Pt 9 struggle for existence Flashcards
Trophic Structure and Food Webs
Trophic Structure Definition: Organizes community members based on how they acquire energy and nutrients.
Trophic Levels:
Primary Producers: Autotrophs (e.g., photosynthesizing plants) forming the first level.
Primary Consumers: Herbivores eating plants.
Secondary Consumers: Carnivores preying on herbivores.
Tertiary Consumers: Higher-level carnivores.
Omnivores: Consume from multiple trophic levels.
Detritivores/Decomposers: Extract nutrients from dead organic matter.
G.E. Hutchinson’s Contributions
Pioneer of studying energy and material flow in ecosystems.
Focus on:
Energy flow from the sun to Earth and back into space.
Closed-system matter cycling on Earth, driven by biogeochemical processes.
Challenges for Herbivores:
Plants defend their tissues (critical for fitness) through structural and chemical means.
Mutualistic tissues like fruits/nectar serve specific purposes (seed dispersal, pollination) and lack defenses.
Plant Defenses:
Structural Defenses:
Examples: Thorns (cacti), abrasive silica (grasses), tough leaves (sclerophyllous species).
Chemical Defenses:
Secondary metabolites: Non-essential biochemicals like alkaloids and tannins.
Initially thought to be waste products, now recognized for deterring or poisoning herbivores.
Evolutionary Arms Race
Mutual adaptation between herbivores and plants:
Specialized Detox Mechanisms: Common in insects reliant on specific plants.
Generalist Strategies: Larger herbivores mitigate toxins by dietary diversity.
Biogeochemical Cycles
Matter recycling powered by energy, linking abiotic and biotic processes.
Key reactive elements: Oxygen, nitrogen, carbon, phosphorus.
Define trophic structure.
A: The organization of a community based on how energy and nutrients are acquired.
How does energy flow differ from nutrient cycling?
A: Energy flows in one direction and is lost as heat, while nutrients are recycled through ecosystems
What did G.E. Hutchinson emphasize in ecosystem studies?
A: The flow of energy from the sun to Earth and the recycling of matter through biogeochemical processes.
Why is the Earth considered a closed system for matter?
A: Matter is cycled and reused, while energy is lost to space as heat.
What are secondary metabolites?
A: Non-essential chemicals produced by plants to deter or poison herbivores.
Provide examples of structural plant defenses.
A: Thorns on cacti, tough leaves in sclerophyllous plants, and abrasive silica in grasses.
How do chemical defenses vary among plants?
A: Some produce alkaloids to poison herbivores, while others use tannins to reduce digestibility.
How do herbivores overcome plant defenses?
A: Through specialized detoxification mechanisms or by adopting diverse diets to dilute toxins.
