Ecology BIO C 322 Ecosystem Cybernetics and Stability

Ecology (BIO C 322) Ecosystem Cybernetics and Stability

Cybernetics • Science of controls. • Homeostasis (set-point controls; at organism level & below). – Brain centre controlling body temperature. • Homeorhesis (diffuse controls; above organism level, ecosystem level). – Interplay of material cycles & energy flows. – Decomposers release of nutrients. • Feedback positive & negative.

Homeorhesis: Control Diffuse and Internal – Controller Unknown? ? ?

Homeorhesis Input Primary subsystem Secondary subsystem System Output

Reward Feedback • Positive feedback (increased growth or survivorship) by an organism or trophic level that sustains the survival of its food resource. • Are predators always harmful for prey? • Are parasites always harmful for hosts?

• In food chains, herbivores & parasites (downstream components) promote the welfare of their prey & hosts (upstream components).

Ecosystem Stability • Resistance stability: Ability of an ecosystem to resist disturbance & maintain its structure & function intact. • Resilience stability: Ability to recover when the system has been disturbed.

Resistance Stability: Ability to Remain Steady in Face of Stress

Resilience Stability: Ability to Recover Quickly After Stress

Ecosystem Function Time

California Redwood Forest: High Stability (thick bark), Low Resilience in Face of Fire

California Chaparral: Low Stability, High Resilience in Face of Fire

Simulation of Ecosystems • Helpful in study of larger ecosystems. • Monitoring the effect of pollutants. • Microcosm: e. g. Microbial culture in a bottle/flask/test tube. – “Derived” systems obtained directly from nature as environmental samples; – “Gnotobiotic” systems obtained from pure/axenic laboratory cultures. • Mesocosm: e. g. Large outdoor tank. • Macrocosm: e. g. Large ecosystems, Earth.

Fish aquarium, a Microcosm

Spacecraft as an Ecosystem

• Storage type of ecosystems: For short space journeys Storage of O 2, CO 2, H 2 O, food. • Regenerative types: For trips to distant planets or establishment of space colonies. – Should be able to thrive as systems (closed to entry/exit of mass), without resupply from Earth. • What will be the requirements of “regenerative spacecraft ecosystems”?

Biosphere-2, A Remarkable Mesocosm

• An enclosure in Sonoran Desert, Arizona USA. • 1. 27 ha, glass-covered, air-tight. • 1991 -93: 8 people sealed inside; emerged healthy & alive. • Contained miniature natural habitats like deserts & rain forests, agricultural land, domestic animals; radio, TV, phone. • ACs to maintain temp, input of solar energy.

• Of the total waking hours: – 45% time on growing/preparing food, 25% on maintenance/repairs, 20% in communication, 5% on small research projects, 5% for relaxation/recreation. • During last 6 months, O 2 deficiency, so replenished from outside. • Reduction in light by glass, cloudy weather outside, rich organic soil reduced photosynthesis, microbial activity.