Ecology and Environment: Populations, Ecosystems and Conservation
Ecology and Environment covers organisms and populations, ecosystem function, biodiversity and conservation, and environmental issues caused by human activity.
Populations and interactions
- Population growth is exponential when resources are unlimited (rate r) and logistic when a carrying capacity K limits it, giving an S-shaped curve.
- Interactions: mutualism (+/+), commensalism (+/0), parasitism and predation (+/−), competition (−/−). Gause's competitive exclusion principle says two species competing for the same resource cannot coexist indefinitely.
Ecosystem function
- NPP = GPP − respiration; only NPP is available to consumers.
- Lindeman's 10% law: energy transfer between trophic levels is about 10%, so food chains stay short.
- Energy flow is unidirectional and non-cyclic; nutrients cycle - gaseous (carbon, nitrogen) and sedimentary (phosphorus).
Worked example
If producers fix 20,000 kJ, herbivores assimilate about 2,000 kJ, secondary consumers 200 kJ and tertiary consumers 20 kJ. A top carnivore therefore has very little energy available, which is why food chains rarely exceed four or five links.
Biodiversity and conservation
- Species–area relationship: log S = log C + Z log A.
- In situ conservation: biosphere reserves, national parks, sanctuaries. Ex situ: zoos, botanical gardens, seed banks, cryopreservation.
- Hotspots are regions of high endemism and high threat.
Environmental issues
- CFCs deplete stratospheric ozone (Montreal Protocol); CO2, CH4, N2O and CFCs are greenhouse gases.
- DDT biomagnifies along food chains; high BOD indicates organic pollution; eutrophication follows nutrient enrichment.
Traps
- Ozone is protective in the stratosphere but a pollutant at ground level.
- Energy is not recycled; nutrients are.
- Residual volume cannot be measured by simple spirometry, nor can it be traded for vital capacity.