Introduction to Ecology

Ecology

• Ecology: the study of organisms interacting with each other and their environment
• Ecologists study
• Distribution: where are individuals?
• Abundance: how many individuals are there?
• There are several branches of ecology:
• Organismal ecology: how individuals interact with each other and with their environment
• Population ecology: how population sizes change over time
• Community ecology: how different species interact with each other
• Ecosystem Ecology: how energy and nutrients flow through the environment

Ecosystems

• Ecosystem: a community of organisms and the physical environment it occupies

Food Webs

• Food Webs: describes the cycle of carbon and energy through the ecosystem
• Also called trophic web
• Primary Producers: organisms that produce energy and growth from the sun, CO2 and water
• Called autotrophs = "Self Energy"
• Provide almost all energy in the entire trophic web
• Consumers: organisms that gain energy and nutrients by consuming other organisms
• Herbivores: consume primary producers (primary consumer)
• Carnivore: consume non-herbivores (secondary consumer)
• Decomposers: break down producers and consumers
• Bacteria and Fungi
• Release carbon and nutrients back into environment

Photo by Siyavul Education | CC BY

Trophic Structure

• Trophic Level: where an organism fits in the food web
• 1st Trophic level: primary producers
• 2nd Trophic level: primary consumers (herbivores)
• 3rd Trophic level: secondary consumers (carnivores)
• Can be additional levels up to the apex predator

• Not all energy is transferred up to the next level
• Only about 10% is transferred up
• 90% is lost as heat (used up)
• You can estimate biomass at each level Example: If the ecosystem contains 1000 kg of grass (therefore photosynthesis), then it can support 100 kg of frogs, which will support 10 kg of snakes and 1 kg of ferrets etc.

• Bottom up ecosystems
• If you increase the primary production, all other levels increase
• Primary production is limiting factor
• Top down ecosystems
• If you decrease the top level consumers, all other levels will increase
• Predation is the limiting factor
• Trophic cascade: changes in higher levels trickle down and affect lower levels
• All ecosystems are really a combination of bottom and top control
• Keystone Species: one species that has a huge effect on the ecosystem