Table of contents
- 1. Introduction to Biology2h 42m
- 2. Chemistry3h 37m
- 3. Water1h 26m
- 4. Biomolecules2h 23m
- 5. Cell Components2h 26m
- 6. The Membrane2h 31m
- 7. Energy and Metabolism2h 0m
- 8. Respiration2h 40m
- 9. Photosynthesis2h 49m
- 10. Cell Signaling59m
- 11. Cell Division2h 47m
- 12. Meiosis2h 0m
- 13. Mendelian Genetics4h 44m
- Introduction to Mendel's Experiments7m
- Genotype vs. Phenotype17m
- Punnett Squares13m
- Mendel's Experiments26m
- Mendel's Laws18m
- Monohybrid Crosses19m
- Test Crosses14m
- Dihybrid Crosses20m
- Punnett Square Probability26m
- Incomplete Dominance vs. Codominance20m
- Epistasis7m
- Non-Mendelian Genetics12m
- Pedigrees6m
- Autosomal Inheritance21m
- Sex-Linked Inheritance43m
- X-Inactivation9m
- 14. DNA Synthesis2h 27m
- 15. Gene Expression3h 6m
- 16. Regulation of Expression3h 31m
- Introduction to Regulation of Gene Expression13m
- Prokaryotic Gene Regulation via Operons27m
- The Lac Operon21m
- Glucose's Impact on Lac Operon25m
- The Trp Operon20m
- Review of the Lac Operon & Trp Operon11m
- Introduction to Eukaryotic Gene Regulation9m
- Eukaryotic Chromatin Modifications16m
- Eukaryotic Transcriptional Control22m
- Eukaryotic Post-Transcriptional Regulation28m
- Eukaryotic Post-Translational Regulation13m
- 17. Viruses37m
- 18. Biotechnology2h 58m
- 19. Genomics17m
- 20. Development1h 5m
- 21. Evolution3h 1m
- 22. Evolution of Populations3h 52m
- 23. Speciation1h 37m
- 24. History of Life on Earth2h 6m
- 25. Phylogeny2h 31m
- 26. Prokaryotes4h 59m
- 27. Protists1h 12m
- 28. Plants1h 22m
- 29. Fungi36m
- 30. Overview of Animals34m
- 31. Invertebrates1h 2m
- 32. Vertebrates50m
- 33. Plant Anatomy1h 3m
- 34. Vascular Plant Transport1h 2m
- 35. Soil37m
- 36. Plant Reproduction47m
- 37. Plant Sensation and Response1h 9m
- 38. Animal Form and Function1h 19m
- 39. Digestive System1h 10m
- 40. Circulatory System1h 49m
- 41. Immune System1h 12m
- 42. Osmoregulation and Excretion50m
- 43. Endocrine System1h 4m
- 44. Animal Reproduction1h 2m
- 45. Nervous System1h 55m
- 46. Sensory Systems46m
- 47. Muscle Systems23m
- 48. Ecology3h 11m
- Introduction to Ecology20m
- Biogeography14m
- Earth's Climate Patterns50m
- Introduction to Terrestrial Biomes10m
- Terrestrial Biomes: Near Equator13m
- Terrestrial Biomes: Temperate Regions10m
- Terrestrial Biomes: Northern Regions15m
- Introduction to Aquatic Biomes27m
- Freshwater Aquatic Biomes14m
- Marine Aquatic Biomes13m
- 49. Animal Behavior28m
- 50. Population Ecology3h 41m
- Introduction to Population Ecology28m
- Population Sampling Methods23m
- Life History12m
- Population Demography17m
- Factors Limiting Population Growth14m
- Introduction to Population Growth Models22m
- Linear Population Growth6m
- Exponential Population Growth29m
- Logistic Population Growth32m
- r/K Selection10m
- The Human Population22m
- 51. Community Ecology2h 46m
- Introduction to Community Ecology2m
- Introduction to Community Interactions9m
- Community Interactions: Competition (-/-)38m
- Community Interactions: Exploitation (+/-)23m
- Community Interactions: Mutualism (+/+) & Commensalism (+/0)9m
- Community Structure35m
- Community Dynamics26m
- Geographic Impact on Communities21m
- 52. Ecosystems2h 36m
- 53. Conservation Biology24m
51. Community Ecology
Community Structure
Problem 7
Textbook Question
Which of the following could qualify as a top-down control on a grassland community?
a. Limitation of plant biomass by rainfall amount
b. Influence of temperature on competition among plants
c. Influence of soil nutrients on the abundance of grasses versus wildflowers
d. Effect of grazing intensity by bison on plant species diversity

1
Understand the concept of top-down control: In ecology, top-down control refers to the influence of predators or consumers on the structure and dynamics of ecosystems. It contrasts with bottom-up control, which is driven by resource availability such as nutrients or sunlight.
Analyze each option to determine if it represents a top-down control: Top-down control typically involves the impact of higher trophic levels (like predators or herbivores) on lower trophic levels (like plants).
Evaluate option a: Limitation of plant biomass by rainfall amount is a bottom-up control because it involves abiotic factors affecting plant growth.
Evaluate option b: Influence of temperature on competition among plants is also a bottom-up control, as it involves abiotic factors affecting plant interactions.
Evaluate option d: Effect of grazing intensity by bison on plant species diversity is a top-down control, as it involves herbivores (bison) affecting the diversity and composition of plant species in the grassland community.

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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Top-Down Control
Top-down control refers to the influence of higher trophic levels on the structure and dynamics of ecosystems. In a grassland community, this could involve predators or herbivores affecting the abundance and diversity of plant species. For example, grazing by bison can regulate plant species diversity by selectively feeding on certain plants, thereby shaping the community composition.
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Trophic Levels
Trophic levels are the hierarchical levels in an ecosystem, comprising producers, consumers, and decomposers. Each level represents a step in the food chain, with energy and nutrients flowing from one level to the next. Understanding trophic levels is crucial for identifying how top-down controls, such as herbivory, can impact lower levels like plant communities in grasslands.
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Community Dynamics
Community dynamics involve the interactions and changes within an ecological community over time. Factors such as predation, competition, and environmental conditions can influence these dynamics. In the context of the question, grazing intensity by bison represents a biotic factor that can alter plant species diversity, demonstrating a top-down control mechanism in the grassland ecosystem.
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