Xiaoli Dong

I am a third year PhD student, working in fluvial landscapes, and am interested in spatial ecology.

As we walk along a stream or a river, we see different species are located in different places. Some sets of species colonize together to form a patch. Some patches have regular patterns while others do not and the geometry of patches may vary widely. Groups of patches are arrayed in space and water flow through and across them. Dissolved nutrients may be taken up or released and organisms can migrate from patch to patch.

Why are ecosystem components located where they are? Is the existing structure optimal for individual within it? How do we even define optimality? How does the spatial structure change over time? Is change directional? If so, what is the mechanism of directionality?

We are puzzled by what we see - the forms of landscapes - and we may contemplate the relationship between form and function. The form-function relationship is a classic concern in physiology and evolutionary biology; yet, the same question, asked at the level of an ecosystem, is stimulating: what is the relationship between landscape heterogeneity and its functioning? To be more specific: how is spatial heterogeneity formed, how does spatial heterogeneity influence ecosystem functioning, and how does ecosystem functioning feedback on spatial structures, if it does so at all? These are the major questions of my dissertation. I do both manipulative experiments in the field and simulation models to answer these questions.

While the amount of work that I can do for my degree is limited, the questions that I propose reach out to more fundamental ideas (1) form-function relationships in complex systems: In physiology, the relationship between form and function is clear: organs are the way they are because they are functional improvements generated by natural selection. However, the form-function relationship gets much more complicated in a complex system like a landscape-ecosystem, a hierarchical level where natural selection does not operate. Rather, self-organization may play an analogous role. This leads to another fundamental idea for ecosystems: (2) Natural selection (NS) vs. self-organization (SO): The definitions of the terms suggest that NS maximizes fitness whereas SO maximize the rate of energy/material flow. As an individual, an organism "tries" to maximize its survivorship and reproduction (e.g. to overcome water and nutrient limitation, etc.). As a group of interacting individuals, organisms are patterned into spatial structures. How are these individuals and collective forces reconciled? Does SO help increase fitness? My research endeavors to develop an integrated framework for ecosystems as complex adaptive systems. The broader theoretical foundation is rooted in the intersection of evolutionary theory and ecosystem ecology and in the intersection of community ecology and ecosystem ecology. I look forward to stimulating and challenging discussions on these topics.