NR 2030 Exam 2 Review: Community Ecology and Species Interactions

Vocabulary flashcards covering key terms, concepts, models, and ecological theories from the NR 2030 Exam 2 review material.

Competition

An interaction between two species that negatively affects each other, occurring because resources such as food and land are finite and organisms must fight for them.

Intraspecific competition

Competition that occurs between members of the same species; serves as a basic factor in natural selection.

Interspecific competition

Competition that occurs between members of different species.

Competitive exclusion principle

The ecological rule stating that two species competing for the same limiting resources cannot coexist in the same niche; a species can persist in the absence of the other, but not in its presence.

Interference competition

A direct ecological interaction where individuals fight each other directly for resources.

Exploitative competition

Indirect competition that occurs by reducing the resource pool, where one species uses a resource first and leaves less or none for other species (e.g., taller trees with wide canopies blocking sunlight).

Apparent competition

An indirect ecological interaction where two distinct prey species negatively affect each other's survival by sharing a common predator; an increase in one prey population attracts more predators, endangering the second prey species.

Priority effect

The ecological concept developed by Tad Fukami stating that the order of species arrival has a major effect on their success in integrating into a community.

Logistic Growth Model

A population model that demonstrates exponential growth until a population reaches its carrying capacity ($K$), where $t = \text{time}$ and $N = \text{population}$.

Lotka-Volterra Model

An equation model depicting the population dynamics between predators and prey, which is limited because it relies on assumptions not found in the real world ($\frac{dN}{dt} = rN\left(\frac{K - N - \alpha_{12}N}{K}\right)$ for Species 1 and $\frac{dN}{dt} = rN\left(\frac{K - N - \alpha_{21}N}{K}\right)$ for Species 2).

Competition coefficient

A factor in the Lotka-Volterra equations denoted as $\alpha_{12}$ (converting individuals of species 2 into species 1) and $\alpha_{21}$ (converting individuals of species 1 into species 2) that represent reciprocal opposites (e.g., if $\alpha_{12} = 4$, then $\alpha_{21} = \frac{1}{4}$).

Coexistence Theory

A theory explaining how competing species maintain biodiversity and avoid competitive exclusion.

Niche Theory

The theory stating that an ecological community consists of a limited number of niches, each occupied by only one species, leading to stable coexistence.

Modern Coexistence theory

A framework proposing that species coexistence is not explained by a single theory but lies along a spectrum where both niche and neutral processes act together.

Neutral theory

The theory that all individuals have identical average probabilities of birth, death, dispersal, and reproduction, where variations in species abundance arise from random drift, resulting in unstable coexistence.

Keystone predators

Predators that maintain community balance by limiting competitive dominant prey species that would otherwise dominate and negatively alter the ecosystem.

Character displacement

An evolutionary response to competition occurring across generations that results in phenotypic change and promotes coexistence by shifting species into different niches (e.g., Darwin's finches).

Niche partitioning

A process in which species that share the same niche coexist by dividing up resources or space (e.g., birds inhabiting different vertical sections of a tree).

Crypsis

A prey defense mechanism based on camouflage to evade predators.

Aposematism

A prey defense strategy that advertises toxicity to potential predators through bright warning coloration.

Mullerian mimicry

A mimicry system where a toxic species mimics another toxic species and is genuinely toxic.

Batesian mimicry

A mimicry system where a harmless, non-toxic species mimics the warning appearance of a toxic species to bluff predators.

Trophic Cascades

Indirect ecological interactions where top predators limit prey abundance, which cascades down to affect lower trophic levels in the food chain.

Top down control

A regulatory structure where predator abundance controls the population size of prey, which indirectly dictates the abundance of primary producers (e.g., foxes controlling grass abundance via rabbits).

Bottom up control

A regulatory structure where the productivity and abundance of a trophic level are limited by the resources and productivity of the level directly below it.

Green World Hypothesis

The hypothesis proposing that predators, rather than plant defenses, keep the world green by consuming herbivores and keeping their populations in check.

Food webs

Conceptual maps that illustrate the feeding system and the transfer of food energy through species in an ecosystem.

Energy flow webs

Conceptual diagrams showing that energy moves upward through trophic levels, with only $10\%$ of energy transferring to the next level.

Functional food webs

Diagrams that map the direct positive or negative impacts that one species' population exerts on another.

Ecology of fear

The concept that the behavioral, physiological, and neurobiological states of prey are altered simply by the perceived threat of predation, negatively impacting reproduction, feeding, and survival.

Landscape of fear

A spatial mapping of how and where prey perceive risk across a physical landscape, leading them to adjust their spatial distribution to avoid predators.

Mutualism

An ecological interaction between two species where both organisms derive a reciprocal benefit.

Facilitation

An interaction where the presence of one species alters the local environment in a manner that enhances the growth or survival of a second species.

Total abundance

The total count of all individual organisms present within a specified area.

Relative abundance

The abundance of an individual species expressed in proportion to the total abundance of all species combined.

Shannon Model

A quantitative index used to measure and compare species diversity between two or more communities.

Alpha diversity

The measure of species diversity within a single local community (conceptually represented by one non-overlapping side of a Venn diagram).

Gamma diversity

The total regional species diversity across all sampled communities (conceptually represented by the entire Venn diagram).

Beta diversity

Species turnover representing the number of species unique to individual communities that are not shared (the outer sections of a Venn diagram excluding the shared middle).

Bob Paine (Pisaster Experiment)

An experiment where starfish were removed from one tide pool and added to another; the pool lacking starfish was overrun by mussels to the exclusion of other species, demonstrating that a keystone predator regulates community structure from the top down.

Robert McArther

An ecologist who helped transform ecology into a mathematical discipline by creating equations to model species coexistence.