G.A. Williams ENVM 7003 MSc in Environmental Management INTRODUCTION TO ECOLOGY
The Ecosystem concept
What is a community/ecosystem? - an assemblage of species populations which occur together in space and time (as defined by energy flow) together with its physical environment (coined by Tansley, 1935). Properties are GREATER than the sum of the individual units. This is the basic unit that we have to deal with in a real world situation - a complex suite of interacting species and physical environmental factors - very difficult to totally understand and assess/manage. Spatial definitions of communities - (Gaia hypothesis) - how do we limit the ecosystem and how do we separate it from communities? The vital point is that ecosystem theory allows the biology of communities and populations to be compared using a COMMON currency (energy transfer and nutrient cycling) Ecosystem properties Biomass and Productivity Primary Production/Secondary Production Energy transfer/flow Nutrient cycling Primary Production and Secondary Production; (energy flow patterns) Global variation and limits to Primary and Secondary production Some definitions: Biomass Standing crop Primary productivity Mass of organisms/area (in terms of energy/dry matter per area) bodies of living organisms with an area rate at which biomass is produced per unit area per time
Net PP Gross rate - respiration of plants = actual production The fate of Primary production: Food chains; energy transfer Secondary production production of biomass by heterotrophs Decomposer and Grazer Pathways and their importance to ecosystem functioning Nutrient cycles Nutrient sources and sinks; the recycling of nutrients within an ecosystem; Local nutrient cycles within an ecosystem; global nutrient cycles - The Nitrogen cycle Lemming population fluctuation – The nutrient recovery hypothesis References Ecology, Individuals, populations and communities. M. Begon, J. Harper and C. Townsend (2nd ed). Blackwell Scientific Publications (especially Chapters 17, 20 & 21) Ecology: Theories and applications. P. Stiling, Prentice Hall (especially Section 5).