Organismal Ecology: How Individuals Sense, Regulate, and Cope with Environmental Change

Response to the environment

Any behavioral, physiological, or structural change that helps an organism maintain internal stability (homeostasis) and survive and reproduce under specific external conditions (e.g., temperature, water availability, predators, light, salinity).

Homeostasis

Maintenance of internal conditions within tolerable ranges despite external environmental change; typically achieved through feedback regulation rather than keeping conditions perfectly constant.

Proximate (how) cause

The immediate mechanism producing a response (e.g., sensory receptors, nervous/endocrine signaling, hormones, gene expression changes).

Ultimate (why) cause

The evolutionary explanation for a response—how the trait or behavior increases survival and reproductive success (fitness).

Stimulus

A measurable environmental change that can trigger a response (e.g., temperature drop, dehydration, predator odor, increasing day length).

Receptor (sensor)

Specialized cells or proteins that detect a stimulus and initiate the response pathway.

Signal transduction and coordination

Internal communication processes (e.g., nervous system, endocrine system, plant hormone pathways) that transmit information from receptors to effectors.

Effector

A muscle, gland, organ, or growth process that carries out the response once it receives a signal.

Negative feedback

A regulatory mechanism in which a change triggers responses that counteract the change, reducing deviation from a set point (common in homeostasis).

Positive feedback

A regulatory mechanism that amplifies a change, driving a process further in the same direction; less common for maintaining stability but useful for completing certain processes.

Taxis

Directional movement toward or away from a stimulus source; requires directional sensing (comparing stimulus direction).

Kinesis

A non-directional change in activity level (speed and/or turning rate) in response to stimulus intensity, increasing the chance of encountering favorable conditions without “aiming” toward the stimulus.

Ectotherm

An organism whose body temperature is strongly influenced by environmental temperature; often relies heavily on behavioral strategies to regulate temperature.

Behavioral thermoregulation

Regulating body temperature through behaviors such as basking, seeking shade or burrows, or changing posture/orientation to sun or wind.

Migration

Seasonal long-distance movement that tracks resources, breeding sites, or favorable climates; commonly cued by factors such as day length (photoperiod), temperature, and food availability.

Dormancy

A lowered metabolic state that helps organisms survive unfavorable periods; includes hibernation (winter), estivation (hot/dry), and diapause (hormonally controlled developmental pause, common in insects).

Circadian rhythm

An internal ~24-hour cycle in physiology and behavior that is commonly reset by light cues (zeitgebers).

Endotherm

An organism (many mammals and birds) that maintains body temperature largely through internal heat production and physiological regulation.

Vasodilation

Widening of blood vessels near the skin, increasing heat loss to the environment and helping cool the body.

Vasoconstriction

Narrowing of blood vessels near the skin, reducing heat loss and helping conserve body heat.

Osmoregulation

Control of water balance and solute (salt/ion) concentrations; crucial in environments with strong differences in water availability or salinity (e.g., freshwater vs marine conditions).

Stomata

Pores in the leaf surface that regulate gas exchange (CO2 entry) and water loss (transpiration); opening stomata increases CO2 uptake but also increases water loss.

Guard cells

Cells surrounding stomata that control stomatal opening/closing; turgid guard cells open stomata, while loss of water causes stomata to close.

Abscisic acid (ABA)

A plant hormone that increases during drought stress and promotes stomatal closure, reducing water loss but also limiting CO2 entry and often lowering photosynthesis.

Auxin (in phototropism)

A plant hormone whose redistribution drives differential growth; in shoots, auxin accumulates more on the shaded side, stimulating greater cell elongation there and bending the shoot toward light.