Ecology Practice Study Guide

Comprehensive practice flashcards in question-and-answer format covering ecology concepts, population dynamics, sampling formulas, and field study calculations from the study guide.

Why does the angle at which sunlight reaches Earth help shape climate zones?

Direct rays concentrate energy over a smaller area, while angled rays spread it over a larger area, making regions receiving direct sunlight warmer than places where sunlight arrives at a lower angle.

How is a wetland defined?

An ecosystem where water covers the soil or is at or near the surface for at least part of the year.

What is the aphotic zone of the ocean?

The permanently dark ocean zone where sunlight does not reach.

What is the key difference between weather and climate?

Weather describes short-term, day-to-day atmospheric conditions, whereas climate describes the average, year-after-year pattern of conditions such as temperature and precipitation over many decades.

How do starting conditions differ between primary succession and secondary succession?

Primary succession begins on bare surfaces where soil is absent (such as bare rock exposed by a landslide), whereas secondary succession begins where soil remains after a disturbance (such as a burned grassland).

How do mutualism, parasitism, and commensalism differ?

In mutualism, both organisms benefit; in parasitism, one organism benefits while the other is harmed; in commensalism, one organism benefits while the other is unaffected.

What is a detritivore, and what is an example?

A detritivore is an organism that feeds on dead organic matter, such as a beetle feeding on decaying leaves on the rainforest floor.

What is predation?

An ecological interaction in which one organism captures and feeds on another.

What distinguishes an abiotic factor from a biotic factor?

An abiotic factor is a nonliving part of an environment (such as water temperature, sunlight, or water), whereas a biotic factor is a living part of an environment or an interaction with other organisms (such as a fish or coral colony).

How do autotrophs differ from heterotrophs?

Autotrophs make their own food (capturing energy, often from sunlight), while heterotrophs obtain energy by consuming other organisms or organic matter.

What constitutes an ecosystem?

All organisms living in a place together with the nonliving environment around them, along with their interactions.

What is an ecological niche?

The conditions an organism lives in and how it obtains what it needs to survive and reproduce (including its role, food sources, and environmental requirements).

What is the correct sequence of ecological levels from smallest to largest?

Species $\rightarrow$ populations $\rightarrow$ communities $\rightarrow$ ecosystem $\rightarrow$ biosphere.

If producers in a food web store $18,000\text{ units}$ of energy, approximately how much energy reaches the next trophic level under the $10\%$ transfer rule?

$1,800\text{ units}$, calculated as $18,000 \times 0.10 = 1,800\text{ units}$.

What is interspecific competition?

Competition between individuals of different species for a shared limited resource.

If a population of $360$ prairie dogs occupies an area of $12\,\text{km}^2$, what is its population density?

$30\,\text{prairie dogs/km}^2$, calculated as $\frac{360}{12} = 30$.

Over one season, $14$ young animals are born, $9$ immigrate, $6$ die, and $4$ emigrate. What is the net population change?

An increase of $13$ individuals (Additions: $14 + 9 = 23$; Losses: $6 + 4 = 10$; Net change: $23 - 10 = +13$).

What is characteristic of logistic population growth?

Population growth that slows and levels off as the population size approaches the environment's carrying capacity.

What happens if a population remains far above its carrying capacity for an extended period?

Resources become more limited, competition increases, and mortality or emigration may increase, causing the population to decline.

How do immigration and emigration differ?

Immigration moves individuals into a population or area, whereas emigration moves individuals out of a population or area.

What is a limiting factor?

A resource or environmental condition (such as water or sunlight) that restricts population growth, size, or distribution.

What are the three population distribution patterns and their characteristics?

Clumped (individuals occur in groups), uniform (individuals are evenly spaced), and random (positions have no predictable pattern).

What is the difference between density-dependent and density-independent limiting factors?

A density-dependent factor's effects become stronger as population density increases (e.g., contagious disease), while a density-independent factor affects a population regardless of its density (e.g., a severe hailstorm).

What is carrying capacity?

The maximum population size an environment can sustain indefinitely with its available resources.

What is the formula for population density and what two pieces of information are required?

$\text{population density} = \frac{\text{number of individuals}}{\text{area}}$; the two required pieces of information are the number of individuals and the area.

How does quadrat sampling work, and why are quadrats placed randomly?

Researchers count organisms within several sample plots of known size to estimate abundance across a larger habitat. Random placement reduces the chance of selecting only unusually crowded or empty spots, making the sample more representative.

In the pika study, five $1\,\text{m}^2$ quadrats contain $6$, $3$, $7$, $4$, and $5$ pikas in a $3\text{-hectare}$ ($30,000\,\text{m}^2$) meadow. What is the estimated population?

$150,000\text{ animals}$. Total count: $6 + 3 + 7 + 4 + 5 = 25$. Average density: $\frac{25}{5} = 5\,\text{animals/m}^2$. Habitat area: $3\,\text{ha} \times 10,000\,\text{m}^2/\text{ha} = 30,000\,\text{m}^2$. Total estimate: $5 \times 30,000 = 150,000\text{ animals}$.

What is the Lincoln–Peterson mark-recapture formula, and what do its variables represent?

$N = \frac{M \times S}{R}$, where $N$ is the estimated population size, $M$ is the number marked and released in the first sample, $S$ is the number caught in the later sample, and $R$ is the number of marked animals found in the later sample.

Researchers mark and release $M = 60$ pikas, then capture $S = 50$ pikas, of which $R = 12$ are marked. What is the estimated population?

$250\text{ animals}$. Step 1: $60 \times 50 = 3,000$. Step 2: $\frac{3,000}{12} = 250\text{ animals}$.

What is the percent error formula, and what is the percent error when comparing an estimate of $250$ animals to a census count of $250$ animals?

Formula: $\text{percent error} = \frac{|\text{estimate} - \text{true}|}{\text{true}} \times 100$. Calculation: $\frac{|250 - 250|}{250} \times 100 = 0\%$.

What are plausible sources of error in real mark-recapture studies?

Marked individuals might not mix evenly back into the population, marks might be lost or affect animal behavior, and births, deaths, or movement (immigration/emigration) between samples can alter results.

What is the biosphere?

All regions of Earth where life exists, including the organisms and environments that support them.

How is symbiosis defined?

A close, long-term relationship between organisms of different species.