Heavy browsing by a mammalian herbivore does not affect fluctuating asymmetry of its food plants

ABSTRACT The only 3 published studies relating vertebrate herbivores to plant fluctuating asymmetry (FA) found significant correlations between grazing intensity and plant FA. The general value of these early findings is unclear, however, because FA studies are sensitive to selective reporting, the tendency to publish only a subset of studies that were undertaken. From 2000 to 2003 we quantified the correlations between past herbivory and plant FA in 3 plant–herbivore systems centred on a single mammal species, the North American porcupine (Erethizon dorsatum). We measured leaf FA in pairs of paper birch (Betula papyriferae; n = 24 pairs), quaking aspen ( Populus tremuloides; n = 25 pairs), and jack pine ( Pinus banksiana; n = 15 pairs) trees each containing a control (uneaten) and test (eaten) tree. Although damage incurred by trees from porcupine browsing was severe, we found no statistical association between plant FA and herbivory. We obtained this finding even though our study design did capture subtle variations in plant FA associated to plant genotype or year of sampling. Our study contrasts with earlier findings that plant FA is related to herbivory pressure. There may have been a publication bias as a result of selective reporting in this field of research. Therefore, replication (same hypothesis, same study system) and quasireplication (same hypothesis, different study system) are particularly important.

[1]  E. Zvereva,et al.  Stress responses of Salix borealis to pollution and defoliation , 1997 .

[2]  K. Lempa,et al.  Effects of stress and rapid growth on fluctuating asymmetry and insect damage in birch leaves , 1999 .

[3]  C. Alados,et al.  Assessment of grazing effects on mediterranean shrubs Phillyrea latifolia L. and Cistus monspeliensis L. with developmental instability and fractal dimension , 2002 .

[4]  B. Wilsey,et al.  Leaf fluctuating asymmetry increases with hybridization and elevation in tree-line birches , 1998 .

[5]  D. Berteaux,et al.  SPRING-TO-FALL MASS GAIN IN A NORTHERN POPULATION OF NORTH AMERICAN PORCUPINES , 2005 .

[6]  T. Cornelissen,et al.  Perfect is best: low leaf fluctuating asymmetry reduces herbivory by leaf miners , 2004, Oecologia.

[7]  R. Julkunen‐Tiitto,et al.  Variation in birch bark secondary chemistry between and within clones: implications for herbivory by hares , 2004 .

[8]  W. T. Jackson,et al.  Impact of feeding damage by the porcupine on western hemlock – Sitka spruce forests of north-coastal British Columbia , 1986 .

[9]  Shaw‐Yhi Hwang,et al.  Clonal variation in foliar chemistry of quaking aspen (Populus tremuloides Michx.) , 1996 .

[10]  A. Palmer.  Fluctuating asymmetry analyses: a primer , 1994 .

[11]  T. Whitham,et al.  BEAVERS AS MOLECULAR GENETICISTS: A GENETIC BASIS TO THE FORAGING OF AN ECOSYSTEM ENGINEER , 2004 .

[12]  T. Markow,et al.  Developmental Instability: Its Origins and Evolutionary Implications , 1994, Contemporary Issues in Genetics and Evolution.

[13]  Michael E O'Neill,et al.  Levene Tests of Homogeneity of Variance for General Block and Treatment Designs , 2002, Biometrics.

[14]  Mikhail V. Kozlov,et al.  Effects of Compensatory Fertilization on Pollution-Induced Stress in Scots Pine , 2002 .

[15]  R. Powell,et al.  The North American Porcupine , 1991 .

[16]  M. Otronen,et al.  Morphological asymmetry and chlorophyll fluorescence in Scots pine (Pinus sylvestris): responses to variation in soil moisture, nutrients and defoliation , 2001 .

[17]  J. M. Emlen,et al.  Instability of development and fractal architecture in dryland plants as an index of grazing pressure , 1998 .

[18]  J. M. Emlen,et al.  The impact of grazing on plant fractal architecture and fitness of a Mediterranean shrub Anthyllis cytisoides L. , 1997 .

[19]  J. L. Tomkins,et al.  Fluctuating paradigm , 1999, Proceedings of the Royal Society of London. Series B: Biological Sciences.

[20]  R. J. Putman,et al.  Impact of deer in lowland Britain on agriculture, forestry and conservation habitats. , 1998 .

[21]  A. Møller,et al.  Leaf-mining insects and fluctuating asymmetry in elm Ulmus glabra leaves , 1995 .

[22]  M. Snyder.  SELECTIVE HERBIVORY BY ABERT'S SQUIRREL MEDIATED BY CHEMICAL VARIABILITY IN PONDEROSA PINE' , 1992 .

[23]  A. Møller,et al.  Herbivore effects on developmental instability and fecundity of holm oaks , 2004, Oecologia.

[24]  A. Møller,et al.  Asymmetry, Developmental Stability, and Evolution , 1998 .

[25]  S. Kark,et al.  The use of bilateral asymmetry in ecology and conservation: Concept, developments & prospects , 2001 .

[26]  Julia Koricheva,et al.  Fluctuating asymmmetry of birch leaves increases under pollution impact , 1996 .

[27]  D. A. Spencer.  PORCUPINE POPULATION FLUCTUATIONS IN PAST CENTURIES REVEALED BY DENDROCHRONOLOGY , 1964 .

[28]  C. M. Lessells,et al.  Unrepeatable repeatabilities: a common mistake , 1987 .

[29]  A. Richard Paime.  FLUCTUATING ASYMMETRY: Measurement, Analysis, Patterns , 1986 .

[30]  Mikhail V. Kozlov,et al.  Difference in needle length : A new and objective indicator of pollution impact on scots pine (Pinus sylvestris) , 1999 .

[31]  J. Strengbom,et al.  Response of galling invertebrates on Salix lanata to reindeer herbivory , 2000 .

[32]  Bernard Cazelles,et al.  Porcupine Feeding Scars and Climatic Data Show Ecosystem Effects of the Solar Cycle , 2004, The American Naturalist.

[33]  A. Palmer,et al.  Waltzing with Asymmetry , 1996 .

[34]  D. C. Freeman,et al.  Developmental Instability and Fitness in Periploca laevigata Experiencing Grazing Disturbance , 2002, International Journal of Plant Sciences.

[35]  Y. Linhart,et al.  Porcupine feeding patterns: selectivity by a generalist herbivore? , 1997 .

[36]  T. Elmqvist,et al.  Are there general patterns in bark-eating by voles on different shoot types from woody plants? , 1987 .

[37]  Ryan D. Csada,et al.  The "File Drawer Problem" of Non-Significant Results: Does It Apply to Biological Research? , 1996 .

[38]  Bjorksten,et al.  What does sexual trait FA tell us about stress? , 2000, Trends in ecology & evolution.

[39]  J. Koricheva,et al.  Covariation of fluctuating asymmetry, herbivory and chemistry during birch leaf expansion , 2000, Oecologia.

[40]  E. Zvereva,et al.  Delayed induced resistance and increase in leaf fluctuating asymmetry as responses of Salix borealis to insect herbivory , 1997, Oecologia.

[41]  A. Palmer,et al.  QUASIREPLICATION AND THE CONTRACT OF ERROR: Lessons from Sex Ratios, Heritabilities and Fluctuating Asymmetry , 2000 .