Summary of Chapter Concepts

Ecological systems and processes vary in time and space. Temporal variation occurs across a range of hours to years with the most extreme variation being the least frequent. Spatial variation also exists due to differences in climate, topography, and soils. The extent of the space affected by an event is usually positively related to an event’s duration in time.

Variable environments favor the evolution of variable phenotypes. Phenotypic plasticity, the ability to produce alternative phenotypes, is favored when organisms experience environmental variation, when reliable cues indicate the current state of the environment, and when no single phenotype is superior in all environments. Phenotypically plastic traits include behavior, physiology, morphology, and life history. Each type of trait differs in how fast it can respond to environmental change and whether the responses are reversible.

Many organisms have evolved adaptations to variation in enemies, competitors, and mates. Responses to enemies include changes in behavior that make individuals harder to detect, morphological defense that makes prey harder to capture, and chemical defense that makes prey less palatable. Responses to competitors include morphological changes in plants to make them better able to obtain resources, morphological changes in animals that make them better able to consume and digest scarce food, and behavioral strategies in animals that improve their ability to find scarce food. Organisms generally favor breeding with another individual, but a scarcity of mates can make self-fertilization a viable alternative for some species.

Organisms can evolve adaptations to variable abiotic conditions. Variation in temperature has favored the evolution of isozymes and switching between microhabitats. Variation in water availability has favored plants that can open and close their stomata and alter their root to shoot ratios. Variation in salinity has favored the evolution of novel ways of adjusting solute concentrations to minimize the cost of osmoregulation. Variation in oxygen can cause adaptive increases in red blood cells and hemoglobin to improve the uptake of oxygen at high altitudes.

Migration, storage, and dormancy are strategies used to survive extreme environmental variation. Migration allows organisms to leave areas with degrading environments, storage allows organisms to have an extra supply of energy to make it through periods of degrading environments, and dormancy allows organisms to shut down their metabolism until the harmful environmental conditions have passed.

Variation in food quality and quantity is the basis of optimal foraging theory. Central place foraging predicts that the amount of time spent foraging at a site and the amount of food brought back to a central nest will depend on the benefits gained over time at the site and the round-trip travel time to the site. Risk-sensitive foragers consider not only the energy to be gained, but also the predation risk posed. Many animals must also consider a range of alternative food items, the energy and abundance of each food item, and whether they should consume a mixture of food items to meet all of their nutritional needs.