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21-3 Ecology of Fungi
Photo credits: ©D. Cavagnaro/DRK Photo
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21-3 Ecology of Fungi
The oldest known fungi fossils are about 460 million years old.
Fungi may have helped early plants obtain nutrients and may have been essential to plants’ colonization of the land.
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3. All Fungi Are Heterotrophs
Fungi rely on other organisms for energy.
Their mycelia can grow very rapidly into the tissues and cells of other organisms.
Many fungi are saprobes, which are organisms that obtain food from decaying organic matter.
Other fungi are parasites, which harm other organisms while living directly on or within them.
Other fungi are symbionts that live in close and mutually beneficial association with other species.
A few feed by capturing live animals.
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Fungi as Decomposers
Fungi as Decomposers
Fungi maintain equilibrium in nearly every ecosystem, where they recycle nutrients by breaking down the bodies and wastes of other organisms.
Without decay, the energy-rich compounds that organisms accumulate during their lifetimes would be lost forever.
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Fungi as Parasites
Fungi as Parasites
Parasitic fungi cause serious plant and animal diseases.
A few fungi cause diseases in humans.
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Fungi as Parasites
Plant Diseases
Fungal diseases are responsible for the loss of approximately 15% of the crops grown in temperate regions of the world.
Ex: corn smut, mildews, wheat rust
In tropical areas, where high humidity favors fungal growth, the loss of crops is sometimes as high as 50%.
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Fungi as Parasites
Human Diseases
Examples of fungus-caused disorders include:
Athlete’s foot
Ringworm
Thrush
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8. Symbiotic Relationships
Some fungi form symbiotic relationships in which both partners benefit.
Two such mutualistic associations, lichens and mycorrhizae, are essential to many ecosystems.
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9. Symbiotic Relationships
Lichens 
Lichens are symbiotic associations between a fungus and a photosynthetic organism.
The fungus is usually a ascomycete or sometimes a basidiomycete.
The photosynthetic organism is either a green alga or a cyanobacterium, or both.
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10. Symbiotic Relationships
Structure of a Lichen
Lichens are a mutualistic relationship between a fungus and an alga or a cyanobacterium, or both. The protective upper surface of a lichen is composed of fungal hyphae. Below this is the layer of cyanobacteria or algae with loosely woven hyphae. The third layer consists of loosely packed hyphae. The bottom layer is a protective surface covered by small projections that attach the lichen to a rock or tree.
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11. Symbiotic Relationships
Lichens are extremely resistant to drought and cold.
The algae or cyanobacteria carry out photosynthesis, providing the fungus with a source of energy.
The fungus provides the algae or bacteria with water and minerals and protects the green cells from intense sunlight.
Lichens are often the first organisms to enter barren environments, breaking down rocks into soil.
They are remarkably sensitive to air pollution, and are used as an air quality monitor.
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12. Symbiotic Relationships
Mycorrhizae  
Fungi also form mutualistic relationships with plants.
The associations of plant roots and fungi are called mycorrhizae.
Mycorrhizae is essential for the growth of many plants.
80% of all plant species form mycorrhizae with fungi.
The hyphae aid plants in absorbing water and minerals. The plants provide the fungi with the products of photosynthesis.
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