Ecosystem disruption and animal responses

Unit 8 of AP Biology asks two broad questions: how do organisms respond to their environment, and what happens to populations and ecosystems when that environment is disrupted? Exam questions on both are almost always scenarios — a plant under attack, a rodent in the cold, a lake after fertilizer runoff, a new beetle on an island — and they reward reasoning from a few core ideas rather than memorized examples. This material trains that reasoning on invented scenarios.

The first group of questions deals with responses and communication. Plants damaged by caterpillars release a chemical signal, and their neighbors start producing defenses before they are attacked. Fish use electrical signals to warn the rest of a school. You separate innate behaviors, performed correctly the first time, from learned ones. A heritable preference for night or day activity comes under natural selection when daytime temperatures rise, and you predict how the population changes without assuming that mutations appear because they are needed.

The second group links energy to physiology. A small rodent has a higher metabolic rate per unit of body mass than a large predator, so it needs relatively more food in the cold. A desert endotherm avoids overheating by seeking shade rather than by changing its metabolism. Water fleas that reproduce asexually while food is plentiful and switch to sexual reproduction when conditions worsen show how reproductive strategy can follow energy availability.

The third group is about disruption. An invasive beetle succeeds because it enters a niche free of predators and competitors. Fertilizer runoff causes an algal bloom whose decomposition lowers dissolved oxygen and whose shade kills submerged plants. A table of pesticide concentrations, rising from the water to fish-eating birds, shows biomagnification. A genetically uniform potato field and a mixed one meet the same new disease, illustrating why ecosystems with little diversity are less resilient. A heterozygote advantage question connects environmental pressure to the maintenance of genetic variation.

The material offers a quiz and a flashcard deck. The quiz explains every prediction in terms of energy, selection or ecosystem structure. The flashcards review metabolic rate and body size, innate and learned behavior, behavioral thermoregulation, induced plant defenses, the fight-or-flight response, biomagnification, eutrophication, invasive species, heterozygote advantage, why mutations are not directed, and the trade-off between asexual and sexual reproduction. The course does not require specific behavioral or physiological mechanisms, and the questions do not rely on them.

• Explain how behavioral and physiological responses, including signaling, affect survival and reproductive success
• Relate body size to metabolic rate per unit mass and compare endotherms and ectotherms
• Explain shifts between asexual and sexual reproduction in terms of energy availability
• Predict the effects of invasive species, eutrophication and biomagnification
• Explain why ecosystems with little diversity are less resilient to disruption

Practice material written by Zestly, based on the College Board AP Biology course framework (topics 8.1, 8.2, 8.6 and 8.7, with topic 2.2 on metabolic rate and body size).