Ch 13 introduces ecology at the organism and population level — responses to abiotic factors, adaptations, population characteristics (density, growth, age structure), growth models, and types of population interactions.
Abiotic factors: temperature, water, light, soil. Responses: regulate (homeostasis), conform, migrate, suspend (dormancy/hibernation/aestivation). Adaptations: desert plants (thick cuticle, CAM), polar mammals (blubber), altitude (higher RBC count). Allen's rule: shorter extremities in cold climates.
Population attributes: density (N/area), natality (births), mortality (deaths), sex ratio, age distribution. Growth models: exponential dN/dt = rN (unlimited resources, J-shaped), logistic dN/dt = rN(K−N)/K (limited resources, S-shaped, carrying capacity K). Interactions: mutualism (+/+, lichens), competition (−/−, Gause exclusion), predation (+/−), parasitism (+/−), commensalism (+/0), amensalism (−/0).
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Carrying capacity (K) is the maximum population size that an environment can sustain indefinitely given the available resources (food, water, space, etc.). In the logistic growth model, population growth slows as N approaches K. At N = K, growth rate becomes zero (births = deaths). K is not fixed — it can change with environmental conditions, resource availability, or human intervention.
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