Map of the world

A generalist approach to specialization


About

Tanjona

My main research topic is to understand how environmental degradation namely habitat destruction and global warming affects biodiversity. A major empirical motivation is the patterns of loss and fragmentation of natural forest in Madagascar and their consequences on its unique biodiversity. I mainly use and develop mathematical models based on physiological, ecological, and evolutionary principle to understand the pattern and process of biodiversity loss.

I obtained a MSc in applied mathematics under the supervision of Arthur Randrianarivony at the University of Antananarivo in Madagascar. Afterwards, I did a PhD with Ilkka Hanksi and Otso Ovaskainen at the University of Helsinki in Finland followed by a postdoc with Emma Goldberg at the University of Minnesota, USA. Currently, I am doing a second postdoc at the University of Wisconsin-Madison working on abrupt changes in ecological system (ACES). It is multidisciplinary project lead by Monica Turner and involves four postdocs and four coPIs. For more information about the exciting project and the fantastic team, see ACES.


Research

short description

Extinction threshold and specialist species

Species with narrow niche breadth are expected to be most vulnerable to habitat destruction. The minimum amount of habitat necessary for the persistence of species is called extinction threshold. The kernel of my work is to better understand factors that influence species' extinction threshold and related metrics (e.g. transient time). I ask how the extinction threshold changes as a function of endogeneous processes such as niche breadth, niche overlap, types of competition, dispersal ability, and exogeneous processes such as the rate of habitat loss and fragmentation, distrubance, stochasticity. My approach is mainly theoretical based on niche theory, metapopulation, and metacommunity models. More broadly, the idea is to develop of comprehensive theory about interactions among the drivers, the processes, and the patterns of extinction.

short description

Body size and thermal performance curve

The thermal performance curve describes the performance of a species as a function of ambient temperature. Knowing the thermal niche can be essential in understanding how a species can be affected by warming, cooling, and increased variation of the thermal environment. Despite the ubiquitous relationship between body size and temperature, the role of body size in shaping thermal performance curve is unclear. I apply the concept of energy budget, i.e. the different between energetic input and output, to understand how thermodynamical, physiological, and ecological processes influcences the fitness of a species. More broadly, the motivation is to develop theoretical foundation for a generalized fitness landscape based on endogeneous and exogenous factors.

photo of a dodo

Phylogeography and radiation

Heterogeneous environment harbors greater biodiversity as it allows to pack a large number of specialist species. The kernel of my work is to develop statistical method for phylogenetic trees to infer the correlation between spatial and temporal heterogeneities and diversification rates. My research extends existing phylogenetic comparative methods for discrete character states to accommodate for more elaborate macroevolutionary model. To fit the model to data, I use Approximate Bayesian Computation. Given the challenge of using ABC, a significant part of my work involves developing summary statistics and test for model adequacy. More broadly, the question is to ask what we can and can't learn from phylogenetic network.

short description

Conservation in Madagascar

Madagascar is one of the hottest biodiversity hotspots. Its natural habitat is declining at rapid rate threatening a large number of its endemic plants and animals. The kernel of my work is to describe the pattern and process of habitat destructions in the past, at the present, and for the future. I combine pollen records, GIS data, ground truthing, and mathematical and statistical models to reconstruct forest cover and quantify spatio-temporal dynamics. Such map is the basis of trying to assess species' response to these disturbances with respect to their niche breadth, dispersal ability, life history, and evolution. More broadly, the project is a concrete application that encapsulates the three previous, more theoretical, projects.


Publications and in prep.

Ramiadantsoa, T., J. Sirén, and I. Hanski. 2017 (in press). Phylogenetic comparative method for geographical radiation. Annales Zoologica Fennica (special issue in honor of Ilkka Hanski)
Ramiadantsoa, T., O. Ovaskainen, J. Rybicki, and I. Hanski. 2015. Large-scale habitat corridors for biodiversity conservation: A forest corridor in Madagascar. PloS ONE 10: e0132126.
Ramiadantsoa, T. 2015. Spatial processes in ecology and evolution, and implications for conservation. Doctoral dissertation, University of Helsinki.


Outreach

Although at the borderline of what would be considered as outreach, I organize events that aim to underscore the importance of Mathematics in Life Sciences and to combat mathphobia. The target audience ranges from highschool to graduate level mainly in Madagascar and the events lie along a gradient of a casual lecture to a week long intensive worhshop. More broadly, I delight in communicating the role of science, especially conservation issues to the public.

My second hobby is to foster cultural exchanges mainly between Finland and Madagascar. I am a member of two societies: the Finnish-based (Suomi-Madagascar Seura) and the Malagasy-based (Madagascar-Finland). On top of cultural exchanges, we organize events to gather fund destined to help underprivileged students in Madagascar. Additionally, I have been organizing Malagasy language course for linguists students at the University of Helsinki.

At the intersection of the two goals above, we are now in the process of creating an association/society based in Madagascar—with close connection with Finnish researchers—to provide financial, material, and technical support for deserving Malagasy students in Life Sciences.


Contact & CV

My CV
Email: ramiadantsoa-AT-wisc.edu
Office: 436 Birge Hall, 458 Lincoln Dr, Madison, 53706 WI, USA
Twitter: @TRamiadantsoa