8 Ecology

Explain how the behavioral and physiological response of an organism is related to changes in internal or external environment.

• Organisms respond to changes in their environment through behavioral and physiological mechanisms.
  • Exclusion: Knowledge of specific behavioral or physiological mechanisms is beyond the scope of the AP Exam.
• Organisms exchange information with one another in response to internal changes and external cues, which can change behavior.

Explain how the behavioral responses of organisms affect their overall fitness and may contribute to the success of a population.

• Organisms communicate through various mechanisms (visual, audible, tactile, electrical, and/or chemical signals).
  • i. Organisms have a variety of signaling behaviors that produce changes in the behavior of other organisms and can result in differential reproductive success.
  • ii. Animals use signals to indicate dominance, find food, establish territory, and ensure reproductive success.
  • Exclusion: Knowledge of specific mechanisms of communication is beyond the scope of the AP Exam.
• Responses to information and communication of information are vital to natural selection and evolution.
  • i. Fitness favors innate and learned behaviors that increase survival and reproductive success.
  • ii. Cooperative behavior tends to increase the fitness of the individual and the survival of the population.
  • Exclusion: The details of the various communications and community behavioral systems are beyond the scope of the AP Exam.

Describe the strategies organisms use to acquire and use energy.

• Organisms use energy to organize, grow, reproduce, and maintain homeostasis.
  • i. Organisms use different strategies to r egulate body temperature and metabolism. Endotherms use thermal energy generated by metabolism to maintain homeostatic body temperatures. Ectotherms lack efficient internal mechanisms for maintaining body temperature, although they may regulate their temperature behaviorally by moving into the sun or shade or by aggregating with other individuals.
  • ii. A net gain in energy results in energy stor age, the growth of an organism, and increased reproductive output.
  • iii. A net loss of energy results in loss of mass, a decreas e in reproductive output, and, eventually, the death of an organism.
• Different organisms use various reproductive strategies in response to energy availability. Some organisms alternate between asexual and sexual reproduction in response to energy availability.

Explain how energy flows and matter cycles through trophic levels.

• Ecological levels of organization include populations, communities, ecosystems, and biomes.
• Energy flows through ecosystems, while matter and nutrients cycle between the environment and organisms via biogeochemical cycles. The cycles are essential for life, and each cycle demonstrates the conservation of matter. The cycles are interdependent.
• Biogeochemical cycles include abiotic and biotic reservoirs, as well as processes that cycle matter between reservoirs.
• The hydrologic (water) cycle involves water movement and storage within the hydrosphere. Reservoirs include oceans, surface water, the atmosphere, and living organisms. Processes include evaporation, condensation, precipitation, and transpiration.
• The carbon cycle involves recycling carbon atoms through Earth’s biosphere into organisms as carbohydrates and back into the atmosphere as carbon dioxide ()CO At the highest levels of organization, 2 . the carbon cycle can be simplified into four parts: photosynthesis, cellular respiration, decomposition, and combustion.
• The nitrogen cycle involves several steps, including nitrogen fixation, assimilation, ammonification, nitrification, and denitrification. These steps are performed by microorganisms in the soil. The largest reservoir of nitrogen is the atmosphere. In nitrogen fixation, nitrogen gas ()N2 is fixed into ammonia ()NH3 , which ionizes to ammonium (NH + 4 ) by acquiring hydrogen ions from the soil solution.
• The phosphorus cycle involves weathering rocks releasing phosphate ()PO 3− 4 into soil and groundwater. Producers take in phosphate, which is incorporated into biological molecules; consumers eat producers, transferring phosphate to animals. Phosphorus returns to the soil via decomposition of biomass, or excretion. Phosphate can also be incorporated back into the environment via decomposition of decaying organic matter.

Explain how changes in energy availability affect populations, communities, and ecosystems.

• Changes in energy availability can result in changes in population size.
• Changes in energy availability can result in disruptions to an ecosystem.
  • i. A change in energy resources such as sunlight can affect the number and size of the trophic levels. Trophic levels include producers; primary, secondary, tertiary, and quaternary consumers; and decomposers.
  • ii. A change in the biomass or number of producers in a given geographic area can affect the number and size of other trophic levels.

Explain how the activities of autotrophs and heterotrophs enable the flow of energy within an ecosystem.

• Autotrophs capture energy from physical or chemical sources in the environment.
  • i. Photosynthetic organisms capture energy present in sunlight contributing to primary productivity.
  • ii. Chemosynthetic organisms capture energy from small inorganic molecules present in their environment, which can occur in the absence of oxygen.
• Heterotrophs, which include carnivores, herbivores, omnivores, decomposers, and scavengers, metabolize carbohydrates, lipids, and proteins as sources of energy. Heterotrophs capture the energy present in carbon compounds by consuming organic matter derived from autotrophs incorporating matter into their tissues. 156AP Biology Course and Exam Description Ecology UNIT 8

Describe factors that influence growth dynamics of populations.

• Populations comprise individual organisms of the same species that interact with one another and with the environment in complex ways.
• Many adaptations in organisms are related to obtaining and using energy and matter in a particular environment.
  • i. Population growth dynamics depend on birth rate, death rate, and population size. Relevant equation: Population Growth— dN dt BD=− where dt = chage in time B = birth rate D = death rate N = population size dN = change in population size

Explain how the density of a population affects and is determined by resource availability in the environment.

• Carrying capacity is the sustainable abundance of a species that can be supported by the ecosystem’s total
• As limits to growth attributable to density-dependent and density-independent factors are imposed, a logistic growth model typically ensues. Relevant equation: Logistical Growth— dN dt rN KN K max= − where dt = change in time N = population size dN = change in population size rmax = maximum per capita growth rate of population K = carrying capacity

Describe the structure of a community according to its species composition and diversity.

• The structure of a community is measured and described in terms of species composition and species diversity. Relevant equation: Simpson’s Diversity Index— Diversity Index = −∑ n N1 2 where n = total number of organisms of a particular species N = total number of organisms of all species

Explain how interactions within and among populations influence community structure.

• Communities are groups of interacting populations of different species that change over time based on the interactions between those populations.
• Interactions among populations determine how they access energy and matter within a community.
• Relationships among interacting populations can be characterized by positive and negative effects and can be modeled. Examples include predator/prey interactions, cooperation, trophic cascades, and niche partitioning.
• Competition, predation, and symbioses, including parasitism, mutualism, and commensalism, can drive population dynamics.

Describe the relationship between ecosystem diversity and its resilience to changes in the environment.

• Natural and artificial ecosystems with fewer component parts, and with little diversity among the parts, are often less resilient to changes in the environment.
• Keystone species, producers, and essential abiotic and biotic factors contribute to maintaining the diversity of an ecosystem.

Explain how the addition or removal of any component of an ecosystem will affect its overall short-term and longterm structure.

• The effects of keystone species on the ecosystem are disproportionate relative to their abundance in the ecosystem. When they are removed from the ecosystem, it often collapses.

Explain the interaction between the environment and random or preexisting variations in populations.

• An adaptation is a genetic variation that is favored by selection and manifests as a trait that provides an advantage to an organism in a particular environment.
• Heterozygote advantage is when the heterozygous genotype has a higher relative fitness than either the homozygous dominant or homozygous recessive genotype.
• Mutations are not directed by specific environmental pressures.

Explain how invasive species affect ecosystem dynamics.

• The intentional or unintentional introduction of an invasive species can allow the species to exploit a new niche free of predators or competitors or to outcompete native species for resources.

Describe human activities that lead to changes in ecosystem structure and dynamics.

• Human impact accelerates changes at local and global levels. These activities can drive changes in ecosystems, such as the following, that cause extinctions to occur:
  • i. Biomagnification
  • ii. Eutrophication

Explain how geological and meteorological activity leads to changes in ecosystem structure and dynamics.

• Geological and meteorological events affect habitat change and ecosystem distribution. Biogeographical studies illustrate these changes.