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Posts from the ‘Modeling’ Category

New paper: modeling the sensitivity to climate change

In a new paper out in Scientific Reports, we use a matrix population model to test how sensitive populations of fairy shrimps are to changes in climate. The stepwise modeling procedure allows to calculate the long term population growth as a measure of fitness. If it is positive, the population will survive, if it is negative it will not. It does this by calculating, for each generation, how many eggs would be produced based on known life history traits of the species and a measure of environmental quality of the inundation (in this case represented by inundation length).

For most species it is very difficult to know how they would respond to changes in climate. However, for our fairy shrimp we have a lot of background information that allows us to make educated guesses about which life history traits could be important. We know for this species that it requires a specific amount of time to reproduce which is related to how long a pool can hold water and on the conditions they need to hatch. We also know how much eggs they can produce per day, how many eggs hatch during each inundation etc…


Population of the fairy shrimp Branchipodopsis wolfi in a temporary rock pool on a mountaintop in South Africa

The length of these inundations is one environmental parameter (of many) that will change under changing climates. But it is an important one that is directly linked to fitness. Shorter inundations means less inundations that are long enough for reproduction.

We were – and are – still ignorant about how these species will respond to these changes. However, the model does allow us to test which life history traits could be important to maintain long term survival of the populations. As such it shows which traits could help populations to survive.

One of the conclusions of the study is that, when inundations are short, it would be beneficial to make sure that a lower fraction of eggs would hatch during a given inundation. Such a mechanism could be an example of a risk spreading theory that is consistent with predictions of evolutionary bet hedging theory.

It is still a simplistic model, so it does not tell us how things will go in the future. It does not capture tradeoffs among life history traits nor the evolutionary potential of the populations.  Yet, it still narrows down the range of possible future scenarios of these populations by showing what the consequences for population survival would be if populations could respond adaptively or plastically and change there life history traits.





NEW PAPER: Exploring the link between ecology and biogeography in African vertebrates

In a new paper out in the journal Ecography, Falko Buschke tried to explain the distribution patterns of all terrestrial vertebrates that occur in sub Sahara Africa using environmental variables and spatial dispersal related variables.

He found that when you map Africa based on how much variation is explained by dispersal based processes vs. environmental niche based filtering, you can see the contours of the biogeographic regions. This suggests that community structuring processes differ among regions within biogeographic realms.

He also showed that corrections for range size are necessary to extract ecologically meaningful patterns from variation partitioning results.

Finally, he found that unexplained variation was highest in species with small distributions… which is worrying from a conservation perspective as these are often threatened. While we can quite accurately predict distributions of widespread animals, we don’t know very well why certain rarer species are range restricted.


An African Black Rhino. One of the species in Falko’s database.

NEW PAPER: Simulating the effects of climate change on habitat suitability and connectivity in a pond metacommunity

In a new paper published in Freshwater Biology, PhD student Karen Tuytens builds further on a hydrological model for temporary pools I developed in my PhD. Temporary pools are expected to be strongly impacted by the effects of global environmental change. Being directly dependent on precipitation (and occasionally ground water) for filling, changes in precipitation and/or evaporation will have an impact on the length (hydroperiod) and the frequency of inundations.


The model that was developed is a realistic simulation model which can be parametrized for individual pools and which can predict the water levels on a day to day basis based on nothing but pool morphometry and precipitation and evaporation data. By making use of historic climate it is possible to reconstruct the inundation history of a pool and, hence, reconstruct the long term disturbance regime which is relevant to explain both patterns of diversity as well as adaptive trait variation among populations.

However, the main advantage explored in this paper is the ability to simulate the effects of different IPCC climate change scenarios on inundation patterns. Karen did not only show that inundations are likely to be become shorter resulting in shorter growing seasons for aquatic fauna, she also modeled connections that are formed between pools during heavy rains. Under future scenarios that include less precipitation and higher evaporation, these connections formed less frequently. Overall, this shows that climate change can not only affect habitat suitability but also connectivity in clusters of aquatic habitats. This is relevant since different levels of connectivity can have pronounced effects, not only on the persistence of populations but also on diversity and the functioning of metacommunities.

The code of the model is optimized for the R programming environment and is readily available in the appendix of the paper. At the moment, the model is optimized to work in very simple aquatic habitats such as rock pools which have no groundwater influence and don’t leak water. However, Karen is currently extending the model to make it applicable for more complex temporary aquatic habitats such as temporary wetlands.