Middle School Life Science Flashcards: Evaluate Population Explanations

What this deck covers

This deck focuses on Evaluate Population Explanations, giving you a quick way to review the definitions, rules, and examples that matter most for Middle School Life Science.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: What is the difference between a density-dependent and a density-independent limiting factor?

Answer: Density-dependent varies with density; density-independent does not. Competition/disease increase with crowding; weather/disasters affect all equally.

Flashcard 2: What is carrying capacity (K) in an ecosystem?

Answer: Maximum population size the environment can support long term. Limited resources prevent indefinite growth.

Flashcard 3: Which option is a density-dependent factor: drought or disease?

Answer: Disease. Spreads faster in crowded populations.

Flashcard 4: Which option is a density-independent factor: hurricane or competition?

Answer: Hurricane. Affects populations regardless of their density.

Flashcard 5: What does a predator-prey cycle typically look like in population data over time?

Answer: Prey peaks first; predator peaks later; both oscillate. Predators lag behind prey abundance changes.

Flashcard 6: Identify the best explanation if prey declines first and predator declines shortly after.

Answer: Prey limitation causing a lagged predator decline. Predators starve when prey becomes scarce.

Flashcard 7: What does a trophic cascade mean in an ecosystem?

Answer: A change at one trophic level causes changes across other levels. Effects ripple through the food web.

Flashcard 8: Which explanation best fits: a new top predator arrives and herbivores decrease?

Answer: Increased predation pressure on herbivores. Direct predation reduces prey numbers.

Flashcard 9: What is the main evidence that competition is limiting a population?

Answer: Reduced growth or survival as density increases due to shared resources. Competition intensifies when resources become scarce.

Flashcard 10: Which pattern most supports resource limitation: stable habitat but gradual leveling of growth?

Answer: Population approaches carrying capacity ($K$). Growth slows as resources become limiting.

Flashcard 11: What is a biotic factor that can change population size?

Answer: A living influence such as predation, disease, or competition. Living organisms affect population dynamics.

Flashcard 12: What is an abiotic factor that can change population size?

Answer: A nonliving influence such as temperature, rainfall, or fire. Physical environment affects survival.

Flashcard 13: Which explanation best fits: sudden crash in many species after a wildfire?

Answer: Density-independent disturbance affecting the ecosystem. Fire kills regardless of population density.

Flashcard 14: Which evidence best supports migration (immigration/emigration) as the cause of change?

Answer: Population shifts without matching changes in births, deaths, or resources. Movement explains changes without birth/death rate shifts.

Flashcard 15: Identify the best explanation if births and deaths stay similar but the count increases sharply.

Answer: Immigration into the population. New individuals entering increases population.

Flashcard 16: What is the most direct sign that a disease outbreak caused a population decline?

Answer: High mortality with symptoms or pathogen presence in many individuals. Disease shows specific symptoms and spreads.

Flashcard 17: Which option best supports overharvesting as the cause: more predators or increased hunting?

Answer: Increased hunting. Human harvest directly removes individuals.

Flashcard 18: Which explanation is best if a pollutant increases and multiple species decline together?

Answer: Abiotic stress from pollution reducing survival and reproduction. Toxins harm all exposed species similarly.

Flashcard 19: Which relationship is shown when predator numbers rise after prey numbers rise, with a time lag?

Answer: Predator–prey cycle with predator lag. Predators increase after prey increases because they need time to reproduce.

Flashcard 20: Which type of evidence best supports a claim about why a population changed: long-term population counts or a single observation?

Answer: Long-term population counts (time-series data). Time-series data shows patterns and changes over time, not just one moment.

Flashcard 21: What is the dependent variable when you investigate why a population size changed in an ecosystem?

Answer: Population size (number of individuals). The dependent variable is what you measure (population) in response to changes.

Flashcard 22: What is the independent variable when testing the effect of food on a consumer population?

Answer: Food availability (resource level). The independent variable is what you manipulate or test (food) to see its effect.

Flashcard 23: Which option is a density-dependent limiting factor: drought or disease spread in crowded conditions?

Answer: Disease spread in crowded conditions. Density-dependent factors affect populations more as density increases.

Flashcard 24: Which option is a density-independent limiting factor: wildfire or competition for mates?

Answer: Wildfire. Density-independent factors affect populations regardless of their density.

Flashcard 25: What term describes the maximum population size an environment can support over time?

Answer: Carrying capacity. Limited by resources like food, water, and space available in the environment.

Flashcard 26: What is the most direct evidence that a new predator caused a prey population decline?

Answer: Predator introduction followed by increased predation and prey decline. Direct cause-and-effect sequence shows predator caused the decline.

Flashcard 27: Choose the correct formula for population change using births (B), deaths (D), immigration (I), emigration (E).

Answer: $\Delta N = (B + I) - (D + E)$. Population change equals gains (births + immigration) minus losses (deaths + emigration).

Flashcard 28: A pond has $B=12$, $D=5$, $I=3$, $E=10$ in one month. What is $\Delta N$ for that month?

Answer: $\Delta N = 0$. $(12+3)-(5+10)=15-15=0$, so no net change.

Flashcard 29: Identify the best explanation if a population drops immediately after a chemical spill, regardless of density.

Answer: Density-independent abiotic disturbance (pollution event). Chemical spills affect all individuals equally, regardless of population density.

Flashcard 30: Identify the best explanation if prey stays constant but predator declines after a disease affects only predators.

Answer: Predator decline caused by density-dependent disease in predators. Disease affecting only predators explains why prey remains stable.