Chapter 6: Ecosystems - Concepts and Fundamentals

Vocabulary terms and definitions covering ecosystem structure, trophic dynamics, thermodynamics, energy flow, and ecological succession from Chapter 6.

Ecosystem

The simplest and minimal entity that has the properties required to sustain life, consisting of a living ecological community and its nonliving physical-chemical environment interacting through chemical cycling and energy flow.

Ecological Community

The living part of an ecosystem, defined either as a set of interacting species found in the same place and functioning together to sustain life, or operationally as all species found in a given area.

Ecosystem Energy Flow

The movement of energy through an ecosystem from the external environment through a series of organisms and back to the external environment.

Food Chain

The linkage of who feeds on whom in an ecosystem, transferring energy, chemical elements, and certain compounds from creature to creature.

Food Web

The network of complex feeding linkages and interactions among multiple species within an ecological community.

Trophic Level

A feeding level consisting of all organisms in a food web that are the exact same number of feeding steps away from the original energy source.

Autotrophs

Self-nourishing organisms on the first trophic level, such as green plants, algae, and photosynthetic bacteria, that produce sugars from inorganic compounds using sunlight or chemical energy.

Heterotrophs

All organisms that do not make their own food and must obtain energy and nutrition by consuming other organisms.

Herbivores

Organisms on the second trophic level that feed directly on autotrophs such as plants, algae, or photosynthetic bacteria.

Carnivores

Meat-eating organisms that feed on herbivores (third trophic level) or higher-level carnivores (fourth trophic level and beyond).

Decomposers

Organisms, primarily bacteria and fungi, that feed on dead organic material and wastes, classified in the highest trophic level of an ecosystem.

Community Effect

An interaction where species have indirect, community-wide consequences on one another and on the overall diversity or structure of the ecosystem.

Keystone Species

A species, such as the sea otter, whose presence and activities have large, critical indirect effects on the persistence and diversity of many other species in its ecological community.

Watershed

An area of land defined by topography where all rain reaching the ground flows out through a single stream; commonly used as a practical boundary for terrestrial ecosystems.

First Law of Thermodynamics

The law of conservation of energy, stating that in any physical or chemical change, energy is neither created nor destroyed, but merely transformed from one form to another.

Second Law of Thermodynamics

The physical law stating that energy transformations can never be $100\%$ efficient, meaning whenever useful work is performed, some energy is inevitably degraded into heat.

Entropy

The thermodynamic measure of the decrease in order or the degree of disorganization and degradation of energy in a system.

Biomass

The total amount of organic matter present in an ecosystem, commonly measured per unit surface area as $\text{g/m}^2$ or $\text{MT/ha}$.

Biological Production

The capture of usable energy from the environment to produce organic matter (growth), which increases biomass over a given period.

Primary Production

The biological production of organic matter carried out by autotrophs such as plants, algae, and chemoautotrophs.

Secondary Production

The biological production of organic matter carried out by heterotrophs through growth and reproduction.

Gross Production (GP)

The total increase in stored organic matter or energy produced by an organism before any is consumed in respiration.

Net Production (NP)

The amount of newly acquired energy or organic matter remaining and stored after accounting for the energy used in respiration ($\text{NP} = \text{GP} - \text{R}$).

Respiration

The biological use of biomass and oxygen to release energy to do work, returning carbon dioxide and water to the environment.

Energy Efficiency

The ratio of energy output to input, commonly defined as the amount of useful work obtained from a given quantity of available energy.

Trophic-Level Efficiency

The ratio of biological production of one trophic level to the biological production of the next-lower trophic level, also known as food-chain efficiency.

Ecological Succession

The repeatable process of ecosystem recovery and development over time following a disturbance or initial creation.

Primary Succession

The establishment and development of an ecological community and ecosystem on a newly formed site where no ecosystem previously existed, such as on fresh lava flows or retreating glacier edges.

Secondary Succession

The reestablishment of an ecosystem following a disturbance that left behind remnants of the previous biological community, such as soil organic matter or seeds.

Early-Successional Species

Pioneer species adapted to the harsh, open, and unstable conditions of early stages of succession, characterized by small stature, rapid growth, and widely dispersing seeds.

Late-Successional Species

Plant species that dominate the late stages of succession, typically characterized by slower growth, longer life spans, shade tolerance, and competitive persistence.

Facilitation

A mechanism of succession in which an earlier-successional species alters the local environment in a way that makes it suitable for species characteristic of a later successional stage.

Interference

A successional interaction in which early-successional species alter the local environment such that it becomes unsuitable for later-successional species to establish or germinate.

Chronic Patchiness

A successional pattern occurring in highly disturbed or stressful environments (such as deserts or open oceans) where species neither help nor hinder one another, and no orderly sequence of species replacement occurs.