Hypothesis-testing methods for multivariate data are needed to make rigorous probability statements about the effects of factors and their interactions in experiments. Analysis of variance is particularly powerful for the analysis of univariate data. The traditional multivariate analogues, however, are too stringent in their assumptions for most ecological multivariate data sets. Non-parametric methods, based on permutation tests, are preferable. This paper describes a new non-parametric method for multivariate analysis of variance, after McArdle and Anderson (in press). It is given here, with several applications in ecology, to provide an alternative and perhaps more intuitive formulation for ANOVA (based on sums of squared distances) to complement the description pro- vided by McArdle and Anderson (in press) for the analysis of any linear model. It is an improvement on previous non-parametric methods because it allows a direct additive partitioning of variation for complex models. It does this while maintaining the flexibility and lack of formal assumptions of other non-parametric methods. The test- statistic is a multivariate analogue to Fisher's F-ratio and is calculated directly from any symmetric distance or dissimilarity matrix. P-values are then obtained using permutations. Some examples of the method are given for tests involving several factors, including factorial and hierarchical (nested) designs and tests of interactions.

/pdf/a-new-method-for-non-parametric-multivariate-analysis-of-2zyb4px7ty.pdf

A new method for non-parametric multivariate analysis of variance

Metabolism provides a basis for using first principles of physics, chemistry, and biology to link the biology of individual organisms to the ecology of populations, communities, and ecosystems. Metabolic rate, the rate at which organisms take up, transform, and expend energy and materials, is the most fundamental biological rate. We have developed a quantitative theory for how metabolic rate varies with body size and temperature. Metabolic theory predicts how metabolic rate, by setting the rates of resource uptake from the environment and resource allocation to survival, growth, and reproduction, controls ecological processes at all levels of organization from individuals to the biosphere. Examples include: (1) life history attributes, including devel- opment rate, mortality rate, age at maturity, life span, and population growth rate; (2) population interactions, including carrying capacity, rates of competition and predation, and patterns of species diversity; and (3) ecosystem processes, including rates of biomass production and respiration and patterns of trophic dynamics. Data compiled from the ecological literature strongly support the theoretical predictions. Even- tually, metabolic theory may provide a conceptual foundation for much of ecology, just as genetic theory provides a foundation for much of evolutionary biology.

/pdf/toward-a-metabolic-theory-of-ecology-1dxmg8xr3n.pdf

Toward a metabolic theory of ecology

The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

The number of prokaryotes and the total amount of their cellular carbon on earth are estimated to be 4-6 3 10 30 cells and 350-550 Pg of C (1 Pg 5 10 15 g), respectively. Thus, the total amount of prokaryotic carbon is 60-100% of the estimated total carbon in plants, and inclusion of prokaryotic carbon in global models will almost double estimates of the amount of carbon stored in living organisms. In addition, the earth's prokaryotes contain 85-130 Pg of N and 9-14 Pg of P, or about 10-fold more of these nutrients than do plants, and represent the largest pool of these nutrients in living organisms. Most of the earth's prokaryotes occur in the open ocean, in soil, and in oceanic and terrestrial subsurfaces, where the numbers of cells are 1.2 3 10 29 , 2.6 3 10 29 , 3.5 3 10 30 , and 0.25-2.5 3 10 30 , respectively. The numbers of het- erotrophic prokaryotes in the upper 200 m of the open ocean, the ocean below 200 m, and soil are consistent with average turnover times of 6-25 days, 0.8 yr, and 2.5 yr, respectively. Although subject to a great deal of uncertainty, the estimate for the average turnover time of prokaryotes in the subsurface is on the order of 1-2 3 10 3 yr. The cellular production rate for all prokaryotes on earth is estimated at 1.7 3 10 30 cellsyyr and is highest in the open ocean. The large population size and rapid growth of prokaryotes provides an enormous capacity for genetic diversity. Although invisible to the naked eye, prokaryotes are an essential component of the earth's biota. They catalyze unique and indispensable transformations in the biogeochemical cy- cles of the biosphere, produce important components of the earth's atmosphere, and represent a large portion of life's genetic diversity. Although the abundance of prokaryotes has been estimated indirectly (1, 2), the actual number of pro- karyotes and the total amount of their cellular carbon on earth have never been directly assessed. Presumably, prokaryotes' very ubiquity has discouraged investigators, because an esti- mation of the number of prokaryotes would seem to require endless cataloging of numerous habitats. To estimate the number and total carbon of prokaryotes on earth, several representative habitats were first examined. This analysis indicated that most of the prokaryotes reside in three large habitats: seawater, soil, and the sedimentysoil subsur- face. Although many other habitats contain dense populations, their numerical contribution to the total number of pro- karyotes is small. Thus, evaluating the total number and total carbon of prokaryotes on earth becomes a solvable problem. Aquatic Environments. Numerous estimates of cell density, volume, and carbon indicate that prokaryotes are ubiquitous in marine and fresh water (e.g., 3-5). Although a large range of cellular densities has been reported (10 4 -10 7 cellsyml), the

/pdf/prokaryotes-the-unseen-majority-3576wrrdep.pdf

Prokaryotes: The unseen majority

All terrestrial ecosystems consist of aboveground and belowground components that interact to influence community- and ecosystem-level processes and properties. Here we show how these components are closely interlinked at the community level, reinforced by a greater degree of specificity between plants and soil organisms than has been previously supposed. As such, aboveground and belowground communities can be powerful mutual drivers, with both positive and negative feedbacks. A combined aboveground-belowground approach to community and ecosystem ecology is enhancing our understanding of the regulation and functional significance of biodiversity and of the environmental impacts of human-induced global change phenomena.

http://science.sciencemag.org/content/sci/304/5677/1629.full.pdf

Ecological linkages between aboveground and belowground biota.

Fundamentals of soil ecology

No-tillage (NT) practices can improve soil aggregation and change the distribution and retention of soil organic matter (SOM) compared with conventional tillage (CT), but the relationships between aggregates and SOM fractions are poorly known. The effects of long-term (13-yr) CT and NT management on water-stable aggregates (WSA) and aggregate-associated SOM were investigated on a Hiwassee sandy clay loam (clayey, kaolinitie, thermic Rhodic Kanhapludult). Samples were collected at two depths in replicated CT and NT plots and separated into five aggregate size classes by wet sieving. The stability of intact WSA was measured turbidimetrically. The C and N content of total, participate (POM), and mineral-associated organic matter was determined for each size class. Whole-soil organic C was 18% higher in NT (30.7 Mg C ha-») than in CT (26.1 Mg C ha"). In CT, macroaggregates (>250 um) were fewer and less stable than those of NT. The POM C made up = 36% of whole soil C regardless of tillage, but the quantity of POM was nearly 20% higher in NT than in CT. The POM comprised a higher percentage of total aggregate N in surface soils of NT than in CT and values increased with increases in aggregate size. In NT, concentrations of total and mineral-associated C and N were higher in the 106to 250-|im WSA than in the other size classes but, in CT, the concentrations were similar among size classes. An alternative view of aggregate organization is discussed in which microaggregates are formed in association with POM at the center of macroaggregates, helping to explain relationships between SOM storage and aggregate size distributions under different management practices. C of soils results in the disruption of soil aggregates and the loss of SOM compared with native sod and pasture soils (van Veen and Paul, 1981; Tisdall and Oades, 1982; Elliott, 1986; Kay, 1990). Under CT practices, plowing, harrowing, and rotary tillage result in mixing of the soil profile and the fragmentation and burial of crop residues. These effects tend to moderate the fluctuations of temperature and water in buried residues and increase their proximity to mineral nutrients, thereby enhancing residue decomposition and organic matter transformations (Blevins et al., 1984; Beare et al., 1992). With NT management, the soil is not plowed and crop residues accumulate on the soil surface as a mulch. Several studies have shown that if residues are not removed, NT management can improve soil aggregation and reduce losses of SOM that result from cultivation (Havlinetal., 1990; Carter, 1992; Weill et al,, 1989). However, other studies report few changes in soil aggregation (Hamblin, 1980) and no effects on SOM content other than changes in the depth distribution of SOM with plowing (Angers et al., 1992; Carter and Rennie, 1982). M.H. Beare, Inst. for Crop and Food Research (Lincoln), Private Bag 4704, Christchurch, New Zealand; and P.P. Hendrix, Dep. of Agronomy and Inst. of Ecology, and D.C. Coleman, Inst. of Ecology, Univ. of Georgia, Athens, GA 30602. Received 8 Mar. 1993. Corresponding author. Published in Soil Sci. Soc. Am. J. 58:777-786 (1994). Kaolinitie soils of the southeast USA are characterized by high dispersibility, a factor that may increase the susceptibility of cultivated soils to aggregate disruption, surface crusting, reduced infiltration, and erosion (Miller and Baharuddin, 1986; Sumner, 1992). In warm humid climatic regimes, these factors can contribute to rapid losses of SOM and a decline in the productivity of agricultural soils (Giddens, 1957; Bruce et al., 1990b; Sanchez et al., 1989). Many studies have investigated relationships between whole SOM and WSA (e.g., Chaney and Swift, 1984; Kemper and Koch, 1966; Angers et al., 1992), but relatively few have attempted to isolate and characterize the SOM associated with WSA (Dormaar, 1983; Baldock et al., 1987; Monrozier et al., 1991). Knowledge of aggregate-associated SOM may be important to understanding how changes in aggregation under different tillage and residue management practices contribute to the accumulation and loss of SOM (Elliott, 1986; Gupta and Germida, 1988). These relationships are largely unknown for soils of the southeastern USA. Furthermore, understanding these relationships is crucial for evaluating the applicability of the hierarchical model of aggregate organization (Tisdall and Oades, 1982) to a broader range of soils and management conditions. Both physical and chemical methods have been used to fractionate and characterize SOM. Although the limitations of these individual techniques are well known (Elliott and Cambardella, 1991; Duxbury et al., 1989), various combinations of physical and chemical separation techniques have been used to successfully characterize the chemical composition of primary organo-mineral particle-size fractions (Turchenek and Oades, 1979; Andersonetal., 1981; Tiessen and Stewart, 1983). Cambardella and Elliott (1992) recently described a simple method combining chemical dispersion with particle-size separation to isolate and subsequently characterize particulate and mineral-associated organic matter of native sod and agricultural soils from the Great Plains. Their results suggest that whole soil POM accounts for much of the SOM lost with cultivation of native sod and that NT practices can significantly reduce these losses. In this study, we combined wet-sieving techniques for the isolation of WSA with the chemical dispersion and physical separation methods of Cambardella and Elliott (1992) to investigate relationships between soil aggregation and the location and composition of aggregateassociated SOM in CT and NT soils. Our objectives were to describe the effects of long-term CT and NT management of a double-cropped soil on (i) the size Abbreviations: NT, no-tillage; SOM, soil organic matter; CT, conventional-tillage; WSA, water-stable aggregates; POM, paniculate organic matter; HSB, Horseshoe Bend Experimental Area; FLPOM, floating particulate organic matter; ASI, aggregate stability index; ANOVA, analysis of variance. 777 Published May, 1994

Water-Stable Aggregates and Organic Matter Fractions in Conventional- and No-Tillage Soils

No-tillage (NT) practices can result in greater soil aggregation and higher soil organic matter (SOM) levels than conventional-tillage (CT) practices, but the mechanisms for these effects are poorly known. Our objectives were to describe the size and quality of biologically active pools of aggregate-associated SOM in long-term CT and NT soils of the southeastern USA. Samples were collected from replicated CT and NT plots on a Hiwassee sandy clay loam (clayey, kaolinitic, thermic Rhodic Kanhapludult) and separated into four aggregate size classes (>2000, 250-2000, 106-250, 53-106 m) by wet sieving. Potentially mineralizable C and N and N2O emissions were measured from 20-d laboratory incubations of intact and crushed macroaggregates (>250 m) and intact microaggregates (<250 m). Three primary pools of aggregate-associated SOM were quantified: unprotected, protected, and resistant C and N. Aggregate-unprotected pools of SOM were 21 to 65% higher in surface soils of NT than of CT, with greater differences in the macroaggregate size classes. Disruption of macroaggregates increased the mineralization of SOM in NT but had little effect in CT. Rates of mineralization from protected and unprotected pools of C were higher in surface soils of CT than of NT. Macroaggregateprotected SOM accounted for 18.8 and 19.1% of the total mineralizable C and N (0-15 cm), respectively, in NT but only 10.2 and 5.4% of the total mineralizable C and N in CT. Our results indicate that macroaggregates in NT soils provide an important mechanism for the protection of SOM that may otherwise be mineralized under CT practices.

Aggregate-Protected and Unprotected Organic Matter Pools in Conventional- and No-Tillage Soils

onservation tillage-crop planting systems that leave 30% or more of crop residues on the soil surface instead of plowing them under-is becoming widely adopted in US agriculture. The total area under conservation tillage is estimated to be between 24 and 36 million hectares, or about one-third of the nation's cropland, which represents an increase of about 1,25% during the past decade (Christensen and Magleby 1983). The primary reasons for this increase are that conservation

Detritus Food Webs in Conventional and No-tillage Agroecosystems

We conducted field experiments to test the general hypothesis that the com- position of decomposer communities and their trophic interactions can influence patterns of plant litter decomposition and nitrogen dynamics in ecosystems. Conventional (CT) and no-tillage (NT) agroecosystems were used to test this idea because of their structural sim- plicity and known differences in their functional properties. Biocides were applied to ex- perimentally exclude bacteria, saprophytic fungi, and microarthropods in field exclosures. Abundances of decomposer organisms (bacteria, fungi, protozoa, nematodes, microar- thropods), decomposition rates, and nitrogen fluxes were quantified in surface and buried litterbags (Secale cereale litter) placed in both NT and CT systems. Measurements of in situ soil respiration rates were made concurrently. The abundance and biomass of all microbial and faunal groups were greater on buried than surface litter. The mesofauna contributed more to the total heterotrophic C in buried litter from CT (6-22%) than in surface litter from NT (0.4-1/1%). Buried litter decay rates (1.4-1.7%/d) were -2.5 times faster than rates for surface litter (0.5-O.7%/d). Ratios of fungal to bacterial biomass and fungivore to bacterivore biomass on NT surface litter generally increased over the study period resulting in ratios that were 2.7 and 2.2 times greater, respectively, than those of CT buried litter by the end of the summer. The exclusion experiments showed that fungi had a somewhat greater influence on the decomposition of surface litter from NT while bacteria were more important in the de- composition of buried litter from CT. The fungicide and bactericide reduced decomposition rates of NT surface litter by 36 and 25% of controls, respectively, while in CT buried litter they were reduced by 21 and 35% of controls, respectively. Microarthropods were more important in mobilizing surface litter nitrogen by grazing on fungi than in contributing to litter mass loss. Where fungivorous microarthropods were experimentally excluded, there was less than a 5% reduction in mass loss from litter of both NT and CT, but fungi- fungivore interactions were important in regulating litter N dynamics in NT surface litter. As fungal densities increased following the exclusion of microarthropods on NT surface litter, there was 25% greater N retention as compared to the control after 56 d of decay. Saprophytic fungi were responsible for as much as 86% of the net N immobilized (1.81 g /m2) in surface litter by the end of the study when densities of fungivorous microarthropods were low. Although bacteria were important in regulating buried litter decomposition rates and the population dynamics of bacterivorous fauna, their influence on buried litter N dynamics remains less clear. The larger microbial biomass and greater contribution of a bacterivorous fauna on buried litter is consistent with the greater carbon losses and lower carbon assimilation in CT than NT agroecosystems. In summary, our results suggest that litter placement can strongly influence the com- position of decomposer communities and that the resulting trophic relationships are im- portant to determining the rates and timing of plant litter decomposition and N dynamics. Furthermore, cross placement studies suggest that the decomposer communities within each tillage system, while not discrete, are adapted to the native litter placements in each.

Paul F. Hendrix

Papers

Fundamentals of soil ecology

Water-Stable Aggregates and Organic Matter Fractions in Conventional- and No-Tillage Soils

Aggregate-Protected and Unprotected Organic Matter Pools in Conventional- and No-Tillage Soils

Detritus Food Webs in Conventional and No-tillage Agroecosystems

Microbial and Faunal Interactions and Effects on Litter Nitrogen and Decomposition in Agroecosystems