 So good morning everyone. My presentation has been recorded due to the time zone difference between Sydney and Boulder and I apologize for this, but feel free to contact me via email if you need further information about clarification. So today I will be looking at quaternary biogeography from a geomorphological point of view looking at how surface processes might have influenced species migration across Southeast Asia. So this work is based on a collaboration with several researchers from the University of Sydney and different groups affiliated to the University of Grenoble, Exxon Province and Paris. So before diving into the course of the talk, I'm going to do a quick presentation of the tool that we are using and this tool is called Badland. It's an open source tool which is available from GitHub or the CSDMS model repository. So the tool itself has been designed to look at surface processes from regional to continental scale and over the years new functionalities, the functionality of the tool has been expanded and there are some of the main components, so we have the ability to impose different precipitation or different conditions, different tectonic regimes. We have a number of incision laws which go from detachment to transport limited. We are able to record stratigraphic architecture and for the marine environment we have also designed some functions to simulate carbonate platform generation, wave induced sediment transport and a gravity driven submarine clearance. So as mentioned in the tool's title we will focus on Southeast Asia and looking at the evolution of the Sandalshev over the last million years. So the Sandaland is of particular interest to biogemographers for its position at the junction between the Australia, ASEAN and Indomalaiso geographic provinces and the regional spaces diversification is actually attributed to several biologic and abiotic factors. So here we are going to focus on abiotic factors but several studies have already been done in the region to for example look at the impact of climate or volcanism but also obviously sea level, tectonic and all this might have contributed to space's diversification. One factor that clearly impacted the quaternary biological diversification as a region has been the eustatic sea level fluctuation mainly due to the geodynamic stability of the Sandalshev during the Pleistocene and also the shelf physiography which is characterized by its low elevation and low relief. So in that sense the speciation would increase during ASEAN and species dispersal will occur during the ASEAN. So this alternation would have remodeled the taxonomy composition of the region and sea level oscillation will act as a space's pump to increase the regional terrestrial biodiversity. However new findings have challenged this idea and the idea of the prevalence in the aesthetic control and have demonstrated that the Sandalshev was subsiding during the late Pleistocene and that basically the shelf was permanently superior before 400,000 years or around like MIS 11. So these results were presented in three different papers from Antaclarus and Laurent who are co-authors on this talk. One looking at the geodynamic and tectonic evolution of the region during the Pleistocene and the other looking at reef morphology and citizens raid across the Sandalshev. So if we are going to consider that Sandaland was actually exposed for such a if sorry we consider that Sandaland was actually exposed for such a long period of time with intermittent flooding only occurring during the last 400,000 years basically the role of sea level is called into question. So it suggests that additional factors are likely triggering the distribution of Sandaland biogeography. So here we are going to evaluate if surface processes could be one of these drivers. So to do so we first created our initial and forcing condition for our numerical model so the region is characterized by several large river systems the main one being the Mekong, Yorho, Siam and East Sanda river basins and we created our initial pilot topography and drainage system based on available data set from either phylogenic studies looking at freshwater fishes such as the one from the boom 2013 but also looking at well logs and seismic studies available for the region. Then after we imposed a climatic condition to simulate precipitation and we use a paleo-clim data set available from Dornetow 2018. Finally we have also tectonic forcing so uplift and sudinus rate which were constrained from regional tectonic studies and we also tested a bunch of two actually a static sea level currents and then we performed a series of multiple simulations but four main one where we vary this forcing condition so one with no tectonic forcing one with an uplift uniform sudinus rate of 0.25 millimeter per year suggested by paper from Monta Clarice and Laurent and then after we use our tectonic map with the two different sea level currents. So for each simulation we first analyzed the flooding history of the shelf and we extracted the percentage of exposed shelf over time and we found that we found that we found that except for the stationary case which is this black line in the graph the shelf was fully exposed prior to 400 000 years like in agreement with previous work where sediment bypassed the shelf and accumulate it and accumulating in this store offshore region during low stand and during marine conservation basically sediment fluxes are mainly deposited on the shelf which act as a sediment thing to sink. So after 400 000 years what we see is that marine incursions across the shelf are highly valuable and depend on the simulated scenarios even when considering the sea level with the highest amplitude so the red line here the flooding of more than 50 percent of the shelf only happen less than 20 percent of the time. So for all tested scenarios with imposter tectonic forcing we also see that land bridges between Borneo and surrounding region are disrupted on several occasions however the terrestrial connection between mainland Asia and Java is preserved and persists up to the other thing. So this results basically contradict the sea level into species pump hypothesis often used to explain this this species diversification found in the region since 400 000 years and it suggests that additional mechanism on driving dispersal and divergence of species in the region. So the next things we did was assessing the region geomorphological evolution by analyzing the characteristic of the main catchment and detailing the major phases of drainage spacing organization. So first we looked at the temporal change in catchment area main river length and shelf elevation for main drainage basins as shown in this figure here. So for all the forcing conditions we found that there is a clear relation as shown by this by the Pearson coefficient here the negative Pearson coefficient between sea level fluctuation and catchment characteristics. When we looked at cases where tectonic forcing is considered the sand ash experiences at least one phase of drainage basins capture of the Euro and Siam catchment for the model which is presented in this slide we see that there is a different phase of organization. So first we've got the Siam and West Borneo basins which are experiencing two capture. We also have the Jor River which is capturing numbering at waters from the Siam basins and finally we see that there is a large capture of part of the Siam at water by the East Sanda basins. So in previous studies physiographic changes were not accounted for and here we show that these changes could be critical to some species especially when considering lowland freshwater biota which have the ability to migrate across the chef from Southeast Asia to the Malay peninsula Sumatra Borneo and Java and this just by looking at how river captures have been organized over time. So we can postulate that successive phases of basins in isolation by fragmenting the habitat could actually foster speciation on the endemis and biodiversity across the region. So we also looked at from our landscape evolution simulation we also tried to quantify the impact of geomorphology by extracting three main landscape features. First the landscape elevation connectivity, the closeness to river and the local slopes. So these features were chosen as a common matrix to evaluate the impact of landscape on species dispersal and migration and from these three features we produce cost surface maps such as the one presented here that represents the cost required to move across different parts of the landscape and we use this surface map in a connectivity model which is called circuit scape to find a preferential paleo-migration pathways over the exposed chef. So the approach is basically agnostic assessing only the contribution of geomorphological properties and ignoring all the biotic or abiotic factors. So the output from the connectivity model shows a current distribution or current flow distribution which can be related to ecological processes. So in the figure that you see here the current flow distribution has been normalized using the z-score statistical parameter. Basically what we've got is highly constrained region which corresponds to the i-z-score or yellow region on this map which represents preferential corridors for species movement and in this corridor in this region even a small loss of aurora will disproportionately compromise connectivity and such and those be the critical regions for species migration. So during a chef exposure like in the middle figure here the region is characterized by mid elevation narrow high current flow pathways which follow the Johor and Siam main paleo drainage systems and these pathways form a continuous corridor across the chef. So during partially flooded periods which are the one on the right and left the chef is characterized by an extended region of high connectivity which are limited to the Malay Peninsula mountain range to the west and the shallow marine incursion to the east. So I want to stress the fact that our approach is not based on macroevolutionary models such as the one available for example with the species evolver component of land lab or the more recent work that has been proposed by Stokes and Perron. So to look at evolution of specific aquatic species under different physiographic changes these two approaches might provide better insights than the one which is proposed here. However one of the advantages of the method here is that we are not limited to aquatic species first and it is essentially easy enough to change or add to our question face to reflect either additional factors or species dependent characteristics. So finally from this current flow maps we can you know we are able to perform the hotspot analysis where we basically superpose each time slice in order to evaluate persistent corridors over geological timescales. So our combined hotspot maps shown here predicts that hotspots are preferentially located across the Paleo, Johor and Siam basins so that the red region here and cold spots are located on the shelf edge and eastern more side of the region between Borneo and Johor. So this geomorphology control hotspot region basically highlight a network of preferential well-connected biodiversity corridors that could favor species migration between the different regions of Southeast Asia. And in summary what we see from this study we can explore we basically explore a new way of looking at species evolution on the geological timescale and we found that physiographic changes might be one of the key drivers which are promoting the quaternary pump species pump observed in the region and we also believe that accounting forces regional scales landscape dynamics would improve biodiversity studies in the future and could help find past biodiversity hotspots and species migration pathways within this region but also other places on earth. So I would like to thank you for your attention and I wish you all a great CSDMS 2021 and everything. Bye.