Royal Netherlands Institute for Sea Research

Koen Siteur

Postdoc
Phone number
+31 (0)113 577 457
Location
Yerseke
Function
Postdoc

Expertise

  • Ecological modelling
  • Mathematical/numerical model analysis
  • Complexity research
  • Ecological regime shifts
  • Spatial self-organization

Understanding "out-of-equilibrium" ecosystem dynamics

A way to understand the complex dynamics of ecosystems is by developing and analysing ecological models. Key mechanisms behind ecosystem dynamics have been identified this way. Examples include discontinuous ecosystem degradation through critical transitions and spatial pattern formation caused by scale-dependend feedbacks. 

Currently we have a relatively good understanding of ecosystems and ecological models that have reached an equilibrium state. However, current human-induced environmental changes - such as climate change and sea level rise - occur at a much higher pace than natural changes, thereby not allowing ecosystems to reach an equilibrium state. In addition, the restoration success of degraded ecosystems depends on the "out-of-equilibrium" dynamics, which are often neglected in theoretical studies.

My research aims to extend established theory by studying the "out-of-equilibrium" dynamics of ecological models. The focus of my research is on ecosystem restoration and on the adaptation of ecosystems to rapid environmental change.

Human-induced environmental changes often occur much faster than natural change. Here the rate of change in atmospheric greenhouse gas concentrations is shown for the past 20.000 years (Joos & Spahni, 2008; PNAS).

 

Rate-induced critical transitions in ecosystems

Understanding the response of ecosystems to environmental change is one of the main objectives in the field ecology. Models suggest that once environmental conditions change beyond some threshold value, ecosystems can shift towards a degraded state. My research shows that in some ecosystems such shifts may or may not occur depending on the rate of environmental change (compare the model runs in the figure below). For example, in salt marshes accretion of sediment enables the marsh vegetation to be sustained as the sealevel rises. However, models suggest that if the rate of sealevel rise exceeds the sediment accretion rate, salt marsh vegetation may "drown", leading to a collapse of the salt marsh ecosystem.

Ecosystems can shift to a degraded state if environmental changes are too fast (Siteur et al., 2016; OIKOS).

 

Spatial patterns as indicators for resilience and restoration

Theory suggests that adaptations of spatial patterns in ecosystems can be used as an indicator for ecosystem resilience (Rietkerk et al., 2004; Science). Advanced model analyses has shown that the adaptation of patterned ecosystems to environmental change can be understood by studying the equilibrium states of so-called reaction-diffusion models (Siteur et al., 2014; Ecological Complexity).

My current research suggests that in a particular class of ecosystems, patterns will never reach an equilibrium. This means that the patterns in these ecosystems are are constantly changing, even without external changes or disturbances. This class of ecosystems includes seagrass meadows like the one in the photo below. I am currently trying to understand the dynamics of these patterns in order to extend the indicator framework to include this class of patterned ecosystems.

Patterns in seagrasses (Van der Heide et al., 2012; PLOS One).

 

Current projects

My current research is funded by the EU project MERCES (Marine Ecosystem Restoration in European Seas) and by personal grant awarded to dr. Quan-Xing Liu (State Key Laboratory of Estuarine and Coastal Research; East China Normal University).

 

Past projects

I attained my PhD at the Copernicus Instite of Sustanable Development of Utrecht University. My PhD research was a collobaration project with Leiden University and was part of the NWO Complexity programme. To download my PhD thesis, please click here.

(c) 2016, Martin Dirks.