Prior to mating in sexual reproduction, individual fungi communicate with other individuals chemically via pheromones. In every phylum at least one pheromone has been characterized, and they range from sesquiterpines and derivatives of the carotenoid pathway in chytridiomycetes and zygomycetes to oligopeptides in ascomycetes and basidiomycetes. Within their varied natural habitats fungi usually are the primary decomposer organisms present. Many species are free-living saprobes (users of carbon fixed by other organisms) in woody substrates, soils, leaf litter, dead animals, and animal exudates.
The large cavities eaten out of living trees by wood-decaying fungi provide nest holes for a variety of animals, and extinction of the ivory billed woodpecker was due in large part to loss, through human activity, of nesting trees in bottom land hardwoods. In some low nitrogen environments several independent groups of fungi have adaptations such as nooses and sticky knobs with which to trap and degrade nematodes and other small animals. A number of references on fungal ecology are available (Carroll and Wicklow, 1992; Cooke and Whipps, 1993; Dix and Webster, 1995).
However, many other fungi are biotrophs, and in this role a number of successful groups form symbiotic associations with plants (including algae), animals (especially arthropods), and prokaryotes. Examples are lichens, mycorrhizae, and leaf and stem endophytes. Although lichens may seem infrequent in polluted cities, they can form the dominant vegetation in nordic environments, and there is a better than 80% chance that any plant you find is mycorrhizal.
The Essay on Endangered Animals
There are around 41,000 endangered species, and around 16,000 of them are on the edge of extinction. There are many reasons for animals to go endangered, such as habitat loss, pollution, disease, predation, illegal killing, and poaching. Habitat loss happens by a mixture of things logging, agriculture, the building of roads and cities, and forest fires. Habitat loss affects China’s giant panda ...
Leaf and stem endophytes are a more recent discovery, and some of these fungi can protect the plants they inhabit from herbivory and even influence flowering and other aspects of plant reproductive biology. Fungi are our most important plant pathogens, and include rusts, smuts, and many ascomycetes such as the agents of Dutch elm disease and chestnut blight. Among the other well known associations are fungal parasites of animals.
Humans, for example, may succumb to diseases caused by Pneumocystis (a type of pneumonia that affects individuals with supressed immune systems), Coccidioides (valley fever), Ajellomyces (blastomycosis and histoplasmosis), and Cryptococcus (cryptococcosis) (Kwon-Chung and Bennett, 1992).
Click on an image to view larger version & data in a new window Figure 2: The fluffy white hyphae of the mycorrhizal fungus Rhizopogon rubescens has enveloped the smaller roots of a Virginia pine seedling.
Note that some of the mycelium extends out into the surrounding environment. Copyright © J. B. Anderson 1996. Click on an image to view larger version & data in a new window Figure 3: Entomophthora, “destroyer of insects”, is the agent of a fungual infection that kills flies. After their death the fungal growth erupts through the fly cuticle, and dispersal by forcible spore discharge is a source of inoculum for infection of new flies. Copyright © G. L. Barron 1996. Fungal spores may be actively or passively released for dispersal by several effective methods.
The air we breathe is filled with spores of species that are air dispersed. These usually are species that produce large numbers of spores, and examples include many species pathogenic on agricultural crops and trees. Other species are adapted for dispersal within or on the surfaces of animals (particularly arthropods).
Some fungi are rain splash or flowing water dispersed. In a few cases the forcible release of spores is sufficient to serve as the dispersal method as well.
The function of some spores is not primarily for dispersal, but to allow the organisms to survive as resistant cells during periods when the conditions of the environment are not conducive to growth. Fungi are vital for their ecosystem functions, some of which we have reviewed in the previous paragraphs. In addition a number of fungi are used in the processing and flavoring of foods (baker’s and brewer’s yeasts, Penicillia in cheese-making) and in production of antibiotics and organic acids.
The Essay on Protection Of Endangered Species
Out of all the species that have ever existed since the beginning of time, 98% of them are extinct (Facts). There are an estimated 5-10 million species that exist currently and only 1.5 million have been identified (Sherry, 2). Scientists classify species into six different groups: plants, animals, insects, algae, fungi, and microorganisms (Todays Situation). In the tropical rainforest alone, most ...
Other fungi produce secondary metabolites such as aflatoxins that may be potent toxins and carcinogens in food of birds, fish, humans, and other mammals. A few species are studied as model organisms that can be used to gain knowledge of basic processes such as genetics, physiology, biochemistry, and molecular biology with results that are applicable to many organisms (Taylor et al. , 1993).
Some of the fungi that have been intensively studied in this way include Saccharomyces cereviseae, Neurospora crassa, and Ustilago maydis.
Most phyla appear to be terrestrial in origin, although all major groups have invaded marine and freshwater habitats. An exception to this generality is the flagellum-bearing phyla Chytridiomycota, Blastocladiomycota, and Neocallimastigomycota (collectively referred to as chytrids), which probably had an aquatic origin. Extant chytrid species also occur in terrestrial environments as plant pathogenic fungi, soil fungi, and even as anaerobic inhabitants of the guts of herbivores such as cows (all Neocallimastigomycota).
