Appendix D

Glossary

Accommodation – A response of a biological system to an environmental stressor that restores the system to its normal or baseline condition or establishes a new set point.

Acute Effect – The severe, often lethal, effect of a stressor on an individual that occurs rapidly and is of short duration (see also Chronic Effect).

Acute Exposure – Exposure to a stressor that occurs for a single, discrete period of time (see also Chronic Exposure and Intermittent Exposure).

Adaptive Management – A systematic approach for improving resource management by learning from management outcomes.

Additive Stressor Effect – The combined effect of two or more stressors is considered additive when the shape of the dose–response function of either stressor does not change in the presence of the other stressor (see also Antagonistic Stressor Interaction, Interactions Among Stressors, Stressor, and Synergistic Stressor Interactions).

Adverse Outcome Pathways – A structured representation of biological events leading to adverse effects that is often considered in risk assessments.

Aggregate Exposure – The combined exposure to one stressor from multiple sources or pathways integrated over a defined relevant period: a day, season, year, or lifetime.

Allostatic Load – An organism’s cumulative physiological degradation resulting from exposure to stressors, as well as from heightened activity of physiological systems or changes in metabolism.

Antagonistic Stressor Interaction – The interaction of two or more stressors is considered antagonistic if the resulting effects are less than the sum of the effects of the individual stressors (see also Additive Stressor Effect, Stressor, and Synergistic Stressor Interactions).

Bias – The difference between a true population parameter and the expected value of the estimate of that parameter (see also Precision).

Chronic Effect – A stressor effect that does not immediately result in death or reproductive failure, but persists or is irreversible, and may influence long-term survival or reproductive success.

Chronic Exposure – Ongoing or continuously occurring exposure to a stressor (see also Acute Exposure and Intermittent Exposure).

Cumulative Risk – The combined risk from exposures to multiple stressors integrated over a defined relevant period: a day, season, year, or lifetime.

Direct Effects – When considering the influences and interactions among species, and between species and their abiotic environment, direct effects are the proximate impacts that one species or factor has on another species or factor without the effect occurring via an intervening species or factor. In the interaction webs in Chapter 6, these direct effects are depicted as single arrows pointing from one node to another node (see also Indirect Effects and Interaction Web).

Dose – The magnitude or amount of a stressor that is directly experienced or ingested, inhaled, or absorbed by an animal, ideally measured by a dosimeter on the animal.

Dose–p(response) Function – The relationship between the dose or dosage of a particular stressor and the probability of a particular response.

Dose–Response Relationship – The relationship between the amount of exposure (dose) to a stressor and the resulting changes in behavior, physiology, or health (response).

Driver – A biotic or abiotic feature of the environment that affects populations directly and/or indirectly by changing exposure to a single (or multiple) extrinsic stressor.

Ecological Driver – A biotic or abiotic feature of the environment that affects multiple components of an ecosystem directly and/or indirectly by changing exposure to a suite of extrinsic stressors. Ecological drivers may operate on multiple species at varying trophic levels, and may affect multiple ecosystems.

Exposure – Contact with or experience of a stressor, ideally measured in the environment near the animal.

Extrinsic Stressor – A factor in an animal’s external environment that creates stress in the animal (see also Intrinsic Stressor and Stressor).

Health – The ability of an organism to adapt and self-manage.

Hearing Threshold – The lowest intensity of a sound at a particular frequency that an organism is able to hear. These thresholds are defined as a function of frequency.

Hearing Threshold Shift – An increase in an organism’s hearing threshold (decrease in sensitivity), often caused by a high-intensity sound. This shift can be either temporary (temporary threshold shift, TTS) or permanent (permanent threshold shift, PTS).

Homeostasis – The tendency of the physiological systems of an organism to maintain internal stability in response to stimulus that might disturb its normal condition or function.

Indirect Effects – Interactions between species or between species and the abiotic environment that occur through one or more intervening species or abiotic factor.

Interaction Web – A means of considering the relationships and interactions among species, and between species and their abiotic environment as defined by Dunne et al. (2002). An interaction web is premised on the idea that the distribution and abundance of species in an ecosystem are determined by the interactions among and between species and abiotic environmental elements (see also Direct Effects and Indirect Effects).

Interactions Among Stressors – Interactions occur when the presence of one stressor changes the shape of the dose–response function of the other stressor (see also Additive Stressor Effect).

Intermittent Exposure – Exposure to a stressor that occurs intermittently, repeatedly, or in cycles (see also Acute Exposure and Chronic Exposure).

Intrinsic Stressor – An internal factor or stimulus that results in a significant change to an animal’s homeostatic set point. Short-term internal stresses that evoke physiological responses occurring daily to maintain an organism near its homeostatic set points are not considered stressors, but natural aspects of an individual’s life cycle (e.g., lactation, migration, molting, and fasting) that result in significant changes to homeostasis are considered stressors (see also Extrinsic Stressor and Stressor).

Masking – Acoustic interference that impedes an organism’s ability to detect biologically important signals.

Noise – Sounds that are unwanted by or are not useful for a receiver.

Oxidative Stress – Stress to an organism caused by a disturbance in the balance of prooxidants and antioxidants.

Population Health – The distribution of health outcomes in a population or a subset of a population, as well as the determinants or factors that influence those outcomes.

Precision – A statistical measure of the repeatability of a sample or an estimate, given by the inverse of the variance (see also Bias).

Recovery – Restoration of normal function after withdrawal of a stressor.

Stressor – Any causal factor or stimulus, occurring in either the animal’s internal or external environment, that challenges homeostasis of the animal.

Synergistic Stressor Interactions – The interaction of two or more stressors is considered synergistic if the resulting effects are more than that of the sum of the effects of the individual stressors (see also Additive Stressor Effect, Antagonistic Stressor Interaction, and Stressor).