BIOL 1010 | Chapter 37 Definitions

community

An assemblage of all populations of organisms living close enough together for potential interaction within a defined area.

community ecologists

Scientists who study the interactions among species within a community, including how these interactions affect species abundance, distribution, and overall community structure.

community dynamics

The variability or stability in the species composition of a community over time, caused by both biotic and abiotic factors.

interspecific interactions

Relationships between individuals of different species in a community that affect population structure and dynamics.

interspecific competition

Occurs when populations of two species compete for the same limited resource, negatively affecting both populations.

mutualism

An interspecific interaction in which both populations benefit from the relationship.

predation

An interaction in which one species (the predator) kills and eats another species (the prey).

herbivory

An interaction in which an animal consumes plant parts or algae, affecting the plant’s survival or reproduction.

ecological niche

The total use of biotic and abiotic resources by a species in its environment, including what it eats, where it lives, how it reproduces, and the conditions it requires to survive.

mutualism

An interspecific interaction in which both species benefit from the relationship.

camouflage

A predator-avoidance adaptation in which an organism’s coloration or pattern blends with its environment, making it difficult for predators to detect.

mechanical defenses

Physical structures such as spines, shells, or quills that protect an organism from being eaten.

chemical defenses

Toxic or unpalatable chemicals produced by an organism that deter predators, often advertised with bright warning coloration.

coevolution

A process in which two species reciprocally influence each other’s evolution through selective pressures over time.

parasite

An organism that lives on or in a host and obtains nourishment from it, often harming the host in the process.

trophic structure

The arrangement of feeding relationships in a community, showing how energy and nutrients move from one organism to another across different levels.

food chain

A linear sequence of organisms through which energy and nutrients pass, starting with producers and moving up through consumers.

producers

Organisms, usually autotrophs, that synthesize organic compounds from inorganic sources using energy from light or chemicals. Examples include plants, algae, and photosynthetic bacteria.

autotrophs

Self-feeding organisms that produce their own food from inorganic materials, such as plants and phytoplankton.

heterotrophs

Organisms that consume other organisms or organic matter for energy and nutrients; all consumers are heterotrophs.

primary consumers

Herbivores that feed directly on producers. Examples include grasshoppers, snails, grazing mammals, and zooplankton.

secondary consumers

Carnivores or omnivores that feed on primary consumers. Examples include mice eating insects, frogs, birds, and small fish eating zooplankton.

tertiary consumers

Carnivores that feed on secondary consumers. Examples include snakes and larger predatory fish.

quaternary consumers

Top predators that eat tertiary consumers, such as hawks on land and killer whales in the ocean.

detritus

Dead organic material, including plant litter, animal wastes, and dead organisms, that serves as a food source for detritus-feeding organisms.

scavengers

Organisms that consume large carcasses or dead animals left by predators. Examples include crows and vultures.

detritivores

Organisms that feed on decaying organic material, breaking it down into smaller pieces. Examples include earthworms and millipedes.

decomposers

Organisms, mainly fungi and prokaryotes, that chemically break down organic material into inorganic compounds for use by producers.

decomposition

The process of breaking down dead organic matter into inorganic compounds, recycling nutrients through the ecosystem.

food web

A complex network of interconnecting food chains showing how energy and nutrients flow through multiple pathways in a community.

species diversity

A measure of the variety of species in a community, combining both the number of species (species richness) and the proportional representation of each species (relative abundance).

species richness

The total number of different species present in a community.

relative abundance

The proportion or percentage of each species relative to the total number of individuals in a community.

monoculture

An ecosystem or agricultural area dominated by a single species, often with low genetic diversity.

polyculture

An ecosystem or agricultural system with multiple species grown together, increasing species and genetic diversity.

keystone species

A species whose impact on its community is disproportionately large relative to its abundance or biomass, often playing a critical role in maintaining community structure and species diversity.

disturbances

Events such as storms, fires, floods, droughts, or human activities that alter biological communities by removing organisms or changing resource availability.

ecological succession

The gradual process of change in species composition in a community following a disturbance.

primary succession

Succession that occurs in a virtually lifeless area with no soil, such as new lava flows or glacial rubble, where colonization begins with autotrophic bacteria, lichens, and mosses.

secondary succession

Succession that occurs in an area where a disturbance cleared an existing community but left the soil intact, such as after fires, floods, or abandoned farmland.

invasive species

Non-native organisms that spread widely in new habitats and cause environmental or economic harm by outcompeting, preying on, or displacing native species.

ecosystem

A system consisting of all organisms in a community and the abiotic environment with which they interact, forming a network of energy flow and chemical cycling.

energy flow

The passage of energy through an ecosystem from producers to consumers to decomposers, with energy entering as sunlight and leaving as heat.

chemical cycling

The transfer and recycling of chemical elements within an ecosystem between biotic components (producers, consumers, decomposers) and abiotic components (air, water, soil).

primary production

The conversion of solar energy into chemical energy by producers through photosynthesis, forming the base of an ecosystem’s energy supply.

gross primary production (GPP)

The total amount of chemical energy produced by photosynthesis in a given area and time, measured in units of energy (kcal or joules) or biomass (tons of organic material).

net primary production (NPP)

The chemical energy remaining after producers use some for their own cellular respiration, representing the energy available to consumers in the ecosystem.

energy pyramid

A graphical representation of energy loss at each trophic level in a food chain, where each tier’s width corresponds to the amount of chemical energy or biomass available at that level.

omnivores

Organisms that eat both plants and animals, allowing them to occupy multiple trophic levels in a food web depending on their diet.

biogeochemical cycles

The movement of chemical elements through biotic (living) and abiotic (nonliving) components of ecosystems, allowing nutrients to be reused by organisms.

abiotic reservoirs

Nonliving sources or stockpiles of chemical elements, such as the atmosphere, soil, water, or rocks, from which organisms obtain essential nutrients.

nitrogen fixation

The biological process by which certain bacteria convert atmospheric nitrogen gas (N₂) into ammonia (NH₃) or ammonium (NH₄⁺), forms usable by plants.

denitrifying bacteria

Soil bacteria that convert nitrate (NO₃⁻) back into nitrogen gas (N₂), returning it to the atmosphere and reducing the soil reservoir of usable nitrogen.

nitrifying bacteria

Soil bacteria that convert ammonium (NH₄⁺) into nitrite (NO₂⁻) and then nitrate (NO₃⁻), making nitrogen more accessible to plants.

eutrophication

The enrichment of aquatic ecosystems with nutrients, particularly nitrogen and phosphorus, which increases primary production and often leads to algal or cyanobacterial blooms, oxygen depletion, and reduced species diversity.

sustainability

The practice of managing and conserving Earth’s resources to meet the needs of the present without compromising the ability of future generations to meet their needs, balancing human use with the preservation of ecosystem services.