Abstract

Environmental change rarely occurs as a single, isolated event; organisms and communities typically experience one stressor against the backdrop of another that has already passed. Arunima Sikder’s doctoral thesis examines whether an organism’s past environment shapes its response to the environment that follows, and whether that influence propagates upward to affect the stability of the communities to which these organisms belong.

The thesis addresses this question in Synechococcus sp., a globally significant marine primary producer, using thermal and chemical stressors as its two environmental drivers. Working across three levels of biological organization, the study examines how past environments shape responses to subsequent ones—whether they occur in sequence, fluctuate, or occur in combination—using functional traits as the common metric for measuring these responses.

The results reveal three key findings. First, sensitivity to a stressor depends on the sequence of exposure, not on the stressor alone. Second, response diversity predicts community stability only when measured under the community’s actual acclimation history, rather than under sustained conditions as conventional wisdom assumes. Third, an apparent contradiction in biodiversity–ecosystem function theory—a negative relationship between functional diversity and performance.

Together, these findings suggest that sensitivity, response diversity, and functional diversity should be treated as state-dependent quantities rather than fixed properties, with implications for how the performance of biological systems is measured and modeled under increasingly variable environmental conditions.

Jury

  • Prof. Alice DENNIS (UNamur), Chair
  • Prof. Frederik DE LAENDER (UNamur), Secretary
  • Prof. Maren STRIEBEL (Carl von Ossietzky University Oldenburg)
  • Prof. Giulia GHEDINI (Monash University)
  • Prof. Eli THORÉ (UNamur)