Chapter 6: Ecosystems and Ecosystem Management

The Ecosystem: Sustaining Life on Earth

• Sustaining life on Earth requires more than individuals

• Life is sustained by interactions of many organisms functioning together in ecosystems– Physical and chemical environments

Basic Characteristics of Ecosystems

• Ecosystems have several fundamental characteristics

• Structure– Made up of two major parts; living (ecological

community)and non living (physical chemical enviro)

Basic Characteristics of Ecosystems

• Processes– Cycling of chemical elements and flow of

energy

• Change– Undergo development through succession

Basic Characteristics of Ecosystems

• For complete recycling of chemical elements to take place, several species must interact.– Photosynthetic organisms produce sugar from

carbon dioxide and water– From sugar and inorganic compound they make

other organic compounds (protein, woody tissue)

– Need decomposers to get back to inorganic compounds

Basic Characteristics of Ecosystems

• At its simplest a community will have– At least one species that is a producer– Another species that is a decomposer– Plus a fluid medium

Ecological Communities

• Ecological community defined in two ways– A set of interacting species found in the same

place and functioning together to maintain life.– Operational def= all the species found in an

area, whether or not they interact.

Food Chains

• Energy, chemicals and some compounds are transferred from creature to creature along food chains (food webs).– The linkage of who feeds on whom

• Grouped by trophic level– # of feeding levels away from original source

of energy

Trophic Levels

• First trophic level– Use energy from the sun and carbon dioxide

from the air to photosynthesizes– Green plants, algae and certain bacteria– Called autotrophs

• Second trophic level– Organisms that feed on autotrophs– Called herbivores

Trophic Levels

• Third trophic level– Feed directly on herbivores– Called carnivores (meat eaters)

• Forth trophic level– Carnivores that feed on third-level carnivores

• Decomposers- feed on waste and dead organisms of all trophic levels

A Terrestrial Food Chain

• Example: North American Temperate Woodland

• 1st level- grasses, herbs and trees

• 2nd level- mice, pine borer and deer

• 3rd level- foxes, wolves, hawks and other predatory birds and insects

• 4th level- humans

An Oceanic Food Chain

• Tend to have more trophic levels

• 1st level- planktonic algae and planktonic bacteria

• 2nd level- zooplankton and some fish

• 3rd level- fish and invertebrates feed on herbivores, baleen whales

• 4th+ levels- killer whales, predatory fish

The Food Web of the Harp Seal

• Food webs are complex because most species feed on several trophic levels.

• Harp seal (shown at 5th level)– Feeds on flatfish (4th level)– But also feed on foods from 2nd – 4th – A species that feeds on several levels placed in

a category one above the highest level it feeds on.

Community Level Interactions

• Indirect and more complicated community wide affects species have on one another.

• Sea otter of the Pacific Ocean– Came close to extinction because of over hunting for

fur

– Feed on shellfish (abalone, sea urchins)

– Where sea otters abundant kelp beds abundant and few sea urchins

– Otters affects the abundance of kelp

• Sea otters have community level effect– Where more kelp is present more habitat for

many species

• Keystone species– A species that has a large effect on its

community or ecosystem

• Holistic view– Ecological community is more than the sum of

its parts

Community Level Interactions

How do you know when you have found an ecosystem?

• An ecosystem is the minimal entity that has the properties required to sustain life.

• Vary greatly in structural complexity and clarity of their boundaries.

• Differ is size, composition, proportion of non-biological constituents and degree of variation in time and space.

Watershed

• Watershed– Commonly used practical delineation of the

boundary of an ecosystem– Determined by topography– United in terms of chemical cycling

Ecosystem Management

• Ecosystem can be natural or artificial

• Can also be managed– Agriculture– Wildlife preserves

• Ecosystem concepts lies at the heart of the management of natural resources.