands to tropical rainforests. During their evolution over millions of years, they managed to adapt to these variable and extreme habitats and climates, and their leaves may have helped them doing so. In this study we test whether open (e.g. mediterranean) and closed (e.g. tropical rainforest) habitats have selected for divergent leaf designs. We also show that the combination of certain leaf traits (e.g. small, sclerophyllous leaves with many teeth) in interaction with certain climatic niches (e.g. warm, dry, mediterranean) may increase diversification rates. This could explain some of the spectacular radiations within the family, for example in genus Banksia in Australia, or the Protea in Africa. Last, we show that there is more stochastic evolution of traits and niches in open habitats, which may explain some of the extreme forms and ‘misfits’ we find here. This “disparification” maybe even led to the process of reproductive isolation and speciation, via ecological divergence, and the ~1700 species of Proteaceae we find on Earth.
Onstein, R.E., Jordan, G.J., Sauquet, H., Weston, P.H., Bouchenak-Khelladi, Y., Carpenter, R.J., Linder, H.P. (2016). “Evolutionary radiations of Proteaceae are triggered by the interaction between traits and climates in open habitats.” Global Ecology and Biogeography 25 (10):1239–1251. doi: 10.1111/geb.12481
New video on rain forest evolution – and why we need the field of evolutionary biology to understand (and possibly change) their fate. Current threat by humans is increasing – but we don’t know how species will adapt, move, evolve. To have a better idea, we need to know which processes have influenced their evolution in the past. Using (phylo)genetics, ecology, functional traits and species distribution modelling we may better understand this.
If selected, this video will be shown at the Evolution meeting in Austin, Texas, this June – I won’t be there, but please vote if you are! Thanks!
Watch the video here.
Yaowu Xing and colleagues (Maria A. Gandolfo, Renske E. Onstein, David J. Cantrill, Bonnie F. Jacobs, Gregory J. Jordan, Daphne E. Lee, Svetlana Popova, Rashmi Srivastava,Tao Su, Sergei V. Vikulin, Atsushi Yabe, and H. Peter Linder) just published an article presenting the CAD (Cenozoic Angiosperm Database): Testing the Biases in the Rich Cenozoic Angiosperm Macrofossil Record in International Journal of Plant Sciences. The database is available from http://www.fossil-cad.net/.
The angiosperms currently have approximately 350,000 species, but how have angiosperms achieved such a high diversity? This question has bothered evolutionary biologists for centuries. The fossil database allows us to understand diversity changes in the past. Especially for angiosperms little is known about the temporal dynamics of species, lineage diversification and richness. It is structured by site (geographical information for each fossil assemblage), geology (name, age, epoch and stages of the formation), taxon (identification reliability and nearest living relatives of each taxon) and taxonomy. We hope that researchers will use the database to understand macro-evolutionary processes in angiosperms – possibly combining data from the database with inferences made from molecular phylogenetics.
For any questions concerning the database, contact Yaowu: yxing (at) fieldmuseum.org.
Have you ever wondered why – evolutionary speaking – the mediterranean floras of the world are so species-rich (e.g. the Cape of South Africa and Western Australia)? And why species look so similar in these systems (small, fibrous leaves adapted to deal with drought and low nutrient soils)?
We (Peter Linder and I) may give you a clue in a recently published study: “Beyond climate: convergence in fast evolving sclerophylls in Cape and Australian Rhamnaceae predates the mediterranean climate” in Journal of Ecology.
Although the very similar climatic conditions among mediterranean-type ecosystems were previously thought to drive this patterns of morphological ‘convergence’, it may not be the only important factor. Furthermore, it seems that these typical morphological characteristics of the plants (i.e. sclerophyllous leaves) may also have influenced their evolutionary fate: well-adapted leaves may reduce your chance to go extinct. Some groups of plants may therefore have evolved a whole bunch of species – all with similar functional traits – and so contributed to the extraordinary species diversity in these mediterranean-type ecosystems.
Last week I traveled back to my scientific roots (Wageningen University) to participate in a course on Structural Equation Modeling (SEM) given by Bill Shipley (he is particularly well known from his book on ‘Cause and Correlation in Biology‘). Structural Equation Models can be used to evaluate the sequence of variables affecting each other, and whether the underlying data supports such a sequence of events (also called path-models). For example – ecosystem functions (e.g. productivity and decomposition) can be affected by the biomass of the vegetation, and this can be affected again by the age of the plot (e.g. during succession) (Lohbeck et al. 2015).
As an evolutionary ecologist I was a bit of a misfit in the group. The group was dominated by Dutch PhD students and professors working in ecology (e.g. functional ecology, community assembly, soil science). They often collect data from plots; data which fit perfectly well in a structural equation model. My data did not – for a couple of reasons. My ‘plots’ are fossil assemblages (species richness = count data, problem 1), collected during the Cenozoic (different time scales, problem 2) and the variables we have are often not assemblage-specific but biased by time, and not normally distributed (e.g. CO2 concentration, temperature, latitude). On the positive side – I have a large sample size (N=666), which is necessary to have enough power to run these SEMs. So how can I test what factors directly and indirectly affect biodiversity (species richness)?
The solution. There is a solution. If your data is spatially, or phylogenetically biased, if your variables are not normally distributed, if you deal with binary/categorical/count data, if you have a nested design… The solution is the d-separation test. (d-sep cannot deal with ‘latent’ variables, e.g. unmeasured variables which may be important for the model).
d-separation in 6 steps:
- your hypothetical model (DAG: “Directed Acyclic Graph” avoid feedback loops in the model!) (for simplicity: A<- B <- C)
- write down each pair not connected by an arrow (in our example only AC)
- causal parents of these? (i.e. causal parent of A = B and of B = C. In our example of AC there is just one causal parent: B)
- run a suitable linear model/generalized linear model/PGLS/mixed model in which you test the effect of your pair variables, conditioned on the parent variables, in our example, of C on A conditioned on B (A ~ B + C)
- sum the probabilities (p values) of the slope coefficients of the regressions (in this case only one regression model was run, and we asses the coefficient of C and it’s p-value)
- calculate the C-statistic: -2 * ln (the sum calculated in step 5) and compare this to a Chi-square distribution. The degrees of freedom are calculated by 2* the number of regressions run (in our case 2 degrees of freedom). If p>0.05, you cannot reject you hypothesized model. If p<0.05 your data do not support the model.
Thanks to the d-separation test we, evolutionary biologist, can still test for causal relationships in our data, even if these data are far from ‘perfect’ or complete. It provides great potential for the field of phylogenetic comparative methods. But how exactly I’m not sure yet….
Madelon Lohbeck, Lourens Poorter, Miguel Martínez-Ramos, and Frans Bongers 2015. Biomass is the main driver of changes in ecosystem process rates during tropical forest succession. Ecology 96:1242–1252. http://dx.doi.org/10.1890/14-0472.1
To study and collect fruits, flowers and leaves of Magnoliales species, Hervé Sauquet, Thomas Couvreur, and I traveled to Sabah, Borneo. We just came back from a very successful trip in which we were amazed by the diversity of Magnoliales in the (mainly lowland) rainforests, and in particular the diversity of flowers and fruits of species belonging to the Annonaceae and Myristicaceae families. These collections wouldn’t have been possible without the help and expertise of our local team from the Forest Research Center (Sabah Forestry Department) in Sepilok.
For a short (informative and entertaining) summary of this trip, watch the video I made.