Chapter 4: Species Interactions and Community Ecology Study Guide

Comprehensive practice question-and-answer flashcards covering species interactions, ecological communities, succession, biomes, Simpson's Diversity Index, and pond water-quality analysis from Chapter 4.

What is the difference between interspecific competition and intraspecific competition?

Interspecific competition occurs between different species, whereas intraspecific competition occurs among members of the same species.

What does the competitive exclusion principle state?

Two species cannot occupy exactly the same niche in the same place for a long time; one may outcompete the other, or the species may divide resources.

What is resource partitioning and what is its ecological effect?

It occurs when competing species use resources in different ways, places, or times, which reduces competition and allows them to coexist.

How does a fundamental niche differ from a realized niche?

A fundamental niche is the full range of conditions and resources a species could potentially use, while a realized niche is the portion it actually uses when competition and other interactions are present.

What are three morphological or visual prey adaptations used to avoid predation?

Camouflage (blends into surroundings), warning coloration (signals that an organism may be toxic or dangerous), and mimicry (resembles another species or object).

How do parasitism and mutualism differ in their effects on interacting organisms?

In parasitism, a parasite benefits while its host is harmed (usually without being killed immediately); in mutualism, both interacting species benefit.

What is herbivory, and what defenses do plants use against it?

Herbivory is an interaction where an animal eats plants or algae; plant defenses include thorns, tough leaves, toxins, or chemicals that discourage herbivores.

Approximately what fraction of energy is transferred from one trophic level to the next?

Only a small fraction—often summarized as about $10\%$—is transferred to the next trophic level, because organisms use energy for life processes and much is lost as heat.

What is a keystone species, and how does the sea otter illustrate this concept?

A keystone species has an unusually large effect on its community relative to its abundance. Sea otters eat sea urchins, preventing them from overgrazing and destroying kelp forests.

What is a trophic cascade?

A process that occurs when changes at one trophic level cause cascading ecological effects across other trophic levels.

How does primary succession differ from secondary succession?

Primary succession begins where no soil exists (such as bare rock after a lava flow or glacial retreat), whereas secondary succession occurs where soil remains after a disturbance (such as after a fire or logging).

What role do pioneer species such as lichens and mosses play in primary succession?

They colonize bare rock and help break it down to build soil, making it possible for subsequent species to establish.

What distinguishes an invasive species from an introduced species?

An introduced species is non-native and moved by humans outside its native range; it becomes an invasive species only if it spreads and causes ecological, economic, or other harm.

What are the two primary climate factors that determine terrestrial biomes?

Temperature and precipitation.

Which biome is characterized by long, cold winters, short summers, and coniferous trees such as spruce and fir?

Boreal forest (taiga).

Which biome has very cold temperatures, low precipitation, a short growing season, and permafrost?

Tundra.

What two components of biodiversity are evaluated by Simpson's Diversity Index?

Species richness (the number of different species present) and species evenness (how evenly individuals are distributed among those species).

What is the formula for Simpson's Index of Diversity ($1 - D$)?

$1 - D = 1 - \left[ \frac{\sum n(n - 1)}{N(N - 1)} \right]$, where $n$ is the number of individuals in one species and $N$ is the total number of individuals of all species.

How is a calculated value interpreted in the $1 - D$ version of Simpson's Index of Diversity?

The result is between $0$ and $1$; a value closer to $1$ indicates higher diversity, while a value closer to $0$ indicates lower diversity.

What is the generally favorable target range for dissolved oxygen (DO) in freshwater ponds, and at what level is water considered hypoxic?

About $5\text{--}6\,\text{mg/L}$ or higher is generally favorable; levels around $1\,\text{mg/L}$ or less are hypoxic and support very little aquatic life.

What level of nitrate reported as nitrate-nitrogen ($\text{NO}_3\text{-N}$) can indicate nutrient pollution in a pond?

Levels above about $3\,\text{mg/L}$ as $\text{NO}_3\text{-N}$ can indicate nutrient pollution and contribute to excessive algae or plant growth.

What is the commonly used favorable pH range for freshwater pond water?

About $6.5\text{--}8.5$ is a commonly used favorable range (with roughly $6.0\text{--}9.0$ considered tolerable depending on species).

Why does dissolved oxygen and pH often rise during the day and drop at night in a pond with high algae levels?

Daytime photosynthesis releases oxygen and removes carbon dioxide (raising DO and pH); at night, photosynthesis stops while cellular respiration consumes oxygen and releases carbon dioxide (lowering DO and pH).

Why does higher water temperature increase stress on pond organisms regarding dissolved oxygen?

Warm water holds less dissolved oxygen than cold water, while simultaneously increasing the metabolic rates and oxygen demands of aquatic organisms.

How does decomposition of dead organic matter affect dissolved oxygen in a pond?

Bacteria and other decomposers consume dissolved oxygen as they break down organic matter, leading to a drop in DO levels.