Community Ecology: Energy Flow, Foraging, Predation, and Keystone Species

Vocabulary practice flashcards spanning salmon-derived nutrient subsidies, energy transfer efficiencies, food webs, climate disturbances, optimal foraging, functional responses, antipredator defenses, and keystone species dynamics.

Anadromous

The life history strategy in which fishes, such as Pacific salmon, migrate from the ocean into freshwater rivers to spawn.

Marine-Derived Nitrogen (MDN)

Nitrogen originating in oceanic environments that is delivered to freshwater and terrestrial riparian ecosystems by returning, spawning, and dying Pacific salmon.

Foliar $\delta^{15}\text{N}$

An isotopic measure representing the ratio of $^{15}\text{N}$ to $^{14}\text{N}$ in plant leaves, used to demonstrate that riparian species (such as Sitka spruce, devil's club, and ferns) absorb salmon-derived nitrogen at spawning sites.

Basal Tree Growth Response to MDN

The tripling of radial tree growth in riparian Sitka spruce (Picea sitchensis) near salmon spawning reaches, enabling trees to reach a $50\,\text{cm}$ diameter in approximately $86\,\text{years}$ compared to $307\,\text{years}$ at reference sites.

Salmon Riparian Feedback Loop

A positive feedback process where spawning salmon deliver marine-derived nutrients that fertilize large riparian trees, which eventually die and fall into streams to create coarse woody debris and pool habitats essential for salmon fry.

Food Web

An ecological network organizing species according to their trophic or energetic interactions, providing a foundational summary of community feeding relationships.

Trophic Level

A functional feeding tier within an ecosystem that groups organisms sharing similar methods of acquiring energy and nutrients (e.g., primary producers, primary consumers, secondary consumers).

Microbial Loop

A pathway in the upper water column (epilimnion) where bacteria consume dissolved organic matter (DOM) and are in turn eaten by protozoa, recycling carbon and nutrients back into the classical planktonic food web.

Sloppy Feeding

Inefficient consumer feeding behavior (such as zooplankton partially consuming phytoplankton) that ruptures cells and releases dissolved organic carbon (DOC) directly into the water.

Second Law of Thermodynamics (in Ecology)

The thermodynamic principle dictating that during each energy transfer between trophic levels, approximately $90\%$ of usable energy is degraded into low-quality heat, leaving roughly $10\%$ available to the next trophic level.

Gross Primary Production (GPP)

The total amount of chemical energy and biomass manufactured by all autotrophic organisms in a specified ecosystem area over a given timeframe.

Net Primary Production (NPP)

The autotrophic biomass remaining after producers satisfy their own metabolic and respiratory requirements, representing the total plant biomass accessible for consumption by herbivores.

Secondary Production

The rate at which heterotrophic consumers synthesize new living biomass by feeding on plants, animals, microbes, fungi, or detritus over a given area and interval.

Assimilation Efficiency ($A/I$)

The proportion of ingested energy ($I$) successfully absorbed across the gut wall into the body ($A$), reflecting an animal's efficiency at extracting nutrients from its consumed food.

Growth Efficiency ($P/I$)

The proportion of total ingested energy ($I$) converted into new consumer biomass or production ($P$); low values typically reflect high metabolic respiration rates or poor dietary quality.

Inverted Aquatic Biomass Pyramid

A trophic structure where primary producer biomass is smaller than consumer biomass at any single moment, occurring because phytoplankton reproduce rapidly and sustain high turnover and productivity despite low standing crop.

Eutrophication

The accelerated nutrient enrichment of aquatic systems (typically driven by phosphorus in freshwater lakes), resulting in explosive primary production and algal blooms.

Trophic Cascade Hypothesis

The concept that top-down predation by higher trophic consumers (piscivores) alters the biomass and abundance of intermediate consumers, ultimately cascading down to control lower trophic levels and primary producer biomass.

Disturbance

Any discrete event in time that disrupts ecosystem, community, or population structure and alters substrate availability, resource levels, or physical environments.

Press Disturbance

A continuous or long-lasting ecological disruption (such as anthropogenically driven climate change), contrasted with an acute, transient pulse disturbance.

Climate vs. Weather

Weather refers to short-term physical conditions of the atmosphere (such as temperature and precipitation), whereas climate represents atmospheric trends and patterns observed over periods spanning $30$ to thousands of years.

Phenological Mismatch

An ecological desynchronization caused by climate warming, as seen in Lake Washington where spring stratification and phytoplankton blooms advanced by roughly $19\text{--}21\,\text{days}$ while photoperiod-cued Daphnia emergence did not shift, leading to starvation.

Handling Time

The duration of time an individual predator requires to pursue, capture, subdue, consume, and digest a single unit of prey.

Functional Response

The behavioral intake response of an individual predator to changes in environmental prey density, categorizable into Type I, Type II, and Type III curves.

Type I Functional Response

A linear increase in feeding rate proportional to prey density up to a maximum saturation point, typically found in passive filter feeders with negligible handling time constraints.

Type II Functional Response

A consumption curve that rises at a decelerating rate until reaching an asymptote, representing predators whose intake is limited primarily by handling time and gut capacity.

Type III Functional Response

An S-shaped (sigmoidal) feeding curve where predation rates remain low at low prey densities due to prey refugia or search image development, accelerate at intermediate densities, and level off at high densities.

Optimal Foraging Theory (OFT)

An evolutionary model predicting that natural selection favors individuals that maximize net energy gain per unit foraging time, balancing handling times and search costs (e.g., bluegills selectively consuming $4\,\text{mm}$ prey).

Coevolutionary Arms Race

A reciprocal evolutionary process in which adaptations developed by prey to minimize predation exert selective pressure on predators to evolve enhanced predatory mechanisms over generations.

Defensive Allomones

Chemical compounds synthesized and released by organisms that deter, poison, or repel potential predators to the physiological benefit of the producer.

Reflex Bleeding

A defensive antipredator response exhibited by aquatic insects, such as stonefly nymphs, that auto-hemorrhage noxious fluids from their joints when attacked.

Kairomones

Chemical secretions released by predators that are opportunistically detected by prey species to induce behavioral, morphological, or life-history defenses (e.g., helmet formation in Daphnia).

Diel Vertical Migration (DVM)

A predator avoidance behavior where zooplankton ascend into food-rich epilimnetic surface waters under darkness at night and retreat to deeper, darker hypolimnetic waters during daylight.

Keystone Species

A species whose total ecological impact on community structure and diversity is disproportionately large relative to its low biomass or abundance.

Dominant (Foundation) Species

A community member that exerts significant control over community structure and habitat provision primarily by virtue of its high abundance and substantial biomass (e.g., forest trees, corals).

Carrying Capacity ($K$)

The maximum population size of a given species that a particular habitat can sustainably support over time without environmental degradation.

Keystone Predator

A top predator (such as Pisaster sea stars in rocky intertidal habitats) that maintains community species diversity by suppressing competitively dominant prey below carrying capacity, preventing competitive exclusion.

Ecosystem Engineer

An organism (such as beavers, American alligators, or burrowing crayfish) that builds, alters, or destroys physical structures in the landscape, generating habitat complexity and heterogeneity.