Trophic Levels, Food Webs, and Population Dynamics

Trophic level

a single step in a food chain or food web

Primary producers

plants and phytoplanktons; produces their own food

Primary consumers

herbivores and zooplanktons; consumes the primary producer

Secondary consumer

carnivores; consumes the primary consumer

Tertiary consumer

carnivores; consumes the secondary consumer

Quarterly consumer

carnivore; consumes the tertiary consumer

Herbivores

eats plants ONLY

Carnivores

eats animals ONLY

Omnivores

eats both plants and animals

Decomposer

externally digest dead organic matter

Detritivore

internally digest dead organic matter

Predation

As the prey population increases, the predator population increases and vice versa.

Disease

Spread easier in large populations

Density

Independent limiting factors limit all population sizes (large or small) and parasites spread easier in large populations

Extreme weather

drought, flood, freezing

Human activities

pollution, habitat destruction

Energy pyramid

shows the relative amount of energy available at each trophic level

Biomass pyramid

represents the amount of living organic matter at each trophic level

Pyramid of numbers

shows the relative number of individual organisms at each trophic level

Biomagnification

concentrations of a harmful substance increase in organisms at higher trophic levels in a food chain or food web

Competition for resources

Competition increases as the population size increases.

Exponential phase

Population shows rapid increase in growth due to unlimited resources.

Plateau phase

the population has reached its carrying capacity, that is to say, the population in a habitat has reached its maximum.