Untitled Quiz

Ecosystems Ecology

• Ecosystems involve the interaction of species with abiotic and biotic factors
• The term was coined by Tansley in 1935
• Ecosystems can be any scale, from a drop of water to a forest
• Key components include biomass (carbon and nitrogen), energy flow, and the availability of rare chemicals or minerals

Trophic Structure

• Trophic structure describes the feeding relationships of organisms
• It involves the transfer of energy between trophic levels
• Two main types of trophic levels:
  • Autotrophy: organisms that get their energy from non-living sources (sunlight or inorganic matter)
    • Photoautotrophs use sunlight
    • Chemoautotrophs use inorganic matter
  • Heterotrophy: organisms that get their energy from other living organisms
    • Predators eat living organisms
    • Detritivores and saprophytes consume dead organisms or organic matter
• Common trophic levels include producers, primary consumers, secondary consumers, etc.

Trophic Levels

• Trophic level of a species is one more than the chain length
• Food chains are typically short (5-6 links maximum)
• Detritivores (organisms that feed on dead organic matter) are important for nutrient recycling
• Detritivores recycle nitrogen and phosphorus back into the ecosystem

Food Webs

• Food webs represent the interconnectedness of many food chains
• Food webs are complex and interconnected
• Three types of food webs
  • Source webs: Focus on the sources and their consumers
  • Sink webs: The consumers and their prey
  • Community webs: Group of species within a defined area, or habitat
• Connectance: Measures the relative complexity of a food web's interactions
• Linkage density: number of links per species in a food web
• Food chain lengths vary, but are frequently shorter on small islands and in environments with frequent disturbances
• The ratio of prey to predator populations is generally around 1:1
• Food webs are often challenged by: - Lack of information on predation, including the quantity of food consumed by various species (amount and type). - Lack of information and data on chemical nutrients and their effects, especially regarding chemical nutrients which supply critical nutrients - Difficulty of defining boundaries of a food web, issues relating to age and variation in diet of numerous species - Difficulty in precisely placing some species into a discrete trophic level based on their activities (e.g., taxa which are both predator and prey)

Functional Units: Guilds

• A guild is a grouping of species that exploit similar resources in a food web for a similar reason.
• It's another way to classify species based on their function within an ecosystem.
• Examples of guilds include frugivore (fruit eaters) and detritivores (organisms that consume detritus).

Energy and Nutrient Flow

• Energy is transferred up the trophic levels in an ecosystem, but some energy is always lost at each step
• The first law of thermodynamics states energy cannot be created nor destroyed, only transformed
• The second law of thermodynamics states there's always energy loss (entropy)

Primary production

• Photosynthesis is the foundation of primary production in most ecosystems
• Gross primary production is the total energy fixed by photosynthesis
• Net primary production is the gross primary production minus energy used in plant respiration

Secondary Production

• Secondary production involves consuming primary producers (herbivores) and/or detritivores.
• Herbivores are consumed by carnivores
• Energy is passed along the food chain from producers to consumers

Nutrient Cycles

• Biogeochemical cycles involve the recycling of nutrients through an ecosystem
• Nutrients can cycle locally or globally
• Key cycles include carbon, nitrogen and phosphorus cycles
• Phosphorus cycle is simpler, as it lacks an atmospheric component