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The phosphoregulation of proteins with multiple phosphorylation sites is governed by biochemical reaction networks that can exhibit multistable behavior. However, the behavior of such networks is typically studied in a single reaction volume, while cells are spatially organized into compartments that can exchange proteins. In this work, we use stochastic simulations to study the impact of compartmentalization on a two-site phosphorylation network. We characterize steady states and fluctuation-driven transitions between them as a function of the rate of protein exchange between two compartments. Surprisingly, the average time spent in a state before stochastically switching to another depends nonmonotonically on the protein exchange rate, with the most frequent switching occurring at intermediate exchange rates. At sufficiently small exchange rates, the state of the system and mean switching time are controlled largely by fluctuations in the balance of enzymes in each compartment. This leads to negatively correlated states in the compartments. For large exchange rates, the two compartments behave as a single effective compartment. However, when the compartmental volumes are unequal, the behavior differs from a single compartment with the same total volume. These results demonstrate that exchange of proteins between distinct compartments can regulate the emergent behavior of a common signaling motif. 

Ecological succession explored at the secondary and postsecondary level is often limited to terrestrial ecosystems. The emphasis is traditionally placed on how deforestation leads to ecological succession. However, aquatic ecological succession is just as important and allows for many connections to be made with other ecological concepts. Succession initiated by beavers (Castor canadensis) in particular links both aquatic and terrestrial ecosystems over time. We present a guide to an inquiry-based lesson for AP Environmental Science and undergraduate ecology courses that explores the effects of aquatic and terrestrial ecological succession initiated by deforestation and beavers. Specifically, the focus is ecological succession and its effects in both terrestrial and aquatic ecosystems. In this lesson, students (1) engage with a preassessment and broad overview of ecological succession, (2) explore authentic research data representing secondary succession in beaver ponds, (3) explain data using detective activities, (4) elaborate with a mystery pond, and (5) evaluate their new understanding by comparing a pre- and postassessment. This lesson plan meets the objectives for AP Environmental Science Biology courses as well as the core concepts and competencies for undergraduate biology education from the Vision and Change report by the American Association for the Advancement of Science in 2011.