It’s been a while. It seems like I did not post anything here for a full year. This is obviously related to COVID-19 delays, a cute baby, and other things that got in the way of life (more about that another time). But – finally – we got the first publication out from the work we started more than 3 years ago when I joined iDiv, and invited a bunch of cool people to work on dispersal of palms on Madagascar.
In particular – my PhD student Laura Méndez started her PhD project on exploring how the extinction of Madagascar’s megafauna has affected the community composition, spatial turnover, and genetic connectivity of palms with ‘megafaunal’ fruits across the island. She sampled several populations and species during a fieldtrip in 2019, and then explored occurence data from well-sampled palm communities to understand what the drivers are of palm spatial turnover (beta-diversity) and the distribution of palm traits.
This study was published in Ecography and all data and R scripts to run the analyses are also provided – here and here. The study is entitled “Megafrugivores as fading shadows of the past: extant frugivores and the abiotic environment as the most important determinants of the distribution of palms in Madagascar” and the story was also picked up by Nature Ecology and Evolution in their ‘research highlights‘.
Figure from the paper illustrating the communities of palms and frugivores and their community-averaged trait values.
In short – we show that the beta-diversity of palms is primarily linked to their dispersal by extant, present-day frugivores, and abiotic conditions, such as climate. This is expected because by feeding on the palm fruits and seeds, these frugivores are able to move plant species between communities and thereby determine the composition and structure of those plant communities. Interestingly, it is not just highly frugivorous lemurs that seem to be important, but also generalist birds and rodents, suggesting that occasional dispersal and secondary seed dispersal may be underappreciated dispersal modes of plants on Madagascar. The abiotic environment has been shown to be important in many parts of the world – constraining palm occurences to predominantly wet and warm places, or on soils with a particular mix of nutrients. Interestingly, the distribution of nowadays extinct frugivores (e.g., elephant birds, giant lemurs) also explained a small part of the beta-diversity of Malagasy palms. Their historical ranges were inferred used fossil data, and especially in the dry western part of Madagascar they may have been common in the past. Last – we show that the composition of the frugivory-related traits in the communities is also determined by a mix of variables related to both the abiotic and biotic environment, illustrating that palm species with large fruits may be suffering from seed dispersal limitation – either because the available frugivores may not be able to disperse the fruits over long distances, or because they are simply not available, or because of increasing human pressures leading to defaunation. This is worrying because these large fruits are also the species which often store most carbon, and their loss may thus have cascading effects on ecosystems and their functions and services for humans.
Madagascar remains an underexplored biodiversity hotspot with a unique evolutionary history and assembly of species. Hopefully soon we will know more about the genetic consequences of their megafauna extinctions for palms with large fruits.