Ecological role of the salamander Ensatina eschscholtzii: direct impacts on the arthropod assemblage and indirect influence on the carbon cycle

in mixed hardwood/conifer forest in Northwestern California

By

Michael Best

A Thesis

Presented to

The faculty of Humboldt State University

In Partial Fulfillment

Of the Requirements for the Degree

Masters of Science

In Natural Resources: Wildlife

August 10, 2012 ABSTRACT

Ecological role of the salamander Ensatina eschscholtzii: direct impacts on the arthropod assemblage and indirect influence on the carbon cycle in mixed hardwood/conifer forest in Northwestern California

Michael Best

Terrestrial salamanders are the most abundant vertebrate predators in northwestern California forests, fulfilling a vital role converting invertebrate to vertebrate biomass. The most common of these salamanders in northwestern California is the salamander Ensatina (Ensatina eschsccholtzii). I examined the top-down effects of

Ensatina on leaf litter invertebrates, and how these effects influence the relative amount of leaf litter retained for decomposition, thereby fostering the input of carbon and nutrients to the forest soil. The experiment ran during the wet season (November - May) of two years (2007-2009) in the Mattole watershed of northwest California. In Year One results revealed a top-down effect on multiple invertebrate taxa, resulting in a 13% difference in litter weight. The retention of more leaf litter on salamander plots was attributed to Ensatina’s selective removal of large invertebrate shedders (beetle and fly larva) and grazers (beetles, springtails, and earwigs), which also enabled small grazers

(mites; barklice in year two) to become more numerous. Ensatina’s predation modified the composition of the invertebrate assemblage by shifting the densities of members of a key functional group (shredders) resulting in an overall increase in leaf litter retention.

Results from year two indicated that these effects were affected by moisture availability, and that direct salamander impacts on invertebrates, and the related indirect effects on the capacity for forest floor leaf litter retention were diminished in the second, wetter year. iii

ACKNOWLEDGMENTS

First and foremost I must thank my parents for constantly nurturing the young scientist within me; allowing their 6 year old son to tromp around the neighborhood with a heavy 35 mm Nikon, enabling me to capture photos of insects and habitat. I am inspired by their endless support and now look to my two children, ripe with a sea of discoveries, directing my constant observation of the World from a new perspective. I am so grateful for the humbling and educational guidance only parenthood could provide.

Next I have to thank Dr. H. Welsh Jr. for bringing me through this process of development into fruition as I (and my work) transitioned from biologist to scientist. I now feel prepared and motivated to tackle any scientific inquiry rigorously and effectively. His expertise and graceful nature offered a singular gracious experience.

I am forever grateful to J. Baldwin for guiding my statistical analysis and writing the many lines of code, enabling me to capture all the results at once rather than clumsily stumbling through it on my own. The completion of this thesis also may not have been possible without a writing grant from the Amphibian and Reptile Conservancy. I must also acknowledge J. Gibbs for initially turning me on to reptile and amphibian conservation and N. Karraker for sending me out to Northern coastal California in 2005, wetting my appetite for the study of California amphibians.

Finally, digging trenches and collecting data in the rain, by my side on cold winter days was my loving life partner Jada. I would not be who I am today without her support. Her unconditional bond and universal wisdom are unprecedented and have forever opened my eyes to the true power of love and commitment. The family she has given me will continue to enrich our lives and inspires me to be the best I can be. iv

TABLE OF CONTENTS

Page

ABSTRACT...... iii

ACKNOWLEDGMENTS...... iv

LIST OF TABLES...... vi

LIST OF FIGURES...... vii

INTRODUCTION...... 1

STUDY SITE...... 4

MATERIALS AND METHODS...... 5

Experimental design...... 5

Timing………………...... 8

Invertebrate samples…...... 8

Leaf litter bags...... 11

Statistical analysis...... 12

RESULTS...... 15

Ensatina effects on invertebrate taxa...... 21

Leaf-litter...... 34

DISCUSSION...... 36

The influence of moisture and prey density……………………………...... 40

Ensatina and optimal foraging theory...... 41

CONCLUSIONS AND RECOMMENDATIONS...... 44

LITERATURE CITED...... 45

APPENDIX A...... 50 v

LIST OF TABLES

Table Page

1 General linear model equation terms and their explanations; used in the Analysis comparing invertebrate samples across plots in each year.………… 14

2 Analysis of the effects of salamander predation, moisture, month, and the interaction of month*moisture, on invertebrate functional groups by size class in two years using a general linear model. Data were analyzed separately by group, size, and year. Results indicated with – were not statistically significant at α = 0.1……………………………………………… 20

3 Analysis of the effects of salamander presence (Control_Treatment), and their interactions with moisture and time interval on invertebrate taxa in two years using a general linear model. Data were analyzed separately by taxon, size class, and year. Results indicated with - were not statistically significant at α = 0.1.……………………………………………………………………… 22

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LIST OF FIGURES

Figure Page

1 Experimental enclosures to assess the impacts of Ensatina on invertebrate and litter turnover in situ at the field location near Ettersburg, California. Enclosure dimensions were 3 m x 3 m x 23 cm, plot dimensions = 1.5 m x 1.5 m x 23 cm. 6

2 Density of invertebrates by functional group, with the two most abundant taxa within the decomposers, mites and springtails represented separately. Invertebrates were extracted from litter samples collected within experimental plots near Ettersburg, California in 2007-2008. Values above bars are relative composition out of all invertebrates found represented as percentage of 100…. 16

3 Density of invertebrates by functional group, with the two most abundant taxa within the decomposers, mites and springtails represented separately. Invertebrates were extracted from litter samples collected within experimental plots near Ettersburg, California in 2008-2009. Values above bars are relative composition out of all invertebrates found represented as percentage of 100…. 17

4 Mean density of: invertebrates and invertebrate decomposers <1mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. The blue line represents the percent litter moisture in 2007-2008. Error bars are ± one standard error…………………... 18

5 Mean density of: invertebrates and invertebrate decomposers <1mm on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. The blue line represents the percent litter moisture in 2008-2009. Error bars are ± one standard error…...... 19

6 Mean density of: Entomobryidae springtails <2mm, beetles <2mm, larvae >2mm, and larvae <2mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error………..……………………………………. 23

7 Mean density of earwigs on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error……………………………………………... 24

8 Mean density of Orabatidae mites <1mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error…………………… 25

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LIST OF FIGURES (CONTINUED)

Figure Page

9 Mean density of spiders <2mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error………………………………… 27

10 Mean density of ants on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error…………………………………………….. 28

11 Mean density of millipedes on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error……………………………….. 29

12 Mean density of true bugs (Hemiptera) on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error……………………………….. 30

13 Mean density of: barklice (Psocoptera) and worms (Annelida) on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error…... 31

14 Mean density of Pseudoscorpions on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.…………………….…………. 32

15 Mean density of: Entomobryidae springtails <2mm, beetles <2mm, Orabatidae mites <2mm and larvae >2mm on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error...... 33

16 Mean leaf litter weight (g) on treatment and control plots in: Year One (2007- 2008); and Year Two (2008-2009), at the Mattole field sites near Ettersburg, California. Error bars are ± one standard deviation.…………………………. 35

viii

INTRODUCTION

Woodland (plethodontid) salamanders are the most abundant vertebrate predators in northwestern California forests (Welsh and Lind 1991), where based on their numbers and biomass they are ecologically dominant, filling a key nutrient cycling role: converting invertebrate to vertebrate biomass (Burton and Likens 1975a). Burton and

Likens (1975b) found one species of plethodontid salamander (Plethodon cinereus) in an eastern U.S. hardwood forest comprised greater biomass than all the songbirds and equal to that of all the small mammals combined. At a North Carolina forest site Petranka and

Murray (2001) reported the entire plethodontid assemblage comprised six times the number of individuals and 14 times the biomass reported by Burton and Likens (1975b).

Welsh and Lind (1992) reported an extremely high density for a single species of plethodontid salamander at a mixed conifer/hardwood forest site in northern California.

In a New York forest, Wyman (1998) found that the consumption of invertebrates by the most abundant plethodontid salamander Plethodon cinereus increased forest floor carbon retention by reducing leaf-litter breakdown 11-17%. Walton (2005) found that this process was not straight-forward, and might be affected by variability in both leaf litter mass and moisture content. Results from other studies have provided evidence that invertebrate densities might have increased in the presence of terrestrial salamanders

(Rooney 2000, Walton et al. 2006) or have had negligible effects on invertebrates

(Homyack et al. 2010), however, having no significant effect on leaf litter breakdown.

Complex food webs can be regulated both from below, where abiotic factors (e.g., nutrients, moisture, etc.) control the potential for productivity (bottom-up effects), and

1

2 simultaneously from above by predation, disease, parasitism, etc. (top-down effects) (e.g.,

Benrong and Wise 1999, Gruner 2004, Bridgeland et al. 2010). The bottom-up effects can both promote or restrict the higher trophic levels from below, while predation or its absence can similarly influence the system from above (McCay and Storm 1997,

Benrong and Wise 1999, Kagata and Ohgushi 2006).

Wyman (1998) found all invertebrate groups he sampled were reduced by salamanders in field enclosures, while other studies using both lab and field enclosures found Podomorphic springtails (Collembola) increased while other invertebrate taxa decreased, in the presence of salamanders (Rooney 2000, Walton and Steckler 2005,

Walton et al. 2006). Walton and Steckler (2005) attributed the increase in Podomorphic springtails to selection by salamanders for larger prey, releasing smaller arthropods from competition and depredation by invertebrate predators, along with the effect of enhancing their microfloral food base via salamander feces deposition. In contrast, avoiding the use of enclosures, Walton (2005) found no significant top-down effects from salamanders over the first year and instead found moisture and litter mass influenced invertebrate densities. However, in the following year, salamander presence was the single significant factor that influenced invertebrate densities in the spring; the combination of salamanders and litter mass significantly influenced invertebrate densities in the fall (Walton 2005).

The Ensatina salamander (Ensatina eschscholtzii; hereafter Ensatina), a member of the family Plethodontidae, is the most abundant terrestrial salamander in the mixed hardwood/ Douglas-fir forests of Northwestern California (Welsh and Lind 1991).

Terrestrial salamanders feed on most arthropods including springtails, mites, and beetles

(Bury and Martin 1973, Lynch 1985, Rooney 2000). Many small arthropods are

3 important decomposers of forest leaf litter, an assemblage dominated by mites and springtails (Gist and Crossley 1975, Singh 1977). An analysis of stomach content of

Ensatina and another common plethodontid species, the California slender salamander

(Batrachoseps attenuatus), in redwood forest (Sequoia sempervirens) found springtails were the most common prey consumed, followed by mites, which were equal in number to springtails in the slender salamander (Bury and Martin 1973). The importance of small invertebrate decomposers in the diets of these abundant salamanders indicates the ecologically dominant influence they can have on the capacity of the forest litter layer to sequester or release carbon and cycle important nutrients at the litter-soil interface (Gist and Crossley 1975, Singh 1977).

Studies of the roles of terrestrial salamanders in forest detrital food web dynamics have not been conducted in the Western United States. The objective of my study was to determine how Ensatina predation impacted the densities of members of the forest invertebrate assemblage, and how this may have affected the breakdown of leaf-litter; which indirectly influenced the relative amount of carbon and nutrients retained at the litter/soil interface in mixed hardwood-conifer forests in Northwestern California.

I evaluated the following hypotheses in a mixed hardwood/conifer forest of northern California: (1) Ensatina had a top down influence via predation on the composition and densities of invertebrates dwelling in the forest floor litter; (2) leaf litter breakdown in this forest floor food web was reduced via this predation on plots with

Ensatina compared to controls; and (3) available moisture affected these dynamics by influencing the relative abundances of the invertebrates and the rate of litter breakdown in this leaf litter food web.

STUDY SITE

I conducted a field experiment in the Mattole river watershed of northwestern

California near the village of Ettersberg (40° 6'3.21"N, 123°58'42.31"W). The study site was 400 meters above sea level on a forested ridge that divides two Mattole River tributaries. This forest is dominated by tanoak (Lithocarpus densiflorus) and Douglas-fir

(Pseudotsuga menziesii), and also contains madrone (Arbutus menziesii), black oak

(Quercus velutina), canyon live-oak (Quercus chrysolepis), and Bay Laurel (Laurus nobilis). The understory consists mostly of huckleberry (Vaccinium ovatum), but this was uncommon in the direct vicinity of the field site. This mixed forest type results in leaf deposition throughout the year; with litter at the study site dominated by madrone leaves in the summer and tanoak leaves in the fall. The area receives little precipitation during spring and summer, with rainfall during the fall and winter months high, averaging over

250 cm (100 inches) and exceeding 500 cm (200 inches) during wet years (Welsh et al.

2005). Summer temperatures often exceed 32OC (90OF); winters are cool with occasional freezing nights and snowfall along ridges (Welsh 2007, personal communication).

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MATERIALS AND METHODS

To test the effects of Ensatina predation on invertebrates I conducted a controlled salamander housing experiment over four winter months during 2007-2008 and 2008-

2009. In order to incorporate the bottom up effects of the living forest floor, salamander barriers were installed directly into the ground (15 cm deep) where they remained, uncovered and exposed. These barriers created 12 similar plots utilized as either controls or treatments (six of each). I collected leaf-litter cores to quantify the invertebrates in each plot before conducting the experiment and then at the end of each 30 day period following the introduction of salamander treatment individuals. Leaf litter bags of a similar composition and pre-determined dry weight were placed within each plot at the initiation of salamander introductions and were removed 120 days later to assess the breakdown of leaf litter in both control and treatment plots.

Experimental design

I used three experimental enclosures, each divided into four plots (1.5 m2); creating a total of six treatment and six control plots (Figure 1). The enclosures were constructed in situ on the forest floor. The walls were buried 15 cm deep into the litter layer down to the mineral soil to ensure that salamanders could not escape beneath the walls. The three enclosures were within a 12 m2 area and all three were enclosed by a chicken wire fence 2.5 meters in height to prevent destruction or predation of Ensatina by wildlife. Enclosures were constructed using 30 cm high metal sheets folded and attached

5

6

Figure 1. Experimental enclosures to assess the impacts of Ensatina on invertebrate and litter turnover in situ at the field location near Ettersburg, California. Enclosure dimensions were 3 m x 3 m x 23 cm, plot dimensions = 1.5 m x 1.5 m x 23 cm.

7 at the corners with steel bolts to form the perimeter and transected with a pair of metal sheets through the center as a perpendicular bisector of each exterior wall to create four equal-sized plots in each enclosure (Figure 1). The use of experimental field enclosures to study food web dynamics has been criticized because it may confound predator-prey interactions, including predator avoidance, and influx of prey from neighboring sites

(Walton 2005, Walton et al. 2006). To address these issues, the four interior walls were equipped with two hardware cloth windows (1.5 cm mesh) measuring 10 cm in height and 35 cm in length fastened to the sheet metal with screws to allow for arthropod migration between the plots while preventing salamanders from moving between them.

Enclosures were equipped with a 10 cm aluminum lip around all edges fastened with binder clips silicone glued to the underside, using duct-tape to seal the adjoining surfaces; preventing salamanders from climbing out. The enclosures remained open at the top to allow rainfall and leaf-litter deposition to occur naturally.

Each four-unit enclosure was systematically assigned two treatment and two control plots with a random start, but so that no two treatment plots were adjacent. One male Ensatina was placed in each treatment plot. Ensatina weighed at least 3.5 grams but not more than 4.5 grams. Each plot was provided with three rough-cut Douglas-fir boards measuring: 45 cm by 15 cm and between five and eight cm high for surface cover.

Salamanders found to already exist within enclosures were removed at the beginning of the experiment. One treatment plot was omitted from the analysis on December 7, 2007 due to escape of the Ensatina salamander. Methodologies were approved by the

8

International Animal Care and Use Committee at Humboldt State University; protocol number was 06/07.W.150.A.

Timing

The salamander predation experiment was initiated on November 1, 2007 with the onset of seasonal rainfall and when Ensatina salamanders were present in the surface litter of the adjacent forest. The salamander treatment plots were populated over the following 3 weeks and were removed on March 22, 2008, 120 days after the last plot was populated. In the winter of 2008 rainfall was delayed and salamander introductions occurred from December 30, 2008 through January 11, 2009. Salamanders were removed from the enclosures on May 15, 2009, 120 days after salamander introductions.

This timing was also consistent with the appearance of local salamanders on the surface of the forest floor, which in both years allowed me to find individuals from the surrounding forest to populate the experimental plots (Welsh unpublished data). HOBO

Pendant data loggers enclosed in water-tight PVC canisters were randomly assigned to one plot within each enclosure to measure air temperature during the experiment.

Invertebrate samples

Five leaf litter cores were extracted from each plot in each time interval (month) to provide invertebrate samples. The litter cores (sub-samples) were collected using a soup can (486 cm3) with both ends removed, pushed firmly down through the leaf-litter until contact with the mineral soil beneath. Sub-sample locations were determined using a random number generator and a 100-point grid, but stratified to encompass three sub- samples along the plot edge and two sub-samples within the interior. It was presumed

9 that the plot edge might accumulate invertebrates by promoting travel along this barrier and as such it would be important to sample this area. Sub-sample locations were not reused. Holes generated from removing litter cores were first measured to determine litter depth then gently collapsed to prevent soil drying and to minimize disturbance to soil strata. The five sub-samples from each plot were combined to create the invertebrate sample for each plot, each month. The litter removal associated with this sampling method totaled approximately 5% of the surface area of each plot in each sampling event; resulting in approximately 25% of the plot surface area sampled over the experiment.

The material removed from a sub-sample core was immediately placed into a labeled quart-sized Ziploc© bag and then into a cooler to prevent the samples from drying out or mobile invertebrates from escaping. The sub-samples were chilled but above freezing (1-5 OC) until they could be processed in Berlese-funnel extractions to collect the arthropods they contained, within 48 hours. The Berlese funnels were setup within a wooden frame approximately one square meter with 30 seven centimeter diameter holes bored into wooden slats fitted atop the frame; each hole with a plastic funnel attached below. The structure was designed to fit a sub-sample can within each position such that the can would rest securely within the funnel. A hardware cloth barrier

(1.5 cm mesh) was placed at the bottom of each can to prevent soil from clogging the funnel. A string of seven watt lights hung above the frame with one light placed within the top of each sampling can. Each can was wrapped shut with aluminum foil to promote the drying of samples and the downward migration of invertebrates. One dram vials filled with 95% ethanol were placed underneath each funnel to collect invertebrates as they fell from the litter sample. Berlese-funnel extractions received continuous heat and

10 light from the seven watt bulbs for four days (96 hours) after which the samples were completely dry (adapted for small, wet samples; see Wyman 1998). The leaf litter sub- samples were weighed before and after the drying extraction process to determine percent moisture; the percent moisture calculations from the sub-samples were averaged for each plot and time. For the statistical analysis invertebrate abundances in each sub-sample were divided by the dry weight of the litter in their respective sub-sample to correct for variable litter depths and to generate invertebrate densities (count/gram of dry leaf litter).

Ensatina has the widest gape of the plethondontid salamanders in the western

U.S., allowing it to consume a variety of prey, with moderate sized adult salamanders

(35-49 mm, snout-vent-length) consuming mostly small (<0.3 mm3) and medium (<19 mm3) sized invertebrate prey; 45% of their diet by volume was small and 55% medium, with less than 0.2% of prey greater than 19 mm3 (Lynch 1985). In order to evaluate differences between control and treatment plots based on both prey type and prey size, I examined invertebrates under a dissecting microscope, identifying them to family, and assigning them to one of three size classes: less than one millimeter, between one and two millimeters, greater than two millimeters (small, medium, and large, respectively). These three length categories captured the variability of prey size consumed by Ensatina defined in Lynch (1985). Invertebrates were organized into: decomposers (shredders/grazers), predators, herbivores, omnivores (ants) (see Peterson 1982). Fly and beetle larvae identified as shredders were combined into a single group (larvae), due to low sample sizes. Invertebrate larvae identified as predators based on morphology were included in: predators; these were comprised of immature stages from the orders Coleoptera, and

Neuroptera. The identification of mites was simplified into two groups: Orabatidae (fully

11 sclerotized) and non-Orabatidae (not or partially sclerotized). Appendix A contains a complete list of invertebrates detected.

Leaf litter bags

Each experimental plot was provided with three mesh bags made of metal window screen (3.0 mm mesh) open at one end and containing 3.0 g of leaf litter (equal amounts of Madrone and Tanoak) which had not begun decomposition and was fully intact. Douglas fir needles were excluded from these procedures as their small size enabled them to slip through the window screen easily thus generating a large source of error. The leaves were collected from an area approximately 50 m2 centered on the location of the experiment. Once a sufficient quantity of leaves was collected they were dried in an oven at 93OC (200OF) for two hours (until completely dry and brittle) and weighed out to 3.0 g increments containing leaves from both dominant species. The 36 litter bags were filled and deployed at one time so that drying and weighing conditions would be consistent for all bags. Leaf-litter bags were collected after the experiment and re-dried at 93OC for two hours and carefully re-weighed immediately upon drying to ensure the accuracy of dry-weight measurements. The change in weight from the initial

3.0 g to final dry weight was averaged across the three litter bags in each plot and used to compare the change in mean leaf weight between control and treatment plots over the course of the experiment. Hardwood leaves are composed of approximately 50% carbon by weight (carbon mass=0.475 * mass of oven dried leaf; Schlesinger 1991) so we assumed that half the change in leaf weight quantified here would serve as a surrogate for the amount of carbon either retained or lost over the four months of the experiment.

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Statistical analysis

The samples of invertebrates yielded counts of their densities from each of the 12 plots: initially (prior to salamander introductions), and after each 30 day period following their introductions (4 months), replicated in both years. Because invertebrate sampling occurred within the same plots over time the samples were considered repeated measures within each year. Walton (2005) demonstrated the significant influence of moisture on invertebrate densities and differences in the effects of top-down regulation by a salamander predator, therefore the distinct differences in rainfall regime between the two years at the site warranted the analysis of each year separately. The depth of each litter core and the amount of moisture each contained were highly correlated, requiring the choice of only one (i.e. percent moisture) in the analysis. Air temperatures were not included in the model because invertebrate samples were collected only once a month which truncated temperature measurements to a scale too coarse to be meaningful.

However, the variable “month” included all effects other than moisture and control/treatment, including temperature extremes (freezing nights, very warm days) and trophic interactions (birth/recruitment, predation, parasitism/disease, movement).

I used a general linear model (GLM) analysis of variance that accommodated repeated measures to test for significant effects of the three independent variables

(treatment, moisture, month), and their interactions, on each invertebrate group. The analysis was conducted using SAS 9.2 (2008). A generalized linear model was not used because the residual error was too large to be considered a good fit; residuals increased consistently with increasing counts. Invertebrate counts were log transformed

[log(Count+1)] to meet the assumptions of normality. Residuals were examined to assess

13 the adequacy of these transformations. The residuals were approximately normal and relatively constant across the predicted values following the transformation.

The response variables used in the general linear model analysis were the log transformed counts of the density of each invertebrate family. Invertebrate families commonly consumed by Ensatina (Bury and Martin 1973) were each broken into three response variables (each size class) to increase the resolution of impacts to these groups.

Invertebrate families not commonly consumed by Ensatina (Bury and Martin 1973) were each analyzed as a single response variable which included all sizes. Invertebrate families identified as Ensatina prey, but which contained insufficient data to be analyzed separately by size class were each treated as a single response variable that included all sizes. Invertebrate families were also combined into functional groups to assess Ensatina effects at a coarse level of resolution; the invertebrate decomposer group contained an adequate sampling size which enabled the analysis of this functional group by size class.

The GLM terms for each response variable were as follows (see Table 1 for definitions):

The plot was the sampling level of the analysis, with 12 plots in total divided equally between control and treatment, N=6. In Year One N=5 due to removal of one treatment plot from analysis due to salamander escape. The GLM was applied once to each invertebrate group in each year in an exploratory and not confirmatory analysis, therefore, Bonferroni adjustments for multiple comparisons were not deemed appropriate.

The change in dry weight of the leaf litter bags from start to end were compared (control vs. treatment) for each year using ANOVA in NCSS (Hintze 2001).

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Table 1. General linear model equation terms and their explanations; used in the analysis comparing invertebrate densities between control and treatment plots in each year. Equation term (Effect) Data type Explanation Month categorical Month of experiment (0-4) Control_Treatment categorical Treatment of plot/ or Control Percent Moisture continuous Percent moisture by weight Month*Control_Treatment categorical Interaction: treatment and month Month*Moisture continuous Interaction: moisture and month Moisture*Control_Treatment continuous Interaction: moisture and treatment Moisture * Month * Treatment continuous 3- interaction: moisture, month, treatment ra continuous Repeated measures error e continuous Residual error, random error aSAS 9.2 2008: PROC MIXED, autoregressive covariance structure of order 1 was used

RESULTS

In Year One (2007-2008), leaf litter cores from the 10 experimental plots yielded

14,401 individual invertebrates (57.4 individuals/gram of leaf litter) from 38 families. In

Year Two (2008-2009), litter cores from the 12 plots yielded 32,721 invertebrates (253.1 individuals/gram of litter) from 48 families (Appendix A). Invertebrates were about half as dense in leaf litter cores during the 2007-2008 sampling year (Figure 2) as they were in the 2008-2009 samples (Figure 3); however, the relative composition of the functional groups was nearly identical in the two years. The majority of invertebrates found in the leaf litter were decomposers (95%); herbivores, predators, and omnivores (ants) together constituted a minority, comprising about 5% of all invertebrates found in litter samples in each year. The decomposers were comprised overwhelmingly of mites (~65%), which were almost 3 times as dense as springtails (~25%); all others constituted about 10%.

Invertebrate density was similar between control and treatment plots prior to salamander introductions in 2007 (t=0.12, df=190, p=0.90, Figure 4) and 2008 (t=-0.05, df=230, p=0.96, Figure 5). Invertebrate density was significantly influenced by percent moisture of litter samples in 2007-2008 (f=17.48, df=190, p<0.0001) and 2008-2009

(f=18.52, df=230, p<0.0001, Table 2). The density of invertebrates appeared to fluctuate with available moisture over time, in each year, with the majority of these fluctuations attributed to small invertebrate decomposers (Table 2, Figures 4 and 5). The presence of

Ensatina did not significantly affect overall invertebrate density in 2007-2008 (f=0.03, df=190, p=0.87) or 2008-2009 (f=0.73, df=230, p=0.39; Table 2), however, Ensatina did influence the densities of individual invertebrate taxa in each year (see below).

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2007-2008

40 63.9 35 30 25 20 15 23.3 10 8.7 5 0.2 2.1 1.9

0 Invertebrate (Count/glitter) densityInvertebrate

Invertebrate group

Figure 2. Density of invertebrates by functional group, with the two most abundant taxa within the decomposers, mites and springtails, reported separately. Invertebrates were extracted from litter samples collected within experimental plots near Ettersburg, California in 2007-2008. Values above bars are relative composition out of all invertebrates found represented as percentage of 100.

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2008-2009

200 68.8 175 150 125 100

75 21.7 50 25 6.1 1.1 1.8 1.4

0 Invertebrate (Count/glitter) densityInvertebrate

Invertebrate group

Figure 3. Density of invertebrates by functional group, with the two most abundant taxa within the decomposers, mites and springtails, reported separately. Invertebrates were extracted from litter samples collected within experimental plots near Ettersburg, California in 2008-2009. Values above bars are relative composition out of all invertebrates found represented as percentage of 100.

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2007-2008 Control Treatment Moisture

3 Ensatina introduction 0.25

2.5 0.2

2 0.15 1.5 0.1

1 Percent litter moisture litter Percent

0.5 0.05

Invertebrate (Count/glitter) densityInvertebrate 0 0

3 0.25

Ensatina introduction

2.5 0.2

2 0.15 1.5 0.1

1 Percent litter moisture litter Percent 0.05

Density of decomposers decomposers of Density 0.5 <1mm (Count/glitter) <1mm long 0 0 Nov Dec Jan Feb Mar

Month Figure 4. Mean density of all invertebrates and invertebrate decomposers <1mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. The blue line represents the percent litter moisture in 2007-2008. Error bars are ± one standard error.

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2008-2009 Control Treatment Moisture

8 Ensatina introduction

0.35

7 0.3 6 0.25 5 0.2 4 0.15 3

0.1 moisture litter Percent 2 1 0.05

Invertebrate density(Count/glitter) Invertebrate

0 0

8 Ensatina introduction 0.35 7 0.3 6 0.25 5 0.2 4 0.15 3 0.1

2 moisture litter Percent Density of decomposers decomposers of Density

<1mm (Count/glitter) <1mm long 1 0.05 0 0 Jan Feb Mar Apr May Month

Figure 5. Mean density of all invertebrates and invertebrate decomposers <1mm on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. The blue line represents the percent litter moisture in 2008-2009. Error bars are ± one standard error.

20

Table 2. Analysis of the effects of salamander predation (Control_Treatment), moisture, month, and the interaction of month*moisture, on invertebrate functional groups by size class in two years using a general linear model. Data were analyzed separately by group, size, and year. Results indicated with – were not statistically significant at α = 0.1. Moisture Month Month*Moisture Control_Treatment Group Size Year F-value P-value F-value P-value F-value P-value F-value P-value Decomposers <1 mm 1 10.31 0.002 - - 2.09 0.083 - - <2 mm 1 9.91 0.002 ------>2 mm 1 ------<1 mm 2 20.94 0.000007 5.01 0.001 5.56 0.0003 - - <2 mm 2 3.92 0.049 3.18 0.014 4.41 0.002 - - >2 mm 2 22.66 0.000003 2.56 0.039 2.37 0.053 - - Omnivores (Ants) All sizes 1 14.24 0.0002 ------All sizes 2 ------Predators All sizes 1 3.64 0.058 ------All sizes 2 - - - - 2.02 0.092 - - Herbivores All sizes 1 ------All sizes 2 - - 9.81 0.000 - - - - All invertebrates All sizes 1 17.48 0.00004 2.09 0.08 2.23 0.07 - - All sizes 2 18.52 0.00002 4.84 0.0009 6.06 0.0001 - -

21

Ensatina effects on invertebrate taxa

In 2007-2008 the densities of 10 invertebrate taxa were significantly affected by

Ensatina presence (6 decreased, 4 increased; Table 3); in contrast, only three taxa were affected by Ensatina in 2008-2009, all of which increased on treatment compared to control plots. Two of the taxa which declined on treatment plots in Year One, rebounded to densities higher than controls following the initial declines (Figure 6). There were no significant declines on treatment plots in Year Two, although two taxa that had declined significantly in Year One showed declining trends in the Year Two but did not achieve statistical significance: medium Entomobryidae springtails and beetles (see Figure 15).

In Year One (2007-2008) the density of medium Entomobryidae springtails

(f=3.32, df=190, p=0.07), medium beetles (f=6.39, df=190, p=0.01), and large larval shredders (f=2.79, df=190, p=0.09) each declined significantly on plots with Ensatina in month one and two (Table 3, Figure 6). The density of medium Entomobryidae springtails and large larval shredders each increased in month three following their declines, to a level greater than adjacent control sites (Figure 6). Large larval shredders remained greater than controls into month four (Figure 6). The density of earwigs declined significantly on treatments in months one and four (f=3.57, df=190, p=0.06,

Figure 7). The density of medium larval shredders remained similar between control and treatment plots in month one, but were found in significantly higher densities on treatments in months two and four (f=3.85, df=190, p=0.05, Table 3, Figure 6).

The density of small Orabatidae mites increased significantly on plots with

Ensatina within the first month following Ensatina introduction and again in month four

(f=2.69, df=190, p=0.32, Table 3, Figure 8); interaction between treatment and month.

22

Table 3. Analysis of the effects of salamander presence (Control_Treatment), and their interactions with moisture and time interval on invertebrate taxa in two years using a general linear model. Data were analyzed separately by taxon, size class, and year. Results indicated with - were not statistically significant at α = 0.1. Control_Treatment Moisture*Treatment Month*Treatment Month*Moisture*Treatment Taxa Size Yea r F-value P-value F-value P-value F-value P-value F-value P-value Springtailsa <2 mm 1 3.32 0.070 3.52 0.062 - - - - <2 mm 2 ------Adult Beetles <2 mm 1 - - 5.27 0.023 - - - - <2 mm 2 ------Larvaeb <2 mm 1 3.85 0.051 ------>2 mm 1 2.79 0.096 ------>2 mm 2 ------Mites_Orabatid. <1 mm 1 - - - - 2.69 0.032 2.16 0.075 <2 mm 2 ------Spiders <2 mm 1 2.79 0.097 2.77 0.098 - - - - Earwigs All sizes 1 3.57 0.060 3.27 0.072 - - - - Ants All sizes 1 - - - - 2.79 0.27 4.09 0.003 Millipedes All sizes 1 - - - - 2.31 0.059 3.36 0.01 True bugs All sizes 1 - - - - 2.71 0.03 3.52 0.008 Bark lice All sizes 2 3.04 0.083 ------Worms All sizes 2 - - 3.40 0.066 - - - - Pseudoscorpions All sizes 2 ------2.07 0.086 aSpringtails determined to be members of the family Entomobryidae by examination of morphological features bLarvae determined to be saprophytic shredders by examination of morphology, includes immature stages of: Coleoptera, Diptera

23

2007-2008

0.06 Ensatina introduction Control Treatment

0.05 0.04 0.03

0.02 (Count/glitter) 0.01 springtails <2 mm mm <2 longspringtails Density of Entomobryidae Entomobryidae of Density 0 0.06

Ensatina introduction 0.05

0.04 0.03

(Count/glitter) 0.02 Density of adultof Density beetles <2 mm long mm <2 beetles 0.01 0 0.06 Ensatina introduction 0.05 0.04 0.03

0.02

0.01 long (Count/glitter) long

Density of larvae >2mm larvae >2mm of Density 0

0.06 Ensatina introduction

0.05 0.04 0.03 0.02

0.01 0

long (Count/glitter) long Nov Dec Jan Feb Mar Density of larvae <2mm larvae <2mm of Density Month Figure 6. Mean density of: Entomobryidae springtails <2mm, beetles <2mm, larvae >2mm, and larvae <2mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

24

2007-2008 Control Treatment 0.008 Ensatina introduction 0.007 0.006 0.005 0.004 0.003 0.002

0.001 Earwing density (Count/glitter) densityEarwing 0 Nov Dec Jan Feb Mar Month

Figure 7. Mean density of earwigs on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

25

Control Treatment

2007-2008

1.2 Ensatina introduction 1 0.8 0.6 0.4 0.2

0

<1 mm (Count/glitter) mm <1 long Density of Orabatidae mites mites Orabatidae of Density Nov Dec Jan Feb Mar Month

Figure 8. Mean density of Orabatidae mites <1mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

26

In Year One medium spiders were found at greater density on plots with Ensatina compared to controls throughout the four months of the experiment (f=2.79, df=190, p=0.097, Table 3, Figure 9). The density of ants was low on all plots through the first three months of Year One, however decreased significantly on plots with Ensatina in the final month of the experiment, indicating the significant interaction between month, moisture, and treatment (f=4.09, df=190, p=0.003, Figure 10). The density of millipedes was greater on treatment plots in months one, two, and four (f=3.36, df=190, p=0.01,

Figure 11). The density of true bugs (Hemiptera) was significantly lower on treatments in

Year One (f=3.52, df=190, p=0.008; Table 3, Figure 12), however, also rare (0.00005% of all invertebrates), likely influencing comparisons and significance.

In Year Two the density of barklice (Psocoptera) increased significantly on plots with Ensatina compared to controls in months two and four (f=3.04, df=230, p=0.08;

Table 3, Figure 13). The density of worms (Annelida) increased significantly on plots with Ensatina over controls during months two and four, indicating an interaction between treatment and moisture (f=3.4, df=230, p=0.07; Table 3, Figure 13). The density of Pseudoscorpions increased significantly on plots with Ensatina in month one and again in months three and four of Year Two (f=2.07, df=230, p=0.09; Table 3, Figure 14); indicating the interaction between month, moisture, and treatment.

During the latter three months of Year Two the densities of four taxa which differed significantly between control and treatment in Year One (Fig. 6, Table 3) showed a similar trend in the second year: medium Entomobryidae springtails, medium beetles, medium Orabatidae mites, and large larval shredders. The differences in densities of these taxa did not achieve statistical significance in the second year (Figure 15, Table 3).

27

2007-2008 Ensatina introduction Control Treatment 0.007

0.006

0.005 0.004 0.003

0.002 (Count/g litter) (Count/g 0.001 0 Density of spiders <2 mm spidersmm <2 of longDensity Nov Dec Jan Feb Mar Month

Figure 9. Mean density of spiders <2mm on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

28

2007-2008 Control Treatment

0.2 Ensatina introduction 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 Ant density Ant (Count/g litter) 0 Nov Dec Jan Feb Mar Month

Figure 10. Mean density of ants on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

29

2007-2008 Control Treatment

0.04 Ensatina introduction 0.035 0.03 0.025 0.02 0.015 0.01 0.005

Millipede density (Count/glitter) density Millipede 0 Nov Dec Jan Feb Mar Month

Figure 11. Mean density of millipedes on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

30

2007-2008 Control Treatment

0.003 Ensatina introduction 0.003

0.002

0.002

0.001

0.001

0.000 Density of true (Count/glitter) true bugsof Density Nov Dec Jan Feb Mar

Month Figure 12. Mean density of true bugs (Hemiptera) on control and treatment plots sampled at 5 monthly intervals in 2007-2008 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

31

Control Treatment

2008-2009

0.05 Ensatina introduction

0.04

0.03

0.02

0.01 0 Barklice density (Count/g litter) Barklice

0.05 Ensatina introduction

0.04

0.03

0.02

0.01

Worm density(Count/g litter) Worm 0 Jan Feb Mar Apr May Month

Figure 13. Mean density of: barklice (Psocoptera) and worms (Annelida) on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

32

2008-2009

0.016 Ensatina introduction Control Treatment 0.014

0.012 0.010 0.008

0.006 (Count/g litter) (Count/g

0.004 Pseudoscorpion density Pseudoscorpion 0.002 0.000 Jan Feb Mar Apr May Month Figure 14. Mean density of Pseudoscorpions on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

33

2008-2009 Control Treatment Ensatina introduction 0.18 0.16 0.14 0.12 0.10 0.08

0.06 (Count/g litter) (Count/g

0.04 springtails <2 mm mm <2 longspringtails

Density of Entomobryidae Entomobryidae of Density 0.02 0.00 0.18 Ensatina introduction

0.16

0.14 0.12 0.10 0.08 0.06

0.04

(Count/g litter) (Count/g Density of adultof Density

beetles <2 mm long mm <2 beetles 0.02 0.00 Ensatina introduction

0.18 0.16 0.14 0.12 0.10 0.08 0.06

(Count/glitter) 0.04 mites <2mm long mites <2mm 0.02 Density of Orabatidae Orabatidae of Density 0.00

0.18 Ensatina introduction 0.16 0.14 0.12 0.10 0.08

>2 mm mm >2 long 0.06 (Count/glitter)

Density of larvae larvae of Density 0.04 0.02 0.00 Jan Feb Mar Apr May Month Figure 15. Mean density of: Entomobryidae springtails <2mm, beetles <2mm, Orabatidae mites <2mm and larvae >2mm, on control and treatment plots sampled at 5 monthly intervals in 2008-2009 from Mattole field sites near Ettersburg, California. Error bars are ± one standard error.

34

Leaf-litter

In Year One (2007-2008) mean leaf litter mass (Χ± SE) was significantly greater on treatments (2.68 g ± 0.06 g) compared with controls (2.28 g ± 0.06 g) after the four months of the experiment (t=-5.32, df=28, p<0.0001; Figure 16). The retention of leaf- litter was significantly greater (leaf-litter breakdown reduced) by 13.3% (± 0.2%) on treatments than on controls in 2007-2008.

In Year Two (2008-2009) the mean litter mass was not significantly different between controls (2.06 g ± 0.07 g) and treatments (2.23 g ± 0.09 g) over the four months of the experiment (t=-1.43, df=34, p=0.16; Figure 16). The average retention of litter mass across all plots (control and treatment) in 2008-2009 (2.04 g ± 0.05 g) was significantly less (t=4.80, df=64, p=0.00001) than it was in 2007-2008 (2.51 g ± 0.05 g

(Figure 16); there was significantly more leaf litter breakdown across all plots in the second year.

35

2007-2008

3.0

2.5

2.0

1.5

maining (dry) leaf litter weight (g) leaf litter (dry) maining Re

1.0 Control Treatment

2008-2009

3.0

(g)

2.5

2.0

1.5 Remaining (dry) leaf litter weight leaf litter (dry) Remaining

1.0 Control Treatment

Figure 16. Mean leaf litter weight (g) on treatment and control plots at the conclusion of the experiment in: Year One (2007-2008); and Year Two (2008-2009), at the Mattole field sites near Ettersburg, California. Error bars are ± one standard deviation.

DISCUSSION

The great abundances of terrestrial salamanders in North American forests (e.g.,

Burton and Likens 1978a, Welsh and Lind 1992, Petranka and Murray 1999) implies an important role in forest floor food web dynamics through predation on invertebrate assemblages including larval shredders and detrital grazers (beetles and springtails).

Members of the invertebrate shredder guild (larvae and worms) physically tear organic material such as leaf litter, conifer needles, and wood on the forest floor into smaller pieces, which are then processed through their gut, inoculated with microflora, and utilized by microfauna (Gist and Crossley 1975). The small decomposers (mites, springtails, and nematodes [together microfauna]) directly mediate the primary productivity of this microfloral resource by fulfilling three ecological functions: grazing, spreading propogules, and preying on one another (McBrayer and Reichle 1971, Singh

1977). Ultimately, this often dense microscopic layer of primary and secondary consumers converts primary microfloral productivity and waste into invertebrate biomass, effectively transferring energy from forest materials up the food web and simultaneously recharging soil nutrients, including carbon and nitrogen, for plant growth

(McBrayer and Reichle 1971, Gist and Crossley 1975, Singh 1977). Ensatina predation on these two critical components of the decomposition food web (grazers, shredders) indicates the potential for terrestrial salamanders to have a top down influence on the processes of nutrient cycling and carbon storage in forests.

While Ensatina preys on many of these invertebrates, exerting a top-down influence on the rate of litter breakdown, this relationship can be affected by moisture.

36

37

Detrital food web processes respond directly to moisture by increasing the densities of invertebrate shredders, grazers, and microfloral growth (Wardle 2002), which increases the rate of leaf litter breakdown (Gist and Crossley 1975, Singh 1977). In Year Two

(2008-2009) there was an initial high pulse of moisture within the first two months of the experiment, probably resulting in the detection of twice as many invertebrates in litter samples than in Year One. Consistent with this pulse of enhanced activity, leaf litter breakdown was greater in Year Two than it was in Year One. Furthermore, significant salamander effects on invertebrate densities were fewer in Year Two: three taxa increased in Ensatina presence (barklice, worms, pseudoscorpions; indirect effects); compared to six taxa which decreased (medium Entomobryidae springtails, medium beetles, earwigs, large larval shredders, ants, true bugs; direct effects) and four taxa which increased (small

Orabatidae mites, medium spiders, medium larva, millipedes; indirect effects), Year One.

In Year One, the direct and indirect effects of Ensatina presence on the invertebrate assemblage was apparent within the first month of the experiment. The densities of three microfloral grazers: medium Entomobryidae springtails, medium beetles and earwigs each decreased immediately following Ensatina introduction. While simultaneously the density of a small microfloral grazer increased: Orabatidae mites less than one millimeter long. The removal of many of these larger grazers by Ensatina would have likely opened up primary resources for the smaller and more numerous mites, allowing them to capitalize on these resources and increase in density (competitive release). A similar relationship was found with Plethodon cinereus where decreases in the abundance of Entomobryidae springtails on salamander plots resulted in an increase in mites and Podomorphic springtails (Walton and Steckler 2005). Rooney (2000) and

38

Walton et al. (2006) also described a similar release of Podomorphic springtails in the presence of this salamander. In my study, the larger and highly mobile millipedes (a microfloral grazer) also apparently capitalized on available microfloral resources, increasing significantly in density on Ensatina plots. Large larval shredders decreased on

Ensatina plots in the first two months, allowing medium larval shredders to increase.

Consistent with the reduced densities of large larval shredders, and microfloral grazers (springtails, beetles, earwigs) on treatments in Year One was an increase to mean leaf litter retention by 13.3%, compared to control plots. Consistent with the pulse of moisture early in the experiment in Year Two, and the high invertebrate densities in that year, was an increase in the breakdown of litter across all plots, compared to Year One.

Consequently, the salamander treatment plots showed a lack of statistically significant declines to invertebrate densities and an insignificant retention of litter on treatment plots in Year Two. While mean dry weight of litter retained on treatments was 5% greater than controls in Year Two, which may indicate the consumption of invertebrate decomposers by Ensatina, there was an insufficient effect to achieve statistical significance.

With a single Ensatina salamander per 1.5 m2 treatment plot, the increased invertebrate densities in Year Two probably decreased the likelihood of a single salamander being able to consume enough invertebrates to achieve a statistically significant decline. However, it appears that these Ensatina did consume high numbers of medium Entomobryidae springtails, beetles, and mites in Year Two despite the lack of statistically significant differences. Evidence of this is apparent in the indirect effect on a small microfloral grazer: barklice (Psocoptera) which increased in density on plots with

Ensatina in month two; precisely when the densities of these three grazers (springtails,

39 beetles, mites) began to fluctuate on treatments. By month four barklice density was three times greater on plots with Ensatina than on controls, indicating the compounding indirect effects of Ensatina predation on larger microfloral grazers (medium-sized

Entomobryidae springtails, beetles, and mites) in the last three months of the experiment in Year Two (2008-2009). Walton (2005) also observed increases in barklice on treatment plots, apparently due to this competitive release phenomenon.

Gnaedinger and Reed (1948) reported the stomachs of 21 Ensatina contained in decreasing frequency: springtails, spiders, millipedes, centipedes, beetles, larvae, and mites, followed by pill bugs, thrips, and wasps. Bury and Martin (1973) found the stomachs of 37 Ensatina contained in decreasing frequency: springtails, spiders, beetles, millipedes, pill bugs, larvae, ants, and mites; with several other taxa including centipedes and pseudoscorpions found in fewer than 5% of stomachs. In both studies the most frequently consumed invertebrates included springtails, spiders, beetles, and larvae; the densities of each differed in the presence of Ensatina in this study.

While I did not detect significant declines to invertebrate predators (possibly due to small sample sizes), there was evidence of an indirect increase to an intermediate invertebrate predator in each year (meso-predator release [Richie and Johnson 2009]). In

Year One medium spiders occurred in higher densities on plots with Ensatina compared to controls. In Year Two Pseudoscorpions occurred in higher densities on plots with

Ensatina compared to controls. Gnaedinger and Reed (1948) and Bury and Martin (1973) indicated spiders as an important food source for Ensatina; Ensatina predation on large spiders may explain the increase in density of medium spiders on treatment plots in Year

One (2007-2008) and Pseudoscorpions in Year Two (2008-2009).

40

The influence of moisture and prey density

In Year One the density of invertebrates was high prior to introduction of

Ensatina, and was quite low on all plots in the first month following Ensatina population.

The density of invertebrates gradually increased from a low in month one through month four of 2007-2008, apparently, as the percent moisture of litter samples increased. In the first two months of the first year Ensatina appeared to capitalize on select invertebrates: large larval shredders, medium Entomobryidae springtails, medium beetles, and earwigs.

By month three the significant differences (control vs. treatment) to these four taxa were no longer apparent and at least two taxa: medium Entomobryidae springtails and large larval shredders began to increase to densities higher than controls. In months three and four invertebrate densities continued to increase and significant differences to these select taxa disappeared: only earwigs and ants were less dense on treatments in month four.

In Year Two (2008-2009) invertebrate density was much higher than in Year One

(2007-2008) and I failed to detect any statistically significant declines to invertebrate taxa on the salamander plots in Year Two (Tables 2 and 3). However, a statistically significant indirect effect of Ensatina presence (e. g. increased density of barklice) suggests Ensatina did consume invertebrate microfloral grazers (e. g. medium Entomobryidae springtails, beetles, and Orabatidae mites) during months two-four of Year Two. Furthermore, these latter three months of Year Two coincide with the decline of moisture in litter samples and declining invertebrate density. This may have forced Ensatina to be more selective of prey species as availability of prey decreased (Jaeger and Barnard 1981); similar to

Stamps et al. (1981) and Diaz and Carrascal (1993) whom found prey selection decrease and eventually disappear as prey availability increased for insectivorous lizards.

41

Ensatina and optimal foraging theory

Optimal foraging theory states that predators will maximize gains and minimize efforts by first selecting prey which provide the most energy gained per energy invested

(most profitable) and then broadening that selection to include less profitable prey as the more preferred prey decline in density (Emlen 1966). This is based on an energy limited model developed primarily for endothermic predators with high caloric requirements.

Salamanders are poikilotherms with low energetic requirements (Pough 1980); Ensatina is more efficient than an endothermic insectivore (e. g. birds utilize 90% of calories for respiration) at converting ingested calories into biomass (Burton and Likens 1975, Pough

1983). The low energetic requirements of Ensatina allow it to include abundant prey even when energetically less profitable (Jaeger and Barnard 1981, Stamps et al. 1981,

Diaz and carascal 1993), and consider the relative nutritional qualities (complimentary amino acids, etc.) of different taxa (Pulliam 1975, Stamps et al. 1981, Mayntz and Toft

2001). These circumstances enabled Ensatina to modulate foraging behaviors (prey selection) in response to environmental conditions (moisture, prey density).

Ensatina is a sit-and-wait predator that invests little energy in foraging behavior so a majority of foraging cost is inherent in the relative percentage of exoskeleton chitin in each invertebrate taxa consumed (Jaeger 1990, Diaz and Carrascal 1993). A regression analysis comparing handling time to prey size (mean dry mass) found relatively shallow slopes (slow increase in handling time with size) for particularly round and/or soft bodied taxa: true bugs, larvae, flies, and spiders but steep slopes (handling times increased rapidly with size) for highly chitinized and elongated taxa: crickets, beetles, ants, etc.

(Jaeger 1990, Diaz and Carrascal 1993). Entomobryidae springtails are armored with

42 hairs and an enlarged dorsal segment which may place them in the high chitin group, along with beetles and ants. Medium Entomobryidae springtails and beetles seem to be important prey types for Ensatina in forests of Northern coastal California as they were consumed in each year. Large beetles and springtails although common in samples

(appendix A) were not significantly reduced by Ensatina, compared to the medium size class of each which were significantly reduced in the first two months of Year One.

Large larval shredders were important prey for Ensatina during the first two months of

Year One in particular, when prey density was the lowest recorded during this study. This is in contrast to medium larval shredders which increased on treatments at the same time.

Temperate invertebrate communities are highly skewed towards smaller species which can provide an ample prey base for small insectivores (Whitaker 1952, Stamps et al. 1981). Jaeger (1980) confirms that prey are only very rarely limiting for terrestrial salamanders, but rather may become temporarily unavailable due to low moisture or high temperatures which can threaten salamanders with desiccation, suggesting moisture availability may influence Ensatina foraging behaviors. During the first two months of

Year One, invertebrate density was slowly increasing from a low point and Ensatina consumed prey within energetically favorable taxa (large larval shredders, medium

Entomobryidae springtails and beetles). In month three of Year One Ensatina did not significantly impact these groups, and as moisture and invertebrate density approached a peak for the experiment in month four, Ensatina consumed ants and earwigs (high chitin).

It may be that relatively limited prey availability in Year One influenced Ensatina to consume more energetically advantageous prey (calories/cost) to maintain a positive energy budget (e.g., Jaeger 1990, Diaz and Carrascal 1993). This may have become less

43 important in months three and four as prey density increased. Alternatively, but not exclusively, it may be that the consumption of prey under cover objects during periods of relatively low moisture (Jaeger 1980) influenced Ensatina to capitalize on particular taxa commonly encountered under the cover provided (beetles, Entomobryidae springtails, larvae). The increased moisture of months three and four of Year One may have enabled

Ensatina to explore more ground during foraging and consume a wider variety of prey.

These two phenomena were likely included in the dynamics of Year Two as well, where top-down salamander effects did not significantly decrease the densities of any invertebrate taxa: with moisture and invertebrate densities high there was nothing to limit the foraging behaviors of Ensatina. Furthermore, the significant indirect effect of

Ensatina presence, which increased the density of barklice, first occurred in month two and again in month four when moisture and invertebrate density were each most limited in Year Two. The early pulse of moisture in Year Two may have limited the ability of

Ensatina to regulate the invertebrate community (bottom-up versus top-down forces) and indirectly influence a greater retention of leaf litter. The differences I found between years in the regulation of invertebrate densities by salamanders due to variation in moisture is consistent with Walton (2005), who also found the downward effects of a woodland salamander on invertebrates to be ameliorated by moisture. The ability of moisture to influence the effects of top-down regulation (top-down cascades) has been well documented for several other insectivorous predators (e.g., Anolis lizards [Spiller and Schoner 1995]; arboreal birds [Bridgeland et al. 2010]), including terrestrial salamanders in the Midwest (Walton 2005).

CONCLUSIONS AND RECOMMENDATIONS

Soils are the third largest active carbon pool globally (2,400 Pg of carbon in the top 2 m) after the lithosphere and hydrosphere (Eshel et al. 2007); representing the largest terrestrial reservoir of carbon (Zhou 2006, Hungate et al. 2009), especially in temperate forests of the northern hemisphere (Beedlow 2004), where woodland salamanders are so abundant and diverse. My results and others (Wyman 1998) indicate that terrestrial salamanders play an ecologically dominant role at the soil-leaf litter interface of forested ecosystems of temperate North America by promoting nutrient cycling and increasing the retention of litter which stores energy, nutrients (nitrogen), and minerals including carbon

(Davic and Welsh 2004). The critical role of predators in maintaining ecosystem functionality is now recognized (Richie and Johnson 2009, Estes et al. 2011). Terrestrial salamanders clearly serve as predators in forested ecosystems, with the ability to generate top-down effects on the invertebrate assemblage and increase the retention of leaf litter, fostering storage of material for decomposition and increasing carbon buildup in the soil.

Further research is needed on the relative influences of sympatric terrestrial salamanders on the detrital food web and on each other, as they relate to environmental factors and leaf litter retention/turnover. As climatic variables continue to respond to the effects of global climate change we need to continue to address the role of ecologically dominant species like Ensatina in response to the impacts of climate extremes on forested ecosystems. Increasing our understanding of the ecological linkages within these forests can enhance our ability to better manage this resource while mitigating the effects of anthropogenic climate change, in order to maintain these life-sustaining environments.

44

LITERATURE CITED

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Beedlow, P. A., D. T. Tingey, D. L. Phillips, W. E. Hogsett, and D. M Olszyk. 2004. Rising atmospheric CO2 and carbon sequestration in forests. Frontiers in Ecology and Environment 2:315-322.

Benrong, C. and D. H. Wise. 1999. Bottom up limitation of predaceous arthropods in a detritus based terrestrial food web. Ecological Society of America 80:761-772.

Bridgeland, W. T., P. Beier, T. Kolb, and T. G. Whitham. 2010. A conditional trophic cascade: birds benefit faster growing trees with strong links between predators and plants. Ecological Society of America 91(1):73-84.

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Appendix A. Invertebrate density (arthropod/g dry leaf litter) by functional group sampled in each time period within control and treatment plots over two years (2007-2009) at Mattole field sites. Values for year 2 always follow values for year 1 by rows under invertebrate headings. Size classes within years are presented in the following order: <1mm, <2mm, >2mm. Invertebrates not analyzed by size class were combined to include all sizes. Invertebrate groups influenced by Ensatina presence are indicated with *. Invertebrate groups with insufficient data to be analyzed on their own are included in Decomposers and Invertebrates groups.

Control Treatment

T0 T1 T2 T3 T4 T0 T1 T2 T3 T4

Group Size Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Beetles <1mm 0.004 0.004 0.001 0.001 0.007 0.005 0.001 0.001 0.000 0.000 0.003 0.003 0.002 0.002 0.002 0.001 0.004 0.004 0.006 0.004

* <2mm 0.004 0.003 0.012 0.006 0.029 0.012 0.027 0.013 0.041 0.019 0.011 0.006 0.005 0.003 0.022 0.006 0.030 0.006 0.039 0.013

>2mm 0.004 0.002 0.002 0.001 0.002 0.001 0.005 0.002 0.008 0.006 0.003 0.002 0.002 0.001 0.002 0.001 0.000 0.000 0.002 0.001

<1mm 0.000 0.000 0.012 0.005 0.001 0.001 0.000 0.000 0.000 0.000 0.003 0.002 0.002 0.002 0.000 0.000 0.004 0.003 0.001 0.001

<2mm 0.042 0.016 0.084 0.019 0.080 0.014 0.041 0.012 0.051 0.020 0.024 0.011 0.104 0.039 0.068 0.015 0.034 0.018 0.032 0.008

>2mm 0.008 0.004 0.003 0.002 0.007 0.002 0.004 0.003 0.005 0.002 0.005 0.003 0.010 0.005 0.003 0.002 0.002 0.002 0.002 0.001

Larvae <1mm 0.015 0.015 0.001 0.001 0.001 0.001 0.002 0.002 0.000 0.000 0.004 0.003 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.027 0.024 0.004 0.002 0.001 0.001 0.024 0.019 0.003 0.002 0.011 0.009 0.005 0.003 0.003 0.001 0.014 0.007 0.015 0.006

* >2mm 0.014 0.006 0.021 0.002 0.035 0.022 0.014 0.004 0.007 0.002 0.009 0.003 0.010 0.003 0.021 0.004 0.028 0.017 0.015 0.007

<1mm 0.003 0.002 0.002 0.002 0.001 0.001 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001

<2mm 0.032 0.010 0.021 0.010 0.025 0.007 0.031 0.020 0.012 0.004 0.041 0.016 0.017 0.005 0.029 0.007 0.020 0.010 0.026 0.012

>2mm 0.069 0.019 0.067 0.016 0.066 0.015 0.016 0.008 0.028 0.009 0.066 0.030 0.073 0.008 0.083 0.024 0.020 0.005 0.023 0.005

Fly larva <1mm 0.015 0.007 0.001 0.000 0.001 0.000 0.002 0.001 0.000 0.000 0.003 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.025 0.010 0.004 0.001 0.001 0.000 0.023 0.008 0.001 0.000 0.007 0.003 0.004 0.001 0.002 0.000 0.011 0.002 0.013 0.003

>2mm 0.008 0.003 0.012 0.002 0.033 0.010 0.009 0.001 0.006 0.001 0.004 0.001 0.005 0.001 0.015 0.002 0.024 0.008 0.010 0.002

<1mm 0.002 0.002 0.002 0.002 0.001 0.001 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<2mm 0.025 0.010 0.013 0.008 0.023 0.006 0.030 0.019 0.010 0.004 0.031 0.015 0.015 0.004 0.026 0.006 0.020 0.010 0.017 0.008

>2mm 0.063 0.018 0.054 0.017 0.058 0.015 0.014 0.008 0.018 0.009 0.052 0.031 0.054 0.013 0.070 0.024 0.009 0.005 0.014 0.006

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51

Control Treatment T0 T1 T2 T3 T4 T0 T1 T2 T3 T4 Group Size Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Beetle Larva <1mm 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.002 0.002 0.001 0.001 0.000 0.000 0.001 0.001 0.002 0.001 0.004 0.003 0.001 0.001 0.000 0.000 0.003 0.002 0.002 0.002

* >2mm 0.005 0.001 0.009 0.002 0.002 0.001 0.004 0.002 0.001 0.001 0.006 0.002 0.005 0.002 0.003 0.002 0.004 0.002 0.004 0.003

<1mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.004 0.002 0.002 0.002 0.001 0.001 0.000 0.000 0.000 0.000 0.011 0.007 0.002 0.002 0.002 0.002 0.000 0.000 0.000 0.000

>2mm 0.005 0.002 0.003 0.002 0.004 0.002 0.000 0.000 0.001 0.001 0.011 0.005 0.012 0.009 0.006 0.004 0.004 0.003 0.003 0.002

Springtails <1mm 0.431 0.296 0.073 0.035 0.073 0.023 0.076 0.045 0.208 0.026 0.473 0.400 0.076 0.028 0.077 0.029 0.162 0.081 0.300 0.082

<2mm 0.099 0.056 0.033 0.006 0.044 0.013 0.057 0.023 0.057 0.010 0.098 0.063 0.034 0.009 0.038 0.011 0.055 0.020 0.103 0.031

>2mm 0.013 0.007 0.005 0.002 0.005 0.003 0.004 0.002 0.002 0.001 0.020 0.013 0.011 0.004 0.008 0.003 0.006 0.004 0.007 0.004

<1mm 0.527 0.121 1.020 0.112 0.578 0.159 0.737 0.369 0.382 0.134 0.466 0.102 0.857 0.301 0.721 0.149 0.509 0.212 0.475 0.066

<2mm 0.252 0.055 0.511 0.071 0.301 0.055 0.188 0.077 0.136 0.054 0.303 0.060 0.437 0.092 0.287 0.068 0.134 0.030 0.165 0.040

>2mm 0.027 0.009 0.038 0.006 0.007 0.002 0.002 0.001 0.000 0.000 0.025 0.008 0.025 0.009 0.013 0.003 0.005 0.003 0.004 0.002

Entomobryidae <1mm 0.011 0.009 0.010 0.007 0.015 0.007 0.012 0.006 0.038 0.015 0.037 0.025 0.019 0.008 0.009 0.003 0.007 0.003 0.030 0.025

* <2mm 0.009 0.008 0.012 0.003 0.012 0.007 0.014 0.003 0.022 0.010 0.019 0.012 0.009 0.002 0.006 0.002 0.020 0.008 0.017 0.009

>2mm 0.006 0.003 0.004 0.002 0.002 0.001 0.002 0.001 0.001 0.001 0.010 0.007 0.006 0.002 0.006 0.003 0.003 0.002 0.003 0.002

<1mm 0.052 0.028 0.106 0.031 0.070 0.015 0.138 0.056 0.122 0.074 0.029 0.011 0.118 0.056 0.081 0.018 0.051 0.016 0.114 0.044

<2mm 0.025 0.010 0.095 0.029 0.087 0.016 0.082 0.044 0.078 0.038 0.028 0.009 0.079 0.029 0.088 0.027 0.064 0.019 0.076 0.026

>2mm 0.013 0.009 0.013 0.005 0.003 0.002 0.002 0.001 0.000 0.000 0.006 0.004 0.014 0.004 0.009 0.002 0.004 0.003 0.004 0.002

Isotomidae <1mm 0.329 0.234 0.058 0.027 0.040 0.015 0.020 0.017 0.057 0.021 0.282 0.244 0.053 0.023 0.059 0.027 0.067 0.044 0.124 0.030

<2mm 0.062 0.033 0.012 0.003 0.016 0.006 0.011 0.010 0.006 0.003 0.025 0.010 0.015 0.006 0.016 0.006 0.012 0.005 0.033 0.009

>2mm 0.004 0.003 0.000 0.000 0.002 0.001 0.001 0.001 0.001 0.001 0.010 0.006 0.003 0.002 0.002 0.001 0.002 0.002 0.004 0.002

<1mm 0.162 0.031 0.661 0.103 0.384 0.128 0.471 0.289 0.120 0.030 0.200 0.065 0.569 0.288 0.465 0.100 0.322 0.151 0.203 0.035

<2mm 0.055 0.007 0.164 0.034 0.108 0.026 0.043 0.023 0.013 0.006 0.065 0.011 0.157 0.043 0.128 0.051 0.024 0.009 0.028 0.009

>2mm 0.008 0.002 0.024 0.006 0.003 0.001 0.000 0.000 0.000 0.000 0.017 0.009 0.007 0.004 0.005 0.003 0.000 0.000 0.000 0.000

52

Control Treatment

T0 T1 T2 T3 T4 T0 T1 T2 T3 T4

Group Size Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Sminthuridae <1mm 0.054 0.033 0.001 0.001 0.000 0.000 0.005 0.005 0.010 0.005 0.058 0.052 0.001 0.001 0.001 0.001 0.006 0.005 0.061 0.039

<2mm 0.012 0.007 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.016 0.014 0.002 0.002 0.002 0.002 0.000 0.000 0.000 0.000

>2mm 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<1mm 0.043 0.026 0.048 0.013 0.020 0.006 0.018 0.011 0.000 0.000 0.009 0.005 0.034 0.016 0.047 0.012 0.012 0.005 0.005 0.005

<2mm 0.023 0.017 0.013 0.007 0.002 0.002 0.000 0.000 0.000 0.000 0.019 0.008 0.013 0.008 0.004 0.002 0.000 0.000 0.000 0.000

>2mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.003 0.003 0.000 0.000 0.000 0.000 0.000 0.000

Onchiuridae <1mm 0.004 0.004 0.000 0.000 0.001 0.001 0.003 0.003 0.025 0.007 0.006 0.006 0.000 0.000 0.000 0.000 0.019 0.018 0.017 0.010

<2mm 0.001 0.001 0.000 0.000 0.002 0.002 0.006 0.004 0.016 0.007 0.007 0.007 0.000 0.000 0.000 0.000 0.006 0.004 0.012 0.007

>2mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<1mm 0.111 0.029 0.107 0.035 0.040 0.019 0.055 0.024 0.065 0.025 0.084 0.027 0.042 0.015 0.043 0.019 0.065 0.033 0.066 0.016

<2mm 0.073 0.019 0.128 0.024 0.038 0.010 0.039 0.022 0.035 0.012 0.107 0.034 0.098 0.031 0.035 0.009 0.027 0.007 0.046 0.007

>2mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000

Hypogastruidae <1mm 0.032 0.018 0.004 0.003 0.017 0.009 0.036 0.019 0.079 0.017 0.089 0.074 0.003 0.002 0.008 0.003 0.064 0.021 0.067 0.023

<2mm 0.015 0.009 0.008 0.002 0.014 0.004 0.025 0.012 0.013 0.003 0.031 0.022 0.008 0.002 0.015 0.006 0.017 0.007 0.042 0.016

>2mm 0.003 0.002 0.001 0.001 0.002 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.001 0.001 0.000 0.000

<1mm 0.159 0.034 0.098 0.022 0.064 0.015 0.055 0.028 0.075 0.024 0.145 0.031 0.093 0.032 0.084 0.027 0.060 0.018 0.088 0.023

<2mm 0.077 0.011 0.111 0.016 0.065 0.026 0.024 0.010 0.011 0.011 0.083 0.014 0.090 0.019 0.032 0.012 0.018 0.007 0.014 0.007

>2mm 0.007 0.004 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000

Mites <1mm 0.821 0.314 0.257 0.070 0.595 0.156 0.728 0.206 0.500 0.077 0.877 0.417 0.488 0.140 0.539 0.230 0.829 0.393 0.962 0.314

<2mm 0.060 0.025 0.034 0.006 0.050 0.019 0.055 0.018 0.049 0.008 0.074 0.032 0.061 0.011 0.063 0.012 0.064 0.026 0.078 0.017

<1mm 2.889 0.759 3.833 0.602 2.396 0.453 2.106 0.789 2.475 0.300 3.288 0.422 3.809 0.655 2.288 0.359 2.003 0.591 2.207 0.362

<2mm 0.209 0.033 0.228 0.037 0.192 0.015 0.140 0.037 0.110 0.033 0.254 0.047 0.251 0.034 0.150 0.031 0.103 0.027 0.081 0.017

53

Control Treatment

T0 T1 T2 T3 T4 T0 T1 T2 T3 T4 Group Size Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Orabatidae * <1mm 0.647 0.256 0.178 0.047 0.363 0.107 0.470 0.133 0.339 0.062 0.693 0.331 0.372 0.115 0.314 0.129 0.442 0.224 0.575 0.166

<2mm 0.046 0.022 0.019 0.002 0.027 0.010 0.036 0.012 0.026 0.002 0.048 0.023 0.043 0.012 0.044 0.009 0.046 0.020 0.050 0.014

<1mm 1.870 0.565 2.277 0.307 1.488 0.273 1.303 0.451 1.518 0.202 2.104 0.304 2.226 0.310 1.246 0.203 1.203 0.328 1.237 0.159

<2mm 0.118 0.024 0.125 0.024 0.093 0.010 0.072 0.021 0.037 0.011 0.144 0.041 0.143 0.023 0.076 0.014 0.059 0.015 0.023 0.005

Non-Orabatidae <1mm 0.174 0.059 0.078 0.024 0.232 0.065 0.258 0.076 0.161 0.017 0.184 0.096 0.116 0.031 0.224 0.105 0.387 0.171 0.387 0.159

<2mm 0.015 0.004 0.015 0.006 0.023 0.010 0.019 0.006 0.023 0.007 0.026 0.009 0.018 0.004 0.018 0.004 0.018 0.006 0.028 0.005

<1mm 1.019 0.206 1.557 0.330 0.908 0.206 0.803 0.347 0.958 0.147 1.184 0.139 1.583 0.372 1.042 0.178 0.799 0.277 0.970 0.206

<2mm 0.091 0.013 0.103 0.025 0.098 0.020 0.068 0.019 0.073 0.023 0.110 0.015 0.108 0.018 0.073 0.018 0.044 0.014 0.058 0.015

Milipedes * All 0.006 0.003 0.001 0.001 0.000 0.000 0.005 0.004 0.000 0.000 0.000 0.000 0.003 0.002 0.002 0.002 0.002 0.001 0.019 0.019

All 0.002 0.002 0.004 0.002 0.000 0.000 0.003 0.002 0.004 0.003 0.002 0.002 0.000 0.000 0.003 0.002 0.003 0.001 0.000 0.000

Worms All 0.002 0.002 0.000 0.000 0.001 0.001 0.001 0.001 0.003 0.002 0.007 0.005 0.002 0.002 0.007 0.004 0.002 0.001 0.003 0.002

* All 0.003 0.002 0.015 0.006 0.010 0.004 0.021 0.009 0.006 0.003 0.013 0.008 0.015 0.005 0.021 0.008 0.025 0.013 0.013 0.002

Diplura All 0.020 0.011 0.001 0.001 0.006 0.003 0.004 0.002 0.005 0.004 0.015 0.009 0.002 0.002 0.005 0.001 0.001 0.001 0.012 0.008

All 0.006 0.002 0.009 0.005 0.011 0.004 0.008 0.006 0.016 0.003 0.015 0.005 0.005 0.003 0.020 0.009 0.014 0.002 0.012 0.005

Protura All 0.066 0.037 0.005 0.003 0.024 0.018 0.012 0.005 0.004 0.002 0.047 0.020 0.016 0.007 0.021 0.010 0.014 0.010 0.004 0.002

All 0.039 0.020 0.013 0.006 0.025 0.014 0.036 0.019 0.019 0.012 0.050 0.019 0.017 0.006 0.015 0.006 0.047 0.038 0.026 0.009

Barklice All 0.001 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.001 0.001

* All 0.003 0.002 0.008 0.003 0.004 0.002 0.021 0.005 0.012 0.007 0.003 0.002 0.008 0.002 0.007 0.004 0.020 0.008 0.037 0.011

Termites All 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* All 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

Symphyla All 0.005 0.002 0.000 0.000 0.005 0.003 0.001 0.001 0.003 0.001 0.007 0.002 0.004 0.001 0.006 0.004 0.007 0.004 0.003 0.001

All 0.022 0.005 0.002 0.002 0.005 0.002 0.009 0.005 0.007 0.005 0.013 0.006 0.004 0.003 0.019 0.008 0.011 0.006 0.021 0.010

Earwigs * All 0.000 0.000 0.005 0.002 0.003 0.002 0.002 0.002 0.002 0.001 0.001 0.001 0.002 0.001 0.003 0.001 0.001 0.001 0.000 0.000

All 0.003 0.001 0.000 0.000 0.000 0.000 0.002 0.002 0.006 0.003 0.004 0.004 0.002 0.002 0.001 0.001 0.000 0.000 0.003 0.002

54

Control Treatment T0 T1 T2 T3 T4 T0 T1 T2 T3 T4 Group Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Decomposers <1mm 1.324 0.627 0.334 0.102 0.686 0.179 0.787 0.251 0.710 0.062 1.410 0.822 0.574 0.157 0.632 0.259 0.997 0.420 1.270 0.341

<2mm 0.222 0.120 0.087 0.013 0.142 0.048 0.174 0.074 0.155 0.026 0.208 0.095 0.116 0.017 0.135 0.028 0.182 0.064 0.246 0.052

>2mm 0.047 0.018 0.033 0.002 0.051 0.024 0.028 0.007 0.019 0.006 0.043 0.020 0.031 0.004 0.048 0.011 0.039 0.018 0.037 0.013

<1mm 3.435 0.876 4.873 0.675 2.977 0.600 2.880 1.162 2.876 0.407 3.780 0.444 4.672 0.924 3.022 0.500 2.556 0.820 2.709 0.400

<2mm 0.576 0.091 0.870 0.105 0.646 0.064 0.432 0.151 0.343 0.065 0.662 0.084 0.837 0.145 0.575 0.113 0.352 0.085 0.363 0.065

>2mm 0.122 0.027 0.130 0.016 0.090 0.015 0.046 0.019 0.056 0.017 0.130 0.040 0.123 0.002 0.130 0.032 0.050 0.015 0.058 0.014

Predators All 0.040 0.017 0.018 0.002 0.022 0.004 0.030 0.010 0.026 0.010 0.025 0.005 0.025 0.006 0.009 0.003 0.023 0.010 0.024 0.006

All 0.076 0.017 0.092 0.009 0.076 0.009 0.060 0.022 0.082 0.029 0.089 0.019 0.075 0.015 0.055 0.009 0.088 0.029 0.071 0.013

Centipedes All 0.011 0.003 0.007 0.003 0.013 0.002 0.011 0.005 0.009 0.002 0.009 0.004 0.008 0.001 0.004 0.002 0.009 0.004 0.009 0.002

All 0.016 0.003 0.035 0.010 0.033 0.008 0.018 0.006 0.031 0.004 0.032 0.008 0.037 0.011 0.019 0.006 0.031 0.010 0.026 0.007

Pseudoscrpions All 0.007 0.003 0.002 0.002 0.002 0.002 0.006 0.004 0.001 0.001 0.004 0.002 0.006 0.005 0.002 0.001 0.002 0.002 0.004 0.002

* All 0.009 0.005 0.004 0.002 0.008 0.003 0.004 0.002 0.006 0.004 0.006 0.002 0.009 0.002 0.007 0.003 0.005 0.003 0.010 0.003

Predatory larva <1mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<2mm 0.002 0.002 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.003 0.002 0.000 0.000

>2mm 0.003 0.002 0.004 0.001 0.003 0.002 0.005 0.002 0.001 0.001 0.003 0.001 0.004 0.002 0.001 0.001 0.002 0.001 0.003 0.002

<1mm 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<2mm 0.007 0.003 0.012 0.004 0.003 0.002 0.005 0.003 0.006 0.004 0.011 0.003 0.002 0.002 0.003 0.002 0.005 0.002 0.010 0.006

>2mm 0.012 0.006 0.012 0.003 0.009 0.005 0.013 0.006 0.006 0.002 0.013 0.006 0.007 0.003 0.005 0.002 0.014 0.009 0.011 0.005

Spiders <1mm 0.008 0.008 0.000 0.000 0.001 0.001 0.002 0.001 0.000 0.000 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.002 0.002 0.001 0.001 0.001 0.001 0.000 0.000 0.003 0.001 0.003 0.001 0.001 0.002 0.001 0.001 0.004 0.001 0.004 0.002

>2mm 0.003 0.003 0.002 0.001 0.001 0.001 0.001 0.001 0.004 0.003 0.003 0.002 0.001 0.001 0.000 0.000 0.001 0.001 0.004 0.002

<1mm 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.002 0.002 0.001 0.001 0.000 0.000 0.002 0.002

<2mm 0.019 0.005 0.015 0.004 0.012 0.003 0.012 0.007 0.023 0.014 0.012 0.005 0.008 0.003 0.012 0.001 0.019 0.007 0.005 0.003

>2mm 0.001 0.001 0.013 0.006 0.003 0.001 0.001 0.001 0.004 0.002 0.009 0.005 0.001 0.001 0.002 0.001 0.007 0.002 0.004 0.002

55

Control Treatment

Group T0 T1 T2 T3 T4 T0 T1 T2 T3 T4

Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE Χ SE

Ants <1mm 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

* <2mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000

* >2mm 0.002 0.002 0.001 0.001 0.001 0.001 0.020 0.012 0.120 0.100 0.022 0.013 0.001 0.001 0.001 0.001 0.016 0.016 0.054 0.039

<1mm 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000

<2mm 0.002 0.002 0.006 0.004 0.031 0.029 0.006 0.003 0.005 0.002 0.002 0.001 0.005 0.002 0.007 0.007 0.007 0.004 0.002 0.002

>2mm 0.017 0.010 0.003 0.002 0.263 0.239 0.005 0.002 0.029 0.008 0.006 0.003 0.002 0.002 0.155 0.140 0.006 0.004 0.015 0.004

Herbivores All 0.002 0.001 0.001 0.001 0.003 0.001 0.003 0.003 0.004 0.002 0.003 0.001 0.002 0.002 0.002 0.001 0.004 0.003 0.002 0.001

All 0.050 0.037 0.021 0.006 0.006 0.002 0.016 0.006 0.157 0.042 0.013 0.002 0.027 0.016 0.006 0.003 0.010 0.007 0.178 0.057

Thrips All 0.000 0.000 0.000 0.000 0.002 0.001 0.001 0.001 0.004 0.002 0.000 0.000 0.001 0.001 0.001 0.001 0.004 0.003 0.001 0.001

All 0.000 0.000 0.010 0.003 0.002 0.001 0.012 0.005 0.152 0.042 0.005 0.003 0.005 0.003 0.003 0.002 0.005 0.002 0.170 0.058

Homoptera All 0.001 0.001 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.002 0.002 0.001 0.001 0.000 0.000 0.000 0.000 0.000 0.000

All 0.050 0.037 0.009 0.007 0.001 0.001 0.003 0.002 0.000 0.000 0.005 0.003 0.019 0.016 0.002 0.001 0.004 0.003 0.004 0.004

Hemiptera * All 0.002 0.001 0.000 0.000 0.000 0.000 0.002 0.001 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001

All 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.000 0.000 0.000 0.000

Invertebrates <1mm 1.334 0.636 0.335 0.102 0.689 0.179 0.814 0.249 0.710 0.062 1.418 0.828 0.574 0.158 0.632 0.259 0.997 0.420 1.270 0.341

<2mm 0.231 0.123 0.090 0.013 0.147 0.049 0.180 0.075 0.163 0.026 0.221 0.099 0.125 0.020 0.141 0.029 0.195 0.068 0.251 0.052

>2mm 0.070 0.023 0.048 0.002 0.071 0.027 0.075 0.029 0.162 0.096 0.080 0.027 0.048 0.004 0.056 0.014 0.070 0.040 0.112 0.050

<1mm 3.445 0.873 4.874 0.676 2.979 0.600 2.881 1.162 2.885 0.409 3.752 0.435 4.677 0.923 3.023 0.501 2.558 0.820 2.735 0.407

<2mm 0.652 0.081 0.923 0.112 0.703 0.052 0.478 0.161 0.531 0.072 0.703 0.083 0.888 0.142 0.611 0.110 0.403 0.087 0.546 0.085

>2mm 0.175 0.038 0.199 0.014 0.403 0.229 0.086 0.027 0.130 0.027 0.199 0.043 0.177 0.013 0.315 0.114 0.106 0.021 0.117 0.025