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Fungal species numbers and decomposition of rabbit faeces
Trans. Br. mycol, Soc. 76 (1),29-32 (1981)
Printedin GreatBritain
FUNGAL SPECIES NUMBERS AND DECOMPOSITION OF RABBIT FAECES By D. T. WICKLOW Northern Regional Research Center, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Peoria, Illinois 61604 D. H. YOCOM Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York 11794 AND
Evidence is presented that additions of fungal species to herbivore dung result in a decreased ability of competing microflora to utilize available substrate. When two or more species of coprophilous fungi were combined in rabbit faeces, faecal decomposition rates were limited to the slower of the rates recorded when the same species were incubated separately. A reduced decomposition rate could enable slower-growing and later-appearing species to secure the substrate resources necessary for mycelial growth and sporulation. Microbial ecologists traditionally have supported the notion that the greater the species riclmess of the saprobic microfloral community colonizing a natural substrate the more rapid the rate of decomposition of that substrate. For example, Waksman & Cordon (1939) argued that no single pure culture could give as extensive and rapid decomposition as the total mixed microbial population of a compost. One might anticipate that the greater the diversity of the microbial decomposer community, the more enzymaticbiochemical diversity the community can draw upon in attacking a substrate, and the more completely that substrate might be utilized. Furthermore, mutualistic associations among certain species populations of saprophytic microbes may also significantly increase decomposition losses (Blanchette & Shaw, 1978; Shortle & Cowling, 1978). Alternatively, competition among species populations also has been shown to reduce the exploitation of a resource (Root, 1969; Wolf & Hainsworth, 1971) or directly interfere with access to a resource (Brown, 1964; Muller, 1966; Miller, 1967; Bruehl, Millar & Cunfer, 1969; Rice, 1974). It can be argued that by increasing the number of saprobic species comprising a decomposer community, one also increases the potential for competitive interactions. This study was designed to explore these contrasting ecological views by examining the effects of increasing fungal species number on resource utilization as measured by decomposition losses from rabbit faeces. Fresh faecal substrates represent unexploited resource islands. Harper &
Webster (1964) describe a methodology that allows one to manipulate the composition of the fungal community on these 'islands' while not affecting other components of the faecal microflora or in any way modifying the structural integrity or chemical composition of the faecal pellets. From a mycologist's perspective, this represents the empirical equivalent of species packing (MacArthur, 1970; Pielou, 1975). METHODS
Packing coprophilous fungi in rabbit faeces The spores of six coprophilous fungi, Sordaria fimicola (Rab.) Ces. & De Not., Sordaria humana (Fckl) Wint., Podospora curoicolla (Wint.) Niessl, Podospora setosa (Wint.) Niessl, Ascodesmis sphaerospora Obrist and an unidentified species of Coprinus, were harvested from cultures grown on autoclaved rabbit dung and suspended in sterile distilled water; the spores of each species were then individually distributed by mist sprayer onto separate lots of non-sterile pellets, of rabbit food (Harper & Webster, 1964). The inoculated rabbit food was allowed to air dry (24 h) beneath a sterile microbiological hood and then was transferred to closed paper containers for storage. Rabbit faeces were naturally inoculated with coprophilous fungi by feeding a laboratory rabbit with a 4 g ration of inoculated rabbit food. When not being fed the inoculated food, the rabbit was otherwise maintained on a diet of commercial, pelleted, rabbit food, free of coprophilous fungi. To obtain combinations of coprophilous fungi in the same faecal pellets, equal portions (2, 4 or 6) of the differently inoculated rabbit food were
Species numbers and decomposition of faeces
3°
combined to total 4 g. At approximately 2 h intervals for the next 18 h, the faeces produced were aseptically transferred from a catch screen beneath the cage to pre-weighed aluminum weighing dishes. Enough faeces were placed in each dish to cover the bottom of the weighing dish, usually about twenty with a dry weight of 3 to 4 g. The weighing dishes were placed under a sterile microbiological hood to allow the faeces to air dry. Prelim inary experiments showed that when the rabbit was fed a single morning ration of inoculated food, most of the faeces the rabbit produced during the next 24 h developed sporocarps of the particular fungus used as the inoculum. Between successive inoculations of faeces with individual fungi or combinations of fungi, the rabbit was maintained on non-inoculated food for at least 1 week, a period that was sufficient to allow for the expulsion of any remaining fungal inoculum. Although considerable effort was made to avoid contamination during the preparation of the fungal inoculum and the collection and incubation offaeces, Chaetomium bostrychodes and one or more species of hyphomycetes were regular contaminants of all treatments except where Podospora setosa was used singly. Faeces were inoculated according to the following scheme; Single species: Ascodesmis sphaerospora, Coprinus sp., Podospora curvico/la, Podospora setosa, Sordaria fimicola, and Sordaria humana; Paired species: P. curoicolla and P. setosa; S. fimicola and S. humana; Multiple species combinations; both Podospora species with both Sordaria species; all fungal isolates (six together) . Ascodesmis sphaerospora was isolated from dried sewage sludge collected near Meadville, Pa.; all other fungal isolates used in this study were taken from laboratory-incubated rabbit faeces. Determination of faecal decomposition rates Air-dried faecal samples were weighed to the nearest tenth of a milligram and saturated with
Table
1.
10 em" sterile distilled water. Each weighing dish was placed in a separate Petri dish 'moist chamber ' for 30 days and incubated at 22 to 24 ° after the method of Angel & Wicklow (1974). At weekly intervals the faecal surfaces were carefully examined microscopically for the presence of fungal sporocarps. Nematodes were not observed in any sample. At the end of the incubation period, five samples from each treatment were selected for reweighing provided that sporocarps of all the fungal species present in the original inoculated rabbit food were found on the faecal surfaces and there were few or no fungi present. Samples selected according to these criteria were oven dried at 60°, cooled in a desiccator, and reweighed and the mean weight loss for cohorts of five samples for each treatment calculated. A one-way analysis of variance (ANOVA) was performed on the percentage weight loss values transformed using the arcsin transformation of Sokal & Rohlf (1969) and a posteriori test (Student-Newrnan-Keuls test), (Sokal & Rohlf, 1969) was carried out to determine which means differed significantly from one another.
RESUL TS AND DISCUSSION
The different combinations of coprophilous fungal species had a significant effect (P < 0'05, ANOVA results) on the percentage of weight lost by the faeces. Values representing the mean weight lost for each treatment and the results of the Student, Newman, Kuels (S.N.K.) test are presented in Table 1. Decomposition losses were greater for single species inoculations of Sordaria fimicola and Coprinus sp. than for any other treatment combination. Somewhat lower percentage weight losses were recorded for Sordaria humana occurring as the sole fungal colonist, and single species inoculations of Podospora curvico/la, P. setosa and
Decomposition (%) of rabbit faeces using different combinations of coprophilous fungi during a 30 d moist chamber incubation at room temperature (23-24 "C) Sordaria fimicola
(24'0%)a}
Sordaria humana
(20'7%)b
Podospora curvicol/a
(16'6 %)C}
Padospora serosa
(14'0 %)C
Coprinus sp.
(24'4 %)a}
(20'8%)b} ( l S'7% )C
(13'9%)c (lS '3 % )c
Ascodesmis sphaerospora (t6'o %)c Values assigned the sameletter (a, b or c) do not differsignificantly (P> 0'05), whereas valuesshowingdifferent letters are significantly different (P < 0'05) .
D. T. Wicklow and D. H. Yocom Ascodesmis sphaerospora. However in no instance did a given pairing or multiple species combination result in weight losses greater than those recorded when each of the participants occurred separately. Instead, species combinations involving individuals showing different amounts of decomposition always resulted in weight losses equal to that of the least efficient decomposer(s). Development of sporocarps was taken as evidence that each fungus successfully produced a mycelial network within the faecal samples to which it was added and therefore made demands on substrate for resources. We made no attempt to quantify the numbers of sporocarps of the individual species. These results support the idea that additions of several species to a resource may lead to increased competition, which in turn prevents the efficient utilization of the resource. In the current Hutchinsonian usage, an organism's niche is an n-dimensional hypervolume, where n is the number of environmental factors affecting the organism (Hutchinson, 1957). The genetic properties of the organism determine its fundamental niche, while the resource structure of the ecosystem and the occurrence of other organisms determine the actual niche dimensions occupied in nature. If there is overlap in the niche hypervolumes of two or more species populations and a particular environmental resource is in insufficient supply to meet the demands of these populations, then interspecific competition ensues. Niche relations within the overlap zones of coprophilous fungal communities are likely to be complex, with multiple interactions of both a co-operative and a dis-operative nature. Harper & Webster (1964) and Ikediugwu & Webster (1970) experimentally altered the realized niche of selected coprophilous fungi by incorporating an aggressive competitor into the fungal community. Fewer apothecia of Ascobolus crenulatus were produced in the presence of Coprinusheptemerus, the latter being antagonistic to A. crenulatus in cultural tests. In this example, addition of C. heptemerus presumably caused some overlap along critical niche parameters. Wicklow & Hirschfield (1979) present evidence of a competitive hierarchy among coprophilous fungal populations colonizing cattle faeces. Slowergrowing and later-appearing successional species were shown to interfere with the growth of aU other fungal colonists in cultural tests. Wicklow & Hirschfield theorized that interference competition would reduce the importance of rapidly growing early sporulating species, thus allowing for a greater subdivision of substrate resources among a potentially larger numbers of species. Our results have important bearing on such a concept. Rapidly growing and early sporulating species such as
Sordaria fimicola and S. humana brought about significantly greater decomposition losses when grown singly or paired with one another than when combined with Podospora curvicolla and P. setosa. Podospora spp. are generally slower to develop perithecia than are Sordaria spp., and appear later in the coprophilous succession (Harper & Webster, 1964; Larsen, 1971; Wicklow & Moore, 1974; Lodha, 1974). Should either or both species of Podospora interfere with the growth of Sordaria spp., this would account for the lowered rate of faecal decomposition. Numerous examples can be cited from the mycological literature showing that interference competition is important in the organization of fungal communities. Few of these studies, however, examine the potential importance of these competitive situations as they affect substrate decomposition. Norman (1930) reported that when species of fungi or actinomycetes isolated from samples of oat or rye straw were combined on sterile (autoclaved) oat straw, the temperatures generated during this fermentation were always depressed as compared with temperatures obtained when the same fungi were cultured individually. In cultural pairings, the combination usually gave a temperature near that of the species with lesser thermogenic capability. Microbial activity and heat produced were greatest and decomposition more rapid and complete when naturally contaminated wheat straw was incubated in the same way, leaving Norman (1930) to conclude that the natural decomposition of plant tissues should probably be viewed in the aggregate as a co-operative decomposition of a high order. The dung microcosm offers an ideal system for experimental studies on the biotic and abiotic factors affecting fundamental versus realized niches of fungi. One can experimentally determine how the addition or elimination of one species affects the growth and sporulation of other species. Our results show that removal of a fungal competitor can result in greater resource exploitation by the remaining species. This research was supported in part by Grant DEB 77-09443 from the National Science Foundation. REFERENCES
ANGEL, K. & WICKLOW, D. T. (1974). Decomposition of rabbit feces: An indication of the significance of the coprophilous rnicroflora in energyflow schemes. Journal of Ecology 6z, 429-437.
BLANCHETTE, R. A. & SHAW, G. C. (1978). Associations among bacteria, yeasts, and basidiomycetes during wooddecay. Phytopathology 68, 631-637.
Species numbers and decomposition of faeces BROWN, J. L . (1964). The evolution of diversity in avian territorial systems. Wilson Bulletin 76,160-169. BRUEHL, G. W., MlLLAR, R. L. & CuNFER, B. (1969). Significance of antibiotic production by Cephalosporium gramineum to its saprophytic survival. Canadian Journal of Plant Science 49,235-246. HARPER, J. E. & WEBSTER, J. (1964). An experimental analysis of the coprophilous fungal succession. Transactions of the British Mycological Society 47, 511-53 0 . HUTCHINSON, G. E. (1957). Concluding remarks. Cold Spri'llf Harbor Symposium on Quantitative Biology ZZ, 415-427. lKEDWGwu, F. ·E . O. & WEBSTER, J. (1970). Antagonism between Coprinus heptemerus and other coprophilous fungi . Transactions of the British Mycological Society 54, 181-204· LARSEN, K. (1971). Danish endocoprophilous fungi and their sequence of occurrence. Botanisk Tidsskrift 66, 1-32. LODHA, B. C. (1974). Decomposition of digested litter. In Biology of Plant Litter Decomposition, I (ed, C. H. Dickinson & G. J. F. Pugh), pp. 213-241. New York: Academic Press. MAcARTHUR, R. (1970). Species packing and competitive equilibrium for many species. Theoretical Population Biology 1, 1-11. MILLER, R. S. (1967). Pattern and process in competition . Advances in Ecological Research 4,1-74. MULLER, C. H . (1966). The role of chemical inhibition (allelopathy) in vegetational composition. Bulletin of the Torrey Botanical Club 93, 332-351.
NORMAN, A. G. (1930). The biological decomposition of plant materials. III. Physiological studies on some cellulose-decomposing fungi. Annals of Applied B iology 17, 575-613. PIELOU, E. C. (1975). Ecological Diversity. New York: J. Wiley & Sons. RICE, E. L. (1974). Allelopathy, New York: Academic Press. ROOT, R. B. (1969). The behavior and reproductive success of the blue-grey gnat catcher. Condor 71, 16-31. SHORTLE, W. C. & COWLING, E. B. (1978). Interaction of live sapwood and fungi commonly found in discolored and decayed wood. Phytopathology 68, 61 7-623. SOKAL, R. R. & ROHLF, J. (1969). Biometry. New York: Freeman. WAKSMAN, S. A. & CORDON, T. C. (1939). Thermophilic decomposition of plant residues in composts by pure and mixed cultures of microorganisms. Soil Science 47, 217-224. WICKLOW, D. T . & HIRSCHFIELD, B. J. (1979). Evidence of a competitive hierarchy among coprophilous fungal populations. Canadian Journal of Microbiology :Z5, 855-858 . WICKLOW, D . T. & MOORE, V. (1974). Effect of incubation temperature on the coprophilous fungal succession. Tran sactions of the British Mycological Society 6z, 411-415. WOLF, L. L . & HAINSWORTH, F. R. (1971). Time and energy budgets of territorial hummingbirds. Ecology 52, 980--988.
(Received for publication 14 February 1980)
Printedin GreatBritain
FUNGAL SPECIES NUMBERS AND DECOMPOSITION OF RABBIT FAECES By D. T. WICKLOW Northern Regional Research Center, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Peoria, Illinois 61604 D. H. YOCOM Department of Ecology and Evolution, State University of New York at Stony Brook, Stony Brook, New York 11794 AND
Evidence is presented that additions of fungal species to herbivore dung result in a decreased ability of competing microflora to utilize available substrate. When two or more species of coprophilous fungi were combined in rabbit faeces, faecal decomposition rates were limited to the slower of the rates recorded when the same species were incubated separately. A reduced decomposition rate could enable slower-growing and later-appearing species to secure the substrate resources necessary for mycelial growth and sporulation. Microbial ecologists traditionally have supported the notion that the greater the species riclmess of the saprobic microfloral community colonizing a natural substrate the more rapid the rate of decomposition of that substrate. For example, Waksman & Cordon (1939) argued that no single pure culture could give as extensive and rapid decomposition as the total mixed microbial population of a compost. One might anticipate that the greater the diversity of the microbial decomposer community, the more enzymaticbiochemical diversity the community can draw upon in attacking a substrate, and the more completely that substrate might be utilized. Furthermore, mutualistic associations among certain species populations of saprophytic microbes may also significantly increase decomposition losses (Blanchette & Shaw, 1978; Shortle & Cowling, 1978). Alternatively, competition among species populations also has been shown to reduce the exploitation of a resource (Root, 1969; Wolf & Hainsworth, 1971) or directly interfere with access to a resource (Brown, 1964; Muller, 1966; Miller, 1967; Bruehl, Millar & Cunfer, 1969; Rice, 1974). It can be argued that by increasing the number of saprobic species comprising a decomposer community, one also increases the potential for competitive interactions. This study was designed to explore these contrasting ecological views by examining the effects of increasing fungal species number on resource utilization as measured by decomposition losses from rabbit faeces. Fresh faecal substrates represent unexploited resource islands. Harper &
Webster (1964) describe a methodology that allows one to manipulate the composition of the fungal community on these 'islands' while not affecting other components of the faecal microflora or in any way modifying the structural integrity or chemical composition of the faecal pellets. From a mycologist's perspective, this represents the empirical equivalent of species packing (MacArthur, 1970; Pielou, 1975). METHODS
Packing coprophilous fungi in rabbit faeces The spores of six coprophilous fungi, Sordaria fimicola (Rab.) Ces. & De Not., Sordaria humana (Fckl) Wint., Podospora curoicolla (Wint.) Niessl, Podospora setosa (Wint.) Niessl, Ascodesmis sphaerospora Obrist and an unidentified species of Coprinus, were harvested from cultures grown on autoclaved rabbit dung and suspended in sterile distilled water; the spores of each species were then individually distributed by mist sprayer onto separate lots of non-sterile pellets, of rabbit food (Harper & Webster, 1964). The inoculated rabbit food was allowed to air dry (24 h) beneath a sterile microbiological hood and then was transferred to closed paper containers for storage. Rabbit faeces were naturally inoculated with coprophilous fungi by feeding a laboratory rabbit with a 4 g ration of inoculated rabbit food. When not being fed the inoculated food, the rabbit was otherwise maintained on a diet of commercial, pelleted, rabbit food, free of coprophilous fungi. To obtain combinations of coprophilous fungi in the same faecal pellets, equal portions (2, 4 or 6) of the differently inoculated rabbit food were
Species numbers and decomposition of faeces
3°
combined to total 4 g. At approximately 2 h intervals for the next 18 h, the faeces produced were aseptically transferred from a catch screen beneath the cage to pre-weighed aluminum weighing dishes. Enough faeces were placed in each dish to cover the bottom of the weighing dish, usually about twenty with a dry weight of 3 to 4 g. The weighing dishes were placed under a sterile microbiological hood to allow the faeces to air dry. Prelim inary experiments showed that when the rabbit was fed a single morning ration of inoculated food, most of the faeces the rabbit produced during the next 24 h developed sporocarps of the particular fungus used as the inoculum. Between successive inoculations of faeces with individual fungi or combinations of fungi, the rabbit was maintained on non-inoculated food for at least 1 week, a period that was sufficient to allow for the expulsion of any remaining fungal inoculum. Although considerable effort was made to avoid contamination during the preparation of the fungal inoculum and the collection and incubation offaeces, Chaetomium bostrychodes and one or more species of hyphomycetes were regular contaminants of all treatments except where Podospora setosa was used singly. Faeces were inoculated according to the following scheme; Single species: Ascodesmis sphaerospora, Coprinus sp., Podospora curvico/la, Podospora setosa, Sordaria fimicola, and Sordaria humana; Paired species: P. curoicolla and P. setosa; S. fimicola and S. humana; Multiple species combinations; both Podospora species with both Sordaria species; all fungal isolates (six together) . Ascodesmis sphaerospora was isolated from dried sewage sludge collected near Meadville, Pa.; all other fungal isolates used in this study were taken from laboratory-incubated rabbit faeces. Determination of faecal decomposition rates Air-dried faecal samples were weighed to the nearest tenth of a milligram and saturated with
Table
1.
10 em" sterile distilled water. Each weighing dish was placed in a separate Petri dish 'moist chamber ' for 30 days and incubated at 22 to 24 ° after the method of Angel & Wicklow (1974). At weekly intervals the faecal surfaces were carefully examined microscopically for the presence of fungal sporocarps. Nematodes were not observed in any sample. At the end of the incubation period, five samples from each treatment were selected for reweighing provided that sporocarps of all the fungal species present in the original inoculated rabbit food were found on the faecal surfaces and there were few or no fungi present. Samples selected according to these criteria were oven dried at 60°, cooled in a desiccator, and reweighed and the mean weight loss for cohorts of five samples for each treatment calculated. A one-way analysis of variance (ANOVA) was performed on the percentage weight loss values transformed using the arcsin transformation of Sokal & Rohlf (1969) and a posteriori test (Student-Newrnan-Keuls test), (Sokal & Rohlf, 1969) was carried out to determine which means differed significantly from one another.
RESUL TS AND DISCUSSION
The different combinations of coprophilous fungal species had a significant effect (P < 0'05, ANOVA results) on the percentage of weight lost by the faeces. Values representing the mean weight lost for each treatment and the results of the Student, Newman, Kuels (S.N.K.) test are presented in Table 1. Decomposition losses were greater for single species inoculations of Sordaria fimicola and Coprinus sp. than for any other treatment combination. Somewhat lower percentage weight losses were recorded for Sordaria humana occurring as the sole fungal colonist, and single species inoculations of Podospora curvico/la, P. setosa and
Decomposition (%) of rabbit faeces using different combinations of coprophilous fungi during a 30 d moist chamber incubation at room temperature (23-24 "C) Sordaria fimicola
(24'0%)a}
Sordaria humana
(20'7%)b
Podospora curvicol/a
(16'6 %)C}
Padospora serosa
(14'0 %)C
Coprinus sp.
(24'4 %)a}
(20'8%)b} ( l S'7% )C
(13'9%)c (lS '3 % )c
Ascodesmis sphaerospora (t6'o %)c Values assigned the sameletter (a, b or c) do not differsignificantly (P> 0'05), whereas valuesshowingdifferent letters are significantly different (P < 0'05) .
D. T. Wicklow and D. H. Yocom Ascodesmis sphaerospora. However in no instance did a given pairing or multiple species combination result in weight losses greater than those recorded when each of the participants occurred separately. Instead, species combinations involving individuals showing different amounts of decomposition always resulted in weight losses equal to that of the least efficient decomposer(s). Development of sporocarps was taken as evidence that each fungus successfully produced a mycelial network within the faecal samples to which it was added and therefore made demands on substrate for resources. We made no attempt to quantify the numbers of sporocarps of the individual species. These results support the idea that additions of several species to a resource may lead to increased competition, which in turn prevents the efficient utilization of the resource. In the current Hutchinsonian usage, an organism's niche is an n-dimensional hypervolume, where n is the number of environmental factors affecting the organism (Hutchinson, 1957). The genetic properties of the organism determine its fundamental niche, while the resource structure of the ecosystem and the occurrence of other organisms determine the actual niche dimensions occupied in nature. If there is overlap in the niche hypervolumes of two or more species populations and a particular environmental resource is in insufficient supply to meet the demands of these populations, then interspecific competition ensues. Niche relations within the overlap zones of coprophilous fungal communities are likely to be complex, with multiple interactions of both a co-operative and a dis-operative nature. Harper & Webster (1964) and Ikediugwu & Webster (1970) experimentally altered the realized niche of selected coprophilous fungi by incorporating an aggressive competitor into the fungal community. Fewer apothecia of Ascobolus crenulatus were produced in the presence of Coprinusheptemerus, the latter being antagonistic to A. crenulatus in cultural tests. In this example, addition of C. heptemerus presumably caused some overlap along critical niche parameters. Wicklow & Hirschfield (1979) present evidence of a competitive hierarchy among coprophilous fungal populations colonizing cattle faeces. Slowergrowing and later-appearing successional species were shown to interfere with the growth of aU other fungal colonists in cultural tests. Wicklow & Hirschfield theorized that interference competition would reduce the importance of rapidly growing early sporulating species, thus allowing for a greater subdivision of substrate resources among a potentially larger numbers of species. Our results have important bearing on such a concept. Rapidly growing and early sporulating species such as
Sordaria fimicola and S. humana brought about significantly greater decomposition losses when grown singly or paired with one another than when combined with Podospora curvicolla and P. setosa. Podospora spp. are generally slower to develop perithecia than are Sordaria spp., and appear later in the coprophilous succession (Harper & Webster, 1964; Larsen, 1971; Wicklow & Moore, 1974; Lodha, 1974). Should either or both species of Podospora interfere with the growth of Sordaria spp., this would account for the lowered rate of faecal decomposition. Numerous examples can be cited from the mycological literature showing that interference competition is important in the organization of fungal communities. Few of these studies, however, examine the potential importance of these competitive situations as they affect substrate decomposition. Norman (1930) reported that when species of fungi or actinomycetes isolated from samples of oat or rye straw were combined on sterile (autoclaved) oat straw, the temperatures generated during this fermentation were always depressed as compared with temperatures obtained when the same fungi were cultured individually. In cultural pairings, the combination usually gave a temperature near that of the species with lesser thermogenic capability. Microbial activity and heat produced were greatest and decomposition more rapid and complete when naturally contaminated wheat straw was incubated in the same way, leaving Norman (1930) to conclude that the natural decomposition of plant tissues should probably be viewed in the aggregate as a co-operative decomposition of a high order. The dung microcosm offers an ideal system for experimental studies on the biotic and abiotic factors affecting fundamental versus realized niches of fungi. One can experimentally determine how the addition or elimination of one species affects the growth and sporulation of other species. Our results show that removal of a fungal competitor can result in greater resource exploitation by the remaining species. This research was supported in part by Grant DEB 77-09443 from the National Science Foundation. REFERENCES
ANGEL, K. & WICKLOW, D. T. (1974). Decomposition of rabbit feces: An indication of the significance of the coprophilous rnicroflora in energyflow schemes. Journal of Ecology 6z, 429-437.
BLANCHETTE, R. A. & SHAW, G. C. (1978). Associations among bacteria, yeasts, and basidiomycetes during wooddecay. Phytopathology 68, 631-637.
Species numbers and decomposition of faeces BROWN, J. L . (1964). The evolution of diversity in avian territorial systems. Wilson Bulletin 76,160-169. BRUEHL, G. W., MlLLAR, R. L. & CuNFER, B. (1969). Significance of antibiotic production by Cephalosporium gramineum to its saprophytic survival. Canadian Journal of Plant Science 49,235-246. HARPER, J. E. & WEBSTER, J. (1964). An experimental analysis of the coprophilous fungal succession. Transactions of the British Mycological Society 47, 511-53 0 . HUTCHINSON, G. E. (1957). Concluding remarks. Cold Spri'llf Harbor Symposium on Quantitative Biology ZZ, 415-427. lKEDWGwu, F. ·E . O. & WEBSTER, J. (1970). Antagonism between Coprinus heptemerus and other coprophilous fungi . Transactions of the British Mycological Society 54, 181-204· LARSEN, K. (1971). Danish endocoprophilous fungi and their sequence of occurrence. Botanisk Tidsskrift 66, 1-32. LODHA, B. C. (1974). Decomposition of digested litter. In Biology of Plant Litter Decomposition, I (ed, C. H. Dickinson & G. J. F. Pugh), pp. 213-241. New York: Academic Press. MAcARTHUR, R. (1970). Species packing and competitive equilibrium for many species. Theoretical Population Biology 1, 1-11. MILLER, R. S. (1967). Pattern and process in competition . Advances in Ecological Research 4,1-74. MULLER, C. H . (1966). The role of chemical inhibition (allelopathy) in vegetational composition. Bulletin of the Torrey Botanical Club 93, 332-351.
NORMAN, A. G. (1930). The biological decomposition of plant materials. III. Physiological studies on some cellulose-decomposing fungi. Annals of Applied B iology 17, 575-613. PIELOU, E. C. (1975). Ecological Diversity. New York: J. Wiley & Sons. RICE, E. L. (1974). Allelopathy, New York: Academic Press. ROOT, R. B. (1969). The behavior and reproductive success of the blue-grey gnat catcher. Condor 71, 16-31. SHORTLE, W. C. & COWLING, E. B. (1978). Interaction of live sapwood and fungi commonly found in discolored and decayed wood. Phytopathology 68, 61 7-623. SOKAL, R. R. & ROHLF, J. (1969). Biometry. New York: Freeman. WAKSMAN, S. A. & CORDON, T. C. (1939). Thermophilic decomposition of plant residues in composts by pure and mixed cultures of microorganisms. Soil Science 47, 217-224. WICKLOW, D. T . & HIRSCHFIELD, B. J. (1979). Evidence of a competitive hierarchy among coprophilous fungal populations. Canadian Journal of Microbiology :Z5, 855-858 . WICKLOW, D . T. & MOORE, V. (1974). Effect of incubation temperature on the coprophilous fungal succession. Tran sactions of the British Mycological Society 6z, 411-415. WOLF, L. L . & HAINSWORTH, F. R. (1971). Time and energy budgets of territorial hummingbirds. Ecology 52, 980--988.
(Received for publication 14 February 1980)