Principles of Ecology

11:704:351

“Principles of Ecology” is team-taught by five professors. My section covers ecosystems ecology; this is a brief introduction to this section of the course

ECOSYSTEMS ECOLOGY

Professor Joan Ehrenfeld

The title “ecosystems ecology” sounds like a redundancy – ecology is often called the study of ecosystems, after all. But the sub-discipline called “ecosystems ecology” explores the subject of ecology from a different point of view than the branches of ecology covered earlier in the semester. Ecosystems ecology concerns phenomena that reflect the activities of groups of organisms (often groups that cut across broad taxonomic divisions),and especially focuses on those activities that result in the movement of materials between the physical (i.e. inanimate) world and the biological world. The field has been likened to the study of the “metabolism of the landscape.” Ecosystem ecologists seek an understanding of such questions as “how do the nutrient elements essential for all life move between organisms and the surrounding soil, water and air, and how do they move between organisms, and what controls these movements?” “what processes are altered, and how are they altered, when an area is polluted by nitrates from car exhaust? What effects do these pollutants have on the resident plants and animals?”

Ecosystems ecology has been placed last on the agenda for this semester for two reasons. First, it ties together all of the other branches of ecology: the physiology of individuals, the dynamics of populations and communities, and the flow of energy all must be considered in understanding how materials move through ecosystems. Second, the perspective of ecosystem ecology is crucial to understanding the multiple, global-scale changes to the Earth that are being perpetrated by humans.

We will first discuss the basic terms and concepts, then use these terms and concepts in reviewing the biology of the major nutrient and pollutant elements, and finally see how human-caused changes to the biology of these materials are causing ecosystems to change in ways that affect all life on Earth, including our own.

BACKGROUND THOUGHTS ON NUTRIENT CYCLES

Here are a few thought to keep in mind as we review the major nutrient cycles in different kinds of ecoystem, and with respect to the many changes taking place in the ecology of globe:

1. The cycling of nutrients is tied to the flow of energy through the chemical linkage of nitrogen, phosphorus, sulfur, etc. with carbon in the organic constituents of plant, animal and microbial biomass.

2. Nutrient cycling involves a traffic in electrons (i.e., redox reactions), which in turn is tied to the physiology of microbes (primarily) and also higher plants. These reactions may consume or produce energy.

3. The cycles of the different nutrients are similarly tied to each other, both through chemical linkages in the compounds that make up living matter, and also through the fact that the nutrient elements and carbon (=energy and structure) are needed in particular ratios (i.e., so many atoms of nitrogen needed per atom of carbon or per atom of phosphorus). These ratios differ among types of organism and among types of tissues within organisms.

4. Organisms differ in their requirements for particular nutrients, different chemical forms of each nutrient, and different ratios of nutrients. Therefore, the species composition of a community can affect, and in turn be affected by, the characteristics of the nutrient cycles in a given environment.

5. The above thoughts provide a pathway for linking the previous parts of this course (physiological ecology, populations, communities and energetics) to each other and to the whole ecosystem level.