Chapter 2 - Human and Environmental Factors Influence Soil ...lab. ... indirectly...

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  • Author's Personal Copy

    Human and Environmental Factors Inf luence Soil Faunal Abundance–Mass

    Allometry and Structure

    DANIEL C. REUMAN, JOEL E. COHENANDCHRISTIANMULDER

    Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 II. Soil Faunal Descriptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

    A. Abundance–Mass Slope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 B. Faunal Diversity and Total Biomass . . . . . . . . . . . . . . . . . . . . . . . . 52 C. Abundance–Mass Intercept and Expected Log Population Density

    of Smallest Taxa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 III. Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

    A. Data on Taxonomy, Average Body‐Mass, and Population Density 53 B. Environmental Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 C. Human‐Use Data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 D. Carbon Resource Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

    IV. Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 A. Classification of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 B. Stepwise Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 C. Testing Assumptions of Linear Models. . . . . . . . . . . . . . . . . . . . . . 56

    V. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 A. Models of Soil Faunal Community Structure . . . . . . . . . . . . . . . . . 57 B. Relative Importance of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 57 C. Interpreting Variation in Structure . . . . . . . . . . . . . . . . . . . . . . . . . 60 D. Testing for Artifacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

    VI. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 A. Food Web Descriptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 B. Relative Importance of Variables . . . . . . . . . . . . . . . . . . . . . . . . . . 70 C. Limitations of This Study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 D. Future Directions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

    Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Appendix I. Stepwise Regression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Appendix II. Testing Assumptions of Linear Models . . . . . . . . . . . . . . . . . . . 75 Appendix III. Detailed Statistical Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

    A. Abundance–Mass Slope. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 B. Log Faunal Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 C. Faunal Diversity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 D. Abundance–Mass Intercept and Expected Log Population

    Density of Smallest Taxa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 E. Log Faunal Population Density . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

    References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

    ADVANCES IN ECOLOGICAL RESEARCH VOL. 41 0065-2504/09 $35.00

    # 2009 Daniel C. Reuman and co-authors. DOI: 10.1016/S0065-2504(09)00402-4 Published by Elsevier Ltd. All rights reserved

  • 46 DANIEL C. REUMAN ET AL.

    Author's Personal Copy

    SUMMARY

    We examined structural variation in soil faunal communities from 146

    agroecosystems in The Netherlands, using a unique database of taxonomi-

    cally highly resolved soil samples gathered by uniform methods. For each

    site, data included measurements of average body mass (M) and population

    density (N) of each detected taxon and environmental and human‐use factors. We used three descriptors of soil faunal community structure:

    abundance–mass slope, which is the slope of the regression line through all

    faunal taxa in a site plotted on log(N)‐versus‐log(M) coordinates (all loga- rithms were base 10); the taxonomic diversity of each community’s fauna

    (number of animal taxa at the finest available level of taxonomic resolution);

    and the total biomass of all fauna. The goal of the study was to account for

    variation in these descriptors and to develop causal hypotheses.

    These structural descriptors varied systematically. More than half of the

    variation in each descriptor was explained by external human, environmen-

    tal, and biotic influences. Few predictors were needed to explain structural

    variation: above‐ground ecosystem type (ET, describing the kind of human management); soil bacterial biomass; and a measure of precipitation. ET was

    the most important predictor of below‐ground faunal community structure. Abundance–mass slopes ranged from –0.85 to –0.07 with mean –0.51;

    only four slopes were more negative than –3/4 (i.e., the log(N)‐versus‐ log(M) regression line was steeper than –3/4). Slopes less negative than –1

    (respectively, –3/4) indicated that, on average, taxon biomass (respectively,

    taxon energy consumption) increased with taxon body mass. Abundance–

    mass slope was more negative in more disturbed sites than in less disturbed

    sites. Disturbance may have produced this pattern by affecting populations

    of large‐M taxa, which are slower to reproduce, more than small‐M taxa. Across some types of site (super‐intensive farms and possibly intensive farms), greater soil bacterial biomass was associated with less‐negative abundance–mass slope, suggesting top‐down control of bacterivorous taxa. ET and soil bacterial biomass were sufficient to explain most of the variation

    in the whole abundance–mass allometric relationship, including slope and

    intercept.

    Total faunal biomasses were higher in recently fertilized sites. Greater soil

    bacterial biomass was associated with the same increase in log faunal bio-

    mass between sites, on average, for all ET. Taxonomic diversity differed in

    sites of different ET in a way related to human disturbance. Precipitation

    was associated oppositely with diversity in sites of different types. Testable

    mechanistic hypotheses for the patterns observed here are discussed.

  • ABUNDANCE–MASS ALLOMETRY IN FOOD WEBS 47

    Author's Personal Copy

    I. INTRODUCTION

    For decades, studies have examined the influence on food web structure of

    factors such as environmental variability (Briand, 1983); three‐ versus two‐ dimensionality of habitat (Briand and Cohen, 1987); amount of primary

    productivity (Briand and Cohen, 1987; Vander Zanden et al., 1999); acidifi-

    cation in lakes (Locke and Sprules, 1994); habitat duration patterns in

    temporary ponds (Schneider, 1997); habitat size (Spencer and Warren,

    1996; Vander Zanden et al., 1999); and disturbance or ‘‘stress’’ (Havens,

    1994; Jenkins et al., 1992). Differences in food web (henceforth web) struc-

    ture by habitat type (e.g., pelagic versus terrestrial; Bengtsson, 1994; Cohen,

    1994; Havens, 1997) and over time and space using habitats of the same type

    (Carney et al., 1997; Clarke, 1998; Closs and Lake, 1994; Schoenly and

    Cohen, 1991) have also been investigated. Differences in web structure

    have typically been measured with a suite of descriptors based on the binary

    predation matrix (P ¼ [pij], where pij is 1 if taxon j eats taxon i, regardless of how often this occurs, and 0 otherwise), such as: link density; various kinds

    of connectances (Warren, 1994, gives definitions); proportions of top, inter-

    mediate, and basal taxa; and minimum, mean, modal, median, and maximal

    food‐chain length (where the length of a food chain is the number of trophic links that comprise it).

    However, web studies have been criticized for using data of poor quality,

    based on insufficient sampling of ecosystems (Bersier et al., 1999; Cohen

    et al., 1993; Hall and Raffaelli, 1991; Martinez, 1991; Polis, 1991; Polis and

    Strong, 1996; Winemiller, 1990). Statistics such as connectance and modal

    food‐chain length depend sensitively on sampling effort (Goldwasser and Roughgarden, 1997; Martinez et al., 1999; Winemiller, 1990). Incomplete

    sampling limits even modern webs (Woodward et al., 2005, their Figure 3).

    Descriptors of web structure based on detailed trophic data are especially

    vulnerable to undersampling because ‘‘the detection of trophic links system-

    atically lags behind the detection and inclusion of species, which may render

    the accurate measurement of many web properties inherently problematic’’

    (Goldwasser and Roughgarden, 1997).

    In response to the sensitivity of traditional web descriptors to sampling

    effort, several authors called for quantitative measures of trophic links, so

    that the inten