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Effects on Ecosystem Processes
A Natural Balance?
Natural systems operate a dynamic equilibrium –
a moving, changing balance. Weather events or
disasters can alter the balance, but the system
gradually adjusts either to new conditions or
revert to previous situation. With the coming of
humans and their domination of so much of the
natural world this balance has been drastically
altered and, in many cases, so quickly that
ecosystems have not been able to adapt.
What are the main processes in an
• Nutrient Cycle – the feedback of minerals from
decomposed organic material back into plants
• Energy Flows – the flow of energy through the
system e.g. food chain or food web
Fallout pathway
Growth or uptake
How can humans influence the
nutrient flow?
Over harvesting
Soil degradation
Read the handout sheet
(p68) from the
Chesapeake Bay, USA
Example of human influence
on the nutrient cycle
Case Study: Giant Kelp, California
• Giant kelp is a type of
seaweed which supports a
wide range of species of the
coast of California
• It acts as a breeding ground
and nursery for many fish
• One herbivore of the giant
kelp is the sea urchin, which
could destroy the habitat
• The sea otter is the predator responsible for
keeping the urchin at bay
• BUT the sea otter was hunted by humans during
the 19th and early 20th Century
• The whole ecosystem collapsed
• The sea otter is known as a keystone species
Food chain in the kelp forest,
Cane Toads, Australia
• Example of the introduction of alien species
causing problems for energy flows