Disturbances Change Populations - Middle School Life Science

1. What is a disturbance in an ecosystem, in the context of population dynamics?

   An event that changes conditions and affects population size or growth. Disturbances disrupt ecosystem balance, causing population fluctuations.

2. Identify the best evidence that a disturbance lowered birth rate rather than increased death rate.

   Fewer juveniles per adult with similar adult survival. Adults survived but reproduced less successfully.

3. What is primary succession?

   Succession starting where no soil exists. Begins on bare rock or lava where organisms must create soil from scratch.

4. What is a population bottleneck caused by a disturbance?

   A sharp size reduction that lowers genetic variation. Few survivors have limited genetic diversity, affecting future generations.

5. Identify the best evidence that a disturbance increased food supply for herbivores.

   Increased plant biomass or plant cover after the event. More plants mean more food available for animals that eat them.

6. What is a population bottleneck caused by a disturbance?

   A sharp population drop that reduces genetic variation. Few survivors have limited genetic diversity for future generations.

7. What is population density?

   Number of individuals per unit area or volume. Measures crowding, which affects competition and resource availability.

8. Identify the density-dependent limiting factor most likely to increase after overcrowding.

   Disease transmission. Close contact in crowded conditions spreads pathogens rapidly.

9. Which evidence most strongly supports that a disturbance reduced habitat: fewer nesting sites or more predators?

   Fewer nesting sites. Lost nesting sites directly show habitat destruction, unlike predator changes.

10. Which disturbance most likely leads to secondary succession: volcanic lava flow or a forest fire?

    A forest fire. Fire leaves soil intact, while lava creates bare rock requiring primary succession.

11. What is population dynamics?

    Changes in population size and composition over time. Tracks how populations grow, shrink, and change through births, deaths, and migration.

12. What is carrying capacity ($K$)?

    The largest population an environment can support long term. Limited by resources like food, water, and space available in the environment.

13. A disease spreads faster as population density rises. What type of limiting factor is this?

    Density-dependent limiting factor. Its impact increases with population density.

14. Choose the best claim supported by evidence: after a flood, insects increased and birds increased later.

    Birds increased due to more insect prey after the flood. Flood created conditions favoring insects, which feed birds.

15. What is ecological succession as it relates to disturbances?

    Predictable community change over time after a disturbance. Species replace each other in predictable patterns as ecosystems recover.

16. What is a likely long-term population effect when a disturbance reduces habitat resources?

    Lower carrying capacity and smaller stable population size. Fewer resources support fewer individuals sustainably.

17. Identify the immediate population response most likely after a severe wildfire in a forest.

    A rapid decrease in population size. Fire kills organisms and destroys habitat, causing immediate population decline.

18. What is population dynamics?

    Changes in population size and structure over time. Tracks how populations grow, shrink, and change composition.

19. What is a common immediate population effect of a wildfire on small mammals?

    Decreased population due to mortality and habitat loss. Fire kills animals directly and destroys shelter and food sources.

20. Which graph pattern best indicates a sudden disturbance: gradual increase or abrupt drop in population size?

    Abrupt drop in population size. Sudden disturbances cause immediate deaths, shown as sharp population drops.

21. Which evidence best shows a disturbance caused a population decline: lower births or higher immigration?

    Lower births. Fewer births directly reduces population, while immigration adds individuals.

22. Which disturbance is most likely to cause a rapid decrease in a fish population: toxic spill or seasonal cooling?

    Toxic spill. Toxins kill fish directly; cooling is gradual and survivable.

23. Which evidence best indicates a population decline after a disturbance?

    Lower population counts and reduced birth rate or higher death rate. Both metrics directly measure population decrease.

24. A storm kills many trees. Which population change is most likely for a bird that nests in trees?

    Decrease due to reduced nesting sites. Birds need trees for breeding and shelter.

25. What is the best definition of a disturbance in an ecosystem in population dynamics?

    An event that changes resource availability and alters population size or growth. Disturbances disrupt ecosystems by changing resources that populations need.

26. What is carrying capacity (K)?

    Maximum population an environment can support long term. Limited by resources like food, water, and space.

27. A disturbance reduces a rabbit population from $200$ to $50$. What is the percent decrease?

    $75\%$ decrease. Calculate: $(200-50)/200 \times 100 = 75\%$.

28. A new predator is introduced. Which evidence best shows it caused the prey decline?

    Prey decline begins after predator arrival; predation marks increase. Temporal correlation and physical evidence link cause to effect.

29. Which option is density-independent: drought or competition for food?

    Drought. Weather events affect populations equally regardless of how crowded they are.

30. Which measurement is best evidence of a population increase after a disturbance: higher survival rate or lower emigration?

    Higher survival rate. More individuals surviving directly increases population size.

31. Which type of organism often increases soon after a disturbance creates open space and resources?

    Pioneer species. Fast-growing species colonize disturbed areas quickly.

32. Which evidence best supports that predation increased after a disturbance removed cover?

    Higher predator success and increased prey mortality rates. Lost vegetation exposes prey to predators.

33. Identify the density-independent limiting factor in this list: drought, disease, competition.

    Drought. Affects all individuals equally, regardless of population density.

34. A drought reduces plant biomass. Which change is most likely for an herbivore population?

    Decrease due to reduced food availability. Herbivores depend directly on plants for food.

35. What is secondary succession?

    Succession after a disturbance where soil remains. Recovery is faster because soil and seeds already exist in the area.

36. What is ecological succession, as it relates to disturbances and populations?

    Gradual community change after a disturbance alters habitats. Species replace each other as conditions change over time.

37. Which option is density-dependent: disease spread or a hurricane?

    Disease spread. Diseases spread faster in crowded populations, making it density-dependent.

38. Which statement best describes how a disturbance can change carrying capacity ($K$)?

    It can reduce or increase available resources, changing $K$. Disturbances alter resource availability, which directly affects carrying capacity.

Study these flashcards